Signaling Fundamentals in Mobile Communication

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Contents

1 Signaling fundamentals11 ATM fundamentals32 Signaling Interfaces253 Radio Access Network signaling314 BICC signaling47

1 ATM fundamentals

1.1 ATM versus STM

First of all let us compare the well known STM (Synchronous Transfer Mode) or better known as its application PCM via TDM (Pulse Code Modulation via time division multiplexing) with the ATM technology or asynchronous transfer mode..

1.1.1 Transmission principle

STM example PCM 30

In the STM we have a fixed frame structure, for example PCM30 has a frame of 32 time slots, each carrying a user information except the time slot 0, which carries synchronization and error correction information. Each timeslot comprises 8 bit, so one frame carries 32X8bit=256bit/frame. The transmission rate is 64kb/s per timeslot or 32X64kb/s=2Mbits/s overall transmission rate. It means one frame is passed through the network in 256bit/frame / 2Mbit/s = 125 s.

So every 125s a frame passes through the network, or every 125 s the information for a certain user or timeslot is transported via a certain link. With the corresponding synchronization it is now easy to fetch the 8 bit information for the user 1 or TS1 every 125 s, the next 8 bits belong to the user 2 and so on.

It means in the STM technology, a good synchronization provided, the user information can be retrieved on the receiving side by a simple access to the arrived bits in a certain time frame.

ATM

In the ATM it is slightly different. Here cells of a certain length (53 byte) are transported through the network. Each cell can contain user information or not.

There is no synchronization in the way that for example the first cell carries information of user 1, the second cell information of user 2 and so on, with a repetition of this pattern after a certain time period or a certain number of cells.

Because it is called asynchronous transfer, the first cell contains for example information of user 3, the next one of user 1, the third one is empty, the fourth one may be again information of user 1 and so on. So there is no time structure concerning the allocation to a certain user channel. There is no numbering of the cells, with a repetition of the numbers after a certain time, but there is simple a continuous cell stream carrying information of the various users or not.

But finally there must be a way to identify the payload in the cells at the receiving side, to allocate the transported information to a certain user or to a certain way through the network.

This allocation is done in the header of each cell, carrying a kind of identifier. Utilizing this identifier the payload of this cell can be allocated on the receiving side to a certain user or to a certain way through the network.

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Fig. 1 Synchronous Transfer Mode: Example PCM30


Fig. 2 Asynchronous Transfer Mode

1.1.2 Benefits of ATM

As we have seen the transmission principle in ATM is different from the STM transmission principle: In STM the payload of a certain user arrives on the receiving side in a fix time period, in ATM the payload can arrive at any time, but the cell contains an identifier, which can be allocated to a certain connection or user. It means the ATM is more flexible as the PCM or STM.

STM example PCM 30

Lets regard a PCM30 connection through a network. On the opposite page you see an example of a through connection from a mobile to a fixed network subscriber.

Before the two human beings can speak to each other a call set up has to be performed. A signaling information is exchanged between the mobile and the MSC and between the different network nodes. In each switching equipment the routing information is evaluated and a setup-information is given to the switching hardware. At the end of the setup a connection in all the nodes and on all the interconnections exists. Each connection consumes resources of 64kb/s until the end of the call, independent if the two human beings are talking or if may be one of them is in the moment out of the room.


Fig. 3 Consuming of resources: Example PCM30

ATM

On the opposite page an example from the data switching world is shown. ATM used to transport CS will be explained later.

In ATM either PVC (permanent virtual connections) or SVC (switched virtual connections) are used. The more common way are permanent switched connections, which are permanently switched through by administration of the network operator.

In our example there are three users connected to an ATM switch. These users (1 to 3) on the left side should be connected through the ATM network to the destination users on the right side. In the simple example the interconnections between the switches are realized with 155Mb/s (STM1 connections). The users 1, 2 and 3 have different requirements. User1 needs a high bandwidth, user 2 a medium bandwidth and user 3 a low bandwidth. The user data are multiplexed in the first switch to the available physical link through the network. If the network is configured in an optimal way each user gets the required bandwidth, this means a high number of cells transport the payload of user 1, a medium number of cells transport the payload of user 2 and a low number of cells transport the information of user 3. So the physical resources are assigned to the requirements of the different users. And in an optimum case the physical resources are used by the users to almost the physical limit. This is a simplified explanation, because the three users have not always the same bandwidth, so in reality traffic policy and buffering is used to allocate the physical resources to the different users.


Fig. 4 Consuming of resources: Example PCM30

1.1.3 Switching of ATM

In the previous chapter we have seen the benefit of ATM in comparison with PCM. In PCM the Resources are consumed all the time during the call, in ATM the resources are allocated dependent on the requirements of bandwidth of the different users.

STM example PCM 30

In PCM the switching of the user information depends on the signaling information during the call setup. An incoming ISUP message contains the B-Number plus the information about the PCM TS, which is allocated to the call. The B-number is evaluated, routing information is found in the switch and at the end an outgoing PCM connection is found and a timeslot on it is seized. In the switching Network the incoming timeslot is interconnected to the outgoing timeslot.


Fig. 5 Switching PCM30

ATM

As it was already stated each ATM cell caries the payload with the user data plus a header which identifies the user or in the ATM network the connection, similar to the CIC which identifies the TS on a certain PCM carrier.

This connection identifier is not a simple identification but a two-stage identification: the so called virtual path and the so called virtual channel. A user connection is identified finally by a certain physical connection terminating on a port of an ATM switch, a virtual path that represents a group (minimum 1) of virtual channels and the virtual channel itself. It is a little bit similar as the principle of trunk group (Group of trunks) and the trunk itself in the PCM EWSD/D900 world.

The two stage handling gives more flexibility and freedom in ATM switching.

Depending on the user or network requirements a whole virtual path/VP (group of user channels) or a single virtual channel/VC can be through connected.

When ever possible: a virtual path should be switched because of better performance and less administrative effort.

When ever necessary: a virtual channel should be switched through.

VP Switching

On the second picture on the opposite page an example for ATM VP switching is shown. There is a permanent virtual connection table administrable by an operation terminal. This table contains information about the interconnection of a certain virtual Path, defined by the virtual path id (VPI), on a certain physical connection or port and a second VPI and physical connection or port.

If a cell arrives on a certain port the PVC table is checked, the allocated outgoing information is read out and the cell is switched to the outgoing port and virtual path.


Fig. 6 Virtual Paths and virtual channels


Fig. 7 Switching ATM VPs

VC Switching

On the third picture on the opposite page an example for ATM VC switching is shown. There is a permanent virtual connection table administrable by an operation terminal. This table contains information about the interconnection of a certain virtual channel, defined by the virtual channel id (VCI), a virtual path id (VPI), on a certain physical connection or port with a second VCI, VPI and physical connection or port.

If a cell arrives on a certain port the PVC table is checked, the allocated outgoing information is read out and the cell is switched to the outgoing port, the virtual path and the virtual channel.


