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• Evaluates the end-to-end packet or volume transfer delay performance for a traffic relation (i.e. a flow identified by the source and destination IP address and by the service class if differentiated service is used) that crosses multiple domains in a Differentiated Services context.
• The delay calculation is totally analytical and based on queuing models for the links and composition of delays experienced on each crossed link.
• The advantage of the analytical approach is to be able to evaluate in near real-time the delay performance. Some suggested application in the InterMON context are:
• rapid comparison (on the base of the delay metric) of alternative routes for the same flow.
• what-if analysis: change in traffic, topology, routing policies results in a new set of inputs for the model then the consequences on the delay performance can be rapidly evaluated.
• Each link is modelled by a one server, multi-class queue with a strict priority class and up to five classes serviced in a round-robin way (this model is similar to the MDRR scheduling discipline implemented on CISCO giga-routers).
• The queue model is derived from the M/G/1 priority queue but takes into account that the M/G/1 priority queue is an inaccurate model for GPS scheduling because the absolute priority doesn’t reflect the scheduler behaviour (the classes are serviced in a round-robin way).
• The evaluated performance delay is significant at the end-user level (i.e. describes how the end-user perceives the performance of the network looking at the application behaviour).
• The packet delay is computed only for the traffic in the strict priority class; it is assumed that in this class are mapped delay-sensitive applications like Voice-Over-IP or interactive applications.
• The traffic mapped on the other classes is supposed to be of type “bulk” (i.e. applications based on large volume transfer, generally using TCP) and the model allows for computing the volume transfer delay. The packet level is neglected because the end-user perceives the network performance relative to the flow level.
• The module can be used also for evaluating delays in an intra-domain context (a particular case is the computation of the intra-domain delay matrices that are needed for calculating the end-to-end delays). The information about the domain to be analysed that are needed for using this function can be stored in a local portion of the InterMON database