IP over Optical Networks

IP over Optical Networks

Debanjan Saha

Bala Rajagopalan

{dsaha, braja}@tellium.com

NANOG, 10/2000 2

BOF Objectives

Determine areas of priority for operators in IP-centric control of optical networks IP over optical network service architectures New services & applications

– Traffic engineering & network re-configuration– Others

NANOG, 10/2000 3

Summary

Motivation

IP over optical network model

IP-centric control plane for optical networks MPLS signaling for optical networks IP routing protocol extensions for optical

networks Optical internetworking

IP over optical networks Service models Traffic engineering

Discussion

NANOG, 10/2000 4

Benefits of Optical Networking

Build Networks for 2/3’s less Optical Meshes are 50% more efficient than TDM Rings Eliminate SONET/DCS Equipment Layer

Dynamic Lambdas Fast provisioning Automatic restoration

NANOG, 10/2000 5

Applications for Dynamic Lambdas

Reconfigure Network to changing traffics Add lambdas on demand between IP Routers “Tune” IP layer topology with changing traffic patterns Just in time lambdas

Dynamic Optical Virtual Private Network (OVPNs) Shared s for bandwidth efficiency

Automatic lightpath restoration Restore at Layer 1 instead of Layer 3 Simplify restoration from large scale failures

– e.g. 100s of lambdas

NANOG, 10/2000 6

Routers experience congestion Step 1 - Router requests additional to relieve congestion Step 2 - Optical Switches dynamically add between congested

routers

Traffic Demand Changes Step 3 - Optical Switches reconfigure

Dynamic Lambdas: Routers request Dynamic

Router Network

Router Network

Step 1 - Request Step 3 - Release

Step 2 - OXC Provides

Optical SubnetOptical Subnet

NANOG, 10/2000 7

Tune IP layer topology to changing traffics

IP Layer Traffic Patterns Change Step 1- Add new from A to B Step 2 - Delete from A to C

OpticalNetwork

Subnet B

Subnet C

Subnet A

Subnet B

Subnet C

OpticalNetwork

NANOG, 10/2000 8

IP over Optical: Network Model

Opticalsubnet

Opticalsubnet

OpticalSubnet

Router NetworkOptical Network

End-to-end path (LSP)

Optical Path

NNI

MPS for signaling and routingwithin the optical network

NNI

NANOG, 10/2000 9

IP-Centric Control of Optical Networks

Ingredients IP addressing for optical network nodes (and termination

points) MPLS-based signaling for lightpath provisioning IP routing protocols adapted for resource discovery Route computation with resource optimization Restoration signaling???

NANOG, 10/2000 10

What is the MPS approach?

Each OXC is considered the equivalent of an MPLS Label-Switching Router (LSR)

MPLS control plane is implemented in each OXC

Lightpaths are considered similar to MPLS Label-Switched Paths (LSPs)

Selection of s and OXC ports are considered similar to selection of labels

MPLS signaling protocols (e.g., RSVP-TE, CR-LDP) adapted for lightpath establishment

IGPs (e.g., OSPF, ISIS) with “optical” extensions used for topology and resource discovery

NANOG, 10/2000 11

Optical Network Functions

Dynamic provisioning of lightpaths Just-in-time provisioning Path selection with constraints

Protection & restoration of lightpaths Protection paths with appropriate service levels

– Node & link disjoint primary & protection paths for resiliency

– Shared protection paths for cost savings Fast restoration of lightpaths after the failure

NANOG, 10/2000 12

Protocols for Realizing Optical Network Functions

Provisioning protocols Automatic neighbor discovery

– Neighbor Discovery Protocol– Link Management Protocol

Topology discovery – OSPF with optical extension– IS-IS with optical extensions

Signaling for path establishment– RSVP-TE, CR-LDP with optical extensions– Generalized MPLS

Restoration Protocols Proprietary techniques

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Physical Topology

O3

O1

O5

O4

O2

Router Network

Router Network

Optical Network

Optical Network

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Topology Abstraction

O3

O1

O5

O4

O2

Router Network

Router Network

Optical Network

Optical Network

UNI

SRG #1

SRG #2 SRG #3

SRG #4 SRG #5

SRG #6

NDP

NDP

NDP NDP

NDP NDP

NDP

NDPUNI

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Neighbor Discovery

NDP allows adjacent OXCs to determine IP addresses of each other and port-level local connectivity information (i.e., port X in OXC O1 connected to port Y in OXC O2)

