Network Working Group D. Papadimitriou Document: draft-poj-optical-multicast-00.txt Dirk Ooms Category: Internet Draft Jim Jones Expires: August 2001 Alcatel Eric Mannie Ebone (GTS) February 2001 Optical Multicast û A Framework draft-poj-optical-multicast-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." 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. 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]. Abstract This contribution defines the optical multicast concepts and the related applications in optical networks. The objective is to extend the multicast concept for transparent and all-optical networks and subsequently the definition of the signalling protocol extensions for optical multicast-capable networks. 1. Introduction As proposed in the contribution OIF2001.067 [1] and already presented during the last IETF meeting in San Diego [2], we develop Internet Draft û Expires August 2001 1 draft-poj-optical-multicast-00.txt February 2001 in the current contribution the basic concepts and future developments needed in the design of optical multicast-capable networks. The concept of multicast has been widely discussed for packetû oriented networks. This proposal extends the multicast concept to optical networks, which provide enhanced performance for, multicast as well as broadcast packet-based applications. The architecture of optical networks needs to balance potentially conflicting design and performance criteria, including: - Minimizing the number of hops traversed - Minimizing some combination of the number of transceivers, amplifiers and optical splitters - Minimize blocking probability - Maximizing the virtual connectivity between nodes of interest - Maintaining a reasonable optical power budget - Solving the routing and wavelength assignment problem This contribution reviews the relationships between these tradeoffs. The optical splitter is a key component to realize multicast in optical networks. The concept of optical multicast is now becoming possible since 1:2 splitters and recently 1:4 splitters are available. The distinction between a optical splitter and an optical tap is related to the output signal ratio: with a splitter the output signal power is equally distributed in contrast with a tap the output signal power ratio is not equally distributed. Optical multicast refers to point-to-multipoint connections in the optical domain also referred to as light-tree. 2. Rationale for Optical Multicast The applications that can utilize the optical multicast concept are numerous and cover a wide range of current ôclientö needs. These applications cover Optical Storage Area Networks (O-SAN), Optical Broadband (video, HDTV, etc.) applications, etc. Optical multicast offers advantages in the following critical aspects of optical networks: - Efficient optical (1+1) optical protection - Improved performance (no store and forward) compared to packet- oriented multicast technology - Reduction of the total number of transceivers in the optical network. - Overall network throughput improvement by reducing the number of wavelengths used per fiber link (i.e. minimizing the overall bandwidth usage per fiber link) However, the major drawback to overcome in optical multicast-capable networks is to compensate the power penalty introduced during the optical signal splitting. Internet Draft û Expires August 2001 2 draft-poj-optical-multicast-00.txt February 2001 Moreover, the multicast problem in communication networks, described by the Steiner Tree Problem applied to communication networks is NP- Complete [6]. The Steiner Tree Problem is defined as follows. Given a Graph G(V,E) where V is a Vertex and E an Edge; a cost function applied to each of the edge of the graph G; and a set of node N included within the graph G; find a sub-tree T = (V[T], E[T]) spanning N and such that its cost C (defined as the sum of individual edge cost C(E)) is minimized. For more detailed explanations concerning this problem and related computational aspects, we refer to [14]. Since the Steiner Tree problem is NP-Complete, some heuristics are needed to perform multicast in an efficient way. Consequently, there a method to optimize the topology of an optical network exists in theory. However, in practice it is not possible to analytically solve this optimization and a heuristic approach is required. For instance, in packet-based multicast networks, shortest-path trees are computed in order to implement a fully distributed on-line computation of the ômulticast-treesö. 