Fig. 8 Switching ATM VCs

1.2 The ATM header

In the last chapter we have seen that a certain user payload and its connection through the network is identified by the virtual path identifier and the virtual channel identifier. Switching can be done either VPI based or VCI based. Both identifiers the VPI and the VCI are transported in the ATM header, a 5 byte subfield in the ATM cell.

Network - Network and User - Network interface

The ATM transmission way comprises different sections from the originating user to the network, from the first ATM switch to the next one and so on to the last section from an ATM switch to the terminating user. So we have sections between the user and the network, called User Network interface and intra network sections called network-network interface. This is important because the ATM header looks different for the two mentioned interfaces. On the User Network Interface (UNI) it might be useful to have the possibility to provide user specific information on one hand (so-called Generic flow control) and on the other hand there is no need that the VP capacity is as high as inside of the ATM network. Therefore a half byte from the VPI field is taken for user information.

The second picture on the opposite page shows the layout of an UNI header and an VPI header.

The most important fields in the Header are the VPI and VCI. In UNI the VPI has 8 bits, so 256 Virtual Paths can be addressed, in NNI we have 12 bits, so 4096 virtual paths can be addressed. It is very important that the interface is configured on both endpoints of a connection in the same way, either UNI or NNI.

The VCI comprises 16 bit, so 65536 virtual channels can be addressed.

The user type contains the information if for example user data or operation and maintenance data are transported.

The CLP field or cell loss priority field is a flag which can be set in case policing is required and the user data received on the interface exceed the limits of the contract. Such a marked cell can be discarded in any ATM switch in case there is a bottleneck of the transmission capacity.

The HEC or Header Error Control contains error correction information for the header, not for the payload.


Fig. 9 UNI and NNI


Fig. 10 The NNI and UNI ATM header

1.3 Adaptation layer

We have discussed how the ATM transport works, how the VPI and VCI influences the switching and were they can be found in the header. Behind the header in the cell we find the payload. Depending on the user data to be transported adaptation has to be done. Therefore on top of the VP and VC layer different adaptation layers can be found.

1.3.1 Signaling ATM Adaptation (SAAL)

The Signaling ATM Adaptation Layer or SAAL is used for adaptations concerning Signaling. It is layered on top of the VP/VC header and is used in our applications as a kind of MTP level 2.

It comprises four sub layers: the segmentation and reassembling (SAR),: the common part convergence sub layer (CPCS), the Service specific connection oriented protocol (SSCOP) and the Service Specific Coordination function (SSCF).

SAR: This layer accepts variable length PDUs from higher layers and generates 48byte PDUs.

CPCS: This sub layer caries 32 bit CRC to detect bit errors in the CPU.

SSCOP: The SSCOP provides sequencing functionality, flow control, keep alive functions, Retransmission and connection establishment and release.

SSCF: The SSCF performs a coordination function between the service required by the signaling layer 3 (Recommendation Q.2931) user and the service provided by SSCOP.


Fig. 11 SAAL

1.3.2 ATM adaptation layer 1 and 2

ATM cells with a length of 53bytes are sent via a virtual channel (VC), which in turn is located in a virtual path (VP = group of virtual channels). All these cells can be uniquely allocated to this virtual connection, since the allocation (virtual path identification and virtual channel identification) is noted in the header of each cell belonging to the virtual connection concerned.

AAL2

AAL2 is the best method of transporting circuit-switched voice or data with a variable bandwidth and short delay times. AAL2 makes it possible to transmit in a PVC (permanent virtual connection) circuits (data assigned to a user, like PCM circuits or time slots) that belong to different circuit connections. In other words, an ATM cell with a combination of virtual-path ID and virtual-channel ID can contain the circuits belonging to different CS connections. This is represented in simplified form in that each item of circuit information in the payload contains a so-called "channel identifier" (CID) in addition to the user data. This channel identifier (CID) is negotiated during the circuit-switched call setup, and it uniquely identifies a circuit-switched connection within the PVC. In addition, AAL2 also has so-called "silent suppressing"; that is to say, empty circuits are not transmitted. An AAL2 connection therefore makes it possible to carry out compressed transmission of circuit-switched voice and data.

The disadvantage of AAL2 is that only complete virtual connections that is to say, either the virtual path alone or the virtual path and the virtual channel can be switched in an ATM switching network. As a consequence, individual circuits can no longer be switched to different destination, but only all the circuits belonging to a PVC.

AAL1

AAL1 is a constant bit rate. It contains sequencing of the information, and is used as circuit emulation. The disadvantages of it compared with AAL2 are nonetheless important. Each circuit connection requires its own virtual connection, and the information from different users (such as PCM TS) cannot be transmitted in the same cell or via the same virtual connection. For example, there are two options in the case of PCM AAL1 conversion. The first option is that only 8-bit information is written into each ATM cell (such as 1 PCM TS of a PCM frame); but this requires a high bandwidth. The other option is that you wait for several PCM frames to fill the cell with information from the same user; but this, in turn, results in considerable delays. The advantage is, however, that the assignment of PCM TS to a virtual connection and ATM cell is very easy, since this is a 1:1 assignment.

The main advantage of AAL1 however is that each PVC contains only one circuit. This therefore makes it possible to switch individual voice or data connections through an ATM switching network to different PCM time slots.


Fig. 12 Simplified principle of AAL2


Fig. 13 Simplified principle of AAL1

AAL2 CPS Packet

The ATM Cell comprises 53 byte overall. 5 byte are used for the ATM Header, which contains the Virtual Path Identifier (VPI) and the virtual Channel Identifier (VCI), Pay Load Type (e.g. user cells or OAM cells), Cell Loss Priority (flag to indicate that the cell can be discarded in case of policing) and the Header Error Control (to detect errors in the cell header). The remaining 48 byte are used to carry the load of higher layers.

This Payload starts with one byte AAL2 start field followed by the CPS (common part sublayer) packets or ATM mini cells.

Each of these CPS packets comprises Packet header information for controlling the packet payload and the payload (user circuit information) itself. In the packet header we can find the Channel identifier (i.e. the user circuit number) between 0 and 255, a length indicator, a User-to-User information field and again Header error control information. The header is followed by the CPS-Packet Payload, which can comprise up to 45 bytes (overall i.e. distributed to several cells) depending on the higher layer e.g. the Iu user plane.

Remaining PDU space in a ATM cell is not padded if the next high layer information does not fit completely into one ATM cell, but the CPS Packets are segmented and filled into two ATM cells.


Fig. 14 AAL2 format

2 Signaling Interfaces

GSM 2G

In the classic GSM world the MSC is integrated into the network with Time Division Multiplexing (TDM) connections.

The Interface towards the BSC (A interface) is realized by PCM30 connections. These PCM 30 connections carry the transport connection used for the user data in one or more (HSCSD) timeslots. This connection could also be called bearer connection. The signaling connection realized by CCS7, SCCP and BSSAP uses as a physical medium also these PCM/TDM connection. During the setup on the A interface, in the BSSAP signaling (Assignment requests) the MSC seizes a certain time slot and informs the BSC about the relation to the bearer with the circuit identification code or CIC.

