1 / 9

SCRIBE - SCalable, Robust, EffIcient Dictionary-Based ComprEssion

SCRIBE - SCalable, Robust, EffIcient Dictionary-Based ComprEssion. March 23, 2001 Zhigang Liu, Khiem Le, Kacheong Leung, Chris Clanton Nokia Research Center Dallas. Highlights.

fidelia-ortiz
Download Presentation

SCRIBE - SCalable, Robust, EffIcient Dictionary-Based ComprEssion

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SCRIBE - SCalable, Robust, EffIcient Dictionary-Based ComprEssion March 23, 2001 Zhigang Liu, Khiem Le, Kacheong Leung, Chris Clanton Nokia Research Center Dallas

  2. Highlights • Scheme to use Dictionary-Based Compression Algorithms when transport between compressor and decompressor is unreliable (errors, losses) • Scalable: Adapt to memory size limitation • Robust: Maintain correctness • Errors • Losses • Efficient • High compression efficiency • Applicable to compression of text-based protocols, in particular SIP • Applicable to cellular environments • Draft at http://38.197.106.103/draft-liu-rohc-scribe-00.txt

  3. Main Concepts of SCRIBE • Cross-Session Dictionary • Checkpoint • Profile-Specific Dictionary • Content Deletion • Sliding Handshake

  4. Cross-Session Dictionary • Dictionary built up in previous sessions is used to jumpstart the compression/decompression of subsequent sessions • Use of cross-session dictionary leads to higher compression of initial messages • Higher compression of initial messages • helps overcome the call set up latency problem • contributes more heavily to the overall compression ratio, when the initial messages are large (especially true for SIP)

  5. Checkpoint • Checkpoint Dictionary • A well defined dictionary snapshot stored by compressor and decompressor • Integrity from strong CRC calculated over the dictionary • Can be referred to by a version number • Checkpoint Establishment • Version number assigned • Strong CRC check • Handshake • Rollback • Rollback to an established checkpoint • Triggered by e.g. detection of dictionary incoherency

  6. Dictionary Download • Done only when needed, e.g. mobile terminal roams to new area • Normally, last established checkpoint is downloaded • Download done at registration time or at beginning of session • Mechanisms similar to those existing in cellular systems • If scheme used in cellular systems, SCRIBE download can be piggybacked on existing download mechanisms

  7. Profile-Specific Dictionary • Dictionary consists of 3 parts • Static: Populated from knowledge of the protocol, protocol-specific, but common to all users; e.g. "From", "To" • Profile-Specific: Populated from knowledge of the user/device profile; specific to user or class of user; e.g. SIP URL, device capabilities • Dynamic: Populated from observation of messages exchanged • Static and profile-specific parts can be pre-populated

  8. Content Deletion • When memory limit is reached, no new item can be added unless some content is deleted • Mobile devices tend to have more memory limitations • When the dictionary is maintained across sessions, memory limit will be eventually reached, even for high-end devices • Common algorithm to select the content to be deleted ---> Implicit agreement, no extra signaling messages are needed • One simple algorithm is to select the oldest part of the dictionary

  9. Sliding Handshake • Used to • update dictionary during session • establish checkpoint • Cumulative and selective acks

More Related