An Introduction to MPLS

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

September 10, 2001

In this article, we will examine how an MPLS network is constructed and how MPLS data flows.  In future MPLS Tutorials, we will examine:

• Introductory MPLS Label Distribution and Signaling
• Advanced MPLS Signaling
• MPLS Network Reliance and Recovery
• Traffic Engineering, MPLambdaS and GMPLS

In order to assist your further study, I have provided an acronym list and a list of related URLs to accompany each article.  

INTRODUCTION

What is this new protocol that leading telecommunication experts claim “will take over the world”?  Well, you can rest your worried mind – IP and ATM are not on death row.  In fact, it is my belief that MPLS will breathe new life into the marriage of IP and ATM.

The best way to describe the function of MPLS is by using an analogy of a large national firm with campuses located throughout the United States.  Each campus has a central mail-processing point through which mail is sent around the world, as well as to its other campuses.  Since its beginning, the mailroom has been under orders to send all intercampus correspondence via standard first-class mail.  The cost of this postage is calculated into the company’s operational budget.

MPLS HIGHLIGHTS MPLS allows for the marriage of IP to layer 2 technologies (such as ATM) by overlaying a protocol on top of IP networks.    Network routers equipped with special MPLS software process MPLS labels contained in the Shim Header.   Raw IP traffic is presented to the LER, where labels are pushed; these packets are forwarded over LSP to LSR where labels are swapped.   At the egress to the network, the LER removes the MPLS labels and marks the IP packets for delivery.    If traffic crosses several networks, it can be tunneled across the networks by using stacked labels.

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