Network Working Group Eiji Oki (Editor) Internet Draft NTT Category: Informational Expires: April 2006 October 2005 PCC-PCE Communication Requirements for Inter-Layer Traffic Engineering draft-oki-pce-inter-layer-req-00.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. Abstract The Path Computation Element (PCE) provides functions of path computation in support of traffic engineering in Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks. MPLS and GMPLS networks may be constructed from layered service networks. It is advantageous for overall network efficiency to provide end-to-end traffic engineering across multiple network layers. PCE is a candidate solution for such requirements. Generic requirements for a communication protocol between Path Computation Clients (PCCs) and PCEs are presented in "PCE Communication Protocol Generic Requirements". This document complements the generic requirements and presents a detailed set of PCC-PCE communication protocol requirements for inter-layer traffic engineering. Conventions used in this document Oki et al. Expires April 2006 [Page 1] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 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]. 1. Contributors The following are the authors that contributed to the present document: Eiji Oki (NTT) Jean-Louis Le Roux (France Telecom) Kenji Kumaki (KDDI) Adrian Farrel (Old Dog Consulting) 2. Terminology LSP: Label Switched Path. LSR: Label Switching Router. 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. TE LSP: Traffic Engineering Label Switched Path. TE LSP head-end: head/source/ingress of the TE LSP. TE LSP tail-end: tail/destination/egress of the TE LSP. 3. Introduction The Path Computation Element (PCE) defined in [PCE-ARCH] is an entity that is capable of computing a network path or route based on a network graph, and applying computational constraints. A network may comprise of multiple layers. These layers may represent separations of technology (e.g., PSC, TDM VC4, TDM VC12, LSC) or a distinction between client and server networking roles. In this multi-layer network, LSP in lower layers are used to carry upper- layer LSPs. The network topology formed by lower-layer LSPs and advertised to the higher layer is called a Virtual Network Topology (VNT) [MRN-REQ]. It is important to optimize network resource utilization globally, i.e. taking into account all layers, rather than optimizing resource utilization at each layer independently. This allows achieving better network efficiency. This is what we call Oki et al. Expires April 2006 [Page 2] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 Inter-layer traffic engineering. This includes mechanisms allowing to compute end-to-end paths across layers, as known as inter-layer path computation, and mechanisms for control and management of VNT by setting up and releasing LSPs in lower layers [MRN-REQ]. Inter-layer traffic engineering is included in the scope of the PCE architecture [PCE-ARCH], and PCE can provide a suitable mechanism for resolving inter-layer path computation issues. The use of PCE for the control of the VNT is for further study. This document presents a set of PCC-PCE communication protocol requirements for inter-layer traffic engineering. It supplements the generic requirements documented in [PCE-COM-REQ]. 4. Inter-Layer Traffic Engineering This section describes key topics of inter-layer traffic engineering in MPLS and GMPLS networks. 4.1. Inter-Layer Path Computation [LSP-HIER] defines a way to signal an upper-layer LSP, whose explicit route includes lower-layer(s) LSP paths. The computation of end-to- end paths across layers is called Inter-Layer Path Computation. An LSR in the higher-layer may not have information on the lower- layer topology, particularly in an overlay or augmented model, and hence may not be able to compute an end-to-end path across layers. PCE-based Inter-Layer path computation, consists of relying on one or more PCEs to compute an end-to-end path across layers. This could rely on single PCE path computation where a single PCE have topology information on multiple layers, and can compute an end-to-end path considering all layers' topology, or on multiple PCEs computation where a set of PCEs have information of a single layer topology and collaborate together to build an end-to-end path. A two-layer network is considered. The higher-layer network can be considered as a packet-based IP/MPLS network or GMPLS network. The lower-layer network is considered as a GMPLS optical network. The bandwidth granularity of the lower layer is coarse. For example, the bandwidth is equal to 2.5 Gbit/s or 10 Gbit/s. On the other hand, the granularity of the higher layer is flexible and well engineered. Consider the case where higher-layer LSPs are to be established end- to-end across a lower-layer network. For example, packet LSPs carried across an optical core. Connectivity across the lower-layer is achieved by tunneling the higher-layer LSPs within lower-layer LSPs. However, when the bandwidths of the higher-layer LSPs are much smaller than the capacity of the lower-layer LSPs, the resources in the lower layer are not fully utilized unless a mechanism is provided to aggregate multiple higher-layer LSPs into a single lower-layer LSP. Oki et al. Expires April 2006 [Page 3] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 There are two main options for routing a higher-layer LSP over a lower-layer network. A single hop route uses a single edge-to-edge lower-layer LSP that is managed