MPLS & Frame Relay

Those of you who have been tracking developments on the MPLS (Multi Protocol Label Switching) front would be aware that the MPLS and the Frame Relay Forums merged to form the MPLS Frame Relay Alliance in April 2003.

The MPLS Frame Relay Alliance is an association of networking and telecom companies working on MPLS. This is also a forum where the users of the standards and the products meet with those who manufacture products and together can also influence standards.

Frame Relay has been in existence for a very long time and is the successor to the X.25 networks. Even now they exist in big numbers with almost everyone running IP over these connections. As a technology, Frame Relay is on the climb down on the longevity curve and will very soon be just relegated to the edge as service providers move away from separate infrastructure at the core for Frame Relay and ATM services to a converged Multi-Service IP/MPLS backbone.

MPLS on the other hand has been deployed on several networks as early as the year 2000 and is fast becoming the protocol of choice on the core of the service provider networks. Several carriers worldwide have deployed MPLS on their core to provide customers with the latest services and also to support the legacy services.. With MPLS deployed at the core now, service providers can aggregate traffic from the different edge network which bring in Frame, ATM and IP to a single core network!

MPLS and Frame Relay are compatible technologies and almost address the same space (layer 2). MPLS has the advantage of the IP background and hence can provide layer 3 services too!

Interworking is the industry term to define the ability of one technology to communicate or interwork with another technology. The root of all these interworking concepts is in the Frame Relay implementation agreements or Frame Relay Forum documents, and as such the concept may not be new. However with MPLS, interworking has got a different meaning because of the ability of MPLS to do much more. There are two levels of interworking: network interworking and service interworking.

Network Interworking is the process of tunneling one protocol or technology across another protocol or technology. In this process tunnels are created to connect the end points talking on the same protocol.

In Service Interworking, two end points running different protocols act like they are communicating with each other. For example, one end point can be talking on FR and the other end point can talk ATM and both the devices can communicate with each other!

Network Interworking is a reality with MPLS and layer 2 MPLS technologies can tunnel almost any of the layer 2 technologies through a MPLS network transparent to the end devices. For example, a Frame Relay connection at one end can transparently be tunneled through a MPLS network to the other end Frame Relay connection. This means customers now have the choice of upgrading their connections quickly at better costs. The same applies for other layer 2 protocols like HDLC, PPP, Ethernet and ATM. This kind of tunneling is also known as AToM (Any Transport over MPLS). A few years back, Frame Relay connections were tunneled through an ATM network and that is also Network Interworking. These kinds of connections exist even today but cannot scale.

What used to be Frame Relay over ATM is now Frame Relay over MPLS. The better part of MPLS is, that it need not be limited to just Frame Relay over MPLS alone. It can be just about any layer 2 payload. The ideal situation to have would be service interworking and that is definitely sometime away. The encouraging fact is that there is a lot of work that is happening to make Multi-Service (Service Interworking) networks a reality and this will for sure make connecting to service provider networks a very simple task!

- C.R. Srinivasan