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UMTS (Protocol layers - CS) - 7

Protocol Layers - CS [Under UMTS]
» Radio interface layer - 25.301 «
» NAS - 24.007/8 «
» UTRAN description - 25.401 «
» UTRAN Iu interface - 25.410 «

UMTS continue to use same GSM NAS entities (may be modified a bit to be more independent of underlying access technology being used, be it over air interface or over RAN interface). Challenge is to be able to use same access stratum in both PS and CS services. We will see in next article that it is the case.

UMTS Circuit Switched bearer services include (AMR) Speech and Video (telephony). Below is a protocol layer diagram for CS bearer services:

RRC takes care of "radio connection", some way similar to GSM-RR. RLC/MAC provide generic QoS based services which makes them common to both PS and CS services.

Though UMTS separate traffic (in CN) as CS and PS, eventually we should have just big cloud of CN taking all types of traffic and distinguishing it only in terms of QoS parameters. Looking at popularity of IP, it seems this CN cloud would be IP based (possibly running on ATM/SONET transport). In fact, both signaling and control planes may merge with a adaptation distinguishing signaling and control plane traffic.

Coming back to protocol layers, ETSI/3GPP continue to use existing protocols for transport in wireline side of UMTS. Iu-CS uses Broadband SS7 SCCP layer sitting on AAL5 (refer ATM article) or IP. RANAP works like UMTS counterpart of BSSAP/BSSGP.

In CS User plane, we expect that we should be using same entities in access stratum. Signaling traffic, though a special one, is still a traffic with specific QoS requirements (like priority, lowest delay, acknowledged, variable bit rate/bursty etc.). Below diagram shows CS User plane layers:

Interesting addition in R5 is RTP/RTCP (possibly for MGW). These are IP based (VoIP) multimedia protocols for real time applications.

We will check protocol layers for PS bearer services in next article.

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

Copyright © Samir Amberkar 2010§

Services « UMTS Index » Protocol layers - PS