BALANCED RESOURCE SHARE MECHANISM

IN OPTICAL NETWORKS

Hyeon Park, Byung-Ho Yae

ETRI, Daejeon, South Korea,

Dong-Hun Lee, Sang-Ha Kim

Chungnam National University, Daejeon, South Korea

Keywords: Resources Share, SRLG, Optical Networks.

Abstract: Existing protection mechanisms to rapidly recover the failures allocate the backup path just SRLG-

disjointed with working path. However, these mechanisms have the low resource utilization because the

resource is not shared among the backup paths. To complement it, Kini (Kini et al., 2002), Somdip (Somdip

et al., 2001) and so on, have proposed the mechanisms to share the resources of the backup paths. Although

these mechanisms can improve the efficiency of bandwidth usage, those did not consider the unbalanced

resource share of backup paths. The backup paths can be centralized on the specific link so that the idle

resource is not used. As a result, as those do not use the resource efficiently the whole resource utilization is

not good. So we propose the mechanism to enhance the resources utilization as settling down the

unbalanced resource share to recover simultaneous failures. We formulate the problem to minimize the

number of the used backup resource (exactly, wavelengths) as considering the maximum link load. We

compare the existing mechanisms with our mechanism by the spare resource capacity as the result of the

simulation.

1 INTRODUCTION

Because the granularity of the optical connection is

coarser than that of the existing network, a single

fiber cut can potentially influence a total of 1.6 Tb/s

of traffic in optical networks. So, the fiber cut results

in the significant loss of traffic and thus the

survivability in optical networks is important.

The mechanism proposed by Kini can save

bandwidth by ensuring the sharing of the backup

path among all working paths with the same source

and destination node. And Somdip’s mechanism can

improve the efficiency of bandwidth usage by

pooling backup path capacity. However, the

resource of these mechanisms can be centralized on

the specific link so that the idle resource is not used.

So we propose the mechanism to enhance the

resources utilization as settling down the unbalanced

resource share. We formulate the problem to

minimize the number of the used backup resource

(exactly, wavelengths) as considering the maximum

link load.

In our mechanism, two-level SRLG for the

backup path selection is used: the first level, Low-

SRLG is for SRLG-disjoint path with its working

path, that is, for the backup path sharing decision

and the second level, High-SRLG is for the same

effect such as the threshold hop limit using the sub-

domain information of the working path. Besides,

this High-SRLG can be the information to eliminate

the link accommodated the unbalanced sharing

backup paths. For the balanced resource sharing

through two-level SRLG the backup paths are

allocated the same as the sub-domain of the working

path as much as possible.

We give the problem definition and Integer Linear

Programming ILP formulations. The ILP

formulation has much more time consumption and is

difficult to solve with increasing problem size. So,

we provide the heuristic algorithm of the proposed

resource shared mechanism and the backup path

selection algorithm and present experimental results.

Park H., Yae B., Lee D. and Kim S. (2006).

BALANCED RESOURCE SHARE MECHANISM IN OPTICAL NETWORKS.

In Proceedings of the International Conference on Signal Processing and Multimedia Applications, pages 97-100

DOI: 10.5220/0001571800970100

 SciTePress

2 RELATED WORKS

2.1 Single Link Failure Recovery

Mechanism (SFRM)

In general, most of the protection and restoration

mechanism consider the failure of just the single

component such as a link or a node. It is a typical

approach to provide the survivability.

In Somdip’s mechanism, when a failure occurs in

the SRLG and the restoration protocol for the

corresponding lightpaths’ activation of the

restoration channels RCs on backup path starts to be

processed, the mechanism finds primarily available

RCs in the pool and uses them for the restoration.

2.2 Multiple Link Failures Recovery

Mechanism (MFRM)

In the real world, in general, several failures in an

optical network occur simultaneously. The

mechanisms for the multiple failures consider the

working/back-up paths with the same source and

destination node.

Doucette proposed the design formulation and

procedure for the planning any span-restorable

network for a known set of SRLGs. And it showed

how total capacity depends on the relative number or

frequency of co-incident SRLGs and quantified how

the type of SRLG will impact design costs. That is,

it emphasizes which SRLG is the most deleterious to

network efficiency. However, because SRLG is

configured at the start of the network initialization

the co-incident SRLGs depends on the network plan

including the placement of SRLGs.

3 PURPOSE OF THE PROPOSED

MECHANISM

Fig. 1 describes why the network needs to

accommodate the balanced sharing backup paths.

All backup paths are allocated to disjoint their

working paths. Fig. 1 (a) represents the backup paths

are not shared on the same wavelength between

node 5 and 6. Therefore, the resources are wasted. In

case of Fig.1 (b), although b1 and b2 share the

wavelength it still wastes the resources due to b3. If

1 fiber accommodates 2 wavelengths, Fig. 1 (b)

needs two fibers. However, if the backup paths are

decentralized to the wavelength in use, the above

resource constraint is fulfilled and the Fig. 1 (c)

satisfies this condition.

As a result, our purpose is to minimize the number

of the wavelength used for the backup path in the

network.

