lec26 - ECE 333: Introduction to Communication Networks...

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1 ECE 333: Introduction to Communication Networks Fall 2002 Lecture 26: Transport layer I 2 Transport Layer In the remaining lectures, we will discuss several issues that are commonly addressed at the transport layer in a network. We will consider several general transport layer issues, and, as a specific example, we will use the transport layer in the Internet. The Internet has two primary transport layer protocols – TCP and UDP – both of these will be discussed. In the Internet architecture, the transport layer sits between the application layer and the network layer. For this reason, it is the most visible layer to application designers. The service of the transport layer is to provide a virtual end-to-end “message-pipe” for applications. In other words, two applications on different hosts can communicate messages to each other as if they are directly connected – the details of the underlying network are hidden.
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3 Transport Layer The transport layer is an end-to-end layer – this means that nodes within the subnet do not participate in transport layer protocols – only the end hosts. As with other layers, transport layer protocols send data as a sequence of packets. In TCP/IP these packets are called segments . 1 Application Transport Internet Host-to- network Internet Host-to- network Internet Host-to- network Application Transport Internet Host-to- network 1 Actually only TCP packets are called segments and UDP packets are referred to as datagrams – but we will use segments to refer to either of these. 4 Transport layer issues Two main issues addressed at the transport layer are Multiplexing Improving the service offered by network layer
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5 Multiplexing The network layer provides communication between two hosts. The transport layer provides communication between two processes running on different hosts. A process is an instance of a program that is running on a host. There may be multiple processes communicating between two hosts – for example,
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lec26 - ECE 333: Introduction to Communication Networks...

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