3.3 Components of Traffic Engineering

One of the strategies for TE using MPLS involves four functional components [3]:

1. Information distribution

2. Path selection

3. Signaling and path set-up

4. Packet forwarding

Now, discussing each of the components in detail:

1. Information Distribution Component: Traffic engineering requires detailed knowledge about the network topology as well as dynamic information about network loading. This can be implemented by using simple extensions to IGP so that link attributes (such as maximum link bandwidth, current bandwidth usage, current bandwidth reservation) are included as part of routers link-state advertisements. The standard flooding algorithm used by link-state IGP ensures that link attributes are distributed to all routers in ISPs routing domain. Each LSR maintains network link attributes and topology information in a specialized TE database (TED), which is used exclusively for calculating explicit paths for placement of LSPs on physical topology.

2. Path Selection Component: On the basis of the network topology and link attributes in the TED and some administrative attributes obtained from user configuration, each ingress LSR calculates the explicit paths for its LSPs, which may be strict or loose. A strict explicit route is one in which the ingress LSR specifies all the LSRs in the LSP, while only some LSRs are specified in a loose explicit path. LSP calculations may also be done offline for optimal utilization of network resources.

3. Signaling and Path-Setup Component: The path calculated by the path selection component is not known to be workable, until LSP is actually established by the signaling component, because it is calculated on the basis of information present in TED, which may not be up-to-date. The signaling component is responsible for establishing LSP state and label binding and distribution in the path set-up process.

4. Packet-Forwarding Component: Once the path is set-up, packet forwarding process begins at the Label Switch Router (LSR) and is based on the concept of label switching. This has been discussed in chapter 2.

The two most popular signaling protocols are:

Resource Reservation Protocol with Traffic engineering Extensions (RSVP-TE) and Constraint-based Router Label Distribution Protocol (CR-LDP). RSVP-TE is discussed in the next chapter.