selecting domain paths in inter-domain mpls-tp and mpls-te networks

Old Dog Consulting

www.mpls2009.com

Selecting Domain Paths in Inter-Domain MPLS-TP and MPLS-TE

NetworksDavid AmzallagBritish Telecom PLC

[email protected]

Adrian FarrelOld Dog Consulting

[email protected]

Daniel KingOld Dog Consulting

[email protected]

Old Dog ConsultingOld Dog Consulting

Agenda

Existing multi-domain PCE techniques Domain meshes Navigating the domain mesh Hierarchical PCE

Objective Functions Procedures & Extensions

Advanced applications Work to be done


Existing Multi-Domain PCE Techniques

PCE can be used to determine end-to-end paths in multi-domain GMPLS and MPLS-TE networks

per-domain path computation techniques Devolve the computation of a path segment to each domain entry point Suits simply-connected domains and where the preferred points of interconnection are known

Backwards Recursive Path Computation (BRPC) Allow the PCEs to collaborate to select an optimal end-to-end path that crosses multiple

domains Suits environments where multiple connections exist between domains and there is no

preference for the choice of points of interconnection

The assumption is the sequence of domains is well known, these techniques do not suit complex domain environments

Large, meshy environments Multi-homed and multiply interconnected domains

How do we derive an optimal end-to-end domain path sequences? Definition of optimal will depend on policy

Optimal trees Small number of domains crossed Reduce the number of border routers used


Existing Multi-Domain PCE Techniques

Per domain With per domain the sequence of domains is known Domain border nodes are also usually known Computation technique builds path segments across individual domains Domain choice is only possible with crankback The mechanism does not guarantee an optimal path

BRPC Current definition (RFC 5441) domain sequence is already known BRPC is good for selecting domain border nodes Computation technique derives optimal end-to-end path BRPC could be applied to domain selection

Functions correctly (optimal solution) Significant scaling issues


Domain Meshes

Optical networks constructed from multiple sub-domains, or multi-AS environments often have multiple interconnect points

In an ASON subnetwork the computation of an end-to-end path requires the selection of nodes and links within a parent domain where some nodes may in fact be subnetwork

The traffic engineering properties of a domain cannot be seen from outside the domain

TE aggregation or abstraction hides information and leads to failed path setup Flooding TE information breaks confidentiality and does not scale in the routing protocol and in the

aggregation process

Domain 2

Domain 2

Domain 5

Domain 5

Domain 3

Domain 3

Domain 4

Domain 4

Domain 1

Domain 1


Navigating the Domain Mesh

A computation solution needs to be scalable and maintain confidentiality while providing the optimal path. It also needs consider a number of factors: Domain and Path Diversity

Domain diversity should facilitate the selection of paths that share ingress and egress domains, but do not share transit domains

Domain path selection should provide the capability to include or exclude specific border nodes

Existing Traffic Engineering Constraints The solution should take advantage of typical traffic engineering constraints (hop

count, bandwidth, lambda continuity, path cost, etc.)

Commercial Constraints The solution should provide the capability to include commercially relevant

constraints such as policy, SLAs, security, peering preferences, and dollar costs


Hierarchical PCE

The Parent PCE maintains a topology map The nodes are the Child domains The map contains the inter-domain links The TE capabilities of the links are also known

Parent PCE knows the identify and location of the child PCEs responsible for the Child domains Statically configured or dynamically discovered

Domain confidentiality A Parent PCE is aware of the topology and connections between domains, but is not

aware of the contents of the domains Child domains are completely confidential

One child cannot know the topology of another Child Child domains do not know the general domain mesh connectivity


Domain 1PCE 1

S

BN 11

BN 12

BN 13

Domain 5

Hierarchical Domain Topology

PCE 5

Domain 2PCE 2

Domain 4PCE 4

Domain 3PCE 3

D

BN 21

BN 22

BN 23

BN 24

BN 31

BN 32

BN 41

BN 42

BN 33


Hierarchical PCE

Each Child PCE is configured with the address of its parent PCE Typical, there will only be one or two Parents of any Child

The Parent PCE also needs to be aware of the Child PCEs for all Child domains

The Parent PCE could be configured with this information The Parent PCE could learn about this information when they connect

Domain interconnection discovery The Child PCE reports the following information to the Parent PCE:

Each Child PCE knows the identity of its neighbor domains The IGP in each domain advertises inter-domain TE link capabilities

No further automated discovery is required Multi-domain and multi-provider discovery is undesirable

Confidentiality Security Scalability


Hierarchical PCE Objective Functions

Metric objectives when computing a inter-domain paths may include: Minimum cost path Minimum load path Maximum residual bandwidth path Minimize aggregate bandwidth consumption Limit the number of domains crossed

Policy objectives Commercial relationships Dollar costs of paths Security implications Domain reliability

Domain confidentiality Intra-domain topologies and paths may be kept confidential

From other Child PCEs From the Parent PCE


Hierarchical PCE Procedures

Hierarchical PCE, initial information exchange

Domain 1PCE 1

BN 11

BN 12

BN 13

PCE 5

Domain 5

1. Child PCE configured for its Parent PCE1. Child PCE configured for its Parent PCE2. Child PCE listens to Child IGP and learns inter-domain connectivity2. Child PCE listens to Child IGP and learns inter-domain connectivity

3. Child PCE establishes contact with Parent PCE3. Child PCE establishes contact with Parent PCE

4. Child PCE reports neighbor domain connectivity

4. Child PCE reports neighbor domain connectivity

5. Child PCE reports inter-domain link status change5. Child PCE reports inter-domain link status change


Domain interconnectivity as seen by the Parent PCE The Parent PCE maintains a topology map of the Child domains and their

interconnectivity

Parent PCE cannot see the internal topology of Child domain


Domain 5

Domain 1

PCE 5

Domain 2 Domain 3

Domain 4


Domain 1

S


PCE 1

BN 11BN 11

BN 12BN 12

BN 13BN 13

PCE 5 Domain 5

Domain 2

PCE 2

Domain 4

PCE 4

Domain 3

PCE 3

D

1. Ingress LSR sends a request to PCE1 for a path to egress

2. PCE 1 determines egress is not in domain 1

3. PCE 1 sends computation request to parent PCE (PCE 5)

5. Parent PCE sends edge-to-edge computation requests to PCE 2 responsible for domain 2, and to PCE 4 responsible for domain 4

4. Parent PCE determines likely domain paths

8. Parent PCE correlates responses and applies policy requirements9. Parent PCE supplies ERO to PCE 1

6. Parent PCE send source to edge request to PCE 1

7. Parent PCE sends edge to egress request to PCE3


Advanced Applications

Confidentiality Simple application of PCE path-key Parent PCE does not need to know the confidential information from domains

Point-to-multipoint Applies to multi-domain networks See later presentation for more information (Multicast over optical multi-domain

networks)

Multi-level hierarchy Parent PCE may itself have a parent Regional and administrative hierarchies

Horizontal cooperation between Parents Parent PCEs could cooperate using existing PCE cooperation techniques Cooperation between peer geographic or administrative hierarchies


Work to be done

How do I know which domain contains my destination? Discovery is impractical unless addressing identifies the domain It is usual for the source to know the destination location

Publish framework draft as RFC draft-king-pce-hierarchy-fwk

Minor protocol extensions Applicability statements

Point-to-multipoint Applicability to ASON routing (G.7715.2)


Questions?

Please feel free to send any questions to:

David Amzallag [email protected] Farrel [email protected] King [email protected]

selecting domain paths in inter-domain mpls-tp and mpls-te networks

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