Transcript IP Optical Networks - City University of New York

Outline
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IP over WDM
 Motivations
 Protocol stacks
 Network architectures
IP/WDM integrated routing
 Problem statement
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Two-layer routing problem
Possible solution strategies
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Integrated routing at IP and WDM layers
• Interaction with the routing protocols used in IP networks
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Greedy distributed solution
Network-wide centralized solution
Extensions
Summary
IP over WDM - Motivations
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IP traffic volumes
 Traffic volumes on the Internet double every six months
 Aggregate bandwidth required by the Internet in the US by the year
2005 is expected to be in excess of 35 Terabytes/sec
New high-capacity networks
 To meet this anticipated need, carriers in the US are in the process
of deploying high-capacity networks (OC-48~2.5 Gbps, and soon
OC-192 ~10Gbps) for the sole purpose of delivering Internet data
 Some new carriers are building networks customized for IP traffic
(most existing “transport” networks were built primarily for voice
traffic)
IP-centric and IP multi-service networks: Voice over IP, Video over IP,
...
IP over WDM - Motivations
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WDM reduces costly mux/demux function, reuses existing optical
fibers.
 Alternative to new fiber installation
 Consolidation of legacy systems
 Maximizes capacity of leased fibers
 Future-proofing of new fiber routes
WDM allows high flexibility in expanding bandwidth
Cost Reduction - integrating optics and eliminating mux stages
Operation Efficiency - elimination of redundant protocol layers
Transport Efficiency - elimination of transport protocol overhead
Emergent technology is evolving WDM from optical transport (point-topoint line systems) to true optical networking (add-drop multiplexers
and cross-connects)
IP over WDM - Protocol stacks
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3
2
IP
AAL5
ATM
IP
PPP
HDLC
IP
SDL
SONET/SDH
SONET/SDH
SONET/SDH
WDM
WDM
WDM
IP: Internet Protocol
[1] W. Simpson, “PPP over SONET/SDH,” IETF
AAL5: ATM Adaptation Layer 5
RFC
1619, May 1994.
[2] J. Manchester, J. Anderson, B. Doshi and S.
ATM: Asynchronous Transfer Mode
SONET: Synchronous Optical NETwork Dravida, “IP over SONET,” IEEE Communications
Magazine, Vol. 36, No. 5, May 1998, pp. 136-142.
PPP: Point-to-Point Protocol
HDLC: High-level Data Link Control
WDM: Wavelength Division Multiplexing
SDL: Simplified Data Link
•provides length-based delineation instead of flag-based delineation
IP over WDM - Network architectures
With and without SONET/SDH multiplexing
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1
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WDM
NE
SXC
SONET/SDH
Cross-Connect
ADM
SONET/SDH
Add-Drop
Multiplexer
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ADM
SXC
WDM
NE
WDM
NE
ADM SONET/SDH ring
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IP Router
WDM
NE
WDM CrossConnect or
Add-Drop
Multiplexer
ADM
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WDM
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• All three protocol stacks can be used in conjunction with SONET/SDH
multiplexing
• Even without SONET/SDH multiplexing (for example R3 to R6
communication), since IP routers have SONET/SDH interfaces, IP over
WDM could involve a SONET/SDH layer
IP over WDM - Network architectures
Multiplex several SONET OC3, OC12, OC48 interfaces on to one fiber using WDM
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WDM
Multiplexer
WDM
Multiplexer
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IP
PPP
HDLC
IP
PPP
HDLC
IP
PPP
HDLC
SONET/SDH
SONET/SDH
SONET/SDH
OC3/OC12/OC48
WDM
OC3/OC12/OC48
* Could even multiplex some IP/AAL5/ATM streams with IP/PPP/HDLC streams
IP/WDM integrated routing - Problem statement
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Develop algorithms for integrated management of routing data in IP
over WDM networks
Problem space
IP over WDM without
multiplexing
capabilities in
intermediate layers
2-layer problem
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IP over WDM with
multiplexing
capabilities in
intermediate layers
Solution space
Centralized
Distributed
3 or 4-layer problem
With SONET cross-connects, it becomes a three-layer problem
With SONET cross-connects and ATM switches, it becomes a fourlayer problem
Two-layer routing problem
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OXC
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OXC
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OXC
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Virtual Topology
Physical Topology
What are the benefits/costs (in terms of network performance and
management complexity) of performing traffic/QoS management and
survivability at the WDM optical layer instead of at the IP layer?
Is there a hybrid or cooperative approach that is more optimal given a set of
realistic performance and complexity constraints?
What is particular about this (IP/WDM) 2-layer
routing problem?
