mesh restorable networks with multiple quality of protection classes

Mesh Restorable Networks with Multiple Mesh Restorable Networks with Multiple Quality of Protection ClassesQuality of Protection Classes

Wayne D. Grover, Matthieu ClouqueurWayne D. Grover, Matthieu [email protected], [email protected]@trlabs.ca, [email protected]

TRTRLabsLabs and University of Alberta and University of Alberta

Edmonton, AB, CanadaEdmonton, AB, Canada

ICOCN 2002, ICOCN 2002, November 11-14, Singapore November 11-14, Singapore

Wayne D. Grover and Matthieu Clouqueur ICOCN ‘02 Singapore 2

Motivation and BackgroundMotivation and Background

• “one grade of protection for all” doesn’t necessarily fit the

customer needs or service provider wishes.

• Prior work on survivable network design almost exclusively

considered 100% restorable single class of service.

• Now consider multiple “Quality of Protection” options.

• Most important properties and insights:

– Mesh restorable networks with no spare capacity

– A premium service class with better than 1+1 availability

– Overall design capability to support highly differentiated service

classes in an economic mesh-based network.


Define Some terms ...Define Some terms ...

QoP - is like QoS but refers to different “Qualityof Protection” service classes.

R1 - a class of service path that is assured of single span failure restorability

-the average level of single failure restorability of a network as a whole

R2 - a class of service path that is assured of restorability to any dual span failure

- the average level of dual failure restorability of a network

spare capacity

- the shared but idle standby capacity of a mesh network that is used to protect services from different failure scenarios


““multi-QoP” service paradigm :multi-QoP” service paradigm :

gold Assured single-failure restorable (R1 service)

Define the following “multi-QoP” service paradigm :

silver Best-efforts restorability

bronze Unprotected service

(economy)

Preemptible unprotected service

Gold and silver may both preempt economy service capacity but silver only does so after all of gold’s requirements are met.


Structure of the Mathematical Model ...Structure of the Mathematical Model ...

Minimize {total cost of capacity installed}

subject to:

- (a) all gold, silver, bronze and economy service demands are

routed and assigned working capacity.

- (b) on any span failure working capacity assigned to gold service paths is 100% restorable

- (c) on every other span the sum of the spare capacity plus and economy capacity is sufficient to support the largest restoration flows needed for (b)

- (optionally) working and spare capacities assigned to each

span fit under a limited set of available modular capacities.


Now consider the following “multi-QoP” service mix:Now consider the following “multi-QoP” service mix:

(economy)

gold 55 %

15 %

30%

silver

bronze


Test Networks ...Test Networks ...

..on every O-D pair in the following test networks ….

Each node pair has 20 lightpath demands : 11 gold (55%), 3 silver-bronze (15%), 6 economy (30%)

(a) (b) (c)


Main Findings ...Main Findings ...

There is no spare capacity needed. (!)

• Restoration requirements for the 55% gold service class are fully met by preemption of economy class services. • Silver class services enjoy ~ 40-50% best efforts restorability.

• Any given economy service path can expect to be disrupted in 12 to 14 % of all failures.


Significance ...Significance ...

• Such network designs are “fully survivable” in the usual sense (for 55% of the customers) but there is no unused standby capacity.

--> All capacity is earning revenue at some level or other.

• Such flexible, highly efficient “multi-QoP” capabilities may turn out to be the most commercially significant advantage (the “killer app”) for mesh-based transport networking.


Wider Study of multi-QoP Design...Wider Study of multi-QoP Design...

Considers four multi-service demand scenarios for testing :

All designs based on span restoration mechanism with hop limit of fiveDesigns are “ jointly optimized” : (-> routing of gold and economy paths are synergistic decisions.) Mathematical model minimizes total capacity cost

economy 30%

gold 55%

silver- bronze 15%

30%

15%

55% 55%

30%

15% 30%

55%

15%

Scenario A: Mostly gold & economy

Scenario B: Most ly economy

Scenario C: Mostly best-efforts

Scenario D: Mostly gold & best-efforts


Sample Results (Study of multi-QoP Design...Sample Results (Study of multi-QoP Design...

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All Gold Mostly Gold Mostly Economy Mostly Best-Efforts Mostly Gold andBest-Efforts

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Gold R1 Silv R1 Econ P(pre) Prop. Preem p. Gold Prop. Preem p. Silv

(Results for network 25n50s1)

Conventional “all gold” design“working”

“spare”



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55, 15,30 mix

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true spare capacity



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(Results for network 25n50s1)30,55,15 mix

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(Results for network 25n50s1)55,30,15 mix

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Restorability of “gold” class (always 100%)



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Best efforts restorability of silver class

(~45%)

(~98%)

(~10%)

(~15%)



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Proportions of gold and silver restorability derived from economy


Important points...Important points...

