Transcript PPT Version
Path Computation Element (PCE) Architecture (draft-ash-pce-architecture-01.txt) Jerry Ash AT&T [email protected] Adrian Farrell Old Dog Consulting [email protected] JP Vasseur Cisco Systems, Inc. [email protected] Outline PCE architecture summary provided in backup slides you read the draft I-D updates based on comments raised on list next step: working group draft 1 PCE Architecture Summary (see backup slides attached) terminology assumptions motivation for PCE architecture PCE architectural considerations security & confidentiality PCE evaluation metrics PCE architecture overview composite PCE external PCE multiple PCE path computation multiple PCE path computation with inter-PCE communication architecture non-goal to specify protocols protocol extensions will be worked out in other IDs 2 Composite PCE Node --------------| --------| Routing ---------| | | | Protocol | | | | TED |<-+----------+-> | | | | | | | | --------| | | | | | | | | | Input | | | | v | | | | --------| | | | | | | | Adjacent | | | PCE | | | Node | | | | | | | | --------| | | | ^ | | | | |Request | | | | |Response| | | | v | | | | --------| | | Service | | | | Signaling| | Request | |Signaling| | Protocol | | ------+->| Engine |<-+----------+-> | | | | | | | | --------| ------------------------ 3 External PCE Node ---------| ----| | | TED |<-+------------> | ----| TED synchronization | | | mechanism (for example, routing protocol) | | | | v | | ----| | | PCE | | | ----| ---------^ | Request/ | Response v Service ---------- Signaling ---------Request| Head-End | Protocol | Adjacent | ---->| Node |<---------->| Node | ------------------- 4 Multiple PCE Path Computation ---------- ---------| | | | | PCE | | PCE | | | | | | ----- | | ----- | | | TED | | | | TED | | | ----- | | ----- | ------------------^ ^ | Request/ | Request/ | Response | Response v v Service ---------- Signaling ------------- Signaling -----------Request| Head-End | Protocol |Intermediate | Protocol |Intermediate| ---->| Node |<---------->| Node |<--------->| Node | --------------------------------- 5 Multiple PCE Path Computation with Inter-PCE Communication ---------- ---------| | Inter-PCE Request/Response | | | PCE |<--------------------------------->| PCE | | | | | | ----- | | ----- | | | TED | | | | TED | | | ----- | | ----- | ------------------^ | Request/ | Response v Service ---------- Signaling ---------- Signaling ---------Request| Head-End | Protocol | Adjacent | Protocol | Adjacent | ---->| Node |<---------->| Node |<---------->| Node | ---------------------------- 6 I-D Updates Based on Issues Raised on List PCE should advertise its capabilities, for example set of constraints it can account for (diversity, SRLGs, optical impairments, wavelength continuity, etc.) text added to Section 6.4 path computation request include if near-disjoint paths acceptable text added to Section 6.6 TED information can include info from sources other than IGP (e.g. LSP routes, reserved bandwidth, measured traffic volume) needed to perform LSP re-optimization needed to reconfigure virtual network topology (VNT) lower layer (e.g., optical) paths text added to Section 6.7 elaborate on advantages of stateful PCE & pitfalls of using stateful PCE in a distributed PCE environment text added to Section 6.8 evaluation metrics should include TED synchronization speed & impact on the data flows text added to Section 7 7 I-D Updates Based on Issues Raised on List identify areas for standardization added Section 5.5 “Areas for Standardization” – based on PCE Charter other editorial changes 8 Next Steps propose draft as PCE WG draft 9 Backup Slides 10 Terminology path computation element (PCE) entity (component, application or network node) capable of computing a network path based on network graph & computational constraints e.g., PCE computes path of a TE LSP by using TED & bandwidth/other constraints path computation client (PCC) any client application requesting a path computation by the PCE domain any collection of network elements within a common sphere of address management or path computational responsibility e.g., IGP areas, AS, multiple ASs within a SP network, multiple ASs across multiple SP networks single PCE path computation: single PCE computes a path in a domain multiple PCE path computation: multiple PCEs compute a path in a domain centralized computation model: all paths in a domain computed by a single, centralized PCE distributed computation model: computation of paths in a domain 11 shared among multiple PCEs Assumptions PCE may or may not be located at head-end e.g. nodes on path contribute to path computation (e.g., loose hops) making them PCEs path computation may be made by PCE physically distinct from the computed path path computed by PCE may be complete: full explicit path of strict hops partial: mix of strict & loose hops (may be an abstract node such as an AS) PCE path computation can be used in conjunction with other path computation models e.g., inter-AS TE LSP may be computed using PCE in some domains but not others no assumptions made about PCE implementation e.g., could be implemented on a router, LSR, dedicated network server, etc. PCE function independent of forwarding capability of node on which it is implemente 12 Motivation for PCE Architecture inter-area/AS optimal path computation (node has partial visibility) computation of inter-area/AS diverse path (node has partial visibility) CPU-intensive path computation/global optimization backup path computation for bandwidth protection with backup capacity optimization multi-layer networks e.g. TDM network provides connectivity for client-layer (IP, MPLS, L2, etc.) absence of TED or use of non-TE-enabled IGP node outside routing domain (e.g., CE to PE path computation) network element lacks control plan or routing capability 13 PCE Architectural Considerations synchronization non-synchronized (e.g., PCE makes multiple individual path computations to generate set of paths) synchronized (e.g., single PCE invokes computations by other PCEs before supplying result to PCC PCE discovery & load balancing detecting PCE liveness PCC-PCE & PCE-PCE communication PCE TED synchronization stateful vs. stateless PCEs monitoring policy & confidentiality must preserve confidentiality across multiple SPs must ensure confidentiality & security of PCC-PCE & PCEPCE messages 14 Security & Confidentiality PCC-PCE communication subject to "usual" security issues snooping not a significant issue – might want to encrypt spoofing is very serious – must offer strong authentication – protocol is P2P so this is relatively easy DoS important because of 'centralized' nature of PCE PCE-PCE communication same as for PCC-PCE, but add confidentiality confidentiality (protection of domain topology information) use loose routes PCE encrypts ERO segments – decrypt on entry to domain replace ERO segment with cookie – entry point to domain consults local PCE using cookie to retrieve next ERO segment 15 PCE Evaluation Metrics optimality scalability load sharing multiple path computation reoptimization path computation time network stability synchronization between TED & network topology/resource states speed of TED synchronization impact of synchronization on data flows 16