Enterasys Networks CSX7000 Manuel d'utilisateur télécharger pdf (Page 412)

USER’S GUIDE

412 CyberSWITCH

COMPRESSION OPTIONS BACKGROUND INFORMATION

The system data compression capability allows the system to negotiate compression algorithms

with a remote device. This compression can be done using some proprietary bridging protocols and

also the PPP CCP protocol.

After successfully negotiating compression, data is compressed by a peer and transmitted to the

system. The system decompresses the data, processes the addressing information contained in the

device data, and transmits the data as required. The converse is also true, the system can receive

data coming from a WAN or LAN, compresses the data before transmitting it to a peer. The net

effect is to increase effective interconnect bandwidth by decreasing transmission time. If

negotiation for compression fails, data is transmitted uncompressed.

The compression algorithm implemented is STAC-LZS. This algorithm is used in all of STAC’s data

compression products. This software version is fully compatible with STAC’s data compression

compressor chips including the multi-tasking features. STAC-LZS data compression is performed

by replacing redundant strings in a data stream with shorter tokens. The STAC-LZS uses a

compression history, or sliding window, as opposed to a structured dictionary. This allows greater

flexibility and a greater number of possible string comparisons during compression process. The

compression history automatically discards old information as new information is processed. Both

the device and system must perform compression using the STAC-LZS data compression

algorithm. The peer and remote compression algorithms must be synchronized, this is

accomplished by negotiating compression at channel connect time. Once this has been

accomplished compressed data can be transmitted. If a transmission problem should ever occur the

problem is detected and compression re-synchronized by the execution of a pre-defined protocol.

OMPRESSION AND CCP

The Compression Control Protocol (CCP) is one of a suite of protocols which operate under the

umbrella of the IETF’s Point-to-Point Protocol (PPP) suite. CCP implementation permits

compression and decompression on PPP links.

During call establishment, an appropriately configured system will attempt to negotiate

compression using CCP and STAC-LZS. The system will support either of two STAC-LZS modes,

sequence numbers or extended mode. This negotiation will take place on all calls. Specific options

used by CCP include:

• STAC-LZS compression algorithm

• one history

• sequence number check mode or extended mode

During CCP negotiations, the system will always propose the use of Sequence Number check mode

first for inbound traffic. The peer has the option to accept or reject this proposal. If the peer rejects

the proposal and counter-proposes STAC-LZS Extended mode, it will be accepted by the system.

For outbound traffic, the system will accept either Sequence Number or Extended Mode.

Once compression has been negotiated, transfers of compressed data can take place across the

Point-to-Point links. Such compressed data packets will be encapsulated as described in the CCP

specification. Received data packets not so encapsulated will be considered to be uncompressed

data and will be forwarded on in the order they were received. Transmitted packets whose

compressed size increases to the point of exceeding the link’s Maximum Receive Unit (MRU) will

be sent uncompressed.

1 2 ... 407 408 409 410 411 412 413 414 415 416 417 ... 728 729

Commentaires sur ces manuels

Pas de commentaire

Enterasys Networks CSX7000 Manuel d'utilisateur Page 412

Commentaires sur ces manuels