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Limit on the number of optical amplifiers a lightpath can traverse before
requiring electronic regeneration
 All wavelengths amplified equally at an optical amplifier
Without wavelength changers at OXCs (Optical Cross-Connects), wavelength
assignments to lightpaths need to ensure availability of selected wavelength on
all fibers on the lighpath
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OXC
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Optical
Amplifier
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OADM
OXC
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OXC
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Solution strategies
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Integrated routing at the IP and WDM layers
 Interaction between existing routing schemes at
the IP layer and this new integrated solution
“Greedy” distributed solution
 Monitor lightpath utilization and change
allocations of lightpaths between pairs or
routers accordingly
Centralized system-wide optimal solution
Generic integrated approach (not specific to IP)
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Solve four sub-problems:
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Sub-problems 1 and 4 are equivalent to a data network design/optimal
routing problem
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Capacity assignments between routers are determined for a given traffic
matrix
Flows are determined along with capacity assignments
Metrics optimized:
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1. Determine virtual topology to meet all-pairs (source-destination) traffic
2. Route lightpaths on the physical topology
3. Assign wavelengths
4. Route packet traffic on the virtual topology
Minimize costs
Subject to an average packet delay constraint
 use M/M/1 queues and independence assumption to determine delay
[3] B. Mukherjee, D. Banerjee, S. Ramamurthy, A. Mukherjee, “Some Principles for Designing a WideArea WDM Optical Network,” IEEE Journal on Selected Areas in Communications, Vol. 4, No. 5, Oct.
1996, pp. 684-696.
Routing protocols used in IP networks
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Link state based routing protocols, e.g., Open Shortest Path First
(OSPF)
 Currently OSPF Link State Advertisements (LSAs) mainly
include operator-assigned link weights
 Shortest-path algorithms used to determine routing table
entries based on these link weights (Dijkstra’s, Bellman-Ford)
 Example: Shortest path from R3 to R7 is via R4 and R5
QoS extensions to OSPF
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Flow-based IP traffic
 Have LSAs include “available bandwidth”
 Each flow has a required bandwidth; delete all links in graph that do
not have requisite available bandwidth
 Then apply shortest-path algorithm using link weights
Connectionless traffic
 Modified Bellman-Ford to determine shortest-paths using link
weights
 If there are multiple paths with the same minimal weight, then the
path with the maximum available bandwidth is chosen
[4] R. Guerin, S. Kamat, A. Orda, T. Przygienda, D. Williams, “QoS Routing Mechanisms
and OSPF Extensions,” IETF Internet Draft, 30 Jan. 1998, draft-guerin-qos-routing-ospf03.txt.
Classification of routing schemes
Routing schemes
Table-based
Shortest-path routing
(user-level
optimization)
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Self-routing
Optimal routing
(system-level
optimization)
Optimal schemes base routing decisions on all-pairs sourcedestination traffic e.g., the integrated four sub-problem solution
Shortest-path schemes make routing decisions for per-nodepair traffic
e.g., OSPF
[5] C. Baransel, W. Dobosiz, P. Gewicburzynski, “Routing in Multihop Packet Switching
Networks: Gb/s Challenge”, IEEE Network Magazine, 1995, pp. 38-61.
Interaction between OSPF and integrated
solution
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No conflict:
 The integrated solution changes “maximum” capacities between
routers
 OSPF (with QoS extensions) uses this information along with
“available” capacities to make routing decisions
Potential conflict:
 Should the integrated solution change the forwarding table entries
based on flows computed as part of the capacity assignment
problem?
 If so, both OSPF and integrated solution are changing forwarding
table entries
Other issues:
 OSPF LSAs need to exchange maximum bandwidths
 Can instabilities result in forwarding data if both OSPF and
integrated IP/WDM routing software make changes?
 What is the time scale of operation for the integrated IP/WDM
Greedy distributed solution
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OXC
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Virtual Topology
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Physical Topology
WDM network routing does not change the virtual topology
It measures utilization on each lightpath (between pairs of routers)
 If under-utilized, decrease number of lightpaths or data rates used on
lightpaths
 If over-utilized, increase number of lightpaths or data rates used on
lightpaths
Using wavelength availability and optical amplifier related constraints, find
shortest path for lightpath and establish crossconnections (“greedy” user-level
optimal)
Centralized network-wide solution
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OXC
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OXC
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Network
Management
System
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OXC
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In greedy distributed solution, there may be instances when a lightpath
could have been accommodated if routes or wavelength assignments
of existing lightpaths had been adjusted
All-pairs traffic demand is given; find optimal routes and wavelength
assignments of lightpaths (also called the RWA problem)
Extensions
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Consider multiple QoS metrics while finding optimal solutions
 For example, in integrated solution, consider packet loss ratio,
packet delay variation, improved packet delay formulations
(assuming MMPP traffic)
Extend solutions to allow for multiple service classes
 Differentiated services in IP networks
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Integration of IP service classification with routing and wavelength
assignment
Allow for network and service survivability
 Use full capacity or have spare capacity
 Use protection fibers for increased throughput, but when fault
occurs, throttle back best-effort traffic and accommodate all higherpriority traffic
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Simple schemes for packet tagging, classification and per-hop
behavior
Summary
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Defined IP over WDM network architectures and protocol stacks
Defined routing problem statement for two-layer networks
 Special features of WDM networks: optical amplifier constraints,
wavelength continuity constraints
Proposed three solution strategies:
 Integrated IP/WDM optimal routing to operate in parallel with OSPF
shortest-path routing
 Greedy distributed solution - monitors traffic offered to WDM
network and determines shortest-paths meeting certain constraints
(user-level optimal)
 Centralized system-wide optimal solution - adjusts existing
lightpaths if needed to accommodate newly requested lightpath
Identified possible extensions