Very Basic MPLS Tutorial
Learn what MPLS networks are, how they work and what they can do for your business.
By: John Shepler
MPLS stands for Multi-Protocol Label Switching. The multi-protocol part gives you an idea of how versatile this type of network is. Like IP or Internet Protocol networks, you need a special setup for MPLS. Of course the same is true for SONET, ATM, Frame Relay and other network protocols. MPLS tries to work with all of these other protocols, mostly by encapsulating them in its own tunnels. Why? To add speed and features that you might not otherwise have.
Step by Step Through The MPLS Network
The way this works is that your packets enter the MPLS network through an ingress router that is also known as a tag router. Think of the MPLS network as a sovereign nation and the ingress routers as the customs checkpoints where you enter the country. To get out, you need to pass through an egress router. While you are traversing the network you are routed by tag switches also called label switch routers. It is important to note that your data packets will be the same when they leave the network as when they entered. In between, they will be in the MPLS protocol.
It's Another Form of Tunneling
If this sounds a little like VPN tunneling, it actually is. Instead of encrypting the packets, MPLS adds a 32 bit tag to the packet headers. The ingress router examines the desired destination address and creates a tag that chooses a virtual circuit or label switch path for that packet. The ingress router will also assign quality of service requirements to the tag. From that point on, the tag switches look only at the tags to determine how to forward the packet. There may be multiple routes available for each label switch path so that the tag switches can manage outages, congestion and differentiated services. At the egress point, the MPLS tag is removed before sending the packets on their way.
Why This Architecture?
Why go to all this trouble? For one thing, processing the relatively small tags is much faster than having to deal with larger headers at each router. For another, the MPLS network can be designed to provide more bandwidth or shorter latency paths for voice packets in VoIP telephone systems. Video packets really need lots of bandwidth available, so you don't want them crammed into paths where computers are backing up large databases. At the very least, voice and video need priorities to commandeer the bandwidth they need to maintain quality service. Most electronic data interchange isn't quite so sensitive.
Where will you find MPLS networks?
Most major legacy and competitive carriers now have them or soon will, perhaps as their primary backbone. Network traffic is evolving from time insensitive data transfers to time critical voice streams that are leaving the traditional public telephone network. Experience shows that just piling voice traffic on top of data traffic on wide area networks can lead to poor voice quality and dropped calls. MPLS supports traffic engineering needed to ensure that each type of packet, including voice, video and data, gets the quality of service it needs while on the network. In fact, MPLS networks are now spreading to include access networks and may eventually find their way into your enterprise network. Service guarantees could be easier to manage when it's MPLS from end to end.
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