Introduction to the Introduction to the Path Computation Element - PowerPoint PPT Presentation

I nternational Telecom m unication Union ITU-T Introduction to the Introduction to the Path Computation Element Path Computation Element Adrian Farrel Old Dog Consulting I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6

Agenda ITU-T o Domains, Path Computation, and TE Abstraction o The Path Computation Element o Basic Architectural Possibilities o PCE-Based Path Computation Examples o Applying PCE to The AS ON Architecture I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 2

Path Com putation ITU-T The selection of the route through the o network taken by a connection Full precomputation 1. On-demand full computation 2. S egment-by-segment computation 3. Hop-by-hop computation 4. I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 3

Dom ains ITU-T “ Any collection of network elements o within a common sphere of address management or path computational responsibility.” Classic examples… o IGP Areas 1. Autonomous S ystems 2. AS ON examples… o S ub-networks 1. Routing levels 2. Layers 3. I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 4

I nterdom ain Routing I ssues ITU-T TE visibility is (completely) limited o Which domain contains the destination? o Which domain to go to next? o Which connection to the next domain? o How to guarantee path diversity for o protection Questions apply to: o Reachability 1. Acceptable paths 2. Optimal paths 3. I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 5

TE Abstraction – A Rejected Option ITU-T Virtual Link Virtual Node “ You can reach this o Hierarchical abstraction o destination across this Presents subnetwork as a o domain with these virtual switch characteristics” Can be very deceptive o BGP-TE model o • No easy way to advertise Requires large amount of o information “ limited cross-connect capabilities” Needs frequent updates o Both rely on crankback signaling and high CPU aggregation I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 6

Path Com putation Elem ent ( PCE) ITU-T A new functional component o Performs path computation 1. Preserves confidentiality 2. Avoids abstraction/ aggregation issues 3. Off-loads computational complexity 4. THE IETF’ s PCE working group defines… o Path Computat ion Element: an entit y • (component, applicat ion or network node) that is capable of comput ing a network path or route based on a network graph and applying computat ional constraints. I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 7

PCE as an NMS Tool ITU-T o PCE can be a tool used by the NMS • May be built into NMS or separate o Traffic Engineering Database (TED) • Fed by configuration, inventory, routing protocols NMS Service Request Config. Request PCE TED IGP Response Service Request Signalling Protocol I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 8

PCE in the Connection Controller ITU-T o PCE can be collocated with the Connection Controller • Easy implementation matches existing code • Request/ response is not a formal interface Config. TED IGP PCE Service Request/Response Request CC CC Signalling Protocol I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 9

The PCE Server ITU-T o PCE implemented as a separate server • Dedicated server or powerful NE o Requires formal request/ response protocol Config. TED IGP PCE Request/Response CC CC Service Signalling Protocol Request I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 1 0

Cooperating PCE Servers ITU-T o PCEs in different domains may cooperate • Use formal request/ response protocol • Increase quality of computed path Config. TED TED IGP Request/Response PCE PCE Request/Response Service Signalling CC CC CC Request Protocol I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 1 1

End-to-end I ndependent PCEs ITU-T o Computation on entry to each domain o S ub-optimal end-to-end paths o Paths may be blocked • Use crankback to recover I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 1 2

End-to-end : Cooperating PCEs ITU-T 3. How should I 2. Thinks… 4. Thinks… reach the Egress? “A looks best” “D would be best” PCE PCE 1. I want to reach 7. I want to reach the Egress the Egress 5. Route thru’ B 8. Route thru’ Y 6. Route thru’ X and B A C Ingress X Y Egress B D I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 1 3

Diverse Path Cooperating PCEs ITU-T 2. Thinks… 4. Thinks… 3. I want disjoint “Need to exit “(D or E) and F” paths to the Egress through A and B” 7. I want to reach PCE the Egress PCE Cookie 1. I want disjoint 5. Route thru’ paths to the Egress 8. Route thru’ Z (A or B) and C Cookies 9. I want to reach the Egress 6. Route thru’ A and XYC Cookie A D 10. Route Ingress thru’ PQ X Z Egress B E Q Y P C F I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 1 4

PCE in the ASON Architecture ITU-T o PCE is applicable to the AS ON Architecture o One PCE per sub-network in peer routing • The model is exactly as j ust demonstrated o One PCE per level in multi-level routing • Hierarchical interaction between PCEs o One PCE per layer in multi-layer routing • Hierarchical interaction between PCEs o New work starting… • G.7715.2 : AS ON routing architecture and requirements for remote path query I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 1 5

Questions? ITU-T o Background reading • draft-ietf-pce-architecture-04.txt • Free download from http:/ / www.ietf.org/ internet-drafts/ o Follow-up off-line • adrian@ olddog.co.uk I TU-T W orkshop “NGN and its Transport Netw orks“ Kobe, 2 0 -2 1 April 2 0 0 6 1 6