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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New RFCs were published to compress new protocols:.

The classification algorithm is not defined by the ROHC protocol itself but left to the equipment vendor’s implementation. Clear description of the referenced document:.

RFC – The RObust Header Compression (ROHC) Framework

The decompressor does not attempt to decompress headers at all in the No Context and Static Context states unless sufficient information is included in the packet itself. Alternatives do not place any particular requirements on the ROHC packet type scheme.

This document describes profiles 0x, 0x, 0x, and 0x; further profiles may be defined when ROHC is extended in the future. When a CRC mismatch is caused by residual bit errors in the current header case 1 abovethe decompressor should stay in its current state to avoid unnecessary loss of subsequent packets. First, attempt to determine whether SN LSB wraparound case 3 is likely, and if so, attempt a correction.


The reconstructed unit has the format: The segmentation scheme was designed to reduce packet size variations that may occur due to outliers in the header size distribution. Using this mechanism, the decompressor may be able to repair the context after excessive loss, at the expense of discarding two packets.

ITU-T work programme

If the first bit is 1, the CID uses two octets. However, residual bit errors in the current header are only detected with good probability, not reliably.

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. Such large overheads may be tolerable in local wired links where capacity is often not an issue, but are excessive for wide area networks and wireless systems where bandwidth is scarce. By using this site, you agree to the Terms of Use and Privacy Policy. Views Read Edit View history. U, O, or R. Clear description of the referenced document: It uses the FCS algorithm with the following generator polynomial: It can typically also refresh parts of the context.

For exact formats of the packet types, see section 5. Other for any supplementary information: Relationship with other existing or emerging documents: Unsourced material may be challenged and removed. The mechanisms used are those described in 4. Upon reception of an ACK for an updating packet, the compressor knows that the decompressor has received the acknowledged packet and the transition to a higher compression state can be carried out immediately.


It may be extended by defining new compression profiles dedicated to specific protocol headers. The compressor normally obtains its confidence about decompressor status by sending several packets with the same information according to the lower compression state.

Data compression Internet Standards. The ROHC feedback scheme requires that a channel carries feedback to at most one compressor. The 3-bit CRC present in some header formats will eventually detect context damage reliably, since the probability of undetected context damage decreases exponentially with each new header processed. The transition to R-mode is achieved in the same way. Initially, all contexts are in no context state, i.

ROHC feedback format Feedback sent on a ROHC channel consists of one or more concatenated feedback elements, where each feedback element has the following format: Such state information can also be marked read-only in the negotiation, which would cause the decompressor to discard any IR packet attempting to modify it.

Comments on RFCs and corresponding changes are accommodated through the existing standardization process. Feedback is described in section 5. Decide whether decompression is allowed In Full Context state, decompression may be attempted regardless of what kind of packet is received. 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.