1st COST270 Workshop onReliability of Optical Networks, Systems and Components

December 13, 2001 - EMPA, Dubendorf, Switzerland

Dominic SchupkeClaus Gruber

Munich University of Technology Institute of Communication Networks

Wayne GroverDemetrios Stamatelakis

TRLabs, University of Alberta

p-Cycles: Network Protectionwith Ring-speed and Mesh-efficiency

• Motivation• Basics• p-Cycles in WDM Networks• Self-organization of p-Cycles• p-Cycles in IP Router Restoration

(Overview)• Summary

Outline

Background and Motivation

“ Ring “A. 50 msec restoration timesB. Complex network planning

and growthC. High installed capacity for

demand-servedD. Simple, low-cost ADMsE. Hard to accommodate

multiple service classes F. Ring-constrained routing

“Mesh”G. Up to 1.5 sec restoration

timesH. Simple, exact capacity

planning solutions

I. well under 100% redundancy

J. Relatively expensive DCS/OXCK. Easy / efficient to design for

multiple service classesL. Shortest-path routing

“ Shopping list” : A, D, H, I, L (and K) please...keep

the rest

• For meshed networks• Pre-reserved protection paths (before failure) • Based on cycles, like rings• Also protects straddling failures, unlike rings• Local protection action, adjacent to failure (in

the order of some 10 milliseconds)• Shared capacity

• “pre-configured protection cycles” p-cycles

p-Cycles: Basics

• A single p-cycle in a network:

p-Cycles: Basics

p-Cycles: Basics

• Protected spans:• 9 „on-cycle“ (1 protection path)

• Protected spans:• 9 „on-cycle“ (1 protection path)• 8 „straddling“ (2 protection paths)

p-Cycles: Basics

Restoration using p-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

Demand(capacity: 22)

106

6

10

10

10

10A possiblep-cycle(protection capacity: 40)

6

6

6

6

4 44

Twop-cycles (protection capacity: 36)

• Optimization problem:Find a set of cycles which minimizesthe protection capacity

Combination of p-Cycles

WP

• „wavelength path“

• Nodes have no wavelength conversion capabilities

• Wavelength cannot change on the path

VWP

• „virtual wavelength path“

• Nodes have full wavelength conversion capabilities

• Wavelength can change on the path

p-Cycles in WDM-Networks

p-Cycle protects demand C-G

p-Cycles in WDM-Networks

WP

• p-cycle must use same wavelength as path:

VWP

• No impact on p-Cycles:

• Multi-layered:– Demand Topology– Duct Topology

• Routing und Cycle Search

– Fiber Topology

• Graph-based Approach:– Library of Efficient Data Types and

Algorithms (LEDA)– Network Planning Library (NPL)

• Optimization (Integer Linear Programming)

– AMPL– CPLEX, LPSOLVE

Implementation

Implementation

Read Demands, Duct-Topologyand Parameters

Create Graphs (Demands, Ducts, Fibers)

Routing of the Demands (Dijkstra, First λ Fit)

Search for Potential Cycles

Create ILP Model (AMPL)

Solve Model (CPLEX, LPSOLVE)

p-Cycles-Allocation und Visualization

Demands,Ducts

Demands,Ducts, Fibers

Ducts, Fibers

Demands,Ducts, Fibers

Demands,Ducts, Fibers

• 2 fibers per duct• 128 wavelengths per fiber

Case Study: COST 239

3000 3500 4000 4500 5000 5500 6000 6500 all

10.0 * Demand5.0 * Demand

2.5 * Demand1.0 * Demand0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

Pro

tect

ion

/ W

ork

ing

Ca

pa

city

Ra

tio

cylce length (km)

Results: VWP Network

(300 MB)

12

34

5

VWP-Network

WP-Network

1.4635

1.3629

1.2919

0.7061 0.8442

1.2939

1.15581.0907

0.6943

0.6312

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

cycle length(km)

1.0 * Demand

Results: WP NetworkP

rote

ctio

n /

Wo

rkin

g C

ap

aci

ty R

atio

1.0 * Demand, Times in Seconds

Cycle-length(km)

GraphCreation

Routing CycleSearch

AMPL-dataCreation

AMPL CPLEX Sum

3000 0,53 0,84 10,12 0,48 0,24 0,3 12,513500 0,53 0,86 41,23 0,99 0,63 0,76 454000 0,53 0,87 173,14 2,43 0,84 3,37 181,184500 0,53 0,87 617,62 5,69 2,49 3,98 631,185000 0,49 0,85 1497,71 11,08 3,94 5,68 1519,755500 0,52 0,87 2944,7 19,07 5,54 9,21 2979,916000 0,5 0,87 4750,35 28,16 7,23 16,48 4803,596500 0,55 0,91 8509,01 46,43 9,66 22,13 8588,69

all 0,56 0,88 8653,03 46,04 9,62 22,09 8732,22

VWP Calculation Times

• Optimal set of p-cycles is depending on routing:

Investigation of shortest path routing with adapting metric (inverse of free capacity on span)

12

1212

12 4*12 = 48

6

6

6

66

6

6

7*6 = 42

Impact of Demands-Routing

70447051707271247231

7427

7704

8003

7468746875347552

7613

7880

8210

6400

6600

6800

7000

7200

7400

7600

7800

8000

8200

8400

3500 4000 4500 5000 5500 6000 6500 all

cycle length (km)

Use

d L

inks

fo

r D

em

an

ds

an

d P

rote

ctio

n

fixed metric (1.0)

34%

44%

59%

52%

Results: Routing Dependence

adapting metric

Optimal 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

Understanding why (optimally planned) p-cycles are so efficient...

