Experimental Demonstration of Adaptive ... - Optics InfoBase

CAI et al.: EXPERIMENTAL DEMONSTRATION OF ADAPTIVE COMBINATIONAL QOT 667

for each demand in

do

— find possible restoration choices and calculate

their required modulation format and

bandwidth.}

while (

is not empty)

— for each demand in do

— calculate the value **of** and for each

choice}

— find the choice with the smallest in ;

— accommodate this choice and delete the

corresponding demand from ;

— update the set **of** choices for each demand left.

Table 1. The Hybrid Objective Algorithm

B. Simulation Results for the Hybrid Objective Algorithm

We evaluate the networking performance **of** ACQR with the

hybrid-objective algorithm in comparison with the conventional

rerouting-based method, which reroutes the flexpath onto the

shortest link-disjoint path available. The simulation is based on

the COST266 Pan-European network topology shown in Fig. 5

[22], where the point-to-point traffic in the demand matrix is

generated according to a normal distribution and the working

paths originally routed by the shortest-path algorithm. We assume

that impairments occur with a uniform probability on each

link. Upon occurrence, the CP with ACQR would perform MFS

or LR on the affected flexpaths. In the simulation, it is assumed

that MFS needs to reduce the SE **of** a flexpath by a factor **of** 2 in

order to restore the QoT to an acceptable level, whereas in the

LR case, the modulation format and bandwidth required depend

on the new path’s distance: we assume that each time when

doubles, the SE would need to decrease by a factor **of** 2. The

simulation results in Fig. 7 show that ACQR significantly reduces

the BP compared with the rerouting method (as much as

10 dB when and %). Specifically, as we have

projected, ACQR with has even better BP performance

than that with , where the interference penalty is not considered.

In addition, ACQR also greatly reduces the spectrum

consumption on the rerouting links (see Fig. 6). This is due to

the fact that ACQR would effectively utilize the spectrum **of** the

impaired link rather than abandon it, which in return helps relieve

the burden **of** rerouting links and reduce the BP.

Fig. 5. Pan European Network for simulation topology.

Fig. 6. SC versus network spectrum utilization when using ACQR with

and .

IV. NETWORKING TESTBED EXPERIMENT

A. Experiment Arrangement

Fig. 8 shows the network testbed setup. There are four nodes

inthenetwork.Nodes1and2areingress nodes, which are implemented

with transmitters and WSSs. Specifically, node 1 is

a1 2WSSandnode2is2 2 WSS made up **of** two 1 2

WSSs. These WSSs operate in 5 THz bandwidth with 7 dB insertion

loss. The channel bandwidth and center frequency are

tunable with 3.125 GHz granularity and the minimum channel

Fig. 7. BP versus network spectrum utilization when using only rerouting and

ACQR with and .

bandwidth is 50 GHz. Node 3 is a passive node and is implemented

by a 2 2 coupler. Node 4 is the egress node and has