Optical NetworksOptical Networks

Rainbow for Communications

Medium SharingMedium Sharing

Time Division Multiplexing (TDM)

Frequency Division Multiplexing

In the optical domain, – Wavelength Division Multiplexing

Time Division MultiplexingTime Division Multiplexing

Wavelength Division MultiplexingWavelength Division Multiplexing

PrinciplePrinciple

Shared Medium

PotentialPotential

Today: each wavelength may carry data rates from 2.5 to 10 Gbps. Commercial systems support up to 160 wavelengths on one strand.

Soon, 1000 ?

Wavelength RoutingWavelength Routing

For any two communicating nodes, establish a lightpath (using the same wavelength all along the path).

The Routing and Wavelength The Routing and Wavelength Assignment Problem (RWA)Assignment Problem (RWA)

NP Problem!

RWA For Different NetworksRWA For Different Networks

Wavelength-continuity constraint: lightpath with the same wavelength from source to destination

Wavelength-convertible networks: All or some nodes are allowed to convert wavelengths (switch wavelength).

RWA Types of ProblemsRWA Types of Problems

Static RWA

Sequential RWA

Dynamic RWA

Strategy to Solve RWAStrategy to Solve RWA

Break RWA:– Routing problem : Dijkstra or Bellman-Ford

– Wavelength assignment: a suggestion?

How About Grooming?How About Grooming?

Grooming adds another dimension to the problem:– Mix together some low rate traffic flows into

one flow to occupy one wavelength.

Switching in Optical NetworksSwitching in Optical Networks

Based on “Techniques for Optical Packet Switching and Optical Burst Switching”,

L. Xu, H.G. Perros, and G. Rouskas

Packet Coding TechniquesPacket Coding Techniques

Bit serial coding

Bit parallel:

Out of band signalling

Bit Serial CodingBit Serial Coding

Optical code-division multiplexing (each bit carries routing information)

Optical pulse interval : header and payload are separate, but transmitted at same rate

Mixed rate techniques: header and payload are separate, but header transmitted slower

Bit Parallel and Out of band Sig.Bit Parallel and Out of band Sig.

Bit parallel: bits are sent in parallel on different wavelength

Out-of-band signalling: – SCM (Subcarrier Multiplexing): header is sent

on electrical carrier.– Dual wavelength: header and payload are sent

on different wavelength

How to Solve Contention?How to Solve Contention?

Optical StoringOptical Storing

Optical Buffering : using optical delay lines

Wavelength Domain: Packet scheduling becomes similar to multiprocessor scheduling

Deflection routing: send out on any available output port