(IETF Status: Link Management Protocol (LMP) is being considered)

Port State Database of O1

TypeID RemotePort

Speed ResourceClass

RemoteNode

Status SROG

1

2

1024

1023

Drop

Network

Network

Network

Up

Up

SF

Up

OC-48

OC-48

OC-48

OC-192

F123, C231

F234, C251

F234, C231

F123, C231

9.2.1.3

8.4.1.3

11.3.1.3

129.2.1.3

10

123

345

15

Primary

Backup

Primary

Primary

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Topology Discovery with OSPF

O3

O1

O5

O4

O2

Router Network

Router Network

OSPFArea

0.0.0.3

UNI

UNIOSPFArea

0.0.0.2

OSPF Area 0.0.0.1

Summary LSA

Summary LSA

Router/Optical LSA

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OSPF Extensions

Recognition of optical link types

Link bundling Multiple, similar links between OXCs are abstracted

as a single link bundle Composition of link bundle described by parameters Single adjacency maintained between OXCs

regardless of the number of links Bundling considerations in preliminary stages in

IETF

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Example Scenario

SRLG S1

SRLG S2

O1 O2

5 OC-48, 2 OC-192,2 10G E/N

5 OC-48, 5 OC-192

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Desired Bundling Structure

5 OC-48, S1

2 OC-192, S1

2 10G E/N, S1

5 OC-48, S2

5 OC-192, S2

O1 O2

Sin

gle

bund

le b

etw

een

node

s

Resource sub-bundle# 1





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OSPF Extensions

New lightpath computation algorithms Path computation based on lightpath attributes and

constraints Proprietary algorithms for efficiency Algorithms not considered in IETF

Source-routing methodology Differs from traditional OSPF Considered in IETF as part of RSVP-TE/CR-LDP extensions

Reduction of link state propagation overhead Thresholds for reducing link state propagation overhead No framework yet in the IETF

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Link State Advertisements

LSA Type LSA IDAdvertising

NodeLSA content

Nodal LSA O1 AOS ID O1 All link bundles on O1Nodal LSA O2 AOS ID O2 All link bundles on O2Nodal LSA O3 AOS ID O3 All link bundles on O3Nodal LSA O4 AOS ID O4 All link bundles on O4Nodal LSA O5 AOS ID O5 All link bundles on O5Optical LSA O1-O2 O1 Link bundle composition between O1 and O2Optical LSA O2-O1 O2 Link bundle composition between O2 and O1Optical LSA O1-O5 O1 Link bundle composition between O1 and O5Optical LSA O5-O1 O5 Link bundle composition between O5 and O1Optical LSA O2-O5 O2 Link bundle composition between O2 and O5Optical LSA O5-O2 O5 Link bundle composition between O5 and O2Optical LSA O3-O4 O3 Link bundle composition between O3 and O4Optical LSA O4-O3 O4 Link bundle composition between O4 and O3Optical LSA O3-O5 O3 Link bundle composition between O3 and O5Optical LSA O5-O3 O5 Link bundle composition between O5 and O3Optical LSA O4-O5 O4 Link bundle composition between O4 and O5Optical LSA O5-O4 O5 Link bundle composition between O5 and O4Summary LSA Area 0002Summary LSA Area 0003

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Link State Database

O1 O2 O3 O4 O5Area

0.0.0.2Area

0.0.0.3Speed SRGs Class

O1

OC-48F123C245

Shared:2Open:5

OC-48 F234Shared:2Open:4

O2

OC-192F457C569

Open:2Shared:4

O3O4O5

Area 0.0.0.2Area 0.0.0.3

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Routing Across the NNI: BGPE-BGP is used between adjacent border OXCs in different sub-networks

I-BGP is used between border OXCs in the same sub-network

External addresses are passed between sub-networks, with indication of egress border OXC information

Routing policies may be applied, as per BGP features

Sub-network 1 Sub-network 2

E-BGP E-BGP

I-BGP

Sub-network 3

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Some Issues to Consider

What other information must be exchanged during neighbor discovery?

