Network Working Group Seisho Yasukawa (NTT) Internet Draft Editor Category: Informational Expiration Date: December 2004 July 2004 Requirements for Point to Multipoint Traffic Engineered MPLS LSPs Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document presents a set of requirements for Point-to-Multipoint(P2MP) Traffic Engineered (TE) Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs). It specifies functional requirements for solutions in order to deliver P2MP applications over a MPLS TE infrastructure. It is intended that solutions that specify procedures for P2MP TE LSP setup satisfy these requirements. Yasukawa,et. al. [Page 1] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 There is no intent to either specify solution specific details in this document or application specific requirements. It is intended that the requirements presented in this document are not limited to the requirements of packet switched networks, but also encompass the requirements of L2SC, TDM, lambda and port switching networks managed by Generalized MPLS (GMPLS) protocols. Protocol solutions developed to meet the requirements set out in this document must attempt to be equally applicable to MPLS and GMPLS. Yasukawa,et. al. [Page 2] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 Table of Contents 1. Introduction ................................................. 04 2. Definitions .................................................. 05 2.1 Acronyms ................................................. 05 2.2 Terminology .............................................. 06 2.3 Conventions .............................................. 07 3. Problem Statement ............................................ 07 3.1 Motivation ............................................... 07 3.2 Requirements Overview .................................... 08 4. Examples of candidate applications that may require P2MP TE LSP ...................................................10 4.1 P2MP TE LSP for IP multicast data ....................... 10 4.2 P2MP TE backbone network for IP multicast network ....... 11 4.3 Layer 2 Multicast Over MPLS ............................. 13 4.4 VPN multicast network ................................... 13 4.5 GMPLS Networks .......................................... 14 5. Detailed requirements for P2MP TE extensions ................. 15 5.1 P2MP LSP tunnels ........................................ 15 5.2 P2MP explicit routing ................................... 15 5.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes.17 5.4 P2MP TE LSP establishment, teardown, and modification mechanisms .............................................. 17 5.5 Fragmentation ........................................... 18 5.6 Failure Reporting and Error Recovery .................... 18 5.7 Record route of P2MP TE LSP tunnels ..................... 19 5.8 Call Admission Control (CAC) and QoS Control mechanism .. 19 5.9 Reoptimization of P2MP TE LSP ........................... 20 5.10 IPv4/IPv6 support ....................................... 20 5.11 P2MP MPLS Label ......................................... 21 5.12 Routing advertisement of P2MP capability ................ 21 5.13 Multi-Area/AS LSP ....................................... 21 5.14 P2MP MPLS OAM ........................................... 21 5.15 Scalability ............................................. 22 5.16 Backwards Compatibility ................................. 22 5.17 GMPLS ................................................... 23 5.18 Requirements for Hierarchical P2MP TE LSPs .............. 24 5.19 P2MP Crankback routing .................................. 24 6. Security Considerations ...................................... 24 7. Acknowledgements ............................................. 25 8. References ................................................... 25 8.1 Normative References ..................................... 25 8.2 Informational References ................................. 26 9. Editor's Address ............................................. 27 10. Authors' Addresses .......................................... 27 11. Intellectual Property Consideration ......................... 29 11.1 IPR Disclosure Acknowledgement .......................... 29 12. Full Copyright Statement .................................... 29 Yasukawa,et. al. [Page 3] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 1. Introduction Existing MPLS Traffic Engineering (MPLS-TE) allows for strict QoS guarantees, resources optimization, and fast failure recovery, but is limited to P2P applications. There are P2MP applications like Content Distribution, Interactive Multimedia and VPN multicast that would also benefit from these TE capabilities. This clearly motivates enhancements of the base MPLS-TE tool box in order to support P2MP applications. This document presents a set of requirements for Point-to-Multipoint(P2MP) Traffic Engineering (TE) extensions to Multiprotocol Label Switching (MPLS). It specifies functional requirements for solutions to deliver P2MP TE LSPs. For the sake of illustration, RSVP-TE [RFC3209] is one possible candidate to provide such a solution so as to deliver P2MP TE LSPs. It is intended that solutions that specify procedures for P2MP TE LSP setup satisfy these requirements. There is no intent to either specify solution specific details in this document or application specific requirements. It is intended that the requirements presented in this document are not limited to the requirements of packet switched networks, but also