Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 329
RSVP and Routers

RSVP also runs in routers and works in conjunction with the requests being transmitted by a network application. RSVP is used in routers to forward QoS requests to all stations along the path or paths of that particular flow. It is also up to the routers to establish and maintain an RSVP state. In other words, if an application makes an RSVP request, each router must forward it to another router en route to the source; yes, the reverse path, receiver to sender.

An RSVP process uses the local route table to obtain routes.

QoS is implemented by a collection of mechanisms known as traffic control. This includes three mechanisms:

Packet classifier: Determines the QoS class and possibly the router for each packet.

Admission control: Determines if resources are available to accept or reject a request.

Packet scheduler: Achieves the promised QoS for each outgoing interface.

The slide shows a block diagram for RSVP. Two modules within RSVP known as admission control and policy control are utilized by a RSVP request. Admission control determines whether the node has the available resources to accept the request (sounds like Call Admission Control under ATM, right?). Policy control determines the permission rights of the requester. If either of these checks fail, the request is discarded and a message is sent back to the requester (the application that made the request) indicating the type of failure. If both of these checks clear, then parameters are set in the packet classifier and the packet scheduler in hopes of obtaining the resources required by the request.

RSVP and Routers