Queueing Modelling Fundamentals || Flow and Congestion Control

✍ Scribed by Ng, Chee-Hock; Soong, Boon-Hee

• Publisher: John Wiley & Sons, Ltd
• Year: 2008
• Tongue: English
• Weight: 154 KB
• Edition: 2
• Category: Article
• ISBN: 0470519576
• DOI: 10.1002/9780470994672.ch9

✦ Synopsis

Flow and Congestion Control

Today, we often experience congestion in modern cities, in terms of long queues of cars, buses and people waiting for services. Congestion is usually caused by unpredictable events. Although the daily rush hour is semi-predictable, congestion can also be random due to breakdowns and accidents that cause delays and long queues stretching for long distances. Therefore, a control mechanism might be implemented, such as using traffi c lights to delay access to a junction or by restricting access to crowded areas in central business districts through tolls and congestion charges.

In general, the communication network is similar to our everyday experiences and consists of fi nite resources, such as bandwidth, buffer capacity for packets and transmission capacity that depend on traffi c control mechanisms to alleviate congestion problems.

There are specifi c requirement guarantees, referred to as Quality of Service (QoS), specifi ed for each traffi c fl ow. When the offered traffi c load from the user to the network exceeds the design limit and the required network resources, congestion will often occur. In this section, we introduce several specifi c examples, where queueing theory has been successfully applied to study the behaviour of the network under these extreme conditions. We describe key parameters of performances, i.e. throughput g and time delay E [T]. It is important to examine the basic functioning of the network, as shown in Figure .1.