encompass the requirements of TDM, lambda and port switching networks managed by Generalized MPLS (GMPLS) protocols. Protocol solutions developed to meet the requirements set out in this document must attempt to be equally applicable to MPLS and GMPLS. Content Distribution (CD), Interactive multi-media (IMM), and VPN multicast are applications that are best supported with multicast capabilities. For some of them , there is a requirement to use P2MP TE LSPs. One possible way to map P2MP flows onto LSPs in a MPLS network is to setup multiple P2P TE LSPs, one to each of the required egress LSRs. This requires replicating incoming packets to all the P2P LSPs at the ingress LSR to accommodate multipoint communication. This is sub-optimal as it places the replication burden on the ingress LSR and hence has very poor scaling characteristics. It also wastes bandwidth resources, memory and MPLS (e.g. label) resources in the network. Hence, to provide TE for a P2MP application in an efficient manner (that is, with scalable impact on signaling and protocol state) in a large-scale environment, P2MP TE mechanisms are required specifically to support P2MP TE LSPs. As of now, existing MPLS TE mechanisms such as [RFC3209] do not support P2MP TE LSPs so new mechanisms must be developed. Yasukawa,et. al. [Page 4] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 This should be achieved without requiring the use of a multicast routing protocol in the network core, and with maximum re-use of the existing MPLS protocols: in particular, MPLS Traffic Engineering. That is, the separation between routing and signaling that exists in the P2P TE network should be maintained within the P2MP TE network, and the construction of the TEDB from which P2MP TE LSP paths are computed should not be constrained to use a multicast protocol. A P2MP TE LSP will be set up with TE constraints and will allow efficient packet or data replication at various branching points in the network. Note that the notion of "efficient" packet replication is relative and may have different meanings depending on the objectives (see section 5.2). For instance, RSVP-TE could be used for setting up a P2MP TE LSP with enhancements to existing P2P TE LSP procedures. P2MP TE LSP setup mechanisms MUST include the ability to add/remove receivers to/from an existing P2MP TE LSP. Note that with existing multicast routing mechanisms, multicast traffic cannot currently benefit from P2P TE LSPs. Hence, Call Admission Control for P2P TE LSP cannot take into account the bandwidth used for multicast traffic. P2MP TE will allow the bandwidth used by both the unicast and multicast traffics to be counted by means of CAC. This document is organized as follows: Section 2 provides a set of definitions used throughout the document. The problem statement is then discussed in Section 3. for the sake of illustration, this document lists various applications that could make use P2MP TE LSP. Detailed application-specific requirements as far as P2MP TE LSP is concerned are out of the scope of this document. Detailed requirements for the support of applications that require P2MP MPLS TE LSPs are described in section 4. The requirement for Multipoint-to-Point and Multipoint-to-Multipoint TE LSPs are outside of the scope of this document. 2. Definitions 2.1 Acronyms P2P: Point-to-point P2MP: Point-to-multipoint Yasukawa,et. al. [Page 5] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 2.2 Terminology The reader is assumed to be familiar with the terminology in [RFC3031] and [RFC3209]. P2MP TE LSP: A traffic engineered label switched path that has one unique ingress LSR (also referred to as the root) and one or more egress LSRs (also referred to as the leaf). P2MP tree: The ordered set of LSRs and links that comprise the path of a P2MP TE LSP from its ingress LSR to all of its egress LSRs. sub-P2MP tree: A sub-P2MP tree is a portion of a P2MP tree starting at a particular LSR that is a member of the P2MP tree and includes ALL downstream LSRs that are also members of the P2MP tree. P2P sub-LSP: The path from the ingress LSR to a particular egress LSR. ingress LSR: The LSR that is responsible for initiating the signaling messages that set up the P2MP TE LSP. egress LSR: One of potentially many destinations of the P2MP TE LSP. Egress LSRs may also be referred to as leaf nodes or leaves. bud LSR: An LSR that is an egress, but also has one or more directly connected downstream LSRs. branch LSR: An LSR that has more than one directly connected downstream LSR. graft LSR: An LSR that is already a member of the P2MP tree and is in process of signaling a new sub-P2MP tree. Yasukawa,et. al. [Page 6] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 prune LSR: An LSR that is a member of the P2MP tree and is in process of tearing down an existing sub-P2MP tree. P2MP-ID (Pid): The ID that can be used to map a set of P2P sub-LSPs to a particular P2MP LSP. 2.3 Conventions 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 [RFC2119]. 