QoT-aware Routing in Impairment-constrained Optical Networks · QoT-aware Routing in Impairment-constrained Optical Networks Jun He⁄, Ma¨ıte Brandt-Pearce´ ⁄, Yvan Pointurier?,

QoT-aware Routing in Impairment-constrained OpticalNetworks

Jun He∗, Maıte Brandt-Pearce∗, Yvan Pointurier?, Suresh Subramaniam+{jh2eu,mb-p}@virginia.edu, [email protected], [email protected]

∗Charles L. Brown Department of Electrical and Computer Engineering

University of Virginia, USA?Department of Electrical and Computer Engineering

McGill University, Montreal, Quebec, Canada+Department of Electrical and Computer Engineering

George Washington University, USA

Funded by NSF

IEEE GLOBECOM 2007November 28, 2007

IEEE GLOBECOM 2007ONSS04-2

Jun He∗, Maıte Brandt-Pearce∗ , Yvan Pointurier?, Suresh Subramaniam+

1/13

Background

I Wavelength routed all optical networks

¥ Circuit switched end-to-end optical channel or lightpath

¥ No optical-electrical-optical regenerators

¥ Advantages• Huge bandwidth,

• Transparency,

• Cost

• Wavelength reuse, etc.

¥ Applications• Backbone network, now being deployed in metropolitan area networks

• Large file transfer and E-science

¥ Problems• Routing and Wavelength Assignment

• Physical impairments in the physical layer

• Challenges to find a good route simultaneously considering both constraints



2/13

Research Motivation

¥ Previous works;

¥ The impact of physical impairments on RWA;

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adjacent−port( ( ( (( ( ( () ) )) ) )

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CH1 CH2 (crosstalk)CH2(λ2)

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CH1 (λ1)

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crosstalk fromLP3

CH1 (λ1)

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¥ Two QoT-aware routing schemes.

• Route admission control with impairment constraints.

• Routing incorporates impairments into the cost of routes.



3/13

BER Estimation Model

DC AG

Hop1

1Link

0 1 i n

DestinationA lightpath

i−1

Linki

Other spansOne spanSource

1

2

Si

Si

λ1, λ2, . . . , λm

12

. . .. . .

. . .. . .

¦ Dominant physical degradations

◦ Amplified spontaneous emission (ASE) noise from EDFAs;

◦ Linear crosstalk from OXCs and Demux;

◦ Nonlinear effect from four-wave mixing (FWM) and cross-phase

modulation (XPM);

◦ Shot noise and thermal noise.

¦ Power of impairments propagates to the next hop until arriving at receiver;

¦ Other linear/nonlinear impairments can be integrated in the model.



4/13

QoT-Aware Routing Algorithms

No

Block the request

threshold BER <

the requestAccept

A request arrives

Find the available path with theshortest distance, fewest hops,

the chosen wavelength

minimized measured Q factors, or lowest variance of noises for

BER estimation of the lightpathand other involved lightpaths

Choose a new wavelength based on wavelengthassignment algorithm, such as FF or RP

No free wavelength

Yes

¦ SD: find a route with shortest fiber length (decreasing link impairments);

¦ FH: find a route passing fewest intermediate nodes (decreasing node impairments);

¦ QM: the link weight is estimated by the average link degradation to the existing;

¦ LV: the link weight is estimated by the impairments variance on candidate wavelength.



5/13

Cost Functions in QoT-Aware Routing

• Routing with QoT constraints: the link weight doesn’t represent QoT

¦ The weight of hopi in Shortest distance routing (SD) is assigned asD(i) =

Length of linki;

¦ The weight of hopi in fewest hop routing (FH) is assigned asD(i) = 1;

• Routing based on QoT: the link weight considers QoT

¦ The weight of hopi in Q-maximizing routing (QM) is assigned as

D(i) =

PTil=1 10 log[Q(s)(i, l)/Q(d)(i, l)]

Ti; (1)

¦ The weight of hopi (if consideringλj) in routing based on least variance (LV) is

assigned as

W (i, j) = σ2XT (i, j) + σ2

NL(i, j) + σ2ASE(i, j) + αi; (2)

αi ⇐= max{αi + ∆α, αmax} if detecting wavelength blocking;

αi ⇐= min{αi −∆α, αmin} if detecting QoT blocking.



6/13

Simulation Settings

NY

CA1CO

MD

4

21

2

2

4

1

11

4

1

1 2

2

2

12

1

2

1

TX

1

MI

NJ

GA

CA2

UT

WA

NE

IL

PA

Topology of a downsized version of the NSF network with 14

nodes and 21 bidirectional links. The numbers on the links

represent number of spans along the link. Each span is70

km long.

Parameters Value

Number of Wavelength 32

Wavelength spacing 25 GHz

Data rate per channel 10 Gps

Fiber loss (Lf ) 0.2 dB/km

ASE factor(nsp) 1.5

Laser source power 0 dBm

ρ 0.95 A/W

BER threshold 10−12

Dispersion compensator 100% post

Chromatic dispersion 17 ps/nm/km

Nonlinearity constant 2.2 (W.m)−1

αmax 3× 10−10 A2

αmin 1× 10−10 A2

∆α 1× 10−11 A2



7/13

Blocking Probability vs Network Load if WA uses FF

120 140 160 180 200 220 24010

−5

10−4

10−3

10−2

10−1

100

Load, erlangs

Blo

ckin

g pr

obab

ility

FFwFRFFwSDFFwFHFFwQMFFwLV



8/13

Blocking Probability vs Network Load if WA uses RP

120 140 160 180 200 220 24010

−5

10−4

10−3

10−2

10−1

100

Load, erlangs

Blo

ckin

g pr

obab

ility

RPwFRRPwSDRPwFHRPwQMRPwLV



9/13

Blocking Probability vs Node Crosstalk if WA uses FF

(−30, −15) (−35, −20) (−40, −20) (−45, −25) (−50, −30)10

−4

10−3

10−2

10−1

100

(Xsw

dB, Xadj

dB)

Blo

ckin

g pr

obab

ility

FFwFRFFwSDFFwFHFFwQMFFwLV



10/13

Blocking Probability vs Node Crosstalk if WA uses RP

(−30, −15) (−35, −20) (−40, −20) (−45, −25) (−50, −30)10

−4

10−3

10−2

10−1

100

(Xsw

dB, Xadj

dB)

Blo

ckin

g pr

obab

ility

RPwFRRPwSDRPwFHRPwQMRPwLV



11/13

Conclusions and Future Work

I Current work

¥ We studied the impact of incorporating QoT constraints on theperformance of adaptive routing algorithms for wavelength-routednetworks.

¥ A new adaptive routing algorithm is proposed and compared with otherrouting algorithms.• New routing algorithm can effectively minimize the blocking probability.

• New routing algorithm only uses the state of the links between a node and its

neighbors.

. Future work◦ More network topologies and traffic patterns are applied to test the new routing

algorithm.

◦ QoT-aware WA algorithms can be applied to our adaptive routing algorithm to

further improve the performance.



12/13

Questions?



13/13

Documents

QoT-aware Routing in Impairment-constrained Optical Networks · QoT-aware Routing in Impairment-constrained Optical Networks Jun He⁄, Ma¨ıte Brandt-Pearce´ ⁄, Yvan Pointurier?,