06.LTE Protocols and Procedures

LTE Protocol and Procedures Training Manual 1 EPS Architecture

Issue 01 (2010-05-01) Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

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1 EPS Architecture

Objectives

On completion of this section the participants will be able to:

1.1 State the main functions of the network elements.

1.2 List the EPS interfaces.

1 EPS Architecture LTE Protocol and Procedures

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1-2 Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

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1.1 EPS Network Elements The term EPS (Evolved Packet System) relates to the Evolved 3GPP Packet Switched Domain. In contrast to the 2G and 3G networks defined by the 3GPP, LTE can be simply divided into a flat IP based bearer network and a service enabling network. The former can be further subdivided into the E-UTRAN (Evolved - Universal Terrestrial Radio Access Network) and the EPC (Evolved Packet Core) where as support for service delivery lies in the IMS (IP Multimedia Subsystem). This reference architecture can be seen in Figure 1-1.

Figure 1-1 LTE Reference Architecture

Whilst UMTS is based upon WCDMA technology, the 3GPP developed new specifications for the LTE air interface based upon OFDMA (Orthogonal Frequency Division Multiple Access) in the downlink and SC-FDMA (Single Carrier - Frequency Division Multiple Access) in the uplink. This new air interface is termed the E-UTRA (Evolved - Universal Terrestrial Radio Access).

1.1.1 User Equipment Like that of UMTS, the mobile device in LTE is termed the UE (User Equipment) and is comprised of two distinct elements; the USIM (Universal Subscriber Identity Module) and the ME (Mobile Equipment).

The ME supports a number of functional entities including:

l RR (Radio Resource) - this supports both the Control Plane and User Plane and in so doing, is responsible for all low level protocols including RRC (Radio Resource Control), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control) and the PHY (Physical) Layer.

l EMM (EPS Mobility Management) - is a Control Plane entity which manages the mobility management states the UE can exist in; LTE Idle, LTE Active and LTE Detached. Transactions within these states include procedures such as TAU (Tracking Area Update) and handovers.



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l ESM (EPS Session Management) - is a Control Plane activity which manages the activation, modification and deactivation of EPS bearer contexts. These can either be default EPS bearer contexts or dedicated EPS bearer contexts.

Figure 1-2 User Equipment Functional Elements

UE

EPS Mobility & EPS Session Management

IP AdaptationFunction

Radio Resource

ControlPlane

UserPlane

EPS Session ManagementBearer ActivationBearer ModificationBearer Deactivation

Radio ResourceRRC, PDCP, RLC, MAC &

PHY Layer Protocols

EPS Mobility ManagementRegistration

Tracking Area UpdateHandover

In terms of the Physical Layer, the capabilities of the UE may be defined in terms of the frequencies and data rates supported. Devices may also be capable of supporting adaptive modulation including QPSK (Quadrature Phase Shift Keying), 16QAM (16 Quadrature Amplitude Modulation) and 64QAM (Quadrature Amplitude Modulation).

In terms of the radio spectrum, the UE is able to support several scalable channels including; 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz whilst operating in FDD (Frequency Division Duplex) and/or TDD (Time Division Duplex). Furthermore, the UE may also support advanced antenna features such as MIMO (Multiple Input Multiple Output).

Table 1-1 UE Categories

UE Category Maximum Downlink Data Rate

Number of Downlink Data Streams

Maximum Uplink Data Rate

Support for Uplink 64QAM

1 10.3Mbit/s 1 5.2Mbit/s No




5 302.8Mbit/s 4 75.4Mbit/s Yes


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UE Identities An LTE capable UE will be allocated / utilize a number of identities during operation within the network. These include:

l IMSI (International Mobile Subscriber Identity) - this complies with the standard 3GPP format and is comprised of the MCC (Mobile Country Code), MNC (Mobile Network Code) and the MSIN (Mobile Subscriber Identity Number). This uniquely identifies a subscriber from within the family of 3GPP technologies - GSM, GPRS, UMTS etc.

l IMEI (International Mobile Equipment Identity) - is used to uniquely identify the ME. It can be further subdivided into a TAC (Type Approval Code), FAC (Final Assembly Code) and SNR (Serial Number).

l GUTI (Globally Unique Temporary Identity) - is allocated to the UE by the MME (Mobility Management Entity) and identifies a device to a specific MME. The identity is comprised of a GUMMEI (Globally Unique MME Identity) and an M-TMSI (MME - Temporary Mobile Subscriber Identity).

l S-TMSI (Serving - Temporary Mobile Subscriber Identity) - is used to protect a subscriber’s IMSI during NAS (Non Access Stratum) signaling between the UE and MME as well as identifying the MME from within a MME pool. The S-TMSI is comprised of the MMEC (MME Code) and the M-TMSI.

l IP Address - the UE requires a routable IP address from the PDN (Packet Data Network) from which it is receiving higher layer services. This may either be an IPv4 or IPv6 address.

1.1.2 Evolved Node B In addition to the new air interface, a new base station has also been specified by the 3GPP and is referred to as an eNB (Evolved Node B). These, along with their associated interfaces form the E-UTRAN and in so doing, are responsible for:

l RRM (Radio Resource Management) - this involves the allocation to the UE of the physical resources on the uplink and downlink, access control and mobility control.

l Date Compression - is performed in both the eNB and the UE in order to maximize the amount of user data that can be transferred on the allocated resource. This process is undertaken by PDCP.

l Data Protection - is performed at the eNB and the UE in order to encrypt and integrity protect RRC signaling and encrypt user data on the air interface.

l Routing - this involves the forwarding of Control Plane signaling to the MME and User Plane traffic to the S-GW (Serving - Gateway).

l Packet Classification and QoS Policy Enforcement - this involves the “marking” of uplink packets based upon subscription information or local service provider policy. QoS (Quality of Service) policy enforcement is then responsible for ensuring such policy is enforced at the network edge.



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Figure 1-3 Evolved Node B Functional Elements

Security in LTE is not solely limited to encryption and integrity protection of information passing across the air interface but instead, NAS encryption and integrity protection between the UE and MME also takes place. In addition, IPSec may also be used to protect user data within both the E-UTRAN and EPC.

eNB Identities In addition to the UE identities already discussed, there are a number of specific identities associated with the eNB. These include:

l TAI (Tracking Area Identity) - is a logical group of neighboring cells defined by the service provider in which UEs in LTE Idle mode are able to move within without needing to update the network. As such, it is similar to a RAI (Routing Area Identity) used in 2G and 3G packet switched networks.

l ECGI (E-UTRAN Cell Global Identifier) - is comprised of the MCC, MNC and ECI (Evolved Cell Identity), the later being coded by each service provider.

Femto Cells In order to improve both network coverage and capacity, the 3GPP have developed a new type of base station to operate within the home or small business environment. Termed the HeNB (Home Evolved Node B), this network element forms part of the E-UTRAN and in so doing supports the standard E-UTRAN interfaces. However, it must be stated that HeNBs do not support the X2 interface.

The architecture may include an HeNB-GW (Home Evolved Node B - Gateway) which resides between the HeNB in the E-UTRAN and the MME / S-GW in the EPC in order to scale and support large numbers of base station deployments.

1.1.3 Mobility Management Entity The MME is the Control Plane entity within the EPC and as such is responsible for the following functions:

l NAS Signaling and Security - this incorporates both EMM (EPS Mobility Management) and ESM (EPS Session Management) and thus includes procedures such as Tracking Area Updates and EPS Bearer Management. The MME is also responsible for NAS security.


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l S-GW and PDN-GW Selection - upon receipt of a request from the UE to allocate a bearer resource, the MME will select the most appropriate S-GW and PDN-GW. This selection criterion is based on the location of the UE in addition to current load conditions within the network.

l Tracking Area List Management and Paging - whilst in the LTE Idle state, the UE is tracked by the MME to the granularity of a Tracking Area. Whilst UEs remain within the Tracking Areas provided to them in the form of a Tracking Area List, there is no requirement for them to notify the MME. The MME is also responsible for initiating the paging procedure.

l Inter MME Mobility - if a handover involves changing the point of attachment within the EPC, it may be necessary to involve an inter MME handover. In this situation, the serving MME will select a target MME with which to conduct this process.

l Authentication - this involves interworking with the subscriber’s HSS (Home Subscriber Server) in order to obtain AAA (Access Authorization and Accounting) information with which to authenticate the subscriber. Like that of other 3GPP system, authentication is based on AKA (Authentication and Key Agreement).

Figure 1-4 MME Functional Elements

1.1.4 Serving Gateway The S-GW terminates the S1-U Interface from the E-UTRAN and in so doing, provides the following functions:

l Mobility Anchor - for inter eNB handovers, the S-GW acts as an anchor point for the User Plane. Furthermore, it also acts as an anchor for inter 3GPP handovers to legacy networks - GPRS and UMTS.

l Downlink Packet Buffering - when traffic arrives for a UE at the S-GW, it may need to be buffered in order to allow time for the MME to page the UE and for it to enter the LTE Active state.

l Packet Routing and Forwarding - traffic must be routed to the correct eNB on the downlink and the specified PDN-GW on the uplink.

l Lawful Interception - this incorporates the monitoring of VoIP (Voice over IP) and other packet services.

l GTP/PMIP Support - if PMIP (Proxy Mobile IP) is used on the S5/S8 Interfaces, the S-GW must support MAG (Mobile Access Gateway) functionality. Furthermore, support for GTP/PMIP chaining may also be required.



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Figure 1-5 S-GW Functional Elements

1.1.5 Packet Data Network - Gateway The PDN-GW is the network element which terminates the SGi Interface towards the PDN (Packet Data Network). If a UE is accessing multiple PDNs, there may be a requirement for multiple PDN-GWs to be involved. Functions associated with the PDN-GW include:

l Packet Filtering - this incorporates the deep packet inspection of IP datagrams arriving from the PDN in order to determine which TFT (Traffic Flow Template) they are to be associated with.

l Lawful Interception - as with the S-GW, the PDN-GW may also monitor traffic as it passes across it.

l IP Address Allocation - IP addresses may be allocated to the UE by the PDN-GW. This is included as part of the initial bearer establishment phase or when UEs roam between different access technologies.

l Transport Level Packet Marking - this involves the marking of uplink and downlink packets with the appropriate tag e.g. DSCP (Differentiated Services Code Point) based on the QCI (QoS Class Identifier) of the associated EPS bearer.

l Accounting - through interaction with a PCRF (Policy Rules and Charging Function), the PDN-GW will monitor traffic volumes and types.

Figure 1-6 PDN-GW Functional Elements


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1.2 EPS Interfaces 1.2.1 E-UTRAN Interfaces

As with all 3GPP technologies, it is the actual interfaces which are defined in terms of the protocols they support and the associated signaling messages and user traffic that traverse them. Figure 1-7 illustrates the main interfaces in the E-UTRAN.

Figure 1-7 E-UTRAN Interfaces

Uu Interface The Uu Interface supports both a Control Plane and a User plane and spans the link between the UE and the eNB / HeNB. The principle Control Plane protocol is RRC (Radio Resource Control) while the User Plane is designed to carry IP datagrams.

X2 Interface The X2 interface interconnects two eNBs and in so doing supports both a Control Plane and User Plane. The principle Control Plane protocol is X2AP (X2 Application Protocol).

S1 Interface The S1 interface can be subdivided into the S1-MME interface supporting Control Plane signaling between the eNB and the MME and the S1-U Interface supporting User Plane traffic between the eNB and the S-GW. The principle Control Plane protocol is S1AP (S1 Application Protocol).

1.2.2 EPC Interfaces Figure 1-8 illustrates the fundamental architecture of the EPC and in so doing identifies the key interfaces which exist between the network elements. It should be stated however that there exists additional interfaces which link the EPC with the IMS and legacy 3GPP / Non 3GPP architectures.



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Figure 1-8 EPC Architecture and Interfaces

1.2.3 Additional Network Elements and Interfaces In addition to the network elements, interfaces and associated protocols discussed so far, the EPC connects with numerous other nodes and networks. These are illustrated in Figure 1-9.


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Figure 1-9 Additional Network Elements and Interfaces

These include, but are not limited to the:

l HSS (Home Subscriber Server) - this can be considered a “master” database within the PLMN. Although logically it is considered as one entity, the HSS in practice is made up of several physical databases depending upon subscriber numbers and redundancy requirements. The HSS holds variables and identities for the support, establishment and maintenance of calls and sessions made by subscribers. It is connected to the MME via the S6a Interface which uses the protocol Diameter.

l PCRF (Policy and Charging Rules Function) - this supports functionality for policy control through the PDF (Policy Decision Function) and charging control through the CRF (Charging Rules Function). As such, it provides bearer network control in terms of QoS and the allocation of the associated charging vectors. The PCRF downloads this information over the Gx Interface using the Diameter protocol.

l ePDG (evolved Packet Data Gateway) - which is used when connecting to Untrusted Non 3GPP IP Access networks. It provides functionality to allocate IP addresses in addition to encapsulating / de-encapsulating IPSec (IP Security) and PMIP tunnels. It connects to the PDN-GW via the S2b Interface.

l RNC (Radio Network Controller) - which forms part of the 3GPPs UTRAN (Universal Terrestrial Radio Access Network), the RNC connects to the S-GW to support the tunneling of User Plane traffic using GTP-U. The interface linking these network elements is the S12 Interface.

l SGSN (Serving GPRS Support Node) - this forms part of the 3GPPs 2G and 3G packet switched core domain. It connects to both the MME and S-GW in order to support



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packet switched mobility and uses the GTPv2-C and GTP-U protocols respectively. The SGSN connects to the MME via the S3 Interface and the S-GW via the S4 Interface.

l EIR (Equipment Identity Register) - this database enables service providers to validate a particular IMEI (International Mobile Equipment Identity) against stored lists. It connects to the MME via the S13 Interface and uses the Diameter protocol for message transfer.


