Network Working Group Eric Mannie (Ebone) - Editor Internet Draft Expiration date: Dec. 2001 Peter Ashwood-Smith (Nortel) Daniel Awduche (Movaz) Ayan Banerjee (Calient) Debashis Basak (Accelight) Lou Berger (Movaz) Greg Bernstein (Ciena) John Drake (Calient) Yanhe Fan (Axiowave) Don Fedyk (Nortel) Gert Grammel (Alcatel) Kireeti Kompella (Juniper) Alan Kullberg (NetPlane) Jonathan P. Lang (Calient) Fong Liaw (Zaffire) Thomas D. Nadeau (Cisco) Dimitri Papadimitriou (Alcatel) Dimitrios Pendarakis (Tellium) Bala Rajagopalan (Tellium) Yakov Rekhter (Juniper) Debanjan Saha (Tellium) Hal Sandick (Nortel) Vishal Sharma (Metanoia) George Swallow (Cisco) Z. Bo Tang (Tellium) John Yu (Zaffire) Alex Zinin (Cisco) June 2001 Generalized Multi-Protocol Label Switching (GMPLS) Architecture draft-ietf-ccamp-gmpls-architecture-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. 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." E. Mannie et. al. Internet-Draft December 2001 1 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 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. Table of Contents 1. Abstract........................................................4 1.1 List of open issues............................................4 2. Conventions used in this document...............................4 3. Introduction....................................................4 3.1. Acronyms & abbreviations......................................5 3.2. Multiple Types of Switching and Forwarding Hierarchies........5 3.3. Extension of the MPLS Control Plane...........................7 3.4. Key Differences Between MPLS-TE and GMPLS....................10 4. Routing and addressing model...................................11 4.1 Addressing of PSC and non-PSC layers..........................12 4.2 GMPLS scalability enhancements................................12 4.3 Extensions to IP TE routing protocols.........................13 5. Unnumbered links...............................................14 5.1 Unnumbered Forwarding Adjacencies.............................15 6. Link bundling..................................................15 6.1 Restrictions on bundling......................................16 6.2 Routing considerations for bundling...........................16 6.3 Signaling considerations......................................17 6.3.1 Mechanism 1: Implicit Indication............................17 6.3.2 Mechanism 2: Explicit Indication by IP Address..............17 6.3.3 Mechanism 3: Explicit Indication by Component Interface ID..17 6.4 Unnumbered Bundled Link.......................................18 6.5 Forming TE links..............................................18 7. UNI and NNI....................................................19 7.1 OIF UNI versus GMPLS..........................................19 7.2 Routing at the UNI............................................20 8. Link Management................................................20 8.1 Control channel and control channel management................21 8.2 Link property correlation.....................................22 8.3 Link connectivity verification................................22 8.4 Fault management..............................................23 9. Generalized Signaling..........................................23 9.1. Overview: How to Request an LSP..............................25 9.2. Generalized Label Request....................................26 9.3. SONET/SDH Traffic Parameters.................................27 9.4. Bandwidth Encoding...........................................28 9.5. Generalized Label............................................28 9.6. Waveband Switching...........................................29 9.7. Label Suggestion by the Upstream.............................29 9.8. Label Restriction by the Upstream............................29 9.9. Bi-directional LSP...........................................30 9.10. Bi-directional LSP Contention Resolution....................31 9.11. Rapid Notification of Failure...............................31 9.12. Link Protection.............................................31 9.13. Explicit Routing and Explicit Label Control.................32 9.14. LSP modification and LSP re-routing.........................33 E. Mannie et. al. Internet-Draft December 2001 2 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 9.15. Route recording.............................................33 10. Forwarding Adjacencies (FA)...................................34 10.1 Routing and Forwarding Adjacencies...........................34 10.2. Signaling aspects...........................................35 10.3 Cascading of Forwarding Adjacencies..........................35 11.1 Network Management Systems (NMS).............................36 12. Security considerations.......................................38 13. Acknowledgements..............................................39 14. References....................................................39 15. Author's Addresses............................................41 Full Copyright Statement..........................................43 Appendix 1 Brief overview of the ITU-T work on G.ASTN/G.ASON......45 A.1 Terminology issues............................................45 A.2 Common Equipment Management [G.cemr]..........................45 A.3 Data Communications Network [G.dcn]...........................46 A.4 Distributed Connection Management [G.dcm].....................46 A.5 Generalized Automatic Neighbor Discovery [G.ndisc]............47 A.6 Generalized Automatic Service Discovery [G.sdisc].............47 A.7 OTN routing [G.rtg]...........................................47 A.8 OTN Connection Admission Control [G.cac]......................47 A.9 OTN Link Management [G.lm]....................................48 E. Mannie et. al. Internet-Draft December 2001 3 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 1. Abstract Future data and transmission networks will consist of elements such as routers, switches, DWDM systems, Add-Drop Multiplexors (ADMs), photonic cross-connects (PXCs), optical cross-connects (OXCs), etc that will use Generalized MPLS (GMPLS) to dynamically provision resources and to provide network survivability using protection and restoration techniques. This document describes the architecture of GMPLS. GMPLS extends MPLS to encompass time-division (e.g. SDH/SONET, PDH, G.709), wavelength (lambdas), and spatial switching (e.g. incoming port or fiber to outgoing port or fiber). The main focus of GMPLS is on the control plane of these various layers since each of them can use physically diverse data or forwarding planes. The intention is to cover both the signaling and the routing part of that control plane. 1.1 List of open issues This section lists several open issues on which the various people are currently working. - Inter-domain operations (e.g. routing with BGP-4). - Protection and restoration for GMPLS. - Multicasting in GMPLS. - Extensions for new technologies like G.709. - VPN support. 2. Conventions used in this document 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 [2]. 3. Introduction The architecture presented in this document covers the main building blocks needed to build a consistent control plane for multiple switching layers. It does not restrict the way that these layers work together. Different models can be applied: e.g. overlay, augmented or integrated. Moreover, each pair of contiguous layer may work jointly in a different way, resulting in a number of possible combinations, at the discretion of manufacturers and operators. This document is a generalization of the MPLS architecture [MPLS- ARCH], and in some cases may differ slightly from that architecture since non packet-based forwarding planes are now considered. It is not the intention of this document to describe concepts already described in the current MPLS architecture. The goal is to describe specific concepts of Generalized MPLS (GMPLS). However, some of the concepts explained hereafter are not part of the current MPLS architecture and are applicable to both MPLS and GMPLS (i.e. link bundling, unnumbered links, and LSP hierarchy). E. Mannie et. al. Internet-Draft December 2001 4 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Since these concepts were introduced together with GMPLS and since they are of paramount importance for an operational GMPLS network, they will be discussed here. The organization of the remainder of this draft is as follows. We begin with an introduction of GMPLS. We then present the specific GMPLS building blocks and explain how they can be combined together to build an operational GMPLS networks. Specific details of the separate building blocks can be found in the corresponding documents. 3.1. Acronyms & abbreviations ABR Area Border Router AS Autonomous System ASBR Autonomous System Boundary Router BGP Border Gateway Protocol CR-LDP Constraint-based Routing LDP CSPF Constraint-based Shortest Path First DWDM Dense Wavelength Division Multiplexing FA Forwarding Adjacency GMPLS Generalized Multi-Protocol Label Switching IGP Interior Gateway Protocol LDP Label Distribution Protocol LMP Link Management Protocol LSA Link State Advertisement LSR Label Switching Router LSP Label Switched Path MIB Management Information Base MPLS Multi-Protocol Label Switching NMS Network Management System OXC Optical Cross-Connect PXC Photonic Cross-Connect RSVP ReSource reserVation Protocol SDH Synchronous Digital Hierarchy STM(-N) Synchronous Transport Module (-N) STS(-N) Synchronous Transport Signal-Level N (SONET) TE Traffic Engineering 3.2. Multiple Types of Switching and Forwarding Hierarchies Generalized MPLS (GMPLS) differs from traditional MPLS in that it supports multiple types of switching, i.e. the addition of support for TDM, lambda, and fiber (port) switching. The support for the additional types of switching has driven GMPLS to extend certain base functions of traditional MPLS and, in some cases, to add functionality. These changes and additions impact basic LSP properties, how labels are requested and communicated, the unidirectional nature of LSPs, how errors are propagated, and information provided for synchronizing the ingress and egress LSRs. The MPLS architecture [MPLS-ARCH] was defined to support the forwarding of data based on a label. In this architecture, Label Switching Routers (LSRs) were assumed to have a forwarding plane E. Mannie et. al. Internet-Draft December 2001 5 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 that is capable of (a) recognizing either packet or cell boundaries, and (b) being able to process either packet headers (for LSRs capable of recognizing packet boundaries) or cell headers (for LSRs capable of recognizing cell boundaries). The original MPLS architecture is here being extended to include LSRs whose forwarding plane recognizes neither packet, nor cell boundaries, and therefore, can't forward data based on the information carried in either packet or cell headers. Specifically, such LSRs include devices where the forwarding decision is based on time slots, wavelengths, or physical ports. So, the new set of LSRs, or more precisely interfaces on these LSRs, can be subdivided into the following classes: 1. Packet Switch Capable (PSC) interfaces: Interfaces that recognize packet boundaries and can forward data based on the content of the packet header. Examples include interfaces on routers that forward data based on the content of the IP header and interfaces on routers that forward data based on the content of the MPLS "shim" header. 2. Layer-2 Switch Capable (L2SC) interfaces: Interfaces that recognize frame/cell boundaries and can forward data based on the content of the frame/cell header. Examples include interfaces on Ethernet bridges that forward data based on the content of the MAC header and interfaces on ATM-LSRs that forward data based on the ATM VPI/VCI. 3. Time-Division Multiplex Capable (TDM) interfaces: Interfaces that forward data based on the data's time slot in a repeating cycle. An example of such an interface is that of a SDH/SONET Cross-Connect (XC), Terminal Multiplexer (TM), or Add-Drop Multiplexer (ADM). Other examples include interfaces implementing G.709 (the "digital wrapper") and PDH interfaces. 4. Lambda Switch Capable (LSC) interfaces: Interfaces that forward data based on the wavelength on which the data is received. An example of such an interface is that of a Photonic Cross-Connect (PXC) or Optical Cross-Connect (OXC) that can operate at the level of an individual wavelength. Additional examples include PXC interfaces that can operate at the level of a group of wavelengths, i.e. a waveband. 5. Fiber-Switch Capable (FSC) interfaces: Interfaces that forward data based on a position of the data in the real world physical spaces. An example of such an interface is that of a PXC or OXC that can operate at the level of a single or multiple fibers. E. Mannie et. al. Internet-Draft December 2001 6 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 A circuit can be established only between, or through, interfaces of the same type. Depending on the particular technology being used for each interface, different circuit names can be used, e.g. SDH circuit, optical trail, light path, etc. In the context of GMPLS, all these circuits are referenced by a common name: Label Switched Path (LSP). The concept of nested LSP (LSP within LSP), already available in the traditional MPLS, facilitates building a forwarding hierarchy, i.e. a hierarchy of LSPs. This hierarchy of LSPs can occur on the same interface, or between different interfaces. For example, a hierarchy can be built if an interface is capable of multiplexing several LSPs from the same technology (layer), e.g. a lower order SDH/SONET LSP (VC-12) nested in a higher order SDH/SONET LSP (VC-4). Several levels of signal (LSP) nesting are defined in the SDH/SONET multiplexing hierarchy. The nesting can also occur between interfaces. At the top of the hierarchy are FSC interfaces, followed by LSC interfaces, followed by TDM interfaces, followed by L2SC, and followed by PSC interfaces. This way, an LSP that starts and ends on a PSC interface can be nested (together with other LSPs) into an LSP that starts and ends on a L2SC interface. This LSP, in turn, can be nested (together with other LSPs) into an LSP that starts and ends on an TDM interface, which in turn can be nested (together with other LSPs) into an LSP that starts and ends on a LSC interface, which in turn can be nested (together with other LSPs) into an LSP that starts and ends on a FSC interface. 