P-Cycles, Ring-Mesh Hybrids and “Ring-Mining:” Options for New and Evolving Optical Networks...

pp-Cycles, Ring-Mesh Hybrids -Cycles, Ring-Mesh Hybrids and “Ring-Mining:”and “Ring-Mining:”

Options for New and Evolving Optical NetworksOptions for New and Evolving Optical Networks

Wayne D. Grover Wayne D. Grover [email protected]@trlabs.ca TRTRLabsLabs and University of Alberta and University of Alberta

Edmonton, AB, CanadaEdmonton, AB, Canada

web site for related papers etc: web site for related papers etc:

http://www.ee.ualberta.ca/~grover/http://www.ee.ualberta.ca/~grover/

Please see also www.drcn.org ( “DRCN 2003” )

OFC 2003, OFC 2003, Tuesday March 25 2003, Atlanta, Georgia Tuesday March 25 2003, Atlanta, Georgia

http://www.ee.ualberta.ca/~grover/

http://www.drcn.org/

A note to recipients following OFC 2003A note to recipients following OFC 2003

Dear colleague

It is my pleasure to provide you with the following softy-copy of the presentation slides I used at OFC 2003. If you wish to rely on this work, you may cite the related OFC paperas follows:

W. D. Grover, “p-Cycles, Ring-Mesh Hybrids and Ring-Mining:Options for New and Evolving Optical Networks,” Optical Fiber Communication Conference (OFC 2003), Atlanta, March 2003, Paper TuI1, Vol. 1, pp. 201- 203.

The paper (just cited) in the OFC Proceedings also gives further individual references on p-cycles,ring-mesh hybrids, and “ring-mining” that may be of use to you.

Thank you very much for your interest in this work. Any feedback, comments or questions aremost welcome.

Best regards,

Wayne Grover [email protected], March 31, 2003

Wayne D. Grover OFC 2003 3

Purpose and OutlinePurpose and Outline

Three recent developments involving both ring and mesh-like attributes

• (1) p- Cycles

– “mesh-efficiency with ring-speed ”

• (2) Forcer-clipping ring-mesh hybrids

– selective use of BLSR rings within a mesh network

• (3) “Ring Mining”

– re-use existing ring infrastructure to support mesh-based growth

Unifying theme: getting the best of both ring and mesh

new ideas and options for network planners to consider


pp-Cycles-Cycles


pp-Cycles - an “on-cycle” failure-Cycles - an “on-cycle” failure

Reaction to an “on-cycle” failure is logically identical to a unit-capacity

BLSR loopback reaction

loopback

loopback

“on-cycle” spans have both working and spare capacity like a BLSR


pp-Cycles - a “straddling span” failure-Cycles - a “straddling span” failure

Reaction to a straddling span failure is to switch failed signals onto two protection pathsformed from the related p-cycle

Break-in

Break-in

Straddling spans have two protected working signal units and haveno spare capacity


A lot !

Re-consider the example:

It consumes 13 unit-hops of spare capacity

It protects one working signal on 13 spans and two working on 9 spans

i.e., spare / working ratio = (13*1 + 9*2 ) / 13

= 42%

How much difference can this make ?How much difference can this make ?

A fully-loaded Hamiltonian p-cycle reaches the redundancy limit, 1/(d-1)

x2x2

x2 x2

x2

x2

x2

x2

x2


Example of a whole Example of a whole pp-cycle network design-cycle network design

Working span capacities arising from one unit of demand on each node-pair:

Total working capacity:158 units

8

1

5

6

9

4

9

4

4

10

73 2

13

11

10

7

6

14

5

7

6

7


Design Solution: 53.8 % overall redundancy Design Solution: 53.8 % overall redundancy

A 1B 1C 1D 2E 2

Total protection capacity: 85 unitsRedundancy: 53.8%Optimal configuration dynamically computable or self-organized

p-Cycle Copies

Total: 7


Understanding Understanding whywhy pp-cycles are so efficient...-cycles are so efficient...

