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UMTS (R5 core network) - 4

R5 core network [Under UMTS >> Network architecture]
» Network architecture - 23.002 R5 «
» Bearer Independent CS Core Network - 23.205 R5 «
» IMS - 23.228 R5 «
» SS7 over IP or ATM - 23.205 R5 «

Release 5 does major additions (1st and 2nd coming from R4) to R99 core network:

1) Transport layers in (SS7) interfaces within core network can be made to run over ATM or IP.

2) MSC functionality split in MSC server and MGW (Media GateWay). MSC server is handle control part and MGW taking care of user data. MSC server controls MGW with MGCP (Media Gateway Control Protocol/Megaco). Megaco is IETF standard, currently maintained by ITU as H.248 standard. Similar apply to GMSC. This has resulted in ISUP interface between MSC and GMSC to be made bearer independent (called as BICC - Bearer Independent Call Control). Splitting user data from control one has obvious advantages: we can have one MGW for both MSC and GMSC, MGW takes care of TRAU functionality and can actually convert speech into 64kpbs rate (or other formats/rates) only during interworking with other networks (like PSTN) resulting in efficiency on resources in core network.

3) IMS (IP Multimedia Sub-system) introduced. The main idea of having IMS is to shift core network to "all IP" operation. Both control and user data will flow through this "all IP" network. VoIP protocol, SIP (Session Initiation Protocol) stacks will take care of creating multimedia sessions. UICC card, which has USIM application will now also have ISIM application. A very rough architecture may look like as below:

R5 network architecture is shown below; IMS can be covered later as a separate topic.

In next article, we will have a brief look at interfaces in R5 based RAN and CN.

References: UMTS by Sanchez and Thioune, and WCDMA for UMTS by Holma and Toskala.

Copyright © Samir Amberkar 2010§

Network architecture « UMTS Index » Interfaces