3.3. Extension of the MPLS Control Plane The establishment of LSPs that span only Packet Switch Capable (PSC) or Layer-2 Switch Capable (L2SC) interfaces is defined for the original MPLS and/or MPLS-TE control planes. GMPLS extends these control planes to support each of the five classes of interfaces (i.e. layers) defined in the previous section. Note that the GMPLS control plane supports an overlay model, an augmented model, and a peer (integrated) model. In the near term, GMPLS is very suitable for controlling each layer independently. This elegant approach will facilitate the future deployment of other models. The GMPLS control plane is made of several building blocks are described in more detail in the following sections. These building blocks are based on well-known signaling and routing protocols that have been extended and/or modified to support GMPLS. They use IPv4 and/or IPv6 addresses. Only one new specialized protocol is required to support the operations of GMPLS, a signaling protocol for link management [LMP]. E. Mannie et. al. Internet-Draft December 2001 7 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 GMPLS is indeed based on the Traffic Engineering (TE) extensions to MPLS, a.k.a. MPLS-TE. This is because most of the technologies that can be used below the PSC level require some traffic engineering. The placement of LSPs at these levels needs in general to take several constraints into consideration (such as framing, bandwidth, protection capability, etc) and to bypass the legacy Shortest-Path First (SPF) algorithm. Note, however, that this is not mandatory and that in some cases SPF routing can be applied. In order to facilitate constrained-based SPF routing of LSPs, the nodes performing LSP establishment need more information about the links in the network than standard intra-domain routing protocols provide. These TE attributes are distributed using the transport mechanisms already available in IGPs (e.g. flooding) and taken into consideration by the LSP routing algorithm. Optimization of the LSP trajectories may also require some external simulations using heuristics that serve as input for the actual path calculation and LSP establishment process. Extensions to traditional routing protocols and algorithms are needed to uniformly encode and carry TE link information, and explicit routes (e.g. source routes) are required in the signaling. In addition, the signaling must now be capable of transporting the required circuit (LSP) parameters such as the bandwidth, the type of signal, the desired protection, the position in a particular multiplex, etc. Most of these extensions have already been defined for PSC and L2SC traffic engineering with MPLS. GMPLS primarily adds additional extensions for TDM, LSC, and FSC traffic engineering. Only a very few elements are technology specific. Thus, GMPLS extends the two signaling protocols defined for MPLS-TE signaling, i.e. RSVP-TE and CR-LDP. However, GMPLS does not specify which one of these two signaling protocols must be used. It is the role of manufacturers and operators to evaluate the two possible solutions for their own interest. Since GMPLS is based on RSVP-TE and CR-LDP, it mandates a downstream-on-demand label allocation and distribution, with an ingress initiated ordered control. Liberal label retention is normally used, but conservative label retention mode could also be used. Furthermore, there is no restriction on the label allocation strategy, it can be request/signaling driven (obvious for circuit switching technologies), traffic/data driven, or even topology driven. There is also no restriction on the route selection; explicit routing is normally used (strict or loose) but hop-by-hop routing could be used as well. GMPLS also extends two traditional intra-domain link-state routing protocols already extended for TE, i.e. OSPF-TE and IS-IS-TE. However, if explicit (source) routing is used, the routing algorithms used by these protocols no longer need to be standardized. Extensions for inter-domain routing (e.g. BGP) are for further study. E. Mannie et. al. Internet-Draft December 2001 8 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 The use of technologies like DWDM (Dense Wavelength Division Multiplexing) implies that we can now have a very large number of parallel links between two directly adjacent nodes (hundreds of wavelengths, or even thousands of wavelengths if multiple fibers are used). Such a large number of links was not originally considered for an IP or MPLS control plane. Some slight adaptations of that control plane are thus required if we want to reuse it in the GMPLS context. For instance, the traditional IP routing model assumes the establishment of a routing adjacency over each link connecting two adjacent nodes. Having such a large number of adjacencies does not scale well. Each node needs to maintain each of its adjacencies one by one, and link state routing information must be flooded throughout the network. To solve this issue the concept of link bundling was introduced. Moreover, the manual configuration and control of these links, even if they are unnumbered, becomes impractical. The Link Management Protocol (LMP) was specified to solve these issues. LMP runs between data-plane adjacent nodes and is used to manage TE links. Specifically, LMP provides mechanisms to maintain control channel connectivity, verify the physical connectivity of the data- bearing links, correlate the link property information, and manage link failures. A unique feature of LMP is that it is able to localize faults in both opaque and transparent networks, independent of the encoding scheme and bit rate used for the data. LMP is defined in the context of GMPLS, but is specified independently of the GMPLS signaling specification since it is a local protocol run between data-plane adjacent nodes. As a result, LMP can be reused in other contexts with non-GMPLS signaling protocols. The MPLS signaling and routing protocols require at least one bi- directional control channel to communicate even if two adjacent nodes are connected by unidirectional links. Several control channels can be used. LMP can be used to establish, maintain and manage these control channels. GMPLS does not specify how these control channels must be implemented, but GMPLS requires IP to transport the signaling and routing protocols over them. Control channels can be either in-band or out-of-band, and several solutions can be used to carry IP. Note also that one type of LMP message is used in-band in the data plane and may not be transported over IP, but this is a particular case, needed to verify connectivity in the data plane. E. Mannie et. al. Internet-Draft December 2001 9 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 3.4. Key Differences Between MPLS-TE and GMPLS Some key differences between MPLS-TE and GMPLS are highlighted in the following. Some of them are key advantages of GMPLS to control TDM, LSC and FSC layers. - In MPLS-TE, links traversed by an LSP can include an intermix of links with heterogeneous label encoding (e.g. links between routers, links between routers and ATM-LSRs, and links between ATM-LSRs. GMPLS extends this by including links where the label is encoded as a time slot, or a wavelength, or a position in the real world physical space. - In MPLS-TE, an LSP that carries IP has to start and end on a router. GMPLS extends this by requiring an LSP to start and end on similar type of LSR. - The type of a payload that can be carried in GMPLS by an LSP is extended to allow such payloads as SONET/SDH, G.709, 1 or 10Gb Ethernet, etc. - For TDM, LSC and FSC interfaces, bandwidth allocation for an LSP can be performed only in discrete units. - It is expected to have (much) fewer labels on TDM, LSC or FSC links than on PSC or L2SC links. - The use of Forwarding Adjacencies (FA), provides a mechanism that can improve bandwidth utilization, when bandwidth allocation can be performed only in discrete units, as well as a mechanism to aggregate forwarding state, thus allowing the number of required labels to be reduced - GMPLS allows for a label to be suggested by an upstream node to reduce the setup latency. This suggestion may be overridden by a downstream node but, in some cases, at the cost of higher LSP setup time. - GMPLS extends on the notion of restricting the range of labels that may be selected by a downstream node. In GMPLS, an upstream node may restrict the labels for an LSP along either a single hop or along the entire LSP path. This feature is useful in photonic networks where wavelength conversion may not be available. - While traditional TE-based (and even LDP-based) LSPs are unidirectional, GMPLS supports the establishment of bi-directional LSPs. - GMPLS supports the termination of an LSP on a specific egress port, i.e. the port selection at the destination side. - GMPLS with RSVP-TE supports an RSVP specific mechanism for rapid failure notification. E. Mannie et. al. Internet-Draft December 2001 10 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 4. Routing and addressing model GMPLS is based on the IP routing and addressing models. This assumes that IPv4 and/or IPv6 addresses are used to identify interfaces and that traditional (distributed) IP routing protocols are also reused. Indeed, the discovery of the topology and the resource state of all links in a routing domain is achieved via these routing protocols. Since control and data planes are de-coupled in GMPLS, one cannot do anymore the assumption that control-plane neighbors (i.e. IGP-learnt neighbors) are data-plane neighbors, hence mechanisms like LMP are needed to associate TE links with neighboring nodes. IP addresses are not used only to identify interfaces of IP hosts and routers, but more generally to identify any PSC and non-PSC interfaces. Similarly, IP routing protocols are used to find routes for IP datagrams with a SPF algorithm, and are also used to find routes for non-PSC circuits by using a CSPF algorithm. However, some additional mechanisms are needed to increase the scalability of these models and to deal with specific traffic engineering requirements of non-PSC layers. These mechanisms will be introduced in the following. Re-using existing IP routing protocols allows for non-PSC layers to take advantages of all the valuable developments that took place since years for IP routing, in particular in the context of intra- domain routing (link-state routing) and inter-domain routing (policy routing). Each particular non-PSC layer can be seen as a set of Autonomous Systems (ASs) interconnected in an arbitrary way. Similarly to the traditional IP routing, each AS is managed by a single administrative authority. For instance, an AS can be an SDH/SONET network operated by a given carrier. The set of interconnected ASs being an SDH/SONET Internetwork. Exchange of routing information between ASs can be done via an inter-domain routing protocol like BGP-4. There is obviously a huge value of re-using well-known policy routing facilities provided by BGP in a non-PSC context. Extensions for BGP traffic engineering in the context of non-PSC layers are for further study. Each AS can be subdivided in different routing domains, and each can run a different intra-domain routing protocol. In turn, each routing-domain can be divided in areas. A routing domain is made of GMPLS nodes. These nodes can be either edge nodes (i.e. hosts, ingress LSRs or egress LSRs), or internal LSRs. An example of non-PSC host is an SDH/SONET Terminal Multiplexer (TM). Another example, is an SDH/SONET interface card within an IP router or ATM switch. E. Mannie et. al. Internet-Draft December 2001 11 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Note that traffic engineering in the intra-domain requires the use of link-state routing protocols like OSPF or IS-IS. GMPLS defines extensions to these protocols. These extensions are needed to disseminate specific TDM, LSC and FSC static and dynamic characteristics related to nodes and links. The current focus is on intra-area traffic engineering. However, inter-area traffic engineering is also under investigation. 4.1 Addressing of PSC and non-PSC layers The fact that IPv4 and/or IPv6 addresses are used doesn't imply at all that they should be allocated in the same addressing space than public IPv4 and/or IPv6 addresses used for the Internet. Each layer could have a different addressing authority responsible for address allocation and re-using the full addressing space, completely independently. Private IP addresses can be used if they don't require to be exchanged with any other operator, public IP addresses are otherwise required. Of course, if an integrated model is used, two layers could share the same addressing space. Note that there is a benefit of using public IPv4 and/or IPv6 Internet addresses for non-PSC layers if an integrated model with the IP layer is foreseen. If we consider the scalability enhancements proposed in the next section, the IPv4 (32 bits) and the IPv6 (128 bits) addressing spaces are both more than sufficient to accommodate any non-PSC layer. We can reasonably expect to have much less non-PSC devices (e.g. SDH/SONET nodes) than we have today IP hosts and routers. Other kinds of addressing schemes (e.g. NSAP) are not considered here since this would imply a modification of the already existing signaling and routing protocols that uses IPv4 and/or IPv6 addresses. This would be incompatible to our objectives of re-using existing IP protocols. 