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System Architecture Evolution
Yousef Zanjireh
Fall 2015
Evolved UMTS Terrestrial Radio Access Network:Architecture of the E-UTRAN
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eNodeB (RBS in Ericsson)
• The RBS is the node in LTE that implements the 3GPP eNodeBconcept.
• The RBS controls the radio connections with connected UE and manages the cell resources including connection mobility control.
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Small Cells and the Home eNB:Conceptual view of HeNB
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Usual architecture of LTE for a roaming mobile that is communicating with the Internet and the IP multimedia subsystem
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LTE Roaming Charging
• The complexities of the new charging mechanisms required to support 4G roaming are much more abundant than in a 3G environment. Few words about both pre-paid and post-paid charging for LTE roaming is given below:
• Prepaid Charging - The CAMEL standard, which enables prepaid services in 3G, is not supported in LTE; therefore, prepaid customer information must be routed back to the home network as opposed to being handled by the local visited network. As a result, operators must rely on new accounting flows to access prepaid customer data, such as through their P-Gateways in both IMS and non-IMS environments or via their CSCF in an IMS environment.
• Postpaid Charging - Postpaid data-usage charging works the same in LTE as it does in 3G, using versions TAP 3.11 or 3.12. With local breakout of IMS services, TAP 3.12 is required.
• Operators do not have the same amount of visibility into subscriber activities as they do in home-routing scenarios in case of local breakout scenarios because subscriber-data sessions are kept within the visited network; therefore, in order for the home operator to capture real-time information on both pre- and postpaid customers, it must establish a Diameter interface between charging systems and the visited network's P-Gateway.
• In case of local breakout of IMS services scenario, the visited network creates call detail records (CDRs) from the S-Gateway(s), however, these CDRs do not contain all of the information required to create a TAP 3.12 mobile session or messaging event record for the service usage. As a result, operators must correlate the core data network CDRs with the IMS CDRs to create TAP records.
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Numbering, Addressing and Identification• Each network is associated with a public land mobile network identity
(PLMN-ID). • This comprises a three digit mobile country code (MCC).• a two or three digit mobile network code (MNC). For example, the mobile country
code for the UK is 234, while Vodafone’s UK network uses a mobile network code of 15.
• Each MME pool area is identified using a 16 bit MME group identity (MMEGI),
• 8 bit MME code (MMEC) uniquely identifies the MME within a pool area.
• Combining them gives the 24 bit MME identifier (MMEI), which uniquely identifies the MME within a particular network.
• By bringing in the network identity, we arrive at the globally unique MME identifier (GUMMEI), which identifies an MME anywhere in the world.
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Numbering, Addressing and Identification• Each tracking area has two main identities.
• The 16 bit tracking area code (TAC) identifies a tracking area within a particular network.
• Combining this with the network identity gives the globally unique tracking area identity (TAI).
• Cells have three types of identity. • The 28 bit E-UTRAN cell identity (ECI) identifies a cell within a particular network,• The E-UTRAN cell global identifier (ECGI) identifies a cell anywhere in the world.• The physical cell identity, which is a number from 0 to 503 that distinguishes a cell
from its immediate neighbors.
• A mobile is also associated with several different identities. • The most important are the international mobile equipment identity (IMEI), which is
a unique identity for the mobile equipment.• The international mobile subscriber identity (IMSI), which is a unique identity for the
UICC and the USIM.9/30/2015 Yousef Zanjireh ([email protected]) 14
Numbering, Addressing and Identification
• The IMSI is one of the quantities that an intruder needs to clone a mobile, so we avoid transmitting it across the air interface wherever possible. Instead, a serving MME identifies each mobile using temporary identities, which it updates at regular intervals.
• The 32 bit M temporary mobile subscriber identity (M-TMSI) identifies a mobile to its serving MME.
• Adding the MME code results in the 40 bit S temporary mobile subscriber identity (S-TMSI), which identifies the mobile within an MME pool area. Finally, adding the MME group identity and the PLMN identity results in the most important quantity, the globally unique temporary identity (GUTI).