The interface towards the Gateway MSC is realized with TDM too. Instead of BSSAP ISUP is used as a signaling. The same principle is used as on the A interface. The MSC or GMSC seizes a certain PCM TS and informs the partner by ISUP signaling about the relation to the bearer sending the CIC.

The CODECs used for speech compression on the air interface are housed in the TRAU (transcoding and rate adaption unit) that is part of the base station system on one side and in the mobile on the other side.

UMTS 3G/2G

In UMTS3G a new Radio System with new interfaces was specified (Iu interface). The Interface towards the RNC was realized on ATM. For the bearer connection ATM/AAL2 was used and for the signaling Radio Access Network Application Part (RANAP) similar as BSSAP was used.

ATM/AAL2 bearer connections require a special way of signaling called AAL2 signaling. It is just used for the bearer establishment, bearer release and the path supervision. AAL2 Signaling is not part of the RANAP. So on the Iu interface there was on one side the general call setup signaling realized by RANAP and the bearer signaling or bearer control realized by AAL2 signaling.

Beside the changes in the signaling the CODECs were moved from the Radio Access Network into the core network. The advantage is obvious: Resources can be saved now not just on the air interface, but also on the Iu interface and inside the Radio Access Network. As CODECs adaptive multi-rate codecs or AMR codecs are used. AMR Codecs are codecs with a flexible transmission rate, very fast adjustable according to the quality on the air interface.

The Interfaces towards the BSS and the MSC stay unchanged.


Fig. 15 GSM via TDM


Fig. 16 UMTS Iu via ATM

UMTS CS 4.0

From UCR 1.0 on ATM/AAL2 was supported on the Iu interface towards the RNC transporting user data to the MSC. In the core network TDM (time division multiplexing) in combination with ISUP was used.

From UCR 3.0/4.0 on ATM/AAL2 is going to be supported in the core network too:

The user data transport is performed utilizing ATM/AAL2 in the well known way (used on Iu interface) and the signaling is done via BICC or bearer independent call control.

The advantage of the ATM bearer are obvious: In opposite to TDM, ATM is a packet transport mode, which just consumes resources if necessary. It means in TDM the resources (time slots) are assigned to a call from the beginning of a call to the end of a call, independent if they are used or not. In ATM, because it is a packet transport medium, the physical resources are shared between users on demand.

In addition ATM allows the transport of compressed (e.g. speech) and uncompressed (e.g. multimedia or 64 kb/s) mode. Compressed mode means adaptive multi rate codecs are not just used in direction to the RNC, but also in the core network for the bearer transport for example between the gateway MSC and the MSC/VLR.

Last not least ATM in core network offers the possibility to exploit an existing ATM backbone network, which may not be fully used for data transport.

The combination with BICC signaling is an investment into the future. BICC is an enhancement of N- ISUP (which just supports TDM call setups) and offers as the name says a bearer independent control of call setups. It is designed to support ATM bearers as well as IP based bearers (voice over IP) or TDM bearers.


Fig. 17 UMTS or GSM via ATM in Core Network

3 Radio Access Network signaling

3.1 Separation of bearer and network control

As already stated the ISUP signaling is not the adequate signaling for ATM. So a different way of signaling is necessary to support ATM transport of user data or with future aspects voice over IP.

Radio Access Network Application Part (RANAP) is a signaling protocol similar to BSSAP, but tailored for the special UMTS requirements.

RANAP was designed by the 3GPP (3rd Generation Partnership Program) to support UMTS services independent from its bearer and its signaling message transport medium.

In opposite to BSSAP, which carries call control (call setup and release) and bearer control (time slot assignment), RANAP signaling just controls the call. The bearer setup is done in a different way, e.g. via IP or AAL Type 2 signaling Protocol. The latter type is the bearer connection control used for ATM on Iu interface.

The advantage of the separation of network and call control on one side and Bearer control on the other side is as follows:

The call or network control signaling is totally independent from the bearer network, which can be realized by ATM, Internet Protocol or TDM (theoretically). The interfaces between the MSC servers and the Media Gateways are standardized and the media specific parameters are transported via this interface and via the BICC signaling in media specific containers.


Fig. 18 Separation of Call Control and Network Control

3.2 Transport or bearer network functional elements

The transport network plane is clearly separated from other planes in BICC networks. The following functional elements are used:

Switching Node (SWN): The very basic function of transport network plane is to route and/or switch data streams across the network. For this purpose the switching node function is defined. It is usually represented by the switch (ATM, PCM etc.) or router (IP). For user data transport there will be a bearer segment between two SWN. The ordered path of all associated bearer segments form the backbone network connection (BNC), used for user data transfer. In many situations a SWN also offers media stream processing functionality like (speech) codec conversion, error detection, etc. SWN can interconnect bearer segments of different transport technologies. So it is possible to convert the transport protocol too.

Bearer Control Function (BCF): Each bearer segment must be controlled for establishment, modification and release. This is task of the BCF. It configures the SWN and exchanges information with the BCF of adjacent SWN. This information exchange is done using a Bearer Control (BC) protocol (e.g. AAL type 2 signaling for ATM AAL2 or IP bearer control protocol for IP). BCF can work standalone (without higher plane influence) or can be guided by higher layer functionality from the network control plane. The Bearer Control Function is the Signaling endpoint. This means the Backbone network connection terminates here and either a transition to classical TDM takes place or a further network call control connection is necessary.

Bearer Inter-working Function (BIWF): To allow network control plane entities to configure a BCF there must be signaling between BCF and network control plane. This signaling runs via the BIWF. The protocol used here is usually called a Call Bearer Control (CBC) protocol. A BIWF terminates CBC signaling and performs the relevant communication with the associated BCF.

Of course BCF, BIWF and SWN are usually physically integrated. The functional unit built from these is called Media Gateway (MGW). MGW form the basic entity of the transport network plane. So a MGW has three types of interfaces:

Transport Link (Bearer Segment): Two MGW connected to each other to transport data (user data or signaling).

Bearer Control: To establish, release and modify transport links (bearer segments) Two adjacent MGW will exchange bearer control signaling with each other.

Call Bearer Control: The commands to establish, release and modify bearer segments initially comes from the network control plane using call bearer control protocol.


Fig. 19 Transport network functional elements

3.3 Network control (RANAP) functional elements

The network control plane is responsible for the logical handling of call control. The main entity in the network control plane is the

Call Service Function (CSF): A call service function handles all logical tasks for call control. This means call control signaling, determination of the bearer path (Backbone Network Connection BNC) and associated resource determination (Media Gateway).

CSF can be connected to one or several MGW for resource allocation. But even a CSF without connected MGW is possible. Such CSF are usually used as central control to determine the path of the backbone network connection (BNC).