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LTE Protocol and Procedures Training Manual 2 EPS Protocols


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2 EPS Protocols

Objectives


2.1 Explain how signaling takes place between the UE and the EPC.

2.2 State the main functions of Radio Resource Control, Packet Data Convergence Protocol, Radio Link Control, Medium Access Control, the Physical Layer and their relations.

2.3 Explain the interaction of the E-UTRAN protocols and the mapping of logical, transport and physical channels.

2 EPS Protocols LTE Protocol and Procedures

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2.1 EPS Signaling The connectivity between the UE and the EPS can be split into a Control Plane and a User Plane. Both of these can further split into the NAS (Non Access Stratum) and AS (Access Stratum). The Access Stratum consist of the protocols and signaling involved with the E-UTRAN, i.e. maintain both the air interface and S1 interfaces. In contrast, the Non Access Stratum, as its name suggests, is not part of the Access Stratum and is defined as higher layer signaling and traffic (IP datagrams).

Control Plane Figure 2-1 illustrates the concept of NAS and AS signaling, i.e. the Control Plane. It is worth noting that the NAS signaling is effectively transparent to the E-UTRAN. Access Stratum signaling provides a mechanism to deliver NAS signaling, as well as the lower layer signaling required to setup, maintain and manage the connections. The X2 interfaces are also part of this methodology and as such it also is part of Access Stratum signaling.

Figure 2-1 NAS and AS Control Plane

User Plane The User Plane focuses on the delivery of IP datagrams to and from the EPC, namely the S-GW and PDN-GW. Figure 2-2 illustrates this concept.

Figure 2-2 NAS and AS User Plane



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In the case of the User Plane the higher layer NAS is an IP datagram. This effectively is delivered between the UE and the PDN-GW, with the eNB and S-GW acting as lower layer relaying devices.

2.2 EPS Protocols 2.2.1 Uu Interface

The Uu Interface supports both a Control Plane and a User plane and spans the link between the UE and the eNB / HeNB. The principle Control Plane protocol is RRC in the Access Stratum and EMM (EPS Mobility Management)/ ESM (EPS Session Management) in the Non Access Stratum. In contrast, the User Plane is designed to carry IP datagrams. However, both Control and User Planes utilize the services of the lower layers, namely PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control) and MAC (Medium Access Control), as well as the PHY (Physical Layer).

Figure 2-3 Uu Interface Protocols

2.2.2 Uu Interface - EMM and ESM The NAS signaling between the UE and the EPC is identified as EMM or ESM. Table 2-1 illustrates the main EMM and ESM signaling procedures.

Table 2-1 NAS EMM and ESM Procedures

EMM Procedures ESM Procedures

Attach Default EPS Bearer Context Activation

Detach Dedicated EPS Bearer Context Activation

Tracking Area Update EPS Bearer Context Modification

Service Request EPS Bearer Context Deactivation


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Extended Service Request UE Requested PDN Connectivity

GUTI Reallocation UE Requested PDN Disconnect

Authentication UE Requested Bearer Resource Allocation

Identification UE Requested Bearer Resource Modification

Security Mode Control ESM Information Request

EMM Status ESM Status

EMM Information

NAS Transport

Paging

EMM Procedures The key EMM procedures include:

l Attach - this is used by the UE to attach to an EPC (Evolved Packet Core) for packet services in the EPS (Evolved Packet System). Note that it can be also used to attach to non-EPS services.

l Detach - this is used by the UE to detach from EPS services. In addition, it can also be used for other procedures such as disconnecting from non-EPS services.

l Tracking Area Updating - this procedure is always initiated by the UE and is used for the various purposes. The most common include normal and periodic tracking area updating.

l Service Request - this is used by the UE to get connected and establish the radio and S1 bearers when uplink user data or signaling is to be sent.

l Extended Service Request - this is used by the UE to initiate a Circuit Switched fallback call or respond to a mobile terminated Circuit Switched fallback request from the network.

l GUTI Reallocation - this is used to allocate a GUTI (Globally Unique Temporary Identifier) and optionally to provide a new TAI (Tracking Area Identity) list to a particular UE.

l Authentication - this is used for AKA (Authentication and Key Agreement) between the user and the network.

l Identification - this is used by the network to request a particular UE to provide specific identification parameters, e.g. the IMSI (International Mobile Subscriber Identity) or the IMEI (International Mobile Equipment Identity).

l Security Mode Control - this is used to take an EPS security context into use, and initialize and start NAS signaling security between the UE and the MME with the corresponding NAS keys and security algorithms.

l EMM Status - this is sent by the UE or by the network at any time to report certain error conditions.

l EMM Information - this allows the network to provide information to the UE. l Transport of NAS messages - this is to carry SMS (Short Message Service) messages in

an encapsulated form between the MME and the UE. l Paging - this is used by the network to request the establishment of a NAS signaling

connection to the UE. Is also includes the Circuit Switched Service Notification



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EMM Procedures The key ESM procedures include:

l Default EPS Bearer Context Activation - this is used to establish a default EPS bearer context between the UE and the EPC.

l Dedicated EPS Bearer Context Activation - this is to establish an EPS bearer context with specific QoS (Quality of Service) and TFT (Traffic Flow Template) between the UE and the EPC. The dedicated EPS bearer context activation procedure is initiated by the network, but may be requested by the UE by means of the UE requested bearer resource allocation procedure.

l EPS Bearer Context Modification - this is used to modify an EPS bearer context with a specific QoS and TFT.

l EPS Bearer Context Deactivation - this is used to deactivate an EPS bearer context or disconnect from a PDN by deactivating all EPS bearer contexts to the PDN.

l UE Requested PDN Connectivity - this is used by the UE to request the setup of a default EPS bearer to a PDN.

l UE Requested PDN Disconnect - this is used by the UE to request disconnection from one PDN. The UE can initiate this procedure to disconnect from any PDN as long as it is connected to at least one other PDN.

l UE Requested Bearer Resource Allocation - this is used by the UE to request an allocation of bearer resources for a traffic flow aggregate.

l UE Requested Bearer Resource Modification - this is used by the UE to request a modification or release of bearer resources for a traffic flow aggregate or modification of a traffic flow aggregate by replacing a packet filter.

l ESM Information Request - this is used by the network to retrieve ESM information, i.e. protocol configuration options, APN (Access Point Name), or both from the UE during the attach procedure.

l ESM Status - this is used to report at any time certain error conditions detected upon receipt of ESM protocol data.

2.2.3 Uu Interface - RRC The main air interface control protocol is RRC (Radio Resource Control). For RRC messages to be transferred between the UE and the eNB it uses the services of PDCP, RLC, MAC and PHY. Figure 2-4 identifies the main RRC functions. In summary, RRC handles all the signaling between the UE and the E-UTRAN, with signaling between the UE and Core Network, i.e. NAS (Non Access Stratum) signaling, being carried by dedicated RRC messages. When carrying NAS signaling, RRC does not alter the information but instead, provides the delivery mechanism.


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Figure 2-4 Main RRC Functions

2.2.4 Uu Interface - PDCP LTE implements PDCP in both the User Plane and Control Plane. This is unlike UMTS, where PDCP was only found in the User Plane. The main reason for the difference is that PDCP in LTE takes on the role of security, i.e. encryption and integrity. In addition, Figure 2-5 illustrates some of the other functions performed by PDCP.

Figure 2-5 PDCP Functions

In the Control Plane, PDCP facilitates encryption and integrity checking of signaling messages, i.e. RRC and NAS. The User Plane is slightly different since only encryption is performed. In addition, the User Plane IP datagrams can also be subjected to IP header compression techniques in order to improve the system’s performance and efficiency. Finally, PDCP also facilitates sequencing and duplication detection.

2.2.5 Uu Interface - RLC The RLC (Radio Link Control) protocol exists in the UE and the eNB. As its name suggests it provides “radio link” control, if required. In essence, RLC supports three delivery services to the higher layers:



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l TM (Transparent Mode) - this is utilized for some of the air interface channels, e.g. broadcast and paging. It provides a connectionless service for signaling.

l UM (Unacknowledged Mode) - this is like Transparent Mode, in that it is a connectionless service; however it has the additional features of sequencing, segmentation and concatenation.

l AM (Acknowledged Mode) - this offers an ARQ (Automatic Repeat Request) service. As such, retransmissions can be used.

These modes, as well as the other RLC features are illustrated in Figure 2-6. In addition to ARQ, RLC offers segmentation, re-assembly and concatenation of information.

Figure 2-6 RLC Modes and Functions

2.2.6 Uu Interface - MAC MAC (Medium Access Control) provides the interface between the E-UTRA protocols and the E-UTRA Physical Layer. In doing this it provides the following services:

l Mapping - MAC maps the information received on the LTE Logical Channels into the LTE transport channels.

l Multiplexing - the information provided to MAC will come from a RB (Radio Bearer) or multiple Radio Bearers. The MAC layer is able to multiplex different bearers into the same TB (Transport Block), thus increasing efficiency.

l HARQ (Hybrid Automatic Repeat Request) - MAC utilizes HARQ to provide error correction services across the air. HARQ is a feature which requires the MAC and Physical Layers to work closely together.

l Radio Resource Allocation - QoS (Quality of Service) based scheduling of traffic and signaling to users is provided by MAC.

In order to support these features the MAC and Physical Layers need to pass various indications on the radio link quality, as well as the feedback from HARQ operation.


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Figure 2-7 Medium Access Control Functions

2.2.7 Uu Interface - Physical The PHY (Physical Layer) in LTE provides a new and flexible channel. It does however utilize features and mechanisms defined in earlier systems, i.e. UMTS. Figure 2-8 illustrates the main functions provided by the Physical Layer.

Figure 2-8 Physical Layer Functions

2.2.8 X2 Interface As previously mentioned, the X2 interface interconnects two eNBs and in so doing supports both a Control Plane and User Plane. The principle Control Plane protocol is X2AP (X2 Application Protocol). This resides on SCTP (Stream Control Transmission Protocol) where as the User Plane IP is transferred using the services of GTP-U (GPRS Tunneling Protocol - User) and UDP (User Datagram Protocol).

Figure 2-9 illustrates the X2 User Plane and Control Plane protocols.



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Figure 2-9 X2 Interface Protocols

2.2.9 X2 Interface - X2 Application Protocol The X2AP is responsible for the following functions:

l Mobility Management - this enables the serving eNB to move the responsibility of a specified UE to a target eNB. This includes Forwarding the User Plane, Status Transfer and UE Context Release functions.

l Load Management - this function enables eNBs to communicate with each other in order to report resource status, overload indications and current traffic loading.

l Error Reporting - this allows for the reporting of general error situations for which specific error reporting mechanism have not been defined.

l Setting / Resetting X2 - this provides a means by which the X2 interface can be setup / reset by exchanging the necessary information between the eNBs.

l Configuration Update - this allows the updating of application level data which is needed for two eNBs to interoperate over the X2 interface.

2.2.10 X2 Interface - Stream Control Transmission Protocol Defined by the IETF (Internet Engineering Task Force) rather than the 3GPP, SCTP was developed to overcome the shortfalls in TCP (Transmission Control Protocol) and UDP when transferring signaling information over an IP bearer. Functions provided by SCTP include:

l Reliable Delivery of Higher Layer Payloads. l Sequential Delivery of Higher Layer Payloads. l Improved resilience through Multihoming. l Flow Control. l Improved Security.

SCTP is also found on the S1-MME Interface which links the eNB to the MME.


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2.2.11 X2 Interface - GPRS Tunneling Protocol - User GTP-U tunnels are used to carry encapsulated PDU (Protocol Data Unit) and signaling messages between endpoints or in the case of the X2 interface. Numerous GTP-U tunnels may exist in order to differentiate between EPS bearer contexts and these are identified through a TEID (Tunnel Endpoint Identifier).

GTP-U is also found on the S1-U Interface which links the eNB to the S-GW and may also be used on the S5 Interface linking the S-GW to the PDN-GW.

2.2.12 S1 Interface The S1 interface can be subdivided into the S1-MME interface supporting Control Plane signaling between the eNB and the MME and the S1-U Interface supporting User Plane traffic between the eNB and the S-GW.

