Network Resources

Sublayers of Optical Networks

Functions of Layers Optical connection is carried on a l-channel By assigning a wavelength By establishing an optical path through a sequence of nodes Role of NASs Tune transceivers to the wavelength of l-channel Establish an optical connection Role of ONNs Create an optical path on the wavelength Establish a potential connection

Network Links Coarse and fine spectrum partitioning Spectrum is divided into wavebands which are further divided into l-channels Typical optical transceivers can handle signals with 10GHz channel spacing. Current ONNs can recognize 100GHz spacing Waveband routing vs. wavelength routing

Optical Network Nodes By functionality of nodes: routing, switching, WC Static nodes Directional couplers Static routers Dynamic nodes Permutation switch Generalized switch Linear divider-combiners Waveband-space switch Waveband-space-time switch Wavelength interchanging switch

Physical topologies based on trees

Static Nodes

Directional Couplers Passive device Power transfer matrix Combining loss when used as a combiner Excess loss due to device imperfection Controllable(dynamic) directional coupler Coupling parameter can be adjusted Can be used as a permutation switch(a=0 or 1) Can be used as an attenuator Large size switches can be constructed

16x16 star coupler

Static Router Without wavelength selectivity, throughput of a BS switch is reduced by a factor of n compared to single fiber capacity Node capacity can be expanded by wavelength routing (e.g., arrayed waveguide gratings) Example of fixed routing k=(i-j) mod n for input j, output i, l=k Latin square When used with tunable transceivers, static router can work as a permutation switch

Dynamic Nodes Space-division switch Optical cross connect(OXC) Routes signals on each input to selected outputs Two types Permutation Generalized switch Linear divider and combiner Any connection pattern, e.g., one-to-many Can have the capability of connection termination Without this property, a closed loop may exist

Permutation Switch Crossbar Point-to-point switch Constructed using controllable couplers Used for both permutation and generalized switches Point-to-point switch Banyan switch Clos switch Cost-effective permutation switch Benes switch

Clos switch

Benes switch (p=m=2)

Blocking Characteristics Rearrangeably non-blocking Complex routing algorithm Interrupt existing connections for new connection Wide-sense non-blocking Any connection pattern is possible with “intelligent algorithm” Strict-sense non-blocking Simple and most practical but not cost-effective # of switches in middle stage: m=2p-1

Optical Switches Compared to electronic switches, the size of optical switches is small (order of ten). Due to small computational overheads, rearrangeably and wide-sense non-blocking switches can be considered. Due to crosstalk problem, switch architectures may not have the minimum number of cross points.

Example 3x3 wide-sense nonblocking switch state-transition diagram

Generalized Optical Switch

s-d linear divider and combiner with 2x2 controllable couplers

Waveband-Space Switch Waveband-selective switch (WSS) Three stage realization Passive stages + dynamic stage (n!)m connection states for permutation Waveband-selective directional couplers Most simple structure Wavelength-selective cross-connect(WSXC) More generally, waveband-space-time switch

Wavelength Converters * (nm)! Connections with WC

Four Types of Wavelength Conversion Computer Communications & Switching Lab.

Wavelength Routing Switch with Add/Drop Computer Communications & Switching Lab.

* Derive the # of WSXCs and DFCs for general cases. WIXC implementation * Derive the # of WSXCs and DFCs for general cases.

Request Blocking in WDM Networks In case there is no wavelength conversion A B C D F E G l 1 3 2 Call blocking at node C Computer Communications & Switching Lab.

Computer Communications & Switching Lab. Wavelength Reuse Computer Communications & Switching Lab.

Network Access Station(NAS)

WADM-NAS Combination

TP and RP Convert logical signals to transmission signals for modulating lasers in electronic domain Subcarrier level modulation is often performed PSK and FSK for digital signals; AM and FM for analog signals Overlay processors Regeneration Wavelength conversion

Logical Network Overlay