 tized application, in all parts of the network. However, resources for the traffic and the application to this is a low quality guarantee as it makes no specific which it corresponds). commitments regarding available bandwidth or latency. On the other hand, consider the quality of guarantee required to support a videoconference. A videoconfer- How RSVP works encing application requires that all subnets between the videoconferencing peers be able to provide a significant PATH messages wind their way through all network amount of bandwidth at a low latency. To do SO efficiently devices en route from sender to receivers. RSVP-aware requires that all devices along the data path commit the devices in the data path note the messages and establish required amount of low latency bandwidth for the du- state for the flow described by the message. ration of the videoconference. As we have seen, high When a PATH message arrives at a receiver, the re- quality guarantees such as these generally require sig- ceiver responds with a RESV message (if the receiving naling across network devices in order to make efficient CHAPTER 3.3 VolP Technology use of network resources. In our sample network, mul- queuing device (usually an IP switch or router) to analyze tiple subnets, based on multiple media (and varying the packets, determine the type of payload the packet is traffic handling mechanisms) must be coordinated via carrying, compare that information to a set of prioriti- this signaling. RSVP is particularly suitable for this zation and bandwidth utilization rules, and order the purpose because it expresses QoS requirements in output according to those rules. high-level, abstract terms. Agents in each subnet are able There are a number of different prioritization schemes to translate the media-independent, abstract requests used in currently available network devices today. The into parameters that are meaningful to the specific most commonly used schemes are known as Priority subnet media. Queuing, Weighted Fair Queuing, and Cl