The practicality of obtaining SRG information

Resource metrics for OSPF

Distributed vs centralized path computation

Interdomain routing with resource constraints

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Multi-protocol Lambda Switching

Each OXC is considered the equivalent of an MPLS Label-Switching Router (LSR). An IP control channel must exist between neighboring OXCs

MPLS control plane is implemented in each OXC

The establishment of a lightpath from an ingress to an egress OXC requires the configuration of the cross-connect fabric in each OXC such that an input port is linked to an output port

MPS signaling allows an OXC to convey to the next OXC in the route the selected output port (“label”)

O3

O1

O5

O4

O2

Request (label)Response (P1)

Request (label)Response (P4)

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Generalized MPLSGMPLS is based on the premise that MPLS can be used as the control plane for different switching applications:

TDM where time slots are labels (e.g., SONET) FDM where frequencies (or s) are labels (e.g., WDM) Space-division multiplexing where ports are labels (e.g.,

OXCs) Generalized labels used in MPLS messaging:

Request Resv/Request Resv/Request

Allocate/Port=43Allocate/Port= 5Allocate/Port= 21

(OXC example)

Allocate/Fiber=43 = 9

Allocate/Fiber= 5 = 18

Allocate/Fiber= 21, = 8

(OXC with built-in WDM)

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Generalized Label

Used in place of traditional labels in MPLS signaling messages

May contain a Link ID in addition to the label value Link ID used when a single control channel is used

to control multiple data channels Label format depends on the link type. Presently

label formats have been defined for SONET/SDH, port, , waveband and generic

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GMPLS Actions

Generalized Label Request Indicates the type of label being requested

Generalized Label Response to label request. Format depends on the type of

label

Label Suggestion Sent along with label request, to aid in certain

optimizations

Label Set Sent along with label request. Constrains the allocation of

labels to those in the set to support OXCs without wavelength conversion capability

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Signaling Requirements: Bi-directional Lightpaths

Why not use two unidirectional paths?

Signaling twice is expensive SONET requires the forward and

backward paths to be on the same circuit pack

Who owns the label space? Avoid label assignment collision Resolve collision after in

happens

A B C D

E

F

L1

L2

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Signaling Requirements: Fault-Tolerance

Lightpaths must not be deleted due to failures in the control plane

Present RSVP/CR-LDP mechanisms associate the control path with data paths

– Failure in the control path is assumed to affect the data path

– Data path is therefore deleted or rerouted

In optical networks, the fabric cross-connects must remain if control path is affected

– Enhancements to RSVP/CR-LDP needed for this.

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Dynamic Provisioning Across the NNI

Lightpath request is routed inside source sub-network to border OXC (D) based on destination address and local routing scheme

D routes request to border OXC K in dest. sub-network (NNI signaling)

K routes request to destination, N based on destination address

Response routed along the reverse path

FE

A

B C

D

Req

Req

Req

Resp

Resp

Resp

K

L M

N

Req

Req

Req

Resp

Resp

Resp

NNI Path Request

NNI Path Resp

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Some Issues to Consider

Service definition and GMPLS semantics for different layer technologies

Optimization of optical layer signaling

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Restoration

Objectives Low restoration latency High restoration capacity efficiency by sharing capacity

among the backup paths High degree of robustness of the restoration protocols and

the related algorithms

Scope Fast and guaranteed restoration of lightpaths after “single

failure” events Best-effort restoration after multiple concurrent failures

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Supported Classes of Service

1+1 path protected Each primary path is protected by a dedicated

backup path No signaling is necessary during switching from the

primary path to the backup path

Mesh restorable Each primary path is protected by a shared backup

path Restoration signaling is necessary during switching

from the primary to the backup path

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Restoration Protocol Components

Primary and backup path setup Path computation from OSPF generated link state

database Path setup using RSVP-TE/CR-LDP signaling protocol May be done through the Wavelength Management

System (WMS)

Link-level restoration protocol Using SONET bit-oriented signaling at the link-level

Path-level restoration protocol Using SONET bit-oriented signaling at the end-to-end

path level

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Link-Level Restoration Overview

A lightpaths is locally restored by selecting an available pair of channels within the same link

If no channel is available then the end-to-end restoration is invoked

3 10 7 5 7

12

75 47

1 9

4

A

B C D

E

Drop port Drop port

14

Original Channel Pair

New Channel Pair

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End-to-End Restoration Overview

