Efficient Algoirthms for Routing Dependable Connections in WDM

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Efficient Algoirthms for Routing Dependable Connections in WDM Optical Networks G. Mohan, C. Siva

Efficient Algoirthms for Routing Dependable Connections in WDM Optical Networks G. Mohan, C. Siva Ram Murthy, and Arun K. Somani Speaker: Jun-Ying Ye P 76921269

Outline n n n Restoration Schemes Primary-backup Multiplexing Estimating Function Performance Study Conclusion

Outline n n n Restoration Schemes Primary-backup Multiplexing Estimating Function Performance Study Conclusion

Network Survivability n n n A very important aspect of modern networks Restoration =

Network Survivability n n n A very important aspect of modern networks Restoration = function of rerouting failed connections Survivability = property of a network to be resilient to failure n Requires physical redundancy and restoration protocols.

Reactive / Proactive Reactive n n n A search is initiated to find a

Reactive / Proactive Reactive n n n A search is initiated to find a new lightpath which does not use the failed components after the failure happens. It can not guarantee successful recovery, Longer restoration time Proactive n Backup lightpaths are identified and resources are reserved at the time of establishing the primary lightpath itself. Taxonomy n n 100 percent restoration Faster recovery

Path / Line Based Protection n n Path-Based : Restoration is handled by the

Path / Line Based Protection n n Path-Based : Restoration is handled by the source and the destination. Line-Based : Restoration is handled by the nodes adjacent to the failure.

Restoration Techniques n Dedicated Back (1+1, 1: 1) n n n One primary lightpath

Restoration Techniques n Dedicated Back (1+1, 1: 1) n n n One primary lightpath have one backup lightpath. Pros: simple for implementation and fast restoration Cons: waste of bandwidth

Restoration Techniques /cont. n Backup Multiplexing (1: N) n n Allows two or more

Restoration Techniques /cont. n Backup Multiplexing (1: N) n n Allows two or more backup lightpaths to share a channel if the corresponding primary lightpaths do not fail simultaneously. Pros: better network utilization.

Restoration Techniques /cont. n Primary-Backup Multiplexing n n n Allows a primary lightpath and

Restoration Techniques /cont. n Primary-Backup Multiplexing n n n Allows a primary lightpath and one or more backup ligthpaths to share a channel. Pros: Best network utilization. Cons: Not 100 restoration guarantee.

Primary-Backup Multiplexing Routing Algorithm n Preliminaries and Definitions n n Alternate routing method. Let

Primary-Backup Multiplexing Routing Algorithm n Preliminaries and Definitions n n Alternate routing method. Let K be a predefined constant denoting the maximum number of candidate routes for any s-d pair. Let H be the hop length of the longest candidate route. Proactive path-based failure-independent lightpath restoration.

Primary-Backup Multiplexing Routing Algorithm /cont. n Preliminaries and Definitions /cont. n n A wavelength

Primary-Backup Multiplexing Routing Algorithm /cont. n Preliminaries and Definitions /cont. n n A wavelength on a fiber is referred to as a channel. A channel which is not currently used by any primary or backup lightpath is called a f-channel. A channel which is being used by a primary lightpath is called a p-channel. A channel which is being used by a backup lightpath is called a b-channel.

Primary-Backup Multiplexing Routing Algorithm /cont. n Preliminaries and Definitions /cont. n n n A

Primary-Backup Multiplexing Routing Algorithm /cont. n Preliminaries and Definitions /cont. n n n A channel which is being shared by a primary lightpath and one or more backup lightpaths is called a pb-channel. A D-connection which backup lightpaths use a pb-channel lose their restoration capability is called a orphan. A p-channel used by a primary lightpath of an orphan is called as a weak channel.

Description of the algorithm for LAO (Limited Average Orphans) n n When a new

Description of the algorithm for LAO (Limited Average Orphans) n n When a new request arrives for a Dconnection <Lp, Lb> is admissible and its cost is minimum. If the average number of orphans per link does not exceed a predefined orphan threshold value T, we say is safe state.

Cost Function for primary lightpath n n n The cost of using an f-channel

Cost Function for primary lightpath n n n The cost of using an f-channel is one. The cost of using a b-channel is zero and the b-channel becomes a pbchannel. The cost of using a pb-channel or pchannel is infinity.

Cost Function for backup lightpath n n n The cost of using an f-channel

Cost Function for backup lightpath n n n The cost of using an f-channel is one. The cost of using a p-channel is zero and the p-channel becomes a pb-channel. The cost of using a set of backup lightpath S is zero, only if the primary route of Lp is linkdisjoint with the primary route of each and every backup lightpath in the set S.

Cost Function n CD(Lp, Lb)=Cp(Lp) + Cb(Lb, Lp) + Penalty. Cost Nd Such the

Cost Function n CD(Lp, Lb)=Cp(Lp) + Cb(Lb, Lp) + Penalty. Cost Nd Such the cost of a lightpath with no pbchannels is less than N, the value of Penalty. Cost may be chosen to be 2 N. Nd is the number of pb-channels on both the primary and backup lightpaths.

