 from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Traffic Engineering for Voice and Data Capacity and Quality Principles Traffic Engineering for Packet Data When we move from circuit-switched to packet traffic engineering, we move our analy- sis from the status of a call to the status of a packet. A circuit-switched link sends all its content (analog or digital) on the same route to the same destination. Once the circuit-switched link is established, traffic engineering has no connection to the qual- ity of the link. Packets are separate entities that can go separate ways to the same des- tination. This allows packet data transport to use resources far more efficiently at the expense of bringing more complex issues into the design stage of a packet pipe. The quality-of-service (QoS) issues of a data link are latency, jitter, and loss, as de- scribed in Sec. 17.3. As a congested link increases packet delay, there is a direct con- nection between the size of a packet pipe and the QoS of each packet connection using that pipe. Packet switches use store-and-forward technology to manage data traffic, es- sentially lining the packets up in a queue for transport, so our packet traffic engineer- ing model is a mathematical queuing model. We will examine the M/M/1 queue, a sim- ple queuing model that fits pretty well to packet-switch behavior. If a packet data service has any kind of delay requirement, then there is some delay beyond which a packet is too late to be useful. After we have described the M/M/1 queue, we will show its distribution of delay probabilities and how that can be used for traffic engineering a packet data link. 23.3.1 Queuing theory The physical picture of a queue has some kind of service being provided to people who arrive to be served. If there are no servers available when a person shows up for ser- vice, then that person waits in some 