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Communication Protocols:Protocol Model
High-level protocol architecture of LTE
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Relationship between the access stratum and the non-access stratum on the air interface
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Air Interface Transport Protocols:Transport protocols used on the air interface. Source: TS 36.300.
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Example Signaling Flows:Access Stratum Signaling
UE capability transfer procedure
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Protocol stacks used to exchange RRC signaling messages between the mobile and the base station. Source: TS 36.300.
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Non-Access Stratum SignalingGUTI reallocation procedure. (a) Non-access stratum messages. (b) Message transport using the access stratum
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Protocol stacks used to exchange non-access stratum signaling messages between the mobile and the MME. Source: TS 23.401.
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Bearer ManagementThe EPS Bearer
• LTE has to address two issues that the internet does not support.• The first of these is mobility.• The second issue is quality of service (QoS)
• To address these issues, LTE transports data from one part of the system to another using EPS bearers.
• An EPS bearer can be thought of as a bi-directional data pipe, which transfers data on the correct route through the network and with the correct quality of service.
• The bearer runs between the mobile and the PDN gateway if the S5/S8 interface is based on GTP or between the mobile and the serving gateway if the S5/S8 interface is based on PMIP.
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Default and Dedicated Bearers:Default and dedicated EPS bearers, when using an S5/S8 interface based on GTP
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Bearer Implementation Using GTP:Bearer architecture of LTE, when using an S5/S8 interface based on GTP. Source:TS 36.300.
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Protocol stacks used to exchange data between the mobile and an external server, whenusing an S5/S8 interface based on GTP. Source: TS 23.401.
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Bearer Implementation Using GRE and PMIP
• The GRE protocol also uses tunnels, each of which is identified using a 32 bit key field in the GRE packet header. Unlike GTP-C, however, PMIP does not include any signaling messages that can specify the quality of service of a data stream.
• If the S5/S8 interface is implemented using GRE and PMIP, then a mobile has only one GRE tunnel on that interface, which handles all the data packets that the mobile is transmitting or receiving without any quality of service guarantees. The EPS bearer only extends as far as the serving gateway [55], but is otherwise implemented in the same way that we have been describing.
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Signaling Radio Bearers (SRB)
• To carry signaling messages between the mobile and the base station.• The mobile and base station can agree on how the signaling messages
should be transmitted and received.• SRB0 is only used for a few RRC signaling messages, which the mobile and
base station• Use to establish communications in a procedure known as RRC connection
establishment. Its• Configuration is very simple and is defined in special RRC messages known
as system information messages, which the base station broadcasts across the whole of the cell to tell the mobiles about how the cell is configured.
• SRB1 is configured using signaling messages that are exchanged on SRB0, at the time when a mobile establishes communications with the radio access network.
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State Diagrams:EPS Mobility Management
• A mobile’s behaviour is defined using three state diagrams, which describe whether the mobile is:• Registered with the EPC
• Whether it is active
• Idle.
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Spectrum Allocation:FDD frequency bands (TS 36.101 and TS 36.104)
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Frequency bands used by operational and planned LTE networks in November 2013.
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2G/3G Versus LTE
2G/3G LTE
GERAN and UTRAN E-UTRAN
SGSN/PDSN-FA S-GW
GGSN/PDSN-HA PDN-GW
HLR/AAA HSS
VLR MME
SS7-MAP/ANSI-41/RADIUS Diameter
DiameterGTPc-v0 and v1 GTPc-v2
MIP PMIP9/30/2015 Yousef Zanjireh ([email protected]) 45
2G/3G – LTE Interworking
S3 – Exchange of bearer information, QoS,
S4 – U-Plane traffic
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Self Organising Network Principles
• Automatic software management
• Self test
• Automatic neighbor relation configuration
• Tracking area planning
• Physical cell ID planning
• Load balancing
• Handover optimisations
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