Thursday, March 10, 2005

Generalized MPLS Improves Optical Networks

MPLS or Multi-Protocol Label Switching is a technology that speeds up networks and carries a variety of protocols including IP, ATM, Frame Relay, and SONET. It does this by encapsulating them in its own tunnels as they enter the network and returns them to their original state when they leave. While they're on the MPLS network, they are routed according to simplified tags that are inserted into the packet headers.

Building this specialized network to carry other network traffic has an advantage of being able to define classes of service to ensure that real time data, like voice and video, gets the bandwidth and low latency it needs to function. The fact that this network is a multi-protocol network makes it especially attractive to carriers who need to transport anything and everything. Now a set of extensions called GMPLS or Generalized Multi-Protocol Label Switching adds even more versatility to an already accommodating network.

While MPLS is intended to control the flow of packets in a packet switched network, GMPLS recognizes that there are other types of networks with elements that are not necessarily packet oriented. For instance, TDM or time division multiplexing, the legacy digital telephony standard and the one used as the foundation of SONET (Synchronous Optical NETwork), is based on time slots not packets. Packets can be carried on TDM networks, but if they are too big they get split into multiple time slots and reassembled later. The advantage of having all of those nice, neat, predictable time slots is lost since they have no relevance in the packet switched world.

GMPLS puts TDM back to work. A time slot can be considered a label. There is no need to add more labels, since the network always knows what data is being carried on what time slot. Likewise, a wavelength or Lambda can be considered a label in a WDM or wavelength division multiplexed network. Even an entire fiber can be treated as a GMPLS label to define a path through the network.

Adding labels to everything the network can use in deciding how to route data packets gives the GMPLS network a lot of self-determination. It accepts data of many different protocols at the ingress point. It then adds its own labels which can be the MPLS "shim" type that are inserted in the packet headers or the "implicit" type that are associated with particular fibers, wavelengths, or TDM time slots. The GMPLS data is routed by the label routing switches over the predetermined paths decided at the ingress point. When packets reach the network edge, the egress point, all labeling information is removed and the various types of data go their separate ways in their native protocols.

Notice that there is no mention of manual intervention to provision circuits or set up routes. One of the advantages of GMPLS networks is that they know what network resources they have to work with and go about setting up and tearing down their label switched paths as needed. As GMPLS networks become widely deployed, it is expected that the laborious job of provisioning services will get much easier and faster because of all this automation.

You may also wish to read my article, "MPLS Networks Are Coming Your Way."

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