4.2 GMPLS scalability enhancements TDM, LSC and FSC layers introduce new constraints on the IP addressing and routing models since several hundreds of parallel physical links (e.g. wavelengths) can now connect two nodes. Most of the carriers already have today several tens of wavelengths per fiber between two nodes. New generation of DWDM systems will allow several hundreds of wavelengths per fiber. It becomes rather impractical to associate an IP address with each end of each physical link, to represent each link as a separate routing adjacency, and to advertise and to maintain link states for each of these links. For that purpose, GMPLS enhances the MPLS routing and addressing models to increase their scalability. E. Mannie et. al. Internet-Draft December 2001 12 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Two optional mechanisms can be used to increase the scalability of the addressing and the routing: unnumbered links and link bundling. These two mechanisms can also be combined. They require extensions to signaling (RSVP-TE and CR-LDP) and routing (OSPF-TE and IS-IS-TE) protocols. 4.3 Extensions to IP TE routing protocols Traditionally, a TE link is advertised as an adjunct to a "regular" OSPF or IS-IS link, i.e., an adjacency is brought up on the link, and when the link is up, both the regular IGP properties of the link (basically, the SPF metric) and the TE properties of the link are then advertised. However, GMPLS challenges this notion in three ways: - First, links that are non-PSC may yet have TE properties; however, an OSPF adjacency cannot be brought up directly on such links. - Second, an LSP can be advertised as a point-to-point TE link in the routing protocol, i.e. as a Forwarding Adjacency (FA); thus, an advertised TE link need no longer be between two OSPF direct neighbors. Forwarding Adjacencies (FA) are further described in a separate section. - Third, a number of links may be advertised as a single TE link (e.g. for improved scalability), so again, there is no longer a one- to-one association of a regular adjacency and a TE link. Thus we have a more general notion of a TE link. A TE link is a logical link that has TE properties, some of which may be configured on the advertising LSR, others which may be obtained from other LSRs by means of some protocol, and yet others which may be deduced from the component(s) of the TE link. An important TE property of a TE link is related to the bandwidth accounting for that link. GMPLS will define different accounting rules for different non-PSC layers. Generic bandwidth attributes are however defined by the TE routing extensions and by GMPLS, such as the unreserved bandwidth, the maximum reservable bandwidth, the maximum LSP bandwidth. It is expected in a dynamic environment to have frequent changes of bandwidth accounting information. A flexible policy for triggering link state updates based on bandwidth thresholds and link-dampening mechanism can be implemented. TE properties associated with a link should also capture protection and restoration related characteristics. For instance, shared protection can be elegantly combined with bundling. Protection and restoration are mainly generic mechanisms also applicable to MPLS. It is expected that they will first be developed for MPLS and later on generalized to GMPLS. E. Mannie et. al. Internet-Draft December 2001 13 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 A TE link between a pair of LSRs doesn't imply the existence of an IGP adjacency between these LSRs. A TE link must also have some means by which the advertising LSR can know of its liveness (e.g. by using LMP hellos). When an LSR knows that a TE link is up, and can determine the TE link's TE properties, the LSR may then advertise that link to its GMPLS enhanced OSPF or IS-IS neighbors using the TE objects/TLVs. We call the interfaces over which GMPLS enhanced OSPF or ISIS adjacencies are established "control channels". 5. Unnumbered links Unnumbered links (or interfaces) are links (or interfaces) that do not have IP addresses. Using such links involves two capabilities: the ability to specify unnumbered links in MPLS TE signaling, and the ability to carry (TE) information about unnumbered links in IGP TE extensions of ISIS-TE and OSPF-TE. A. The ability to specify unnumbered links in MPLS TE signaling requires extensions to RSVP-TE and CR-LDP. The MPLS-TE signaling doesn't provide support for unnumbered links, because it doesnÆt provide a way to indicate an unnumbered link in its Explicit Route Object/TLV and in its Record Route Object (there is no such TLV for CR-LDP). GMPLS defines simple extensions to indicate an unnumbered link in these two Objects/TLVs, using a new Unnumbered Interface ID sub-object/sub-TLV. Since unnumbered links are not identified by an IP address, then for the purpose of MPLS TE each end need some other identifier, local to the LSR to which the link belongs. Note that links are directed, i.e., a link l is from some LSR A to some other LSR B. LSR A chooses the interface identifier for link l, we call this the "outgoing interface identifier from LSR A's point of view". If there is a reverse link from LSR B to LSR A, B chooses the outgoing interface identifier for the reverse link, we call this the linkÆs "incoming interface identifier" from LSR AÆs point of view. There is no a priori relationship between the two interface identifiers. Both ends must also agree on each of these identifiers. The new Unnumbered Interface ID sub-object/sub-TLV for the ER Object/TLV contains the Router ID of the LSR at the upstream end of the unnumbered link and the outgoing interface identifier with respect to that upstream LSR. The new Unnumbered Interface ID sub-object/sub-TLV for the RR Object contains the outgoing interface identifier with respect to the LSR that adds it in the RR Object. B. The ability to carry (TE) information about unnumbered links in IGP TE extensions requires new sub-TLVs for the extended IS reachability TLV defined in ISIS-TE and for the TE LSA (which is an opaque LSA) defined in OSPF-TE. An Outgoing Interface Identifier sub-TLV and an Incoming Interface Identifier sub-TLV are defined. E. Mannie et. al. Internet-Draft December 2001 14 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 5.1 Unnumbered Forwarding Adjacencies If an LSR that originates an LSP advertises this LSP as an unnumbered FA in IS-IS or OSPF, the LSR must allocate an Interface ID to that FA. If the LSP is bi-directional, the tail end LSR advertises the reverse LSP as an unnumbered FA, the tail end LSR must allocate an Interface ID to the reverse FA. Signaling has been enhanced to carry the Interface ID. When an LSP is created which will be advertised as an FA, the head-end LSR includes its Interface ID in the Path/REQUEST. The tail end LSR responds by including its reverse LSPÆs Interface ID in the Resv/MAPPING. The Interface ID is transported in the new LSP Tunnel Interface ID object/TLV called the Forward Interface ID when it appears in a Path/REQUEST message, and the Reverse Interface ID when it appears in the Resv/MAPPING message. The LSP Tunnel Interface ID object/TLV contains the Router ID of the LSR that generates it, and the Interface ID. Note that if the forward or reverse LSP is part of a bundled link, the Interface ID is set to the Component Interface ID of that LSP (as defined in the next section). 6. Link bundling The concept of link bundling is essential in certain networks employing the GMPLS control plane. A typical example is an optical meshed network where adjacent optical cross-connects (LSRs) are connected by several hundreds of parallel wavelengths. In this network, consider the application of link state routing protocols, like OSPF or IS-IS, with suitable extensions for resource discovery and dynamic route computation. Each wavelength must be advertised separately in order to be used, except if link bundling is used. When a pair of LSRs is connected by multiple links, it is possible to advertise several (or all) of these links as a single link into OSPF and/or IS-IS. This process is called link bundling, or just bundling. The resulting logical link is called a bundled link as its physical links are called component links. The purpose of link bundling is to improve routing scalability by reducing the amount of information that has to be handled by OSPF and/or IS-IS. This reduction is accomplished by performing information aggregation/abstraction. As with any other information aggregation/abstraction, this results in losing some of the information. To limit the amount of losses one need to restrict the type of the information that can be aggregated/abstracted. E. Mannie et. al. Internet-Draft December 2001 15 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 6.1 Restrictions on bundling The following restrictions are required for bundling links. All component links in a bundle must begin and end on the same pair of LSRs; and share some common characteristics or properties, i.e. they must have the same: - Link Type (i.e. point-to-point or multi-access) [OSPF-TE/ISIS-TE], - TE Metric (i.e. an administrative cost) [OSPF- TE/ISIS-TE], - Set of Resource Classes (i.e. colors) [OSPF-TE/ISIS-TE], - Link Multiplex Capability (e.g. FSC, LSC or TDM) [HIERARCHY]. Note that bundling may be applied recursively; a component link may itself be a bundled link. An FA may also be a component link. In fact, a bundle can consist of a mix of point-to-point links, FAs, and bundled links, but all sharing some common properties. 6.2 Routing considerations for bundling A bundled link is just another kind of TE link such as those defined by OSPF-TE or IS-IS-TE. The liveness of the bundled link is determined by the liveness of each of the component links within the bundled link. The liveness of a component link can be determined by any of several means: IS-IS or OSPF hellos over the component link, or RSVP Hello (hop local), or LMP hellos (link local), or from layer 1 or layer 2 indications. Note that according to the RSVP-TE Tunnel specification the RSVP Hello mechanism is intended to be used when notification of link layer failures is not available and unnumbered links are not used, or when the failure detection mechanisms provided by the link layer are not sufficient for timely node failure detection. Once a bundled link is determined to be alive, it can be advertised as a TE link and the TE information can be flooded. If IS-IS/OSPF hellos are run over the component links, IS-IS/OSPF flooding can be restricted to just one of the component links. Note that advertising a (bundled) TE link between a pair of LSRs doesn't imply that there is an IGP adjacency between these LSRs that is associated with just that link. In fact, in certain cases a TE link between a pair of LSRs could be advertised even if there is no IGP adjacency at all between the LSR (e.g. when the TE link is an FA). Forming a bundled link consist in aggregating the identical TE parameters of each individual component link to produce aggregated TE parameters. A TE link as defined by [OSPF-TE-GMPLS] and [ISIS-TE- GMPLS] has many parameters, adequate aggregation rules must be defined for each one. Some parameters can be sums of component characteristics such as the unreserved bandwidth and the maximum reservable bandwidth. Bandwidth E. Mannie et. al. Internet-Draft December 2001 16 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 information is an important part of a bundle advertisement and it must be clearly defined since an abstraction is done. A GMPLS node with bundled links must apply admission control on a per-component link basis. 6.3 Signaling considerations Typically, an LSP's explicit route (contained in an explicit route) will choose the bundled link to be used for the LSP, but not the component link(s), since information about the bundled link is flooded, but information about the component links is kept local to the LSR. The choice of the component link to use is always made by an upstream node. If the LSP is bidirectional, the upstream node chooses a component link in each direction. Three mechanisms for indicating this choice to the downstream node are possible. 6.3.1 Mechanism 1: Implicit Indication This mechanism requires that each component link has a dedicated signaling channel (e.g. the link is a Sonet/SDH link using the DCC for in-band signaling). The upstream node tells the receiver which component link to use by sending the message over the chosen component link's dedicated signaling channel. Note that this signaling channel can be in-band or out-of-band. In this last case, the association between the signaling channel and that component link need to be explicitly configured. 6.3.2 Mechanism 2: Explicit Indication by IP Address This mechanism requires that each component link has a unique remote IP address. The upstream node can either send messages addressed to the remote IP address for the component link or encapsulate messages in an IP header whose destination address is the remote IP address. This mechanism does not require each component link to have its own control channel. In fact, it doesn't even require the whole (bundled) link to have its own control channel. 6.3.3 Mechanism 3: Explicit Indication by Component Interface ID With this mechanism, each component link in unnumbered and is assigned a unique Component Interface Identifier (32 bits value). The two LSRs at each end of the bundled link exchange these identifiers. An upstream node indicates the choice of a component link by including the corresponding identifier in signaling messages. Discovering Component Interface Identifiers at bootstrap may be accomplished by configuration, by means of a protocol such as LMP (preferred solution), by means of RSVP/CR-LDP (especially in the E. Mannie et. al. Internet-Draft December 2001 17 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 case where a component link is a Forwarding Adjacency), or by means of IS-IS or OSPF extensions. New objects are needed to indicate Component Interface Identifiers in signaling. GMPLS defines one Component Upstream Interface ID object/TLV used to indicate the component interface to be used for traffic flowing in the upstream direction; and one Component Downstream Interface ID object/TLV used to indicate the component interface to be used for traffic flowing in the downstream direction. Since the choice of the component link to use is always made by an upstream node, these objects/TLVs are included in the Path/REQUEST message send downstream. With RSVP-TE they are included in the sendor descriptor of the Path message. 