CHAPTER 2 - The Open Systems Interconnect Model

Abstract

This chapter focuses on the Open Systems Interconnect (OSI) model and provides an overview of Transmission Control Protocol/Internet Protocol (TCP/IP). The OSI model is broken down using more layers than other protocols such as TCP/IP or Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX). The OSI model has more layers, which allows for a better definition of what should happen at each level. Each of the protocol stacks has some similarities in each of the layers. Some protocol stacks have layers that are combined differently than others, but overall, they can be mapped back to the OSI model. The TCP/IP protocol suite provides the purpose of allowing one networked system to talk to another. Each layer in the stack receives help from the layer below it and provides help to the layer above it. The Internet layer would receive the segment from the transport layer and then place a header onto it to include the source, and destination IP address along with source, and destination port numbers. The application layer protocols of the TCP/IP protocol suite operate at the session, presentation, and application layers of the OSI model. In the Department of Defense (DoD) model, this layer enables applications to communicate with one another, and it provides access to the services of the other underlying layers.