as a single hop within the higher layer. A multiple hop route uses a series of lower-layer LSPs each of which appears to the higher-layer LSP as a single hop. Lower-layer LSPs form a Virtual Network Topology, which can be used for routing higher-layer LSPs or to carry IP traffic. Inter-layer path computation for end-to-end LSPs in the higher-layer network that span the lower-layer network may utilize the VNT, and PCE is a candidate for computing the paths of such higher-layer LSPs within the higher-layer network. PCEs could: - perform a single computation on behalf of the ingress LSR using information gathered from more than one layer. This mode is referred as to Single PCE Computation in [PCE-ARCH]. - perform a set of cooperated path computations on behalf of the ingress LSR through cooperation between PCEs responsible for each layer. This mode is referred as to Multiple PCE Computation with inter-PCE communication in [PCE-ARCH]. - perform separate path computations on behalf of the TE LSP head-end and each transit LSR that is the entry point to a new layer. This mode is referred as to Multiple PCE Computation (without inter-PCE communication) in [PCE-ARCH]. This option utilizes per-layer path computation performed independently by successive PCEs. Since there is no PCE-PCE communication, and since each PCE is responsible for a single layer only, there are no requirements placed on the PCC-PCE communications protocol above those already defined for single domain operation described in [PCE-COM-REQ]. Therefore this option is not discussed further in this document. When PCE returns to PCC a computed explicit path that would be acceptable for use for MPLS and GMPLS LSPs once converted to an Explicit Route Object (ERO) for use in RSVP-TE signaling, two options could be considered as: -Option 1: Mono-layer path. There are two cases. The first case is that the PCE computes a path that includes already established lower layer-LSPs: that is the ERO includes sub-object(s) corresponding to lower layer hierarchical LSPs. This does not trigger new lower layer- LSP setup but the utilization of existing lower-layer LSPs. The other is that the PCE computes a path that includes loose hop(s). The higher layer would select which lower layers to use and would select the entry and exit points from those layers, but would not select the path across the layers. A transit LSR corresponding to the entry point is expected to expand the loose hop. Path expansion process on border LSR may result either in the selection of an existing lower layer LSP, or in the computation and setup of a new lower-layer LSP. -Option 2: Multi-layer path. The PCE computes a "multi-layer" path that can include the complete path of one or more lower-layer LSPs not yet established. In that case the ERO contains paths of lower- layer LSPs to be established. The signaling of the higher-layer LSP will trigger the establishment of the lower-layer LSPs (nested signaling). Oki et al. Expires April 2006 [Page 4] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 4.2. VNT Management As a result of inter-layer path computation, PCE may determine that there are insufficient lower-layer LSPs to support this or future higher-layer LSPs. New lower-layer LSPs are needed in order to satisfy the high-layer LSP requests or to efficiently manage the utilization of lower-layer network resources. In other words, the VNT needs to be controlled or managed in cooperation with inter-layer path computation. While PCE is responsible for inter-layer path computation, VNT management may be performed by other network elements. The relationship between VNT management and PCE for inter-layer computation is for further study. 5. Inter-layer Path Computation Models The generic PCC-PCE communication protocol requirements [PCE-COM-REQ] are limited to basic path computation scenarios and generic concerns. They do not necessarily cover all the requirements for inter-layer traffic engineering and further requirements are stated in section 6 of this document to address the specific problem statements set out in this section. As stated in Section 4.1, two PCE modes defined in the PCE architecture can be used to perform inter-layer path computation. They are discussed below. 5.1. Single PCE Inter-Layer Path Computation In Figure 1, higher-layer LSRs (H1, H2, H3 and H4) are connected by an end-to-end higher-layer LSP. This is supported by a lower-layer LSP (H2-L1-L2-H3) that traverses the lower-layer LSRs (L1 and L2) but is presented as a single hop (H2-H3) in the higher-layer. A single PCE manages the entire network and has visibility into both layers. ----- | PCE | ----- ----- ----- ----- ----- | LSR |--| LSR |................| LSR |--| LSR | | H1 | | H2 | | H3 | | H4 | ----- -----\ /----- ----- \----- -----/ | LSR |--| LSR | | L1 | | L2 | ----- ----- Figure 1 : Single PCE with Multi-Layer Visibility Oki et al. Expires April 2006 [Page 5] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 5.2. Multiple PCE Inter-Layer Path Computation In Figure 2, there is one PCE in each layer. PCEs of each layer collaborate together to compute an end-to-end path across layers. PCE Hi is responsible for computations in the higher layer and may “consultEwith PCE Lo to compute paths across the lower layer. PCE Lo is responsible for path computation in lower layer. A simple cooperation could be: PCE Hi requests a path H2-H3 to PCE Lo. Of course more complex cooperation may be required if an end-to-end optimal path is desired. ----- | PCE | | Hi | --+-- | ----- ----- | ----- ----- | LSR |--| LSR |............