Network Working Group Y. Lee Internet-Draft Huawei Intended status: Standards Track JL. Le Roux Expires: January 15, 2009 France Telecom D. King Old Dog Consulting E. Oki NTT July 14, 2008 Path Computation Element Communication Protocol (PCECP) Requirements and Protocol Extensions In Support of Global Concurrent Optimization draft-ietf-pce-global-concurrent-optimization-04.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 15, 2009. Lee, et al. Expires January 15, 2009 [Page 1] Internet-Draft PCE Global Concurrent Optimization July 2008 Abstract The Path Computation Element (PCE) is a network component, application, or node that is capable of performing path computations at the request of Path Computation Clients (PCCs). The PCE is applied in Multiprotocol Label Switching Traffic Engineering (MPLS-TE) networks and in Generalized MPLS (GMPLS) networks to determine the routes of Label Switched Paths (LSPs) through the network. In this context a PCC may be a Label Switching Router (LSR), a Network Management System (NMS), or another PCE. The Path Computation Element Communication Protocol (PCEP) is specified for communications between PCCs and PCEs, and between cooperating PCEs. When computing or re-optimizing the routes of a set of LSPs through a network it may be advantageous to perform bulk path computations in order to avoid blocking problems and to achieve more optimal network- wide solutions. Such bulk optimization is termed Global Concurrent Optimization (GCO). A GCO is able to simultaneously consider the entire topology of the network and the complete set of existing LSPs, and their respective constraints, and look to optimize or re-optimize the entire network to satisfy all constraints for all LSPs. A GCO may also be applied to some subset of the LSPs in a network. The GCO application is primarily a Network Management System (NMS) solution. While GCO is applicable to any simultaneous request for multiple LSPs (for example, a request for end-to-end protection), it is not invisaged that global concurrent reoptimization would be applied in a network (such as an MPLS-TE network) that contains a very large number of very low bandwidth or zero bandwidth LSPs since the large scope of the problem and the small benefit of concurrent reoptimization relative to single LSP reoptimization is unlikely to make the process worthwhile. Further, applying global concurrent reoptimization in a network with a high rate of change of LSPs (churn) is not advised because of the likelihood that LSPs would change before they could be gloablly reoptimized. Global reoptimization is more applicable to stable networks such as transport networks or those with long-term TE LSP tunnels. This document provides application-specific requirements and the PCEP extensions in support of GCO applications. Lee, et al. Expires January 15, 2009 [Page 2] Internet-Draft PCE Global Concurrent Optimization July 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Applicability of Global Concurrent Optimization (GCO) . . . . 7 3.1. Application of the PCE Architecture . . . . . . . . . . . 7 3.2. Greenfield Optimization . . . . . . . . . . . . . . . . . 8 3.2.1. Single-layer Traffic Engineering . . . . . . . . . . . 8 3.2.2. Multi-layer Traffic Engineering . . . . . . . . . . . 8 3.3. Re-optimization of Existing Networks . . . . . . . . . . . 8 3.3.1. Reconfiguration of the Virtual Network Topology (VNT) . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3.2. Traffic Migration . . . . . . . . . . . . . . . . . . 9 4. PCECP Requirements . . . . . . . . . . . . . . . . . . . . . . 11 5. Protocol Extensions for Support of Global Concurrent Optimization . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1. Global Objective Function (GOF) Specification . . . . . . 15 5.2. Indication of Global Concurrent Optimization Requests . . 16 5.3. Request for The Order of LSP . . . . . . . . . . . . . . . 16 5.4. The Order Response . . . . . . . . . . . . . . . . . . . . 17 5.5. GLOBAL CONSTRAINTS (GC) Object . . . . . . . . . . . . . . 18 5.6. Error Indicator . . . . . . . . . . . . . . . . . . . . . 19 5.7. NO-PATH Indicator . . . . . . . . . . . . . . . . . . . . 20 6. Manageability Considerations . . . . . . . . . . . . . . . . . 21 6.1. Control of Function and Policy . . . . . . . . . . . . . . 21 6.2. Information and Data Models, e.g. MIB module . . . . . . . 21 6.3. Liveness Detection and Monitoring . . . . . . . . . . . . 21 6.4. Verifying Correct Operation . . . . . . . . . . . . . . . 21 6.5. Requirements on Other Protocols and Functional Components . . . . . . . . . . . . . . . . . . . . . . . . 22 6.6. Impact on Network Operation . . . . . . . . . . . . . . . 22 7. Security Considerations . . . . . . . . . . . . . . . . . . . 23 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 9.1. Request Parameter Bit Flags . . . . . . . . . . . . . . . 25 9.2. New PCEP TLV . . . . . . . . . . . . . . . . . . . . . . . 25 9.3. New PCEP Object . . . . . . . . . . . . . . . . . . . . . 25 9.4. New PCEP Error Codes . . . . . . . . . . . . . . . . . . . 26 9.4.1. New Error-Values for Existing Error-Types . . . . . . 26 9.4.2. New Error-Types and Error-Values . . . . . . . . . . . 26 9.5. New No-Path Reasons . . . . . . . . . . . . . . . . . . . 26 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 10.1. Normative References . . . . . . . . . . . . . . . . . . . 27 10.2. Informative References . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Intellectual Property and Copyright Statements . . . . . . . . . . 