W1 W3

b3b1 b2

Node 2-Node3

W1:

W3 :

Node 5-Node6

b1:

b2 :

b3 :

W4 :

No d e 7- Node 8

b4:

W2 :

W1 W3

b3b1 b2

Node 2-Node3

W1:

W3 :

Node 5-Node6

b1:

b2 :

b3 :

W4 :

No d e 7- Node 8

b4:

W2 :

(a) Unshared backup paths

W1 W3

b3b1,b2

No de 2- No de 3

W1:

W3 :

No de 5- Node 6

b1,b2:

b3 :

W4 :

No de 7- Node 8

b4:

W2 :

W1 W3

b3b1,b2

No de 2- No de 3

W1:

W3 :

No de 5- Node 6

b1,b2:

b3 :

W4 :

No de 7- Node 8

b4:

W2 :

(b) Shared backup paths without considering

maximum link load

W1 W3

b1,b2

b3,b4

Node 2-Node3

W1:

W3 :

Nod e 5-No de 6

b1,b2:

W4 :

Nod e 7-No de 8

b3,b4:

W2 :

W1 W3

b1,b2

b3,b4

Node 2-Node3

W1:

W3 :

Nod e 5-No de 6

b1,b2:

W4 :

Nod e 7-No de 8

b3,b4:

W2 :

(c)

Proposed Shared backup paths with considering

maximum link load

Figure 1: The resource (wavelengths) sharing in the

network.

4 PROBLEM DEFINITION AND

BACKUP PATH ALGORITHM

4.1 ILP Formulations

The proposed mechanism includes two level SRLG,

Low-SRLG and High-SRLG. Low-SRLG means a

group of links that are subject to a common risk,

such as a conduit cut. High-SRLG is defined to

select the backup path closed to its working path due

to the hop counts or the link length. In addition to

the link length, High-SRLG is defined to avoid the

unbalanced link load due to the concentrated sharing

in a link. Thus, this High-SRLG is defined into the

geographical region as a domain concentrated with

the network nodes.

We formulate the problem to minimize the used

resource. We consider the SRLG information (two-

level SRLG) to select the backup paths. We give the

ILP formulation to provide optimal solution as

follows: The objective function equation (1)

SIGMAP 2006 - INTERNATIONAL CONFERENCE ON SIGNAL PROCESSING AND MULTIMEDIA

APPLICATIONS

minimizes the sum of the number of wavelengths

(w) used for backup paths (B) on the link i, j

between source s and destination d.

∑∑∑

ijw

sd ij w

Objective

MIN B

(1)

For the objective function the constraints are as

follows:

(2) The number of backup paths is the same as the

number of working paths in the network. (It

means that there are the source and terminal

node over its paths in the network whether the

distance of the paths is long or short.)

(3) The total link capacity (the number of

wavelengths) in link i,j is greater than the total

number of wavelengths used for backup paths in

link i,j.

(4) The backup path is conserved at each link along

the path (In case of the working path, this

constraint is not necessary).

(5) The spare capacity in the link i,j is that one

subtracted the working path capacity (the

number of wavelengths used for the working

paths) from the total capacity in the link i,j.

Subjects to:

∈

⋅= = ∀ = ≠ ≠

∀

=≠≠ =

∑∑∑ ∑∑

,, ,

,,(,),

(,),

sd w sd

ijw uvw b b b

sd ij w W uv w

pp p p

B P P P iji sit js

uv u s u t v s v t

(2)

≤∀=

∑∑ ∑

max max

., (,),

sd sd

ijw ij ijw

sd w ijw

BLC ijL IntB

(3)

ββ

⋅− ⋅ = ∀ ≠ ≠

∑∑ ∑∑

(, ) ( ,)

0, , , ,

sd w sd w

ijw jiw b b

jij w i ji w

BB sdisit

(4)

ββ

⋅− ⋅= ∀ = ≠

⋅− ⋅=− ∀ ≠ =

≤=− ∀

∑∑ ∑∑

(, ) ( ,)

1, , , ,

,,(,)

sd w sd w

ijw jiw b b

jijw ijiw

sd w sd w

iw jiw b b

jijw ijiw

sd sd

ijw ij ij ij ijw

sd w w

BBsdisit

BB sdisit

BS SC P ij

(5)

In addition to single failure, the constraint for dual

failures is considered as shown in Fig. 2. The link cd

on the backup path p1 is simultaneously failed when

the link ij on the backup path B1 of the working path

w1, B2, and B3 is failed. For the previous objective

function, the constraint of the dual failures is as

follow:

Γ≤ ∀ ∀

∑∑

i ,(,),(,)

sd ab

ijw ijw ij

sd w

BSijab

(6)

(6) There is enough spare capacity to recover the

dual failures (two links or two paths at once. (If

the required capacity (at the left side) is greater than

the spare capacity, it is infeasible. For example, if 3

backup paths share the wavelength w, to recover the

failure of the link (i,j) 3 wavelengths are needed in

link (a,b)).

≤≤

constant

: The total number of wavelengths oneach link and 1 .

: The total link capacityunits(totalwavelengths)on thelink ( , ).