3. Lightpath and Light-tree Concepts 3.1 Lightpath A lightpath is defined is defined in the context of wavelength (or optical channel) routing through a wavelength router which also referred to as a Photonic Cross-Connect (PXC) within an all-optical network or an Optical Cross-Connect within a transparent optical network. A unicast connection (i.e. a point-to-point connection) in a transparent (all-) optical network is carried on a lightpath defined as a transparent (all-optical) channel used to transport packets or circuits transparently within the optical network. With point-to-point optical channel networks, the number of transmitters (TX) needed within the transparent (all-) optical network equals the number of receivers (RX). Under the wavelength continuity constraint (i.e. in the absence of wavelength converters) within transparent optical networks, the routing and wavelength assignment (RWA) is the most challenging problem. Selecting the best combination of route and wavelength for each unicast connection such that the number of lightpaths established is maximized and such that two lightpaths sharing a common fiber link do not use the same wavelength. However, the routing and wavelength assignment problem for unicast connections in optical networks has been demonstrated in [4] to be NP-Complete. 3.2 Light-tree The concept of a light-tree has been introduced in [3] and explicitly refers to point-to-multipoint non-looping optical channels established in optical networks. A light-tree is formally defined as a directed Steiner tree [7] that is rooted at the source Internet Draft û Expires August 2001 3 draft-poj-optical-multicast-00.txt February 2001 node and spans all the destinations (each of the nodes providing optical multicast function require optical power splitters). A light-tree enables an upstream node to have more than one logical downstream neighbor. Consequently, the use of optical point-to- multipoint in transparent optical networks reduces theoretically the number of transmitters compared to the number of receivers. So, one of the objective of optical multicast is to minimize the total number of transceivers used within the transparent optical network. However, in all-optical multicast-capable networks, and per light- tree, the number of transmitters equal 1 and the number of receivers equal N. So that the optimization of the total number of transceivers used applies only to transparent optical networks. For the purpose of this memo, we propose to extend the definition proposed in [3], by allowing light-tree to also cover shortest-path trees. For instance, a Steiner tree could represent the light-tree concept here below: 5 1 F --------------------- G ---------- | | | |1 |1 | 5 | 1 5 | 1 | A ------- B --------- C --------- D --------- E | | | | |1 |5 |1 | | 5 | 1 | 1 | H --------- I --------- J ---------- The node A is the root of the following light-tree with equal cost nodes, where each of the link cost is indicated, so the resulting light-tree has a minimized cost set of paths starting at node A reaching each of the leaf (or destination) nodes included in the topology. In this example, node D ôexecutesö a form of ôdrop-and- continueö function since it terminates one of the output of the split signal and continues the other output of the split signal toward Node E. F G | | | | | | A ------- B -------- C D -------- E | | | | | | | | | H I----------J Internet Draft û Expires August 2001 4 draft-poj-optical-multicast-00.txt February 2001 From A to B: Cost = 5 From A to C: Cost = 6 From A to D: Cost = 13 From A to E: Cost = 14 Etc. If we consider only a subset of destination nodes, for instance D, G and J then we obtain the following light-tree (which does not correspond to the shortest-path tree): F G | |1 5 1 5 | A ------- B --------- C --------- D E | |1 | H I J From A to D: Cost = 11 From A to G: Cost = 12 From A to J: Cost = 12 Steiner Tree Cost C(E) = 13 If we had to compute the shortest-path tree for the same group of destination nodes we would obtain the following tree: 5 F --------------------- G | |1 5 | 1 5 A ------- B --------- C --------- D E | |1 | J From A to D: Cost = 11 From A to G: Cost = 11 From A to J: Cost = 12 Note that the node and link cost minimization is only one of the possible constraint applicable to an optical multicast-capable Internet Draft û Expires August 2001 5 draft-poj-optical-multicast-00.txt February 2001 network. If the jitter accumulation has to be minimized, then a shortest-path tree computation can be used for that purpose. Consequently, the ôlogical connectivityö of the optical network is increased with respect to the number of wavelengths used within the optical domain when using point-to-multipoint optical channels (or light-trees) which enable communication between a source (root) and a set of destination nodes. This in turn increases the overall network throughput. 