Figure 2-10 S1 Interface Protocols

2.2.13 S1 Interface - S1 Application Protocol The S1AP spans the S1-MME Interface and in so doing, supports the following functions:

l E-RAB (E-UTRAN - Radio Access Bearer) Management - this incorporates the setting up, modifying and releasing of the E-RABs by the MME.

l Initial Context Transfer - this is used to establish an S1UE context in the eNB, setup the default IP connectivity and transfer NAS related signaling.

l UE Capability Information Indication - this is used to inform the MME of the UE Capability Information.

l Mobility - this incorporates mobility features to support a change in eNB or change in RAT.

l Paging. l S1 Interface Management - this incorporates a number of sub functions dealing with

resets, load balancing and system setup etc.



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l NAS Signaling Transport - this is used for the transport of NAS related signaling over the S1-MME Interface.

l UE Context Modification and Release - this allows for the modification and release of the established UE Context in the eNB and MME respectively.

l Location Reporting - this enables the MME to be made aware of the UEs current location within the network.

2.2.14 S1 Interface - SCTP and GTP-U The S1-MME and S1-U lower layer protocols are similar to the X2 interface. As such, they also utilize the services of SCTP (discussed in Section 2.2.10 ) and GTP-U (discussed in Section 2.2.11 ).

2.2.15 S11 Interface The S11 Interface links the MME with the S-GW in order to support Control Plane signaling. In so doing, it utilizes GTPv2-C (GPRS Tunneling Protocol version 2 - Control) which, like all other interfaces which use variants of GTP, uses the services of UDP and IP.


GTPv2-C is also found on the S5/S8 Interface between the S-GW and PDN-GW and the S10 Interface between MMEs. Furthermore, it can also be found on the S3 and S4 interfaces when interconnecting with an SGSN (Serving GPRS Support Node).

2.2.16 GPRS Tunneling Protocol version 2 - Control GTPv2-C supports the transfer of signaling messages between the MME and the S-GW and as such is responsible for the exchange of the following message types:

l Path Management - this incorporates Echo Request and Echo Response messages to ensure ongoing connectivity across the link.

l Tunnel Management - these messages are used to activate, modify and delete the EPS bearers and sessions spanning the network.

l Mobility Management - these messages ensure mobility is supported through a combination of relocation and notification procedures.


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l CS (Circuit Switched) Fallback - this incorporates suspend and resume procedures during fallback to circuit switched operation.

l Non 3GPP Access - these messages support the establishment of tunnels to forward packet data between the 3GPP and Non 3GPP networks.

2.2.17 S5/S8 Interface The S5/S8 Interface links the S-GW with the PDN-GW and supports both a Control Plane and User Plane. The term S5 is used when these elements reside within the same PLMN (Public Land Mobile Network) and S8 when the interface spans a HPLMN (Home Public Land Mobile Network) / VPLMN (Visited Public Land Mobile Network).

The GTPv2-C protocol operates on the Control Plane for both of these interfaces whereas GTP-U or PMIP is used on the User Plane.

2.2.18 Proxy Mobile IP Defined by the IETF, PMIP supports mobility when a UE moves from one S-GW to another during a handover procedure. Data is tunneled between the PDN-GW, which supports HA (Home Agent) functionality and the S-GW, which acts as the FA (Foreign Agent).

It is anticipated that PMIP will be used by 3GPP2 based networks migrating to LTE as they already utilize PMIP within their 3G architectures. 3GPP based networks however are expected to use GTP-U instead.

Figure 2-12 S5/S8 Interface Protocols

2.2.19 S10 Interface The S10 Interface links two MMEs in order to pass Control Plane signaling. In so doing, it uses the services of GTPv2-C.



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2.2.20 SGi Interface The SGi Interface connects the PDN-GW to an external PDN. This could be the public Internet, Corporate Intranets or a service provider’s network supporting services such as the IMS. Although defined by the 3GPP, the protocols which operate over the SGi Interface are defined by the IETF and include TCP, UDP in addition to a host of application specific protocols.

Figure 2-14 SGi Interface Protocols

2.3 E-UTRAN Channel Mapping The concept of “channels” is not new. Both GSM and UMTS defined various channel categories, however LTE terminology is closer to UMTS. Broadly there are four categories of channel.


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Figure 2-15 LTE Channels

2.3.1 Logical Channels In order to describe Logical Channels it is best to identify where Logical Channels are located in relation to the LTE protocols and the other channel types. Figure 2-16 shows Logical Channels located between the RLC and the MAC layers.

Figure 2-16 Location of Channels

Logical channels are classified as either Control Logical Channels, which carry control data such as RRC signaling, or traffic Logical Channels which carry User Plane data.

Control Logical Channels The various forms of these Control Logical Channels include:

l BCCH (Broadcast Control Channel) - this is a downlink channel used to send SI (System Information) messages from the eNB. These are defined by RRC.

l PCCH (Paging Control Channel) - this downlink channel is used by the eNB to send paging information.

Figure 2-17 BCCH and PCCH Logical Channels



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l CCCH (Common Control Channel) - this is used to establish a RRC (Radio Resource Control) connection, also known as a SRB (Signaling Radio Bearer). The SRB is discussed further in Section 错误！未找到引用源。. The SRB is also used for re-establishment procedures. SRB 0 maps to the CCCH.

l DCCH (Dedicated Control Channel) - this provides a bidirectional channel for signaling. Logically there are two DCCH activated: − SRB 1 - this is used for RRC messages, as well as RRC messages carrying high

priority NAS signaling. − SRB 2 - this is used for RRC carrying low priority NAS signaling. Prior to its

establishment low priority signaling is sent on SRB1.

Figure 2-18 CCCH and DCCH Signaling

Traffic Logical Channels Release 8 LTE has one type of Logical Channel carrying traffic, namely the DTCH (Dedicated Traffic Channel). This is used to carry DRB (Data Radio Bearer) information, i.e. IP datagrams.

Figure 2-19 Dedicated Traffic Channel

The DTCH is a bidirectional channel that can operate in either RLC AM or UM mode. This is configured by RRC and is based on the QoS (Quality of Service) of the E-RAB (E-UTRAN - Radio Access Bearer).

2.3.2 Transport Channels Historically, Transport Channels were split between common and dedicated channels. However, LTE has moved away from dedicated channels in favor of the common/shared channels and the associated efficiencies provided. The main Release 8 Transport Channels include:


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l BCH (Broadcast Channel) - this is a fixed format channel which occurs once per frame and carries the MIB (Master Information Block). Note that the majority of System Information messages are carries on the DL-SCH (Downlink - Shared Channel).

l PCH (Paging Channel) - this channel is used to carry the PCCH, i.e. paging messages. It also utilizes DRX (Discontinuous Reception) to improve UE battery life.

l DL-SCH (Downlink - Shared Channel) - this is the main downlink channel for data and signaling. It supports dynamic scheduling, as well as dynamic link adaptation. In addition, it supports HARQ (Hybrid Automatic Repeat Request) operation to improve performance. As previously mentioned it also facilitates the sending of System Information messages.

l RACH (Random Access Channel) - this channel carries limited information and is used in conjunction with Physical Channels and preambles to provide contention resolution procedures.

l UL-SCH (Uplink Shared Channel) - this is similar to the DL-SCH, this channel supports dynamic scheduling (eNB controlled) and dynamic link adaptation by varying the modulation and coding. In addition, it also supports HARQ (Hybrid Automatic Repeat Request) operation to improve performance.

Figure 2-20 LTE Release 8 Transport Channels

2.3.3 Physical Channels The Physical Layer facilitates transportation of MAC Transport Channels, as well as providing scheduling, formatting and control indicators.

Downlink Physical Channels There are a number of downlink Physical Channels in LTE. These include:

l PBCH (Physical Broadcast Channel) - this channel carries the BCH. l PCFICH (Physical Control Format Indicator Channel) - this is used to indicate the

number of OFDM symbols used for the PDCCH. l PDCCH (Physical Downlink Control Channel) - this channel is used for resource

allocation. l PHICH (Physical Hybrid ARQ Indicator Channel) - this channel is part of the HARQ

process. l PDSCH (Physical Downlink Shared Channel) - this channel carries the DL-SCH.

Uplink Physical Channels There are a number of Uplink Physical Channels in LTE. These include:



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l PRACH (Physical Random Access Channel) - this channel carries the Random Access Preamble. The location of the PRACH is defined by higher layer signaling, i.e. RRC signaling.

l PUCCH (Physical Uplink Control Channel) - this channel carries uplink control and feedback. It can also carry scheduling requests to the eNB.

l PUSCH (Physical Uplink Shared Channel) - this is the main uplink channel and is used to carry the UL-SCH (Uplink Shared Channel) Transport Channel. It carries both signaling and user data, in addition to uplink control. It is worth noting that the UE is not allowed to transmit the PUCCH and PUSCH at the same time.

2.3.4 Radio Channels The term “Radio Channel” is typically used to describe the overall channel, i.e. the downlink and uplink carrier for FDD or the single carrier for TDD.

Figure 2-21 Radio Channel

2.3.5 Channel Mapping There are various options for multiplexing multiple bearers together, such that Logical Channels may be mapped to one or more Transport Channels. These in turn are mapped into Physical Channels. Figure 2-22 and Figure 2-23 illustrate the mapping options.


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Figure 2-22 Downlink Channel Mapping



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Figure 2-23 Uplink Channel Mapping

In order to facilitate the multiplexing from Logical Channels to Transport Channels, the MAC Layer typically adds a LCID (Logical Channel Identifier).


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LTE Protocol and Procedures Training Manual 3 LTE/SAE Quality of Service


3-1

3 LTE/SAE Quality of Service

Objectives


3.1 Explain the purpose of EPS Bearer Services and E-UTRA Radio Bearers.

3.2 List the different attributes of the E-UTRA Radio Bearer and explain how they are used.

3 LTE/SAE Quality of Service LTE Protocol and Procedures

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3.1 EPS Bearer Services and E-UTRA Radio Bearers 3.1.1 QoS in Packet Switched Networks

In order to support a mixture on non-real time and real time applications such as voice and multimedia, the issues associated with radio access based contention means that delay and jitter may become excessive if the flows of traffic are not coordinated. Modern packet switches are now termed “QoS aware”, in that they are able to classify, schedule and forward traffic based on the destination address, as well as the type of media being transported. Figure 3-1 illustrates how the concept of packet classification and scheduling is part of the eNB, S-GW and PDN-GW responsibilities.

Figure 3-1 QoS Packet Scheduling

The main functions associated with QoS in a packet switch (router) are the:

l Packet Classifier - this function analyses packets and based on a set of filters classifies the packet. As such, it receives the correct packet forwarding treatment and scheduling.

l Packet Scheduler - this schedules packets based on priority. In so doing various methods are used to ensure low latency data, e.g. voice, is optimally scheduled.

3.1.2 LTE Bearers The LTE system utilizes the concept of bearers. In so doing, a bearer has been defined to be the aggregate of one or more IP flows related to one or more services.

Figure 3-2 illustrates the main bearer terminology in LTE. Note that if the system employs PMIP (Proxy MIP) on the S5/S8 interfaces then the EPS Bearers effectively terminate on the S-GW.



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Figure 3-2 LTE Bearers

End to End Bearer Service The end to end service runs between the UE and the peer entity, such as a call server, web server etc. This is supported by an EPS Bearer plus external bearers that may support the equivalent QoS across the external networks, i.e. beyond the SGi Interface.

EPS Bearer Service The EPS Bearer extends between the UE and the PDN-GW. It is defined as a logical aggregate of one or more SDF (Service Data Flow). The EPS Bearer QoS is managed and controlled in the EPC / E-UTRAN. Figure 3-3 illustrates the concept of Service Data Flows mapping into the same EPS bearer. Note that the S-GW and eNB are both unaware of the mapping.

Figure 3-3 Service Data Flows

EPS Radio and Access Bearer The EPS Bearer consist of two parts the EPS Radio Bearer and the EPS Access Bearer. The EPS Radio Bearer facilitates the transport of the EPS Bearer traffic between the UE and the eNB. Note that the eNB manages the QoS. The EPS Access Bearer service provides the


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transport between the S-GW / PDN-GW and eNB according to the EPS QoS profile associated with each EPS Bearer.

3.1.3 The Default EPS Bearer LTE enables the UE to operate as “always on”. This is achieved by establishing a default EPS bearer during the LTE Attach process. The default EPS bearer is configured as non-GBR (non - Guaranteed Bit Rate) and carries all traffic which is not associated with a dedicated bearer.

Figure 3-4 Default and Dedicated EPS Bearers

It is possible for the UE to establish more than one default EPS bearer, however this is via a different APN (Access Point Name).

3.1.4 Dedicated EPS Bearers Dedicated EPS bearers carry traffic for IP flows that have been identified to require a specific QoS. This classification is achieved using a TFT (Traffic Flow Template) at the PDN-GW and UE. The TFT, i.e. filters, for the UE to utilize for each dedicated EPS bearer are passed to the UE in NAS ESM signaling.

Dedicated EPS bearers may be established during the Attach. For example, in the case of services that require “always-on” connectivity and higher QoS than that provided by the default bearer. Dedicated bearers can be either GBR (Guaranteed Bit Rate) or non-GBR.

