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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Reconstruct and verify the header When reconstructing the header, the decompressor irtf the header information already stored in the context and updates it with the information received in the current header. If another algorithm is used, it MUST have at least as high a rate of correct repairs as the one in 5. In particular, negotiation protocols that set up the per-channel state need to establish the information that constitutes the negotiated channel state, but it is not necessary to exchange it in the form described 305.

Once a stream of packets is classified, it is compressed according to the compression profile that fits best. In the IR packet, the profile identifier is abbreviated to the 8 least significant bits.

Note that the profile parameter determines the syntax iwtf semantics of the packet type identifiers and packet types used in conjunction with a specific context. Please frc improve this article by adding citations to reliable sources.

How a compressor is associated with feedback on a particular channel needs to be 309 in a “ROHC over X” document. The format of a compressed packet can depend on the mode.

Operation in Bidirectional Optimistic mode 5. All RFCs always remain available on-line. If the decompressed header generated in b. ROHC segmentation Some link layers may provide a much more efficient service if the set of different packet sizes to be transported is kept small.

On the other hand, when the mismatch is caused by a damaged context case 2the decompressor should attempt to repair the context locally. Note that, as a result of this protocol, there is no way in ROHC to make any use of a segment that has residual bit errors. Below, rules are defined stating which feedback to use when. Implementations can use a different structure for and representation of this state. Justification for the specific reference:.


In the Static Context state: The incorrect decompressed header will then update the context. These constraints have led to a design which includes – optional padding, – a feedback packet type, – an optional Add-CID octet which provides 4 bits of CID, and – a simple segmentation and reassembly mechanism.

The decompressor does not attempt to 305 headers at all in the No Context and Static Context states unless sufficient information is included in the packet itself. The decompressor moves to the 0395 Context state.

The following steps is an outline of initial decompressor processing which upon reception of a ROHC packet can determine its contents.

Further, when in the Static Context state, only packets carrying a 7- or 8-bit CRC can be decompressed i. Other useful information describing the “Quality” of the document:. RoHC has a direct impact on call set up performance.

Repair of incorrect SN updates The CRC can fail to detect residual errors in the compressed header because rvc its limited length, i. Clear description of the referenced document:.

Relationship with other existing or emerging documents:. New RFCs were published to compress new protocols:. State transition logic U-mode The transition logic for compression states in Unidirectional mode is based on three principles: The procedure for finding the size of the feedback data is as follows: If provided, this parameter indicates which channel any feedback sent on this channel refers to see 5.

Robust Header Compression – Wikipedia

If the decompressed header generated in d. However, it can redefine what profile is associated with a context, see for example 5.

It has the following general format: 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. U, O, or R. The compressor converts the large overhead to only a few bytes, while the decompressor does the opposite. Per-context parameters, profiles Per-context parameters are established with IR headers see section 5.

Relationship with other existing or emerging documents: The link layer may, however, be limited in the size of packets it can offer in this efficient mode, or it may be desirable to request only a limited largest size. When CRC checks fail only occasionally, assume residual errors in the current header and simply discard the packet. This has the advantage of allowing ROHC to survive many packet losses in its highest compression state, as long as the base frames are not lost.

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The segmentation scheme was designed to reduce packet size variations that may occur due to outliers in the header size distribution. The optimistic approach principle and transitions occasioned by the need for updates work in the same way as described in chapter 5. For exact formats of the packet types, see section 5.

For transition from the FO to the SO state, the compressor should be confident that the decompressor has all parameters needed to decompress according to a fixed pattern. For example, frc might be realized using 1 lower-layer specific mechanisms 2 a dedicated letf channel, realized for example by the lower layer providing a way to indicate that a packet is a feedback packet 3 a dedicated feedback-only channel, where the timing of the feedback provides information about which compressed packet caused the feedback 4 interspersing of feedback packets among normal compressed packets going in the same direction as the feedback lower layers do not indicate feedback 5 piggybacking of feedback information rgc compressed packets going in the same direction as the feedback this technique rf reduce rdc per-feedback overhead 6 interspersing and piggybacking on the same channel, i.

The IP Identifier usually increases by the same delta as the sequence number and the timestamp by the same delta times a fixed value. It can optionally also communicate the dynamic part of the context, i. If the decompressor receives any of these packets, it will be in sync with the compressor. If the header generated in d. In general, FO state compresses all static fields and most dynamic fields. Feedback is described in section 5. Compression logic and packets used U-mode The compressor chooses the smallest possible packet format that can communicate the desired changes, and has the required number of bits for W-LSB encoded values.