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4.1 RTP Packet Syntax

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The size of the RTP payload format header, as specified in section 2.2.1, varies from 4 to 16 bytes, depending on how the R, D, and I fields are set. When none of the fields are set to 1, the size of the RTP payload format header is 4 bytes. When only one of the fields is set to 1, the size of the RTP payload format header is 8 bytes. When two fields are set to 1, the size of the RTP payload format header is 12 bytes. When all three fields are set to 1, the size of the RTP payload format header is 16 bytes.

The following illustration represents an ASF data packet as it would be sent on the network. In this typical scenario, the total packet size is 1,500 bytes, which includes the following headers and payloads:

  • IP header = 20 bytes

  • UDP header = 8 bytes

  • RTP header = 12 bytes

  • RTP payload format header = 4 bytes

  • ASF data packet header = 12 bytes

  • ASF payload headers and compressed media data = 1,444 bytes

Therefore, the header overhead is approximately 3.73 percent. For smaller RTP packet sizes, such as 1,000 bytes, the overhead is increased to approximately 5.6 percent.

RTP packet diagram

Figure 7: RTP packet diagram