Multi Protocol Label Switching is a mechanism made use of in high performance networks of communications. Its purpose is to carry data between network nodes through the use of labels. The technology makes possible the creation of virtual links between remote nodes. Originally, its presentation was to advance the forwarding speed of routers. Currently, it does offer Internet Protocol new capabilities. The MPLS technology is the most superior for use in Virtual Private Network support and traffic engineering.
The basic essence of this system is to generate short fixed length labels that are assigned to data packets. The labels act as shorthand representations headers of IP packets. Forwarding decisions of the packets are made exclusively depending on the label contents. There is totally no need to examine the packets. This works much in the same way as ZIP codes. It leads to the creation of continuous circuits across the mediums of transport using any protocol.
Traditional routed networks did the processing of information at each router in a given path. MPLS eliminates this dependence on links and eliminates requirement of multiple Layer 2 networks for the satisfaction of different traffic types. The IP packets are usually encapsulated with the labels by the original Multi Protocol Label Switching device they come across as they get into the networks.
It is important to understand how the technology works. First, the packets are prefixed with headers containing one or more labels. Each of these has four fields. The first of these is a 20 bit label. Secondly, there is a 3 bit Traffic Class field that acts as a quality of service priority as well as for Explicit Congestion Notification. There is also an 8 bit time to live field, commonly called a TTL field. Finally, there exists a 1 bit bottom of the stack flag. These get switched subsequent to label lookup as opposed to a lookup into the IP table.
Routers that only perform routing based functions only are known as Label Switched Routers, LSRs. The term is derived from the fact that forwarding of packets is done by implementing switching decisions based entirely on the MPLS labels. The points of entry and exit of networks are called Label Edge Routers, LERs. Distribution of labels between LSRs and LERs is done using the Label Distribution Protocol, LDP. The LSRs frequently change label and reachability data with each other.
Installation and removal of paths is done using two standard protocols, the first being Label Distribution Protocol, LDP. The other is RSVP TE, which is an extension of Resource Reservation Protocol made use of in traffic engineering. These are used in management of the paths.
The system is presently made use of in IP only networks. Its standardization is done by the Internet Engineering Task Force, IETF in RFC3031. Its deployment is for connection of as few as two amenities to extremely large deployments. However, it is mainly used for forwarding of IP datagrams.
MPLS is not the only of its kind in the market. There are several competitors with newer switching methods. These include CAM, TCAM and ASIC switching systems.
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