The ROHC framework, along with a set of compression profiles, was initially defined in RFC To improve and simplify the ROHC specifications, this. Canonical URL: ; File formats: Plain Text PDF Discuss this RFC: Send questions or comments to [email protected] Robust Header Compression (ROHC) is a standardized method to compress the IP, UDP, The ROHC compression scheme differs from other compression schemes, such as IETF RFC and RFC , by the fact that it performs According to RFC , the ROHC scheme has three modes of operation, as follows.
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RFC – part 3 of 7
The sequence number is reconstructed by replacing the sequence number LSBs in the context with those received in the header. Operation in Bidirectional Optimistic mode 5. Set of nonnegative integers, each integer indicating a profile supported by the decompressor.
Optional octet indicating the size of the feedback data field in octets. The details of each state, state transitions, and compression logic are given subsequent to the figure.
A small CID with the value 0 is represented using zero bits. Setting the mode parameter in the ACK packet to U indicates that the compressor is to stay in Unidirectional mode.
Clear description of the referenced document:. Decide whether decompression is allowed In Full Context state, decompression may be attempted regardless of what kind of packet is received. If no profile is noted in the context, no further action is taken.
The segmentation scheme was designed to reduce packet size variations that may occur due to outliers in the header size distribution. Decompressor states and logic O-mode The decompression states and the state transition logic are the same as for the Unidirectional case see section 5.
ITU-T work programme
This is part of the normal decompression procedure prior to any CRC test failures. Details of the transitions between states and decompression logic are given subsequent to the rfv.
When these bits arethe size of the feedback data rrc given by the bits; 0, a Size octet, which explicitly gives the size of the feedback data, is present after the feedback type octet. Retrieved from ” https: The optimistic approach principle and transitions occasioned by the need for updates work in the same way as described in chapter 5. The reconstructed unit has the format: The Bidirectional Optimistic mode is similar to the Unidirectional mode, except that a feedback channel is used to send error iehf requests and optionally acknowledgments of significant context updates from the decompressor to compressor.
The context table is indexed using the CID which is sent along with compressed headers and feedback information.
Justification for the specific reference: The mechanisms used are those described in 4. This section describes some of this state information in an abstract way. Padding or Add-CID octet They may then ietc to O-mode if a usable return link is available, and the decompressor sends a positive acknowledgement, with O-mode specified, to the compressor.
If defined by a “ROHC over X” document, per-channel negotiation can be used to pre-establish state information for a context e.
It has the following general format. Alternatives do, however. Current information, if any, about IPR issues:. In order to handle potential decompression errors, the compressor sends periodic refreshes of the stream context to the decompressor. IR This packet type communicates the static part of the context, i.
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This, the minimal, packet type is used when parameters of all SN- functions are known by the 30095, and the header to be compressed adheres to these functions. Feedback is described in section 5. The next packets contain variable information, e.
In summary, Ietff segmentation should be used with a relatively low frequency in the packet flow. Reconstruct and verify the header When reconstructing the header, the decompressor takes the header information already stored in the context and updates it with the information received in the current header. It is anticipated that feedback to the compressor can be realized in many ways, depending on the properties of the particular lower layer.
Robust Header Compression
From Wikipedia, the free encyclopedia. Implementations can use a different structure for and representation of this state. Feedback in Unidirectional mode The Unidirectional mode of operation is designed 309 operate over links where a feedback channel is not available. All RFCs always remain available on-line. This explicit length information allows piggybacking and also sending more than one feedback element in a packet.
State transition logic The transition logic for compression states in Bidirectional Optimistic mode has much in common with the logic of the Unidirectional mode. U, O, or R. Alternatives 1 and 2 apply only to compressed headers in channels where the CID space is small. Feedback elements always start with a packet type indication.
Several compression profiles are available, including the following:. The procedure for finding the size of the feedback data is as follows: Other useful information describing the “Quality” of the document: Data compression Internet Standards.
The total size of the feedback data field is determinable upon reception by the decompressor, by inspection of the Code field and possibly the Size field. Once a stream of packets is classified, it is compressed according to the compression profile that fits best. A compression profile defines the way to compress the different fields in the network headers. Segmentation usage considerations The segmentation protocol defined in ROHC is not particularly efficient.