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    RSVP Overview

    RSVP is a resource reservation setup protocol that is used by both network hosts and routers. Hosts use RSVP to request a specific class of service (CoS) from the network for particular application flows. Routers use RSVP to deliver CoS requests to all routers along the data path. RSVP also can maintain and refresh states for a requested CoS application flow.

    RSVP treats an application flow as a simplex connection. That is, the CoS request travels only in one direction—from the sender to the receiver. RSVP is a transport layer protocol that uses IP as its network layer. However, RSVP does not transport application flows. Rather, it is more of an Internet control protocol, similar to the Internet Control Message Protocol (ICMP) and Internet Group Management Protocol (IGMP). RSVP runs as a separate software process in the Junos OS and is not in the packet forwarding path.

    RSVP is not a routing protocol, but rather is designed to operate with current and future unicast and multicast routing protocols. The routing protocols are responsible for choosing the routes to use to forward packets, and RSVP consults local routing tables to obtain routes. RSVP only ensures the CoS of packets traveling along a data path.

    The receiver in an application flow requests the preferred CoS from the sender. To do this, the receiver issues an RSVP CoS request on behalf of the local application. The request propagates to all routers in reverse direction of the data paths toward the sender. In this process, RSVP requests might be merged, resulting in a protocol that scales well when there are a large number of receivers.

    Because the number of receivers in an application flow is likely to change and the flow of delivery paths might change during the life of an application flow, RSVP takes a soft-state approach in its design, creating and removing the protocol states in routers and hosts incrementally over time. RSVP sends periodic refresh messages to maintain its state and to recover from occasional lost messages. In the absence of refresh messages, RSVP states automatically time out and are deleted.

    Modified: 2017-08-31