|...........| LSR |--| LSR | | H1 | | H2 | | | H3 | | H4 | ----- -----\ --+-- /----- ----- \ | PCE | / \ | Lo | / \ ----- / \ / \----- -----/ | LSR |--| LSR | | L1 | | L2 | ----- ----- Figure 2 : Cooperating Single-Layer PCEs 6. PCC-PCE Communication Requirements for Inter-Layer Traffic Engineering This section sets out additional requirements not covered in [PCE- COM-REQ] specific to the problems of multi-layer TE. 6.1. PCC-PCE Communication The PCC-PCE communication protocol MUST allow requests and replies for inter-layer path computation. This requires no additional messages, but implies the following additional constraints to be added to the PCC-PCE communication protocol. 6.1.1 Control of Inter-Layer Path Computation A request from a PCC to a PCE SHOULD indicate whether inter-layer path computation is allowed. In the absence of such an indication, the default is that inter-layer path computation is not allowed. Oki et al. Expires April 2006 [Page 6] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 Therefore, a request from a PCC to a PCE MUST support the inclusion of such an indication. 6.1.2 Control of Type of Path to be Computed A request from a PCC to a PCE MUST allow controlling the type path to be computed: A mono-layer path that includes already established lower layer-LSP, a mono-layer path that includes loose hop(s), or a multi-layer path that can include the complete path of one or more lower-layer LSPs not yet established. When multi-layer path computation is requested, a response from a PCE to a PCC MUST support the inclusion, as part of end-to-end path, of the path of the lower-layer LSPs to be established. 6.1.3 Communication of Inter-Layer Constraints A request from a PCC to a PCE MUST support the inclusion of constraints for multiple layers. This includes the switching type(s) and encoding type(s) that can, must, or must not be used. 6.1.4 Cooperation Between PCEs When each layer is controlled by a PCE, which only has access to the topology information of its layer, the PCEs of each layer need to cooperate to perform inter-layer path computation. In this case, communication between PCEs is required for inter-layer path computation. A PCE that behaves as a client is defined as a PCC [PCE- ARCH]. The PCC-PCE communication protocol MUST allow requests and replies for cooperative inter-layer path computation. 6.1.5 Inter-Layer Diverse paths The PCE communication protocol MUST allow for the computation of diverse inter-Layer paths. A request from a PCC to a PCE MUST support the inclusion of multiple path request, with the desired level of diversity at each layer (link, node, SRLG). 6.2. Supportive Network Models The PCC-PCE communication protocol SHOULD allow several architectural alternatives for interworking between MPLS and GMPLS networks: overlay, integrated and augmented models [RFC3945]. 7. Manageability considerations Manageability of inter-layer traffic engineering with PCE must address the following consideration for section 6.1. - need for a MIB module for control and monitoring - need for built-in diagnostic tools Oki et al. Expires April 2006 [Page 7] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 - configuration implication for the protocol 8. Security Considerations Inter-layer traffic engineering with PCE may raise new security issues when PCE-PCE communication is done between different layer networks for inter-layer path computation. Security issues may also exist when a single PCE is granted full visibility of TE information that applies to multiple layers. It is expected that solutions for inter-layer protocol extensions will address these issues in detail using security techniques such as authentication. 9. Acknowledgment We would like to thank Kohei Shiomoto and Ichiro Inoue for their useful comments. 10. References 10.1 Normative Reference [RFC2119] Bradner, S., "Key words for use in RFCs to indicate requirements levels", RFC 2119, March 1997. [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching Architecture", RFC 3945, October 2004. 10.2 Informative Reference [PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, "Path Computation Element (PCE) Architecture", draft-ietf-pce-architecture (work in progress). [PCE-COM-REQ] J. Ash, J.L Le Roux et al., "PCE Communication Protocol Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs (work in progress). [PCE-DISC-REQ] JL Le Roux et al., "Requirements for Path Computation Element (PCE) Discovery", draft-ietf-pce-discovery-reqs (work in progress). [MRN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi- region networks (MRN) ", draft-shiomoto-ccamp-gmpls-mrn-reqs (work in progress). 11. AuthorsEAddresses Eiji Oki NTT Oki et al. Expires April 2006 [Page 8] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 3-9-11 Midori-cho, Musashino-shi, Tokyo 180-8585, Japan Email: oki.eiji@lab.ntt.co.jp Jean-Louis Le Roux France Telecom R&D, Av Pierre Marzin, 22300 Lannion, France Email: jeanlouis.leroux@francetelecom.com Kenji Kumaki KDDI Corporation Garden Air Tower Iidabashi, Chiyoda-ku, Tokyo 102-8460, JAPAN Phone: +81-3-6678-3103 Email: ke-kumaki@kddi.com Adrian Farrel Old Dog Consulting Email: adrian@olddog.co.uk 12. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE Oki et al. Expires April 2006 [Page 9] Internet Draft draft-oki-pce-inter-layer-req-00.txt October 2005 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). 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. Oki et al. Expires April 2006 [Page 10]