Chapter 3, Review Question #5

[army]

Hi all


CCNA Exam 640-802

I'm up to:
- Chapter 3
- Review Question 5



From the book:

============

Question:

Which of the following are layers in the TCP/IP model?
A. Application
B. Session
C. Transport
D. Internet
E. Datalink
F. Physical

Answer:
A, C, D

"... First, the Session layer is not in the TCP/IP model; neither are the Data Link and Physical layers. This leaves us with the Transport layer (Host-to-Host in the DoD model), Internet layer (Network layer in the OSI), and Application layer (Application/Process in the DoD)"


============


TCIP/IP model = DoD model.

DoD model:
Process Application Layer
Host-to-Host Layer
Internet Layer
Network Access Layer


So basically the answer is
A. Application (Agreed, this is listed above)
C. Transport (Don't understand, this is not listed as a layer in DoD, BUT it is part of the Host-to-Host model in DoD)
D. Internet (Agreed, this is listed above)


What I don't understand is
- "First, the Session layer is not in the TCP/IP model; neither are the Data Link and Physical layers."


But the answer to the question (option C) includes the Transport layer (which is what is used in OSI model not DoD model)


Could somebody care to explain what I'm missing?


Many thanks :)

[ciscodaze]

Depending on the book you are reading, the TCP/IP model calls it Transport or Host to Host...almost all the books I have call it Transport.

Saying that the Session, Data link, and Physical layers are not in the TCP/IP model does not mean the technology is not there...obviously you need a physical layer. Just think of the DOD model as a compressed OSI model.

Some people, (such as the author who just came out with Core Network Protocols, published by O'Reilly) break the DOD Network Access layer in two parts...Data link and Physical, just like the OSI model.

But for the exam, just do what Todd tells you :)

[lammle]

The DoD created the Internet Protocol stack (TCP/IP is slang for IP Stack).
This was a decade before the OSI model was created.

However, the seven layers of the OSI match up well with the four layers of the DoD model. The OSI just broke the layers into smaller sections, which made sense since we were using many, many different protocols and the DoD model was created to use the IP stack only.

The Host to Host layer of the DoD model provides the same functionalilty as the Transport layer of the OSI model, so Cisco uses those terms interchangabily. Same as with the Network layer of the OSI and the Internet layer of the DoD.

With that said, I do not make this stuff up. I write the questions based on the objectives of the CCNA and Cisco can use either term to refer to the functions of a layer. Transport = Host to Host, Network = Internet. Why? Because do you use any other protocols besides IP today? no.

Todd Lammle