OSI and TCP/IP Layers

AvgITGeek

The OSI hasn't changed from the time I first picked up the ICND1 book years ago. It is still the same. The thing that I found odd is the TCP/IP model. Years ago it was Application, Transport, Internet and Network Access but now after watching a Bryant video and doing some research, it seems like it now morphed into Application, Transport, Network, Data Link and Physical. When did this happen? I know how they all line up with each other (new and old) but am curious what brought around the change?

Any thoughts?

kaiju

That is just an incorrect expansion of information since the OSI model split the original TCP/IP model Link layer into the Data Link and Physical layers.

I think the reason why some authors/publications are splitting the original TCP/IP Link layer into Data Link and Physical layers is to differentiate between bits and frames. And to make things a little more confusing, some authors/publications refer to TCP/IP layer 1 by different names:

Link Layer (RFC 1122) - 4 layer model

Network Interface Layer (Cisco) - 4 Layer model

Network Access (multiple authors/publications) - 4 layer model layer 1 and 5 layer model layer 2.

I think the best reference is RFC 1122 that describes the TCP/IP as 4 layers with Link, Internet, Transport and Application layers. And Cisco Academy also uses a 4 model layer.

 

AvgITGeek

Thank you for the RFCs!

I completely agree that the top 3 are combined into Application. Transport and Network are cool as there you have segments and packets but the final one is where I'm conflicted. I'll read the rfcs but for the purpose of the exam just knowing that the bottom are kind of physical as you have the MAC address and the bits being transferred.

Going deeper into objectives never hurt anyone.