Dense wave division multiplexing recently burst onto the network scene promising dramatically increased data transport capacity with relatively low cost. Now intense development is focused on transforming DWDM into something radically different – and better. So sweeping are the proposed upgrades, they’re being described as a new technology, with titles such as lambda switching.
Like DWDM, lambda switching uses small amounts of fibre-optic cable and differing light wavelengths (called lambdas) to transport many high-speed datastreams to their destinations. But unlike DWDM, lambda switching injects intelligence, built around a set of evolving industry standards, into optical network gear.
Lambda-switching technology will provide optical network managers with benefits such as the ability to engineer traffic (specifying how, when and where data flows), while offering innovative services using equipment from multiple vendors. With lambda switching, new optical net designs can be implemented to provide customers with better performance. It also can ease management while boosting fault tolerance to unprecedented levels.
The key to lambda switching is the ability to automatically connect optical network endpoints. In the past, arranging optical net communications required tedious, expensive configuration of each device, fibre, lambda and even higher-level protocols such as SONET and routing.
Because lambda switching connections, or light paths, are set up on the fly, using a scheme that’s integrated with upper-layer protocols, network configuration can be simplified. And because light paths streamline operation, highly redundant network designs, previously deemed impossible to manage, can now be built.
When a new technology’s shrink-wrapped package boasts of simple operation and increased flexibility, there’s likely to be more complexity inside, and lambda switching is no exception. Light paths are dynamic compositions of wavelengths that flash across the fibres interconnecting lambda-switching equipment called optical cross connects (OXC).
OXCs are expected to rely on optically upgraded versions of already tough-to-understand technologies, including advanced routing protocols and Multi-protocol Label Switching (MPLS).
Light paths are usually based on the information distributed by lambda switching variants of protocols such as the Open Shortest Path First (OSPF) routing protocol. In addition to permitting OXCs to advertise network reachability information (over dedicated “control lambdas”), extended OSPF might provide detailed data regarding bandwidth, quality of service and more. Using the information presented by extended OSPF, each OXC can form network topology maps, called traffic engineering tables, readying them for subsequent lambda switching steps.
The next phase of light path construction – signaling – will probably fall to enhanced MPLS and adaptations of protocols such as Resource Reservation Protocol (RSVP). When a connection between optical endpoints is needed, ingress OXCs can send extended RSVP setup messages requesting that downstream OXCs provide one or more lambdas (or SONET channels) for the light path.
To engineer how traffic flows, extended RSVP messages can follow paths programmed by net managers or abstract routes that meet connection criteria (like bandwidth), using the traffic engineering tables. For fault tolerance, back-up light paths can be requested, and because of MPLS’s and RSVP’s flexibility, unique services such as virtual private optical networks can be rendered. After processing setup messages, OXCs signal successful light-path resource allocation by handing RSVP messages containing lambda- or channel-associated MPLS labels to upstream neighbours. When each OXC between ingress and egress assigns a label, the optical connection is complete and ready to transport data arriving at the lambda switching net edge.
Lambda switching promises numerous benefits, but there is work left to determine how standard protocols will deliver them. Judging from the enormous developmental energy converging on lambda switching, it might be the end of DWDM.
Giacalone is a principal consultant at Predictive Systems, an international network consulting firm. He can be reached at spencer.giacalone@predictive.com.