6.4 Unnumbered Bundled Link A bundled link may itself be numbered or unnumbered independent of whether the component links are numbered or not. This affects how the bundled link is advertised in IS-IS/OSPF, and the format of LSP EROs that traverse the bundled link. Furthermore, unnumbered Interface Identifiers for all unnumbered outgoing links of a given LSR (whether component links, Forwarding Adjacencies or bundled links) MUST be unique in the context of that LSR. 6.5 Forming TE links The generic rule for bundling component links is to place those links that are correlated in some manner in the same bundle. If links may be correlated based on multiple properties then the bundling may be applied sequentially based on these properties. For instance, links may be first grouped based on the first property. Each of these groups may be then divided into smaller groups based on the second property and so on. The main principle followed in this process is that the properties of the resulting bundles should be concisely summarizable. Link bundling may be done automatically or by configuration. Automatic link bundling can apply bundling rules sequentially to produce bundles. For instance, the first property on which component links may be correlated could be the Link Multiplex Capability, the second property could be the Link Type, the third property could be the Administrative Weight (cost), the fourth property could be the Resource Classes and finally links may be correlated based on other metrics such as SRLG (Shared Risk Link Groups) or delay. When routing an alternate path for protection purposes, the general principle followed is that the alternate path is not routed over any link belonging to an SRLG that some link in the primary path belongs to. Thus, the rule to be followed is to group links belonging to exactly the same set of SRLGs. This type of sequential sub-division may result in a number of bundles between two adjacent nodes. In practice, however, the link properties may not be very heterogeneous among component links E. Mannie et. al. Internet-Draft December 2001 18 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 between two adjacent nodes. Thus, the number of bundles in practice may not be large. 7. UNI and NNI The interface between an edge GMPLS node and a GMPLS LSR on the network side may be referred to as a User to Network Interface (UNI), while the interface between two network side LSRs may be referred to as a Network to Network Interface (NNI). GMPLS does not specify separately a UNI and an NNI. Edge nodes are connected to LSRs on the network side, and these LSRs are in turn connected between them. Of course, the behavior of an edge node is not exactly the same as the behavior of an LSR on the network side. Note also, that an edge node may run a routing protocol, however it is expected that in most of the cases it will not (see also section 7.2 and the section about signaling with an explicit route). Conceptually, a difference between UNI and NNI make sense either if both interface uses completely different protocols, or if they use the same protocols but with some outstanding differences. In the first case, separate protocols are often defined successively, with more or less success. The GMPLS approach consisted in building a consistent model from day one, considering both the UNI and NNI interfaces at the same time. For that purpose a very few specific UNI particularities have been ignored in a first time. GMPLS is being enhanced to support such particularities at the UNI by some other standardization bodies, like the OIF. 7.1 OIF UNI versus GMPLS The current OIF UNI specification [OIF-UNI] defines an interface between a client SDH/SONET equipment and an SDH/SONET network, each belonging to a distinct administrative authority. The OIF UNI defines additional mechanisms on the top of GMPLS for the UNI. For instance, the OIF service discovery procedure is a precursor to obtaining UNI services. Service discovery allows a client to determine the static parameters of the interconnection with the network, including the UNI signaling protocols, the type of concatenation, the transparency levels as well as the type of diversity (node, link, SRLG) supported by the network. Since the current OIF UNI interface does not cover photonic networks, G.709 Digital Wrapper, etc, it is a sub-set of the GMPLS Architecture. E. Mannie et. al. Internet-Draft December 2001 19 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 7.2 Routing at the UNI This section discusses the selection of an explicit route by an edge node. The selection of the first LSR by an edge node connected to multiple LSRs is part of that problem. An edge node (host or LSR) can participate more or less deeply in the GMPLS routing. Four different routing models can be supported at the UNI: configuration based, partial peering, silent listening and full peering. - Configuration based: this routing model requires the manual or automatic configuration of an edge node with a list of neighbor LSRs sorted by preference order. Automatic configuration can be achieved using DHCP for instance. No routing information is exchanged at the UNI, except maybe the ordered list of LSRs. The only routing information used by the edge node is that list. The edge node sends by default an LSP request to the preferred LSR. ICMP redirects could be send by this LSR to redirect some LSP requests to another LSR connected to the edge node. GMPLS does not preclude that model. - Partial peering: limited routing information (mainly reachability) can be exchanged across the UNI using some extensions in the signaling plane. The reachability information exchanged at the UNI may be used to initiate edge node specific routing decision over the network. GMPLS does not have any capability to support this model today. - Silent listening: the edge node can silently listen to routing protocols and take routing decisions based on the information obtained. An edge node receives the full routing information, including traffic engineering extensions. One LSR should forward transparently all routing pdus to the edge node. An edge node can now compute a complete explicit route taking into consideration all the end-to-end routing information. GMPLS does not preclude this model. - Full peering: In addition to silent listening, the edge node participates within the routing, establish adjacencies with its neighbors and advertises LSAs. This is useful only if there are benefits for edge nodes to advertise themselves traffic engineering information. GMPLS does not preclude this model. 8. Link Management In the context of GMPLS, a pair of nodes (e.g., a photonic switch) may be connected by tens of fibers, and each fiber may be used to transmit hundreds of wavelengths if DWDM is used. Multiple fibers and/or multiple wavelengths may also be combined into one or more bundled links for routing purposes. Furthermore, to enable communication between nodes for routing, signaling, and link management, control channels must be established between a node pair. E. Mannie et. al. Internet-Draft December 2001 20 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Link management is a collection of useful procedures between adjacent nodes that provide local services such as control channel management, link connectivity verification, link property correlation, and fault management. The Link Management Protocol (LMP) has been defined to fulfill these operations. LMP was initiated in the context of GMPLS but is a generic toolbox that can be also used in other contexts. Control channel management and link property correlation are mandatory procedures of LMP. Link connectivity verification and fault management are optional procedures. 8.1 Control channel and control channel management LMP control channel management is used to establish and maintain control channels between nodes. Control channels exist independently of TE links, and can be used to exchange MPLS control-plane information such as signaling, routing, and link management information. An "LMP adjacency" is formed between two nodes that support the same LMP capabilities. Multiple control channels may be active simultaneously for each adjacency. A control channel can be either explicitly configured or automatically selected, however, LMP currently assume that control channels are explicitly configured. For the purposes of LMP, the exact implementation of the control channel is left unspecified. The control channel(s) between two adjacent nodes is no longer required to use the same physical medium as the data-bearing links between those nodes. For example, a control channel could use a separate wavelength or fiber, an Ethernet link, or an IP tunnel through a separate management network. A consequence of allowing the control channel(s) between two nodes to be physically diverse from the associated data-bearing links is that the health of a control channel does not necessarily correlate to the health of the data-bearing links, and vice-versa. Therefore, new mechanisms must be developed to manage links, both in terms of link provisioning and fault isolation. LMP does not specify how control channels are implemented, however it states that messages transported over a control channel must be IP encoded. Furthermore, since the messages are IP encoded, the link level encoding is not part of LMP. A 32-bit non-zero integer control channel identifier (CCId) is assigned to each direction of a control channel. Each control channel individually negotiates its control channel parameters and maintains connectivity using a fast Hello protocol. The latter is required if lower-level mechanisms are not available to detect link failures. E. Mannie et. al. Internet-Draft December 2001 21 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 The Hello protocol of LMP is intended to be a lightweight keep-alive mechanism that will react to control channel failures rapidly so that IGP Hellos are not lost and the associated link-state adjacencies are not removed unnecessarily. The Hello protocol consists of two phases: a negotiation phase and a keep-alive phase. The negotiation phase allows negotiation of some basic Hello protocol parameters, like the Hello frequency. The keep- alive phase consists of a fast lightweight bi-directional Hello message exchange. If a group of control channels share a common node pair and support the same LMP capabilities, then LMP control channel messages (except Configuration messages, and Hello) may be transmitted over any of the active control channels without coordination between the local and remote nodes. For LMP, it is essential that at least one control channel is always available. In the event of a control channel failure, it may be possible to use an alternate active control channel without coordination. 8.2 Link property correlation As part of LMP, a link property correlation exchange is defined. The exchange is used to aggregate multiple data-bearing links (i.e. component links) into a bundled link and exchange, correlate, or change TE link parameters. The link property correlation exchange may be done at any time a link is up and not in the Verification process (see next section). It allows for instance to add component links to a link bundle, change a link's protection mechanism, change port identifiers, or change component identifiers in a bundle. This mechanism is supported by an exchange of link summary messages. 8.3 Link connectivity verification Link connectivity verification is an optional procedure that may be used to verify the physical connectivity of data-bearing links as well as to exchange the link identifiers that are used in the GMPLS signaling. The use of this procedure is negotiated as part of the configuration exchange that take place during the negotiation phase of the Hello protocol. This procedure should be done initially when a data- bearing link is first established, and subsequently, on a periodic basis for all unallocated (free) data-bearing links. The verification procedure consists of sending Test messages in-band over the data-bearing links. This requires that the unallocated links must be opaque; however, multiple degrees of opaqueness (e.g., examining overhead bytes, terminating the payload, etc.), and hence different mechanisms to transport the Test messages, are specified. E. Mannie et. al. Internet-Draft December 2001 22 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Note that the Test message is the only LMP message that is transmitted over the link, and that Hello messages continue to be exchanged over the control channel during the link verification process. Data-bearing links are tested in the transmit direction as they are unidirectional. As such, it is possible for both nodes to exchange the Test messages simultaneously. To initiate the link verification procedure, a node must first notify the adjacent node that it will begin sending Test messages over a particular data-bearing link, or over the component links of a particular bundled link. The node must also indicate the number of data-bearing links that are to be verified; the interval at which the test messages will be sent; the encoding scheme, the transport mechanism that are supported, data rate for Test messages; and, in the case where the data-bearing links correspond to fibers, the wavelength over which the Test messages will be transmitted. Furthermore, the local and remote bundled link identifiers are transmitted at this time to perform the component link association with the bundled link identifiers. 