: The working path with wavelength w on the link( , ).

,:T

uvw

Notation

wwW

he starting or terminal nodeof the working path p.

variable

: 1, if the backup path for a working path( , )uses

wavelength in link(i,j), 0, otherwise.

: The inverse of the number of the backup paths

ijw

Bsd

λβ

≤≤

sharing

the wavelength w, (1 )

(If 3 backup paths share wavelength ,then is 1/

: Spare capacity(the number of wavelengths)on thelink ( , ).

:The number of backup paths sah

ijw

Sij

ring the wavelength w link (i,j)

The number of wavelength needed to recover the backup paths

in link (a,b)

, : The starting or terminal nodeof the backup path b.

Figure 2: Simultaneous link failures in the network.

4.2 Algorithm for Backup Paths

The working path and the backup path are basically

selected based on Low-SRLG mechanism like

Somdip’s mechanism. In addition to Low-SRLG, the

High-SRLG (Fig. 3) is added in the proposed

mechanism. The backup paths is selected the same

as the sub-domain of the working path as much as

possible.

Figure 3: Backup path selection algorithm : Low-SRLG

and High-SR LG based.

cur_connection : current connections

WP_list : the link list of the selected working paths

accept_region = find_region() //find the whole sub-domains

on the working path //find the rest sub-domains

not_accept_link_list =

find_not_accept_region (accept_region)

// disable the links on the rest of the working paths

set_link_disable(not_accept_link_list)

result = find_Low_backup()//applies the Low-SRLG

algorithm

if result == fail

then set_link_enable(not_accept_link_list) //discharges the

sub-domains

find_Low_backup()

end if

set_link_enable(){

for bk_link // for all backup links

if (backup Path == share)//check the backup path with the

others

then increase band-width of backup links

else not increase band-width of backup links

increase simultaneous two failures count

end for }

BALANCED RESOURCE SHARE MECHANISM IN OPTICAL NETWORKS

5 SIMULATION RESULTS

We assumed that the working path of the proposed

mechanism is selected by the shortest. The test

network model is consisted of 7 sub-domains, 39

nodes and 69 links. The nodes from the node

number 1 to 18 are used as a source node and the

nodes from the node number 19 to 39 are used as a

destination node.

For the comparison, we simulated the algorithm for

the Somdip’s mechanism represent by Low-SRLG

algorithm, without considering unbalanced link load.

And High-SRLG algorithm means the proposed

mechanism with considering unbalanced link load

by High-SRLG identification. We setup 50

connections, 1connection a unit time. And it is

repeated 50 through 100 times. We suppose the

shortest working and backup paths. We considered

the following cases.

Static path selection: predefined working paths and

backup paths for the simultaneous two failures : Fig. 4

: The resource usage of working/backup paths

by Low-SRLG algorithm/by High-SRLG algorithm

Dynamic (Random) path selection: dynamically select

working paths and backup paths for the simultaneous two

failures : Fig. 5

: The resource usage of working/backup paths

by Low-SRLG algorithm/by High-SRLG algorithm

As shown Fig. 4, the High-SRLG algorithm

compared with the Low-SRLG can distribute more

resource in case of the dynamic connection. That is,

the number of non shared backup paths in case of

High-SRLG is 216 and Low-SRLG is 184. In Fig. 5,

the high-SRLG algorithm also can distribute more

resource in case of static connection

# of Label

Link ID

Hi g hSRL G

LowSRLG

Figure 4: The resource usage of working paths/backup

paths: Low-SRLG/High-SRLG algorithm under Random

Connections.

1010

11 1

8 88

11 111

# of Label

Link ID

HighSRLG

LowSRLG

Figure 5: The resource usage of working paths/backup

paths: Low-SRLG/High-SRLG algorithm under Static

Connections.

6 CONCLUSIONS

In this paper, we proposed the shared resource path

provisioning mechanism to guarantee the

survivability. We presented the capacity design

method and the optimization model to improve the

link utilization and simulated to measure the

resource utilization of the proposed mechanism.

REFERENCES

S. Kini et al., 2002. Shared backup Label Switched Path

Restoration. IETF Internet-draft, draft-kini-

restoration-shared-backup-00.txt, November 2000.

S. Datta et al., 2001. Efficient Channel Reservation for

Backup Paths in Optical Mesh Networks,

Proceedings of GLOBECOM.

S. D. Maesschalck et al., 2001. From Network Design to

Dynamic Provisioning and Restoration in Optical

Cross-Connect Mesh Networks: An Architectural and

Algorithm Overview, IEEE Commun. Mag., vol.39,

no. 1, Jan. 2001, pp.42-49.

Y. Ye et al., 2001. A Simple Dynamic Integrated

Provisioning/Protection Scheme in IP over WDM

Networks, IEEE Commun. Mag., Nov. 2001, pp. 174-

182.

J. Doucette et al., 2002, Capacity design studies of span-

restorable mesh transport networks with shared-risk

link group (SRLG)effects, Proveedings SPIE Optical

Networking and Communications Conference

(OptiComm 2002), Boston, MA, July-August 2002.

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