3. Problem Statement 3.1 Motivation Content Distribution (CD), Interactive multi-media (IMM), and VPN multicast are applications that are best supported with multicast capabilities. IP Multicast provides P2MP communication. However, there are no Traffic Engineering (TE) capabilities or QoS guarantees with existing IP multicast protocols. Note that Diff-serv (see [RFC2475],[RFC2597] and [RFC3246]) combined with IP multicast routing may not be sufficient for P2MP applications for many of the same reasons that it is not sufficient for unicast applications. Note also that multicast trees provided by existing IP multicast routing protocols are not optimal from a bandwidth usage perspective, which may lead to significant bandwidth wasting. TE and Constraint Based Routing, including Call Admission Control(CAC), explicit source routing and bandwidth reservation, is required to enable efficient resource usage and strict QoS guarantees. Furthermore there are no existing P2MP mechanisms for carrying layer 2 or SONET/SDH multicast traffic over MPLS. TE capabilities are desirable for both these applications; the related set of application requirements are outside of the scope of this document and might require special pseudowire encapsulation. Yasukawa,et. al. [Page 7] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 One possible solution would be to setup multiple P2P TE LSPs, one to each of the required egress LSRs. This requires replicating incoming traffic to all the P2P LSPs at the ingress LSR to accommodate multipoint communication. This is clearly sub-optimal as it places the replication burden on the ingress LSR and hence has very poor scaling characteristics. It also wastes bandwidth resources, memory and MPLS(e.g. label) resources in the network. Hence, to provide MPLS TE [RFC2702] for a P2MP application in an efficient manner (that is, with scalable impact on signaling and protocol state) in a large scale environment, P2MP TE mechanisms are required. Existing MPLS P2P TE mechanisms have to be enhanced to support P2MP TE LSP. 3.2. Requirements Overview This document states basic requirements for the setup of P2MP TE LSPs and a solution SHOULD satisfy them without requiring that a multicast routing protocol is used, although such a protocol MUST NOT be prohibited. It is desirable to maximize the re-use of existing MPLS TE techniques and protocols. Note that the use of MPLS forwarding to carry the multicast traffic may also be useful in the context of some network designs where it might be desired to avoid running some multicast routing protocol like PIM [PIM-SM] or BGP (which might be required for the use of PIM). A P2MP TE LSP path will be computed taking into account various constraints such as bandwidth, affinities, required level of protection and so on. The solution MUST allow for the computation of P2MP TE LSP paths satisfying constraints with the objective of supporting various optimization criteria such as delays, bandwidth consumption in the network, or any other combinations. This document does not restrict the choice of signaling protocol used to set up a P2MP TE LSP, but it should be noted that [RFC3468] states ... the consensus reached by the Multiprotocol Label Switching (MPLS) Working Group within the IETF to focus its efforts on "Resource Reservation Protocol (RSVP)-TE: Extensions to RSVP for Label-Switched Paths (LSP) Tunnels" (RFC 3209) as the MPLS signaling protocol for traffic engineering applications... The P2MP TE LSP setup mechanism MUST include the ability to add/remove egress LSRs to/from an existing P2MP TE LSP and MUST allow for the support of all the TE LSP management procedures already defined for P2P TE LSP such as the non disruptive rerouting (the so called "Make before break" procedure). Yasukawa,et. al. [Page 8] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 The computation of P2MP TE trees is implementation dependent and is beyond the scope of the solutions that are built with this document as a guideline. A separate document(s) will specify how to build P2MP TE LSPs. The usage of those solutions will be application dependent and is out of the scope of this document. However, it is a requirement that those solutions attempt to be applicable to GMPLS as well as to MPLS so that only a single set of solutions are developed. Consider the following figure. Source 1 (S1) | I-LSR1 | | | | R2----E-LSR3--LSR1 LSR2---E-LSR2--Receiver 1 (R1) | : R3----E-LSR4 E-LSR5 | : | : R4 R5 Figure 1 Figure 1 shows a single ingress (I-LSR1), and four egresses(E-LSR2, E-LSR3, E-LSR4 and E-LSR5). I-LSR1 is attached to a traffic source that is generating traffic for a P2MP application. Receivers R1, R2, R3 and R4 are attached to E-LSR2, E-LSR3 and E-LSR4. The following are the objectives of P2MP LSP establishment and use. a) A P2MP TE LSP tree which satisfies various constraints is pre-determined and supplied to ingress I-LSR1. Note that no assumption is made on whether the tree is provided to I-LSR1 or computed by I-LSR1. Note that the solution SHOULD also allow for the support of partial path by means of loose routing. Yasukawa,et. al. [Page 9] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 Typical constraints are bandwidth requirements, resource class affinities, fast rerouting, preemption, to mention a few of them. There should not be any restriction on the possibility to support the set of constraints already defined for point to point TE LSPs. A new constraint may specify which LSRs should be used as branch points for the P2MP LSR in order to take into account some LSR capabilities or network constraints. b) A P2MP TE LSP is set up from I-LSR1 to E-LSR2, E-LSR3 and E-LSR4 using the tree information. c) In this case, the branch LSR1 should replicate incoming packets or data and send them to E-LSR3 and E-LSR4. d) If a new receiver (R5) expresses an interest in receiving traffic, a new tree is determined and a sub-P2MP tree from LSR2 to E-LSR5 is grafted onto the P2MP tree. LSR2 becomes a branch LSR. 4. Examples of candidate applications that may require P2MP TE LSP This section describes some of the candidate applications that P2MP MPLS TE is applicable to. The purpose of this section is not to mandate how P2MP TE LSPs must be used in certain application scenarios. Rather it is to illustrate some of the potential application scenarios so as to highlight the features and functions that any P2MP solution must provide in order to be of wide use and applicability. This section is not meant to be exhaustive, and P2MP is not limited to the described applications. 