3.1.5 EPS QoS Parameters EPS Bearers may support Guaranteed or Non Guaranteed Bit Rate services. As such various parameters are used to control and identify the QoS.

GBR QoS Information The GBR QoS Information parameter provides the eNB with information on the uplink and downlink rates. It can include:

l E-RAB Maximum Downlink Bit Rate. l E-RAB Maximum Uplink Bit Rate. l E-RAB Guaranteed Downlink Bit Rate. l E-RAB Guaranteed Uplink Bit Rate.



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AMBR (Aggregate Maximum Bit Rate) Non Guaranteed EPS Bearers are subject to control through an AMBR (Aggregate Maximum Bit Rate). The AMBR applies to both the subscriber and APN (Access Point Name) associated with the subscriber.

l UE AMBR (User Equipment Aggregate Maximum Bit Rate) - this value applies to the total bit rate that can be allocated to a subscriber for all its non-GBR services.

l APN AMBR (Access Point Name Aggregate Maximum Bit Rate) - this value applies to the total bit rate that can be allocated to the subset of a subscriber’s services associated with a particular APN.

QoS Class Indicator QCI (QoS Class Indicator) provides a simple mapping from an integer value to specific QoS parameters that controls bearer level packet forwarding treatment. Currently eight label types have been defined, these are illustrated in Table 3-1.

Table 3-1 QCI Attributes

QCI Type Priority Packet Delay Budget (ms)

Packet Error Rate

Example Service

1 GBR 2 100 10-2 Conversational Voice

2 GBR 4 150 10-3 Conversational Video

3 GBR 3 50 10-3 Real Time Gaming

4 GBR 5 300 10-6 Non-Conversational Voice

5 Non-GBR 1 100 10-6 IMS Signaling

6 Non-GBR 6 300 10-6 Video, TCP Based

7 Non-GBR 7 100 10-3 Voice, Video, Interactive Gaming



ARP (Allocation and Retention Priority) The ARP (Allocation and Retention Priority) indicates if a bearer establishment or modification request can be accepted. In addition, it may be used to indicate which bearers are dropped when there is congestion in the network. The main parameters include:

l Priority Level (0 to 15) - Value 15 means "no priority", whereas values between 1 and 14 are ordered in decreasing order of priority, i.e. 1 is the highest and 14 the lowest, with value 0 being reserved.


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l Pre-emption Capability - this indicates the pre-emption capability on other E-RABs. In so doing, it indicates whether the E-RAB will not pre-empt other E-RABs or, the E-RAB may pre-empt other E-RABs.

l Pre-emption Vulnerability - this indicates the vulnerability of the E-RAB to preemption of other E-RABs.

3.2 E-UTRA Radio Bearers The LTE air interface has two types of radio bearers, namely Signaling Radio Bearers and Data Radio Bearers.

3.2.1 Signaling Radio Bearers A SRB (Signaling Radio Bearer) is a RB (Radio Bearer) that is only used for the transmission of RRC and NAS messages. More specifically, the following three SRBs are defined:

l SRB0 - this is for RRC messages using a CCCH logical channel, e.g. RRC Connection Request, Setup and Re-establishment.

l SRB1 - this is mainly for RRC messages using a DCCH logical channel. It can also be used for NAS messages prior to the establishment of SRB2.

l SRB2 - this is for NAS messages using a DCCH logical channel. Note that SRB2 has a lower-priority than SRB1 and is always configured by the E-UTRAN after security activation.

Figure 3-5 Signaling Radio Bearers

Uu S1-U S5/S8 SGi

UEeNB S-GW PDN-GW

SRB 2

SRB 1RRC (High Priority)

NAS (Lower Priority)

3.2.2 Data Radio Bearers In addition to Signaling Radio Bearers, at least one DRB (Data Radio Bearer) needs to be established for the Default EPS bearer. There are various identities used in LTE at different layers to identify the EPS bearers. The main higher layer identifier is the EPS Bearer Identity, this has a value between 0 to 15. In a UMTS network this is referred to as a NSAPI (Network layer Service Access Point Identifier). When the EPS bearer is established an associated DRB Identity is assigned. These have values between 1 and 32. Finally, the lower layers, i.e. MAC, allocate the LCID (Logical Channel Identity). There are only 10 available for Radio Bearers, with the values 1 and 2 mapping to SRB1 and SRB2 respectively. In so doing, the remaining eight LCID are available for Data Radio Bearers (1 Default EPS Bearer and 7 Dedicated EPS Bearers).

Figure 3-6 illustrates how the Data Radio Bearer relates to an EPS bearer. In this case the Default EPS Bearer.



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Figure 3-6 Data Radio Bearers

3.2.3 Radio Bearer QoS The QoS for Data Radio Bearers is provided to the eNB by the MME using the standard QoS attributes such as QCI and ARP, as well as maximum and guaranteed bit rates in the uplink and downlink direction. Based on these the eNB configures the UE E-UTRA layers and manages the ongoing scheduling of uplink and downlink traffic.

Figure 3-7 E-RAB QoS Parameters to the eNB


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E-UTRA Configuration In order to achieve the QoS for the E-RAB the eNB configures the lower layer protocols, namely PDCP, RLC, MAC and the Physical Layers.

Figure 3-8 E-UTRA E-RAB QoS

There are various parameters that could be configured/modified to influence the performance of the E-UTRA and thus aid the eNB QoS scheduling requirements. These include:

l PDCP Compression. l RLC AM or UM. l RLC AM Polling Configuration. l Uplink MAC Priority. l Uplink MAC Prioritized Bit Rate. l Uplink MAC Bucket Size Duration. l HARQ Configuration and re-transmissions. l BSR (Buffer Status Report) Configuration. l SPS (Semi Persistent Scheduling) Configuration. l Physical Channel and Power Configuration.

LTE Protocol and Procedures Training Manual 4 X2/S1 Interface and Protocols


4-1

4 X2/S1 Interface and Protocols

Objectives


4.1 Explain the main functions and procedures of X2AP signaling protocol.

4.2 Explain the main functions and procedures of S1AP signaling protocol.

4.3 Explain the main functions and procedures of the User Plane protocol GTP.

4 X2/S1 Interface and Protocols LTE Protocol and Procedures

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4.1 X2AP Functions and Procedures The X2 interface links an eNB to its neighbors. It is sub-divided into a Control Plane and User Plane, these are illustrated in Figure 4-1. The messages required to invoke the X2 interface services are carried by X2AP (X2 Application Part) in the Control Plane. The User Plane utilizes the services of GTPv1-U (GPRS Tunneling Protocol Version 1 - User Plane). The E-UTRAN interfaces use similar terminology to that of UMTS, in that the interfaces are divided into a RNL (Radio Network Layer) and a TNL (Transport Network Layer). The Radio Network Layer supports the higher layer functions, incorporating X2AP and the user’s IP streams.

Figure 4-1 X2 Control and User Plane

The Transport Network Layer Control Plane and User Plane both use the service of IP; however a reliable robust delivery protocol in the form of SCTP (Stream Control Transmission Protocol) exists within the Control Plane. In contrast, the User Plane utilizes GTP-U and the services of the UDP (User Datagram Protocol). Note that an eNB may have one or multiple IP addresses at the Transport Network Layer for both the Control and User Planes.

4.1.1 Functions of the X2 Application Protocol The X2AP has the following functions:

l Mobility Management - this function allows the eNB to move the responsibility of a certain UE to another eNB. Forwarding of User Plane data, Status Transfer and UE Context Release function are parts of the mobility management.

l Load Management - this function is used by eNBs to indicate resource status, overload and traffic load to each other.

l Reporting of General Error Situations - this function allows reporting of general error situations, for which function specific error messages have not been defined.

l Resetting the X2 - this function is used to reset the X2 interface. l Setting up the X2 - this function is used to exchange necessary data for the eNB for setup

the X2 interface and implicitly perform an X2 Reset. l eNB Configuration Update - this function allows updating of application level data

needed for two eNBs to interoperate correctly over the X2 interface.



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The X2AP consists of various EP (Elementary Procedures). Table 4-1illustrates the mapping between the functions provided by the X2 interface and the actual Elementary Procedure(s) that are used to support this functionality.

Table 4-1 Mapping between X2AP Functions and X2AP EPs

Function Elementary Procedure(s)

Mobility Management a) Handover Preparation. b) SN Status Transfer. c) UE Context Release. d) Handover Cancel.

Load Management a) Load Indication. b) Resource Status Reporting Initiation. c) Resource Status Reporting.

Reporting of General Error Situations Error Indication.

Resetting the X2 Reset.

Setting up the X2 X2 Setup.

eNB Configuration Update eNB Configuration Update.

4.1.2 X2 Elementary Procedures The X2AP consists of various Elementary Procedures. Class 1 procedures, i.e. EPs including a request and response, are illustrated in Table 4-2.

Table 4-2 Class 1 Elementary Procedures

Elementary Procedure

Initiating Message

Successful Outcome Unsuccessful Outcome

Response message Response message

Handover Preparation

HANDOVER REQUEST

HANDOVER REQUEST ACKNOWLEDGE

HANDOVER PREPARATION FAILURE

Reset RESET REQUEST RESET RESPONSE

X2 Setup X2 SETUP REQUEST

X2 SETUP RESPONSE

X2 SETUP FAILURE

eNB Configuration Update

ENB CONFIGURATION UPDATE

ENB CONFIGURATION UPDATE ACKNOWLEDGE

ENB CONFIGURATION UPDATE FAILURE

Resource Status Reporting Initiation

RESOURCE STATUS REQUEST

RESOURCE STATUS RESPONSE

RESOURCE STATUS FAILURE


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The X2AP also supports various Class 2 procedures, i.e. EPs without a response message.

Elementary Procedure Initiating Message

Load Indication LOAD INFORMATION

Handover Cancel HANDOVER CANCEL

SN Status Transfer SN STATUS TRANSFER

UE Context Release UE CONTEXT RELEASE

Resource Status Reporting RESOURCE STATUS UPDATE

Error Indication ERROR INDICATION

The role of the X2 interface may be divided into two main groups. These are:

l X2AP Basic Mobility Procedures - these relate to procedures used to handle the UE mobility within E-UTRAN.

l X2AP Global Procedures - these relate to procedures that are not related to a specific UE.

4.1.3 Message Formatting X2AP messages and S1AP messages consist of individual IE (Information Elements) and groups of Information Elements that are nested together. Each message must start with the element defining the “Message Type”. This will be followed by a series of Information Elements.

Presence The presence of Information Elements within a message depends on a number of factors including the scenario in which the message has been invoked. Consequently, Information Elements may be:

l M (Mandatory) - these IE are always included in the message. l O (Optional) - these IE may or may not be included in the message. l C (Conditional) - these IE are included in the message only if the condition is satisfied.

Range The Range indicates the number of copies of repetitive Information Elements that are allowed in the message. E.g. there may be three cells configured and each has its associated parameters.

Criticality In each protocol message, there is criticality information set for individual and/or groups of IE that comprise it. This criticality information instructs the receiver how to act when receiving an IE that is in error or not comprehended. This criticality information may be applied as follows:

l Null - no criticality information is applied explicitly.



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l Yes - criticality information is applied only for non-repeatable IE. l Global - the Information Element and all its repetitions have common criticality

information. l Each - each repetition of the Information Element has its own criticality information.

Based on the criticality information, the receiver may take the following action if errors are encountered in the Information Element:

l Reject. l Ignore. l Ignore and Notify.

4.1.4 X2 Basic Mobility Procedures - Handover Preparation Based on radio resource requirements the source eNB will decide to initiate a handover procedure with the target eNB. The source eNB initiates the procedure by sending the Handover Request message to the target eNB. Note that the following messages are also included in mobility scenarios in Section 错误！未找到引用源。.

Handover Request The Handover Request message includes the following information:

l Old eNB UE X2AP ID - this provides the X2 signaling association for future messages between the source and target eNBs.

l Cause - this element indicates to the MME the reason for the handover including reasons such as the radio network layer, transport network layer etc.

l ECGI - this is the global id of the eNB and is expressed as a PLMN identity plus the entire 28bit cell identity.

l GUMMEI (Globally Unique MME Identifier) - this is the identity of the MME that is currently serving the UE.

l UE Context Information - this contains the following information: − MME UE S1AP ID - this provides the target eNB with the signaling association

reference with the MME across the S1-MME interface for specific UE. − UE Security Capabilities - this information element defines the UE capabilities in

terms of its RF, E-RAB formats etc. These are typically defined by referencing the category of the LTE device.

− AS Security Information - the purpose of the Security Context IE is to provide security related parameters to the eNB. These are used to derive security keys for User Plane traffic and RRC signaling messages and for security parameter generation for subsequent X2 or intra eNB handovers.

− UE Aggregate Maximum Bit Rate - this element is used to define the total bandwidth in Mbit/s that can be allocated to the UE for all E-RABs that are established.

