IP-MPLS Technology| IP MPLS in Indian Railways 

 IP-MPLS Technology

Multi protocol Label Switching (MPLS) is an emerging network protocol that provides mechanisms for establishing flows through an Internet Protocol (IP) network.

 These Label Switched Paths (LSPs) allow network operators and users to direct traffic through an explicitly defined network path, allowing default traffic routes to be overridden if network conditions require it (e.g., network congestion).

 This ability to establish LSPs allows users or network management personnel to assign Quality of Service (QoS) attributes, and to perform traffic engineering.

Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networksthat directs data from one node to the next based on short path labels rather than long network addresses, thus avoiding complex lookups in a routing table and speeding traffic flows. 

The labels identify virtual links (paths) between distant nodes rather than endpoints. MPLS can encapsulate packets of various network protocols, hence the "multiprotocol" reference on its name. 

MPLS supports a range of access technologies, including T1/E1, ATM, Frame Relay,and DSL

What this means is that the router no longer forwards packets based on a software dependent and longer look-up in the route table but fast switches packets based on the label. 

This delivers huge performance benefits as well as flexibility.

Functioning of MPLS

MPLS is scalable and protocol-independent.

 In an MPLS network, data packets are assigned labels. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. 

This allows one to create end-to- end circuits across any type of transport medium, using any protocol. 

The primary benefit is to eliminate dependence on a particular OSI model data link layer (layer 2) technology, such as Asynchronous Transfer Mode (ATM), Frame Relay, Synchronous Optical Networking (SONET) or Ethernet, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. 

Multiprotocol label switching belongs to the family of packet-switched networks.

MPLS operates at a layer that is generally considered to lie between traditional definitions of OSI Layer 2 (data link layer) and Layer 3 (network layer), and thus is often referred to as a layer 2.5 protocol.

 It was designed to provide a unified data-carrying service for both circuit- based clients and packet switching clients which provide a datagram service model.

 It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and Ethernet frames.

A number of different technologies were previously deployed with essentially identical goals, such as Frame Relay and ATM.

 Frame Relay and ATM use "labels" to move frames or cells throughout a network. The header of the Frame Relay frame and the ATM cell refers to the virtual circuit that the frame or cell resides on.

 The similarity between Frame Relay, ATM, and MPLS is that at each hop throughout the network, the ―label value in the header is changed. 

This is different from the forwarding of IP packets.

 MPLS technologies have evolved with the strengths and weaknesses of ATM in mind. MPLS is designed to have lower overhead than ATM while providing connection-oriented services for variable-length frames, and has replaced much use of ATM in the market.

MPLSComponents

Label Edge Router (LER)

LER's are located at the boundary of the MPLS network. They apply label to packets for transmission across the MPLS network. 

LER's are responsible for classifying incoming IP traffic and relating the traffic to the appropriate label. The LER converts IP packets into MPLS packets, and MPLS packets into IP packets. 

In MPLS, this classification process is called forward equivalence class (FEC).

Label Switch Router (LSR)

These devices are routers, and they examine incoming packets, providing that a label is present. The LSR will look up and follow the label instruction and then forward the packet according to the instruction. In general, the LSR performs a label swapping function.

When the packets leave the LER, they are destined for LSR where they are examined for the presence of label. The LSR looks to its forwarding table (called a label information base LIB or a connectivity table) for instructions. The LSR will swap labels according to the LIB instructions.

Label Switch Path (LSP)

In between LER and LSR paths are established, these paths are called LSP. The paths are designed for their traffic characteristic; as such, they are very similar to ATM paths. The traffic handling capabilities of each path is calculated. These characteristics can include peak traffic load, inter-packet variation, and dropped packet percentage calculation.

Label Distribution Protocol (LDP)

LDP's are used to distribute label information between LSR's and LER's. It also defines a new protocol, existing protocols, such as BGP and RSVP, have been extended to enable label distribution to be stacked on them.