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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Indicates that the dynamic context of the decompressor is out of sync. This section describes some of this state information in an abstract way. It is interpreted according to the profile indicated in the Profile field. The Bidirectional Optimistic mode is similar to the Unidirectional mode, except that a feedback channel is used to send error recovery requests and optionally acknowledgments of significant context updates from the decompressor to compressor.
ITU-T work programme
Ietr states and logic U-mode Below is the state machine for the decompressor in Unidirectional mode. Decompression logic, timer-based timestamp decompression In 33095 mode or if there is some other way for the compressor to obtain the decompressor’s clock resolution and the link’s jittertimer-based timestamp decompression may be used to improve compression efficiency when RTP Timestamp values are proportional to wall-clock time.
New RFCs were published to compress new protocols:. Acknowledges successful decompression of a packet, which means that the context is up-to-date with a high probability. SO state is compressing all dynamic fields predictively using a sequence number and checksum. Header either starts with a packet type indication or has a packet type indication immediately following an Add-CID Octet. Repair of incorrect SN updates The CRC can fail to detect residual errors in the compressed header because of its limited length, i.
Other for any supplementary information:.
State transition logic The transition logic for compression states in Bidirectional Optimistic mode has much in common with the logic of the Unidirectional mode. Segment Other packet types can be used at will by individual profiles. The following principal kinds of feedback are supported. 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 309 processed.
If any of the three decompression attempts in d. This document describes profiles 0x, 0x, 0x, and 0x; ffc profiles may be defined when ROHC is extended in the future. 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.
Nonupdating values can be provided for other fields using an extension UOID. Its coverage is profile-dependent, but it MUST cover ietff least the initial part of the packet rfd with the Profile field. Segmentation usage considerations The segmentation protocol defined in ROHC is not particularly efficient. A compression profile defines the way to compress the different fields in the network headers.
In the Full Context state: The number of consecutive packets to send for confidence is not defined in this document.
If the decompressed header generated in b. Comments on RFCs and corresponding changes are accommodated through the existing standardization process. If the header generated in b. For better performance, the packets are classified into streams before being compressed.
Robust Header Compression
Committed to connecting the world. Note that case 3 does not occur in R-mode. In the IR packet, the profile identifier is abbreviated to the 8 least tfc bits.
The segmentation scheme was designed to reduce packet size variations that may occur due to outliers in the header size distribution. U, O, or R. Views Read Edit View history.
Robust Header Compression – Wikipedia
The decompressor might be able to detect this situation and avoid context damage by using a local clock. The following algorithm MAY be used: Relationship with other existing or emerging documents:.
If a reconstructed packet is not produced, this finishes the processing of the original packet. This is the size of the largest reconstructed unit in octets that the decompressor is expected to reassemble from segments see 5. Other for any supplementary information: It has the following general format. If decompression of the third packet using the new context also succeeds, the context repair is deemed successful and this and subsequent decompressed packets are delivered to the upper layers.
First, attempt to determine whether SN LSB wraparound case 3 is likely, and if so, attempt a correction. However, in Optimistic mode there are no timeouts. Any information which initializes the context of the decompressor should be protected by the CRC. The details of each state, state transitions, and compression logic are 30955 subsequent to the figure.