− E-RABs to be Setup List - this identifies the E-RAB ID, E-RAB QoS, GTP information and RRC Context for each EPS Bearer. The latter provides details on the current configuration and the implementation of the air interface protocols.

l UE History Information -this is information about cells that a UE has been served by in the active state prior to the target cell.

l Trace Activation - this O (Optional) parameter is able to start trace procedures on the Target eNB. In so doing, it indicates which interfaces to trace and where to send the information.


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l SRVCC Operation Possible - this indicates to the target eNB whether SRVCC (Single Radio Voice Call Continuity) is available, i.e. the UE can be handed over from the E-UTRAN to CS (Circuit Switched) 2G/3G systems.

Figure 4-2 X2 Handover Request

Handover Request Acknowledge The allocation of E-RAB resources will be based on those received in the Handover Request procedure. Note that if conflicts occur the target eNB can utilize the ARP (Allocation and Retention Priority) parameter (part of the E-RAB QoS) to help resolve the issue. In so doing, the target eNB admits the E-RABs and sends the Handover Request Acknowledge message back to the source eNB. The message contains the following information:

l Old eNB UE X2AP ID - this is the X2 signaling association of the source eNB. l New eNB UE X2AP ID - this is the X2 signaling association of the target eNB. l E-RABs Admitted List - this details the list of E-RAB(s) that have been admitted based

on the resources available in the target eNB. l E-RABs Not Admitted List - this identifies the E-RAB(s) which are not admitted.



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l Target eNB To Source eNB Transparent Container- this includes handover information for the UE. This, in essence, is an RRC Connection Reconfiguration message defining the lower layer configuration on the new cell.

l Criticality Diagnostics - this is sent by the eNB when parts of a received message have not been comprehended or were missing, or if the message contained logical errors. When applicable, it contains information about which parameters were not comprehended or were missing.

Handover Preparation Failure There are a number of reasons why the Handover Preparation Failure message may be sent, typical examples include:

l If the target eNB does not admit at least one non-GBR E-RAB. l The target eNB receives a Handover Request message and the RRC Context parameter

does not include required information. l A failure occurs during the Handover Preparation.

In these instances, the target eNB sends the Handover Preparation Failure message to the source eNB with the appropriate cause parameter indicated.

Figure 4-3 X2 Handover Preparation Failure

SN Status Transfer The SN Status Transfer procedure is used to transfer the uplink and downlink PDCP (Packet Data Convergence Protocol) SN (Sequence Number) and HFN (Hyper Frame Number) status from the source eNB to the target eNB during an X2 handover for each respective E-RAB for which PDCP SN and HFN status preservation applies. These E-RAB(s) are identified in the handover preparation phase based on the RRC Context parameters in the Handover Request.


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Figure 4-4 X2 SN Status Transfer

The source eNB initiates the SN Status Transfer procedure. In so doing, it stops the assignment of PDCP SNs to downlink SDUs and stops delivering uplink SDUs towards the EPC (Evolved Packet Core). Finally it sends the SN Status Transfer message to the target eNB.

For E-RAB that have had forwarding preservation agreed the source eNB forwards the uplink packets to the target eNB and routes downlink packets to the target eNB that will assign its own sequence numbers to the packets based on the value of the PDCP DL Count received from the target eNB.

The information in the SN Status Transfer message includes:

l Old eNB UE X2AP ID - this is the X2 signaling association of the source eNB. l New eNB UE X2AP ID - this is the X2 signaling association of the target eNB. l E-RABs Subject to Transfer - this lists the E-RAB that have been identified to have

forwarding applied based on their QoS. Each E-RAB will have the following parameters detailed for them: − Receive Status of UL PDCP SDUs - this optional parameter provides a bit map of

missing PDCP Sequence Numbers. − UL Count Value - this is the PDCP-SN and HFN of the next uplink SDU (Service

Data Unit) to be forwarded to the EPC. − DL Count Value - this is the PDCP-SN and HFN of the first downlink SDU to be

formatted into a PDCP SU for delivery to the UE.

UE Context Release The UE Context Release message is sent once a handover has been successfully completed and enables the source eNB to release all resources associated with the UE.



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Figure 4-5 X2 UE Context Release

UE Context Release

eNB eNB

UE Context ReleaseOld eNB UE X2AP ID New eNB UE X2AP ID

Source Target

Handover Cancel The Handover Cancel message is sent from the source eNB to the target eNB to cancel a handover that is currently in progress.

Figure 4-6 X2 Handover Cancel

Handover Cancel

eNB eNB

Handover CancelOld eNB UE X2AP ID New eNB UE X2AP IDCause

Source Target

4.1.5 X2 Load Indication The Load Indication message transfers load and interference coordination information between neighboring eNBs that are operating on the same carrier frequency. It enables an eNB to indicate the interference it is experiencing on particular PRB (Physical Resource Block) and the sensitivity to interference for each PRB.

The message contains the following information:

l Cell ID - this indicates the cell to which the report relates. l UL Interference Load Indication - this is used to report to a neighbor eNB that specific

PRBs are experiencing interference. This may be defined as high, medium or low. PRB are listed with PRB 0 being the first in the list, PRB 1 is the second and so on.

l UL High Interference Indication - this message indicates the sensitivity of PRB to interference. A bit map is used, with a 0 indicating low sensitivity and 1 indicating high sensitivity.

l RNTP (Relative Narrowband Tx Power) - this indicates, per PRB, whether downlink transmission power is lower than the value indicated by the RNTP threshold. The receiving eNB may take such information into account when setting its scheduling policy and can consider the received RNTP value valid until reception of a new Load Information message carrying an update.


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Figure 4-7 X2 Load Indication

Figure 4-8 illustrates how two of the Load Indication message parameters can be set to indicate the uplink overload and interference requirements on an eNB.

Figure 4-8 X2 Uplink Interference

The Load Indication message also provides the Relative Narrowband Tx Power bitmap and associated parameters. This effectively indicates to neighboring cells the power levels transmitted per PRB.

Figure 4-9 Downlink RNTP



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4.1.6 X2 Resource Status Reporting Closely associated with load reporting is resource status reporting, this is used by an eNB to request updated information regarding load information etc from its neighbors.

Resource Status Request The Resource Status Request message is sent from one eNB to its neighbor. It is used to register (start) measurement reports or to deregister (stop) these reports. It is also used to request the periodicy of reports and to specify the specific cells on which reports are required.

Figure 4-10 X2 Resource Status Request

The Reported Characteristics parameter is used to indicate: PRB Periodic, TNL load Indication Periodic or HW Load Indication Periodic.

Resource Status Response The Resource Status Response message indicates if the request can be performed. Subsequent messages are then sent in Resource Status Update messages.

Resource Status Failure The Resource Status Failure message is sent when requested measurements cannot be initiated.

Resource Status Update The Resource Status Update message is used to send the requested results. It includes the requested report.


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Figure 4-11 X2 Resource Status Update

4.1.7 X2 Setup The purpose of the X2 Setup procedure is to exchange application level configuration data needed for two eNBs to interoperate correctly over the X2 interface. This procedure erases any existing application level configuration data in the two nodes and replaces it by the one received. This procedure also resets the X2 interface in a similar fashion to a Reset procedure.

X2 Setup Request The X2 Setup Request message includes:

l Global eNB ID - this is the global id of the eNB and is expressed as the first 20bits of the cell ID in the case of a macro eNB and for a home eNB it is the entire 28bit cell identity.

l Served Cells - this contains a list of the cells supported by the eNB. For each cell the following information is provided: − ECGI (E-UTRAN Cell Global Identifier). − PCI (Physical Cell Identifier). − EARFCN (E-UTRA Absolute Radio Frequency Channel Number). − TAC (Tracking Area Code). − Broadcast PLMNs - including FDD and TDD configuration. − Neighbor Cells - including ECGI, PCI and EARFCN.

l GU Group ID (Globally Unique Group Identifier) - this is all the pools to which the eNB belongs to.



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Figure 4-12 X2 Setup Request

X2 Setup Request

X2 Setup Response

eNB eNB

X2 Setup ResponseGlobal eNB IDServed Cells- Served Cell Information- Neighbor Information-- ECGI-- PCI-- EARFCNGU Group Id List (C)Criticality Diagnostics

X2 Setup RequestGlobal eNB IDServed Cells- Served Cell Information- Neighbor Information-- ECGI-- PCI-- EARFCNGU Group Id List (C)

X2 Setup Response The X2 Setup Response message simply reflects the information included in the request but this time the values are associated with the neighbor that received the request message.

4.1.8 X2 eNB Configuration The purpose of the eNB Configuration Update procedure is to update application level configuration data needed for two eNBs to interoperate correctly over the X2 interface.

eNB Configuration Update The eNB Configuration Update includes updates and modification to the eNB configuration.

eNB Configuration Update Acknowledge The eNB Configuration Update Acknowledge message is returned to indicate to the sending eNB that the necessary updates have been completed in the target eNB.


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Figure 4-13 eNB Configuration Update

eNB Configuration Update Failure If the eNB cannot accept the update it responds with an eNB Configuration Update Failure message and the appropriate cause value. If the message includes the Time To Wait parameter the eNB waits at least for the indicated time before reinitiating the eNB Configuration Update procedure towards the same eNB. Both eNBs continue to communicate on the X2 interface with their existing configuration data.

4.2 S1AP Functions and Procedures The S1AP, which resides on the S1-MME interface within the E-UTRAN, uses the concept of an EP (Elementary Procedure). These interactions comprise of a series of protocol messages which in turn consist of one or more IE (Information Element). Like the X2 interface, the S1 interface can be split into a RNL (Radio Network Layer) and TNL (Transport network Layer). Figure 4-14 illustrates this split, as well as the associated protocols.

Figure 4-14 S1 Control and User Plane

IP

Layer 2

Layer 1

SCTP

S1AP

IP

Layer 2

Layer 1

UDP

GTP-U

Control Plane User Plane

IPRNL

S1-MME S1-U



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4.2.1 S1AP Functions S1AP is defined as being able to perform the following functions:

l E-RAB Management - this overall functionality is responsible for setting up, modifying and releasing E-RABs, which are triggered by the MME. Note that the release of E-RABs may be triggered by the eNB as well.

l Initial Context Transfer - this is used to establish an S1 UE context in the eNB, to setup the default IP connectivity, to setup one or more E-RAB(s) if requested by the MME, as well as to transfer NAS (Non Access Stratum) signaling related information to the eNB if needed.

l UE Capability Information Indication - this functionality is used to provide the UE Capability Information when received from the UE to the MME.

l Mobility - this function is for UEs in LTE_ACTIVE in order to enable: − a change of eNBs within the SAE/LTE (Inter MME/Serving SAE-GW Handovers)

via the S1 interface (within EPC involvement). − a change of RAN nodes between different RATs (Inter-3GPP-RAT Handovers) via

the S1 interface (with EPC involvement). l Paging - this functionality provides the EPC with the capability to page the UE. l S1 Interface Management - this function comprise of the:

− Reset functionality - this ensures a well defined initialization on the S1 interface. − Error Indication - this is to allow proper error reporting/handling in cases where no

failure messages are defined. − Overload - this is used to indicate the load situation in the Control Plane of the S1

interface. − Load balancing -this is used to ensure equally loaded MMEs within an MME pool

area. − S1 Setup - this is used for initial S1 interface setup for providing configuration

information. − eNB and MME Configuration Update - these are used to update application level

configuration data needed for the eNB and MME to interoperate correctly on the S1 interface.

l NAS Signaling Transport - this is between the UE and the MME and is used to: − transfer NAS signaling related information and to establish the S1 UE context in the

eNB. − transfer NAS signaling related information when the S1 UE context in the eNB is

already established. l S1 UE Context Release - this functionality manages the release of UE specific contexts

in the eNB and the MME. l UE Context Modification - this functionality allows the partial modification of the

established UE Context. l Status Transfer - this functionality transfers PDCP SN Status information from the

source eNB to target eNB in support of in-sequence delivery and duplication avoidance for intra LTE handover.

l Trace - this functionality is to control a trace recording for a UE in ECM_CONNECTED.

l Location Reporting - this functionality allows MME to be aware of the UEs current location.


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l S1 CDMA2000 Tunneling - this functionality is to carry CDMA2000 signaling between the UE and CDMA2000 RAT over the S1 interface.

l Warning Message Transmission - this functionality provides the means to start and overwrite the broadcasting of warning messages.

l RIM (RAN Information Management) - this functionality allows the request and transfer of RAN system information (e.g. GERAN system information) between two RAN nodes via the core network.

l Configuration Transfer - this functionality allows the request and transfer of RAN configuration information (e.g. SON information) between two RAN nodes via the core network.

4.2.2 S1AP Elementary Procedures The S1AP, like X2AP, consists of different classes of procedures, namely Class 1 (with response) and Class 2 (without response). Table 4-3 illustrates the Class 1 S1AP Procedures and associated messages.

