MPLS Tutorial: What is MPLS (Multi Protocol Label Switching)?
The exponential growth of the Internet over the past several years has placed a tremendous strain on the service provider networks. Not only has there been an increase in the number of users but there has been a multifold increase in connection speeds, backbone traffic and newer applications. Initially ordinary data applications required only store and forward capability in a best effort manner. The newer applications like voice, multimedia traffic and real-time e-commerce applications are pushing toward higher bandwidth and better guarantees, irrespective of the dynamic changes or interruptions in the network.
To honor the service level guarantees, the service providers not only have to provide large data pipes (which are also costlier), but also look for architectures which can provide & guarantee QoS guarantees and optimal performance with minimal increase in the cost of network resources.
MPLS technology enables Service Providers to offer additional services for their customers, scale their current offerings, and exercise more control over their growing networks by using its traffic engineering capabilities. On the other hand, Diffserv using its scalable differentiation enables differential pricing scheme for providing differential QoS. Putting it simply, MPLS is a switching technology used to get packets from one place to another through a series of hops while DiffServ governs what happens to the packet at each hop. The marriage of these two technologies, Diffserv over MPLS, provides another interesting alternative solution to the bag of existing ones.
On the other hand, compared to Diffserv over MPLS which is still an evolving technology, SNMP is a widely deployed network management protocol capable of catering to a large number of device classes. SNMP, being such a widely accepted and understood management protocol standard, can be effectively used to gather traffic characteristics from the routers in the core network. The information gathered can be used for provisioning and for traffic engineering by the network operators at the Network Operating Centre (NOC).
MPLS and Its Benefits
2.1 MPLS Operation
IP-based networks typically lack the quality-of-service features available in circuit-based networks, such as Frame Relay and ATM. MPLS brings the sophistication of a connection-oriented protocol to the connectionless IP world. Based on simple improvements in basic IP routing, MPLS brings performance enhancements and service creation capabilities to the network.
MPLS stands for Multiprotocol Label Switching; multiprotocol because its techniques are applicable to ANY network layer protocol, of which IP is the most popular.
Before explaining MPLS, here are some of the terms which are used extensively in MPLS jargon:
1. Forwarding Equivalence Class (FEC): a group of IP packets which are forwarded in the same manner (e.g., over the same path, with the same forwarding treatment).
2. MPLS header: The 32-bit MPLS header contains the following fields:
i. The label field (20-bits) carries the actual value of the MPLS label.
ii. The Class of Service (CoS) field (3-bits) can affect the queuing and discard algorithms applied to the packet as it is transmitted through the network. Since the CoS field has 3 bits, therefore 8 distinct service classes can be maintained.
iii. The Stack (S) field (1-bit) supports a hierarchical label stack. Although MPLS supports a stack, the processing of a labeled packet is always based on the top label, without regard for the possibility that some of other labels may have been above it in the past, or that some number of other labels may be below it at present. An unlabeled packet can be thought of as a packet whose label stack is empty (i.e., whose label stack has depth 0). If a packet's label stack is of depth m, we refer to the label at the...
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