Traffic Engineering; Te Metric (Is-Is And Ospf) - Alcatel-Lucent 7450 Manual

Traffic Engineering

Traffic Engineering
Without traffic engineering, routers route traffic according to the SPF algorithm, disregarding
congestion or packet types.
With traffic engineering, network traffic is routed efficiently to maximize throughput and
minimize delay. Traffic engineering facilitates traffic flows to be mapped to the destination
through a different (less congested) path other than the one selected by the SPF algorithm.
MPLS directs a flow of IP packets along a label switched path (LSP). LSPs are simplex, meaning
that the traffic flows in one direction (unidirectional) from an ingress router to an egress router.
Two LSPs are required for duplex traffic. Each LSP carries traffic in a specific direction,
forwarding packets from one router to the next across the MPLS domain.
When an ingress router receives a packet, it adds an MPLS header to the packet and forwards it to
the next hop in the LSP. The labeled packet is forwarded along the LSP path until it reaches the
destination point. The MPLS header is removed and the packet is forwarded based on Layer 3
information such as the IP destination address. The physical path of the LSP is not constrained to
the shortest path that the IGP would choose to reach the destination IP address.

TE Metric (IS-IS and OSPF)

When the use of the TE metric is selected for an LSP, the shortest path computation after the TE
constraints are applied will select an LSP path based on the TE metric instead of the IGP metric.
The user configures the TE metric under the MPLS interface. Both the TE and IGP metrics are
advertised by OSPF and IS-IS for each link in the network. The TE metric is part of the traffic
engineering extensions of both IGP protocols.
A typical application of the TE metric is to allow CSPF to represent a dual TE topology for the
purpose of computing LSP paths.
An LSP dedicated for real-time and delay sensitive user and control traffic has its path computed
by CSPF using the TE metric. The user configures the TE metric to represent the delay figure, or a
combined delay/jitter figure, of the link. In this case, the shortest path satisfying the constraints of
the LSP path will effectively represent the shortest delay path.
An LSP dedicated for non delay sensitive user and control traffic has its path computed by CSPF
using the IGP metric. The IGP metric could represent the link bandwidth or some other figure as
required.
When the use of the TE metric is enabled for an LSP, CSPF will first prune all links in the network
topology that do not meet the constraints specified for the LSP path. These constraints include
bandwidth, admin-groups, and hop limit. CSPF will then run an SPF on the remaining links. The
shortest path among the all SPF paths will be selected based on the TE metric instead of the IGP
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