9 Spares cover 9 Workers

9 Spares

cover 29 working

on 19 spans

Spare

Working Coverage

UPSR or

BLSR

p-Cycle…with same

spare capacity

“the clam-shell diagram”


ADM-like nodal device for ADM-like nodal device for pp-cycle networking-cycle networking

nodal redundancy =

spare 2 1

working 2 2 1

: 3 25%

R

k k

example k R


Summary: Important Features of Summary: Important Features of pp-Cycles-Cycles

• Working paths go via shortest routes over the graph

• p-Cycles are formed only in the spare capacity

• Can be either OXC-based or based on ADM-like nodal devices

• a unit-capacity p-cycle protects:– one unit of working capacity for “on cycle” failures– two units of working capacity for “straddling” span failures

• Straddling spans:– there may be up to N(N-1)/2 -N straddling span relationships– straddling spans each bear two working channels and zero spare– -> mesh capacity efficiency

• Only two nodes do any real-time switching for restoration – protection capacity is fully pre-connected– switching actions are known prior to failure– -> BLSR speed


Ring-Mesh Hybrid Networks based on the “forcer-clipping”

principle


The architecture of integrated ring-mesh transportThe architecture of integrated ring-mesh transport

Physical Topology

Logical Demand

Ring-2

Ring-1Ring-1

Selected “Forcer clipping” Rings

“ Residual Mesh”

ADM

Glassthrough

X-connect

hybrid transport

network


The Forcer Concept

13271,29,-27

174,53,46

753,74,32

6555,20,24

54

7

371,19,17

816,45,-29

453,0,-37

1248,27,1

968,14,-8

1316,41,16

8

1059,18,1

1481,0,-12

652,6,-32

1747,28,1

1841,16,41

11

9

10

1151,39,13 15

50,3,-37 1648,23,-3

1957,3,-30

2265,33,-14

2064,22,-4

2334,78,19

2178,34,53

2Span NumberWorking links, Spare links, Forcer Threshold

Forcer Span

Working, spare, forcer strength


The Concept of “Forcer Clipping” Rings

Hypothesis: Certain rings can efficiency “clip the tops off ” strong forcers in the mesh, resulting in savings exceeding the cost of the rings.

Self-contained BLSR “clips” off strong forcers

Reduces & levels underlying mesh

Residual mesh forcer landscape and “forcer-clipping” rings

Forcer span

spare capacity

Forcer span

‘hidden’ forcer

“forcer” landscape of a pure-mesh network

economies arise from:

1) enhancement of the residual mesh capacity efficiency, due to forcer clipping

2) creation of a well-loaded ring, displacing working quantities from the mesh, lowering relative termination costs.


A

F

G

Z

E

C

B(9,10)

(7,14)(16,14)

(10,10)

(16,0)

(9,10)

(14,20)

(14,20)

(29,16)

(30,15)

Pure mesh:

Redundancy =

129 / 154 = 84 %(9,9)

(7,8)(16,8)

(10,9)

(16,3)

(9,10)

(2,9)

(2,9)

(17,10)

(18,9)

Test ring 1: Revised mesh:

Redundancy =

84 / 106 = 0.79

Capacity return ratio =

(129-84) + (154-106) 4 x 12 x 2

= 97 %

(9,10)

(0,13)(4,3)

(10,10)

(16,0)

(9,10)

(14,20)

(14,20)

(17,17)

(30,14)

Test ring 2:Revised mesh:

Redundancy = 117 / 123 = 0.95

Capacity return ratio =

(129-117) + (154-123) 4 x 12 x 2

= 45 %

Example of Forcer-clipping effects

CRR: Capacity return ratio = total mesh capacity reduction total capacity of ring placed High CRR --> good economics

Example uses a 12 unit-capacity ring


Heuristic Algorithm based on “Forcer Clipping”

Forcer analysis of initial mesh

Find all cycles of network graph

Use forcer assessments to build ranked “short-list” of ring placements

Place a “short-list” ring

Residual mesh re-design

Assess total economic impact

Callable CPLEX

Place max-payback ring and permanently alter the residual mesh design

Repeat until no further rings prove-in

no further gainfrom any ring

at least onering proves in


Combined Cost of Rings and Mesh

1600

1650

1700

1750

1800

1850

1900

0 1 2 3 4

Number of Rings Used

Co

st

Evidence of a true Cross-Architectural Optimum design point


Understanding why the hybrid worksUnderstanding why the hybrid works

• A good forcer clipping ring pays for itself by:

– (1) attaining good utilization for itself, while displacing mesh

capacity

– (2) enhancing the mesh efficiency through forcer-levelling.

