The 4-Layer TCP/IP Network Model

By Dan DiNicolo, August 26th, 2005 Posted in CCNA Study Guide Chapter 01. Subscribe to our RSS Feed

The Department of Defence TCP/IP model is a 4-layer model that defines areas of responsibility much like the OSI, while providing insight into the functions of the different protocols that make up the TCP/IP suite. The model provides an excellent point of reference when compared to the OSI. We won’t look at all the details of the TCP/IP model just yet – the majority will be covered in Chapter 4. My feeling is that the data encapsulation process is much better explained using a popular protocol suite.

To begin, let’s take a look at how the TCP/IP model maps to the OSI model. While the names of the TCP/IP layers are different, they generally encompass the same responsibilities as one or more OSI layers. Consider the diagram below.

Figure: Comparing the OSI and TCP/IP network models.

Tip: Although the layers of the TCP/IP model technically use different names, Cisco will still refer to protocols by their associated OSI layer name. For example, Cisco will describe TCP as being a Transport layer protocol.

For the sake of illustration, I’ve included some of the key protocols that make up the TCP/IP suite in the figure below. Be aware that the terms data, segment, packet, and frame still apply as data is encapsulated in the TCP/IP model.

Figure: TCP/IP protocol stack including common protocols and network technologies.

Written by Dan DiNicolo - Visit Website

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