9 Spares cover 9 Workers

9 Spares

cover 19 Workers

Spare

Working Coverage

UPSR or

BLSR

p-Cycle…same spare

capacity

“the clam-shell diagram”

Further comparing p-cycles to rings

ADM-like “capacity-slice” nodal device for p-cycle networking

nodal redundancy =

spare 1

working 1

: 3 25%

R

k

example k R

Self-organization of the p-cycles ...

• p-cycles certainly could be centrally computed and configured. – based on the preceding formulation

However, an interesting option is to consider if the network can adaptively and continually self-organize - a near-optimal set of p-cycles within itself, - for whatever demand pattern and capacity

configuration it currently finds.

Self-organization of the p-cycles

• Based on an extension / adaptation of SHN™ distributed mesh restoration algorithm– “DCPC” = distributed cycle pre-configuration protocol

• Operates continually in background– Non-real time phase self-organizes p-cycles

– Real time phase is essentially BLSR switching

– p-cycles in continual self-test while in “storage”

• Centralized “oversight” but not low-level control– Method is autonomous, adaptive

• Networks actual state on the ground is the database

Key concepts of DCPC protocol

• Node roles:– Cycler node state , Tandem node state

• DCPC implemented as event-driven Finite State Machine

(FSM)

• Nodal interactions are (directly) only between adjacent nodes– Indirectly between all nodes (organic self-organization)– via “statelets” on carrier / optical signal overheads

• Three main steps / time-scales / processes– Each nodes act individually, “exploring” network from its standpoint as

cycler node.– All nodes indirectly compare results – Globally best p-cycle is created

Overview of DCPC protocol

How DCPC discovers “best p-cycles” (2)

How DCPC discovers “best p-cycles” (1)

DCPC Performance studies

Illustrating the Real time phase

Adapting p-cycles to the IP-layer …

IP Network Restoration

• IP Networks are already “Restorable”• Restoration occurs when the Routing protocol updates

the Routing Tables• This update can take a Minute or more - Packets are lost

until this happens

• Speed-up of IP Restoration is needed• Not losing packets would be great too• Also some control over capacity / congestion impacts

needed

• p-cycles proposed as “fast” part of a fast + slow strategy that retains normal OSPF-type routing table re-convergence

Operation of IP-layer p-cycles

Failed Link

Router

Data De-Encapsulation

Data Encapsulation

Router

p-cycle

(a) On-Cycle Failure (1 restoration Path)

(b) Straddling Failure

(2 Restoration paths)

• Node Encircling p-Cycles. Each Node has a p-Cycle dedicated to its failure

• For each Node, a p-Cycle is chosen which includes all logically “Adjacent” Nodes but not the Protected Node

Router Failure Restoration using“Node-Encircling” p-Cycles

Node-Encircling p-

cycle

Other Nodes

Encircled Node

p-Cycles are Virtual Circuits/Protection Structures which can redirect Packets around Failures– Plain IP is Connectionless but p-Cycles can be realized with

MPLS, IP Tunneling/Static Routes

Router Restoration using“Node-Encircling” p-Cycles

Node Failure

Investigation on WDM-networks:• p-cycles are suitable and efficient for

converting and non-converting WDM-networks

• Short off-line calculation times for fully converting networks

• Results are depending on demands routing• Only some improvement by non-simple

cyclesOutlook:• Partial wavelength conversion• Multiple failures

Concluding Comments

Concluding Comments

• p-cycles offer new approaches to both WDM and IP-layer transport

– “ mesh-like efficiency with ring-like speed ”

• Capacity-planning theory

– for 100% span restoration in WDM / Sonet with mesh sparing

– for controlled worst-case over-subscription in IP-layer

• “Node-encircling” p-cycles

– fast integrated restoration against either router or link-failures

• Nortel has implemented span-restoration via IP p-cycles

– ~ 10 msec restoration time, no packet loss in their experiments

• Ongoing studies:

• Integrated planning of composite node / link restoration p-cycles

• Availability analysis of p-cycles

• [1]    W.D. Grover, D. Stamatelakis, "Cycle-Oriented Distributed Preconfiguration: Ring-like Speed

with Mesh-like Capacity for Self-planning Network Restoration," Proc. IEEE International Conf.

Commun. (ICC'98), Atlanta, June 8-11, 1998. pp. 537-543. 

• [2]    D. Stamatelakis, W.D. Grover, "Theoretical Underpinnings for the Efficiency of Restorable

Networks Using Pre-configured Cycles ("p-cycles")", to appear in IEEE Transactions on

Communications, accepted December 1999 (contact TRLabs for an advance copy)

• [3]    W.D. Grover, D Stamatelakis, "Bridging the ring-mesh dichotomy with p-cycles", Proc. Design

of Reliable Communication Networks (DRCN 2000), Technical University of Munich, April 2000, pp.

92-104.

• [4]    D. Stamatelakis, W.D. Grover, "Rapid Restoration of Internet Protocol Networks using Pre-

configured Protection Cycles," Proc. 3rd Can. Conf. On Broadband Research (CCBR'99), Nov. 7, 9,

Ottawa, 1999

• [5] D.A. Schupke, C.G. Gruber, A. Autenrieth, “Optimal Configuration of p-Cycles in WDM

Networks,” submitted to ICC 2002

References on p-Cycles