• But even when ring transport is up to 40% cheaper than mesh, a

hybrid is optimum; not a pure ring outcome. why?

• (1) “rings must be rings” …closing the circle limits ring

efficiency.

• (2) mesh residual approaches limiting efficiency


“Mining the Rings”:serving demand growth through ring to

mesh conversion


The “Ring-mining” PerspectiveThe “Ring-mining” Perspective

1) “Cap and grow:” Keep all current demands in the ring network and serve new demands in a new mesh network built on top of it

2) “Ring Mining:” Convert ring capacity to mesh capacity by conversion and/or re-use of transmission equipment

cap the

rings

grow new

mesh

convert operation to mesh

break open the

ringsi.e. What rings? - I only seecapacity on the ground.


Approaches to studying the ring-mining ideaApproaches to studying the ring-mining idea

• Q1 “pure ring mining”: If rings were simply “broken up” and reconfigured in a mesh architecture, how much total growth over existing demand could be served without having to add any new capacity?

Such that:

• all di,j demand quantities are multiplied by

• all (scaled up) demands are routed

• all (scaled up) demands are 100% span-restorable

• the total of routing and restoration flows over any

span uses only the capacity of the prior rings (W+P)

Maximize a total uniform growth multiplier


Sample ResultsSample Results

•35 % of the test cases could sustain a doubling of the demand or more.

• Three test networks could sustain ~ 3 x growth in demand...

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.6 2.9

, maximum sustainable growth multiplier

Rela

tive

Fre

quency

in +

/- 0

.1 b

ins.

17 ring-based test networks

• Ring mining tests on 17 efficient multi-ring network designs • Each design is at exhaust under its initial demand matrix


Why / How Ring Mining works …Why / How Ring Mining works …

• (1) Ring protection capacity is reclaimed – for general use as mesh working and spare capacity– 100% redundancy is reduced to mesh redundancy

• (2) Ring “stranded capacity” is freed.

• (3) New (growth) demands follow shortest-path routes over the facilities graph.


Ring Mining with Selective Capacity AdditionRing Mining with Selective Capacity Addition

• Pure mesh growth requires a high immediate investment in capacity

•Ring Mining with selective additions defers expenditure until 50% to 290 % growth.

Test case for 32 node, 45 span network initially with 7 rings covering 42 spans (3 “span eliminations”) optimized to serve the baseline demand before ring-to-mesh conversion.

0

20

40

60

80

100

120

1 1.5 2 2.5 , total uniform growth multiplier

Requir

ed C

apaci

ty I

nve

stm

ent New Mesh

Ring Mining

Range where other test case ring networks transition from pure ring mining to selected capacity additions


Ring-Mining Ring-Mining to to pp-cycles-cycles as the target architecture as the target architecture

Ring 4

Ring 5 Two (of seven) rings in the initial ring-based design:

• protect 24 spans

• use 29 units spare capacity

• Spare/working ratio = 121 %

• plus ring-constrained working routes


Convert those two rings to one Convert those two rings to one pp-cycle-cycle

p-cycle • No new capacity added

• 8 ADMs have p-cycle straddling span interface units added

• All other ADMs re-used as-is.