CSF are interconnected with each other to exchange call control signaling. The protocol used here is Radio Access Network Application Part (RANAP). RANAP is a UMTS specific signaling, such that a CSF is independent of the used transport bearer technology. So RANAP is also able to support call bearers with arbitrary quality of service requirements.

Using CBC (Call Bearer Control) protocol a CSF can send commands to a MGW. Such commands can be used establish or prepare bearer segments, release or modify bearer segments. In contrast to RANAP it is fact that a CBC protocol is specific to the type of bearer technology used. This means, that a CSF must map the bearer independent RANAP signaling into bearer dependent CBC signaling to allocate a referenced resource.


Fig. 20 Network control plane architecture for Iu networks

3.4 Protocol stacks

3.4.1 RANAP message transport

RANAP messages are exchanged between CSF and CSF to provide bearer independent call handling like setup, release and modification of call services.

For signaling message transport of RANAP protocol there is the following realization foreseen:

SS7 over ATM: In an ATM environment SS7 signaling message can be sent within an ATM virtual channel connection provided by AAL5 (ATM Adaptation Layer 5) and SAAL (Signaling ATM Adaptation Layer). AAL5 allows a message oriented data transfer with error detection, whereas SAAL is responsible for a reliable data transfer using a retransmission mechanism. Signaling message routing is again provided by MTP level 3, but in an adapted version called MTP3B (MTP level 3 Broadband). MTP3B still uses signaling point codes SPC for routing.


Fig. 21 Signaling message transport for RANAP protocol

3.4.2 Bearer control signaling message transport

On the Layer 1 between two switching nodes - for example MSC Media Gateway and RNC STM1 155Mbit/s is used.

The layer 2 is realized by ATM. Here an ATM PVC (virtual path and virtual channel) between the nodes is used to carry the high layer information.

On top of the ATM layer the ATM adaptation Layer 5 is used, which can provide the adaptation for example to transport IP over ATM or signaling information. The ATM Adaption layer 5 comprises the segmentation and reassembling (SAR) like other adaptation layers and the so-called Convergence Sub-layer (CS). The Convergence sublayer has a common and a service specific part. The service specific part contains in the case of AAL Type 2 Signaling a Signaling ATM Adaptation Layer (SAAL) which is responsible for sequence integrity, error correction by retransmission, Flow control and connection establishment. It means it performs typical MTP layer 2 functionality.

On top of the ATM/SAAL the Message Transfer Part level 3 broadband is used. This fulfills the same tasks as the CCITT No. 7 signaling MTP 3 except for that broad band connections can be used instead of 64 kb/s.

The AAL Type 2 Signaling protocol responsible for the establishment, release and the maintenance of AAL2 connections is used on the MTP3-B. It is specified in the ITU-T recommendation Q.2630.


Fig. 22 Signaling message transport for AAL type 2 signaling protocol

3.4.3 Bearer connection

In the same way as the signaling connection STM1 SDH (155Mb/s) technology, for instance, is used for transporting circuit-switched voice and data on level 1.

This forms the basis of the ATM layer as level 2. ATM is used here to make it possible to achieve fast transmission that can be easily adapted to the data rates required. ATM PVCs (permanent virtual connections) are set up between the MGW and an ATM switch, ATM switches and MGWs. They are used to transport the ATM cells for circuit-emulated traffic.

The ATM AAL type 2 is used to transport compressed voice or uncompressed data information.

The Iu User Plane protocol in accordance with 3GPP TS 25.415 includes, for instance, the transmission of adapted data rates for AMR voice (adaptive multirate such as12.2kb/s), transparent transmission of multimedia 64kb/s, frame handling, initializing, and CRC header handling.


Fig. 23 Bearer connection

3.5 Radio Access Network call scenarios

Mobile-Originating Call

1. The UE sends a CM_Service_Request (for MOC, for instance) to the RNC. The RNC sends an SCCP Connect Request (CR) message with the initial UE message: CM_Service_Request over the MP:SLT (SSNC) to the MSC server. The SCCP message contains "RANAP" as a subsystem ID.

2. The MSC server responds with a Connection Confirm, which contains the CM Service Accept message. This message is passed to the RNC. The RNC is addressed as the Destination Point Code. As a result, an SCCP connection is set up. The rest of the MSC Server - RNC dialog takes place over the SCCP connection set up in this way. The Service Accept message is passed to the UE.

3. Next, the UE sends a setup message, which contains, for instance, the number of the called party and the bearer capabilities. The setup message is passed from the RNC in an SCCP Data Form 1 (DT1) to the MSC Server.

4. The setup message of the UE is acknowledged by the MSC Server via the RNC.

5. Now the Bearer setup is required. The MSC server request with a CBC Add Request the address "BIWF addr" of the media gateway (signaling endpoint address) and a call reference "BNCid" from the Media gateway.

6. The Media Gateway provides this information with an Add Response Message.

7. Now the MSC Server provides these retrieved connection parameters inclusive bearer relevant parameters like CODE information, Service information, Bandwidth information in the RANAP message RAB_Assignment_Request (RAB = Radio Access Bearer). This message is passed within a DT1 to the RNC.

8. The RNC now selects a so-called "path identifier" which is a synonym for the AAL2 bearer VPI and VCI and a channel ID (CID). It sends these parameters back to the Media Gateway with the AAL2 signaling Message Establish Request (ERQ).

9. The Media Gateway establishes the connection and acknowledges the establish request with an Establish Confirm (ECF) message.

10. The Media gateway confirms the bearer setup towards the MSC server with the CBC message NotifyIndication: established.

11. which is then acknowledged by the MSC server with a Notify Response.

12. After establishment of the radio bearer the RNC acknowledges the RAB assignment request with the corresponding response Message.


Fig. 24 Call flow AAL2 bearer setup

4 BICC signaling

4.1 Separation of bearer and network control

As already stated the ISUP signaling is not the adequate signaling for ATM. So a different way of signaling is necessary to support ATM transport of user data or with future aspects voice over IP.

Bearer Independent Call Control (BICC) is a signaling protocol based on the well known N-ISUP standard. N-ISUP was used to support narrowband ISDN services.

BICC was designed by the ITU-T in the recommendation Q.1901 to support narrowband ISDN services independent from its bearer and its signaling message transport medium.

In opposite to ISUP, which carries call control (call setup and release) and bearer control (time slot assignment), BICC signaling just controls the call. The bearer setup is done in a different way, e.g. via IP or AAL Type 2 signaling Protocol. The latter type already known from the Iu interface is the bearer connection control used for ATM in Core Network UCR 3.0/4.0.

The advantages of the separation of network and call control on one side and Bearer control on the other side are as follows:

A network can be controlled by one or several MSC server, which are responsible for the routing in general through the network. It means a kind of overlay call control network can be set up with interconnections to the different media gateways. Dependent on the capacity of the MSC Server it could be realized by one single MSC Server may be operated in a redundant mode with a second one.