A shared backup path is “soft-setup” for each restorable primary path When local restoration fails, triggers are sent to the end-nodes End-to-end signaling over the backup path activates it and completes

end-to-end restoration

3 10 7 5 7

12

75 4

8 7 9 485

7

1 9

4

A

B C D

E

HGF

Drop port Drop port

14

Primary Path

Shared Backup

Path

Local Restoration

Failure

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Optical Control Plane: Restoration

Multi-domain restoration: Allow possibility of proprietary restoration in each sub-network Specify an overall end-to-end restoration scheme as backup. Signaling and routing for end-to-end restoration

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Issues to Consider

IP-based restoration protocol Protocol must satisfy time constraints Should a new “fast” protocol be developed?

Inter-domain restoration Is there a need for end-to-end restoration

across domains? Can this need be satisfied by domain-local

restoration plus re-provisioning as a fall-back?

Restoration time requirements

IP-Optical Internetworking

NANOG, 10/2000 41

IP over Optical Service Models: Domain Services Model

Optical network provides well-defined services (e.g., lightpath set-up)

IP-optical interface is defined by actions for service invocation

IP and optical domains operate independently; need not have any routing information exchange across the interface

Lightpaths may be treated as point-to-point links at the IP layer after set-up

Optical Cloud

Router Network Router Network

Service Invocation Interface Physical connectivity

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Optical Network Services

Discrete capacity, high-bandwidth connectivity (lightpaths)

Lightpath Creation, Deletion, Modification, Status Enquiry

Directory Services Determine client devices of interest

Supporting Mechanisms Neighbor discovery Service discovery

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UNI Abstract Messages

Lightpath Create Request - UNI-C UNI-N

Lightpath Create Response - UNI-N UNI-C

Lightpath Delete Request - UNI-C UNI-N

Lightpath Delete Response - UNI-N UNI-C

Lightpath Modify Request - UNI-C UNI-N

Lightpath Modify Response - UNI-N UNI-C

Lightpath Status Enquiry - UNI-C UNI-N

Lightpath Status Response - UNI-N UNI-C

Notification - UNI-N UNI-C

Concrete realization based on MPλS signaling constructs

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Signaling Example

Optical Network

Lightpath Create Request

UNI-C(Terminating)

Lightpath Create Response

UNI-C(Initiating)

UNI-C(Initiating)

UNI-C(Terminating)

1 2

34

Lightpath Create Request

Lightpath Create Response

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UNI Parameters

Identification-related

Service-related

Routing-related

Security-related

Administrative

Miscellaneous

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Service Models: Unified Service ModelNo distinction between UNI, NNI and router-router (MPLS) control plane

Services are not specifically defined at IP-optical interface, but folded into end-to-end MPLS services.

Routers may control end-to-end path using TE-extended routing protocols deployed in IP and optical networks.

Decision about lightpath set-up, end-point selection, etc similar in both models.

Optical Network


NANOG, 10/2000 47

IP over Optical Services Evolution Scenario

First phase: Domain services model realized using appropriate MPλS signaling constructs

Optical Cloud(with or w/o internal

MPλS capability)

MPλS-based signaling forservice invocation, No routing exchange


NANOG, 10/2000 48

Evolution Scenario

Second phase: Enhanced MPλS signaling constructs for greater path control outside of the optical network.

Abstracted routing information exchange between optical and IP domains.

MPλS-based signaling forservice invocation (enhanced). Abstracted

routing information exchange


Optical Cloud(with internal MPλS

capability)

NANOG, 10/2000 49

Evolution Scenario

Third Phase: Peer organization with the full set of MPλS mechanisms.

MPλS-based signaling for end-to-end path set-up.MPλS-based signaling within IP and optical networks.

Full routing information exchange.


Optical Cloud(with internal MPλS capability)

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Routing for Interworking: BGPClient network sites belong to a VPN. Client border devices and border OXCs run E-BGP. Routing in optical and client networks can be different

Address prefixes in each site (along with VPN id) are advertised by border devices to optical network.