Admissibility Test function Test(Lp, Lb) : boolean begin x = X(Lp) y = Y(Lp,

Admissibility Test function Test(Lp, Lb) : boolean begin x = X(Lp) y = Y(Lp, Lb) if Lorp + x + y > T then return false Lorp = Lorp + x + y return true end

Admissibility Test /cont. n n If Lp has at least one pb-channel, then the

Admissibility Test /cont. n n If Lp has at least one pb-channel, then the number of weak channels(m) induced by Lp is computed using the estimator function X(Lp) = m/L

Admissibility Test /cont. n n If the backup lightpath Lb has at least one

Admissibility Test /cont. n n If the backup lightpath Lb has at least one pb-channel, then the channels used by the primary lightpath Lp are made weak. function Y(Lp, Lb) = h/L, where h is the hop length of Lp

Estimating The Number Of Orphans n Needed Information n n Let ni be the

Estimating The Number Of Orphans n Needed Information n n Let ni be the number of backup lightpaths multiplexed onto edge i. Let mi be the number of back lightpaths that use edge I and continue to the next edge i+1 edge i v ni edge i+1 mi

Estimating The Number Of Orphans /cont. n Computing the N(Bp) n Let Bp is

Estimating The Number Of Orphans /cont. n Computing the N(Bp) n Let Bp is the set of distinct backup lightpaths that use some channels of a primary lightpath Lp. Lb 1 Lb 2 Lb 3 Lp

Computing the N(Bp) /cont. n Let ei, 0<i<H be the number of backup lightpaths

Computing the N(Bp) /cont. n Let ei, 0<i<H be the number of backup lightpaths that use edge i and do not use any of the edges 0 through i-1.

Computing the ei n n Let ti be the number of backup paths that

Computing the ei n n Let ti be the number of backup paths that use some edge j<i, use edge i, but do not use any of the edges j+1, j+2, …, i-1. ei=ni-ti-mi-1 Lb 1 edge i Lb 2 Lp

Computing the ti n Let kj, i be the number of backup paths that

Computing the ti n Let kj, i be the number of backup paths that use edge j and use edge i without using any of the edges j+1, j+2, …, i-1.

Computing the kj, i n n Kj, i = total no pass j+1, …,

Computing the kj, i n n Kj, i = total no pass j+1, …, i-1 through i Part 1 : total n Let kj be the number of backup paths that use edge j, but do not continue to the next edge j+1. Therefore, kj = nj – mj.

Computing the kj, i /cont. n Part 2 : no pass j+1, …, i-1

Computing the kj, i /cont. n Part 2 : no pass j+1, …, i-1 n n Let an arbitrary path Lb among the kj paths traverse X edges, excluding the edges incident on v, to append edge i. The probability r = X/(L-(D+I)). j I edges D edges X edges i Lp

Computing the kj, i /cont. n Part 3 : through i n Let qi

Computing the kj, i /cont. n Part 3 : through i n Let qi denotes the probability that a backup path on edge i does not enter from edge i 1, then it is calculated as qi = (ni – mi 1)/ni, for ni 0, otherwise qi=0.

Computing the Number of Weak Channels n Definition n A b-channel is said to

Computing the Number of Weak Channels n Definition n A b-channel is said to cover a p-channel if the primary lightpath that uses the pchannel has a backup lightpath that uses the b-channel. Lp 3 1 5 2 4 6 Lb 7 8 9

Computing the Number of Weak Channels /cont. n n Let ni be used to

Computing the Number of Weak Channels /cont. n n Let ni be used to denote the number of p-channels covered by edge i. Let mi be used to denote the number of p-channels covered by edge i and edge i+1.

Estimate Function n function Estimate(Lp) : Given a path Lp with h edges and

Estimate Function n function Estimate(Lp) : Given a path Lp with h edges and their n and m values. n Step 1) e 0=n 0 ; e 1=n 1 -m 0 ; val=e 0+e 1 k 0=n 0 -m 0 ; k 1=n 1 -m 1 S 0=k 0 ; S 1=k 0+k 1

Estimate Function /cont. n Step 2) For i=2 to h-1 do begin If ni=0

Estimate Function /cont. n Step 2) For i=2 to h-1 do begin If ni=0 then qi=0 else qi=(ni-mi-1)/ni ti=r qi Si-2 ei=ni-ti-mi-1 val=val+ei ki=ni-mi Si=Si+ki end

Estimate Function /cont. n Step 3) return val

Estimate Function /cont. n Step 3) return val

The Constant Value j I edges D edges X edges i Lp

The Constant Value j I edges D edges X edges i Lp

Performance Study n 21 -nodes and 26 -duplex links APRA-2 network. Every simplex link

Performance Study n 21 -nodes and 26 -duplex links APRA-2 network. Every simplex link is assumed to have eight wavelengths. n n X = 4 and D+I = 6. 16 -nodes and 32 -duplex links Meshtorus network. Every simplex link is ssumed to have eight wavelengths n X = 3 and D+I = 5.

Performance Metrics

Performance Metrics

Performance Metrics

Performance Metrics

Performance Metrics /cont.

Performance Metrics /cont.

Conclusion n n Efficient algorithm is to achieve significant gain in network blocking performance.

Conclusion n n Efficient algorithm is to achieve significant gain in network blocking performance. 90% performance gain at the expense of less than 10% reduction in restoration guarantee, under light load conditions.