The call or network control signaling is totally independent from the bearer network, which can be realized by ATM, Internet Protocol or TDM. The interfaces between the MSC servers and the Media Gateways are standardized and the media specific parameters are transported via this interface and via the BICC signaling in media specific containers.


Fig. 25 Separation of Call Control and Network Control 1


Fig. 26 Separation of Call Control and Network Control 2

4.2 Transport or bearer network functional elements

The transport network plane is clearly separated from other planes in BICC networks. The following functional elements are used:

Switching Node (SWN): The very basic function of transport network plane is to route and/or switch data streams across the network. For this purpose the switching node function is defined. It is usually represented by the switch (ATM, PCM etc.) or router (IP). For user data transport there will be a bearer segment between two SWN. The ordered path of all associated bearer segments form the backbone network connection (BNC), used for user data transfer. In many situations a SWN also offers media stream processing functionality like (speech) codec conversion, error detection, etc. SWN can interconnect bearer segments of different transport technologies. So it is possible to convert the transport protocol too.

Bearer Control Function (BCF): Each bearer segment must be controlled for establishment, modification and release. This is task of the BCF. It configures the SWN and exchanges information with the BCF of adjacent SWN. This information exchange is done using a Bearer Control (BC) protocol (e.g. AAL type 2 signaling for ATM AAL2 or IP bearer control protocol for IP). BCF can work standalone (without higher plane influence) or can be guided by higher layer functionality from the network control plane. The Bearer Control Function is the Signaling endpoint. This means the Backbone network connection terminates here and either a transition to classical TDM takes place or a further network call control connection is necessary.

Bearer Inter-working Function (BIWF): To allow network control plane entities to configure a BCF there must be signaling between BCF and network control plane. This signaling runs via the BIWF. The protocol used here is usually called a Call Bearer Control (CBC) protocol. A BIWF terminates CBC signaling and performs the relevant communication with the associated BCF.

Of course BCF, BIWF and SWN are usually physically integrated. The functional unit built from these is called Media Gateway (MGW). MGW form the basic entity of the transport network plane. So a MGW has three types of interfaces:

Transport Link (Bearer Segment): Two MGW connected to each other to transport data (user data or signaling).

Bearer Control: To establish, release and modify transport links (bearer segments) Two adjacent MGW will exchange bearer control signaling with each other.

Call Bearer Control: The commands to establish, release and modify bearer segments initially comes from the network control plane using call bearer control protocol.


Fig. 27 Transport network functional elements

4.3 Network control functional elements

The network control plane is responsible for the logical handling of call control. The main entity in the network control plane is the

Call Service Function (CSF): A call service function handles all logical tasks for call control. This means call control signaling, determination of the bearer path (Backbone Network Connection BNC) and associated resource determination (Media Gateway).

CSF can be connected to one or several MGW for resource allocation. But even a CSF without connected MGW is possible. Such CSF are usually used as central control to determine the path of the backbone network connection (BNC).

CSF are interconnected with each other to exchange call control signaling. The protocol used here is Bearer Independent Call Control (BICC). BICC is a variation of ISUP, such that a CSF is independent of the used transport bearer technology. So BICC is also able to support call bearers with arbitrary quality of service requirements.

Using CBC (Call Bearer Control) protocol a CSF can send commands to a MGW. Such commands can be used establish or prepare bearer segments, release or modify bearer segments. In contrast to BICC it is fact that a CBC protocol is specific to the type of bearer technology used. This means, that a CSF must map the bearer independent BICC signaling into bearer dependent CBC signaling to allocate a referenced resource.


Fig. 28 Network control plane architecture for BICC networks

4.4 Protocol stacks

4.4.1 BICC message transport

BICC messages are exchanged between CSF and CSF to provide bearer independent call handling like setup, release and modification of call services.

For signaling message transport of BICC protocol there are several possibilities allowed:

classical SS7 transport: As BICC is a modification of ISUP, it can be transported over the classical SS7 protocol stack. This means, the physical layer is provided by MTP level 1 which can be identified with the PCM timeslot used as signaling link. MTP level 2 is situated on top of MTP level 1 and provides a sequenced, reliable data transfer using backward error correction. Signaling message routing is provided by MTP level 3. Routing is done by MTP addresses which are classical signaling point codes SPC. This possibility is used for the realization in UCR3.0.

SS7 over ATM: In an ATM environment SS7 signaling message can be sent within an ATM virtual channel connection provided by AAL5 (ATM Adaptation Layer 5) and SAAL (Signaling ATM Adaptation Layer). AAL5 allows a message oriented data transfer with error detection, whereas SAAL is responsible for a reliable data transfer using a retransmission mechanism. Signaling message routing is again provided by MTP level 3, but in an adapted version called MTP3B (MTP level 3 Broadband). MTP3B still uses signaling point codes SPC for routing.

SS7 over IP: In IP networks SIGTRAN (Signaling Transport ) specifies mechanisms for SS7 message transfer. Here on IP the stream control transmission protocol (SCTP) provides a reliable message oriented data transfer for multiple independent streams between two IP endpoints. On top of SCTP M3UA (MTP level 3 User Adaptation) provides a MTP level 3 emulation. M3UA only provides the higher layer interface of MTP level 3. But routing is typically not done by M3UA. Instead all routing is organized by IP layer using IP addresses and SCTP port numbers.

The interface between CSF and CSF may be implemented using a direct physical link, but can also be cross connected via the MGW.


Fig. 29 Signaling message transport for BICC protocol

4.4.2 Bearer control signaling message transport

In the following the bearer signaling is shown on the example of AAL Type 2 Signaling protocol used in UCR3.0/4.0.

The AAL2 Type 2 Signaling is already well known from the Iu interface used there as the Bearer Control Protocol to set up the AAL2 circuit emulation connection between the MSC interworking function and the RNC.

On the Layer 1 between two switching nodes - for example two ATM switches or an ATM switch and an MSC or two MSC STM1 155Mbit/s is used.

As the name of the feature "ATM in Core Network" says the layer 2 is realized by ATM. Here an ATM PVC between the nodes is used to carry the high layer information.

On top of the ATM layer the ATM adaptation Layer 5 is used, which can provide the adaptation for example to transport IP over ATM or signaling information. The ATM Adaption layer 5 comprises the segmentation and reassembling (SAR) like other adaptation layers and the so-called Convergence Sub-layer (CS). The Convergence sublayer has a common and a service specific part. The service specific part contains in the case of AAL Type 2 Signaling a Signaling ATM Adaptation Layer (SAAL) which is responsible for sequence integrity, error correction by retransmission, Flow control and connection establishment. It means it performs typical MTP layer 2 functionality.

On top of the ATM/SAAL the Message Transfer Part level 3 broadband is used. This fulfills the same tasks as the CCITT No. 7 signaling MTP 3 except for that broad band connections can be used instead of 64 kb/s.