• 7units of protection capacity reclaimed as working

• 15 spans obtain on-cycle protection

• 5 spans obtain (x2) straddler protection

• fully loaded spare / working ratio 17/(17+5*2) = 63%

• pus working paths take shortest routes over topology


Straddling Span Interface Unit (SSIU)Straddling Span Interface Unit (SSIU)

• Converts an ADM to function as a p-cycle node

Long haul

Long haul Long haul

Long haul

Local Add Drop ChannelsW

S

W

W WW

S

W

Existing Ring ADM /OADM

Additional Local Add Drop Channels

p-cycle straddling span interface unit

“Extra Traffic” line-rate access to protection


SummarySummary

Three new options and architectural principles described

– p-Cycles • Mesh efficiency with ring-speed

– Ring-mesh hybrids based on forcer-clipping principle• Selective continued use of rings

• Possible target architecture of ring mining

– “Ring- mining”• A strategy for evolving legacy ring networks to a mesh future

… provide additional options and strategies for vendors and operators considering new and evolving optical networks. All involve aspects of harnessing both ring and mesh efficiencies


Selected References and Further ReadingSelected References and Further Reading• [1] W. Grover, D Stamatelakis, "Bridging the ring-mesh dichotomy with p-cycles", Proc. DRCN 2000,

Munich.

• [2] -------, "Cycle-oriented distributed preconfiguration: Ring-like speed with mesh-like capacity…," Proc. ICC'98, 1998, pp. 537-543.

• [3] ------, "OPNET Simulation of Self-organizing Restorable SONET Mesh Transport Networks", Proc. OPNETWORKS '98 (CD-ROM), Wash. D.C., April 1998, paper 04.

• [4] -----, "IP layer restoration … based on virtual protection cycles," IEEE JSAC, Oct. 2000, pp. 1938 - 1949.

• [5] D. A. Schupke, et.al., "Optimal configuration of p-cycles in WDM networks," Proc. ICC'02, NYC, 2002.

• [6] L.Lipes, "Understanding the trade-offs associated with sharing protection," OFC 2002, ThGG121.

• [7] W. D. Grover, J. E. Doucette, "Advances in optical network design with p-cycles: Joint optimization and pre-selection …," in Proc. IEEE-LEOS Topical Meetings, Quebec, July 15-17, 2002.

• [8] W.D. Grover, D.Y. Li, "The forcer concept and its applications to express route planning in mesh survivable networks," JNSM (Plenum Press), vol. 7, no.2, June 1999, pp. 199-223.

• [9] W. D. Grover, R. G. Martens, "Optimized Design of Ring-Mesh Hybrid Networks," DRCN 2000, Munich, April 2000.

• [10] M. Clouqueur, et. al. "Mining the Rings: Strategies for Ring-to-Mesh Evolution," DRCN 2001,

Budapest, October 2001.

Supplementary slidesSupplementary slides


The Unique Position The Unique Position pp-Cycles Occupy-Cycles Occupy

Redundancy

Speed

“50 ms”

100 %50 % 200 %

Path rest, SBPP

Span (link)rest.

UPSR

200 ms

p -cycles: BLSR speed

mesh efficiency

BLSR


Test Case Example of a whole network designTest Case Example of a whole network design

• Pattern of non-identical working span capacities:

Demands: 1 unit (between every node pair)

Working capacities: 1 - 13 unitsTotal working capacity: 168 units

1

4

7

4

12

10

4

4

8

10

311

10

9

13

3

3

5

9

13

7

7

11


Test Case #4 SolutionTest Case #4 Solution

• Optimal solution:

A 3

B 1

C 1

D 4

E 1

F 1

G 2

Spans with overlapping cycles: 16Total protection capacity: 120 unitsDistance-weighted redundancy:65.9%

p-Cycle Copies

Total: 13


Efficiency of Efficiency of pp-Cycles-Cycles

(Logical) Redundancy =

2 * no. of straddling spans + 1* no. on-cycle spans

------------------------------------------------------------------

no. spans on cycle

7 spans on-cycle,

2 straddlers :

7 / ( 7 + 2*2) = 0.636

Example:

Limiting case: p-cycle redundancy = N / ( N 2 - 2N)


Protection using Protection using pp-cycles-cycles

A p-cycle

A span on the cycle fails - 1 Restoration Path, BLSR-like

A span off the p-cycle fails - 2 Restoration Paths, Mesh-like

A. Form the spare capacity into a particular set of pre-connected cycles !

," 1 " case

i jx

," 2 " case

i jx

If span i fails,p-cycle j provides

one unit of restoration capacity

If span i fails,p-cycle j provides

two units of restoration capacity

i j

i

j


Optimal Spare capacity design with Optimal Spare capacity design with pp-cycles-cycles

Step 1: Find set of elementary cycles of the network graph

Step 2: For each cycle, determine x i,j : the no. of restoration paths that cycle i contributes for failure j. x i,j

Step 3: Integer Program to select optimal p-cycle set:

Objective: minimize: total cost of spare capacity.

