Session Layer vs. Transport Layer

bmunroe

Alright, I have another OSI model question. The Sybex book I'm reading states;

The Session layer is responsible for setting up, managing, and then tearing down sessions...

The Tranport layer... can establish a logical connection between the sending host and destination host on an internetwork.

These two things sound like the same thing to me. Both layer 5 and layer 4 can set up sessions/connections. What's the difference? Please help me distinguish between them. Thanks!

Pash

bmunroe wrote:

Alright, I have another OSI model question. The Sybex book I'm reading states;

The Session layer is responsible for setting up, managing, and then tearing down sessions...

The Tranport layer... can establish a logical connection between the sending host and destination host on an internetwork.

These two things sound like the same thing to me. Both layer 5 and layer 4 can set up sessions/connections. What's the difference? Please help me distinguish between them. Thanks!

Hi bmunroe,

The two layers in essence are very different. The session layer is used rarely but for technology standards that require precision in synchronization of data, it is important. For example, video conference systems, scientific and research data streaming. The session layer doesnt care about delivery of data or connection, only creating a start stop and maybe pauses in the middle depending on the requirements.

The Transport Layer is fundamentally the most important thing you will learn about in networking. It is responsible for the end to end delivery of data NOT the route taken. TCP is a 3-way handshake connection based protocol. UDP is connectionless and doesnt care much for reliability. Remember that not all Transport Protocols rely on a connection to deliver data end to end.

Also it acts as the bridge from the lower layers to your high layers. For example using the netstat command from a cmd prompt on a windows machine gives us something like this (play about with the flags):-

TCP 127.0.0.1:80 listening - PID xxx

This tells us that our localhost machine is listening on TCP port 80 (typically used for http traffic). Now it also tells us the process/service that is listening on that port. You can then use the tasklist command from a cmd prompt on a windows machine to match the Process ID with the port it is listening on. In this example you might have apache web server or IIS installed, listening on that port to service website user requests as they come in.

HTH.

Cheers,