RFC 2736 (rfc2736) - Page 2 of 10
Guidelines for Writers of RTP Payload Format Specifications
Alternative Format: Original Text Document
RFC 2736 Guidelines for Writers of RTP Payload Formats December 1999
order with respect to other ADUs. Thus the ADU is the minimum unit
of error recovery.
The key property of a transport protocol for ADUs is that each ADU
contains sufficient information to be processed by the receiver
immediately. An example is a video stream, wherein the compressed
video data in an ADU must be capable of being decompressed regardless
of whether previous ADUs have been received. Additionally the ADU
must contain "header" information detailing its position in the video
image and the frame from which it came.
Although an ADU need not be a packet, there are many applications for
which a packet is a natural ADU. Such ALF applications have the
great advantage that all packets that are received can be processed
by the application immediately.
RTP was designed around an ALF philosophy. In the context of a
stream of RTP data, an RTP packet header provides sufficient
information to be able to identify and decode the packet irrespective
of whether it was received in order, or whether preceding packets
have been lost. However, these arguments only hold good if the RTP
payload formats are also designed using an ALF philosophy.
Note that this also implies smart, network aware, end-points. An
application using RTP should be aware of the limitations of the
underlying network, and should adapt its transmission to match those
limitations. Our experience is that a smart end-point implementation
can achieve significantly better performance on real IP-based
networks than a naive implementation.
3. Channel Characteristics
We identify the following channel characteristics that influence the
best-effort transport of RTP over UDP/IP in the Internet:
o Packets may be lost
o Packets may be duplicated
o Packets may be reordered in transit
o Packets will be fragmented if they exceed the MTU of the
underlying network
The loss characteristics of a link may vary widely over short time
intervals.
Handley & Perkins Best Current Practice