4. Virtual Topologies A virtual topology is defined on top of a given physical topology (as described in [5]) which by definition is a fixed topology. Compared to the packet-oriented sessions established on top of this virtual topology, the virtual topology changes are less frequent. Moreover, as proposed in [15], a methodology has been described to obtain new constraint based virtual topology by simultaneously minimizing the changes required to obtain new virtual topology from the current virtual topology. However, the proposed technique is up to now beyond the scope of this document. When considering the following example, the virtual topology can be defined as the set of point-to-multipoint connections (S, D) where S is the source node (here Node A and Node K). Node A is multicasting on wavelength L1 and Node K is multicasting on wavelength L2. In this example, the sets of destinations nodes D are Nodes C, F, H, J and Nodes B, D, E, G, I respectively since wavelength L1 reaches Nodes C, F, H, J and wavelength L2 reaches Nodes B, D, E, G, I. xF -------------------+G ---------- x| +| | x| +| | xxxxxxxxxx|xxxxxxxxxx +| | A -------xB+--------xC --------+D -------- E+ ------- K x|+++++++++x|+ +|+++++++++++|+++++++++++ x| x|+ +| | x| x|++++++++++| | xH --------xI+--------xJ ---------- xxxxxxxxxxxx Since a light-tree is trivial generalization of lightpath, the set of light-tree based virtual topologies is a superset of the set of lightpath based virtual topologies. Therefore, an ôoptimumö light- tree based virtual topology is guaranteed to have better performance than an ôoptimumö lightpath based virtual topology. Consequently, the optimization problem in optical multicast-capable networks can be either the minimization of the number of links (distance) on top of the physical network topology or the Internet Draft û Expires August 2001 6 draft-poj-optical-multicast-00.txt February 2001 minimization of the total number of transceivers in the network (as described in section 4). However, the routing problem in optical multicast-capable networks referred to as multicast-routing and wavelength assignment (MCRWA) problem is NP-Complete since it includes the RWA problem which is NP-Complete as demonstrated in [4]. 5. Optical Splitters and Optical Network Topology In an optical multicast network, the splitter is the key hardware component. The optical splitter is a passive optical device, which enables the splitting of the input signal. A n-way splitter is defined as an optical device which equally splits the input signal among n outputs, thus reducing the power of each output to (1/n) times the original signal power (n value is called the splitting ratio). A large number of splitters require a large number of optical amplifiers to balance the optical power loss. A special case of a light splitter is a tap. A tap does not split equally the power of the input signal over the outgoing ports, it only splits of a low-power signal. Consequently, an optical multicast-capable network will require a more detailed power budget computation since any optical power splitter introduces optical power loss. So, one of the major constraints when designing an optical multicast network is to define a design that reduces the number of splitters with minimal effects on the network blocking performance. Nevertheless, the optical splitters give the capability to split the optical signal without any knowledge about the optical characteristics of that signal (BER, Q-Factor, etc.). When compared to packet-oriented multicast systems such as classical routers, the use of optical splitters allows optical networks to support multicasting without store-and-forward. As proposed in [8], a power-efficient design methodology is based on a two-dimensional design space: - The splitter-sharing dimension focused on minimizing the number of splitters inside the PXC itself. - The splitter-tap dimension focused on minimizing the number of multicastûcapable PXCÆs in the overall optical network taking into account the blocking probability. The splitter-tap problem has been extended to the coarse-grain splitter placement optimization problem [9] in optical networks so that blocking probability is minimized. The splitter placement problem is also NP-complete (since it includes the RWA problem which is NP-complete). Note that the most important result obtained in [9] is that for a wide variety of optical network topologies and different traffic patterns, no more than 50% of the PXCÆs need to include optical power splitters. Having more than 50% of PXCÆs with multicast-capable hardware only slightly enhances the blocking performance of the optical network. Internet Draft û Expires August 2001 7 draft-poj-optical-multicast-00.txt February 2001 6. Optical Multicast-capable Networks Applications of optical multicast are straightforward: it will provide efficient dual-homing protection at the O-UNI. The application of the optical multicast concept will also facilitate the implementation of the