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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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.
Decompressor states and logic U-mode Below is ietr state machine for the decompressor in Unidirectional mode. In O-mode and R-mode, feedback is sent according to sections 5. This classification takes advantage of inter-packet redundancy. In other cases, segmentation should be done at lower layers. The decompressor moves to the No Context state. Several compression profiles are available, including the following:.
If the decompressor receives any of these packets, it will be in sync with the compressor. Feedback logic O-mode The feedback logic defines what feedback to send due to different events when operating in the various states. Actions upon CRC failure This section is written so that it is applicable to all modes.
Compression logic and packets used U-mode The compressor chooses the smallest possible packet format that can communicate the desired changes, uetf has the required number of bits for W-LSB encoded values.
RFC – The RObust Header Compression (ROHC) Framework
State transition logic The transition logic for ieetf states in Bidirectional Optimistic mode has much in common with the logic of the Unidirectional mode. Committed to connecting the world.
In order to handle potential decompression errors, the compressor sends periodic refreshes of the stream context to the decompressor.
If any of the three decompression attempts in d.
Details of the transitions between states and decompression logic are given subsequent to the figure. Current information, if any, about IPR issues: Note that this size includes the CRC.
Robust Header Compression
This step is not applicable to R-mode. State transition logic U-mode The transition logic for compression states in Unidirectional mode is based on three principles: This is the size of the largest reconstructed unit in octets that the decompressor is expected to reassemble from segments see 5. Repeated 30955 decompression will force the decompressor to transit downwards to a lower state. This document describes profiles 0x, 0x, 0x, and 0x; further profiles may be defined when ROHC is extended in the future.
When the compressor receives such a message, it MAY disable or increase the interval between periodic IR refreshes. RoHC has a direct impact on call set up performance.
ITU-T A.5 reference justification
The segmentation scheme should only be used for packet sizes that are larger than the maximum size in the allowed set of sizes from the lower layers. This can lead to an erroneous reference SN being used in W-LSB decoding, as the reference SN is updated for each successfully decompressed header of certain types.
ROHC feedback Feedback carries information from decompressor to compressor. A small CID with the value 0 is represented using zero bits. It is anticipated that feedback to the compressor can be realized in many ways, depending on the properties of the particular lower layer.
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. Views Read Edit View history. If the local repair attempt fails, it must move to a lower state to avoid.
The profile to be associated with the CID. 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.
Let an update event be when a sequence of UOR-2 headers are sent to communicate an irregularity in the packet stream. Optimistic approach, upwards transition Transition to a higher compression state in Unidirectional mode is carried out according to the optimistic approach principle.
ITU-T work programme
The packet type is able to carry variable-length feedback information. Such large overheads may rcf 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.
Its coverage is profile-dependent, but it MUST cover at least the initial part of the packet ending with the Profile field. Justification for the specific reference: When CRC checks fail only occasionally, assume residual errors in the current header and simply discard the packet.