Cisco Wide Area Virtualization Engine 274 Troubleshooting Guide download pdf (Page 26)

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Cisco Wide Area Application Services Configuration Guide

OL-26579-01

Chapter 1 Introduction to Cisco WAAS

Overview of the WAAS Interfaces

BIC TCP

Binary Increase Congestion (BIC) TCP is a congestion management protocol that allows your network

to recover more quickly from packet loss events.

When your network experiences a packet loss event, BIC TCP reduces the receiver’s window size and

sets that reduced size as the new value for the minimum window. BIC TCP then sets the maximum

window size value to the size of the window just before the packet loss event occurred. Because packet

loss occurred at the maximum window size, the network can transfer traffic without dropping packets

whose size falls within the minimum and maximum window size values.

If BIC TCP does not register a packet loss event at the updated maximum window size, that window size

becomes the new minimum. If a packet loss event does occur, that window size becomes the new

maximum. This process continues until BIC TCP determines the new optimum minimum and maximum

window size values.

Compression

Cisco WAAS uses the following compression technologies to help reduce the size of data transmitted

over your WAN:

• Data Redundancy Elimination (DRE)

• LZ compression

These compression technologies reduce the size of transmitted data by removing redundant information

before sending the shortened data stream over the WAN. By reducing the amount of transferred data,

WAAS compression can reduce network utilization and application response times.

When a WAE uses compression to optimize TCP traffic, it replaces repeated data in the stream with a

much shorter reference, then sends the shortened data stream out across the WAN. The receiving WAE

uses its local redundancy library to reconstruct the data stream before passing it along to the destination

client or server.

The WAAS compression scheme is based on a shared cache architecture where each WAE involved in

compression and decompression shares the same redundancy library. When the cache that stores the

redundancy library on a WAE becomes full, WAAS uses a FIFO algorithm (first in, first out) to discard

old data and make room for new.

LZ compression operates on smaller data streams and keeps limited compression history. DRE operates

on significantly larger streams (typically tens to hundreds of bytes or more) and maintains a much larger

compression history. Large chunks of redundant data is common in file system operations when files are

incrementally changed from one version to another or when certain elements are common to many files,

such as file headers and logos.

Application-Specific Acceleration

In addition to the TCP optimization features that speed the flow of traffic over a WAN, Cisco WAAS

includes these application acceleration features:

• Operation prediction and batching—Allows a WAAS device to transform a command sequence into

a shorter sequence over the WAN to reduce roundtrips.

• Intelligent message suppression—Decreases the response time of remote applications. Even though

TFO optimizes traffic over a WAN, protocol messages between branch office clients and remote

servers can still cause slow application response time. To resolve this issue, each WAAS device

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