WAAS Overview

WAAS WAEs are deployed at the edge/field sales offices and core sites at the network entry and exit points. A single WAE is deployed in the field sales office, while more than one WAE is deployed in the core sites for redundancy. WAAS provides transparent optimizations by requiring two WAEs to be in the path of a TCP connection to be optimized. The two WAEs participating at both ends of the network are auto discovered during the TCP three way hand shake, all WAEs sitting in between the paths of the two WAEs will put the TCP session flow in pass through. The auto discovery is performed for each TCP session; any TCP session that is in progress is put in pass through and not optimized.
For management and monitoring of the WAAS enterprise, WAEs must also be deployed to host the Central Manager application, which is made redundant by using two WAEs.
WAAS edge and core WAEs relies on network interception and redirection to receive the TCP packets that should be optimized. WCCPv2 is used in the Cisco enterprise to support the interception and redirection of the TCP traffic flows by the router to the WAEs. WCCP redirect lists/ACLs are used on the routers to control the IP subnets and traffic that should be intercepted and redirected to the WAEs. When the packets get redirected to the WAE, the WAE will apply the appropriate optimization based on the application policies.
Cisco WAAS uses a variety of transport flow optimization (TFO) features to optimize TCP traffic intercepted by the WAAS devices. TFO protects communicating clients and servers from negative WAN conditions, such as bandwidth constraints, packet loss, congestion, and retransmission. TFO includes the following optimization features:
• Compression Using DRE & LZ techniques
• Windows Scaling
• TCP Initial Window Size Maximization
• Increased Buffering
• Selective Acknowledgment
• Binary Increase Congestion (BIC) TCP