Drop-and-Continue functionality between optical rings [10]. Other applications of optical multicast at O-UNI [IPO-OUNI] as well as the O-NNI [IPO-ONNI] will be detailed in next releases of this document. They will be focused on æclassicalÆ multicast applications such as HDTV, Video, etc. However, as described in [11], the scheduling of multicast traffic in an optical multicast-capable network needs to take into account two conflicting objectives: low bandwidth utilization at the packet- layer and high optical channel capacity utilization. Moreover, as stated in [12] more practical traffic patterns and real network scenarios must be considered, since in optical network topologies both unicast and multicast traffic will be simultaneously present within the same optical network. Taking into account these considerations is key to a successful deployment of optical multicast-capable networks. 7. Signalling in Optical Multicast-capable Networks It is widely accepted that point-to-multipoint applications such as HDTV and Video Streams will comprise a large portion of the multicast application space. The proposed signalling model is designed to efficiently handle such cases where sources are well known. This is specifically the case with optical multicast were the sources S are in most cases well defined (location, address, etc.) Signalling in optical multicast-capable networks is realized through GMPLS signalling as described in [GMPLS-SIG]. Since an optical multicast tree is unidirectional, the suggested label mechanism defined for bi-directional LSP setup is not applicable here. In this section, a node is independently referred (at the signalling plane level) to as a PXC or an OXC or using the GMPLS terminology [18] as an LSR. A lightpath is independently referred to as an LSP. 7.1 Optical Network Architecture The Optical Cross-Connect (OXC) system architecture for lambda switching has been introduced in the [16] and [17]. The OXC interfaces considered includes, as described in [18], Lambda Switch Capable (LSC) interfaces that switches the lightpath segment based on the incoming wavelength and Fiber-Switch Capable (FSC) interfaces that switches the lightpath based on the spatial position of the incoming data stream in the physical space. An OXC has several incoming and outgoing LSC interfaces or ports, connected to adjacent OXCÆs, and several incoming and outgoing LSC interfaces or ports attached to an edge device that can be a router Internet Draft û Expires August 2001 8 draft-poj-optical-multicast-00.txt February 2001 (or any other kind of device supporting termination capable interfaces). An OXC includes mainly two functional parts: an OXC Switch Controller (OSCtrl) and OXC optical matrix. The OSCtrl communicates through Optical Supervisory Channels (OSC) i.e. out-of-band signalling transport mechanism or through dedicated and physically diverse control network i.e. out-of-network signalling transport mechanism. OSCtrlÆs and OSCÆs define the signalling plane of the optical network. --- OSC --- OSC +++++| S |++++++++++++++++| S |+++++++++++++ + --- --- + + | | | | + OSC+ | F |----------------| G |---- +OSC + --- --- | + + | | | + + | | | + --- OSC --- | --- OSC --- | --- +++| S |+++++++| S |+++++++++| S |+++++++++| S |++++++++++| S |+++ + --- --- | --- --- | --- + + | | | |---- | | | | -----| | + + | A |-------| B |---------| C |---------| D |----------| E | + + --- --- --- --- --- + + | | | | + + | | | | + + | | | | + + --- --- --- | + + | H |---------| I |---------| J |------------ + + | | | | | | + + OSC --- OSC --- OSC --- OSC + +++++++++++++++| S |+++++++++| S |+++++++++| S |++++++++++++++++++ --- --- --- When receiving a signalling message, the OSCtrl translate to an internal control command, and sends this command to the OXC optical matrix. The commands to control the OXC optical matrix are as follows: connect (and disconnect) between an incoming LSC interface and an outgoing LSC interface. The OSCtrl is also capable to process status requests, lightpath modification requests as well as notification messages. The same commands apply when the OXC is connected to an LSC capable edge device. Based on these commands, a chain of connections through OXCs can form a point-to-point optical channel i.e. a lightpath (as described in section 3.1). The ingress OXC is the node where the multicast tree starts (sender), the egress OXC(s) are the destination nodes (receivers) and the OXCs in the middle of the tree are referred to as intermediate OXCs. Internet Draft û Expires August 2001 9 draft-poj-optical-multicast-00.txt February 2001 An OXC optical matrix receives commands from the OSCtrl, and replies whether the command was successful or not. The OSCtrl then converts the result into a message that it sends via the OSC channel throughout the