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B Examples of adaptation scenarios  B.1 Video bitrate adaptation 
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B  Examples of adaptation scenarios  p. 323

B.1  Video bitrate adaptation  p. 323

It is recommended in clauses 7.3.3 and 10.3 that a video sender adapts its video output rate based on RTCP reports and TMMBR messages. The following examples illustrate the usage:
EXAMPLE 1 - Handover to a different cell:
  1. A video session is established at 100kbps. 5kbps is allocated for RTCP and trr-int is set to 500 ms. This allows an MTSI client in terminal to send regular RTCP reports with an average 500 ms interval consuming less than 5 kbps for RTCP. At the same time it allows the MTSI client in terminal to send an early RTCP packet and then send the next one already after 800 ms instead of after 1 000 ms.
  2. The receiver is now subject to a reduced bandwidth, e.g. 60 kbps, due to handover to a different cell. The network indicates the reduced bandwidth to the receiver. The receiver generates a TMMBR message to inform the sender of the new maximum bitrate, 60 kbps.
  3. The sender receives the TMMBR message, adjusts its output bitrate and sends a TMMBN message back.
  4. The receiver sends a SIP UPDATE message to the sender indicating 60 kbps
  5. The receiver travels into an area with full radio coverage. A new bandwidth of 100 kbps is negotiated with the network. It sends a SIP UPDATE message for 100 kbps.
  6. The sender receives the SIP UPDATE message, and adjusts its output bitrate.
EXAMPLE 2 - Bad coverage or congestion:
  1. A video session is established at 100kbps. 5kbps is allocated for RTCP and trr-int is set to 500 ms. This allows an MTSI client in terminal to send regular RTCP reports with an average 500 ms interval consuming less than 5 kbps for RTCP. At the same time it allows the MTSI client in terminal to send an early RTCP packet and then send the next one already after 800 ms instead of after 1 000 ms.
  2. The receiver detects congestion and estimates a preferred video transmission rate of e.g. 60 kbps. The receiver generates a TMMBR message to inform the sender of the new maximum bitrate, 60 kbps.
  3. The sender receives the TMMBR message, adjusts its output bitrate and sends a TMMBN message back.
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