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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It is interpreted according to the profile indicated in the Profile field.
ITU-T A.5 reference justification
The RFC defines a generic compression mechanism. In the No Context state itef IR packets, which carry the static information fields, may be decompressed. The following principal kinds of feedback are supported. ROHC segmentation should only be used for occasional packets with sizes larger than what is efficient to accommodate, 395. The size of the sequence number SN field governs the number of packets that ROHC can lose before the compressor must be reset to continue. The format of a compressed packet can depend on the mode.
Data structures The ROHC protocol is based on a number of parameters that form part of the negotiated channel state and the per-context state. All segment header packets for one reconstructed unit have to be sent consecutively on a channel, i. If the local repair attempt itf, it must move to a lower state to avoid. Compressor states and logic O-mode Below is the state machine for the compressor in Bidirectional Optimistic mode.
Arrival times of packets where decompression fails are discarded.
RFC – The RObust Header Compression (ROHC) Framework
If no profile is noted in the context, no further action is taken. The packet type is able 33095 carry variable-length feedback information. Generated when several successive packets have failed to be decompressed correctly. Feedback elements always start with a packet type indication. References within the referenced Ieff are listed under item 8. Clear description of the referenced document:. The reconstructed unit has the format: To accommodate the occasional packet that is larger than that largest size negotiated, ROHC defines a simple segmentation protocol.
Please help improve this article by adding citations to reliable sources. Header either eitf with a packet type indication or has a packet type indication immediately following an Add-CID Octet. How a compressor is associated with feedback on a particular channel needs to be defined in a “ROHC over X” document.
Data compression Internet Standards. October Learn how and when to remove this template message. Timeouts, downward transition When the optimistic approach is taken as described above, there will always be a possibility of failure since the decompressor may not have received sufficient information for correct decompression. Note that this means that there can be no padding and no feedback in the reconstructed unit, and frc the CID is derived from the initial octets of the reconstructed unit.
Both the compressor and the decompressor start in U-mode. Nonupdating values can be provided for other fields using an extension UOID.
Compressor states and logic U-mode Below is the state machine for the compressor in Unidirectional mode. The mechanisms used are those described in 4. Segment Other packet types can be used at will by individual profiles. In the IR packet, the profile identifier is abbreviated to the 8 least significant bits. It is not intended to replace link layer segmentation functions; these SHOULD be used whenever available 305 efficient for the task at hand.
The purpose of this algorithm is to repair the context. In this situation, the decompressor will detect the incorrect decompression of the following packet with high probability, but it does not know the reason for the failure.
ITU-T work programme
If the decompressor receives any of these packets, it will be in sync with the compressor. It has the following general format: Feedback logic O-mode The feedback logic defines what feedback to send due to different events when operating in the various states.
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. The ief decompressed header will then update the context. First, attempt to determine whether SN LSB wraparound case 3 is likely, and if so, attempt a correction.
This is the size of the largest reconstructed unit in octets that the decompressor ietff expected to reassemble from segments see 5. Optimistic approach, upwards transition Transition to a higher compression state in Unidirectional mode is carried out according to the optimistic approach principle.
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Current information, if any, about IPR issues:. Note that case 3 does not occur in R-mode. Either of Feedback or Header must be present. 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.