4.1 P2MP TE LSP for IP multicast data One typical scenario is to use P2MP TE LSPs as P2MP tunnels carrying multicast data traffic (e.g. IP mcast). In this scenario, a P2MP TE LSP is established between an ingress LSR which supports IP multicast source and several egress LSRs which support several IP multicast receivers. A P2MP TE LSP is established over the network and IP multicast data are tunneled from an ingress LSR node to multiple egress leaf LSRs with data replication at the branch LSRs in the network core. Figure 2 shows an example. Yasukawa,et. al. [Page 10] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 Note that a P2MP TE LSP can be established over multiple areas/ASs and that the egress LSRs may deliver data into an IP multicast network. Mcast Source | +---------------I-LSR0----------------+ | | | | LSR0 +----E-LSR2---R2 | / \ / | R1---E-LSR1---LSR2-----LSR1 LSR3----LSR4----E-LSR3---R3 | / \ \ | | / \ +----E-LSR4---R4 +-------B-LSR1---------B-LSR2---------+ +-------- / ------++------ \ ---------+ | | || | R5---E-LSR5--------LSR5 || IPmcast Network | | / \ || | +-E-LSR6---E-LSR7-++----MR0--MR1------+ | | | | R6 R7 R8 R9 Figure 2 4.2 P2MP TE backbone network for IP multicast network P2MP TE LSPs are applicable in a backbone network to construct or support a multicast network(e.g. IPmcast network). The IP multicast access networks are interconnected by P2MP TE LSPs. A P2MP TE LSP is established from an ingress LSR which accommodates an IP multicast network that has a multicast source to multiple egress LSRs which each accommodate an IP multicast network. In this scenario, ingress/egress LSRs placed at the edge of multicast network handle an IP multicast routing protocol. This means that the ingress/egress LSRs exchange IP multicast routing messages as neighbor routers. Figure 3 shows a network example of this scenario. A P2MP TE LSP is established from a I-LSR1 to E-LSR2, E-LSR3, E-LSR4 and the ingress/egress LSR exchanges the multicast routing messages with each other. Yasukawa,et. al. [Page 11] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 As specified in the section related to the problem statement it should be possible for a solution to add/remove egress LSRs to/from the P2MP MPLS TE LSP. IP multicast group membership distribution between the egress LSRs may change frequently. This in turn may require a potential P2MP MPLS TE solution, that is suitable for IP multicast, to handle additions/deletions of egress LSRs with an appropriate reactiveness. It is recommended to support a message exchange mechanism on top of P2MP LSP setup mechanism to support multicast (S, G) Join/Leave. Though several schemes exist to handle this scenario, these are out of scope of this document. This document only describes requirements to setup a P2MP TE LSP. Mcast Source | +-----MR-----+ | | | | MR | +------|-----+ +---------------I-LSR1----------------+ | // ||| \\ | | // ||| \\ | | // |LSR| \\ | | ___//____/|_____\\____ | | / // ||| \\ \ | | | // ||| \\ | | +-----E-LSR2----E-LSR3-----E-LSR4-----+ +---- / ---++------|------++--- \ ----+ | | || | || | | R1---MR---MR || MR || MR__ | | / \ || / \ || / \ \MR---R8 +--MR--MR--++----MR--MR---++--MR--MR--+ | | | | | | R2 R3 R4 R5 R6 R7 Figure 3 Yasukawa,et. al. [Page 12] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 4.3 Layer 2 Multicast Over MPLS Existing layer 2 networks offer multicast video services. These are typically carried using layer 2 NBMA technology such as ATM or layer 2 Broadcast Access technology such as Ethernet. It may be desirable to deliver these layer 2 multicast services over a converged MPLS infrastructure where P2MP TE LSPs are used instead. For instance, several SPs provision P2MP ATM VCs for TV/ADSL services. These P2MP VCs are setup between a video server and a set of ATM DSLAMs. Each channel is carried in a distinct P2MP VC. These VC maybe be routed independently, or may all be nested into a unique PVC, connecting the video sever to all DSLAMs. Such service could benefit from a P2MP MPLS-TE control plane. An option is to setup a permanent P2MP TE LSP between the video server and all DSLAMs, that would correspond to a PVC carrying all channel VCs. In this case each DSLAM receives all channels, even if there are no receivers that are registered for a given channel. This ensure fast zapping, but lead to significant bandwidth wasting. A second option is to setup a distinct P2MP TE LSP per channel. If a client, behind a DSLAM, zaps to a new channel, then the DSLAM has to be added to the P2MP TE LSP carrying this channel using a P2MP TE grafting procedure, if it is not already egress LSR for that LSP. Pruning procedure has to be used to remove a DSLAM from the P2MP TE LSP when there is no longer any client behind the DSLAM, watching the channel. 