Table 4-3 S1AP Class 1 Elementary Procedures

Elementary Procedure

Initiating Message Successful Outcome

Unsuccessful Outcome

Response message Response message

Handover Preparation

HANDOVER REQUIRED

HANDOVER COMMAND

HANDOVER PREPARATION FAILURE

Handover Resource Allocation

HANDOVER REQUEST

HANDOVER REQUEST ACKNOWLEDGE

HANDOVER FAILURE

Path Switch Request PATH SWITCH REQUEST

PATH SWITCH REQUEST ACKNOWLEDGE

PATH SWITCH REQUEST FAILURE

Handover Cancellation

HANDOVER CANCEL

HANDOVER CANCEL ACKNOWLEDGE

E-RAB Setup E-RAB SETUP REQUEST

E-RAB SETUP RESPONSE

E-RAB Modify E-RAB MODIFY REQUEST

E-RAB MODIFY RESPONSE

E-RAB Release E-RAB RELEASE COMMAND

E-RAB RELEASE RESPONSE

Initial Context Setup INITIAL CONTEXT SETUP REQUEST

INITIAL CONTEXT SETUP RESPONSE

INITIAL CONTEXT SETUP FAILURE

Reset RESET RESET ACKNOWLEDGE



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S1 Setup S1 SETUP REQUEST

S1 SETUP RESPONSE

S1 SETUP FAILURE

UE Context Release UE CONTEXT RELEASE COMMAND

UE CONTEXT RELEASE COMPLETE

UE Context Modification

UE CONTEXT MODIFICATION REQUEST

UE CONTEXT MODIFICATION RESPONSE

UE CONTEXT MODIFICATION FAILURE

eNB Configuration Update

ENB CONFIGURATION UPDATE

ENB CONFIGURATION UPDATE ACKNOWLEDGE

ENB CONFIGURATION UPDATE FAILURE

MME Configuration Update

MME CONFIGURATION UPDATE

MME CONFIGURATION UPDATE ACKNOWLEDGE

MME CONFIGURATION UPDATE FAILURE

Write-Replace Warning

WRITE-REPLACE WARNING REQUEST

WRITE-REPLACE WARNING RESPONSE

The S1AP also include various Class 2 procedures which are always considered to be successful and therefore do not require a response.

Table 4-4 S1AP Class 2 Elementary Procedures

Elementary Procedure Message

Handover Notification HANDOVER NOTIFY

E-RAB Release Indication E-RAB RELEASE INDICATION

Paging PAGING

Initial UE Message INITIAL UE MESSAGE

Downlink NAS Transport DOWNLINK NAS TRANSPORT

Uplink NAS Transport UPLINK NAS TRANSPORT

NAS non delivery indication NAS NON DELIVERY INDICATION

Error Indication ERROR INDICATION

UE Context Release Request UE CONTEXT RELEASE REQUEST

DownlinkS1 CDMA2000 Tunneling DOWNLINK S1 CDMA2000 TUNNELING

Uplink S1 CDMA2000 Tunneling UPLINK S1 CDMA2000 TUNNELING

UE Capability Info Indication UE CAPABILITY INFO INDICATION

eNB Status Transfer eNB STATUS TRANSFER


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MME Status Transfer MME STATUS TRANSFER

Deactivate Trace DEACTIVATE TRACE

Trace Start TRACE START

Trace Failure Indication TRACE FAILURE INDICATION

Location Reporting Control LOCATION REPORTING CONTROL

Location Reporting Failure Indication

LOCATION REPORTING FAILURE INDICATION

Location Report LOCATION REPORT

Overload Start OVERLOAD START

Overload Stop OVERLOAD STOP

eNB Direct Information Transfer eNB DIRECT INFORMATION TRANSFER

MME Direct Information Transfer MME DIRECT INFORMATION TRANSFER

eNB Configuration Transfer eNB CONFIGURATION TRANSFER

MME Configuration Transfer MME CONFIGURATION TRANSFER

Cell Traffic Trace CELL TRAFFIC TRACE

4.2.3 S1 Setup The S1 Setup procedure is used to exchange configured data which is required in the MME and in the eNB respectively to ensure a proper interoperation. The S1 Setup procedure is triggered by the eNB and is the first S1AP procedure which will be executed. Figure 4-15 illustrates the S1 Setup Request parameters.

Figure 4-15 S1 Setup Request



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The eNB informs the MME of its Global eNB Identity, supported TA (Tracking Areas), Broadcasted PLMN(s) and CSG information, as well as Default Paging DRX information.

In response to the S1 Setup Request messages the MME sends a S1 Setup Response. This includes the served GUMMEI(s) and relative MME capacity. In addition, this message can also include a MME name, e.g. “Primary MME”.

Figure 4-16 S1 Setup Response

4.2.4 eNB and MME Configuration Update Both the eNB and MME can also send a configuration update message to update information previously sent in the S1 Setup procedure. These messages carry similar information to the S1 Setup Request and S1 Setup Response messages.

4.2.5 NAS Transport The role of NAS transport is to transparently move messages between the UE and the MME that have no relevance to the eNB. The procedures providing this functionality are the Initial UE Message, Uplink NAS Transport, Downlink NAS Transport, Downlink NAS Non Delivery Indication.

Initial UE Message When the eNB has received, from the radio interface, the first Uplink NAS message transmitted on an RRC connection to be forwarded to an MME, the eNB invokes the NAS Transport procedure and sends the Initial UE Message to the MME including the NAS message as a NAS-PDU. Note that the first Uplink NAS message is always received in the RRC Connection Setup Complete message.


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The Initial UE Message contains the following information:

l eNB - UE S1AP ID - the eNB allocates a unique eNB UE S1AP ID to be used for the UE and this identifies the UE association over the S1 interface.

l NAS PDU - this contains the NAS message, e.g. EMM Attach with PDN Connectivity Request.

l TAI - this contains the PLMN Code and TA Code of the TA in which the UE has sent the NAS message.

l E-UTRAN CGI - contains the cell identify from which the UE has sent the NAS message.

l S-TMSI - this is the identity of the UE and is sent to the MME if it was received on the air interface.

l CSG ID - this identifies the CSG (Closed Subscriber Group). l RRC Establishment Cause - indicates to the MME the reason for RRC connection

establishment. l GUMMEI - conveys the Globally Unique MME Identity.

Figure 4-17 S1 Initial UE Message

Downlink and Uplink NAS Transport Subsequent NAS signaling between the UE and MME can be carried by various S1 signaling messages, such as Downlink NAS Transport and Uplink NAS Transport. However, other S1AP messages can also carry NAS signaling, these include the Initial Context Setup Request, E-RAB Setup, E-RAB Modification and E-RAB Release messages. Figure 4-18 illustrates the Downlink and Uplink NAS transport messages, as well as their contents. It is worth noting that these messages are independent of each other.



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Figure 4-18 S1 Downlink and Uplink NAS Transport

The Downlink NAS Transport message contains the identifiers referencing the UE, the NAS-PDU and a possible Handover Restriction List. The latter is used to update the eNB on roaming area or access restrictions.

The Uplink NAS Transport message is similar, however the current E-UTRAN CGI and TAI are added.

NAS Non Delivery Indication If a eNB decides not to start the delivery of a NAS message or the eNB is unable to ensure that the message has been received by the UE, it sends a NAS Non Delivery Indication message to the MME. This includes the non-delivered NAS message and an appropriate cause value e.g. "S1 intra system Handover Triggered", "S1 inter system Handover Triggered" or "X2 Handover Triggered". Note that the X2 interface cannot carry or forward NAS PDUs as part of the handover.

4.2.6 Initial Context Setup The Initial Context Setup message is used to pass the relevant information in order to establish the UEs context. Figure 4-19 illustrates the parameters in the Initial Context Setup Request message. In addition to the MME UE S1AP ID and eNB UE S1AP ID association identifiers, the other parameters include:

l UE Aggregate Maximum Bit Rate - this indicates to the eNB the total aggregate data rate assigned to the UE.

l RAB to be Setup List - this includes the E-RAB context information. Each E-RAB includes an E-RAB ID, QoS parameters and User Plane tunnel information, i.e. an IP address and TEID (Tunnel Endpoint Identifier).

l UE Security Capabilities - this indicates the security algorithms supported by the UE. l Security Key - the purpose of the Security Key IE is to provide security related

parameters to the eNB. l Trace Activation - this optional parameter is able to setup RRC, X2 and S1AP tracing for

a UE.


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l Handover Restriction List - this optional parameter is used to update the eNB on roaming area or access restrictions.

l UE Radio Capability - this optional parameter provides the eNB with initial UE radio capability.

l Subscriber Profile ID for RAT/Frequency Priority - this optional parameter is used to define camp priorities in Idle Mode and to control inter-RAT/inter-frequency handover in Active Mode.

l CS Fallback Indicator - this optional parameter indicates that a fallback to the CS domain is needed.

l SRVCC Operation Possible - this optional parameter indicates if SRVCC is possible.

Figure 4-19 S1 Initial Context Setup Request

Initial Context Setup Response The eNB sends the Initial Context Setup Response message back to the MME indicating the E-RABs setup or failed. In addition, for each E-RAB established the eNB provides User Plane tunnel information in the form of a Transport Layer Address and TEID.

Finally, a Criticality Diagnostics parameter may be included if parts of a received message have not been comprehended or were missing.



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Figure 4-20 Initial Context Setup Response

Initial Context Setup Failure If the eNB is not able to establish an S1 UE context, or cannot even establish one non GBR bearer it considers the procedure to have failed and replies with the Initial Context Setup Failure message. This includes a cause and optionally the criticality diagnostics parameter.

UE Context Modification The purpose of the UE Context Modification procedure is to modify the established UE Context. It enables the MME to modify the:

l Security Key. l Subscriber Profile ID for RAT/Frequency priority. l UE Aggregate Maximum Bit Rate. l CS Fallback Indicator.

4.2.7 E-RAB Establishment The E-RAB Setup procedure is used to setup UE resources, i.e. additional EPS Bearers. Figure 4-21 illustrates the key parameters. Note that these are identical to the ones used in the Initial Context Setup Request and Response messages, i.e. involves interaction between MME and S-GW.


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Figure 4-21 S1 E-RAB Setup Request

Figure 4-22 illustrates the E-RAB Setup Response message and the eNB E-RAB address parameters for downlink data delivery.

Figure 4-22 S1 E-RAB Setup Response

E-RAB Modification Request and Response This message is sent due to the requirement to modify the E-RAB, i.e. a change to the QoS or the TFT (Traffic Flow Template) filters. The E-RAB modification message is almost identical to the E-RAB Setup however it does not include the User Plane Tunnel information (since it already exists). The main parameters are the E-RAB QoS and the associated NAS signaling.



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E-RAB Release Command and Response Assuming that one or more EPS Bearer needs to be released (not all) the MME can sent a E-RAB Release Command message to the eNB. This includes the E-RAB ID and optionally associated NAS signaling.

E-RAB Release Indication The eNB is able to trigger the releasing of one or more E-RAB(s) belonging to a UE. This is achieved using the E-RAB Release Indication message which includes the E-RAB ID(s).

Figure 4-23 E-RAB Release Indication

If the eNB wants to remove all remaining E-RABs e.g. for user inactivity, the UE Context Release Request procedure is used instead.

4.2.8 S1 Handover The E-UTRAN supports multiple scenarios for handover, for example intra MME, inter MME, inter S-GW, inter RAT, etc. For these different scenarios typically the same message set is used, however the information elements within the messages may be different. A handover involves three phases:

l Handover preparation. l Handover resource allocation. l Handover notification.

Correlation of S1AP handover messages is examined in Section 错误！未找到引用源。.

Figure 4-24 illustrates a scenario resulting in an intra MME handover with possible S-GW change.


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Figure 4-24 Requirement for S1 Handover Procedures

Handover Preparation Phase - Handover Request The purpose of the Handover Preparation procedure is to request the preparation of resources at the target side via the EPC. The source eNB initiates the handover preparation by sending the Handover Required message to the serving MME. Figure 4-25 illustrates the S1AP Handover Required message.

Figure 4-25 S1 Handover Required

eNBMME

Handover Required

Handover RequiredMME UE S1AP IDeNB UE S1AP IDHandover TypeCauseTarget IDDirect Forwarding Path Availability (O) SRVCC HO Indication (O)Source to Target Transparent ContainerSource to Target Transparent Container Secondary (O)MS Classmark 2 (C) if SRVCC to GERANMS Classmark 3 (C) if SRVCC to GERAN

Source



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The message contains the following information elements:

l MME UE S1AP ID - this is used to associate signaling relating to a specific UE on the S1 interface at the MME.

l eNB UE S1AP ID - this is used to associate signaling relating to a specific UE on the S1 interface at the eNB.

l Handover Type - this defines the type of handover that is required. These include: − Intra LTE. − LTE to UTRAN. − LTE to GERAN.

l Cause - this element indicates to the MME the reason for the handover including reasons with the radio network layer, transport network layer, NAS and protocol.

l Target ID - for intra LTE mobility this is the Global eNB ID and is expressed as the first 20bits of the cell ID in the case of macro eNB and for Home eNB it is the entire 28bit cell identity. For inter-RAT mobility this parameter relates to the target cell, e.g. the CGI (Cell Global Identifier).

l Direct Forwarding Path Availability - this indicates to the MME if traffic can be forwarded directly from the source to the target eNB or if it must be routed through the EPC.

l SRVCC HO Indication - this indicates that SRVCC (Single Radio Voice Call Continuity) procedures need to be supported as part of this handover. SRVCC is the architecture defined to ensure call continuity between IMS, over PS access, and CS access for calls that are anchored in the IMS when the UE is capable of transmitting/receiving on only one of those access networks at a given time.

l Source to Target Transparent Container - this element contains the transparent container which includes radio related information that must be passed between the source and target eNB through the EPC. Note that depending on the mobility scenarios it could include inter-RAT containers. In addition, when SRVCC is used and the handover is to GERAN with DTM (Dual Transfer Mode) HO support a “secondary” Source to Target Transparent Container is sent.

l MS (Mobile Station) Classmark 2 and 3 - these are included as part of a SRVCC handover to GERAN.