signalling plane of the optical network. To cover any kind of optical network, we consider as specified in [16] the following distinction between Optical Cross-Connect (OXC) in transparent optical networks and Photonic Cross-Connect (PXC) in Optical networks. Basically, OXC devices included within Transparent optical networks performs O/E/O conversion at each of their interfaces while PXC devices included within optical networks do not perform O/E/O conversion at all so they are defined as pure O-O devices (including tunable lasers). We consider here that all the interfaces of an OXC as well as all the interfaces of a PXC are LSC interfaces. Moreover, in order to enable optical multicast functionality, OXCs and PXCs must include optical splitters included in splitter banks. In the remaining parts of this document, nodes are considered as optical PXC (so these considerations can also be applied to OXC). 7.2 Shortest-Path Trees Typically in packet-networks, multicast routing protocols create shortest-path trees. These trees are non-optimal (as described in section 5), but the algorithm is distributed and allows the dynamic adding and removal of the multicast tree branches. The mapping of these trees onto LSPs is discussed for Protocol Independent Multicast (PIM) Sparse Mode (PIM-SM) in [19] and more specifically in [20]. PIM Source Specific Multicast (PIM-SSM) extension is an extension of PIM-SM. We describe in the two sub-sequent sections PIM Sparse Mode (PIM-SM) and PIM Source Specific Multicast (PIM-SSM) defined as receiver initiated approaches. Nevertheless, one of the key issues with this approach is the merging of user signalling-plane with the optical signalling-plane when considering a unified service model between the edge router and the optical domain. 7.2.1 Source/Share Multicast Trees In classical packet multicast [19], IP multicast routing protocols create either source trees (S, G), i.e. a tree per source (S) and per multicast group (G), or shared trees (*, G), i.e. one tree per multicast group (Figure 1). ---- ---- ---- ---- | S1 |----- -----| R1 | -----| R1 | -----| R1 | ---- | / ---- / ---- / ---- --- ---- ---- ---- ---- ---- | C |------| R2 | | S1 |------| R2 | | S2 |------| R2 | --- ---- ---- ---- ---- ---- Internet Draft û Expires August 2001 10 draft-poj-optical-multicast-00.txt February 2001 ---- | \ ---- \ ---- \ ---- | S2 |----- -----| R3 | -----| R3 | -----| R3 | ---- ---- ---- ---- Shared tree Source trees In packet-based multicast-capable networks, the advantage of using shared trees, when label switching is applied, is that shared trees consume less labels than source trees (1 label per group versus 1 label per source and per group). 7.2.2 Receiver Initiated Approach - PIM-SM PIM Sparse Mode (PIM-SM) constructs a single spanning multicast tree rooted at a core rendezvous point (RP) for all group members within a given domain. PIM-SM enables to construct unidirectional shared trees to forward data from senders to receivers of a multicast group. PIM-SM also allows the construction of source specific trees. Moreover in [22], PIM-SM (PIMv1 and PIMv2) has been extended to combine MPLS label distribution with the distribution of (*,G) join state, (S,G) join state, or (S,G) RPT-bit prune state. Note that (*,G) join state implications need to be evaluated in optical multicast because the elimination of the shared tree concept is the key to implementing SSM. This because PIM-SSM eliminates the need for starting with a shared tree and then switching to a source- specific tree (see section 7.2.3). In PIM-SM MPLS extension, labels and multicast routes are sent together in one message. We propose here to extend this method for optical multicast-capable networks. We will refer to this method as Optical PIM-SM. The design described in [22], specifies that Multicast label distribution procedures should not depend on the media type. Note also that when a multicast routing table change requires a label distribution change, the latency between the two should be minimized, both to improve performance and to minimize the possibility of race conditions. On receiving PIM Join/Prune messages from an edge router, a PXC that supports optical multicast (i.e. that includes optical splitters) sends PIM Join/Prune messages on behalf of hosts that join groups. It sends Join/Prune messages to upstream neighboring PXCs toward the Rendezvous Point (RP) for the shared-tree (*,G) or toward a source for a source-tree (S,G). Wavelength Labels, described in [18], are distributed by being associated with IPv4 multicast addresses (address issue is considered in section 7.2.3) in the join list or the prune list. As described in [23], the label distribution mode is thus a downstream-on-demand distribution and the LSP control is independent. --- --- Leaf Internet