8.4 Fault management Fault management is an important requirement from the operational point of view. When a failure occurs an operator needs to know exactly where it happened. It can also be used to support some specific local protection/restoration mechanisms. Logically, fault localization can occur only after a fault is detected. LMP provides a fault notification procedure that can be used to rapidly localize link failures. In new technologies such as transparent photonic switching currently no method is defined to locate a fault, and the mechanism by which the fault information is propagated must be sent "out of band" (via the control plane). As part of the fault notification procedure, the downstream LMP neighbor that detects data link failures will send an LMP message to its upstream neighbor notifying it of the failure. When an upstream node receives a failure notification, it can correlate the failure with the corresponding input ports to determine if the failure is between the two nodes. Once the failure has been localized, the signaling protocols can be used to initiate span or path protection/restoration procedures. 9. Generalized Signaling The GMPLS signaling extends certain base functions of the RSVP-TE and CR-LDP signaling and, in some cases, adds functionality. These changes and additions impact basic LSP properties, how labels are requested and communicated, the unidirectional nature of LSPs, how errors are propagated, and information provided for synchronizing the ingress and egress. E. Mannie et. al. Internet-Draft December 2001 23 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 The core GMPLS signaling specification is available in three parts: 1. A signaling functional description [GMPLS-SIG]. 2. RSVP-TE extensions [RSVP-TE-GMPLS]. 3. CR-LDP extensions [CR-LDP-GMPLS]. In addition, independent parts are available per technology: 1. GMPLS extensions for SONET and SDH control [SONETSDH-GMPLS]. The following MPLS profile applies to GMPLS: - Downstream-on-demand label allocation and distribution. - Ingress initiated ordered control. - Liberal (typical), or conservative (could) label retention mode. - Request, traffic/data, or topology driven label allocation strategy. - Explicit routing (typical), or hop-by-hop routing (could). The GMPLS signaling defines the following new building blocks on the top of MPLS-TE: 1. A new generic label request format. 2. Labels for TDM, LSC and FSC interfaces, generically known as Generalized Label. 3. Waveband switching support. 4. Label suggestion by the upstream for optimization purposes (e.g. latency). 5. Label restriction by the upstream to support some optical constraints. 6. Bi-directional LSP establishment with contention resolution. 7. Rapid failure notification to ingress node. 8. Protection information currently focusing on link protection, plus primary and secondary LSP indication. 9. Explicit routing with explicit label control for a fine degree of control. 10. Specific traffic parameters per technology. These building blocks will be described in mode details in the following. A complete specification can be found in the corresponding documents. Note that GMPLS is highly generic and has many options. Only building blocks 1, 2 and 10 are mandatory, and only within the specific format that is needed. Typically building blocks 6 and 9 should be implemented. Building blocks 3, 4, 5, 7 and 8 are optional. A typical SDH/SONET switching network would implement building blocks: 1, 2 (the SDH/SONET label), 6, 9 and 10. Building blocks 7 and 8 are optional since the protection/restoration can be achieved using SDH/SONET overhead bytes. E. Mannie et. al. Internet-Draft December 2001 24 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 A typical wavelength switching network would implement building blocks: 1, 2 (the generic format), 4, 5, 6, 7, 8 and 9. Building block 3 is only needed in the particular case of waveband switching. A typical fiber switching network would implement building blocks: 1, 2 (the generic format), 6, 7, 8 and 9. A typical MPLS-IP network would not implement any of these building blocks, since the absence of building block 1 would indicate regular MPLS-IP. Note however that building block 1 and 8 can be used to signal MPLS-IP as well. In that case, the MPLS-IP network can benefit from the link protection type (not available in CR-LDP, some very basic form being available in RSVP-TE). Building block 2 is here a regular MPLS label and no new label format is required. GMPLS does not specify any profile for RSVP-TE and CR-LDP implementations that have to support GMPLS - except for what is directly related to GMPLS procedures. It is to the manufacturer to decide which are the optional elements and procedures of RSVP-TE and CR-LDP that need to be implemented. Some optional MPLS-TE elements can be useful for TDM, LSC and FSC layers, for instance the setup and holding priorities that are inherited from MPLS-TE. 9.1. Overview: How to Request an LSP A TDM, LSC or FSC LSP is established by sending a PATH/Label Request message downstream to the destination. This message contains a Generalized Label Request with the type of LSP (i.e. the layer concerned), and its payload type. An Explicit Route (ERO) is also normally added to the message, but this can be added and/or completed by the first/default LSR. The requested bandwidth is encoded in the RSVP-TE SENDER_TSPEC object, or in the CR-LDP Traffic Parameters TLV. Specific parameters for a given technology are given in these traffic parameters, such as the type of signal, concatenation and/or transparency for a SDH/SONET LSP. For some other technology there could just one bandwidth parameter indicating the bandwidth as a floating-point value. The requested local protection per link may be requested using the Protection Information Object/TLV. The end-to-end protection type is for further study. If the LSP is a bi-directional LSP, an Upstream Label is also specified in the Path/Label request message. This label will be the one to use in the downstream to upstream direction. Additionally, a Suggested Label, a Label Set and a Waveband Label can also be included in the message. Other operations are defined in MPLS-TE. E. Mannie et. al. Internet-Draft December 2001 25 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 The downstream node will send back a Resv/Label Mapping message including one Generalized Label object/TLV that can contain several Generalized Labels. For instance, if a concatenated SDH/SONET signal is requested, several labels can be returned. In case of SDH/SONET virtual concatenation, a list of labels is returned. Each label identifying one element of the virtual concatenated signal. This limits virtual concatenation to remain within a single (component) link. In case of any type of SDH/SONET contiguous concatenation, only one label is returned. That label is the lowest signal of the contiguous concatenated signal (given an order specified in [SONETSDH-GMPLS]). In case of SDH/SONET "multiplication", i.e. co-routing of circuits of the same type but without concatenation but all belonging to the same LSP, the explicit list of all signals that take part in the LSP is returned. 9.2. Generalized Label Request The Generalized Label Request is a new object/TLV to be added in an RSVP-TE Path message instead of the regular Label Request, or in a CR-LDP Request message in addition to the already existing TLVs. Only one label request can be used per message, so a single LSP can be requested at a time per signaling message. The Generalized Label Request gives two major characteristics (parameters) required to support the LSP being requested: the LSP encoding type, and the LSP payload type called Generalized PID (G- PID). The LSP encoding type indicates the encoding type that will be used with the data associated with the LSP, i.e. the type of technology being considered. For instance, it can be SDH, SONET, Ethernet, ANSI PDH, etc. It represents the nature of the LSP, and not the nature of the links that the LSP traverses. This is used hop-by-hop by each node. A link may support a set of encoding formats, where support means that a link is able to carry and switch a signal of one or more of these encoding formats. The LSP payload type (G-PID) identifies the payload carried by the LSP, i.e. an identifier of the client layer of that LSP. For some technologies it also indicates the mapping used by the client layer, e.g. byte synchronous mapping of E1. This must be interpreted according to the LSP encoding type of the LSP and is used by the nodes at the endpoints of the LSP to know to which client layer a request is destined, and in some cases by the penultimate hop. Other technology specific parameters are not transported in the Generalized Label Request but in technology specific traffic E. Mannie et. al. Internet-Draft December 2001 26 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 parameters as explained hereafter. Currently, only one specific set of traffic parameters is defined, for SONET/SDH. Note that it is expected than specific traffic parameters will be defined in the future for photonic (all optical) switching. 9.3. SONET/SDH Traffic Parameters The SDH/SONET traffic parameters [SONETSDH-GMPLS] specify indeed a powerful set of capabilities for SONET (ANSI T1.105) and SDH (ITU-T G.707). Optional non-standard capabilities are also available. The first traffic parameter specifies the type of the elementary SONET/SDH signal that comprises the requested LSP, e.g. VC-11, VT6, VC-4, STS-3c, etc. Several transforms can then be applied successively on the elementary Signal to build the final signal being actually requested for the LSP. These transforms are the contiguous concatenation, the virtual concatenation, the transparency and the multiplication. Each one is optional. They must be applied strictly in the following order: - First, contiguous concatenation can be optionally applied on the Elementary Signal, resulting in a contiguously concatenated signal. - Second, virtual concatenation can be optionally applied either directly on the elementary Signal, or on the contiguously concatenated signal obtained from the previous phase. - Third, some transparency can be optionally specified when requesting a frame as signal rather than a container. Several transparency packages are defined. - Fourth, a multiplication can be optionally applied either directly on the elementary Signal, or on the contiguously concatenated signal obtained from the first phase, or on the virtually concatenated signal obtained from the second phase, or on these signals combined with some transparency. For RSVP-TE, the SONET/SDH traffic parameters are carried in a new SENDER-TSPEC and FLOWSPEC. The same format is used for both. There is no Adspec associated with the SENDER_TSPEC, either it is omitted or a default value is used. The content of the FLOWSPEC object received in a Resv message must be identical to the content of the SENDER_TSPEC of the corresponding Path message. In other words, the receiver is not allowed to change the values of the traffic parameters. However some level of negotiation may be achieved as explained in [SONETSDH-GMPLS] For CR-LDP, the SONET/SDH traffic parameters are simply carried in a new TLV. E. Mannie et. al. Internet-Draft December 2001 27 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 9.4. Bandwidth Encoding Some technologies that do not have (yet) specific traffic parameters just require a bandwidth encoding transported in a generic form. Bandwidth is carried in 32-bit number in IEEE floating-point format (the unit is bytes per second). Values are carried in a per protocol specific manner. For non-packet LSPs, it is useful to define discrete values to identify the bandwidth of the LSP. It should be noted that this bandwidth encoding do not apply to SONET/SDH, for which bandwidth the traffic parameters fully defined the requested SONET/SDH signal. The bandwidth is coded in the Peak Data Rate field of Int-Serv objects for RSVP-TE and in the Peak and Committed Data Rate fields of the CR-LDP Traffic Parameters TLV. 9.5. Generalized Label The Generalized Label extends the traditional MPLS label by allowing the representation of not only labels that travel in-band with associated data packets, but also (virtual) labels that identify time-slots, wavelengths, or space division multiplexed positions. For example, the Generalized Label may identify (a) a single fiber in a bundle, (b) a single waveband within fiber, (c) a single wavelength within a waveband (or fiber), or (d) a time-slot within a wavelength (or fiber). It may also be a generic MPLS label, a Frame Relay label, or an ATM label (VCI/VPI). The format of a label can be as simple as an integer value such as a wavelength label or can be more elaborated such as an SDH/SONET label. SDH and SONET define each a multiplexing structure. These multiplexing structures will be used as naming trees to create unique labels. Such a label will identify the exact position (times- lot(s)) of a signal in a multiplexing structure. Since the SONET multiplexing structure may be seen as a subset of the SDH multiplexing structure, the same format of label is used for SDH and SONET. Since the nodes sending and receiving the Generalized Label know what kinds of link they are using, the Generalized Label does not identify its type, instead the nodes are expected to know from the context what type of label to expect. A Generalized Label only carries a single level of label, i.e. it is non-hierarchical. When multiple levels of labels (LSPs within LSPs) are required, each LSP must be established separately. E. Mannie et. al. Internet-Draft December 2001 28 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 9.6. Waveband Switching A special case of wavelength switching is waveband switching. A waveband represents a set of contiguous wavelengths, which can be switched together to a new waveband. For optimization reasons it may be desirable for a photonic cross-connect to optically switch multiple wavelengths as a unit. This may reduce the distortion on the individual wavelengths and may allow tighter separation of the individual wavelengths. A Waveband label is defined to support this special case. Waveband switching naturally introduces another level of label hierarchy and as such the waveband is treated the same way all other upper layer labels are treated. As far as the MPLS protocols are concerned there is little difference between a waveband label and a wavelength label except that semantically the waveband can be subdivided into wavelengths whereas the wavelength can only be subdivided into time or statistically multiplexed labels. 