30 Lee, et al. Expires January 15, 2009 [Page 3] Internet-Draft PCE Global Concurrent Optimization July 2008 1. Introduction [RFC4655] defines the Path Computation Element (PCE) based Architecture and explains how a PCE may compute Label Switched Paths (LSPs) in Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS) networks at the request of Path Computation Clients (PCCs). A PCC is shown to be any network component that makes such a request and may be for instance a Label Switching Router (LSR) or a Network Management System (NMS). The PCE, itself, is shown to be located anywhere within the network, and may be within an LSR, an NMS or Operational Support System (OSS), or may be an independent network server. The PCE Communication Protocol (PCEP) is the communication protocol used between PCC and PCE, and may also be used between cooperating PCEs. [RFC4657] sets out generic protocol requirements for PCEP. Additional application-specific requirements for PCEP are defined in separate documents. This document provides a set of requirements and PCEP extensions in support of concurrent path computation applications. A concurrent path computation is a path computation application where a set of TE paths are computed concurrently in order to efficiently utilize network resources. The computation method involved with a concurrent path computation is referred to as global concurrent optimization in this document. Appropriate computation algorithms to perform this type of optimization are out of the scope of this document. The Global Concurrent Optimization (GCO) application is primarily an NMS or a PCE Server based solution. Owing to complex synchronization issues associated with GCO applications, the management based PCE architecture defined in section 5.5 of [RFC4655] is considered as the most suitable usage to support GCO application. This does not preclude other architectural alternatives to support GCO application, but they are NOT RECOMMENDED. For instance, GCO might be enabled by distributed LSRs through complex synchronization mechanisms. However, this approach might suffer from significant synchronization overhead between the PCE and each of the PCCs. It would likely affect the network stability and hence significantly diminish the benefits of deploying PCEs. The need for global concurrent path computation may also arise when network operators need to establish a set of TE LSPs in their network planning process. It is also envisioned that network operators might require global concurrent path computation in the event of catastrophic network failures, where a set of TE LSPs need to be optimally rerouted. The nature of this work promote the use of such systems for offline processing. Online application of this work Lee, et al. Expires January 15, 2009 [Page 4] Internet-Draft PCE Global Concurrent Optimization July 2008 should only be considered with proven empirical validation. As new LSPs are added or removed from the network over time, the global network resources become fragmented and the existing placement of LSPs within network no longer provides optimal use of the available capacity. A global concurrent path computation is able to simultaneously consider the entire topology of the network and the complete set of existing LSPs and their respective constraints, and look to re-optimize the entire network to satisfy all constraints for all LSPs. Alternatively, the application may consider a subset of the LSPs and/or a subset of the network topology. While GCO is applicable to any simultaneous request for multiple LSPs (for example, a request for end-to-end protection), it is not invisaged that global concurrent reoptimization would be applied in a network (such as an MPLS-TE network) that contains a very large number of very low bandwidth or zero bandwidth LSPs since the large scope of the problem and the small benefit of concurrent reoptimization relative to single LSP reoptimization is unlikely to make the process worthwhile. Further, applying global concurrent reoptimization in a network with a high rate of change of LSPs (churn) is not advised because of the likelihood that LSPs would change before they could be gloablly reoptimized. Global reoptimization is more applicable to stable networks such as transport networks or those with long-term TE LSP tunnels. As the PCE has the potential to provide solutions in all path computation solutions in a variety of environments and is a candidate for performing path computations in support of GCO. The main focus of this document is to highlight the PCC-PCE communication needs in support of a concurrent path computation applications and to define protocol extensions to meet those needs. The PCC-PCE requirements addressed herein are specific to the context where the PCE is a specialized PCE that is capable of performing computations in support of GCO. Discovery of such capabilities might be desirable and could be achieved through extensions to the PCE discovery mechanisms [RFC4674], [RFC5088], [RFC5089], but that is out of the scope of this document. It is to be noted that Backward Recursive Path Computation (BRPC) [BRPC] is a multi-PCE path computation technique used to compute a shortest constrained inter-domain path wheres this ID specifies a technique where a set of path computation requests are bundled and send to a PCE with the objective of "optimizing" the set of computed paths. Lee, et al. Expires January 15, 2009 [Page 5] Internet-Draft PCE Global Concurrent Optimization July 2008 2. Terminology Most of the terminology used in this document is explained in [RFC4655]. A few key terms are repeated here for clarity. PCC: Path Computation Client: Any client application requesting a path computation to be performed by a Path Computation Element. PCE: Path Computation Element: An entity (component, application or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. TED: Traffic Engineering Database which contains the topology and resource information of the domain. The TED may be fed by IGP extensions or potentially by other means. PCECP: The PCE Communication Protocol: PCECP is the generic abstract idea