Handover Preparation Phase - Handover Command The Handover Command message is sent by the MME to indicate to the source eNB that the handover has been prepared by the target.


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Figure 4-26 S1 Handover Command

The Handover Command message includes similar parameters to other S1 messages. In addition, it includes NAS security parameters when handing over from E-UTRAN to a 3G/2G system. It also indicates if any of the E-RAB need to be released.

Handover Preparation Phase - Handover Preparation Failure The Handover Preparation failure message is sent by the MME to inform the source eNB that the Handover Preparation has failed.

Handover Resource Allocation Phase - Handover Request The purpose of Handover Resource Allocation Phase is to identify and reserve resources for the handover at the target eNB. Figure 4-27 illustrates the Handover Request message. The parameters are similar to the Initial Context Setup Request message however additional handover security parameters for interworking are included.



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Figure 4-27 S1 Handover Request

The Request Type parameter is part of Location Reporting and is detailed in Section 4.2.15

Handover Resource Allocation Phase - Handover Request Acknowledge On receiving the Handover Request message from the MME the eNB sends a Handover Request Acknowledge message.

Figure 4-28 illustrates the Handover Request Acknowledge message. This includes the admitted E-RAB(s) and associated parameters for handling the User Plane tunnels, namely eNB Transport Layer Address and GTP-TEID. In addition, it can also include:

l DL Transport Layer Address and DL GTP-TEID - these parameters (optionally) are passed to the source to indicate where to deliver forwarded downlink PDCP SDUs.

l UL Transport Layer Address and UL GTP-TEID - these parameters (optionally) are passed to the source to indicate where to deliver forwarded uplink PDCP SDUs.


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Figure 4-28 Handover Request Acknowledge

Handover Resource Allocation Phase - Handover Failure The Handover Failure message is sent by the target eNB to inform the MME that the preparation of resources has failed. It includes an appropriate cause value.

Handover Notification Phase The purpose of notification is to inform the MME that the UE has successfully been handed over to the target eNB. Figure 4-29 illustrates the Handover Notify message and associate parameters.

Figure 4-29 Handover Notify

4.2.9 Path Switch The Path Switch Request message is sent by the eNB to request the MME to switch downlink GTP tunnel termination point(s) from one end-point to another. Note it is also discussed in Section 错误！未找到引用源。.



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Path Switch Request Figure 4-30 illustrates an example whereby the handover has taken place between two eNBs. On completion of the handover the target eNB sends the Path Switch Request message to the MME indicating a new eNB UE S1AP ID, as well as the original MME UE S1AP ID. The MME on receiving this message triggers a GTPv2-C Modify Bearer procedure towards the S-GW.

Figure 4-30 S1 Path Switch Request

Path Switch Request Acknowledge The MME, on successfully updating the S-GW, forwards the Path Switch Request Acknowledge message to the target eNB.

Figure 4-31illustrates the Path Switch Request Acknowledge message and its parameters. The MME has assigned a new MME UE S1AP ID and other parameters are similar to previous S1AP messages.

It is worth noting that if multiple EPS Bearers (multiple E-RABs) were active, each would be assigned a new Transport Layer Address and GTP-TEID.


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Figure 4-31 Path Switch Request Acknowledge

4.2.10 Handover Cancel The purpose of the Handover Cancel procedure is to enable a source eNB to cancel an ongoing handover preparation or an already prepared handover. Figure 4-32 illustrates the Handover Cancel procedure.

Figure 4-32 Handover Cancel



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4.2.11 Status Transfer The purpose of the eNB Status Transfer procedure and MME Status Transfer procedure is to transfer the uplink PDCP-SN and HFN receiver status and the downlink PDCP-SN and HFN transmitter status from the source eNB to the target eNB via the MME during an intra LTE S1 handover for each respective E-RAB for which PDCP-SN and HFN status preservation applies. These messages carry a container which includes similar parameters to the X2 Status Transfer message discussed in Section 4.1.4 .

4.2.12 UE Context Release The UE Context Release procedure enables the MME to release of the UE associated logical connection due to various reasons, for example:

l Completion of a transaction between the UE and the EPC. l Completion of successful handover. l Completion of handover cancellation. l Release of the old UE associated logical S1-connection when two UE-associated logical

S1-connections toward the same UE are detected after the UE has initiated the establishment of a new UE associated logical S1-connection.

The procedure uses UE-associated S1 connection.

Figure 4-33 illustrates the UE Context Release Command message towards the MME. This contain the UE S1AP ID pair parameter (if available), otherwise it contain the MME UE S1AP ID.

Figure 4-33 UE Context Release

UE Context Release Request - eNB Initiated The purpose of the UE Context Release Request procedure is to enable the eNB to request the MME to release the UE associated logical S1 connection due to E-UTRAN generated reason.


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Figure 4-34 UE Context Release Request

4.2.13 Reset The purpose of the Reset procedure is to initialize or re-initialize the E-UTRAN, or part of E-UTRAN S1AP UE-related contexts, in the event of a failure in the EPC or vice versa.

Figure 4-35 S1 Reset

4.2.14 S1 Trace Procedures The E-UTRAN includes the ability to activate tracing of the S1, X2 and Uu Interfaces.

Trace Start The purpose of the Trace Start procedure is to allow the MME to request the eNB to start a trace session for a UE in ECM_Connected mode.

The Trace Activation parameter includes:

l E-UTRAN Trace ID - this is the E-UTRAN Trace ID and is composed of the Trace Reference (leftmost 6 octets) and Trace Recording Session Reference (last 2 octets).

l Interfaces To Trace - this is a bit map with each position represents a eNB interface. The first bit =S1-MME, second bit =X2, third bit =Uu with all other bits reserved for future use. The value ‘1’ indicates ‘should be traced’ and the value ‘0’ indicates ‘should not be trace’.

l Trace depth - this indicates the level of the trace, options include: − Minimum. − Medium.



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− Maximum. − Minimum without Vendor Specific Extension. − Medium without Vendor Specific Extension. − Maximum without Vendor Specific Extension.

l Trace Collection Entity IP Address - this is the Transport Layer Address to send the trace.

Figure 4-36 S1 Trace Start

Trace Failure Indication The purpose of the Trace Failure Indication procedure is to allow the eNB to inform the MME that a Trace Start procedure or a Deactivate Trace procedure has failed due to an interaction with a handover procedure.

Deactivate Trace The purpose of the Deactivate Trace procedure is to allow the MME to request the eNB to stop the trace session, for the indicated trace reference.

Cell Traffic Trace All conditions for Cell Traffic Trace are defined by the O&M (Operations and Maintenance). When the condition to start the trace recording is fulfilled the eNB will allocate a Trace Recording Session Reference and send it together with the Trace Reference to the MME in a Cell Traffic Trace message over the S1 interface. Note that the Cell Traffic Trace will not be propagated on the X2 interface or on the S1 interface in case of handover.

4.2.15 Location Reporting Control The purpose of Location Reporting Control procedure is to allow the MME to request the eNB to report where the UE is currently located.

The Request Type contains two parameters:

l Event - this can indicate Direct, Change of service cell, Stop Change of service cell. l Report Area - this has only one option, i.e. ECGI.


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Figure 4-37 Location Report Control

4.2.16 Overload The purpose of the Overload Start procedure is to inform an eNB to reduce the signaling load towards the concerned MME.

Figure 4-38 Overload Start

The Overload Start message indicates the Overload Action to be performed. This is either:

l Reject all RRC connection establishments for non-emergency Mobile Originated Direct Transfer.

l Reject all RRC connection establishments for Signaling. l Permit Emergency Sessions only.

Overload Stop The purpose of the Overload Stop procedure is to signal to an eNB the MME is connected to that the overload situation at the MME has ended and normal operation can resume.

4.2.17 Direct Information Transfer The purpose of the eNB Direct Information Transfer procedure and MME Direct Information Transfer procedure is to transfer RAN (Radio Access Network) information to and from the eNB. Note that the MME does not interpret the transferred RAN information. The payload includes RIM (RAN Information Management) to and from a GERAN BSS (Base Station Subsystem).



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4.2.18 Paging The paging of UEs in Idle Mode is facilitated by the MME to send a Paging message to all eNBs managing the UEs TAI (Tracking Area Identity) or TAIs. Figure 4-39 illustrates the Paging message and its parameter.

Figure 4-39 Paging

The key parameters include:

l UE Identity Index Value - this is used by the eNB for calculating the paging occurrence. The value relates to the IMSI mod 1024.

l UE Paging Identity - this is the S-TMSI for the UE. l Paging DRX (O) - this indicates the default Paging DRX value. l CN Domain - this indicates whether this is a PS (Packet Switched) or CS (Circuit

Switched) paging request. l List of TAIs - this indicates to the eNB which TAI(s) the paging message should be send. l CSG Id List - this indicates which CSG (Closed Subscriber Group) Identity cells should

be paged.

4.3 User Plane GTP Functions and Procedures There are various types and version of GTP (GPRS Tunneling Protocol). The E-UTRAN specifically uses GTPv1-U (GPRS Tunneling Protocol Version 1 - User) on the X2 and S1-U interfaces. It is worth noting that GTPv1-U is also in the User Plane tunnel in the EPC.

4.3.1 GTP Tunnels Many UE PDN (Packet Data Network) sessions, termed GTP Tunnels, may be multiplexed across the GTP Path using the TEID (Tunnel Endpoint Identifier). The receiving side of a GTP tunnel locally assigns the TEID value the transmitting side has to use. The TEID values are exchanged between tunnel endpoints using S1AP messages on the S1-MME interface and GTPv2-C (GPRS Tunneling Protocol Version 2 - Control) messages on the S11 interface. Figure 4-40 illustrates the concept of a GTP tunnel and the associated endpoints.


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Figure 4-40 GTP Tunnel

Each GTP Tunnel supports one EPS Bearer, i.e. E-RAB. Thus multiple tunnels exist for multiple UEs.

4.3.2 GTPv1-U Header It is worth noting the headers for GTPv1-U are different to GTPv2-C. Figure 4-41 illustrates the GTPv1-U header, highlighting the TEID field.

Figure 4-41 GTPv1-U Header

The parameters in the header include:

l Version - this field is used to determine the version of the GTP-U protocol, i.e. version 1. l PT (Protocol Type) - this bit is used as a protocol discriminator between GTP (when PT

is '1') and GTP’ (when PT is '0'). Note GTP’ is not used in the E-UTRAN. l E (Extension) - this flag indicates the presence of a meaningful value of the Next

Extension Header Type field. When it is set to '1', the Next Extension Header field is present and interpreted.



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l S (Sequence) - this flag indicates the presence of a meaningful value of the Sequence Number field. For the Echo Request, Echo Response, Error Indication and Supported Extension Headers Notification messages, the S flag is be set to '1'. Since the use of Sequence Numbers is optional for G-PDUs, the PDN-GW, S-GW and eNB should set the flag to '0'. However, when a G-PDU is being relayed by the Indirect Data Forwarding for Inter RAT HO procedure, then if the received G-PDU has the S flag set to '1', then the relaying entity shall set S flag to '1' and forward the G-PDU.

l PN (N-PDU Number) - this flag indicates the presence of a meaningful value of the N-PDU Number field. When it is set to '1', the N-PDU Number field is present and interpreted.

l Message Type - this field indicates the type of GTP-U message. l Length - this field indicates the length in octets of the payload, i.e. the rest of the packet

following the mandatory part of the GTP header (that is the first 8 octets). l TEID (Tunnel Endpoint Identifier) - this field unambiguously identifies a tunnel

endpoint in the receiving GTP-U protocol entity. The receiving end side of a GTP tunnel locally assigns the TEID value the transmitting side has to use. The TEID is used by the receiving entity to find the EPS Bearer, except for the following cases: − The Echo Request/Response and Supported Extension Headers notification messages,

where the Tunnel Endpoint Identifier is set to all zeroes. − The Error Indication message where the Tunnel Endpoint Identifier is set to all zeros.

Optional Fields l Sequence Number - this is used for G-PDUs, an increasing sequence number for the

original IP packets transmitted via GTP-U tunnels, when transmission order must be preserved.

l N-PDU Number - this is used at the Inter SGSN Routing Area Update procedure and some inter-system handover procedures (e.g. between 2G and 3G radio access networks). It coordinates the data transmission for acknowledged mode of communication between the 2G MS (Mobile Station) and the SGSN (Serving GPRS Support Node).

l Next Extension Header Type - this defines the type of Extension Header that follows this field in the GTP-PDU, e.g. PDCP PDU number.

