Priority Queueing

Distributed Denial of service (DDoS) attacks affect millions of users and businesses across the globe every year. With the ever-increasing sophistication and complexity of these attacks services and resources are at the mercy of the attacker, with very little in the way of prevention against these kinds of attacks. Voice over internet protocol (VoIP) and Video Conferencing are most affected by these attacks because they rely on real-time packet delivery whereas applications such as Web browsing can be resent. For the client to be satisfied by application performance, Quality of Service (QoS) needs to be measured. This is usually defined in a service level agreement and is the overall quality of an application. For instance, if the QoS of VoIP is not maintained, then the call quality is severely degraded, and thus the call session is lost.

The future broadband ISDN needs a high degree of flexibility in order to cope with a great variety of services with widely differing bandwidth and quality of service requirements. The asynchronous transfer mode (ATM), which is now widely accepted as the basis for this network [2], offers very flexible information transfer with respect to bandwidth requirements. The introduction of a special class of priorities, called space priorities, adds a quality of service flexibility to the ATM bearer service. This paper describes various space priority mechanisms and their detailed performance evaluation. Furthermore, a comparative performance study is given, indicating the excellent performance characteristics of a simple buffer management scheme called partial buffer sharing.

In order to accomodate different services, Broadband ISDN networks may have to offer several bearer services. A single server queue modelling the output buffers of ATM switches is presented. 2 buffer management schemes which respectively realize time and loss priority are implemented: non-preemptive Head Of the Line (time) and Pushout (loss). Loss probabilities and delay characteristics are studied for a wide range of parameter values. Pros and cons of simultaneously offering both kind of priorities are pointed out. Examples of applications are given.