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.

Author: Dajinn Nitilar
Country: Cameroon
Language: English (Spanish)
Genre: Education
Published (Last): 20 January 2007
Pages: 92
PDF File Size: 13.64 Mb
ePub File Size: 20.46 Mb
ISBN: 169-5-53727-471-4
Downloads: 12367
Price: Free* [*Free Regsitration Required]
Uploader: Faubar

The O-mode aims to rrc compression efficiency and aims for sparse usage of the feedback channel. In this state, the 8-bit ROHC header contains three fields:. 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.

Details of the transitions between states and decompression logic are given subsequent to the figure. Instead, the Optimistic mode makes use of feedback from decompressor to compressor for transitions in the backward direction and for OPTIONAL improved forward transition.

Redundant information is transmitted in the first packets only.

Arrival times of packets where decompression fails are discarded. 395 within the referenced RFC are listed under item 8. The reconstructed unit has the format: State transition logic The transition logic for compression states in Bidirectional Optimistic mode has much in common with the logic of the Unidirectional mode.

A type 0 packet carries a packet header compressed according to a fixed pattern, while type 1, 2 and IR-DYN packets are used when this pattern is broken. Segment Other packet types can be used at will by individual profiles. IR This packet type communicates the static part of the context, i. It has the following general format: If a reconstructed packet is produced, it is fed into step 1 above. 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.


ITU-T A.5 reference justification

Once a stream of packets is classified, it is compressed according to the compression profile that fits best. 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 ROHC feedback scheme requires that a channel carries feedback to at most one 33095. The same arguments for not having sequence numbers in the segments but instead providing a strong CRC in the reconstructed unit apply here as well.

Clear description of the referenced document:. 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.

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. If the first bit is 0, the CID uses one octet.

RFC – part 3 of 7

Indicates that the static context of the decompressor is not valid or has not been established. For such link layers, these sizes will normally be chosen to transport frequently occurring packets efficiently, with less frequently occurring packets possibly adapted to the next larger size by the addition of padding. Compression logic and packets used The compression logic is the same for the Bidirectional Optimistic mode as for the Unidirectional mode see section 5.


If defined by a “ROHC over X” document, per-channel negotiation can be used to pre-establish state information for a context e. Header either starts with a packet type indication or has a packet type indication immediately following an Add-CID Octet. When receiving an ACK Uthe compressor should reduce the frequency of IR packets since the static information has been correctly received, but it is not required to stop sending IR packets.

Data compression Internet Standards.

Feedback logic O-mode The feedback logic defines what feedback to send due to different events when operating in the various states. The decompressor maintains two decompressed sequence numbers: Unsourced material may rtc challenged and removed.

In the Unidirectional mode of operation, packets are only sent in one direction: Clear description of the referenced document: Note that this means that there can be no padding and no feedback in the reconstructed unit, and that the CID is derived from the initial octets of the reconstructed unit.

Robust Header Compression

They may then transition to O-mode if a usable return link is available, and the decompressor sends a positive acknowledgement, with O-mode rdc, to the compressor. Comments on RFCs and corresponding changes are accommodated through the existing standardization process. 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.