of a protocol that is used to communicate path computation requests a PCC to a PCE, and to return computed paths from the PCE to the PCC. The PCECP can also be used between cooperating PCEs. PCEP: The PCE communication Protocol: PCEP is the actual protocol that implements the PCECP idea. GCO: Global Concurrent Optimization: A concurrent path computation application where a set of TE paths are computed concurrently in order to efficiently utilize network resources. A GCO path computation is able to simultaneously consider the entire topology of the network and the complete set of existing LSPs, and their respective constraints, and look to optimize or re-optimize the entire network to satisfy all constraints for all LSPs. A GCO path computation can also provide an optimal way to migrate from an existing set of LSPs to a reoptimized set (Morphing Problem). The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. These terms are also used in the parts of this document that specify requirements for clarity of specification of those requirements. Lee, et al. Expires January 15, 2009 [Page 6] Internet-Draft PCE Global Concurrent Optimization July 2008 3. Applicability of Global Concurrent Optimization (GCO) This section discusses the PCE architecture to which GCO is applied. It also discusses various application scenarios for which global concurrent path computation may be applied. 3.1. Application of the PCE Architecture Figure 1 shows the PCE-based network architecture as defined in [RFC4655] to which GCO application is applied. It must be observed that the PCC is not necessarily an LSR [RFC4655]. The GCO application is primarily an NMS-based solution in which an NMS plays the function of the PCC. Although Figure 1 shows the PCE as remote from the NMS, it might be collocated with the NMS. Note that in the collocated case there is no need for a standard communication protocol; this can rely on internal APIs. ----------- Application | ----- | Request | | TED | | | | ----- | v | | | ------------- Request/ | v | | PCC | Response| ----- | | (NMS/Server)|<--------+> | PCE | | | | | ----- | ------------- ----------- Service | Request | v ---------- Signaling ---------- | Head-End | Protocol | Adjacent | | Node |<---------->| Node | ---------- ---------- Figure 1: PCE-Based Architecture for Global Concurrent Optimization Upon receipt of an application request (e.g., a traffic demand matrix is provided to the NMS by the operator's network planning procedure), the NMS requests a global concurrent path computation from the PCE. The PCE then computes the requested paths concurrently applying some algorithms. Various algorithms and computation techniques have been proposed to perform this function. Specification of such algorithms Lee, et al. Expires January 15, 2009 [Page 7] Internet-Draft PCE Global Concurrent Optimization July 2008 or techniques is outside the scope of this document. When the requested path computation completes, the PCE sends the resulting paths back to the NMS. The NMS then supplies the head-end LSRs with a fully computed explicit path for each TE LSP that needs to be established. 3.2. Greenfield Optimization Greenfield optimization is a special case of GCO application when there are no LSPs already set up in the network. The need for greenfield optimization arises when network planner wants to make use of a computation server to plan the LSPs that will be provisioned in the network. When a new TE network needs to be provisioned from a greenfield perspective, a set of TE LSPs needs to be created based on traffic demand, network topology, service constraints, and network resources. In this scenario, the ability to perform concurrent computation is desirable, or required, to utilize network resources in an optimal manner and avoid blocking. 3.2.1. Single-layer Traffic Engineering Greenfield optimization can be applied when layer-specific TE LSPs need to be created from a greenfield perspective. For example, an MPLS-TE network can be planned based on layer 3 specific traffic demands, the network topology, and available network resources. Greenfield optimization for single-layer traffic engineering can be applied to optical transport networks such as SDH/Sonet, Ethernet Transport, WDM, etc. 3.2.2. Multi-layer Traffic Engineering Greenfield optimization is not limited to single-layer traffic engineering. It can also be applied to multi-layer traffic engineering [PCE-MLN]. Both the client and the server layers network resources and topology can be considered simultaneously in setting up a set of TE LSPs that traverse the layer boundary. 3.3. Re-optimization of Existing Networks The need for global concurrent path computation may arise in existing networks. When an existing TE LSP network experiences sub-optimal use of its resources, the need for re-optimization or reconfiguration may arise. The scope of re-optimization and reconfiguration may vary depending on particular situations. The scope of re-optimization may be limited to bandwidth modification to an existing TE LSP. However, Lee, et al. Expires January 15, 2009 [Page 8] Internet-Draft PCE Global Concurrent Optimization July 2008 it could well be that a set of TE LSPs may need to be re-optimized concurrently. In an extreme case, the TE LSPs may need to be globally re-optimized. In loaded networks, with large size LSPs, a sequential re- optimization may not produce substantial improvements in terms of overall network optimization. Sequential re-optimization refers to a path computation method in which to compute the re-optimized path of one LSP at a time without giving any consideration to the other LSPs that need to be re-optimized in the network. The potential for network-wide gains from reoptimization of LSPs sequentially is dependent upon the network usage and size of the LSPs being optimized. However, the key point remains: computing the reoptimized path of one LSP at a time without giving any consideration to the other LSPs in the network could result in sub-optimal use of network resources. This may be far more visible in an optical network with a low ratio of potential LSPs per link, and far less visible in packet networks with micro-flow LSPs. With regards to applicability of GCO in the event of catastrophic failures, there may be a real benefit in computing the paths of the LSPs as a set rather than computing new paths from the head-end LSRs in a distributed manner. GCO could prevent race condition (i.e., competing for the same resource from different head-end LSRs) that may be associated with a distributed computation. However, a centralized system will typically suffer from a slower response time than a distributed system. 