1 st cost270 workshop on reliability of optical networks, systems and components december 13, 2001 -...
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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