9.7. Label Suggestion by the Upstream GMPLS allows for a label to be optionally suggested by an upstream node. This suggestion may be overridden by a downstream node but in some cases, at the cost of higher LSP setup time. The suggested label is valuable when establishing LSPs through certain kinds of optical equipment where there may be a lengthy (in electrical terms) delay in configuring the switching fabric. For example micro mirrors may have to be elevated or moved, and this physical motion and subsequent damping takes time. If the labels and hence switching fabric are configured in the reverse direction (the norm) the MAPPING/Resv message may need to be delayed by 10's of milliseconds per hop in order to establish a usable forwarding path. It can be important for restoration purposes where alternate LSPs may need to be rapidly established as a result of network failures. 9.8. Label Restriction by the Upstream An upstream node can optionally restrict (limit) the choice of label of a downstream node to a set of acceptable labels. Giving lists and/or ranges of inclusive (acceptable) or exclusive (unacceptable) labels in a Label Set provides this restriction. If not applied, all labels from the valid label range may be used. There are four cases where a label restriction is useful in the "optical" domain. 1. The first case is where the end equipment is only capable of transmitting and receiving on a small specific set of wavelengths/bands. 2. The second case is where there is a sequence of interfaces, which cannot support wavelength conversion and require the same wavelength be used end-to-end over a sequence of hops, or even an entire path. E. Mannie et. al. Internet-Draft December 2001 29 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 3. The third case is where it is desirable to limit the amount of wavelength conversion being performed to reduce the distortion on the optical signals. 4. The last case is where two ends of a link support different sets of wavelengths. The receiver of a Label Set must restrict its choice of labels to one that is in the Label Set. A Label Set may be present across multiple hops. In this case each node generates it's own outgoing Label Set, possibly based on the incoming Label Set and the node's hardware capabilities. This case is expected to be the norm for nodes with conversion incapable interfaces. 9.9. Bi-directional LSP GMPLS allows establishment of bi-directional symmetric LSPs (not of asymmetric LSPs). A symmetric bi-directional LSP has the same traffic engineering requirements including fate sharing, protection and restoration, LSRs, and resource requirements (e.g., latency and jitter) in each direction. In the remainder of this section, the term "initiator" is used to refer to a node that starts the establishment of an LSP and the term "terminator" is used to refer to the node that is the target of the LSP. For a bi-directional LSPs, there is only one initiator and one terminator. Normally to establish a bi-directional LSP when using [RSVP-TE] or [CR-LDP] two unidirectional paths must be independently established. This approach has the following disadvantages: 1. The latency to establish the bi-directional LSP is equal to one round trip signaling time plus one initiator-terminator signaling transit delay. This not only extends the setup latency for successful LSP establishment, but it extends the worst-case latency for discovering an unsuccessful LSP to as much as two times the initiator-terminator transit delay. These delays are particularly significant for LSPs that are established for restoration purposes. 2. The control overhead is twice that of a unidirectional LSP. This is because separate control messages (e.g. Path and Resv) must be generated for both segments of the bi-directional LSP. 3. Because the resources are established in separate segments, route selection is complicated. There is also additional potential race for conditions in assignment of resources, which decreases the overall probability of successfully establishing the bi-directional connection. 4. It is more difficult to provide a clean interface for SDH/SONET equipment that may rely on bi-directional hop-by-hop paths for protection switching. Note that existing SDH/SONET gear transmits the control information in-band with the data. E. Mannie et. al. Internet-Draft December 2001 30 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 5. Bi-directional optical LSPs (or lightpaths) are seen as a requirement for many optical networking service providers. With bi-directional LSPs both the downstream and upstream data paths, i.e. from initiator to terminator and terminator to initiator, are established using a single set of signaling messages. This reduces the setup latency to essentially one initiator- terminator round trip time plus processing time, and limits the control overhead to the same number of messages as a unidirectional LSP. For bi-directional LSPs, two labels must be allocated. Bi- directional LSP setup is indicated by the presence of an Upstream Label in the appropriate signaling message. 9.10. Bi-directional LSP Contention Resolution Contention for labels may occur between two bi-directional LSP setup requests traveling in opposite directions. This contention occurs when both sides allocate the same resources (ports) at effectively the same time. The GMPLS signaling defines a procedure to resolve that contention, basically the node with the higher node ID will win the contention. To reduce the probability of contention, some mechanisms are also suggested. 9.11. Rapid Notification of Failure GMPLS defines three signaling extensions for RSVP-TE that enable expedited notification of failures and other events to nodes responsible for restoring failed LSPs, and modify error handling. For CR-LDP there is not currently a similar mechanism. The first extension identifies where event notifications are to be sent. The second provides for general expedited event notification. Such extensions can be used by fast restoration mechanisms. The final extension is an RSVP optimization to allow the faster removal of intermediate states in some cases. 9.12. Link Protection Protection information is carried in the new optional Protection Information Object/TLV. It currently indicates the desired link protection for each link of an LSP. If a particular protection type, i.e., 1+1, or 1:N, is requested, then a connection request is processed only if the desired protection type can be honored. Note that GMPLS advertises the protection capabilities of a link in the routing protocols. Path computation algorithms may take this information into account when computing paths for setting up LSPs. Protection information also indicates if the LSP is a primary or secondary LSP. A secondary LSP is a backup to a primary LSP. The resources of a secondary LSP are normally not used until the primary E. Mannie et. al. Internet-Draft December 2001 31 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 LSP fails, but they may be used by other LSPs until the primary LSP fails over the secondary LSP. At that point, any LSP that is using the resources for the secondary LSP must be preempted. Six link protection types are currently defined as individual flags and can be combined: enhanced, dedicated 1+1, dedicated 1:1, shared, unprotected, extra traffic. See [GMPLS-SIG] section 7.1 for a precise definition of each. 9.13. Explicit Routing and Explicit Label Control Using an explicit route can control the path taken by an LSP more or less precisely. Typically, the node at the head-end of an LSP finds a more or less precise explicit route and builds an Explicit Route Object (ERO)/ Explicit Route (ER) TLV that contains that route. Possibly, the edge node doesnÆt build any explicit route, and just transmit a signaling request to a default neighbor LSR (as IP hosts today). For instance, an explicit route could be added to a signaling message by the first switching node, on behalf of the edge node. Note also that an explicit route is altered by intermediate LSRs during its progression towards the destination. The explicit route is originally defined by MPLS-TE as a list of abstract nodes (i.e. groups of nodes) along the explicit route. Each abstract node can be an IPv4 address prefix, an IPv6 address prefix, or an AS number. This capability allows the generator of the explicit route to have imperfect information about the details of the path. In the simplest case, an abstract node can be a full IP address (32 bits) that identifies a specific node (called a simple abstract node). MPLS-TE allows strict and loose abstract nodes. The path between a strict node and its preceding node must include only network nodes from the strict node and its preceding abstract node. The path between a loose node and its preceding node may include other network nodes that are not part of the strict node or its preceding abstract node. This explicit route was extended to include interface numbers as abstract nodes to support unnumbered interfaces; and further extended by GMPLS to include labels as abstract nodes. Having labels in an explicit route is an important feature that allows controlling the placement of an LSP with a very fine granularity. This is more likely to be used for TDM, LSC and FSC links. In particular, the explicit label control in the explicit route allows terminating an LSP on a particular outgoing port to an egress node. This can also be used when it is desirable to "splice" two LSPs together, i.e. where the tail of the first LSP would be "spliced" into the head of the second LSP. E. Mannie et. al. Internet-Draft December 2001 32 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Another use is when an optimization algorithm is used for an SDH/SONET network. This algorithm can provide very detailed explicit routes, including the label (time-slot) to use on a link, in order to minimize the fragmentation of the SDH/SONET multiplex on the corresponding interface. Another use is when the label indicates a particular component in a bundle in order to stay diverse with other components of that bundle, i.e. to control the usage of components in a bundle for different LSPs. 9.14. LSP modification and LSP re-routing LSP modification and re-routing are two features already available in MPLS-TE. GMPLS does not add anything new. Elegant re-routing is possible with the concept of "make-before-break" whereby an old path is still used while a new path is set up by avoiding double reservation of resources. Then, the node performing the re-routing can swap on the new path and close the old path. This feature is supported with RSVP-TE (using shared explicit filters) and CR-LDP (using the action indicator flag). LSP modification consists in changing some LSP parameters, but normally without changing the route. It is supported using the same mechanism as re-routing. However, the semantic of LSP modification will differ from one technology to the other. For instance, further studies are required to understand the impact of dynamically changing some SDH/SONET circuit characteristics such as the bandwidth, the protection type, the transparency, the concatenation, etc. 9.15. Route recording In order to improve the reliability and the manageability of the LSP being established, the concept of the route recording was introduced in RSVP-TE to function as: - First, a loop detection mechanism to discover L3 routing loops, or loops inherent in the explicit route (this mechanism is strictly exclusive with the use of explicit routing objects). - Second, a route recording mechanism collects up-to-date detailed path information on a hop-by-hop basis during the LSP setup process. This mechanism provides valuable information to the source and destination nodes. Any intermediate routing change at setup time, in case of loose explicit routing, will be reported. - Third, a recorded route can be used as input for an explicit route. This is useful if a source node receives the recorded route from a destination node and applies it as an explicit route in order to "pin down the path". Within the GMPLS architecture only the second and third functions are mainly applicable for TDM, LSC and FSC layers. E. Mannie et. al. Internet-Draft December 2001 33 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 10. Forwarding Adjacencies (FA) To improve scalability of MPLS TE (and thus GMPLS) it may be useful to aggregate multiple TE LSPs inside a bigger TE LSP. Intermediate nodes see the external LSP only, they don't have to maintain forwarding states for each internal LSP, less signaling messages need to be exchanged and the external LSP can be somehow protected instead (or in addition) to the internal LSPs. This can considerably increase the scalability of the signaling. The aggregation is accomplished by (a) an LSR creating a TE LSP, (b) the LSR forming a forwarding adjacency out of that LSP (advertising this LSP as a unidirectional link into ISIS/OSPF), (c) allowing other LSRs to use forwarding adjacencies for their path computation, and (d) nesting of LSPs originated by other LSRs into that LSP (e.g. by using the label stack construct in the case of IP). An LSR may (under its local configuration control) announce an LSP as a link into ISIS/OSPF. When this link is advertised into the same instance of ISIS/OSPF as the one that determines the route taken by the LSP, we call such a link a "forwarding adjacency" (FA). We refer to the LSP as the "forwarding adjacency LSP", or just FA- LSP. Note that since the advertised entity is a link in ISIS/OSPF, both the endpoint LSRs of the FA-LSP must belong to the same ISIS level/OSPF area (intra-area improvement of scalability). In general, creation/termination of a FA and its FA-LSP could be driven either by mechanisms outside of MPLS (e.g., via configuration control on the LSR at the head-end of the adjacency), or by mechanisms within MPLS (e.g., as a result of the LSR at the head-end of the adjacency receiving LSP setup requests originated by some other LSRs). ISIS/OSPF floods the information about FAs just as it floods the information about any other links. As a result of this flooding, an LSR has in its TE link state database the information about not just conventional links, but FAs as well. An LSR, when performing path computation, uses not just conventional links, but FAs as well. Once a path is computed, the LSR uses RSVP- TE/CR-LDP for establishing label binding along the path. FAs need simple extensions to signaling and routing protocols. 