Optical network passes these addresses to border devices in other sites of the same VPN (along with egress OXC address)

Network N1 Network N3

Network N2

R1 R2

R3

R6 R5

R4

x.y.a.*, x.y.b.*

x.y.c.*a.b.c.*

O1O2

O3

O4O5

NANOG, 10/2000 51

Issues to Consider

Which service model? Determines complexity of signaling at

the IP-optical interface

What are the service requirements on routing and signaling?

Traffic Engineering

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IP-over-Optical TE Example : Peer Model

Optical network links are OC-48 (2.5 Gbps) Sequence:

1. 100 Mbps LSP from R3 to R82. 300 Mbps LSP from R1 to R63. 200 Mbps LSP from R2 to R12

Optical Network

Router Network

Router Network

R5R4

R6

R9

R8R7

Router Network

R1R2

R3

O12O15

O14

O13Router Network

R10R11

R12

O10

O11

NANOG, 10/2000 54

TE Example Cont. To set up LSP1:

1. R3 computes path R3-R2-O12-R7-R82. R2 establishes an OC-48 FA to R73. LSP occupies 100 Mbps on the FA4. Links R2-O12, R7-O12 must be removed from database when FA R2-R7 is advertised.

FA, 2.5G

Optical Network

Router Network

Router Network

R5R4

R6

R9

R8R7

Router Network

R1R2

R3

O12O15

O14

O13Router Network

R10R11

R12

O10

O11

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TE Example Cont.

To set up LSP2 (R1-R6):1. Path: R1-R2-O11-O13-O14-R4-R62. R2 establishes an OC-48 FA to R43. LSP occupies 300 Mbps on the FA4. Link R2-OC11 removed from database

FA, 2.5G

Optical Network

R9

R8R7R1

R2

R3

O12O15

O14

O13R10R11

R12

R4R5

R6

O10

O11

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TE Example Cont.

R9

R8

R7R1 R2

R3

To set up LSP3 (R2-R12):1. Path: R2-R7-R9-O15-O14-O13-O10-R10-R122. R9 establishes an OC-48 FA to R103. LSP occupies 200 Mbps on the FA4. Link R9-O15 & R10-O10 removedfrom database.

The next LSP set-up utilizes an overlaytopology of FAs only!

It may make sense to change this topologybased on observed traffic pattern betweenrouters

Thus, the design of this overlay is an importantTE issue.

R10R11

R12R5

R4

R6

NANOG, 10/2000 57

Topology Design

General objective Design topology of least cost that accommodates traffic demand

When LSPs are routed over an FA topology Routers may have to optimize overlay topology to utilize

available resources (ports, etc) efficiently and minimize cost Co-ordination among routers may be required for this

Internally, some optimizations are possible in the optical network to minimize capacity usage, based on overall view of lightpaths routed. It is difficult to push this functionality outside of the optical network

NANOG, 10/2000 58

IP-over-Optical TE Example : Domain Model

1. Each border router gets reachability of others2. Each border router keeps track of availability of edge links3. Lightpaths are set up internally in optical network4. Overlay virtual link (VL) topology is formed based on LSP demand between router networks.

Optical Network

Router Network

Router Network

R5R4

R6

R9

R8R7

Router Network

R1R2

R3

O12O15

O14

O13Router Network

R10R11

R12

O10

O11

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TE Example - Domain Model To set up LSP1:

1. R3 computes path R3-R2-<unspecified>-R82. R2 sends a request to optical net to set-up a path to R73. Lightpath is established from R2 to R74. LSP occupies 100 Mbps on the virtual link5. The VL is also a new routing adjacency

FA, 2.5G

Optical Network

Router Network

Router Network

R5R4

R6

R9

R8

R7

Router Network

R1R2

R3

O12O15

O14

O13Router Network

R10R11

R12

O10

O11

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IP-over-Optical TE Issues

TE rules should be incorporated in all routers to decide when to select new optical paths, as opposed to using existing FAs or VLs

Should resource optimization in optical network be an objective of LSP routing? (This requirement may be handled best internally in the optical network)

TE work must investigate to what degree internal optical network information (topology, etc) aid in IP over optical TE decisions.

Specifically, with regard to protection, requiring physical topology characteristics (e.g. SRLG) of optical network at the IP layer for computing alternate paths may be impractical.

NANOG, 10/2000 61

Finally….

What applications may be built based on dynamic bandwidth provisioning?

IP over Optical Networks

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