Draft û Expires August 2001 11 draft-poj-optical-multicast-00.txt February 2001 | F |-----------------------| G |---------- --- --- | | | | | | | Root | | | --- --- --- --- --- | A |--------| B |---------| C |---------| D |--------| E | --- <+++++++ --- <++++++++ --- <++++++++ --- --- |+ (4) | (3) | (2) |^ | |+ | | |+ (1) | |+ | | |+ | |+ --- --- --- Leaf | |+ | H |---------| I |---------| J |---------- |+ --- --- --- |+ |^ |+ PIM/Join |+ PIM/Join |+ |+ ————————————————————————————————————————————————————————————— |+ |+ |v |+ --- --- | R | | R | --- Packet-based Multicast --- ————————————————————————————————————————————————————————————— Router R and PXCs are included in the same signalling plane i.e. the mechanism described here applies to a unified service model [18]. So that the generalization of the mechanism defined in packet multicast-capable networks to the optical multicast-capable networks need to be considered as described in [22]. 7.2.3 Receiver Initiated Approach - PIM-SSM Protocol Independent Multicast - Source Specific Multicast (PIM-SSM) defines a method of multicast forwarding restricted to shortest path trees to specific sources. This method refers to Source-Specific Multicast (SSM) service model that supports source-based multicast trees. We will refer to this model as PIM-SSM. The key difference between PIM-SM and PIM-SSM is that eliminates the need for starting with a (*,G) shared tree and then switching to a source-specific tree. More precisely, when a DR (for instance, a boundary PXC) identifies request to join a specific source in a group with a SSM group address (232/8), it always initiates a (S,G) join and never a (*,G) join. Moreover, unlike PIM-SM, it need not send a (S,G) prune towards the RP. PIM-SSM enables that a single source S can transmit to a channel (S,G) where G is an PIM-SSM address. Each receiver is capable of specifying the specific sources from which it would like to receive content. This would in turn enable a direct mapping of PIM-SSM to optical multicast. Internet Draft û Expires August 2001 12 draft-poj-optical-multicast-00.txt February 2001 7.2.4 PIM-SM versus PIM-SSM As discussed in the previous sections, shared trees (*,G) join state are only used to discover new sources of the group and after a switchover to a source tree is performed. However, the end-to-end mapping of a (*,G) shared tree implies the setup of multipoint-to-multipoint trees (i.e. light-trees). The problem is that in the optical domain, labels represent wavelengths which are by definition non-mergeable. Consequently, optical multipoint-to-multipoint light-trees are not applicable in optical multicast since label merging is not feasible. Since the difference between PIM-SM and PIM-SSM is that the latter eliminates the need for starting with a (*,G) shared tree and then switching to a source-specific tree, this restricts the choice to PIM-SSM for shortest-path tree receiver initiated approach. 7.3 Non-Shortest-Path Trees The shortest-path tree approach could be taken for optical multicast but there are several reasons to consider another means: @ The diversity of the nodes in optical networks: PXCs without and with support for multicast, the latter can be Splitter and Delivery (SaDs) or Multicast optical SaDs (MoSads) [8] @ The multicast light-trees tend to be more stable (branches added and removed sporadically) @ Shortest-path trees are not optimal (as described previously) @ Internal PXCs might not be aware of global routing information (when using an overlay signalling plane), so a PXC wonÆt be able to determine where to send a PIM Join if the source S is outside of the optical domain @ MCRWA constraints (see section 4) Because of the above reasons, it might be useful to consider a non- shortest-path tree approach combined with an offline traffic- engineering tool. This offline tool performs the computation by taking into account the variety of constraints set by optical networks and that calculates a more optimal tree than the shortest- path tree one. Many heuristics exist to approximate e.g. the optimal Steiner Tree [18]. To establish the calculated tree in the network one can use a management interface (e.g. SNMP) to every on-tree PXC or one can introduce the use of GMPLS signalling protocol [GMPLS-SIG]. The latter can be downstream or upstream signalling. So that the non- Shortest-Path trees could be either root or receiver initiated. 