resource reservation protocol originally used for call admission control,
this is why it deals with bandwidth, but later got te extensions
which is just the capability to request a label towards a given
pe (called tail end) with the path message, and signal the allocated
label backards (to the head end) with the resv message. the protocol initially had the
capabilities to describe the p routers the path need
to traverse with the explicit route, probably this is why it was selected
for te operations. later the protocol got the point to multipoint
extension which is useful for effective multicast distribution.
the rsvp peers does not form neighborship but request a path when needed,
and this path need to be refreshed periodically, otherwise lsp expires
resulting in an implicit path error.
here are the captures for
interestingly, rsvp te extension was proposed by juniper
and they seems to prefer it over ldp with the automesh functionality
which is a control plane construct. every given pe builds
a te tunnel to all the service endpoints discovered from
bgp advertisements. this results in an end to end full mesh
of lsps between the pe routers.