Outline

IP over WDM Motivations Protocol stacks Network architectures

IP/WDM integrated routing Problem statement

Two-layer routing problem Possible solution strategies

Integrated routing at IP and WDM layers• Interaction with the routing protocols used in IP networks

Greedy distributed solution Network-wide centralized solution

Extensions Summary

IP over WDM - Motivations

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

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-to-

point line systems) to true optical networking (add-drop multiplexers and cross-connects)

IP: Internet ProtocolAAL5: ATM Adaptation Layer 5ATM: Asynchronous Transfer ModeSONET: Synchronous Optical NETworkPPP: Point-to-Point ProtocolHDLC: High-level Data Link ControlWDM: Wavelength Division MultiplexingSDL: Simplified Data Link

•provides length-based delineation instead of flag-based delineation

WDM

SONET/SDH

ATM

AAL5

IP

1

WDM

SONET/SDH

HDLC

PPP

IP

2

WDM

SONET/SDH

SDL

IP

3

[1] W. Simpson, “PPP over SONET/SDH,” IETF RFC 1619, May 1994.[2] J. Manchester, J. Anderson, B. Doshi and S. Dravida, “IP over SONET,” IEEE Communications Magazine, Vol. 36, No. 5, May 1998, pp. 136-142.

IP over WDM - Protocol stacks

IP over WDM - Network architectures

With and without SONET/SDH multiplexing

•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

SXC

ADM

R

WDMNE

R1

R2

R3

R6

WDMNE

WDMNE

WDMNE

R4

WDMNE

SONET/SDH ring

ADM

ADM

ADMSXC

R7

R5

SONET/SDHCross-Connect

SONET/SDHAdd-Drop Multiplexer

IP Router

WDM Cross-Connect or Add-Drop Multiplexer

Multiplex several SONET OC3, OC12, OC48 interfaces on to one fiber using WDM

OC3/OC12/OC48

SONET/SDH

HDLC

PPP

IP

OC3/OC12/OC48

SONET/SDH

HDLC

PPP

IP

Could even multiplex some IP/AAL5/ATM streams with IP/PPP/HDLC streams

R

R

R

R

WDM Multiplexer

WDM Multiplexer

WDM

SONET/SDH

HDLC

PPP

IP

IP over WDM - Network architectures

IP/WDM integrated routing - Problem statement

Develop algorithms for integrated management of routing data in IP over WDM networks

With SONET cross-connects, it becomes a three-layer problem With SONET cross-connects and ATM switches, it becomes a four-

layer problem

Problem space

IP over WDM without multiplexing capabilities in

intermediate layers

2-layer problem

IP over WDM with multiplexing capabilities in

intermediate layers

3 or 4-layer problem

Solution space

Centralized Distributed

Two-layer routing problem

R1

R2

R3

R5

R6

R7

R4

Virtual Topology Physical Topology

R1

R2

R3

R6

R7

OXC OXC

OXC

OXC

R5

R4

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? 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

R1

R3

R6

R7

OADM OXC

OXC

OXC

R5

R4R

2

Optical Amplifier

Solution strategies

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)

Solve four sub-problems: 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

Sub-problems 1 and 4 are equivalent to a data network design/optimal routing problem Capacity assignments between routers are determined for a given traffic

matrix Flows are determined along with capacity assignments

Metrics optimized: 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

Wide-Area 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

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

R1

R2

R3

R5

R6

R7

R4

12

1

4

1

1 1

3

QoS extensions to OSPF

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-ospf-03.txt.

Classification of routing schemes

Optimal schemes base routing decisions on all-pairs source-destination 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.

Routing schemes

Table-based Self-routing

Shortest-path routing (user-level

optimization)

Optimal routing (system-level optimization)

Interaction between OSPF and integrated solution 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

software?

Greedy distributed solution

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)

Basis: optical layer routing should not change IP-layer routing data

R1

R2

R3

R5

R6

R7

R4

R1

R2

R3

R6

R7

OXC OXC

OXC

OXC

R5

Virtual Topology Physical Topology

R4

Centralized network-wide solution

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)

Network Management

System

R1

R2

R3

R6

R7

OXC OXC

OXC

OXC

R5

R4

Extensions

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

Simple schemes for packet tagging, classification and per-hop behavior

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 higher-priority traffic

Summary

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