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Transcoder Placement in All IP Network

Transcoder Placement in All IP Network. MAY 1, 2001. 1. Transcoder Placement in the Media Gateway with Legacy MS Domain Support for Control and Bearer. Transcoder Placement in the Media Gateway with IP Multimedia Domain Support For Control and Bearer View. 2.

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Transcoder Placement in All IP Network

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  1. Transcoder Placement in All IP Network MAY 1, 2001 1

  2. Transcoder Placement in the Media Gateway with Legacy MS Domain Support for Control and Bearer

  3. Transcoder Placement in the Media Gateway with IP Multimedia Domain Support For Control and Bearer View. 2

  4. Motivation for Moving the Transcoders • Better utilization of resources • e.g., Bandwidth requirements of network are reduced by transporting wireless encoded voice to the gateway instead of PCM voice. • Scalability • Adding transcoders at a few gateways vs adding transcoders to many BSCs. 3

  5. Issues with Moving the Transcoders to the MGW • Impact of Jitter on Voice Quality • - IP-related delay variations reduces the accuracy of recreation of the voice signal • Impact of Delay on Conversation Quality • - jitter buffering improves voice quality but increases the end-to-end call path delay • Impact of FS and Transcoder Separation on Forward Link Signaling • - dim and burst vs. blank and burst signaling • - affects voice quality 5

  6. Example Jitter Solution Forward Link Buffer • RTP stores packets into buffer • Must be stored in sequence • Oldest packet dropped in case of overflow Jitter buffer in RNC • No additional buffering in the gateway • Buffer size is typically 1 to 2 packets per call in a well-managed network • Maintained by RTP • RTP sequence number and timestamp used to administer buffer • Sequence number allows detection of out of sequence or lost packets • Erasure packet inserted for lost packets • Timestamp allows RNC to control playout • Oldest packet dropped in case of overflow • Local timing adjustments between FS and BTS • Accommodate mobile timer drift and soft HO window adjustments • Based on BTS feedback • No timing adjustment between FS in RNC and Vocoder in Gateway • May result in buffer underflow/overflow • Expected to happen no more frequently than 2/3 times an hour

  7. Jitter Reverse Link Buffer • Jitter Buffer in the Gateway • - Characteristics and operation similar to that for forward link buffer in RNC • 20 to 40 msecs of Added Delay Due to Jitter Buffering • - Equates to about 150-170 msecs of one-way delay from mobile to PSTN, excluding transmission delay. • - 230-250 msecs of one-way delay mobile-to-mobile

  8. Dim and Burst Support Signaling in RTP for EVRC • draft-mccann-avt-rtp-evrc-00.txt • Specifies 3 bits in the RTP payload to control the vocoder output in the reverse direction.Allows the Frame Selector at the RNC/BSC to request 1/2 rate or 1/8 rate frame from the transcoder in the MGW. • Issue: Will this technique provide timely space for the RNC to insert signaling to the mobile station? • There will be a certain round trip delay in seeing the results of a request for 1/2 rate or 1/8 rate frames. • --- Some signaling may be able to wait for this delay.--- Some signaling may not be able to wait - blank and burst will be needed.--- It seems that this technique will certainly improve voice quality. • Does a similar technique need to be applied to the RFC for 13K transcoders?--- Do operators need to support 13K transcoders in the MGW? --- Only EVRC and SMV?

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