R2511-HP MSR Router Series ACL and QoS Configuration Guide(V5)

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Figure 31 RTP packet format
The fields are described as follows:
• V—2 bits, version number.
• P—1 bit, padding flag.
• X—1 bit, packet header extension flag.
• CC—4 bits, contributor count.
• M—1 bit, special event flag.
• PT—7 bits, payload type flag.
• Sequence Number—16 bits, data packet sequence number.
• Time Stamp—32 bits, time stamp.
• SSRC—32 bits, synchronization source identifier.
• CSRC identifiers—32 bits, list of contributing source identifiers. The number of contributing source
identifiers depends on the value of the CC field. The CSRC identifiers field can contain up to 15
contributing source identifiers.
• Payload—Packet payload.
RTCP packet
An RTCP packet is encapsulated in a UDP packet. Usually a UDP packet carries at least two RTP packets,
and such a UDP packet is called a "compound RTCP packet."
Figure 32 Compound RTCP packet format
As shown in Figure 32, the random 32-bit prefix in the header exists only when the RTCP packet is
encrypted. An encrypted RTCP packet no longer has the features of an RTCP packet and requires no
special processing. Each packet in the figure represents an RTCP packet, and no space exists between
two RTCP packets. The type of the first RTCP packet in a compound RTCP packet must be SR or RR.
015
Payload
V Sequence Number
31
Time Stamp
P X CC M PT
23 8
SSRC
CSRC identifiers
……
SR
SSRC
Sender
report
SSRC SSRC
Site 1 Site 2
SD
ES
SSRC
Cname Phone
SSRC
SSRC
Cname Loc
BYE
SSRC
Reason
packet
If encrypted: random 32-bit integer
Receiver reports item item item item
chunk chunk
packet packet