• Gold class always 100% restorable

• No spare capacity perse, except with maximum imbalance of gold and economy

• Best efforts restorability changes greatly depending in economy percentage

• Virtually all gold & silver restoration is obtained by economy preemption

So how bad is life for the economy class services ?

• Separate analyses of results shows the average economy service path faces ~ 1-in-10 to 1-in-20 chance of disruption given any other single span failure.


But there can be But there can be anotheranother Service Class as well.. Service Class as well..

Platinum

gold

silver

bronze

(economy)

Prior QoP paradigm

Assured dual-failure restorable (“R2”) service


Key Concept leading to “Platinum” Service Class...Key Concept leading to “Platinum” Service Class...

In a mesh-restorable network it is possible to have

- a pre-planned “protection” response to any single failure

and

- an adaptive (state-dependent) “restoration” response to any dual or subsequent failure.

We call this strategy

First failure protection, second failure restoration

or

“1FP-2FR” for short.

~ 200 to 500 ms

< 2 seconds


Prior Finding of High Dual-failure Restorability in Networks Prior Finding of High Dual-failure Restorability in Networks Designed for Single Failure Protection / Restoration ...Designed for Single Failure Protection / Restoration ...

100 %

R1

(Single failure restorability)R2

(Dual failure restorability)

Between 50 % and

99 % R2(i j) on individual scenarios

70 % to 90 % network

average R2

In a mesh-restorable network design for R1=1 begets high R2 as a side-effect.

--- > R2 is never 0% (unless at a degree-2 node)


Implications ...Implications ...

Any first failure that affects your service path:

R1 = 1 (by design)

Any second failure that affects your service path:

R2 = 1 as well ! (by priority access to a non-zero partial R2

recovery)

AND ...

Imagine that you have a “platinum service” path through a network operating with 1FP-2FR.


Such a class of Priority service in a mesh-restorable network get Such a class of Priority service in a mesh-restorable network get better thanbetter than 1+1 APS availability ... 1+1 APS availability ...

1+1 APS

“1FP 2FR” mesh (for a priority path)

Normal

First failure -> protection

Second failure -> outage

R2(ij) =0

Normal

First failure -> protection

Second failure -> restoration !

(adaptive)

no outage yet

R2(ij) >0

“Takes a licking and keeps on ticking” :-)


Summary, Notes, and Further WorkSummary, Notes, and Further Work

Key points:

(1) Mesh-restorable networks are extremely well-suited to support multi-QoP operation and business strategies. Restoration requirements for gold can be fully met through economy preemption and / or small amounts of shared spare capacity. Over a range of service mixes no spare capacity is needed.

(2) Because R1=1 implies R2 >0 for virtually all cases in a mesh restorable design, it is possible to support a “platinum” (R2=1) service class under 1F-2R operation. Such service gets better than 1+1 availability.

Provisos:

- economy routing complexity increased (is not shortest-path)

- degree 2 nodes not applicable

Further Work Direction:

- Integrate design with platinum services with other QoP stack under min total cost.

- Bi-criterion studies enhancing best-efforts to target levels.

- Convert optimal solution models to incremental operational heuristics.


To delve further …To delve further …

Papers available on request:

[1] W.D. Grover, M.Clouqueur, “Span-Restorable Mesh Networks with Multiple Quality of Protection (QoP) Service Classes,” in review with Optical Networks Magazine, September 2002.

[2] M. Clouqueur, W. D. Grover, "Mesh-restorable Networks with Complete Dual-failure Restorability and with Selectively Enhanced Dual-failure Restorability Properties," Proc. SPIE Optical Networking and Communications Conference (OptiComm 2002), Boston, July 29-Aug. 2, 2002, paper 4874-1, pp.1-12. (view paper)

[3] M. Clouqueur, W. D. Grover, “Computational and Design Studies on the Unavailability of Mesh-restorable Networks,” in Proc. DRCN 2000, Munich, Germany, April 2000, pp. 181-186. (view paper)

See also related presentation at Tech Forum 2002 : “Mesh Restorable Networks with Enhanced Dual-Failure Restorability Properties” (M.Clouqueur, Wed. Oct 23, FP13, Morning Session)

mesh restorable networks with multiple quality of protection classes

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