how many layers on TCP/IP

tcp/ip have 4 layers or 5 ? mcgraw hill book says 5 ? I am confused

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TCP/IP layer contains only 4 layers which are (from Top to Down):

Application Layer
Transport Layer
Internet Layer
Network Access Layer

Best wishes

lwwarner

eng has given you the "According to the Gospel of Cisco" answer above. However, non-Cisco authors, including those who were actually involved in the early days of the TCP/IP Internet development such as Doug Comer[1], often include the Physical or Hardware layer and present a 5-layer[2] model:

Application Transport Internet Network Interface Physical Hence, the 4/5 layer discrepancy. For a decidedly non-Cisco perspective on the OSI model, check out Comer's essay:
The True Story Of Network Layering And The Origin Of The OSI Model

I still get a chuckle whenever I read that.

Let's face it, we live in a TCP/IP world. TCP/IP won and OSI lost. Does anyone remember CLNP or TP4?? Yet Cisco (and others) still clings religously to the OSI model.

Disclaimer: Prof. Comer was my teacher and research advisor long before I entered the Wonderful World of Cisco, so I may be ever so slightly biased.

[1]http://www.cs.purdue.edu/people/faculty/dec/

[2]http://www.netbook.cs.purdue.edu/othrpags/qanda68.htm