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What Are MPLS Networks? How do they work?

About Multi–Protocol Label Switching (MPLS) Networks

– MPLS or the Multi–Protocol label switching is the mechanism behind the high performance of the telecommunications networks that we use today.
– The purpose of this mechanism is directing the data from one node of the network to the next one as per what are called the short path labels.
– It does not follow the traditional network addresses that are quite long.
– It prevents the complex look-ups in the table used for routing.
– The paths which are actually the virtual links between the various nodes are identified by the labels rather than having end points being identified.
– MPLS is also used for encapsulating the various network protocol IP packets.
– A wide range of technologies are supported by the MPLS networks:

  • T1/ E1
  • ATM
  • Frame relay
  • DSL

– There are 3 major characteristics of the MPLS networks:

  • They are highly scalable
  • Data – carrying mechanism
  • Protocol agnostic

– The labels are assigned to the data packets.
– The decisions regarding the forwarding of the packet are made based up on the content of these labels.
– This eliminates the need for examining the packet.
– It is because of this that the creation of end–to–end circuits had become possible and that too in any medium of transport and using any protocol.
– There is a lot of dependence on the technologies such as:

  • ATM or asynchronous transfer mode
  • Frame relay
  • SONET or synchronous optical networking
  • Ethernet

– With a mechanism such as MPLS, this dependence is reduced to a great extent.
– It also eliminates the requirement of multiple second layer networks in order to keep different type of traffic under satisfaction.
– MPLS networks fall under the category of the packet – switched networks.
– The layer at which the MPLS operates lies between the network layer (layer 3) and the data link layer (layer 2) and therefore this layer has been termed as the layer 2.5 and so MPLS is also called as the layer 2.5 protocol.
– It has been designed in such a way that it provides a unified data carrying service for both the types of clients i.e., the packet – switching clients and the circuit – based clients.
– All these together form a datagram service model.
– This is what makes the MPLS so capable of carrying a wide range of traffic.
– The development of MPLS took place keeping in view the plus and minus points of the ATM.
– Many technologies have been replaced by the MPLS recently.
– It’s been recognized by the MPLS that there is no requirement of the small ATM cells in the modern networks since we have now the optical networks which are very fast.
– MPLS does make attempts at preserving the out of band control and traffic engineering because of which the ATM and frame relay appeared to be very attractive to the deployment of large scale networks.
– There are many benefits in traffic management if MPLS is used such as increased performance and reliability.
– But there are disadvantages too for the IT sector such as loos of access and visibility in to the cloud.

Operation of MPLS

– The packets are prefixed with an MPLS header that contains labels called a label stack.
– Each label stack has 4 parts namely: 20 bit value, 3 – bit traffic class, 1 – bit bottom of stack flag and 8 – bit ttl.
– After a label look-up the packet switching starts with the help of routers called the LSRs or the label switch routers.
– LDP (label distribution protocol) is the protocol that is used for the distribution of the labels between the routers.

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