3.3.1. Reconfiguration of the Virtual Network Topology (VNT) Reconfiguration of the VNT [MLN-REQ] [PCE-MLN] is a typical application scenario where global concurrent path computation may be applicable. Triggers for VNT reconfiguration, such as traffic demand changes, network failures, and topological configuration changes, may require a set of existing LSPs to be re-computed. 3.3.2. Traffic Migration When migrating from one set of TE LSPs to a reoptimized set of TE LSPs it is important that the traffic be moved without causing disruption. Various techniques exist in MPLS and GMPLS, such as make-before-break [RFC3209], to establish the new LSPs before tearing down the old LSPs. When multiple LSP routes are changed according to the computed results, some of the LSPs may be disrupted due to the resource constraints. In other words, it may prove to be impossible to perform a direct migration from the old LSPs to the new optimal LSPs without disrupting traffic because there are insufficient network resources to support both sets of LSPs when make-before-break Lee, et al. Expires January 15, 2009 [Page 9] Internet-Draft PCE Global Concurrent Optimization July 2008 is used. However, a PCE may be able to determine a sequence of make- before- break replacement of individual LSPs or small sets of LSPs so that the full set of LSPs can be migrated without any disruption. It may be the case that the reoptimization is radical. This could mean that it is not possible to apply make-before-break in any order to migrate from the old LSPs to the new LSPs. In this case a migration strategy is required that may necessitate LSPs being rerouted using make-before-break onto temporary paths in order to make space for the full reoptimization. A PCE might indicate the order in which reoptimized LSPs must be established and take over from the old LSPs, and may indicate a series of different temporary paths that must be used. Alternatively, the PCE might perform the global reoptimization as a series of sub-reoptimizations by reoptimizing subsets of the total set of LSPs. The benefit of this multi-step rerouting includes minimization of traffic discruption and optimization gain. However this approach may imply some transient packets desequencing, jitter as well as control plane stress. Note also that during reoptimization, traffic disruption may be allowed for some LSPs carrying low priority services (e.g., Internet traffic) and not allowed for some LSPs carrying mission critical services (e.g., voice traffic). Lee, et al. Expires January 15, 2009 [Page 10] Internet-Draft PCE Global Concurrent Optimization July 2008 4. PCECP Requirements This section provides the PCECP requirements to support global concurrent path computation applications. The requirements specified here should be regarded as application-specific requirements and are justifiable based on the extensibility clause found in section 6.1.14 of [RFC4657]: The PCECP MUST support the requirements specified in the application-specific requirements documents. The PCECP MUST also allow extensions as more PCE applications will be introduced in the future. It is also to be noted that some of the requirements discussed in this section have already been discussed in the PCECP requirement document [RFC4657]. For example, Section 5.1.16 in [RFC4657] provides a list of generic constraints while Section 5.1.17 in [RFC4657] provides a list of generic objective functions that MUST be supported by the PCECP. While using such generic requirements as the baseline, this section provides application-specific requirements in the context of global concurrent path computation and in a more detailed level than the generic requirements. The PCEP SHOULD support the following capabilities either via creation of new objects and/or modification of existing objects where applicable. o An indicator to convey that the request is for a global concurrent path computation. This indicator is necessary to ensure consistency in applying global objectives and global constraints in all path computations. Note: This requirement is covered by "synchronized path computation" in [RFC4655] and [RFC4657]. However, an explicit indicator to request a global concurrent optimization is a new requirement. o A Global Objective Function (GOF) field in which to specify the global objective function. The global objective function is the overarching objective function to which all individual path computation requests are subjected in order to find a globally optimal solution. Note that this requirement is covered by "synchronized objective functions" in section 5.1.7 [RFC4657] and that [PCE-OF] defined three global objective functions as follows. A list of available global objective functions SHOULD include the following objective functions at the minimum and SHOULD be expandable for future addition: * Minimize aggregate Bandwidth Consumption (MBC) Lee, et al. Expires January 15, 2009 [Page 11] Internet-Draft PCE Global Concurrent Optimization July 