OPTICAL COMMUNICATION



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INTRODUCTION

Today's telecommunications service providers are faced with what appears to be an insoluble problem. They must maintain and even increase profitability, while responding to an exponential growth in demand with networks that are even more complex and costly to deploy and maintain.
Since the requirements for both profitability and the ability to offer new, revenue-rich services are givens, the solution must be found in the networks Service providers must find a way to build networks with the flexibility of IP, the reliability of SONET/SDH, and the scalability of optics at costs that will allow them to offer services at competitive prices. Photonic Service Switching (PSS) offers exactly that: a new network model that permits graceful evolution to simpler, more cost-effective core networks.



MESH TOPOLOGIES

The ring versus mesh debate is all but closed. SONET rings are reliable, but they lack the flexibility required by today's market, are costly, and are inefficient. They do not make best use of available bandwidth. 1+1 protection, for example, uses only half the available bandwidth, with the other half on reserve as protection against failures.


CONSOLIDATING LAYERS

Two important alternatives have been proposed to the traditional layered network model. The first, IP over optics, separates services from the optical transport but must maintain separate network elements for the various services carried. The second, Photonic Service Switching brings together services and transport through one core network element.



IP over OXC/DWDM

The IP over OXC/DWDM (in fact IP over OXC over DWDM) approach extends the IP over DWDM model to include wavelength services as shown in the Figure 1. It proposes using routers to aggregate traffic and wavelength switches to handle transit traffic. IP over OXC/DWDM requires additional core network devices to aggregate TDM traffic, and hence still relies on overlay network architecture for service integration. As such, it does not scale well.



PHOTONIC SERVICE SWITCHING (PSS)

Photonic Service Switching introduced in 2001 goes the final step to enabling an intelligent, peer-based core network solution. Using TOPS (TDM + Optical+ Packets) architecture enabled by G-MPLS (Generalized Multi-Label Switching Protocol), PSS supports the G-MPLS view of a common control plane for all layers of services.



PSS NETWORK (PSSN)

A Photonic Service Switching network is a peer-based intelligent optical core network. It applies the power of peering, traditionally found in data networks to transport services. All network elements peer with all other elements. Through an Inter-Gateway Protocol (IGP) they have network information (such as page link type, page link and bandwidth availability, and route reachability) and use this information dynamically and intelligently. The evolution to Photonic Service Switching networks is made possible by three recent innovations as shown in the Figure 2. G-MPLS, which extends the capabilities of MPLS to TDM and wavelength. TOPS architecture, which consolidates timeslot, wavelength and packet traffic onto one network layer.