Routing in Optical Networks

Markus Isomäki

IP and MPLS in Optical Domain

Agenda• Trends in IP over optical networking

– Traditional and new models

• Optical network terminology and evolution– Future expectations

• IP routing in optical domain– Different models– Requirements & possible solution frameworks

• MPLS in optical domain - MPLambdaS• Proposed enhancements for routing and signaling

– OSPF/IS-IS and RSVP/CR-LDP

Standardization Organizations and Industry Foras

• Internet Engineering Task Force (IETF)– MPLS Working Group– IP over Optical Working Group starting

• ITU-T SG 13– Optical Transport Network architecture and requirements

• ODSI– Allow IP routers to make dynamic bandwidth requests to the

optical network– Started in January 2000

• Optical Internetworking Forum (OIF)

Traditional Model - IP over ATM over SDH

• IP routers connected to each other via ATM switches which are connected to each other over SDH

• Known problems– Different management (fault, configuration, …) at each layer

adds complexity– Each layer has independent routing = Overlay

• Different physical & logical topology

– Redundant functionality at each layer• Multiplexing, QoS (mapping mismatch), protection…

=> ATM will not survive in the backbone

Current Model - IP over SDH

IP over SDH Pros & Cons • Advantages compared to IP over ATM over SDH

– Easier management– No “cell tax”– IP QoS mapping straightforward

• Major drawbacks– Protection switching consumes half of the capacity– Cumbersome provision of connections - no dynamics– Still two layers of management– Circuit switched!!!– May stop at 9.9 Gbps (STM-64 / OC-192)

=> More flexible & dynamic methods needed– IP Optimization wanted!!!

Other Existing Models• Gigabit Ethernet in Metro networks (10GE in 2001?)

– Simple & cheap– No standard protection technology– Reach may cause problems

• Cisco Systems’ Dynamic Packet Transfer (DPT)– Dual ring like FDDI– Spatial reuse of capacity– No unused protection capacity– Good for multicast– Proprietary

Toward IP over Optical Networking

But how to do routing, path setup, QoS, traffic engineering, protection & restoration etc.=> Basic IP has not enough intelligence!

The common view is this

Optical Network Evolution & Terminology

• Wavelength Division Multiplexing (WDM)– Multiple colors in a single fiber, each color carries SDH,

Gigabit Ethernet etc.– Density grows every year

• Optical Cross-Connects (OXC)– A box that switches a wavelength from an incoming fiber to

an outgoing fiber– Wavelength continuity or conversion– All-optical (transparent) or electro-optical (opaque) – Erbium doped fiber amplifiers (EDFA)

IP over Optical Vision

Composite Link4 λ

Composite Link3 λ

Optical Switches

IP Router

Routers connected to each other over OXC core using WDM wavelenghts

Router Interconnection Requirements

• The routers have to be able to dynamically (on-demand) make connections to each other– Fast provision!!!– Connection capacity

• Protection and restoration needed– Ask for a protected connection (1+1, 1:1, M:N)

• Traffic engineering– Constraint-based and explicit routing

=> Use IP routing in the optical domain?!!!

Routing Models• Overlay

– Independent routing on different layers – Router is client to optical network (some kind of UNI), optical switch

computes the path (IP router does not “see” the topology of the optical network)

– Similar to Classical IP over ATM or MPOA– Good when optical network owned by different organization than the

router network

• Integrated / Peer– Single routing instance run over both networks– Router is able to compute the path

• Augmented– Separate routing instances, some information leaked

MultiProtocol Lambda Switching

• IDEA: Use MPLS control plane machinery to implement traffic engineering, restoration etc. in OXCs (also SDH equipment) - Wavelength ~ Label

MPLSControl Plane

Control Adaptation

OXC SwitchController

OXC Switch FabricOXC Data Plane

MPLambdaS Benefits & Specialities

• Real-time provisioning of connections• Distributed IP routing control• No need for new control protocols

Optical domain(Like nested LSPs)

OXCs unable to terminate LSPs

MPLambdaS & OXC Requirements

• OXCs should be able exchange control information– Control plane topology may be different from data plane (in-

band or out-of-band control); (Similar to SS7)

• Automatic neighbor discovery and registration– Neighboring nodes should know which fiber ports are

connected to each other

• Robustness– A transient fault at the control plane should not affect the

existing connections (soft state unacceptable?) – Fast restoration (fault handling)

Enhancements for Routing ProtocolsOSPF and IS-IS

• New link attributes (TLVs)– Link type

• Packet switch capable• TDM capable• Lambda switch capable• Fiber switch capable• Forwarding adjacency

– Link media type• SDH, Gigabit Ethernet etc.• Termination capability

– Shared Risk Link Group information• For example, if two fibers are in the same conduit they are in the

same SRLG => Cannot be used for each other’s protection

Also informationon physical properties• BER• Wavelength conversion

Enhancements for Signaling ProtocolsRSVP and CR-LDP

• Label objects should contain information on – Fiber– Lambda– Channel

• Convey information on requested media type• Capability to request protected connections!• For RSVP reservation confirmation should be used

At least two proposals submitted

Conclusions• Future networks based on IP routers connected to

each other via Optical Cross-connects• IP routing and MPLS good candidates for controlling

OXCs - IP optimization & synergy• Enhancements needed for routing & signaling

protocols

=> Will happen because major support: Cisco, Nortel, ...• Other solutions possible

– Use of GSMP– Use of traffic driven connection setup