4.3.3 Extension Header Figure 4-42 illustrates the GTP extension header. This includes the content and its length, i.e. the type field in the GTP header indicated what was included.

Figure 4-42 GTP Extension Header

Following the Extension Header Content a “Next Extension Header Content” is added. This indicates if an additional extension header is added, if not, it is set to zero.

Currently there are two defined extension headers, namely UDP Port and PDCP PDU number.


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Extension Header - UDP Port This extension header is usually transmitted in Error Indication messages to provide the UDP Source Port of the G-PDU that triggered the Error Indication.

Extension Header - PDCP PDU Number This extension header is transmitted between eNBs when PDCP PDU packets are forwarded between the source and target eNBs. The use of this extension header is discussed in Section 错误！未找到引用源。.

4.3.4 Handling of Sequence Numbers For PDN-GW, S-GW and eNB the usage of sequence numbers in G-PDUs is optional, but if present GTP-U protocol entities in these nodes are relaying G-PDUs to other nodes, then they relay the sequence numbers.

4.3.5 GTPv1-U Procedures Table 4-5 lists the various GTPv1-U messages. The G-PDU is used to tunnel IP datagrams to and from the eNB.

Table 4-5 Messages in GTP-U

Message Type Value Message

1 Echo Request

2 Echo Response

3-25 Reserved

26 Error Indication

27-30 Reserved

31 Supported Extension Headers Notification

32-253 Reserved

254 End Marker

255 G-PDU

4.3.6 Path Management

Echo Procedure GTP-U peer entities can send an Echo Request on a path to find out if it is alive. The Echo Request messages can also be sent for each path in use, i.e. for each EPS Bearer. The procedure can be repeated periodically and whilst the timing is implementation specific it is not sent more often than every 60s on each path. Note that this does not prevent resending an Echo Request with the same sequence number based on response timers.



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Figure 4-43 GTP Echo Procedure

For the GTP-U tunnel setup between two nodes for forwarding user traffic, e.g. between eNBs for direct forwarding over X2, Echo Request path maintenance message are not sent except if the forwarded data and the normal data are sent over the same path.

Path Failure A path counter is used to manage each path. This is used in conjunction with a T3-Response Timer and N3-Requests parameter. The path counter is reset each time an Echo Response is received on the path and incremented when the T3-Response Timer expires for any Echo Request message sent on the path. The path is classed as down if the counter exceeds N3-Requests. In this case, the GTP-U peer may notify the Operation and Maintenance network element. In addition, the GTP-U peer will also notify the upper layer of the path failure, so that EPS contexts associated with the path may be deleted. The recommended value for the N3-Requests parameter is 5 and the T3-Response Timer is usually 20 seconds.

Supported Extension Headers Notification Procedure The Supported Extension Headers Notification message indicates a list of supported Extension Headers that the GTP entity on the identified IP address can support.

Figure 4-44 Supported Extension Headers Notification


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This message is sent only in case a GTP entity was required to interpret a mandatory Extension Header but the GTP entity was not yet upgraded to support that extension header. The peer GTP entity may retry to use all the extension headers with that node, in an attempt to verify it has been upgraded.

Error Indication Procedure When a GTP-U node receives a GTP-U PDU for which no EPS Bearer context exists the GTP-U node discards it and returns a GTP error indication to the originating node. Note that the GTP entities may include the "UDP Port" extension header (Type 0x40), in order to simplify the implementation of mechanisms that can mitigate the risk of Denial-of-Service attacks in some scenarios.

End Marker Procedure The End Marker procedure is one of the key procedures performed by GTPv1-U. Figure 4-45 illustrates a handover scenario whereby the End Maker message is sent following the last packet to the source eNB. Note that multiple End Marker messages may be sent, for example one for each EPS Bearer.

Figure 4-45 End Marker Procedure

4.3.7 UDP header and Port Numbers The registered port for GTP-U is 2152 and depending on the actual GTP message or procedure this value, or a different value, may be used. The different

l Echo Request Message - the UDP Destination Port number for GTP-U request messages is 2152. The UDP Source Port is a locally allocated port number at the sending GTP-U entity.

l Echo Response Message - the UDP Destination Port value is the UDP Source Port of the corresponding request message. The UDP Source Port is the value from the UDP Destination Port of the corresponding request message.

l Encapsulated T-PDUs - the UDP Destination Port number is 2152. The UDP Source Port is a locally allocated port number at the sending GTP-U entity.

l Error Indication - the UDP destination port for the Error Indication is the User Plane UDP port (2152). The UDP source port is locally assigned at the sending node.



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NOTE: In network deployments including non-GTP-aware stateful firewalls, those firewalls must be configured to allow response messages coming from a different UDP port and IP address than the triggering message.

l Supported Extension Headers Notification - the UDP destination port for the Supported Extension Headers Notification is the User Plane UDP port (2152). The UDP source port is locally assigned at the sending node.



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5 Glossary

Numerics

16 QAM (Quadrature Amplitude Modulation) 64QAM (Quadrature Amplitude Modulation) 2G (Second Generation) 3G (Third Generation) 3GPP (Third Generation Partnership Project) 4G (Fourth Generation)

A

AAA (Access Authorization and Accounting) AC (Access Class) AES (Advanced Encryption Standard) AKA (Authentication and Key Agreement) AM (Acknowledged Mode) AMBR (Aggregate Maximum Bit Rate) AMD (Acknowledged Mode Data) APN (Access Point Name) APN AMBR (Access Point Name Aggregate Maximum Bit Rate) ARP (Allocation and Retention Priority) AS (Access Stratum)

B

BCCH (Broadcast Control Channel) BCH (Broadcast Channel) BI (Backoff Indicator) BSR (Buffer Status Report)

C

C (Conditional)

CCCH (Common Control Channel) CGI (Cell Global Identifier) CQI (Channel Quality Indication) CRF (Charging Rules Function) CS (Circuit Switched) CSG (Closed Subscriber Group)

D

D/C (Data/Control) dB (Decibels) DCCH (Dedicated Control Channel) DL-SCH (Downlink - Shared Channel) DRB (Data Radio Bearer) DRX (Discontinuous Reception) DSCP (Differentiated Services Code Point) DTCH (Dedicated Traffic Channel) DTM (Dual Transfer Mode)

E

E (Extension) EARFCN (E-UTRA Absolute Radio Frequency Channel Number) ECGI (E-UTRAN Cell Global Identifier) ECI (Evolved Cell Identity) EIR (Equipment Identity Register) EMM (EPS Mobility Management) eNB (Evolved Node B) EP (Elementary Procedures) EPC (Evolved Packet Core) ePDG (evolved Packet Data Gateway) EPS (Evolved Packet System)

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E-RAB (E-UTRAN - Radio Access Bearer) ESM (EPS Session Management) ESM (Evolved Session Management) E-UTRA (Evolved - Universal Terrestrial Radio Access) E-UTRAN (Evolved - Universal Terrestrial Radio Access Network)

F

FAC (Final Assembly Code) FDD (Frequency Division Duplex) FI (Frame Information) FO (First-Order)

G

GBR (Guaranteed Bit Rate) GERAN (GSM/EDGE Radio Access Network) GTP (GPRS Tunneling Protocol) GTP-U (GPRS Tunneling Protocol - User) GTPv1-U (GPRS Tunneling Protocol Version 1 - User Plane) GTPv2-C (GPRS Tunneling Protocol Version 2 - Control) GU Group ID (Globally Unique Group Identifier) GUMMEI (Globally Unique MME Identifier) GUTI (Globally Unique Temporary Identity)

H

HA (Home Agent) HARQ (Hybrid Automatic Repeat Request) HeNB (Home Evolved Node B) HeNB-GW (Home Evolved Node B - Gateway) HFN (Hyper Frame Number) HPLMN (Home Public Land Mobile Network) HRPD (High Rate Packet Data) HSS (Home Subscriber Server)

I

IE (Information Elements) IETF (Internet Engineering Task Force)

IMEI (International Mobile Equipment Identity) IMS (IP Multimedia Subsystem) IMSI (International Mobile Subscriber Identity) IR (Initialization and Refresh)

L

LCG ID (Logical Channel Group Identity) LCID (Logical Channel Identifier) LI (Length Indicator) LSF (Last Segment Flag) LTE (Long Term Evolution)

M

M (Mandatory) MAC (Medium Access Control) MAC-I (Message Authentication Code - Integrity) MAG (Mobile Access Gateway) MCC (Mobile Country Code) ME (Mobile Equipment) MIB (Master Information Block) MIMO (Multiple Input Multiple Output) MME (Mobility Management Entity) MMEC (MME Code) MNC (Mobile Network Code) MS (Mobile Station) MSB (Most Significant Bits) MSIN (Mobile Subscriber Identity Number) M-TMSI (MME - Temporary Mobile Subscriber Identity)

N

NAS (Non Access Stratum) non-GBR (non - Guaranteed Bit Rate) NSAPI (Network layer Service Access Point Identifier)

O

O (Optional) O&M (Operations and Maintenance) OFDMA (Orthogonal Frequency Division Multiple Access)

P

P (Polling)



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PBCH (Physical Broadcast Channel) PBR (Prioritized Bit Rate) PCCH (Paging Control Channel) PCFICH (Physical Control Format Indicator Channel) PCH (Paging Channel) PCI (Physical Cell Identifier) PCRF (Policy and Charging Rules Function) PDCCH (Physical Downlink Control Channel) PDCP (Packet Data Convergence Protocol) PDF (Policy Decision Function) PDN (Packet Data Network) PDSCH (Physical Downlink Shared Channel) PDU (Protocol Data Unit) PH (Power Headroom) PHICH (Physical Hybrid ARQ Indicator Channel) PHR (Power Headroom Report) PHY (Physical Layer) PL (Pathloss) PLMN (Public Land Mobile Network) PMIP (Proxy Mobile IP) PN (N-PDU Number) PRACH (Physical Random Access Channel) PRB (Physical Resource Block) PS (Packet Switched) PT (Protocol Type) PUCCH (Physical Uplink Control Channel) PUSCH (Physical Uplink Shared Channel)

Q

QCI (QoS Class Identifier) QoS (Quality of Service) QPSK (Quadrature Phase Shift Keying)

R

RA (Random Access) RACH (Random Access Channel) RAI (Routing Area Identity) RAN (Radio Access Network) RAPID (Random Access Preamble Identifier) RAR (Random Access Response) RAT (Radio Access Technology)

RB (Radio Bearer) RLC (Radio Link Control) RLF (Radio Link Failure) RNC (Radio Network Controller) RNL (Radio Network Layer) RNTP (Relative Narrowband Tx Power) ROHC (Robust Header Compression) RR (Radio Resource) RRC (Radio Resource Control) RRM (Radio Resource Management) RSRP (Reference Signal Received Power) RSRQ (Reference Signal Received Quality)

S

S (Sequence) S1AP (S1 Application Protocol) SC-FDMA (Single Carrier - Frequency Division Multiple Access) SCTP (Stream Control Transmission Protocol) SDF (Service Data Flow) SDU (Service Data Unit) SGSN (Serving GPRS Support Node) S-GW (Serving - Gateway) SI (System Information) SIB 1 (System Information Block 1) SMS (Short Message Service) SN (Sequence Number) SNR (Serial Number) SO (Second-Order) SO (Segment Offset) SPS (Semi-Persistent Scheduling) SRB (Signaling Radio Bearer) SRNC (Serving RNC) SRS (Sounding Reference Signal) SRVCC (Single Radio Voice Call Continuity) S-TMSI (Serving - Temporary Mobile Subscriber Identity)

T

TA (Timing Advance) TA (Tracking Areas) TAC (Tracking Area Code) TAC (Type Approval Code) TAI (Tracking Area Identity)

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TAU (Tracking Area Update) TB (Transport Block) TCP (Transmission Control Protocol) TCP/IP (Transmission Control Protocol, Internet Protocol) TDD (Time Division Duplex) TEID (Tunnel Endpoint Identifier) TFT (Traffic Flow Template) Thresh1 (Threshold1) Thresh2 (Threshold2) TM (Transparent Mode) TMD (Transparent Mode Data) TNL (Transport network Layer) TPC (Transmit Power Control) TTT (Time To Trigger)

U

UDP (User Datagram Protocol) UE (User Equipment) UE AMBR (User Equipment Aggregate Maximum Bit Rate) UL (Uplink) UL-SCH (Uplink Shared Channel) UM (Unacknowledged Mode) UMD (Unacknowledged Mode Data) USIM (Universal Subscriber Identity Module) UTRA (Universal Terrestrial Radio Access) UTRAN (Universal Terrestrial Radio Access Network)

V

VoIP (Voice over IP) VPLMN (Visited Public Land Mobile Network)

W

WCDMA (Wideband CDMA)

X

X2AP (X2 Application Part) X2AP (X2 Application Protocol)



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Documents

06.LTE Protocols and Procedures