Delay, Loss, and Throughput in Packet-Switched Networks

Delay, Loss, and Throughput in Packet-Switched Networks

Back in "What is the Internet", we described that the Internet can be viewed as an infrastructure that gives services to allocated applications running on end systems. Preferably, we would like Internet services to be able to move as much data as we want between any two end systems, immediately, without any data loss. Unfortunately, this is a lofty goal, one that is unattainable in fact. Instead, computer networks essentially constrain throughput  (the amount of data per second that can be transferred) between end systems, introduce delays between end systems, and can in fact lose packets. On one hand, it is unfortunate that the physical laws of reality introduce delay and loss as well as constrain throughput. On the other hand, because computer networks have these problems, there are many fascinating issues surrounding how to deal with the problems - more than enough issues to fill a course on computer networking and to stimulate hundreds of PhD theses! In this section, we'll begin to study and quantify delay, loss, and throughput in computer networks.

Overview of Delay in Packet-Switched Networks

Recall that a packet starts in a host (the source), passes through a series of routers, and ends its journey in another host (the destination). As a packet travels from one node (host or router) to the succeeding node (host or router) along this path. The packet suffers from several types of delays at each node along the path. The most important of these delays are the nodal processing delay, queuing delay, transmission delay, and propagation delay; together, these delays build up to give a total nodal delay. In order to obtain a deep understanding of packet switching and computer networks, we must understand the nature and importance of these delays.

The nodal dalay at router A


throughput, host, packet switching

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