The AAL Type 2 Signaling protocol responsible for the establishment, release and the maintenance of AAL2 connections is used on the MTP3-B. It is specified in the ITU-T recommendation Q.2630.


Fig. 30 Signaling message transport for AAL type 2 signaling protocol

4.4.3 Bearer connection

In the following the bearer is shown on the example of AAL Type 2 transport protocol used in UCR3.0/4.0.

In the same way as the signaling connection STM1 SDH (155Mb/s) technology, for instance, is used for transporting circuit-switched voice and data on level 1.

This forms the basis of the ATM layer as level 2. ATM is used here to make it possible to achieve fast transmission that can be easily adapted to the data rates required. ATM PVCs (permanent virtual connections) are set up between the MGW and an ATM switch, ATM switches and MGWs. They are used to transport the ATM cells for circuit-emulated traffic.

The ATM AAL type 2 is used to transport compressed voice or uncompressed data information.

The Iu User Plane protocol in accordance with 3GPP TS 25.415 includes, for instance, the transmission of adapted data rates for AMR voice (adaptive multirate such as12.2kb/s), transparent transmission of multimedia 64kb/s, frame handling, initializing, and CRC header handling.


Fig. 31 Bearer connection

4.5 BICC call scenarios

4.5.1 Call Instance Code CIC

In ISUP identification of calls is done by the CIC (Circuit Identity Code). The CIC uniquely describes PCM system and timeslot used for the call between to switches. This concept of call identification will no longer work in BICC networks, because there are no longer predefined resources for calls.

In BICC networks a call will be identified between two CSF with a Call Instance Code (CIC). The CIC is a four byte value used as logical identifier for the call. It must be unique between two CSF.

All CIC that can be used between two CSF are initially created in a so called CIC Pool. When a call is set up, then the initiating serving node will select one CIC from the CIC Pool and will remove it from the pool. So in the CIC Pool only free CIC are contained. Internally the selected CIC also identifies the bearer segments and the bearer control signaling (BC). This is not explicitly possible, usually other identifiers are used in MGW (e.g. Backbone Network Connection ID BNC-ID).

To avoid collisions during CIC allocation, there will be a CIC prioritization mechanism used like the ones used in ISUP. Typically one of the serving nodes will select odd CIC, whereas the other selects even CIC with priority. Other mechanism are possible too, but both SN should use the same mechanism.


Fig. 32 Identification of call instance by CIC

4.5.2 Backward BNC (Backbone Network Connection) establishment

1. The A- Call Service Function (CSF) sends a CBC command "add request" to the Bearer Control Function BCF with the transaction "Prepare_BNC_Notify" to get the so-called BIWF address (own node address), a BNC id (identification of the BNC). The transaction is identified by a so-called transaction id provided by the CSF.

2. The BCF answers with an CBC message "add response" to the CSF with the transaction "BNC prepared" to provide the required information.

3. The CSF sends an initial address message similar to the ISUP message to the CSF responsible for the termination of the BNC. This message contains, beside the normal ISUP parameters like calling party and called party information, the action id = connect backward, the BIWF address, and the BNC id.

4. The B-CSF on the BNC termination replies with a BICC "Application Message" and provides the codec information in there.

5. The A-CSF informs the A-BCF about an eventual Codec modification. This is done by a CBC message "modify request" which is replied by a "modify response" message.

6. The B-CSF sends the CBC message "add request" to the BCF with the transaction "establish BNC_notify" to inform the BCF about the A-side BIWF address and the BNC id and to request a bearer establishment. This message is acknowledged by a "add response" message from the B-BCF.

7. The B-CSF sets up a bearer connection to the A-BCF. It selects a virtual ATM path and channel (AAL 2 parameter Pathid), provides the served user generated reference (BNC id in BICC), an AAL2 Circuit id, the AAL2 Service endpoint identification (BIWF address = NSEA address of A-BCF) and the originating id (own AAL2 transaction id) and sends these parameters in an establish request to the BCF of a switching node (if available) between the two MSCs.In the intermediate switching node AAL2 switching takes place based on the AAL2 Service endpoint identification and the "establish request" is forwarded to the A-BCF.

8. The A BCF acknowledges the bearer setup with an AAL2 "establish confirm" message which is routed via a switching node (if available) to the B-BCF.

9. The A-BCF informs the A-CSF with an CBC message "notify indication" about the bearer setup. This notification is acknowledged by the A-CSF with an "Notify response".

10. The same happens in the B-BCF and the B_CSF: The BCF informs the CSF with an CBC message "notify indication" about the bearer setup. This notification is acknowledged by the CSF with an "Notify response".

11. After successful localization of the B-subscriber in GSM or in the fixed network an address complete message is received and forwarded as a BICC message to the A-CSF.

12. When the B-subscriber answers an answer message is received and forwarded to the A-CSF as a BICC message.


Fig. 33 Backward BNC establishment (ITU-T Q Supplement 32 TRQ2141/Application inform. acc to Q.765.5)

4.5.3 Forward BNC (Backbone Network Connection) establishment

The main difference between the forward and the backward establishment is the direction of the bearer connection set up. In the forward direction the bearer is set up in the same direction as the call goes.

1. The A- Call Service Function (CSF) sends a CBC command "add request" to the Bearer Control Function BCF with the transaction "Prepare_BNC_Notify" to get the so-called BIWF address (own node address), a BNC id (identification of the BNC). The transaction is identified by a so-called transaction id provided by the CSF.

2. The BCF answers with an CBC message "add response" to the CSF with the transaction BNC prepared to provide the required information.

3. The CSF sends an initial address message similar to the ISUP message to the CSF responsible for termination of the BNC. This message contains, beside the normal ISUP parameters like calling party and called party information, the action id = connect forward, the BIWF address, and the BNC id of the A-BCF.

4. The B-CSF sends the CBC message "add request" to the BCF with the transaction "prepare BNC_notify" to inform the BCF about the A-side BIWF address and the BNC id and to request the own BIWF address and the BNC id.

5. This message is acknowledged by a "add response" message from the B-BCF.

6. The B-CSF on the BNC termination sends a BICC "application message" and provides the codec information, B-BIWF address and the B-BNC id in there.

7. The A-CSF request with a "modify request" transaction type "Establish BNC Notify" the setup of the Bearer connection. This is replied by a "modify response" message.

8. The A-CSF sets up a bearer connection to the B-BCF. It selects a virtual ATM path and channel (AAL 2 parameter Pathid), provides the served user generated reference (BNC id in BICC), a AAL2 Circuit id, the AAL2 Service endpoint identification (BIWF address = NSEA address of B-BCF) and the originating id (own AAL2 transaction id) and sends these parameters in an "establish request" to the BCF of a switching node (if available) between the two MSCs.In the intermediate switching node AAL2 switching takes place based on the AAL2 Service endpoint identification and the establish request is forwarded to the B-BCF.

9. The B-BCF acknowledges the bearer setup with an AAL2 "establish confirm" message which is routed via a switching node (if available) to the A-BCF.

