Monday, 2 June 2014

WAAS Optimiation

As you have always seen many application works very well when any one tries to access it from the LAN , but the same will respond slow when someone tries to access it over the WAN.
In this section we will see how WAAS helps to reduce the above issue and give the user the same feel as he/she is accessing it from the LAN .

WAAS have some optimization technique which it puts for each and every TCP session.

Transport flow optimization (TFO)

There are barrier when data is carried by TCP over the WAN , you can think of TCP optimization with WAAS as a enabled proxy which shields communicating nodes from performance limiting WAN conditions(such as packet loss , latency etc), thereby increasing throughput.
TFO enable the nodes to make use of WAN bandwidth more effectively and minimize the impact of TCP retransmissions.

TFO provides following optimizations:-
1)Large initial window- We all know TCP grows from a slow start and then it goes to congestion avoidance phase , what if we reduce the slow start phase , yes we will mitigate the latency associated with initial connection setup , this is what TFO is : it increases the initial congestion window , which helps the connection to identify the bandwidth ceiling at a early stage and let the connection to enter into congestion avoidance phase rapidly.

2)Selective Acknowledgement -  Before RFC 2018 there was no proper scheme like SAck , which in simple words is : if a block of data is lost or unacknowledged then the transmitting  node will get to know  and have to retransmit that block of data only . This will tremendously reduce the bandwidth consumption upon retransmission of lost segment .

3)Windows Scaling - Found in RFC 1323 , allows communicating nodes to have large window , which enable large amount of data to unack in the network at any time , which allows end nodes to better utilize the available bandwidth . 

4)Large Buffers - The key point of this is to keep the WAN bandwidth with full of data , large TCP buffers on WAE allow to accomplish this. Also WAAS provide adaptive buffer allocation depending upon connection as compare to tedious static buffer allocation which results in inefficient memory allocation.

5)Advanced congestion handling- Through intelligent handling of TCP message congestion scenarios, Cisco WAAS can more efficiently retransmit lost data when necessary and return to higher levels of throughput on the network much more quickly, resulting in better application performance .

Data redundancy elimination (DRE)

What if there could be a mechanism which can see the bytes flying on the WAN and could generate some pattern for that ,and when the same byte have to fly will send the generated pattern only (which is very small in size as compare to those bytes) for that, which on the receiving end regenerate the same bytes which need to be fly ...This is amazing yes this is what DRE is....

Lempel-Ziv (LZ) compression

LZ compression is a standards-based compression that can be applied to further reduce the amount of bandwidth consumed by a TCP flow. LZ compression can be used in conjunction with DRE or independently. LZ compression can provide from 2:1 to 4:1 compression, depending on the application being used and the data being transmitted. This feature is especially helpful for data that has not been previously seen and suppressed by DRE because the pattern identifiers are highly compressible.


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