Frames, Packets, and Sessions


Frames , Packets, and Sessions

Throughout this book, we will talk about frames, packets, and sessions. In a very basic way, a frame is what is used to communicate at Layer 2 and holds the MAC address and protocol type information, among others. Packets are traditionally used for layer 3 communications and have the source and destination IP address within the header. A packet is inserted into a frame for communication across a network. A session is made up of a series of packets transporting user requests to a server. Today, most traffic sent across content switches is HTTP. Each object retrieved for a Web page or similar is seen as a single TCP session. When a user requests a page, some having up to 80 or more objects, a session needs to be set up for each object. All of these sessions are "collated" and referred to as a user session.

Determining switch performance, however, relies on session setup. The quicker we can set up a session and tear it down, the quicker we can complete the user session and ultimately display the content requested . Having a low session setup rate can impact the performance of a network and severely delay user response times. Some content switch manufacturers promote simultaneous session support as the key area in order to mask their inefficiencies in the session setup arena.

Lets look at an example. In Table 4-1, we can see that while content switch manufacturer A only supports 500,000 simultaneous sessions, it can set up and tear down 300,000 per second. Content switch manufacturer B can support 2,000,000 simultaneous sessions, but can only set up 10,000 per second.

Table 4-1. Session Per Second vs. Simultaneous Sessions
 

M ANUFACTURER A

M ANUFACTURER B

Maximum simultaneous sessions supported

500,000

2,000,000

Maximum sessions setups per second

300,000

10,000

Time taken to setup 300,000 sessions

1 second

30 seconds

As you can see, the ability to set up and tear down sessions is far more important than maximum simultaneous sessions.



Optimizing Network Performance with Content Switching
Optimizing Network Performance with Content Switching: Server, Firewall and Cache Load Balancing
ISBN: 0131014684
EAN: 2147483647
Year: 2003
Pages: 85

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net