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Vocoder Placement Issues in Ericsson CDMA: Evolution of Signaling for Compressed Voice

This document analyzes vocoder placement challenges within Ericsson CDMA systems, focusing on IS-95/2000 signaling messages crucial for media gateways (MGW) and radio access networks (RAN). It highlights requirements for supporting multimedia and legacy mobiles, emphasizing the transition to an all-IP architecture. Key topics include IP transport for compressed voice, signaling interfaces, QoS requirements, and the impact of vocoder placement on latency and transcoding. The study further explores handoff procedures between legacy and evolved architectures, addressing open issues like header compression and multiplexing.

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Vocoder Placement Issues in Ericsson CDMA: Evolution of Signaling for Compressed Voice

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  1. VOCODER PLACEMENT ISSUES Ericsson CDMA Systems Roger Gustavsson Qiang Gao Ake Jansson

  2. IS-95/2000 Signaling Msgs Vocoder IP Network PTSN PTSN Proposed Architecture Evolution RAN A1 MS A2 MSC RAN MSC Server A1* IS-95/2000 Signaling Msgs Ax MS Vocoder MGW IP Transport for compressed voice CDMA SYSTEMS Vocoder Placement Issues

  3. Vocoder Placement Requirements • For support of Multimedia mobiles the vocoders shall be located in the Media Gateway (MGW) • For support of Legacy mobiles the vocoders can be located in the RAN or MGW • IP Transport for compressed voice • evolution to All-IP Architecture • Smooth migration towards an unified IP transport platform for both voice and data • Open Issues • header compression, e.g., RTP/UDP/IP header compression • Multiplexing at Link Layer e.g. PPP Mux • End to End Multiplexing at Application Layer

  4. Impact of Vocoder Placement in MGW • New Protocol Stack (A2*) for compressed voice: IOS Application RTP/UDP/IP Link Layer Physical Layer • QoS Requirements • current IP transport (IOS v4.1) supports best effort delivery. • need to provide guaranteed service • Evolved signaling interface (A1*) to MSC server (to allow for resource allocation and management) • New signaling interface between MSC server and MGW

  5. IS-95/2000 Signaling Issues related to Vocoder Placement • Blank-and-Burst and V2 mode not affected • Dim-and-burst • requires the vocoder to lower the coding rate upon request • Vocoder Rate Control • In-band • use the 8 encoder tail bits • Same as the voice transport latency • Out-of-band • Specify explicit signaling between BSC/MSC Server/MGW • signaling latency can be different than voice latency (additional complexity) • Latency requirements on IP transport imposed by air interface signaling delay requirements e.g. HHO to be completed within TBD msecs

  6. Roaming and Inter-operability Issues • Handoff between legacy/evolved architecture • Handoff from legacy to evolved architecture will require changes to existing signaling procedures (e.g. target to specify vocoder assignment) • Transcoding Issues • With support for EVRC/13K/SMV enhancements needed for TFO operation • Mobile to Mobile transcoding (selection of MGW i.e. edge of core network vs. interior to core network)

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