2008 * Minimize the load of the Most Loaded Link (MLL) * Minimize Cumulative Cost of a set of paths (MCC) o A Global Constraints (GC) field in which to specify the list of global constraints to which all the requested path computations should be subjected. This list SHOULD include the following constraints at the minimum and SHOULD be expandable for future addition: * Maximum link utilization value -- This value indicates the highest possible link utilization percentage set for each link. (Note: to avoid floating point numbers, the values should be integer values.) * Minimum link utilization value -- This value indicates the lowest possible link utilization percentage set for each link. (Note: same as above) * Overbooking Factor -- The overbooking factor allows the reserved bandwidth to be overbooked on each link beyond its physical capacity limit. * Maximum number of hops for all the LSPs -- This is the largest number of hops that any LSP can have. Note that this constraint can also be provided on a per LSP basis (as requested in [RFC4657] and defined in [PCEP]). * Exclusion of links/nodes in all LSP path computation (i.e., all LSPs should not include the specified links/nodes in their paths). Note that this constraint can also be provided on a per LSP basis (as requested in [RFC4657] and defined in [PCEP]). * An indication should be available in a path computation response that further reoptimization may only become available once existing traffic has been moved to the new LSPs. o A Global Concurrent Vector (GCV) field in which to specify all the individual path computation requests that are subject to concurrent path computation and subject to the global objective function and all of the global constraints. Note that this requirement is entirely fulfilled by the SVEC object in the PCEP specification [PCEP]. Since the SVEC object as defined in [PCEP] allows identifying a set of concurrent path requests, the SVEC can be reused to specify all the individual concurrent path requests for a global concurrent optimization. Lee, et al. Expires January 15, 2009 [Page 12] Internet-Draft PCE Global Concurrent Optimization July 2008 o An indicator field in which to indicate the outcome of the request. When the PCE cannot find a feasible solution with the initial request, the reason for failure SHOULD be indicated. This requirement is partially covered by [RFC4657], but not in this level of detail. The following indicators SHOULD be supported at the minimum: * no feasible solution found. Note that this is already covered in [PCEP]. * memory overflow * PCE too busy. Note that this is already covered in [PCEP]. * PCE not capable of concurrent reoptimization * no migration path available * administrative privileges do not allow global reoptimization o In order to minimize disruption associated with bulk path provisioning, the following requirements MUST be supported: * The request message MUST allow requesting the PCE to provide the order in which LSPs should be reoptimized (i.e., the migration path) in order to minimize traffic disruption during the migration. That is the request message MUST allow indicating to the PCE that the set of paths that will be provided in the response message (PCRep) has to be ordered. * In response to the "ordering" request from the PCC, the PCE MUST be able to indicate in the response message (PCRep) the order in which LSPs should be reoptimized so as to minimize traffic disruption. It should indicate for each request the order in which the old LSP should be removed and the order in which the new LSP should be setup. If the removal order is lower than the setup order this means that make-before-break cannot be done for this request. It MAY also be desirable to have the PCE indicate whether ordering is in fact required or not. * As stated in RFC 4657, the request for a reoptimization MUST support the inclusion of the set of previously computed paths along with their bandwidth. This is to avoid double bandwidth accounting and also this allows running an algorithm that minimizes perturbation and that can compute a migration path (LSP setup/removal orders). This is particularly required for stateless PCEs. Lee, et al. Expires January 15, 2009 [Page 13] Internet-Draft PCE Global Concurrent Optimization July 2008 * During a migration it may not be possible to do a make-before- break for all existing LSPs. The request message MUST allow indicating for each request whether make-before-break is required (e.g. Voice traffic) or break-before-make is acceptable (e.g. Internet traffic). The response message must allow indicating LSPs for which make-before-break reoptimization is not possible (this will be deduced from the LSP setup and deletion orders). Lee, et al. Expires January 15, 2009 [Page 14] Internet-Draft PCE Global Concurrent Optimization July 2008 5. Protocol Extensions for Support of Global Concurrent Optimization This section provides protocol extensions for support of global concurrent optimization. Protocol extensions discussed in this section are built on [PCEP]. The format of a PCReq message after incorporating new requirements for support of global concurrent optimization is as follows: ::= [] The is changed as follows: :: = [] [] [] [] Note that three optional objects are added, following the SVEC object: the OF (Objective Function) object, which is defined in [PCE-OF], the GC (Global Constraints) object, which is defined in this document (section 5.5), as well as the eXclude Route Object (XRO) which is defined in [PCE-XRO]. The placement of the OF object (in which the global objective function is specified) in the SVEC- list is defined in [PCE-OF]. Details of this change will be discussed in the following sections. Note also that when the XRO is global to a SVEC, and F bit is set, it SHOULD be allowed to specify multiple Reported Route Objects (RROs) in the PCReq message. 