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p-Cycles: Network Protection
with Ring-speed and Mesh-efficiency
1st COST270 Workshop on
Reliability of Optical Networks, Systems and Components
December 13, 2001 - EMPA, Dubendorf, Switzerland
Dominic Schupke
Claus Gruber
Wayne Grover
Demetrios Stamatelakis
Munich University of Technology
Institute of Communication Networks
TRLabs, University of Alberta
Outline
•
•
•
•
•
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Motivation
Basics
p-Cycles in WDM Networks
Self-organization of p-Cycles
p-Cycles in IP Router Restoration (Overview)
Summary
Background and Motivation
“ Ring “
“Mesh”
A. 50 msec restoration times
B. Complex network planning and
growth
C. High installed capacity for
demand-served
D. Simple, low-cost ADMs
E. Hard to accommodate multiple
service classes
F. Ring-constrained routing
G. Up to 1.5 sec restoration times
H. Simple, exact capacity planning
solutions
I. well under 100% redundancy
J. Relatively expensive DCS/OXC
K. Easy / efficient to design for
multiple service classes
L. Shortest-path routing
“ Shopping list” : A, D, H, I, L (and K) please...keep the rest
p-Cycles: Basics
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•
•
•
•
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
• Protected spans:
• 9 „on-cycle“
(1 protection path)
p-Cycles: Basics
• Protected spans:
• 9 „on-cycle“
• 8 „straddling“
(1 protection path)
(2 protection paths)
Restoration using p-cycles
A. Form the spare
capacity into a
particular set of
pre-connected
cycles !
i
j
If span i fails,
p-cycle j provides
one unit of
restoration
capacity
A span on the cycle fails - 1 Restoration Path, BLSR-like
j
A p-cycle
i
" xi , j  1 " case
If span i fails,
p-cycle j provides
two units of
restoration
capacity
A span off the p-cycle fails - 2 Restoration Paths, Mesh-like
" xi , j  2 " case
Combination of p-Cycles
• Optimization problem:
10
6
Find a set of cycles which minimizes
the protection capacity
6
6
10
10
6
4
10
10
Demand
(capacity: 22)
A possible
p-cycle
(protection
capacity: 40)
4
4
6
6
Two
p-cycles
(protection
capacity: 36)
p-Cycles in WDM-Networks
VWP
WP
• „virtual wavelength path“
• „wavelength path“
• Nodes have full wavelength
conversion capabilities
• Wavelength can change on the
path
• Nodes have no wavelength
conversion capabilities
• Wavelength cannot change
on the path
p-Cycles in WDM-Networks
VWP
• No impact on p-Cycles:
p-Cycle
protects demand C-G
WP
• p-cycle must use same
wavelength as path:
Implementation
• 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
Read Demands, Duct-Topology
and Parameters
Demands,
Ducts
Create Graphs (Demands, Ducts, Fibers)
Demands,
Ducts, Fibers
Routing of the Demands (Dijkstra, First λ Fit)
Demands,
Ducts, Fibers
Search for Potential Cycles
Ducts, Fibers
Create ILP Model (AMPL)
Solve Model (CPLEX, LPSOLVE)
p-Cycles-Allocation und Visualization
Demands,
Ducts, Fibers
Case Study: COST 239
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•
2 fibers per duct
128 wavelengths per fiber
Results: VWP Network
Protection / Working Capacity Ratio
1,2
1,1
1
0,9
0,8
0,7
0,6
0,5
1.0 * Demand
2.5 * Demand
5.0 * Demand
10.0 * Demand
0,4
3000 3500
4000
4500
5000
cylce length (km)
5500
6000
6500
all
Protection / Working Capacity Ratio
Results: WP Network
1.6
1.4635
1.4
1.3629
1.2
1.2919
1
0.8442
0.7061
1.2939
0.8
1.1558
1.0907
0.6
0.4
0.6943
0.2
0.6312
(300 MB)
0
WP-Network
1
2
3
cycle length(km)
VWP-Network
4
5
1.0 * Demand
VWP Calculation Times
Cyclelength
(km)
Graph
Creation
Routing
Cycle
Search
AMPL-data
Creation
AMPL
CPLEX
Sum
3000
3500
4000
4500
5000
5500
6000
6500
all
0,53
0,53
0,53
0,53
0,49
0,52
0,5
0,55
0,56
0,84
0,86
0,87
0,87
0,85
0,87
0,87
0,91
0,88
10,12
41,23
173,14
617,62
1497,71
2944,7
4750,35
8509,01
8653,03
0,48
0,99
2,43
5,69
11,08
19,07
28,16
46,43
46,04
0,24
0,63
0,84
2,49
3,94
5,54
7,23
9,66
9,62
0,3
0,76
3,37
3,98
5,68
9,21
16,48
22,13
22,09
12,51
45
181,18
631,18
1519,75
2979,91
4803,59
8588,69
8732,22
1.0 * Demand, Times in Seconds
Impact of Demands-Routing
• Optimal set of p-cycles is depending on routing:
6
6
12
12
12
6
6
6
12
4*12 = 48
6
6
7*6 = 42
Investigation of shortest path routing with adapting metric
(inverse of free capacity on span)
Results: Routing Dependence
59%
Used Links for Demands and Protection
8400
8210
8200
8003
8000
7800
7880
fixed metric (1.0)
52%
7704
7613
7600
44%
7552
7534
7468
7468
7051
7044
7427
7400
7231
7124
7200
7000
7072
adapting metric
34%
6800
6600
6400
3500
4000
4500
5000
5500
cycle length (km)
6000
6500
all
Optimal Spare capacity design Typical Results
• “Excess Sparing” = Spare Capacity compared to Optimal SpanRestorable Mesh
Test
Network
Excess
spare
capacity
# of unitcapacity
p-cycles
formed
# of
distinct
cycles
used
1
2
3
4
5
9.09 %
3.07 %
0.0 %
2.38 %
0.0 %
5
88
250
2237
161
5
10
10
27
39
i.e., “mesh-like” capacity
Understanding why (optimally
planned) p-cycles are so efficient...
Spare
p-Cycle
UPSR
or
BLSR
9 Spares
cover 9
Workers
…same spare
capacity
Working
Coverage
9 Spares
cover 19
Workers
“the clam-shell
diagram”
Further comparing p-cycles to
rings
ADM-like “capacity-slice” nodal
device for p-cycle networking
nodal redundancy R =
 spare  1
 working k  1
example : k  3  R  25%
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 selforganize
- 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
Data Encapsulation
Router
Failed Link
Data De-Encapsulation
Router
p-cycle
(a) On-Cycle Failure
(1 restoration Path)
(b) Straddling Failure
(2 Restoration paths)
Router Failure Restoration using
“Node-Encircling” p-Cycles
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•
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
NodeEncircling pcycle
Other
Nodes
Encircled
Node
Router Restoration using
“Node-Encircling” p-Cycles
Node
Failure
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
Concluding Comments
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 cycles
Outlook:
• Partial wavelength conversion
• Multiple failures
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
References on p-Cycles
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[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