10. The B-BCF informs the B-CSF with an CBC message "notify indication" about the bearer setup. This notification is acknowledged by the B-CSF with an "Notify response".

11. The same happens in the A-BCF and the A_CSF: The BCF informs the CSF with an CBC message notify indication about the bearer setup. This notification is acknowledged by the CSF with an "Notify response".

12. After successful localization of the B-subscriber in GSM or in the fixed network an address complete message is received and forwarded as a BICC message to the A-CSF.

13. When the B-subscriber answers an answer message is received and forwarded to the A-CSF as a BICC message.


Fig. 34 Forward BNC establishment (ITU-T Q Supplement 32 TRQ2141

Signaling fundamentals

Kunde_CodMN3003EU04MN_0002

2008 Siemens AG

MN3003EU04MN_0002Kunde_Cod

2008 Siemens AG

_150717492.ppt

VPI 32VCI 1

PayloadUser1

VPI 32VCI 2

PayloadUser2

VPI 36VCI 1

PayloadUser3

PVC Table

Port 1 VPI 32 VCI 1 - Port2 VPI 45 VC I2

Port 1 VPI 32 VCI 2 Port3 VPI 45 VCI 2

Port 1 VPI 36 VCI 1 Port2 VPI 40 VCI 3

Port 1

Port 2

Port 3

2

2

2

3

4

3

3

4

4

1

Virtual Channel Switching

VPI 45VCI 2

PayloadUser1

VPI 45VCI 2

PayloadUser2

VPI 40VCI 3

PayloadUser3

_158299512.ppt

MSC/VLR

GMSC

ATM/AAL2

A M R

CODEC

ISUP

TDM

RANAP

A M R

CODEC

_317186172.ppt

Media Gateway

Bearer Control

Bearer Segment

CBC

CSF

MSC Server control function

RANAP

RNC

BCF

Backbone Network Connection

CSF

_317189372.ppt

Bearer

Bearer Control

Network or Call Control



Bearer Control

Bearer

Bearer Control

Bearer

Bearer Control

Bearer

Bearer

Bearer Control

Bearer Control

Bearer

Bearer

Bearer Control

_369312512.ppt

Switching Node

Media Gateway

Media Gateway

CBC

BCF

Bearer Control

Bearer Segment

Bearer Control

Bearer Segment

CSF


Media Gateway

BCF

Bearer Control

Bearer Segment

Bearer Control

Bearer Segment

CBC

CSF


CBC

BICC


e.g ATM Switch

e.g ATM Switch

_369314112.ppt

Switching Node

Media Gateway

CBC

CSF

MSC Server control function/VLR

Switching Node

Media Gateway

CBC

CSF


Switching Node

BCF

BICC

_401232004.ppt

Switching Node

Media Gateway

CBC

CSF


Switching Node

Media Gateway

CBC

CSF


Switching Node

BCF

e.g. ATM Switch

CIC Call Instance Code

CICPool

CICPool

_401233604.ppt

BCF

IAM (action= connect forward, BIWF addr = a1, BNCid = a2,...,suported codeclist)

AddReq (Prepare_BNC_notify, BIWF addr = ?, BNCid = ?,..)

AddResp(BIWF addr = a1, BNCid = a2,..)

e.g. UMSC A

e.g. ATM switch

e.g. GMSC B

ERQ (SUGR=b2, AAL2SEPT=b1,Pathid,CID, Orig id,Dest id,...)

ERQ (SUGR=b2, AAL2SEPT=b1, Pathid,CID, Orig id,Dest id...)

ECF (Orig id, Dest id)

CBC

CBC

BICC

AAL2

AAL2

AAL2

AAL2


NotifyInd (Event=EST,...)

CBC

NotifyResp (Event=EST,...)

ACM (....)

BICC

ANM (...)

BICC

ACM (....)

ANM (...)

CBC

CBC

BICC/ISUP

BICC/ISUP

1

2

3

4

8

8

9

9

10

10

12

12

13

13

APM (action= forward response, BIWF addr = b1, BNCid = b2, selected codec list,supported codeclist.)

6

ModReq (Est_BNC_notify, BIWF addr = b1, BNCid = b2,..)

ModResp()

CBC

CBC

7

7

AddResp (BIWF addr = b1, BNCid = b2,..)

CBC

5



CBC

CBC

11

11


_369314752.ppt

Switching Node

Media Gateway

CBC

CSF


Switching Node

Media Gateway

CBC

CSF


Switching Node

BCF

e.g. ATM Switch

BICC

Bearer Control

Bearer Control

_369313152.ppt

CBC

CSF


CBC

CSF


Layer 1

MTP

Layer 1

ATM

Layer 2

AAL5

IP

MTP2

SAAL

SCTP

MTP3B

STC

MTP3

M3UA

BICC

_369311872.ppt

Switching Node

CBC

Switching Node

Switching Node

Media Gateway

Media Gateway

CBC

BCF

Bearer Control

Bearer Segment

Bearer Control

Bearer Segment


AAL2 Signaling endpoint


_317188412.ppt

CR (Service_Request)

CC (Service_Accept)

DT1 (Setup)

MediaGateway

MSCServer

1

2

3

DT1 (RAB_Assignment Request)

ERQ (Path Id, CID)

Path Identifier = VPI/VCICID = Circuit identifier

ECF

// AAL2 L3

DT1 (RAB_Assignment Response)

ERQ (Path Id, CID)

ECF

// AAL2 L3

7

9

10

ERQ (Path Id, CID)

ECF

ERQ (Path Id, CID)

ECF

8

9

12

DT1 (Call Proceed)

4


AddResp(BIWF addr, BNCid ,..)

CBC

CBC

RANAP

RANAP

RANAP

RANAP

RANAP



CBC

AAL2

AAL2

CBC

5

6

10

11

RNC

_317188732.ppt

Switching Node

Switching Node

Switching Node

Media Gateway

Media Gateway

Bearer Control

Bearer

Bearer Control

Bearer

MSC Server

MSC Server


_317186812.ppt

CBC

CSF


RNC

BCF

RANAP

CSF

_158301112.ppt

Switching Node

CBC

Switching Node

RNC

Media Gateway

BCF

Bearer Control

Bearer Segment




_158301432.ppt

Switching Node

RNC

Media Gateway

Bearer Control

Bearer

MSC Server


_158299832.ppt

MSC/VLR

GMSC

ATM/AAL2

A M R

BICC

ATM/AAL2

A M R

CODEC

CODEC

RANAP

_150720052.ppt

Circuit 2

Circuit 3

Circuit 4

Circuit 5

Circuit 6

Circuit 1

VPI=XVCI=A

simplified

empty

Represents one virtual channel in a virtual path

ATM cell 53 byte

CID=a

ATM switch

VPI=XVCI=A

Circuit1

Circuit3

Circuitn

Circuit1

Circuit3

Circuitn

CID=b

CID=c

CID=d

CID=e

VP/VC switching

_158298552.ppt

ATM-Cell ( 53 Byte)