10.1 Routing and Forwarding Adjacencies Forwarding adjacencies may be represented as either unnumbered or numbered links. A FA can also be a bundle of LSPs between two nodes. FAs are advertised as GMPLS TE links such as defined in [HIERARCHY]. GMPLS TE links are advertised in OSPF and ISIS such as defined in [OSPF-TE-GMPLS] and [ISIS-TE-GMPLS]. These last two specifications enhance [OSPF-TE] and [ISIS-TE] that defines a base TE link. E. Mannie et. al. Internet-Draft December 2001 34 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 When a FA is created dynamically, its TE attributes are inherited from the FA-LSP that induced its creation. [HIERARCHY] specifies how each TE parameter of the FA is inherited from the FA-LSP. Note that the bandwidth of the FA must be at least as big as the FA-LSP that induced it, but may be bigger if only discrete bandwidths are available for the FA-LSP. In general, for dynamically provisioned forwarding adjacencies, a policy-based mechanism may be needed to associate attributes to forwarding adjacencies. A FA advertisement could contain the information about the path taken by the FA-LSP associated with that FA. Other LSRs may use this information for path computation. This information is carried in a new OSPF and IS-IS TLV called the Path TLV. It is possible that the underlying path information might change over time, via configuration updates, or dynamic route modifications, resulting in the change of that TLV. If forwarding adjacencies are bundled (via link bundling), and if the resulting bundled link carries a Path TLV, the underlying path followed by each of the FA-LSPs that form the component links must be the same. It is expected that forwarding adjacencies will not be used for establishing ISIS/OSPF peering relation between the routers at the ends of the adjacency. 10.2. Signaling aspects For the purpose of processing the explicit route in a Path/Request message of an LSP that is to be tunneled over a forwarding adjacency, an LSR at the head-end of the FA-LSP views the LSR at the tail of that FA-LSP as adjacent (one IP hop away). 10.3 Cascading of Forwarding Adjacencies With an integrated model several layers are controlled using the same routing and signaling protocols. A network may then have links with different multiplexing/demultiplexing capabilities. For example, a node may be able to multiplex/demultiplex individual packets on a given link, and may be able to multiplex/demultiplex channels within a SONET payload on other links. A new OSPF and IS-IS sub-TLV has been defined to advertise the multiplexing capability of each interface: PSC, L2SC, TDM, LSC or FSC. This sub-TLV is named the Link Multiplex Capability sub-TLV and complements the sub-TLVs defined in [OSPF-TE-GMPLS] and [ISIS-TE- GMPLS]. The information carried in this sub-TLV is used to construct LSP regions, and determine regionÆs boundaries. Path computation may take into account region boundaries when computing a path for an LSP. For example, path computation may restrict the path taken by an LSP to only the links whose multiplexing/demultiplexing capability is PSC. When an LSP need to E. Mannie et. al. Internet-Draft December 2001 35 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 cross a region boundary, it can trigger the establishment of an FA at the underlying layer (i.e. the L2SC layer). This can trigger a cascading of FAs between layers with the following obvious order: L2SC, then TDM, then LSC, and then finally FSC. 11. Network Management Service Providers (SPs) use network management extensively to configure, monitor or provision various devices in their network. It is important to note that a SPÆs equipment may be distributed across geographically separate sites, making distributed management even more important. The service provider should utilize an NMS system and standard management protocols such as SNMP [RFC1901] [RFC1902] [RFC1903] [RFC1904] [RFC1905] [RFC1906] and its associated MIBs as standard interfaces to configure, monitor and provision devices at various locations. The service provider may also wish to use the command line interface (CLI) provided by vendors with their devices, but this however, is not a standard or recommended solution due to the fact that there is no standard CLI language or interface, which results in N different CLIÆs in a network with devices from N different vendors. In the context of GMPLS, it is extremely important for standard interfaces to the SPÆs devices (SNMP) to exist due to the nature of the technology itself. Since GMPLS comprises many different layers of control-plane and data-plane technology, it is important for management interfaces in this area to be flexible enough to allow the manager to manage GMPLS easily, and in a standard way. 11.1 Network Management Systems (NMS) The NMS system should maintain the collective information about each device within the system. Note that the NMS system may actually be comprised of several distributed applications (i.e.: alarm aggregators, configuration consoles, polling applications, etc...) that collectively comprises the SPÆs NMS. In this way, it can make provisioning and maintenance decisions with the full knowledge of the entire SP network. Configuration or provisioning information (i.e.: requests for new services) could be entered into the NMS and subsequently distributed via SNMP to the remote devices, making the SPÆs job of managing the network much more compact and effortless than having to manage each device individually (i.e.: via CLI). Security and access control can be achieved through the use of SNMPv3 and the View Access Control Model [SNMPv3VACM]. This approach can be very effectively used within an SP network, since the SP has access to and control over all devices within its domain. Standardized MIBs will need to be developed before this approach can be used ubiquitously to provision, configure and monitor devices in non-heterogeneous networks or across SP boundaries. E. Mannie et. al. Internet-Draft December 2001 36 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 11.2 Management Information Base (MIB) In the context of GMPLS, it is extremely important for standard interfaces to devices to exist due to the nature of the technology itself. Since GMPLS comprises many different layers of control-plane technology, it is important for SNMP MIBs in this area to be flexible enough to allow the manager to manage the entire control plane. This should be through a set of MIBs that may cooperate (i.e.: coordinated row-creation on the agent), or through more generalized MIBs that aggregate some of the desired actions to be taken and push those details down to the devices. It is important to note that in certain circumstances, it may be necessary to duplicate some small subset of manageable objects in new MIBs for the convenience of management. Control of some parts of GMPLS may also be achieved though the use of existing MIB interfaces (i.e.: existing SONET MIB), or though separate ones, which are yet to be defined. MIBs may have been previously defined in the IETF or ITU. Existing MIBs may need to be extended to facilitate some of the new functionality desired by GMPLS. In these cases, the working group should work on new versions of these MIBs so that these extensions can be added. 11.3 Tools As in traditional networks, standard tools such as traceroute [RFC1393] and ping [RFC1739] are needed for debugging and performance monitoring of GMPLS networks, and mainly for the control plane topology that will mimic the data plane topology. Furthermore, such tools provide network reachability information. The GMPLS control protocols will need to expose certain pieces of information in order for these tools to function properly and to provide information germane to GMPLS. These tools should be made available via the CLI. These tools should also be made available for remote invocation via the SNMP interface [RFC2925]. 11.4 Fault Correlation Between Multiple Layers Due to the nature of GMPLS and the fact that potential layers may be involved in the control and transmission of GMPLS data and control information, it is therefore required that a fault in one layer be passed to the adjacent higher and lower layers in an effort to notify them of the fault. However, due to nature of these many layers, it is possible and even probable, that hundreds or even thousands of notifications may need to transpire between layers. This is undesirable for several reasons. First, these notifications will overwhelm the device. Second, if the device(s) are programmed to emit SNMP Notifications [RFC1901] then the large number of notifications the device may attempt to emit may overwhelm the network with a storm of notifications. Furthermore, even if the device emits the notifications, the NMS that must process these notifications will either be overwhelmed, or will be processing redundant information. That is, if 1000 interfaces at layer B are stacked above a single interface below it at layer A, and the interface at A goes down, the interfaces at layer B should not emit E. Mannie et. al. Internet-Draft December 2001 37 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 notifications. Instead, the interface at layer A should emit a single notification. The NMS receiving this notification should be able to correlate the fact that this interface has many others stacked above it and take appropriate action, if necessary. Devices that support GMPLS should provide mechanisms for aggregating, summarizing, enabling and disabling of inter-layer notifications for the reasons described above. In the context of SNMP MIBs, all MIBs that are used by GMPLS must provide enable/disable objects for all notification objects. Furthermore, these MIBs must also provide notification summarization objects or functionality (as described above) as well. NMS systems and standard tools which process notifications or keep track of the many layers on any given devices must be capable of processing the vast amount of information which may potentially be emitted by network devices running GMPLS at any point in time. 12. Security considerations GMPLS defines a new control plane architecture for multiple types of network elements. In general, since LSPs established using GMPLS are expected to carry high volumes of data and consume significant network resources, security mechanisms are required to safeguard the underlying network against attacks on the control plane and/or unauthorized usage of data transport resources. Security requirements depend on the level of trust between nodes that exchange GMPLS control messages as well as the exposure of the control channel to third parties. In general, a network node may apply more relaxed security requirements when exchanging GMPLS control messages with nodes under the same administrative domain than when talking to nodes in a different domain. In this respect, network to user (UNI) and network-to-network interfaces are expected to have higher security requirements than node-to-node interfaces. Security mechanisms can provide two main properties: authentication and confidentiality. Authentication can provide origin verification, message integrity and replay protection, while confidentiality ensures that a third party cannot decipher the contents of a message. In situations where GMPLS deployment requires primarily authentication, the respective authentication mechanisms of the GMPLS component protocols may be used ([RFC2747], [LDP], [RFC2385], [LMP]). Additionally, the IPSEC suite of protocols ([RFC2402], [RFC2406], [RFC2409]) may be used to provide authentication, confidentiality or both, for a GMPLS control channel; this option offers the benefit of combined protection of all GMPLS component protocols. Note however that GMPLS itself introduces no new security considerations to the current MPLS-TE signaling (RSVP-TE, CR-LDP), routing protocols (OSPF-TE, IS-IS-TE) or network management protocols (SNMP). E. Mannie et. al. Internet-Draft December 2001 38 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 13. Acknowledgements This draft is the work of numerous authors and consists of a composition of a number of previous drafts in this area. Many thanks to Ben Mack-Crane (Tellabs) for all the useful SDH/SONET discussions that we had together. Thanks also to Pedro Falcao (Ebone) and Michael Moelants (Ebone) for their SDH/SONET and optical technical advice and support. Finally, many thanks also to Krishna Mitra (Calient) and Curtis Villamizar (Avici). A list of the drafts from which material and ideas were incorporated follows: [GMPLS-SIG] draft-ietf-mpls-generalized-signaling-04.txt Generalized MPLS - Signaling Functional Description [RSVP-TE-GMPLS] draft-ietf-mpls-generalized-rsvp-te-03.txt Generalized MPLS Signaling - RSVP-TE Extensions [CR-LDP-GMPLS] draft-ietf-mpls-generalized-cr-ldp-03.txt Generalized MPLS Signaling - CR-LDP Extensions [SONETSDH-GMPLS] draft-ietf-ccamp-gmpls-sonet-sdh-01.txt GMPLS Extensions for SONET and SDH Control [LMP] draft-ietf-mpls-lmp-01.txt Link Management Protocol (LMP) [HIERARCHY] draft-ietf-mpls-lsp-hierarchy-02.txt LSP Hierarchy with MPLS TE [RSVP-TE-UNNUM] draft-ietf-mpls-rsvp-unnum-01.txt Signalling Unnumbered Links in RSVP-TE [CR-LDP-UNNUM] draft-ietf-mpls-crldp-unnum-01.txt Signalling Unnumbered Links in CR-LDP [BUNDLE] draft-kompella-mpls-bundle-05.txt Link Bundling in MPLS Traffic Engineering [OSPF-TE-GMPLS] draft-kompella-ospf-gmpls-extensions-01.txt OSPF Extensions in Support of Generalized MPLS [ISIS-TE-GMPLS] draft-ietf-isis-gmpls-extensions-02.txt IS-IS Extensions in Support of Generalized MPLS 14. References [RFC1393] G. Malkin, "Traceroute Using an IP Option", IETF RFC 1393, January 1993. [RFC1901] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Introduction to Community-based E. Mannie et. al. Internet-Draft December 2001 39 