Cr-Ldp; Rsvp-Te - HP HSR6800 Configuration Manual

Reoptimization
Traffic engineering is a process of allocating or reallocating network resources. You can configure it
to meet desired QoS.
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 traverse. If a
better route is found for an existing CR-LSP, a new CR-LSP is established to replace the old one, and
services are switched to the new CR-LSP.

CR-LDP

Constraint-based Routed Label Distribution Protocol (CR-LDP) is an extension to LDP. It is used in
MPLS TE to create an explicit path with resource reservation between the ingress node and the
egress node.
When initiating an LSP at the ingress, CR-LDP appends some constraints in the label request
message.

RSVP-TE

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.
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
Soft state—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. 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.
Resource reservation style—Assigned to each LSP set up using RSVP-TE. During an RSVP
session, the receiver decides which reservation style can be used for this session and which LSPs
can be used. The following reservation styles are available:
•
FF—Fixed-filter style, where resources are reserved for individual senders and cannot be
shared among senders on the same session.
•
SE—Shared-explicit style, where resources are reserved for senders on the same session and
shared among them. SE is only used for make-before-break because multiple LSPs cannot be
present on the same session.
Make-before-break
Make-before-break is a mechanism to change MPLS TE tunnel attributes with minimum data loss
and without extra bandwidth.
41