7.3.1 Root Initiated Internet Draft û Expires August 2001 13 draft-poj-optical-multicast-00.txt February 2001 The explicit routing signalling is based on the computation of the explicit multicast route from the root to each of the (intermediate) destination nodes. In the root-initiated case, the signalling flows from root to destinations. This approach requires that a multicast tree route object [19] is signaled. For instance, if we refer to the previous example: F G | |1 5 1 5 | A ------- B --------- C --------- D E | |1 | H I J The explicit multicast tree route that the node A has computed can be represented as: A [B [C [D [(G, J)]]]] More precisely, as defined in [20], each of the link bundles of a PXC can be numbered (by an IPv4 address) or unnumbered (by a Node ID and Link bundle index). So that the identification of the nodes can be expressed by using the bundle address included within the multicast tree. The multicast explicit route could be included within the [21] Explicit Route TLV (ER-TLV). The content of an ER-TLV is defined as a series of variable length ER-Hop TLVs. We consider here ER-Hop Type being IPv4 prefix. The IPv4 prefix represents the IP address of the link bundle of each node through which the multicast tree need to be established. The L bit defines whether the value of the attribute is loose. In this case, the value of the attribute is strict so that the L bit is not set. For an edge router to become a member of a particular optical multicast group, the router has to register multicast group membership with a specific query to the PXC that handles the multicast group membership. Protocol like IGMP could be used for that purpose. Multicast-capable PXCs then exchange messages with each other through IGP multicast-capable routing protocol to construct a distribution tree connecting all the edge routers. 7.3.2 Receiver Initiated Alternatively the signalling can start at the receiver side [20]. The signalling starting at a receiver is sent in the direction of the root along an explicit path. In this case, the (wavelength) label distribution mode is a downstream-on-demand distribution and the LSP control is ordered. However, the signalling goes in the Internet Draft û Expires August 2001 14 draft-poj-optical-multicast-00.txt February 2001 upstream direction from the destination node (receiver) to the source node (sender). The Downstream on Demand procedures applies to multicast distribution trees. Independent LSP control is needed so that different downstream branches of a multicast distribution tree can join the tree independently. 7.3.4 Additional Considerations After calculating the multicast tree, the offline tool can decide to already assign the wavelength for every link on every branch. Alternatively, it can leave it up to the individual PXCs and send the explicit multicast route to the source node and setup the corresponding light-tree through GMPLS signalling. In packet networks unicast and multicast have their own separate label spaces, this is no longer true for optical networks since wavelengths are physical, non-shareable and non-mergeable entities. If the PXCs perform the label allocation it would be advisable to define an allocation mechanism (downstream, downstream-on-demand, etc.) that is similar to the one used for unicast traffic. This in order to avoid simultaneous allocation of the same wavelength by the upstream and the downstream PXC. 7.4 User-plane Signalling Up to now, we donÆt address one of the key issues with optical multicast: the merging of user signalling-plane with the optical signalling-plane when considering a unified service model between the edge router and the optical domain. By applying one of the approaches defined in the previous, we obtain a transport-plane optical light-tree (which is by definition unidirectional) from the source S to the destination. So that a single source router can be reach simultaneously several destination belonging to the same multicast group. However, this document does not describe a mechanism in order to enable the destination to reach the source at the packet LSP level (i.e. at the user-plane level) since these considerations are out of the scope of this document. If the same administrative authority manages both the edge routers and the optical network, then a peer relationship between the PIM instance of the optical network and the client network can be defined. PIM Client <---------------------------------------------------------> --- --- --- --- | S |------| R | | R |------| D | --- --- --- --- <========= | |<========== PIM/Join | | PIM/Join Internet Draft û Expires August 2001 15 draft-poj-optical-multicast-00.txt February 2001 —| |— ++++++++++++—+++++++++++++++++++++++++++++++++++++—+++++++++++++ —| |— —| PIM Optical |— —| <-------------------> |— Trigger —| --- --- --- |— — -----| S |-----| I |-----| D |----- — ————————--- --- ---———————— <======== x <======== PIM/Join PIM/Join ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Otherwise, if the edge routers and the optical network belong to distinct administrative authorities, then a mapping between PIM instances need to be defined (see Figure). 