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UMTS (Network architecture) - 3

Network architecture [Under UMTS]
» Network architecture - 23.002 «
» QoS architecture - 23.107 «

GSM stream of wireless standards started by ETSI always tried to maintain as much backward compatibility as would be possible. This has helped both new and existing network operators. In addition to international nature of standardisation, backward compatibility is another possible reason for popularity that 3GPP standards have received and continues to receive.

Below diagram show logical domains of UMTS network.

UTRAN (UMTS Terrestrial Access Network) consists of Node Bs connected RNCs (Radio Network Controller). Node B can be considered as UMTS counterpart of GSM BTS and RNC as similar to BSC.

Core network consists of MSC/VLR/GMSC for CS operations, SGSN/GGSN for PS operations, and other GSM elements like HLR, AuC, EIR etc. Yes, UMTS distinguish between CS and PS operations. Services which require CS operations like voice call, video telephony will be sent over CS network elements and PS based services like internet access will be over PS network elements. This mean RNC will be connected to both MSC/VLR and SGSN as shown in R99 based UMTS architecture below:

As can be seen GSM/GPRS interfaces are reused in core network. TRAU (not shown) will be located at MSC location. Note that MSC and SGSN need to support new Iu interfaces with RNC. Also, there is (open) interface between RNCs to handle handover without much of involvement from core network elements. This is an important step as core network become more independent of actual radio technology being used.

A RNC and its connected Node Bs collectively known as RNS (Radio Network Subsystem). In GSM A-bis interface (between BTS and BSC) was not defined thoroughly (or openly), eventually there being proprietary solutions. This is not the case with Iub interface between Node B and RNC.

Below is UMTS QoS architecture diagram showing how UMTS tries to achieve end-to-end service.

In next article, we will have a look at Rel 5 architecture.

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

Copyright © Samir Amberkar 2010§ §

Introduction « UMTS Index » R5 core network