Subject to:

1. Restorability: All working links on each span have

(simultaneously feasible) access to one or more p-cycles.

2. Spare Capacity: All p-cycles placed are feasible within the

span spare capacities assigned


Optimal Spare capacity design - Typical ResultsOptimal Spare capacity design - Typical Results

TestNetwork

Excesssparecapacity

# of unit-capacityp-cyclesformed

# ofdistinctcyclesused

1 9.09 % 5 52 3.07 % 88 103 0.0 % 250 104 2.38 % 2237 275 0.0 % 161 39

• “Excess Sparing” = Spare Capacity compared to Optimal Span-Restorable Mesh

i.e., “mesh-like” capacity


Results in Results in COST239 European Study NetworkCOST239 European Study Network

Ref [5] to the paper…

• Pan European optical core network

• 11 nodes, 26 spans

• Average nodal degree = 4.7

• Demand matrix

– Distributed pattern

– 1 to 11 lightpaths per node pair (average = 3.2)

• 8 wavelengths per fiber

• wavelength channels can either be used for demand routing or connected into p-cycles for protection

10

1

56

783

9

0 2 4

Copenhagen

LondonAmsterdam Berlin

Paris

Brussels LuxembourgPrague

Vienna

Zurich

Milan

WDM designs could have as little as 34%

redundancy for 100%span restorability


SummarySummary

• p-Cycles offer a promising new option for efficient realization of network protection– are preconfigured structures– use simple BLSR-like realtime switching– but are mesh-like in capacity efficiency

• Other recent advances can be superficially confused with p-cycles:– enhanced rings reduce ring network redundancy by sharing protection

capacity between adjacent rings– oriented cycle (double) covers adopt a undirectional graph cycle-

covering approach to avoid span overlaps

• Neither involves straddling spans; spans with working but no spare capacity– Both aim to approach their lower limits of 100% redundancy from well

above 100%– p-cycles are well below 100% redundancy


Corroborating Results...Corroborating Results...

See: Schupke et al… ICC 2002

Schupke found p-cycle WDM designs

could have as little as 34%redundancy for 100%

span restorability


Some Results ( ….. where optimal and heuristic can be compared)

Ring cost factor = 0.8

Objective function values, (% savings),execution time, number of rings

“Cost savings” arerelative to objectivefunction value for

“pure-mesh”

Network #1

11 nodes

23 spans

Network #2

11 nodes

20 spans

Network #3

15 nodes

28 spans

Average cost

savings %

Initial Mesh

(reference case)1877 1705 2211

Heuristic #1

1750 (6.8 %)

7.3 min

1 ring

1504 (11.8%)

1.7 min

1 ring

2092 (5.4 %)

50.8 min

1 ring

8.0

Heuristic #2

1705 (9.2 %)

20.1 min

3 rings

1509 (11.5 %)

2.1 min

1 ring

2092 (5.4 %)

38.4 min

1 ring

8.7

Optimal Solution

Method

1667 (11.2 %)

36.9 min

4 rings

1487 (12.8 %)

6.3 min

3 rings

2088 (5.6 %)

25.3 hrs

4 rings

9.9

LP Lower Bound 1617 1437 1888

*

* result obtained with MIPGAP = 200


Results ( ….. where optimal and heuristic can be compared)

Ring cost factor = 0.6

Objection function values (total cost), execution times, and number of rings placed

Network #1

11 nodes

23 spans

Network #2

11 nodes

20 spans

Network #3

15 nodes

28 spans

Average

cost

Savings %

Initial Mesh

(reference case)1877 1705 2211

Heuristic #1

1589 (15.3 %)

