Multiprotocol Label Switching Networks

IP networks were initially designed with network survivability in a decentralized networking as the central goal. Thus the Internet infrastructures and protocols were intended from the very beginning for this purpose. As the Internet is evolving into a general-purpose communications network, the new realities require the development of new Internet infrastructure to support real-time-sensitive and multimedia applications such as voice over IP and video conference calls (Smith & Collins, 2001).

Back in the mid to late 1990s, when most routers were predominantly based on software forwarding rather than hardware forwarding, a number of vendors devised proprietary mechanisms to switch packets far more efficiently than was possible with forwarding based entirely on hop-by-hop longest match IP address lookups. Various aspects of these proprietary mechanisms were effectively merged and developed by the MPLS working groups at the IETF and produced what we know today as MPLS (Edwards, Syngress, McCullough, & Lawson, 2000).

MPLS is a key component of the new Internet infrastructure and represents a fundamental extension to the original IP-based Internet with changes to the existing infrastructure (Wang, 2002).

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Multiprotocol Label Switching (MPLS)

MPLS introduces connection orientation and packet switching in IP networks. IP datagrams are forwarded by MPLS routers along pre-established paths, based on a short label. This reduces the amount of routing computations, which are carried out only at the times of setting up new paths. MPLS allows introducing new traffic engineering techniques which apply for connection-oriented networks can be applied to MPLS networks. One of these techniques is dynamic routing.

Another important application for MPLS networks is the configuration of Virtual Private Networks (VPNs) over a public IP network. The benefit of MPLS for this application is that private IP addresses, which may be not unique, are separated from the world-wide valid public IP addresses used in the public IP network. The separation of addresses is realized by building MPLS tunnels through the public IP network. The MPLS protocol can also be run on ATM networks and frame relay networks. This simplifies the interworking between these networks and IP networks (Smith & Collins, 2001).

MPLS connections are well suited to the fast-forwarding (also called switching) of any type of network layer protocol (not just IP), hence the word multiprotocol in the name. it will be widely used for two main types of application:

First, it adds controllability of IP networks. As already noted, an IP network is much like a “free-for-all” highway without traffic control, to use the analogy of a highway system. All the traffic can be crammed onto the highway at once, and each router along the way tries its best to get the traffic through without any guarantee of succeeding, MPLS marks ‘lanes’ with labels for the IP highway, and each packet flow has to follow a predefined lane or path. Once the ‘lanes’ are marked, a set of traffic parameters can be associated with each lane to guarantee the service delivery. It reduces randomness and adds controllability to the IP network (Edwards et al., 2000).

Second, MPLS adds switching capability to the routing-based IP network. The traditional Internet structure has every router along the way examine the destination address inside a packet and determine the next hop. In a switched network, each switch routes the traffic from the input port to a predetermined output port without examining the contents of each packet. This is also called route once and switch many times, since the packet contents are examined only at the entry of the MPLS network to determine a proper ‘lane’ for the packet. The benefits of this change include speedup of network traffic and network scalability(Smith & Collins, 2001).

Summary and Conclusion

Label switching is something that has been significant interest from the Internet community, and significant effort has been made to define a protocol called Multiprotocol Label Switching (MPLS).

MPLS involves the attachment of a short label to a packet in from of the IP header. This effectively is like inserting a new layer between the IP layer and the underlying link layer of the OSI model. The label contains all the information that a router needs to forward a packet. The value of a label may be used to look up the next hop in the path and forward to the next router. The difference between this and standard IP routing is that the match is an exact one and is not a case of looking for the longest match (that is, the match with the longest subnet mask). This enables faster routing decisions within routers (Wang, 2002).

The expansion rates for Internet protocol (IP) interchange and users persist to be very remarkable. What once was a technology principally used within the territories of academe and leisure is now being utilized around the world for conventional commerce submissions, like e-commerce, Web-based industry in the development of the carrier system as service contributors around the world concentrate on optimization and benefit efficiency (Edwards et al., 2000).

In many ways, MPLS is as much of a traffic engineering protocol as it is a Quality of Service (QoS) protocol. It is somewhat analogous to the establishment of virtual circuits in ATM and can lead to similar QoS benefits. It helps to provide QoS by helping to better manage traffic. Whether it should be called traffic engineering protocol of QoS protocol hardly matters if the end results is better QoS (Wang, 2002).

References:

Edwards, M. J., Syngress, R. F., McCullough, A., & Lawson, W. (2000). Building Cisco Remote Access Networks. Rockland, MA: Syngress.

Smith, C., & Collins, D. (2001). 3G Wireless Networks. New York: McGraw-Hill Professional.

Wang, H. H. (2002). Packet Broadband Network Handbook. New York: McGraw-Hill Professional.

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