5.1. Global Objective Function (GOF) Specification The global objective function can be specified in the PCEP Objective Function (OF) object, defined in [PCE-OF]. The OF object includes a 16 bit Objective Function identifier. As per discussed in [PCE-OF], objective function identifier code points are managed by IANA. Three global objective functions defined in [PCE-OF] are used in the context of GCO. Lee, et al. Expires January 15, 2009 [Page 15] Internet-Draft PCE Global Concurrent Optimization July 2008 Function Code Description 4 Minimize aggregate Bandwidth Consumption (MBC) 5 Minimize the load of the Most Loaded Link (MLL)* 6 Minimize Cumulative Cost of a set of paths (MCC) * Note: This can be achieved by the following objective function: minimize max over all links {(C(i)-A(i))/C(i)} where C(i) is the link capacity for link i and A(i) is the total bandwidth allocated on link i. 5.2. Indication of Global Concurrent Optimization Requests All the path requests in this application should be indicated so that the global objective function and all of the global constraints are applied to each of the requested path computation. This can be indicated implicitly by placing the GCO related objects (GOF, GC or XRO) after the SVEC object. That is, if any of these objects follows the SVEC object in the PCReq message, all of the requested path computations specified in the SVEC object are subject to GOF, GC or XRO. 5.3. Request for The Order of LSP In order to minimize disruption associated with bulk path provisioning, the PCC may indicate to the PCE that the response MUST be ordered. That is, the PCE has to include the order in which LSPs MUST be moved so as to minimize traffic disruption. To support such indication a new flag, the D flag, is defined in the RP object as follows: D bit (orDer - 1 bit): when set, in a PCReq message, the requesting PCC requires the PCE to specify in the PCRep message the order in which this particular path request is to be provisioned relative to other requests. To support the determination of whether make-before-break optimization is required, a new flag, the M flag, is defined in the RP object as follows. M bit (Make-before-break - 1 bit): when set, this indicates that a make-before-break reoptimization is required for this request. When M bit is not set, this implies that a break-before-make Lee, et al. Expires January 15, 2009 [Page 16] Internet-Draft PCE Global Concurrent Optimization July 2008 reoptimization is allowed for this request. Note that M bit can be set only if the R (Reoptimization) flag is set. 5.4. The Order Response The PCE MUST specify the order number in response to the Order Request made by the PCC in the PCReq message if so requested by the setting of the D bit in the RP object in the PCReq message. To support such ordering indication a new optional TLV, the Order TLV, is defined in the RP object. The Order TLV is an optional TLV in the RP object, that indicates the order in which the old LSP must be removed and the new LSP must be setup during a reoptimization. It is carried in the PCRep message in response to a reoptimization request. The Order TLV SHOULD be included in the RP object in the PCRep message if the D bit is set in the RP object in the PCReq message. The format of the Order TLV is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Delete Order | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Setup Order | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: The Order TLV in the RP object in the PCRep Message Type: To be defined by IANA (suggested value = 5) Length: Variable Delete Order: 32 bit integer that indicates the order in which the old LSP should be removed Setup Order: 32 bit integer that indicates the order in which the new LSP should be setup The delete order SHOULD not be equal to the setup order. If the Lee, et al. Expires January 15, 2009 [Page 17] Internet-Draft PCE Global Concurrent Optimization July 2008 delete order is higher than the setup order, this means that the reoptimization can be done in a make-before-break manner, else it cannot be done in a make-before-break manner. For a new LSP the delete order is not applicable. The value 0 is designated to specify this case. When the value of the delete order is 0, it implies that the resulting LSP is a new LSP. To illustrate this, consider a network with two established LSPs: R1 with path P1 and R2 with path P2. During a reoptimization the PCE may provide the following ordered reply: R1, path P1', remove order 1, setup order 4 R2, path P2', remove order 3, setup order 2 This indicates that the NMS should do the following sequence of tasks: 1: Remove path P1 2: Setup path P2' 3: Remove path P2 4: Setup path P1' That is, R1 is reoptimized in a break-before-make manner and R2 in a make-before-break manner. 5.5. GLOBAL CONSTRAINTS (GC) Object The GLOBAL CONSTRAINTS (GC) Object is used in a PCReq message to specify the necessary global constraints that should be applied to all individual path computations for a global concurrent path optimization request. GLOBAL CONSTRAINTS Object-Class is to be assigned by IANA (recommended value=24) GLOBAL CONSTRAINTS Object-Type is to be assigned by IANA (recommended value=1) The format of the GC object body that includes the global constraints is as follows: Lee, et al. Expires January 15, 2009 [Page 18] Internet-Draft PCE Global Concurrent Optimization July 2008 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MH | MU | mU | OB | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Optional TLV(s) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: GC body object format MH (Max Hop: 8 bits): 8 bit integer that indicates the maximum hop count for all the LSPs. MU (Max Utilization Percentage: 8 bits) : 8 bits integer that indicates the upper bound utilization percentage by which all link should be bound. Utilization = (Link Capacity - Allocated Bandwidth on the Link)/ Link Capacity mU (minimum Utilization Percentage: 8 bits) : 8 bits integer that indicates the lower bound utilization percentage by which all link should be bound. OB (Over Booking factor Percentage: 8 bits) : 8 bits integer that indicates the overbooking percentage that allows the reserved bandwidth to be overbooked on each link beyond its physical capacity limit. The value, for example, 10% means that 110 Mbps can be reserved on a 100Mbps link. Reserved bits (24 bits) of the GLOBAL CONSTRAINTS Object SHOULD be transmitted as zero and SHOULD be ignored upon receipt. The exclusion of the list of nodes/links from a global path computation can be done by including the XRO object following the GC object in the new SVEC list definition. 