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 SNMPv2", IETF RFC 1901, January 1996. [RFC1902] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Structure of Management Information for Version 2 of the Simple Network Management Protocol (SNMPv2)", IETF RFC 1901, January 1996. [RFC1903] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Textual Conventions for Version 2 of the Simple Network Management Protocol (SNMPv2)", IETF RFC 1901, January 1996. [RFC1904] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Conformance Statements for Version 2 of the Simple Network Management Protocol (SNMPv2)", IETF RFC 1901, January 1996. [RFC1905] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)", IETF RFC 1905, January 1996. [RFC1906] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)", IETF RFC 1906, January 1996. [SNMPv3VACM] Wijnen, B., Presuhn, R., and K. McCloghrie, "View- based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", IETF RFC 2575, April 1999. [RFC1739] G. Kessler, S. Shepard , "A Primer On Internet and TCP/IP Tools", RFC1739, December 1994. [RFC2328] J. Moy, "OSPF Version 2", RFC 2328, Standard Track, April 1998. [RFC2370] R. Coltun, "The OSPF Opaque LSA Option", RFC 2370 Standard Track, July 1998. [RFC2385] A. Heffernan, "Protection of BGP Sessions via the TCP MD5 Signature Option," IETF RFC 2385. [RFC2402] S. Kent and R. Atkinson, "IP Authentication Header," RFC 2402. [RFC2406] S. Kent and R. Atkinson, "IP Encapsulating Security Payload (ESP)," IETF RFC 2406. [RFC2409] D. Harkins and D. Carrel, "The Internet Key Exchange (IKE)", IETF RFC 2409. [RFC2747] F. Baker et al. "RSVP Cryptographic Authentication", E. Mannie et. al. Internet-Draft December 2001 40 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 IETF RFC 2747. [RFC2925] K. White , "Definitions of Managed Objects for Remote Ping, Traceroute, and Lookup Operations", IETF RFC 2925, September 2000. [LPD] L. Andersson, P. Doolan, N. Feldman, A. Fredette, B. Thomas, "LDP Specification", IETF RFC 3036, January 2001. [OSPF-TE] D. Katz, D. Yeung, and K. Kompella, "Traffic Engineering Extensions to OSPF" draft-katz-yeung-ospf- traffic-05.txt. [LMP-WDM] A. Fredette et al., "Link Management Protocol (LMP) for WDM Transmission Systems," Internet Draft, Work in Progress, draft-fredette-lmp-wdm-01.txt, March 2001. [MPLS-TEO] D. Awduche et al., "Multi-Protocol Lambda Switching: Combining MPLS Traffic Engineering Control With Optical Crossconnects," Internet Draft, Work in Progress, draft-awduche-mpls-te-optical-03.txt, April 2001. 15. Author's Addresses Peter Ashwood-Smith Eric Mannie (editor) Nortel Networks Corp. Ebone (GTS) P.O. Box 3511 Station C, Terhulpsesteenweg 6A Ottawa, ON K1Y 4H7 1560 Hoeilaart Canada Belgium Phone: +1 613 763 4534 Phone: +32 2 658 56 52 Email: Email: eric.mannie@gts.com petera@nortelnetworks.com Daniel O. Awduche Thomas D. Nadeau Movaz Networks Cisco Systems, Inc. 7296 Jones Branch Drive 250 Apollo Drive Suite 615 Chelmsford, MA 01824 McLean, VA 22102 USA USA Phone: +1 978 244 3051 Phone: +1 703 847-7350 Email: tnadeau@cisco.com Email: awduche@movaz.com Ayan Banerjee Dimitri Papadimitriou Calient Networks Alcatel - IPO NSG 5853 Rue Ferrari Francis Wellesplein, 1 San Jose, CA 95138 B-2018 Antwerpen USA Belgium Phone: +1 408 972-3645 Phone: +32 3 240-84-91 Email: abanerjee@calient.net Email: dimitri.papadimitriou@alcatel.be E. Mannie et. al. Internet-Draft December 2001 41 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Debashis Basak Dimitrios Pendarakis Accelight Networks Tellium, Inc. 70 Abele Road, Bldg.1200 2 Crescent Place Bridgeville, PA 15017 P.O. Box 901 USA Oceanport, NJ 07757-0901 Phone: +1 412 220-2102 (ext115) USA email: dbasak@accelight.com Email: DPendarakis@tellium.com Lou Berger Bala Rajagopalan Movaz Networks, Inc. Tellium, Inc. 7926 Jones Branch Drive 2 Crescent Place Suite 615 P.O. Box 901 MCLean VA, 22102 Oceanport, NJ 07757-0901 USA USA Phone: +1 703 847-1801 Phone: +1 732 923 4237 Email: lberger@movaz.com Email: braja@tellium.com Greg Bernstein Yakov Rekhter Ciena Corporation Juniper 10480 Ridgeview Court Email: yakov@juniper.net Cupertino, CA 94014 USA Phone: +1 408 366 4713 Email: greg@ciena.com John Drake Hal Sandick Calient Networks Nortel Networks 5853 Rue Ferrari Email: San Jose, CA 95138 hsandick@nortelnetworks.com USA Phone: +1 408 972 3720 Email: jdrake@calient.net Yanhe Fan Debanjan Saha Axiowave Networks, Inc. Tellium Optical Systems 100 Nickerson Road 2 Crescent Place Marlborough, MA 01752 Oceanport, NJ 07757-0901 USA USA Phone: +1 508 460 6969 Ext. 627 Phone: +1 732 923 4264 Email: yfan@axiowave.com Email: dsaha@tellium.com Don Fedyk Vishal Sharma Nortel Networks Corp. Metanoia, Inc. 600 Technology Park Drive 335 Elan Village Lane Billerica, MA 01821 San Jose, CA 95134 USA USA Phone: +1-978-288-4506 Phone: +1 408 943 1794 Email: Email: vsharma87@yahoo.com dwfedyk@nortelnetworks.com E. Mannie et. al. Internet-Draft December 2001 42 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Gert Grammel George Swallow Alcatel Cisco Systems, Inc. Via Trento, 30 250 Apollo Drive 20059 Vimercate (Mi) Chelmsford, MA 01824 Italy USA Email: gert.grammel@alcatel.it Phone: +1 978 244 8143 Email: swallow@cisco.com Kireeti Kompella Z. Bo Tang Juniper Networks, Inc. Tellium, Inc. 1194 N. Mathilda Ave. 2 Crescent Place Sunnyvale, CA 94089 P.O. Box 901 USA Oceanport, NJ 07757-0901 Email: kireeti@juniper.net USA Phone: +1 732 923 4231 Email: btang@tellium.com Alan Kullberg John Yu NetPlane Systems, Inc. Zaffire Inc. 888 Washington 2630 Orchard Parkway St.Dedham, MA 02026 San Jose, CA 95134 USA USA Phone: +1 781 251-5319 Email: jzyu@zaffire.com Email: akullber@netplane.com Jonathan P. Lang Alex Zinin Calient Networks Cisco Systems 25 Castilian 150 W. Tasman Dr. Goleta, CA 93117 San Jose, CA 95134 Email: jplang@calient.net Email: azinin@cisco.com Fong Liaw Zaffire Inc. 2630 Orchard Parkway San Jose, CA 95134 USA Email: fliaw@zaffire.com Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. E. Mannie et. al. Internet-Draft December 2001 43 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." E. Mannie et. al. Internet-Draft December 2001 44 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 Appendix 1 Brief overview of the ITU-T work on G.ASTN/G.ASON This appendix gives a brief overview of the work performed in ITU-T related to the control plane for transport networks, and briefly links it to the IETF related work. In ITU-T the work is performed in Study Group (SG) 13/Question 10 for G.astn, SG15/Q12 for G.ason and SG15/Q14 for G.dcn, G.dcm, G.ndisc, G.sdisc and G.cemr. G.astn describes the network level requirements for the control plane of Automatically Switched Transport Networks (ASTNs). Such a network provides a set of control functions for the purpose of setting up and releasing connections across a network. It is recognized that transport networks support multiple clients. As such, ASTNs are intended to be client independent. A.1 Terminology issues A common misunderstanding is related to the usage of terms like layer, LSP and client/server. In IETF the expression "layer" is attached to a technology present in a network like e.g. OTN, SDH, ATM, IP. However ITU-T uses the term "layer" for any kind of mapping. This includes the mapping between different technologies like SDH/SONET in OTN as well as internal mappings like SDH/SONET low order layer and high order layer. In this case a client server relationship between layers is automatically present. In order to avoid misunderstandings the term "technology" is used hereafter to represent the IETF understanding of a layer. In GMPLS the notion of Label Switched Path (LSP) is defined to describe connections between two Label Switch Routers (LSRs). In packet switched networks LSPs can be "tunneled" by encapsulating a packet into another packet within the same technology (also known as "label stacking"). What is considered to be encapsulation in IETF is considered to be a mapping in ITU-T that implies the use of a client-server layer relationship. In ITU-T the terms "client" and "server" are used to define the role of a layer with respect to another layer e.g. SDH can be the client layer of an OTN server layer network. This distinction is not used in IETF where a layer is associated to a certain type of technology. Instead the term "client" is used for a customer device attached to a service provider network, both belonging to distinct administrative authorities. A.2 Common Equipment Management [G.cemr] The G.cemr recommendation specifies those Equipment Management Functions (EMF) requirements that are common for SDH and OTN. The equipment management function (EMF) provides the means through which a Network Element Level manager manages the Network Element Function (NEF). E. Mannie et. al. Internet-Draft December 2001 45 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 These kinds of functions are not detailed in the current GMPLS work since it is focused on control plane related aspects. Network Management aspects are subject of other working groups in IETF. A.3 Data Communications Network [G.dcn] According to G.dcn the various functions, which constitute a telecommunications network, can be classified into two broad functional groups. One is the transport functional group, which transfers any telecommunications information from one point to another point(s). The other is the control functional group, which realizes various ancillary services and operations and maintenance functions. The Data Communications Network (DCN) provides transport for the applications associated with the control functional group. Examples of such applications that are transported by the DCN are: transport network operations/management applications, DCN operations/management applications, Automatic Switched Transport Services (ASTN) control plane applications, voice communications, etc. The IP-based DCN provides Layer 1 (physical), Layer 2 (data-link) and Layer 3 (network) functionality and consists of routing/switching functionality interconnected via links. These links can be implemented over various interfaces, including WAN and LAN interfaces. This recommendation provides the architecture requirements for an IP-based DCN, the requirements for inter-working between an IP-based DCN and an OSI-based DCN, and the IP-based DCN interface specifications. Since in GMPLS the signaling and management plane are orthogonal to each other, different kinds of networks can be used for both tasks. In GMLS, LMP defines mechanisms for the control channel management, which is used to establish and maintain control channels between nodes. However, GMPLS assume that messages are transported by IP but doesnÆt specify how the DCN should be implemented. A.4 Distributed Connection Management [G.dcm] The G.dcm Recommendation covers the areas associated with the signaling aspects of automatic switched transport network, such as attribute specifications, the message sets, the interface requirements, the DCM state diagrams, and the interworking functions for the distributed connection management This is the main purpose of the GMPLS signaling, using extensions to protocols like CR-LDP and RSVP-TE. E. Mannie et. al. Internet-Draft December 2001 46 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 A.5 Generalized Automatic Neighbor Discovery [G.ndisc] The G.ndisc Recommendation provides the requirements and message sets for the automatic neighbor for the User-to-Network Interface (UNI), Internal Node-to-Node Interface (I-NNI), External Node-to- Node Interface (E-NNI) and Physical Interface (PI). These requirements determine the discovery process across these interfaces that aid automated connection management. GMPLS is an IP centric control plane incorporating protocols defined for routing and neighbor discovery such OSPF and IS-IS. In addition, LMP fulfills some of these requirements as well, especially for the component links of bundled link. A.6 Generalized Automatic Service Discovery [G.sdisc] The G.sdisc Recommendation provides the requirements and message sets for the automatic service discovery for the User-to-Network Interface (UNI), Internal Node-to-Node Interface (I-NNI), External Node-to-Node Interface (E-NNI) and Physical Interface (PI). These requirements determine the discovery process across these interfaces that aid automated connection management. GMPLS signaling and routing protocols LMP allows some level of automatic service discovery. A.7 OTN routing [G.rtg] No ITU-T contribution available yet. IP based intra-domain (e.g. OSPF, IS-IS) and inter-domain (e.g. BGP- 4) routing protocols are the strength of a GMPLS control plane. Moreover, BGP-4 is the only practical solution for policy routing between different operators that was proved on a very large scale. GMPLS extends the TE extensions to OSPF and IS-IS. Work on BGP-4 is ongoing. A.8 OTN Connection Admission Control [G.cac] According to G.astn, Connection Admission Control (CAC) is necessary for authentication of the user and controlling access to network resources. CAC shall be provided as part of the control plane functionality. It is the role of the CAC function to determine if there is sufficient free resource available to allow a new connection. If there is, the CAC may permit the connection request to proceed, alternatively, if there is not, it shall notify the originator of the connection request that the request has been denied. Connections may be denied on the basis of available free capacity or alternatively on the basis of prioritization. CAC policies are outside the scope of standardization. GMPLS achieves authentication (and other security related features) using the broad range of security mechanisms available in the GMPLS protocols themselves and/or using IPSEC. E. Mannie et. al. Internet-Draft December 2001 47 draft-ietf-ccamp-gmpls-architecture-00.txt June 2001 A.9 OTN Link Management [G.lm] No ITU-T contribution available yet. The Link Management Protocol (LMP) of GMPLS is a collection of procedures between adjacent nodes that provide local services such as control channel management, link connectivity verification, link property correlation, and fault management. E. Mannie et. al. Internet-Draft December 2001 48