3Com S7906E Configuration Manual page 1654

Reoptimization
Traffic engineering is a process of allocating/reallocating network resources. You may configure it to
meet desired QoS.
Normally, service providers use some mechanism to optimize CR-LSPs for best use of network
resources. They can do this manually but CR-LSP measurement and tuning are required. Alternatively,
they can use MPLS TE where CR-LSPs are dynamically optimized.
Dynamic CR-LSP optimization involves periodic calculation of paths that traffic trunks should traverse. If
a better route is found for an existing CR-LSP, a new CR-LSP will be established to replace the old one,
and services will be switched to the new CR-LSP.
RSVP-TE
This section covers these topics:
Overview
Basic concepts of RSVP-TE
Make-before-break
RSVP-TE messages
Setting up an LSP tunnel
RSVP refresh mechanism
PSB, RSB and BSB timeouts
RSVP-TE GR
Overview
Currently, two QoS models are available: Integrated Service (IntServ) and Differentiated Service
(DiffServ).
Resource Reservation Protocol (RSVP) is designed for IntServ. It reserves resources on each node
along a path. RSVP operates at the transport layer but does not participate in data transmission. It is an
Internet control protocol similar to ICMP.
The following are features of RSVP:
Unidirectional
Receiver oriented. The receiver initiates resource reservation requests and is responsible for
maintaining the reservation information.
Using soft state mechanism to maintain resource reservation information.
Extended RSVP can support MPLS label distribution and allow resource reservation information to be
transmitted with label bindings. This extended RSVP is called RSVP-TE, which is operating as a
signaling protocol for LSP tunnel setup in MPLS TE.
Basic concepts of RSVP-TE
1) Soft state
Soft state is a mechanism used in RSVP-TE to periodically refresh the resource reservation state on a
node. The resource reservation state includes the path state and the reservation state. The path state is
generated and refreshed by the Path message, and the reservation state is generated and refreshed by
the Resv message. A state is to be removed if no refresh messages are received for it in certain interval.
2) Resource reservation style
1-5