5.6. Error Indicator To indicate errors associated with the global concurrent path optimization request, a new Error-Type (14) and subsequent error- values are defined as follows for inclusion in the PCEP-ERROR object: A new Error-Type (15) and subsequent error-values are defined as follows: Error-Type=15 and Error-Value=1: if a PCE receives a global Lee, et al. Expires January 15, 2009 [Page 19] Internet-Draft PCE Global Concurrent Optimization July 2008 concurrent path optimization request and the PCE is not capable of processing the request due to insufficient memory, the PCE MUST send a PCErr message with a PCEP ERROR object (Error-Type=15) and an Error-Value (Error-Value=1). The PCE stops processing the request. The corresponding global concurrent path optimization request MUST be cancelled at the PCC. Error-Type=15; Error-Value=2: if a PCE receives a global concurrent path optimization request and the PCE is not capable of global concurrent optimization, the PCE MUST send a PCErr message with a PCEP-ERROR Object (Error-Type=15) and an Error-Value (Error-Value=2). The PCE stops processing the request. The corresponding global concurrent path optimization MUST be cancelled at the PCC. To indicate an error associated with policy violation, a new error value "global concurrent optimization not allowed" should be added to an existing error code for policy violation (Error-Type=5) as defined in [PCEP]. Error-Type=5; Error-Value=5: if a PCE receives a global concurrent path optimization request which is not compliant with administrative privileges (i.e., the PCE policy does not support global concurrent optimization), the PCE sends a PCErr message with a PCEP-ERROR Object (Error-Type=5) and an Error-Value (Error-Value=5). The PCE stops the processing the request. The corresponding global concurrent path computation MUST be cancelled at the PCC. 5.7. NO-PATH Indicator To communicate the reason(s) for not being able to find global concurrent path computation, the NO-PATH object can be used in the PCRep message. The format of the NO-PATH object body is defined in [PCEP]. The object may contain a NO-PATH-VECTOR TLV to provide additional information about why a path computation has failed. Two new bit flags are defined to be carried in the Flags field in the NO-PATH-VECTOR TLV carried in the NO-PATH Object. Bit 6: When set, the PCE indicates that no migration path was found. Bit 7: When set, the PCE indicates no feasible solution was found that meets all the constraints associated with global concurrent path optimization in the PCRep message. Lee, et al. Expires January 15, 2009 [Page 20] Internet-Draft PCE Global Concurrent Optimization July 2008 6. Manageability Considerations Manageability of Global Concurrent Path Computation with PCE must address the following considerations: 6.1. Control of Function and Policy In addition to the parameters already listed in section 8.1 of [PCEP], a PCEP implementation SHOULD allow configuring the following PCEP session parameters on a PCC: o The ability to send a GCO request. In addition to the parameters already listed in section 8.1 of [PCEP], a PCEP implementation SHOULD allow configuring the following PCEP session parameters on a PCE: o The support for Global Concurrent Optimization. o The maximum number of synchronized path requests per request message. o A set of GCO specific policies (authorized sender, request rate limiter, etc). These parameters may be configured as default parameters for any PCEP session the PCEP speaker participates in, or may apply to a specific session with a given PCEP peer or a specific group of sessions with a specific group of PCEP peers. 6.2. Information and Data Models, e.g. MIB module Extensions to the PCEP MIB module defined in [PCEP-MIB] should be defined, so as to cover the GCO information introduced in this document. 6.3. Liveness Detection and Monitoring Mechanisms defined in this draft does not imply any new liveness detection and monitoring requirements in addition to those already listed in section 8.3 of [PCEP]. 6.4. Verifying Correct Operation Mechanisms defined in this draft do not imply any new verification requirements in addition to those already listed in section 8.4 of [PCEP] Lee, et al. Expires January 15, 2009 [Page 21] Internet-Draft PCE Global Concurrent Optimization July 2008 6.5. Requirements on Other Protocols and Functional Components The PCE Discovery mechanisms ([RFC 5088] and [RFC 5089]) may be used to advertise global concurrent path computation capabilities to PCCs. 6.6. Impact on Network Operation Mechanisms defined in this draft do not imply any new network operation requirements in addition to those already listed in section 8.6 of [PCEP]. Lee, et al. Expires January 15, 2009 [Page 22] Internet-Draft PCE Global Concurrent Optimization July 2008 7. Security Considerations When global re-optimization is applied to an active network, it could be extremely disruptive. Although the real security and policy