4.4 VPN multicast network In this scenario, P2MP TE LSPs could be utilized to construct a provider network which can deliver VPN multicast service(s) to its customers. A P2MP TE LSP is established between all the PE routers which accommodate the customer private network(s) that handle the IP multicast packets. Each PE router must handle a VPN instance. For example, in Layer3 VPNs like BGP/MPLS based IP VPNs [BGPMPLS-VPN], this means that each PE router must handle both private multicast VRF tables and common multicast routing and forwarding table. And each PE router exchanges private multicast routing information between the corresponding PE routers. In case of high rate source, the need for P2MP TE LSP can be envisaged for Layer3 VPN data transmission. Another example is a Layer2 VPN that supports multipoint LAN connectivity service. In an Ethernet network environment, IP multicast data is flooded to the appropriate Ethernet port(s). Yasukawa,et. al. [Page 13] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 An Ethernet multipoint Layer2 VPN service provided by MPLS, this function is achieved by switching MPLS encapsulated frames towards the relevant PE nodes. But if existing P2P TE LSPs are used as tunnels between PEs, any ingress PE must duplicate the frames and send them to the corresponding PEs. This means the data stream is flooded just from the ingress PE, which will waste the provider's network resources. So, for Layer 2 VPNs that are required to support multicast traffic, it might be desirable that P2MP MPLS TE LSPs are used for data transmission with an appropriate layer 2 encapsulation technique (for example, pseudo wire) instead of P2P MPLS TE LSPs, contributing in turn to savings of network resources. This document does not set requirements for how multicast VPNs are provided, but it does set requirements for the function that must be available in P2MP MPLS solutions. Therefore, it is not a requirement that multicast VPNs utilize P2MP TE LSPs, but it is a requirement that P2MP MPLS solutions should be capable of supporting multicast VPNs. As already pointed out, application-specific requirements are out of the scope of this document. 4.5 GMPLS Networks GMPLS currently supports only P2P TE-LSPs just like MPLS. GMPLS enhances MPLS to support four new classes of interfaces: Layer-2 Switch Capable (L2SC), Time-Division Multiplex (TDM), Lambda Switch Capable (LSC) and Fiber-Switch Capable (FSC) in addition to Packet Switch Capable (PSC) already supported by MPLS. All of these interface classes have so far been limited to P2P TE LSPs (see [RFC3473] and [RFC 3471]). The requirement for P2MP services for non-packet switch interfaces is similar to that for PSC interfaces. In particular, cable distribution services such as video distribution are prime candidates to use P2MP features. Therefore, it is a requirement that reasonable attempts must be made to make all the features/mechanisms (and protocol extensions) that will be defined to provide MPLS P2MP TE LSPs equally applicable to P2MP PSC and non-PSC TE-LSPs. If the requirements of non-PSC networks over-complicate the PSC solution a decision may be taken to separate the solutions. This decision must be taken in full consultation with the MPLS and CCAMP working groups. Yasukawa,et. al. [Page 14] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 5. Detailed requirements for P2MP TE extensions 5.1 P2MP LSP tunnels The P2MP TE extensions MUST be applicable to the signaling of LSPs of different traffic types. For example, it MUST be possible to signal a P2MP TE LSP to carry any kind of payload being packet or non-packet based (including frame, cell, TDM un/structured, etc.) Carrying IP multicast or Ethernet traffic within a P2MP tunnel are typical examples. As with P2P MPLS technology [RFC3031], traffic is classified with a FEC in this extension. All packets which belong to a particular FEC and which travel from a particular node MUST follow the same P2MP tree. In order to scale to a large number of branches, P2MP TE LSPs SHOULD be identified by a unique identifier (the P2MP ID or Pid) that is constant for the whole LSP regardless of the number of branches and/or leaves. Therefore, the identification of the P2MP session by its destination addresses is not adequate. 5.2 P2MP explicit routing Various optimizations in P2MP tree formation need to be applied to meet various QoS requirements and operational constraints. Some P2MP applications may request a bandwidth guaranteed P2MP tree which satisfies end-to-end delay requirements. And some operators may want to set up a cost minimum P2MP tree by specifying branch LSRs explicitly. The P2MP TE solution therefore MUST provide a means of establishing arbitrary P2MP trees under the control of an external tree computation process or path configuration process or dynamic tree computation process located on the ingress LSR. Figure 4 shows two typical examples. Yasukawa,et. al. [Page 15] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 A A | / \ B B C | / \ / \ C D E F G | / \ / \/ \ / \ D--E*-F*-G*-H*-I*-J*-K*--L H I J KL M N O Steiner P2MP tree SPF P2MP tree Figure 4 Examples of P2MP TE LSP topology One example is the Steiner P2MP tree (Cost minimum P2MP tree) [STEINER]. This P2MP tree is suitable for constructing a cost minimum P2MP tree so as to minimize the bandwidth consumption in the core. To realize this P2MP tree, several intermediate LSRs must be both MPLS data terminating LSRs and transit LSRs (LSRs E, F, G, H, I, J and K in the figure 4). This means that the LSRs must perform both label swapping and popping at the same time. Therefore, the P2MP TE solution MUST support a mechanism that can setup this kind of bud LSR between an ingress LSR and egress LSRs. Note that this includes constrained Steiner trees that allow for the computation of