8. Security Considerations Security-related considerations are left for further considerations 9. References [1] A. Saleh et al, æProposal to form a Project on Architectures and Signaling for Configurable All-Optical NetworksÆ, OIF Contribution 67, January 2001. [2] D. Papadimitriou et al., æEnhanced LSP ServicesÆ, Internet Draft, draft-papadimitriou-enhanced-lsps-02.txt, February 2001. [3] B. Mukherjee et al, æLight-Trees: Optical Multicasting for Improved Performance in Wavelength-Router NetworksÆ, IEEE Communication Magazine, February 1999. [4] A. Ganz et al, æLightpath Communications: An approach to high- bandwidth optical WANÆsÆ, IEEE Transactions on Communications, Volume 40, July 1992. [5] D. Papadimitriou et al, æInference of Shared Risk Link GroupÆ, Internet Draft, draft-many-inference-srlg-00.txt, February 2001. [6] R.M. Karp, ÆReducibility among combinatory problemsÆ, in Complexity of Computer Communications Magazine, Miller and Thatcher Editions, New-York: Plenum, 1972. [7] A. Gibbons, æAlgorithmic Graph TheoryÆ, New-York, Cambridge University Press, 1985. [8] A. Maher et al, æPower-Efficient Design of Multicast Wavelength- Routed NetworksÆ, IEEE Journal on Selected Areas in Communications, Volume 18, Number 10, October 2000 Internet Draft û Expires August 2001 16 draft-poj-optical-multicast-00.txt February 2001 [9] A. Maher et al, æAllocation of Splitting Nodes in All-Optical Wavelength-Routed NetworksÆ, Photonic Network Communications, Volume 2, Number 3, August 2000 [10] D. Papadimitriou et al, æOptical Rings and Optical Hybrid Meshû Rings TopologiesÆ, Internet Draft, draft-papadimitriou-optical- rings-00.txt, February 2001. [11] Z. Ortiz et al, æScheduling of multicast traffic in tunable- receiver WDM networks with non-negligible tuning latenciesÆ, Proceedings of SIGCOMMÆ97, Cannes û France, September 1997 [12] H. Perros et al, æScheduled Combined Unicast and Multicast Traffic in Broadcast WDM NetworksÆ, Photonic Network Communications, Volume 2, Number 2, May 2000 [14] F.K Hwang et al, æThe Steiner Tree ProblemÆ, Annals of Discrete Mathematics, Volume 53, Amsterdam, North-Holland Editions, 1992. [15] D. Banerjee et al, æWavelength-Routed Optical Networks: Linear Formulation, Resource Budgeting Tradeoffs, and a Reconfiguration StudyÆ, IEEE/ACM Transactions on Networking, Volume 8, Number 5, October 2000. [16] B. Rajagopalan et al., æIP over Optical Networks: A Framework,Æ Internet Draft, draft-many-ip-optical-framework-02.txt, November 2000. [17] D. Awduche et al., æMulti-Protocol Lambda Switching: Combining MPLS Traffic Engineering Control With Optical Crossconnects,Æ Internet Draft, draft-awduche-mpls-te-optical- 02.txt, July 2000. [18] P. Ashwood-Smith et al., æGeneralized MPLS Signaling û Signaling Functional Requirements,Æ Internet Draft, draft-ietf-mpls- generalized-signalling-01.txt, November 2000. [19] D. Ooms et al., æFramework for IP Multicast in MPLS,Æ Internet Draft, draft-ietf-mpls-multicast-05.txt, November 2000. [20] D. Farinacci et al., æUsing PIM to Distribute MPLS Labels for Multicast Routes,Æ Internet Draft, draft-farinacci-mpls-multicast- 03.txt, November 2000. [21] D. Ooms et al., æMPLS Multicast Traffic EngineeringÆ, Internet Draft, draft-ooms-mpls-multicast-te-00.txt, February 2001. [22] B. Rajagopalan et al., æLink Bundling in Optical Networks,Æ Internet Draft, draft-rs-optical-bundling-01.txt, November 2000. [23] K. Kompella et al., æLink Bundling in MPLS Traffic Engineering,Æ Internet Draft, draft-kompella-mpls-bundle-04.txt, November 2000. Internet Draft û Expires August 2001 17 draft-poj-optical-multicast-00.txt February 2001 [24] B. Jamoussi et al., æConstraint-Based LSP Setup using LDP,Æ Internet Draft, draft-ietf-mpls-cr-ldp-04.txt, July 2000. [25] E. Rosen et al., æMultiprotocol Label Switching Architecture,Æ Internet Draft, draft-ietf-mpls-arch-07.txt, July 10. Acknowledgments The authors would like to thank Bernard Sales, Emmanuel Desmet, Hans De Neve, Fabrice Poppe and Gert Grammel for their constructive comments. 11. Author's Addresses Papadimitriou Dimitri Alcatel û IPO NSG Francis Wellesplein 1, B-2018 Antwerpen, Belgium Phone: +32 3 240-8491 Email: dimitri.papadimitriou@alcatel.be Ooms Dirk Alcatel û MCT NSG Francis Wellesplein 1, B-2018 Antwerpen, Belgium Phone: +32 3 240-7893 Email: dirk.ooms@alcatel.be Jim Jones Alcatel TND-USA 3400 W. Plano Parkway, Plano, TX 75075, USA Phone: +1 972 519-2744 Email: jim.d.jones1@usa.alcatel.com Eric Mannie Ebone/GTS Terhulpsesteenweg 6A 1560 Hoeilaart, Belgium Phone: +32 2 658-5652 Email: eric.mannie@gts.com Internet Draft û Expires August 2001 18 draft-poj-optical-multicast-00.txt February 2001 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 Internet Draft û Expires August 2001 19 draft-poj-optical-multicast-00.txt February 2001 Internet Draft û Expires August 2001 20