Overview - Nokia 7705 SAR-W Series Manual

MPLS and RSVP-TE

3.1 Overview

The 7705 SAR provides MPLS technology using static LSPs, RSVP-TE for
traffic-engineered signaled routing of LSPs and LDP for non-traffic-engineered
signaled routing of LSPs. A network operator may choose to use any combination of
static LSPs, RSVP-TE, and LDP to establish paths for services. RSVP-TE and LDP
are considered to be Layer 2.5 protocols.
The 7705 SAR can be used as an ingress and egress Label Edge Router (iLER and
eLER), and as a transit router. A transit router is also referred to as a Label Switch
Router (LSR).
OSPF and IS-IS are the interior gateway protocols with traffic engineering extensions
(IGP-TE) available to the 7705 SAR. These are the Layer 3 protocols. Typically, one
or the other of these gateway protocols will be in use in the network. Whichever
protocol is the chosen gateway protocol, it must be working in order for LDP or
RSVP-TE to function. These Layer 3 protocols identify the next hop, which is
information needed by the Layer 2.5 protocols (LDP or RSVP-TE) in order to assign
labels.
In addition, the 7705 SAR provides link and node redundancy protection through
LSP redundancy and Fast Reroute (FRR) features.
The LSP redundancy and FRR features have the ability to take shared risk link
groups (SRLGs) into consideration when the Constrained Shortest Path First (CSPF)
algorithm is used to determine an alternate LSP. The selection of a route is
determined by the IGP-TE protocol. The added constraints imposed by SRLGs and
CSPF ensure that the redundant route selected will be unique from the principal
route (route being protected); that is, it will use physical equipment that is different
from the equipment that carries the principal route. CSPF will constrain the alternate
route to be the shortest possible alternative route. There may be more than one
alternative route.
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MPLS Guide
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