a minimal cost trees with some other constraints such as a bounded delay between the source and every receiver. Another example is a CSPF (Constraint Shortest Path First) P2MP tree. By some metric (which can be set upon any specific criteria like the delay, bandwidth, a combination of those), one can calculate a shortest path P2MP tree. This P2MP tree is suitable for carrying real time traffic. The solution MUST allow the operator to make use of any tree computation technique. In the former case an efficient/optimal tree is defined as a minimal cost tree (Steiner tree) whereas in the later case it is defined as the tree that provides shortest path between the source and any receiver. To support explicit setup of any reasonable P2MP tree shape, a P2MP TE solution MUST support some form of explicit source-based control of the P2MP tree which can explicitly include particular LSRs as branch nodes. This can be used by the ingress LSR to setup the P2MP TE LSP. For instance, a P2MP TE LSP can be simply represented as a whole tree or by its individual branches. Yasukawa,et. al. [Page 16] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 5.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes A P2MP tree is completely specified if all of the required branches and hops between a sender and leaf LSR are indicated. A P2MP tree is partially specified if only a subset of intermediate branches and hops are indicated. This may be achieved using loose hops in the explicit path, or using widely scoped abstract nodes such as IPv4 prefixes shorter than 32 bits, or AS numbers. A partially specified P2MP tree might be particularly useful in inter-area and inter-AS situations although P2MP requirements for inter-area and inter-AS are beyond the scope of this document. Protocol solutions SHOULD include a way to specify loose hops and widely scoped abstract nodes in the explicit source-based control of the P2MP tree as defined in the previous section. Where this support is provided, protocol solutions MUST allow downstream LSRs to apply further explicit control to the P2MP tree to resolve a partially specified tree into a (more) completely specified tree. Protocol solutions MUST allow the P2MP tree to be completely specified at the ingress where sufficient information exists to allow the full tree to be computed. In all cases, the egress nodes of the P2MP TE LSP must be fully specified. In case of a tree being computed by some downstream LSRs (e.g. the case of hops specified as loose hops), the solution MUST provide the ability for the ingress LSR of the P2MP TE LSP to learn the full P2MP tree. Note that this requirement MAY be relaxed in some environments (e.g. Inter-AS) where confidentiality must be preserved. 5.4 P2MP TE LSP establishment, teardown, and modification mechanisms The P2MP TE solution MUST support establishment, maintenance and teardown of P2MP TE LSPs in a scalable manner. This MUST include both the existence of very many LSPs at once, and the existence of very many destinations for a single P2MP LSP. In addition to P2MP TE LSP establishment and teardown mechanism, it SHOULD implement partial P2MP tree modification mechanism. For the purpose of adding sub-P2MP TE LSPs to an existing P2MP TE LSP, the extensions SHOULD support a grafting mechanism. For the Yasukawa,et. al. [Page 17] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 purpose of deleting a sub-P2MP TE LSPs from an existing P2MP TE LSP, the extensions SHOULD support a pruning mechanism. It is RECOMMENDED that these grafting and pruning operations do not cause any additional processing in nodes except along the path to the grafting and pruning node and its downstream nodes. Moreover, both grafting and pruning operations MUST not be traffic disruptive for the traffic currently forwarded along the P2MP tree. 5.5 Fragmentation The P2MP TE solution MUST handle the situation where a single protocol message cannot contain all of the information necessary to signal the establishment of the P2MP LSP. It MUST be possible to establish the LSP in these circumstances. This situation may arrise in either of the following circumstances. a. The ingress LSR cannot signal the whole tree in a single message. b. The information in a message expands to be too large (or is discovered to be too large) at some transit node. This may occur because of some increase in the information that needs to be signaled or because of a reduction in the size of signaling message that is supported. 5.6 Failure Reporting and Error Recovery Failure events may cause egress nodes or sub-P2MP LSPs to become detached from the P2MP TE LSP. These events MUST be reported upstream as for a P2P LSP. The solution SHOULD provide recovery techniques such as protection and restoration allowing recovery of any impacted sub-P2MP TE LSPs. In particular, a solution MUST provide fast protection mechanisms applicable to P2MP TE LSP similar to the solutions specified in [FRR] for P2P TE LSPs. Note also that no assumption is made on whether backup paths for P2MP TE LSPs should or should not be shared with P2P TE LSPs backup paths. Note that other application-specific requirement documents may introduce even more stringent requirement such as non packet loss, at the cost of some increased bandwidth consumption. The solution SHOULD also support the ability to meet other network recovery requirements such as bandwidth protection and bounded propagation delay increase along the backup path during failure. A P2MP TE solution MUST support P2MP fast protection mechanism to