3.2.5 Message Processing Events and Sequencing Rules

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 RTPME processes RTCP-related packets as specified in [RFC3550] and [RFC3551], with the following additional notes.

The following rules apply to every RTCP packet:

  • The participant timeout timer (section 3.1.2) corresponding to the packet's SSRC MUST be restarted.

The following rules apply to specific types of RTCP packets:

RTCP Probe Packet: Its arrival time is recorded and the packet is discarded.

RTCP Compound Packet: The following rules apply:

  • If there is a record of a previous RTCP probe packet, ReceivingRTCPPacketPairs is set to "true" and an arrival time gap is computed as the difference between the arrival time of this packet and the probe packet, the packet length of the RTCP compound packet includes all headers up to the network layer. For example, if the transport mechanism is UDP the RTCP Compound Packet will include RTP, UDP, and IP headers. These two values are used to compute the bandwidth perceived by these two packets while traversing the path from their source up to their destination, as the RTCP compound packet length divided by the arrival time gap. The process of estimating bandwidth from individual calculations is implementation-specific.

  • If FastRTCPPacketPairCount is zero and RTCPSendingRate is "normal", RTCPSendingRate is set to "fast", and the RTCP send timer MUST be set to 250 milliseconds. If the received packet has a profile specific extension with a positive bandwidth report, and RTCPSendingRate is "fast", that variable is set to "normal".

RTCP APP Packet: This packet is ignored.

RTCP BYE: The SSRC from which this packet was sent is designated as having sent an RTCP BYE and its RTCP bye timer is started.