RFC 3243 (rfc3243) - Page 2 of 6
RObust Header Compression (ROHC): Requirements and Assumptions for 0-byte IP/UDP/RTP Compression
Alternative Format: Original Text Document
RFC 3243 Reqs and Assumptions for 0-byte ROHC RTP April 2002 However, all-IP cellular networks will also be built with already existing air interfaces such as GSM and IS-95, which are less flexible using radio bearers optimized for specific frame sizes matching the speech codecs used. This means that not a single octet of header can be added without switching to the next higher fixed packet size supported by the link, something which is obviously very costly. In the long term, this drawback should of course be eliminated with new, more flexible air interfaces, but in the short term it would be desirable if an efficiency comparable to the circuit switched case could also be achieved for already deployed speech codecs when used over the existing air interfaces. To achieve that, it must be possible to completely eliminate the headers for a majority of the packets during normal operation, and this is the purpose of 0-byte header compression. All functionality normally provided by the 1-octet header must then be provided by some other means, typically by utilizing functionality from the lower layer. It is important to remember that the purpose of 0-byte header compression is to provide optimal efficiency for applications matching the link layer characteristics, not efficiency in general. As a starting point for these requirements, the well-established requirements base developed in the ROHC WG has been used. From that, the requirements have evolved through input from the 3GPP2 community and from discussions within the WG. 2. Assumptions for the Applicability of 0-byte RTP Header Compression The purpose of 0-byte header compression is to provide optimal usage of certain links when the traffic pattern of a packet stream completely matches the characteristics of that link. There are no assumptions that only packet streams complying with that pattern will occur, but optimal efficiency cannot of course be provided when this is not the case. To make 0-byte header compression feasible, it is assumed that lower layers can provide the necessary functionality needed to replace the 1-octet headers and fulfill the requirements defined in section 3. An example is the synchronized nature of most cellular links, which can provide sequencing and timing information and make packet loss detection possible. 3. Requirements on 0-byte RTP Header Compression Since 0-byte header compression for ROHC IP/UDP/RTP is a variant of regular ROHC RTP compression [ROHC], these requirements are described as deltas to those defined in the regular RTP requirements [RTP-REQ]. For simplicity, this section is also separated into the same three subsections as the requirements in [RTP-REQ], where the first deals Jonsson Informational
