MPLS Traffic Engineering

Rick Gallaher is course director for CCI, President of Telecommunications Technical Services Inc., and author of  Rick Gallaher's MPLS Training Guide

January 24, 2002

In previous articles, we discussed data flow, signaling, and rapid recovery. This article addresses the subject of traffic engineering.

Vocabulary:

• Silence Suppression:  Not using bandwidth when there is no data to send.
• CR-LDP: Constraint Route Label Distribution Protocol.
• Over-provisioning:  Having more bandwidth than allocated traffic.
• Over-subscribing: Having more allocated traffic than available bandwidth. (Telco)
• RSVP-TE: Resource Reservation Setup Protocol with Traffic Engineering
• Under-subscribing: Having more bandwidth than allocated traffic. (Telco)
• Under-provisioning: Having more allocated traffic than available bandwidth.

Introduction:

There is a road in Seattle, Washington that I drove years ago called Interstate 5.  From the suburb of Lynnwood, I could get on the highway and drive into the city, getting off at any exit.  If I wanted to go from Lynnwood into the heart of Seattle, I could get onto the express lanes.  This express lane is like an MPLS tunnel.  If my driving characteristics matched the requirements of the express lane, then I could use it.

Figure 5.1: Express Lane

Taking this illustration further, let’s say that I enter the freeway and want to drive into the heart of Seattle. I might ask myself, “Which is faster: the express lane or the regular highway? Is there an accident on the express lane?  Is the standard freeway faster?”

It would be nice to have traffic report, but traffic reports are not given in real time – by the time that I would find out about a slowdown, I would be stuck in it.  I could make the mistake of entering the express lane just as an accident happens 5 miles ahead and be trapped for hours.

It would be great if I had a police escort.  The police would drive in front of me; if there were an accident or a slowdown, then they would take me on a detour of similar quality to ensure that I arrive at my destination on time.

On the Internet, we have thousands of data roads just like Interstate 5. With MPLS, we have a road dedicated to traffic with certain characteristics – much like the express lane. To ensure that the express lane is available and free of congestion, we can use protocols like CR-LDP and RSVP-TE.  These protocols are discussed in greater detail in the article Advanced MPLS Signaling.  Currently, the most popular of these two protocols appears to be RSVP-TE, because it acts like a police escort to ensure that, if there is congestion, it can be re-routed around the problem area.

When looking at traffic patterns around the country, often freeways experience congestion and delays, while other roads are open and allow traffic to flow freely. The traffic is just in the wrong area. Wouldn’t it be nice if the highway engineers and the city planners could find ways to route heavy traffic to roads that could handle the traffic load and to adjust the road capacity as needed to accommodate traffic volume?

Next page >>

Page 1 of 7