Staged Refresh Timers for RSVP
    
              Ping Pan              Henning Schulzrinne
       IBM T. J. Watson Research    Columbia University
           pan@watson.ibm.com       hgs@cs.columbia.edu


Abstract:

The current resource Reservation Protocol (RSVP) design has no
reliability mechanism for the delivery of control messages.  Instead,
RSVP relies on periodic refresh between routers to maintain reservation
states.  This approach has several problems in a congested network.  End
systems send PATH and RESV messages to set up RSVP connections.  If the
"first" PATH or RESV message from an end system is accidentally
lost in the network, a copy of the message will not be retransmitted
until the end of a refresh interval, causing a delay of 30 seconds or
more until a reservation is established.  If a congested link causes a
tear-down message (PATHTEAR or RESVTEAR) to be dropped, the
corresponding reservation will not be removed from the routers until the
RSVP cleanup timer expires.

We present an RSVP enhancement called staged refresh timers to support
fast and reliable message delivery that ensures hop-by-hop delivery of
control messages without violating the soft-state design.  The
enhancement is backwards-compatible and can be easily added to current
implementations.  The new approach can speed up the delivery of trigger
messages while reducing the amount of refresh messages. The approach is
also applicable to other soft-state protocols.