Session layer in OSI and TCP/IP

[Naruto Uzumaki]

Hello!
I've certain questions regarding how session layer functionalities are implemented in OSI and TCP/IP. I know that there's no session layer in TCP/IP. I just want to focus on its functionalities.

According to OSI model session layer provides connection establishment, management and termination. So does this mean that in OSI TCP 3-way handshake and graceful connection termination is initiated by session layer and the transport layer is concerned with data transfer and reliability of communication only?
But in TCP/IP the connection establishment and termination along with reliability are part of the transport layer and no session layer is used. Is this statement correct?

Eg.- I want to browse a website.
a) So according to OSI, firstly I resolve domain name using the DNS in application layer, then my web browser asks the session layer to initiate a session. Session layer asks the transport layer to make suitable TCP packets to perform a 3 way handshake. Then HTTP packets are transported using the transport layer.

b) According to TCP/IP, firstly I resolve domain name using DNS in application layer. Then my application layer requests the transport layer to connect to a webserver on port 80. Transport layer makes a TCP 3-way handshake. After connection establishment HTTP packets are transported using transport layer.

[PrntRhd]

The OSI model explains how the TCP/IP protocol works but the model is not the actual code of the instruction set that makes it work.
Some say there are 4 actual working layers instead of 7 layers and some merge the data link layer functions into the adjacent layers.
It really doesn't matter how many layers are listed as long as the data transfer works, but the "book answer" is always 7 layers for certification testing purposes.

[yawningdog]

This looks familiar.

There are at least two networking models you're going to run into if you're serious about your IT career. The one that you're going to be forced to learn is the OSI model. It was written for the OSI protocol stack which is almost never used or seen. There is another model written for the TCP/IP stack, and it works a lot better for the question you are asking.

So why do we spend so much time learning the OSI model when we are using the TCP/IP protocol? Beats me. Makes not a bit of sense. But that's how we roll and that's what you're going to be using.

In the TCP/IP model, there is no session layer. The session protocols are rolled into the data link layer, as you appear to have noticed. Sometimes in the TCP/IP model there is no session layer at all, as in UDP which is sessionless. (Which technically would be UDP/IP I suppose, but if you ever use that in conversation people are going to think you're weird. Trust me on this.) Novell's IPX is also a session oriented 4th layer. ICMP is not, since it's purpose is to check network integrity to begin with.

As if that's not confusing enough, there are some session-like characteristics in some of the layer 2 protocols like frame relay and ATM. They use what's called a Data Link Connection Identifier (DLCI). So you can see that the OSI model is good for a thorough understanding of network theory, but there are few hard and fast rules and you must learn to be flexible with it.