Wavelength Assignment in Waveband Switching Networks with Wavelength Conversion

Xiaojun Cao; Chunming Qiao; Anand, V. Jikai LI

GLOBECOM '04. IEEEVolume 3, 29 Nov.-3 Dec. 2004 Page(s):1943 - 1947 Vol.3

Reporter: Chia-Nung Wang

2

Outline

Introduction Wavelength conversion in WBS

networks Waveband Assignment with Path-

Graph (WAPG) Performance evaluation Conclusion

3

Introduction (1/5) Optical network employ WDM to meet the hig

h bandwidth requirement. Waveband switching (WBS)

Wherein wavelengths are grouped in to band and switched as a single entity.

Demultiplex the band to switch individual wavelength only when some traffic needs to be added/dropped.

It can reduce cost and complexity of switching nodes by minimizing the port count.

4

Introduction (2/5) Recently, WBS in conjunction with ne

w Multi-Granular Optical Cross-connection (MG-OXCs).

An MG-OXCs that can switch traffic at fiber, waveband and wavelength granularities.

The overall port counts of the MG-OXCs can reduced by using WBS.

5

Introduction (3/5) Wavelength converter can efficiently

reduce the blocking probability of Wavelength routed networks.

But wavelength converter is expensive and can result in degradation of signal quality.

Hence, sparse placement of limited number of wavelength converters and limited-range wavelength converters is recently researches.

6

Introduction (4/5) There are three unique issues related to wavel

ength conversion in WBS networks. Request blocking may come from not only the limit

ed number of wavelengths, but also the limited number of ports at the MG-OXCs.

One may use intra-band wavelength conversion which is different from limited-range wavelength conversion.

Performing wavelength conversion requires all the wavelengths in a band to be demultiplexed and hence consuming more ports, which in turn, may result in blocking of future requests.

7

Introduction (5/5)

In this paper, author develop a novel algorithm called Waveband Assignment with Path-Graph (WAPG).

Author also apply the WAPG algorithm to WBS networks using MG-OXCs with varying port count and Wavelength Conversion capability.

8

Wavelength Conversion in WBS networks

Describe the architecture of MG-OXC and discuss different wavelength conversion technologies.

Reconfigurable (Flexible) MG-OXC architecture: Similar to a static (non-reconfigurable) MG-OXC, it includes: Fiber cross-connect (FXC). Band cross-connect (BXC). Wavelength cross-connect (WXC).

9

Reconfigurable MG-OXC architecture (1/2)

Wadd

INPUT

INPUT

INPUTOUTPUT

OUTPUT

OUTPUT

WdropBaddBdrop

FdropFadd

Band to Wavelength demultiplexers

Wavelength to Band multiplexers

Band to Fiber multiplexers

Fiber to Band demultiplexers

Z: The number of incoming fibers

Y: The number of BXC ports from FTB

10

Reconfigurable MG-OXC architecture (2/2)

This MG-OXC architecture is reconfigurable (and hence flexible) in that : any [αZ] fibers can be demultiplexed into bands. any [βY] of these bands can be demultiplexed into

wavelengths. Here, we set:

α=1 to allow any fiber to be demultiplexed to bands. Β<1 allowing only a limited number of bands to be

demultiplexed into wavelengths simultaneously.

11

Wavelength Conversion (1/2)

Wavelength conversion can be full or limited-ranged.

In original limited-range wavelength conversion: A wavelength can be converted only to a subs

et of wavelength. e.g, wavelength λ can only be converted to th

e wavelength within the range [λ-δ, λ+δ].

12

Wavelength Conversion (2/2)

A dedicated number (d≦X) of wavelength converters are associated with each outgoing link.

(For WBS networks) Intra-band wavelength conversion: Where a wavelength can only be converted to a

ny other wavelengths in the same band. For example, if band size is 3, w1, w2, w3 are in

the same band b1, then w3 can only be converted to w1 or w2.

13

Waveband Assignment with Path-Graph (WAPG)

At first, we assume that: The existing connection are not re-arrangeable. The heuristic algorithm is base on the layer-gra

ph approach. Fixed routing (shortest path first), is used in WB

S networks with intra-band wavelength conversion.

The algorithm can be applied to different wavelength conversion and routing scheme.

14

WAPG Parameter setting:

A lightpath request using path l that s=s0s1s2, …sisi+1, …sn=d.

H is the number of hops along the path. Each link has X wavelength, partition into B bands,

each consisting of W wavelength. b is the index of waveband set £ ={1, 2, ...[X/B]}. Then wavelength 1≦λ ≦X belongs to band b=[λ/B].

15

WAPG algorithm (1/5)

16

WAPG algorithm (2/5)

17

WAPG algorithm (3/5)

18

WAPG algorithm (4/5)

19

WAPG algorithm (5/5) According to the way we set the weigh

t of each link, Dijkstra algorithm will: First try to find a wavelength-continuous

lightpath . Then try to find a non wavelength contin

uous path using minimum number of wavelength converter.

Here will compare WAPG with FirstFit and RandomFit algorithm.

20

Performance evaluation (1/5)

Assume that the traffic and topology is : Uniformly distributed to all node pairs In the USANet topology with 46 nodes and

76 links. The lightpath requests arrive according to

Poisson process. Every link has one bi-directional fiber, each

fiber has 20 bands and each band has 4 wavelength.

21

Performance evaluation (2/5)

Focus on the blocking probability and the number of used wavelength converters.

Above USANet with or without wavelength converter, we use: NWC: Without any wavelength converter. IWC: Maximum number of intra-band wavelength c

onverters. FWC: Maximum number of full wavelength converte

rs. LWC: Limited number of full wavelength converters.

22

Performance evaluation (3/5)

When β=1 :

23

Performance evaluation (4/5)

When β=0.75 :

24

Performance evaluation (5/5)

RandomFit is ill-suited for this networks: It assign the wavelength randomly and does not t

ake waveband grouping into consideration. It consumes a large number of wavelength conver

ter. FirstFit :

The sequentially assignment helps in wavebanding and reducing the number of used ports and blocking probability.

But it does not minimize the number of wavelength conversion.

25

Conclusion In this work, author have developed an

efficient heuristic algorithm call WAPG. The WAPG has been applied to the case with

full WC, intra-band WC and limited WC to accommodate fully dynamic traffic.

WAPG is significant better in terms of minimizing the number of used wavelength converters and outperforms than others in terms of blocking probability.

26

Thanks for listening!!