traffic grooming for survivable wdm networks – shared protection

10/6/2003 Kevin Su ([email protected]) 1

Traffic Grooming for Survivable WDM Networks – Shared Protection

Kevin Su

University of Texas at San Antonio


Outline

• Introduction

• Motivation

• System Model– Grooming Node Architecture

– Network Model

• Proposed Schemes– Protection-at-lightpath (PAL) level

– Mixed protection-at-connection (MPAC) level

– Separated protection-at-connection (SPAC) level

• Heuristic Algorithms

• Performance Evaluation


Introduction

• WDM: stands for wavelength division multiplexing, it is a technology that divides the bandwidth of an optical fiber into many non-overlapping wavelengths, so that multiple communication channels can operate simultaneously on different wavelengths.– Increases the transmission capacity of optical fibers.

– Allows simultaneously transmission of multiple wavelengths within a single fiber.

– Up to 320 wavelengths per fiber; per wavelength, 10Gb/s, STS-192 (OC-192), today; expected to grow to 40Gb/s, STS-768(OC-768), soon.


Introduction

• Traffic Grooming: refers to problem of efficiently packing low-speed connections onto high-capacity lightpaths to better utilize network resourses. – The bandwidth requirement of a typical connection request is between

STS-1 (51.84 Mb/s) and STS-192(full wavelength)

• Protection: is a proactive procedure in which spare capacity is reserved during connection setup.– Working path: a path that carries traffic during normal operation

– Backup path: a path over which the connection is rerouted when a working path fails

– Single Failure (single-fiber failure, single-node failure) ---0---

---0------0---

– Dedicated Protection

– Shared Protection


Introduction


Motivation

• Survivable Traffic Grooming– Efficiently utilize the network resources (traffic grooming)

– A failure of a network element can cause the failure of several lightpaths, thereby leading to large data and revenue loss (protection)

• Static Case

• Dynamic Case


Grooming Node Architecture


Network Model

• A network is represented as a weighted, directed graph

G=(V, E, C, λ, P)– V: set of nodes

– E: set of unidirectional fibers (referred to links)

– C: the cost function for each link

– λ: the number of wavelengths on each link

– P: number of grooming ports at each node

• Connection request is represented as a quadruple <s, d, B, >– s: source node

– d: destination node

– B: bandwidth requirement

– : holding time

ht

ht


Proposed Schemes - PAL

• Protection-at-lightpath (PAL) level provides end-to-end protection w.r.t. lightpath. Under PAL, a connection is routed through a sequence of protected lightpath, or p-lightpath.

• A p-lightpath has a lightpath as working path and link-disjoint path as backup path

• Working path consumes a grooming-add port at the source node and a grooming-drop port at the destination node

• Backup path doesn’t consume any grooming port and wavelengths along a backup path are only reserved

• When working path fails, backup path is set up as a lightpath by utilizing the grooming ports previously used by the working path

• Two p-lightpaths can share wavelengths along common backup links if their working paths are link-disjoint.



• Initial network configuration • Edge represents bidirectional fiber, each fiber has 2 wavelengths• Wavelength capacity STS-192, every node has 3 grooming ports• c1<0,2,STS-12, t1>; c2 < 0,3,STS-3, t2>; c3 <4,3,STS-48, t3>



• After provisioning c1

• c1<0,2,STS-12, t1>; c2 < 0,3,STS-3, t2>; c3 <4,3,STS-48, t3>


Proposed Schemes – MPAC

• Mixed Protection-at-Connection (MPAC) level provides end-to-end protection w.r.t. connection. Under MPAC, a connection is routed via link-disjoint working path and backup path, each of which traverses a sequence of lightpaths.

• A lightpath traversed by a working path utilizes a portion of its capacity to carry traffic during normal operation

• A lightpath traversed by a backup path reserves part of its capacity for that backup path

• “Mixed” means that capacity of one wavelength can be utilized by both working paths and backup paths.


Proposed Schemes - MPAC




Proposed Schemes – SPAC

• Separated Protection-at-Connection (MPAC) level provides end-to-end protection w.r.t. connection. Under SPAL, a connection is routed via link-disjoint working path and backup path.

• A working path traverses a sequence of lightpath.

• A backup path traverses a sequence of links, each of which has judiciously reserved a number of wavelengths as backup resourses

• “Separated” means that the capacity of a wavelength can be utilized by either working paths or backup paths, but not both.


Proposed Schemes - SPAC




Proposed Schemes


Heuristic Algorithm

• It is NP-complete to provision a connection request with shared protection.

• The Author proposed heuristic for MPAC, SPAC, PAL

• MPAC– Backup-sharing measuring

Every lightpath is associated with a conflict set to identify the sharing potential between paths.

conflict set for lightpath can be represented as an integer set

{ } where represents the amount of traffic that will be rerouted on lightpath when link e fails. The amount of backup capacity reserved on lightpath is thus

– Route computation• Enumerates K candidate working paths

• For each candidate working path, computes a disjoint minimal-cost path as backup path based on some cost function

• Selects the path pair of minimal cost

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Heuristic Algorithm

• SPAC (the same as MPAC except)– Different backup-sharing measurement

– Different cost function in route computation

• PAL– Different backup-sharing measurement

– Route computation• Extend a stand shortest-path algorithm such that every hop along the resultant

shortest path corresponds to a p-lightpath, which can be either an exisiting p-lightpath or a new p-lightpath consisting of fresh wavelength links and free grooming ports


Performance Evaluation

• Connection-arrival process is Poisson process

• Connection-holding time follows a negative exponential distribution

• Capacity of wavelength is STS-192

• # of connection requests follows the distribution STS-1: STS-3: STS-12: STS-48: STS-192 = 300: 20: 6: 4 :1

• Load (in Erlang) is defined as connection-arrival rate times average holding time times a connection’s average bandwidth normalized in the unit of STS-192

• Number of grooming ports is set as # of wavelengths times its nodal degree times a scalar ( implies that any incoming wavelength to the W-Fabric can be dropped to the G-Fabric)

• The number of alternate paths K = 2

• Measurement metrics– Bandwidth-blocking Ratio

– Resource-Efficiency Ratio

1,10

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offeredbandwidthofamount

blockedbandwidthofamount


Network Topology

24-node example network topology



BBR versus network offered load with k =1,2 and 3


Conclusion and Future Work

• Investigate the survivable traffic-grooming problem in dynamic case– PAL, MPAC, SPAC

– Findings:• It is beneficial to groom working paths and backup paths separately as in

PAL and SPAC

• Separately protecting each individual connection yields the best performance when the number of ports is suffcient

• Protecting each specific lightpath achieves the best performance when the # of grooming ports is moderate or small

• Future work– Considering the residual connection holding time


References

• C. Ou, K. Zhu, H. Zang, L. H. Sahasrabuddhe, and B. Mukherjee. “Traffic Grooming for Survivable WDM Networks – Shared Protection”. Accepted to IEEE Journal of Selected Area in Communication 2004.

• H. Zhu, H.Zang, K. Zhu, and B. Mukherjee, “A novel, generic graph model for traffic grooming in heterogeneous WDM mesh networks” IEEE/ACM Trans. Neworking, vol.11 pp.285-299, Apr. 2003

traffic grooming for survivable wdm networks – shared protection

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