AAL2StartField1Byte

CPS-Packet Header( 3 Byte )

CID 8 B i t

LI 6 B i t

HEC 5 B i t

CPS-packet payload

ATM-PDU (Cell Payload )( 48 Byte )

UUI 5 B i t

Common Part Sublayer PDU (1 Byte Start field and max 47 Byte CPS-PDU Payload )

CPS PH( 3 Byte )

CPS Packet x

CPS Packet x+1

ATM Cell / AAL2 Packet format

CID = Channel Identifier (0-255 , 0=not used; 1=Layer Management; 2=AAL-2 signalling; 3-7=reserved; 8-255=user connections)LI = Length IndicatorUUI = User to User IndicationHEC= Header Error Control

ATM-CellHeader( 5 Byte )

_158299192.ppt

MSC/VLR

GMSC

CODEC

ISUP

TDM

CODEC

_158298232.ppt

e.g.padded

Circuit 2

Circuit 1

VPI=XVCI=A

simplified

empty

8bit

VPI=YVCI=B

8bit

e.g.padded

e.g.padded

Circuit 2

Circuit 1

empty

VPI=XVCI=A

8bit

256bit / 125 sec

13568bit

ATM switch

VPI=XVCI=A

Circuit1

Circuit1

Circuit1

Circuit1

Circuit1

Circuit1

VPI=YVCI=B

Circuitn

Circuitn

Circuitn

Circuitn

Circuitn

Circuitn

376 bits

376 bits

376 bits

Circuit switching

_150718132.ppt

VPI

VCI

VPI

VCI

Type

VCI

CLP

HEC

7 6 5 4 3 2 1 0

5 octets

Payload

Generic Flow Control

VCI

VPI

VCI

Type

VCI

CLP

HEC

7 6 5 4 3 2 1 0

5 octets

Payload

NNI

UNI

VPI

VPI 12 bit = 4096 VPIVCI 16 bit = 65536 VCI

VPI 8 bit = 256 VPIVCI 16 bit = 65536 VCI

_150719092.ppt

SAAL

Physical Layer

ATM VP/VC Layer

SAR

SSCOP

CPCS

SSCF

E.g. STM1

VP/VC switching

Segmentation and reassembling to and from 48 byte PDUs

CRC 32

Sequencing Flowcontrol Retransmission Connection management

Service coordination

MTP level 2

_150719412.ppt

RNC

BCF

CSF

Switching Node

Media Gateway

CBC

CSF


RANAP

_150718452.ppt

RNC

BCF

CSF

Switching Node

Media Gateway

CBC

CSF


RANAP

_150717812.ppt

User Network Interface(UNI)

User Network Interface (UNI)

Network Network Interface(NNI)

_150564080.ppt

User 1

ATM Switch

ATM Switch

e.g. STM1 155Mb/sMedium sharedResources on demand

3

High data rate

Medium data rate

low data rate

User 2

User 3

User 1

User 2

User 3

3

High data rate

Medium data rate

low data rate

PVC or SVC

PVC or SVC

PVC or SVC

1

1

1

e.g. STM1 155Mb/sMedium sharedResources on demand

2

2

2

2

2

3

2

1

1

1

1

2

High bandwidth allocated

Medium bandwidth allocated

Low bandwidth allocated

available Bandwidth

_150716852.ppt

VP32

PaylodUser1

VP36

PaylodUser2

VP40

PaylodUser3

PVC Table

Port 1 VP 32 - Port2 VP45

Port 1 VP 36 Port3 VP32

Port 1 VP 40 Port2 VP33

Port 1

Port 2

Port 3

VP45

PaylodUser1

VP32

PaylodUser2

VP33

PaylodUser3

2

2

2

3

4

3

3

4

4

1

Virtual Path switching

_150717172.ppt

virtual channel: VCI=s

transmission line end point

virtual path end point

VC end points

virtual path:VPI=x

Virtual Path:VPI=z

virtual channel: VCI=t

virtual path:VPI=y

ATM Switch

ATM Switch

_150716532.ppt

MSC

IAM (called Party address, CIC=0-3,....)

Called PA Routing Outgoing PCM/TS

IAM (called Party address, CIC=0-1,....)

1

2

3

4

4

_150563440.ppt

1a

1b

1c

2a

2a

2b

3a

3b

3c

user1

user2

user2

Transmit

1a

1b

1c

2a

2a

2b

3a

3b

3c

Receive

29a

29b

29c

user29

31a

31b

31c

user31

30a

30b

30c

user30

Asynchronous Transmission

Continous Cell StreamNo Frame Structure

29a

29b

29c

31a

31b

31c

30a

30b

30c

user1

user2

user2

user29

user31

user30

Cell 53 byte

Payload

Empty Cell

Header

Reassambling

Segmentation

_150563760.ppt

BSC

MSC

GMSC

ISDNExchange

64kb/sconsumed

64kb/sconsumed

64kb/sconsumed

Setup

Setup

Setup

1

1

1

2

2

2

2

2

2

Bla, BlahBlah, blah

3

Bla, BlahBlah, blah

3

3

3

3

....................................

4

....................................

4

4

4

4

_69037612.ppt

1a

1b

1c

2a

2a

2b

3a

3b

3c

user1

user2

user2

Transmit

1a

1b

1c

2a

2a

2b

3a

3b

3c

Receive

1 frame 125 micro s

Every 125 micro s transmission of the the the same user

Synchronous Transmission

2Mb/s

64kb/s

user1

user2

user2

29a

29b

29c

user29

31a

31b

31c

user31

30a

30b

30c

user30

29a

29b

29c

31a

31b

31c

30a

30b

30c

user29

user31

user30

Transmission of Timeslots organized in Frames

_69036972.ppt

BCF

IAM (action= connect backward, BIWF addr = a1, BNCid = a2,...,suported codeclist)


AddResp(BIWF addr = a1, BNCid = a2,..)

e.g. UMSC A

e.g. ATM switch

e.g. GMSC B

ERQ (SUGR=a2, AAL2SEPT=a1,Pathid,CID, Orig id,Dest id,...)

ERQ (SUGR=a2, AAL2SEPT=a1, Pathid,CID, Orig id,Dest id...)


CBC

CBC

BICC

AAL2

AAL2

AAL2

AAL2



AddReq (Est.BNC_Notify,BIWF addr = a1,BNCid = a2, selected codec..)

CBC


ACM (....)

BICC

ANM (...)

BICC

ACM (....)

ANM (...)

CBC

CBC

BICC/ISUP

BICC/ISUP

1

2

3

6

7

7

8

8

10

10

11

11

12

12

APM (action= codec selected, selected codec list,supported codeclist.)

4

ModReq (Modify_Bearer_Char, Selected Codec)

ModResp()

CBC

CBC

5

5

AddResp (...)

CBC

6



CBC

CBC

9

9

Documents

Signaling Fundamentals in Mobile Communication