handle P2MP applications sensitive to traffic disruption. The report of the failure of delivery to fewer than all of the egress nodes SHOULD NOT cause automatic teardown of the P2MP TE LSP. Yasukawa,et. al. [Page 18] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 That is, while some egress nodes remain connected to the P2MP tree it should be a matter of local policy at the ingress whether the P2MP LSP is retained. When all egress nodes downstream of a branch node have become disconnected from the P2MP tree, and the some branch node is unable to restore connectivity to any of them by means of some recovery or protection mechanisms, the branch node MAY remove itself from the P2MP tree provided that it is not also an egress LSR. Since the faults that severed the various downstream egress nodes from the P2MP tree may be disparate, the branch node MUST report all such errors to its upstream neighbor. The ingress node can then decide to re-compute the path to those particular egress nodes, around the failure point. Solutions MAY include the facility for transit LSRs and particularly branch nodes to recompute sub-P2MP trees to restore them after failures. In the event of successful repair, error notifications SHOULD NOT be reported to upstream nodes, but the new paths are reported if route recording is in use. Crankback requirements are discussed in Section 5.18. 5.7 Record route of P2MP TE LSP tunnels Being able to identify the established topology of P2MP TE LSP is very important for various purposes such as management and operation of some local recovery mechanisms like Fast Reroute [FRR]. A network operator uses this information to manage P2MP TE LSPs. Therefore, topology information MUST be collected and updated after P2MP TE LSP establishment and modification process. The P2MP TE solution MUST support a mechanism which can collect and update P2MP tree topology information after P2MP LSP establishment and modification process. For example, the P2P MPLS TE mechanism of route recording could be extended and used if RSVP-TE was used as the P2MP signaling protocol. It is RECOMMENDED that the information is collected in a data format by which the sender node can recognize the P2MP tree topology without involving some complicated data calculation process. The solution MUST support the recording of both outgoing interfaces and node-id [NODE-ID]. 5.8 Call Admission Control (CAC) and QoS Control mechanism of P2MP TE LSPs P2MP TE LSPs may share network resource with P2P TE LSPs. Therefore it is important to use CAC and QoS in the same way as P2P TE LSPs for easy and scalable operation. In particular, it should be highlighted that because Multicast Yasukawa, et. al. [Page 19] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 traffic cannot make use of P2P TE LSP, multicast traffic cannot be easily taken into account by P2P TE LSPs when performing CAC. The use of P2MP TE LSP will now allow for an accounting of the unicast and multicast traffic for bandwidth reservation. P2MP TE solutions MUST support both resource sharing and exclusive resource utilization to facilitate co-existence with other LSPs to the same destination(s). P2MP TE solution MUST be applicable to DiffServ-enabled networks that can provide consistent QoS control in P2MP LSP traffic. Any solution SHOULD also satisfy the DS-TE requirements [RFC3564] and interoperate smoothly with current P2P DS-TE protocol specifications. Note that this requirement document does not make any assumption on the type of bandwidth pool used for P2MP TE LSPs which can either be shared with P2P TE LSP or be dedicated for P2MP use. 5.9 Reoptimization of P2MP TE LSP The detection of a more optimal path (for example, one with a lower overall cost) is an example of a situation where P2MP TE LSP re-routing may be required. While re-routing is in progress, an important requirement is avoiding double bandwidth reservation (over the common parts between the old and new LSP) thorough the use of resource sharing. Make-before-break MUST be supported for a P2MP TE LSP to ensure that there is no traffic disruption when the P2MP TE LSP is re-routed. For example, the P2P MPLS TE make-before-break mechanism could be extended and used if RSVP-TE was used as the P2MP signaling protocol. It is possible to achieve make-before-break that only applies to a sub-P2MP tree without impacting the data on all of the other parts of the P2MP tree. The solution SHOULD allow for make-before-break reoptimization of a sub-tree with no impact on the rest of the tree (no label reallocation, no change in identifiers, etc.). The solution SHOULD also provide the ability for the ingress LSR to have a strict control on the reoptimization process. Such reoptimization MAY be initiated by the sub-tree root branch node (that is, the branch node MAY setup a new sub-tree, then splice traffic on the new subtree and delete the former sub-tree). 5.10 IPv4/IPv6 support Any P2MP TE solution MUST be equally applicable to IPv4 and IPv6. Yasukawa,et. al. [Page 20] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 5.11 P2MP MPLS Label A P2MP TE solution MUST support establishment of both P2P and P2MP TE LSPs and MUST NOT impede the operation of P2P TE LSPs within the same network. A P2MP TE solution MUST be specified in such a way that it allows P2MP and P2P TE LSPs to be signaled on the same interface. Labels for P2MP TE LSPs and P2P TE LSPs MAY be assigned from shared or dedicated label space(s). Label space shareability is implementation specific. 