10.5 min

2 rings

1350 (20.8 %)

2.5 min

2 rings

1913 (13.5 %)

2.1 hrs

3 rings

16.5

Heuristic #2

1507 (19.7 %)

20.9 min

4 rings

1373 (19.5 %)

2.1 min

1 ring

1740 (21.3 %)

4.4 hrs

4 rings

20.2

Optimal Solution

Method

1411 (24.8 %)

10.9 hrs

5 rings

1275 (25.2 %)

31.2 min

5 rings

1873* (15.3 %)

23.3 hrs

8 rings

21.8

LP Lower Bound 1311 1175 1473

* result from optimal formulation after 24

hours


Other Results (“ where only the heuristic can go”):

Heuristic

#2

% savings over optimal pure mesh

Number of rings placed

CPU time

Net #4

19 nodes

39 spans

Net #5

16 nodes

29 spans

Net #6

27 nodes

48 spans

23.8%

8 rings

11.9 hrs

38.6%

12 rings

1.0 hr

39.5%

11 rings

2.3 hrs


Summary of Main FindingsSummary of Main Findings

• The “forcer-clipping” hypothesis is suggested as an effective principle in ring-mesh hybrid network design.

• Advent of DCS with integrated ADM shelf functionality motivates / enables this type of true hybrid.

• Heuristics observed to be within ~ 5% of optimal for test cases

– This is taken as confirming the basic validation of the forcer-clipping insight.

• Heuristic #2 seems superior, and executes in reasonable time for large problems

– Heuristic 2 thought to be “selecting in” more co-forcer and latent-forcer combinations which the economic trial placements then discover and exploit

• This work suggests that in general even mesh networks should be examined for “express ring” opportunities.


Other possibilities in ring-mining strategiesOther possibilities in ring-mining strategies

• ADM removal (and salvage?) is another option. Re-terminate line system on OCX directly.

• Not all ADMs need to be converted to facilitate the ring-to-mesh evolution– Some ADMs can remain in “re-use mode” in degree-2 sites of the

overall mesh network

• Cost of ADM “conversion” and the line capacity accessed are the main parameters.


Ring-mining” access to ring capacityRing-mining” access to ring capacity … …can be can be many alternativesmany alternatives

• “nail up” ADM in max add/drop configuration and access protection capacity via “extra traffic” ports.

OC-n ring ADMworking

protection

working

protection

“extra traffic”

(Or…) just salvage ADMs and re-terminate optical lines on OXCs

maximal workingadd / drop

up to 2 x OC-n total capacity to mesh cross-connect


Growth Multiples supported by ring to p-cycle Growth Multiples supported by ring to p-cycle evolutionevolution

Demand Growth Sustained without capacity Addition

0

12

3

4

56

7

1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9

Demand Growth Lambda

Nu

mb

er

of

Ne

two

rks

p-Cycles

Span Restorable Mesh

p-Cycle straddling span interface

Long haul

Long haul Long haul

Long haul

Local Add Drop ChannelsW

S

W

W WW

S

W

Ring ADM /OADM

Additional Local Add Drop Channels


Cross-office Electrical/optical ring line rate

interface

“Extra Traffic” line-rate access to protection fiber(IF – 1 )

“Extra Traffic” line-rate access to protection fiber(IF

– 2 )

All Working fiber pairs ( ring line-rate ) that can be used to interface with straddler spans.

Patent Pending

Assuming that the protection fiber ( S) is

independently accessible through the “extra traffic” feature

interface

Source : “Ring-like speed with mesh-like capacity” presentation to Nortel by Dr Wayne Grover on 29th Aug 2002 : http://www.ee.ualberta.ca/~grover

Device used to interface straddling spans.


Staddling Span Interface Unit (SSIU)Staddling Span Interface Unit (SSIU)

• Converts an existing ADM to function as a p-cycle node

W

W

P

W

P

ADM

LS tributary add/ drop

additional LS tributary add/ drop

W W W


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P-Cycles, Ring-Mesh Hybrids and “Ring-Mining:” Options for New and Evolving Optical Networks...

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