issues apply at the NMS, if the wrong results are returned to the NMS, the wrong actions may be taken in the network. Therefore, it is very important that the operator issuing the commands has sufficient authority and is authenticated, and that the computation request is subject to appropriate policy. The mechanism defined in [PCEP] to secure a PCEP session can be used to secure global concurrent path computation requests/responses. Lee, et al. Expires January 15, 2009 [Page 23] Internet-Draft PCE Global Concurrent Optimization July 2008 8. Acknowledgements We would like to thank Jerry Ash, Adrian Farrel, J-P Vasseur, Ning So, Lucy Yong and Fabien Verhaeghe for their useful comments and suggestions. Lee, et al. Expires January 15, 2009 [Page 24] Internet-Draft PCE Global Concurrent Optimization July 2008 9. IANA Considerations IANA maintains a registry of PCEP parameters. IANA is requested to make allocations from the sub-registries as described in the following sections. 9.1. Request Parameter Bit Flags As described in Section 5.3, two new bit lfags are defined for inclusion in the Flags field of the RP object. IANA is requested to make the following allocations from the "Request Parameter Bit Flags" sub-registry. Bit Name Description Reference 11 D-bit Report the request order [This.I-D] 12 M-bit Make-before-break [This.I-D] 9.2. New PCEP TLV As described in Section 5.4, a new PCEP TLV is defined to indicate the setup and delete order of LSPs in a GCO. IANA is requested to make the following allocation from the "PCEP TLV Types" sub-registry. TLV Type Meaning Reference 5 Order TLV [This.I-D] 9.3. New PCEP Object As descried in Section 5.5, a new PCEP object is defined to carry global constraints. IANA is requested to make the following allocation from the "PCEP Objects" sub-registry. Object Name Reference Class 24 GLOBAL-CONSTRAINTS [This.I-D] Object-Type 1: Global Constraints [This.I-D] Lee, et al. Expires January 15, 2009 [Page 25] Internet-Draft PCE Global Concurrent Optimization July 2008 9.4. New PCEP Error Codes As described in Section 5.6, new PCEP error codes are defined for GCO errors. IANA is requested to make allocations from the "PCEP Error Types and Values" sub-registry as set out in the following sections. 9.4.1. New Error-Values for Existing Error-Types Error Type Meaning Reference 5 Policy violation Error-value=5: [This.I-D] Global concurrent optimization not allowed 9.4.2. New Error-Types and Error-Values Error Type Meaning Reference 15 Global Concurrent Optimization Error [This.I-D] Error-value=1: Insufficient memory [This.I-D] Error-value=2: Global concurrent optimization not supported [This.I-D] 9.5. New No-Path Reasons IANA is requested to make the following allocations from the "No-Path Reasons" sub-registry for bit flags carried in the NO-PATH-VECTOR TLV in the PCEP NO-PATH object as described in Section 5.7. Bit Number Name Reference 6 No GCO migration path found [This.I-D] 7 No GCO solution found [This.I-D] Lee, et al. Expires January 15, 2009 [Page 26] Internet-Draft PCE Global Concurrent Optimization July 2008 10. References 10.1. Normative References [BRPC] Vasseur, JP., Ed., "A Backward Recursive PCE-based Computation (BRPC) procedure to compute shortest inter- domain Traffic Engineering Label Switched Paths, draft-ietf-pce-brpc, work in progress". [PCE-OF] Le Roux, JL., Vasseur, JP., and Y. Lee, "Objective Function encoding in Path Computation Element communication and discovery protocols, draft-leroux-pce-of, work in progress". [PCE-XRO] Oki, E. and A. Farrel, "Extensions to the Path Computation Element Communication Protocol (PCEP) for Route Exclusions, draft-ietf-pce-pcep-xro, work in progress". [PCEP] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) communication Protocol (PCEP) - Version 1, draft-ietf-pce-pcep, work in progress". [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. [RFC5088] Le Roux, J., Vasseur, J., Ikejiri, Y., and R. Zhang, "OSPF Protocol Extensions for Path Computation Element (PCE) Discovery, RFC 5088, January 2008.". [RFC5089] Le Roux, J., Vasseur, J., Ikejiri, Y., and R. Zhang, "IS-IS Protocol Extensions for Path Computation Element (PCE) Discovery, RFC 5089, January 2008.". 10.2. Informative References [MLN-REQ] Shiomoto, K., Ed., "Requirements for GMPLS-based multi- region and multi-layer networks (MRN/MLN), draft-ietf-ccamp-gmpls-mln-reqs, work in progress". [PCE-MLN] Oki, E., Le Roux, J., and A. Farrel, "Framework for PCE- based inter-layer MPLS and GMPLS traffic engineering, draft-ietf-pce-inter-layer-frwk, work in progress.". [PCEP-MIB] Lee, et al. Expires January 15, 2009 [Page 27] Internet-Draft PCE Global Concurrent Optimization July 2008 Stephen, E. and K. Koushik, "PCE communication protocol(PCEP) Management Information Base, draft-kkoushik-pce-pcep-mib, work in progress.". [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture, RFC 4655, August 2006". [RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements, RFC 4657, September 2006". [RFC4674] Le Roux, J., "Requirements for Path Computation Element (PCE) Discovery, RFC 4674, October 2006.". Lee, et al. Expires January 15, 2009 [Page 28] Internet-Draft PCE Global Concurrent Optimization July 2008 Authors' Addresses Young Lee Huawei 1700 Alma Drive, Suite 100 Plano, TX 75075 US Phone: +1 972 509 5599 x2240 Fax: +1 469 229 5397 Email: ylee@huawei.com JL Le Roux France Telecom 2, Avenue Pierre-Marzin Lannion 22307 FRANCE Email: jeanlouis.leroux@orange-ftgroup.com Daniel King Aria Networks United Kingdom Phone: Fax: Email: daniel@olddog.co.uk Eiji Oki NTT Midori 3-9-11 Musashino, Tokyo 180-8585 JAPAN Email: oki.eiji@lab.ntt.co.jp Lee, et al. Expires January 15, 2009 [Page 29] Internet-Draft PCE Global Concurrent Optimization July 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Lee, et al. Expires January 15, 2009 [Page 30]