5.12 Routing advertisement of P2MP capability Several high-level requirements have been identified to determine the capabilities of LSRs within a P2MP network. The aim of such information is to facilitate the computation of P2MP trees using TE constraints within a network that contains LSRs that do not all have the same capabilities levels with respect to P2MP signaling and data forwarding. These capabilities include, but are not limited to: - the ability of an LSR to support branching. - the ability of an LSR to act as an egress and a branch for the same LSP. - the ability of an LSR to support P2MP MPLS-TE signalling. It is expected that it may be appropriate to gather this information through extensions to TE IGPs (see [RFC3630] and [IS-IS-TE]), but the precise requirements and mechanisms are out of the scope of this document. It is expected that a separate document will cover this requirement. 5.13 Multi-Area/AS LSP P2MP TE solutions SHOULD support multi-area/AS P2MP TE LSPs. The precise requirements in support of multi-area/AS P2MP TE LSPs is out of the scope of this document. It is expected that a separate document will cover this requirement. 5.14 P2MP MPLS OAM Management of P2MP LSPs is as important as the management of P2P LSPs. The MPLS and GMPLS MIB modules MUST be enhanced to provide P2MP TE LSP management. In order to facilitate correct management, P2MP TE LSPs MUST have unique identifiers. Yasukawa,et. al. [Page 21] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 OAM facilities will have special demands in P2MP environments especially within the context of tracing the paths and connectivity of P2MP TE LSPs. The precise requirements and mechanisms for OAM are out of the scope of this document. It is expected that a separate document will cover these requirements. 5.15 Scalability Scalability is a key requirement in P2MP MPLS systems. Solutions MUST be designed to scale well with an increase in the number of any of the following: - the number of recipients - the number of branch points - the number of branches. Both scalability of performance and operation MUST be considered. Key considerations SHOULD include: - the amount of refresh processing associated with maintaining a P2MP TE LSP. - the amount of protocol state that must be maintained by ingress and transit LSRs along a P2MP tree. - the number of protocol messages required to set up or tear down a P2MP LSP as a function of the number of egress LSRs. - the number of protocol messages required to repair a P2MP LSP after failure or perform make-before-break. - the amount of protocol information transmitted to manage a P2MP TE LSP (i.e. the message size). - the amount of potential routing extensions. - the amount of control plane processing required by the ingress, transit and egress LSRs to add/delete a branch LSP to/from an existing P2MP LSP. It is expected that the applicability of each solution will be evaluated with regards to the aforementioned scalability criteria. 5.16 Backwards Compatibility It SHOULD be an aim of any P2MP solution to offer as much backward compatibility as possible. An ideal which is probably impossible to achieve would be to offer P2MP services across legacy MPLS networks without any change to any LSR in the network. If this ideal cannot be achieved, the aim SHOULD be to use legacy nodes as both transit non-branch LSRs and egress LSRs. Yasukawa,et. al. [Page 22] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 It is a further requirement for the solution that any LSR that implements the solution SHALL NOT be prohibited by that act from supporting P2P TE LSPs using existing signaling mechanisms. That is, unless administratively prohibited, P2P TE LSPs MUST be supported through a P2MP network. Also, it is a requirement that P2MP TE LSPs MUST be able to co-exist with IP unicast and IP multicast networks. 5.17 GMPLS Solutions for MPLS P2MP TE-LSPs when applied to GMPLS P2MP PSC or non-PSC TE-LSPs MUST be backward and forward compatible with the other features of GMPLS including: - control and data plane separation (IF_ID RSVP_HOP and IF_ID ERROR_SPEC), - full support of numbered and unnumbered TE links (see [RFC 3477] and [GMPLS-ROUTE]), - use of the GENERALIZED_LABEL_REQUEST, the GENERALIZED_LABEL (C-Type 2 and 3), the SUGGESTED_LABEL and the RECOVERY_LABEL, in conjunction with the LABEL_SET and the ACCEPTABLE_LABEL_SET object, - processing of the ADMIN_STATUS object, - processing of the PROTECTION object, - support of Explicit Label Control, - processing of the Path_State_Removed Flag, - handling of Graceful Deletion procedures. - E2E and Segment Recovery procedures. In addition, since non-PSC TE-LSPs may have to be processed in environments where the "P2MP capability" could be limited, specific constraints may also apply during the P2MP TE Path computation. Being technology specific, these constraints are outside the scope of this document. However, technology independent constraints (i.e. constraints that are applicable independently of the LSP class) SHOULD be allowed during P2MP TE LSP message processing. It has to be emphasized that path computation and management techniques shall be as close as possible to those being used for PSC P2P TE LSPs and P2MP TE LSPs. Yasukawa,et. al. [Page 23] Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004 5.18 Requirements for Hierarchical P2MP TE LSPs [LSP-HIER] defines concepts and procedures for P2P LSP hierarchy. These procedures SHOULD be extended to support P2MP LSP hierarchy. The P2MP MPLS-TE solution SHOULD support the concept of region and region hierarchy (PSC1