Network Working Group J. Macker, editor Internet-Draft NRL Expires: September 6, 2006 SMF Design Team IETF MANET WG March 5, 2006 Simplified Multicast Forwarding for MANET draft-ietf-manet-smf-02 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 6, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document describes the Simplified Multicast Forwarding (SMF) protocol that provides a basic IP multicast forwarding capability within mobile ad-hoc networks (MANET). SMF is designed to have limited applicability as a forwarding mechanism for multicast packets within MANET routing areas. In addition, it provides mechanisms to support interoperability with a connected wired infrastructure. SMF uses a simplified forwarding mechanism that delivers multicast Macker, editor & SMF Design Team Expires September 6, 2006 [Page 1] Internet-Draft SMF for MANET March 2006 packets to all MANET multicast receivers within a MANET routing area. The core design does not use receiver specific group information in favor of reduced complexity and state maintenance within the mobile topology. Such extensions may follow in later specifications. The design accounts for the unique nature and behavior of MANET interfaces and takes advantage of efficient relay set algorithms previously designed and applied in the MANET routing control plane. This document describes the SMF forwarding mechanisms in detail, specifies an optional SMF neighborhood discovery protocol, and describes several efficient relay set algorithms that have been implemented in conjunction with SMF. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 2] Internet-Draft SMF for MANET March 2006 Table of Contents 1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7 2.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 7 3. SMF Design Considerations . . . . . . . . . . . . . . . . . . 8 3.1. Previous Related Work . . . . . . . . . . . . . . . . . . 9 4. SMF Packet Processing and Forwarding . . . . . . . . . . . . . 10 5. SMF Duplicate Packet Detection . . . . . . . . . . . . . . . . 13 5.1. SMF IPv4 Duplicate Packet Detection . . . . . . . . . . . 14 5.2. SMF IPv6 Duplicate Packet Detection . . . . . . . . . . . 15 5.2.1. IPv6 SMF-DPD Header Option Format . . . . . . . . . . 16 6. Relay Set Selection . . . . . . . . . . . . . . . . . . . . . 17 7. Baseline SMF Neighborhood Discovery Protocol (NDP) . . . . . 18 7.1. SMF NDP Description . . . . . . . . . . . . . . . . . . . 18 7.2. SMF NDP Messaging . . . . . . . . . . . . . . . . . . . . 19 7.2.1. SMF_HELLO Message Header . . . . . . . . . . . . . . . 20 7.2.2. SMF_HELLO Message TLVs . . . . . . . . . . . . . . . . 20 7.2.3. SMF_HELLO Address Block TLVs . . . . . . . . . . . . . 20 8. SMF Multicast Border Gateway Considerations . . . . . . . . . 23 8.1. Forwarded Multicast Groups . . . . . . . . . . . . . . . . 23 8.2. Multicast Group Scoping . . . . . . . . . . . . . . . . . 23 8.3. Duplicate Packet Detection Marking . . . . . . . . . . . . 23 8.4. Interface with Exterior Multicast Routing Protocols . . . 24 8.5. Multiple Gateways . . . . . . . . . . . . . . . . . . . . 24 9. Security Considerations . . . . . . . . . . . . . . . . . . . 25 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 12.1. Normative References . . . . . . . . . . . . . . . . . . . 28 12.2. Informative References . . . . . . . . . . . . . . . . . . 28 Appendix A. Source-based Multipoint Relay (S-MPR) . . . . . . . . 30 A.1. S-MPR Relay Set Selection . . . . . . . . . . . . . . . . 30 A.2. Neighborhood Discovery Requirements . . . . . . . . . . . 31 Appendix B. Essential Connecting Dominating Set (E-CDS) Algorithm . . . . . . . . . . . . . . . . . . . . . . 32 B.1. E-CDS Relay Set Selection . . . . . . . . . . . . . . . . 32 B.2. E-CDS Forwarding Rules . . . . . . . . . . . . . . . . . . 32 B.3. Neighborhood Discovery Requirements . . . . . . . . . . . 33 Appendix C. Multipoint Relay Connected Dominating Set (MPR-CDS) Algorithm . . . . . . . . . . . . . . . . . 34 C.1. MPR-CDS Relay Set Selection . . . . . . . . . . . . . . . 34 C.2. MPR-CDS Forwarding Rules . . . . . . . . . . . . . . . . . 34 C.3. Neighborhood Discovery Requirements . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 Intellectual Property and Copyright Statements . . . . . . . . . . 36 Macker, editor & SMF Design Team Expires September 6, 2006 [Page 3] Internet-Draft SMF for MANET March 2006 1. Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 4] Internet-Draft SMF for MANET March 2006 2. Introduction Design and implementation progress has been made in developing and implementing more efficient ways to flood control packets within MANET wireless routing protocol designs. For example, algorithms within MANET RFC 3626 [RFC3626]and RFC 3684 [RFC3684] specify distributed methods of dynamically electing reduced relay sets for the purposes of optimizing the flooding routing control packets to all MANET nodes. In this document, we specify the Simplified Multicast Forwarding (SMF) framework. The main purpose of SMF is to adapt efficient flooding designs in MANET environments and apply these mechanisms to IP multicast packet forwarding. When efficient flooding is a sufficient technique, SMF can make multicast forwarding available to data flows within a MANET routing area. The SMF baseline design limits the scope to basic, best effort multicast forwarding and its applicability is intended to be constrained within a MANET routing area. Figure 1 provides an overview of the logical SMF node architecture, consisting of "Neighborhood Discovery", "Relay Set Selection" and "Forwarding Process" components. Typically, relay set selection (or even self-election) will occur based on input from a neighborhood discovery process, and the forwarding process will be controlled by status based upon relay set selection. In some cases, the forwarding decision for a packet may also depend on previous hop or incoming interface information. The asterisks (*) in Figure 1 mark the primitives and relationships needed by relay set algorithms requiring previous-hop packet forwarding knowledge. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 5] Internet-Draft SMF for MANET March 2006 ______________ _____________ | | | | | Neighborhood | | Relay Set | | Discovery |------------->| Selection | | Protocol | neighbor | Algorithm | |______________| info |_____________| \ / \ / neighbor\ /fowarding info* \ ____________ / status \ | | / `-->| Forwarding |<--' | Process | ~~~~~~~~~~~~~~~~~>|____________|~~~~~~~~~~~~~~~~~> incoming packet, forwarded packets interface id, and previous hop* Fig. 1 - SMF Node Architecture This document describes a network layer multicast forwarding process compatible with different neighborhood discovery protocols and relay set selection algorithms. Different discovery mechanisms or relay set algorithms may be applicable for different MANET routing protocols and deployments. In the simplest case, Classical Flooding (CF) can be supported, eliminating the need for any relay set algorithm or neighborhood topology information. However, it is expected that more efficient flooding techniques will be preferred due to expected gains in network efficiency and reductions in wireless congestion and contention. Efficient flooding is realized by selecting a _subset_ of all possible nodes in a MANET area as the forwarding relay set. Algorithms exist that can make use of local network neighborhood topology information to determine an appropriate relay set in a distributed, dynamic fashion. These relay set selection algorithms can be used to provide a distribution tree for user multicast data[MDC04]. A few such relay set selection algorithms are described in Appendices of this document, but it is possible that additional relay set algorithms or extensions may be specified in the future for use with SMF. As noted, neighborhood topology information is usually needed for a relay set selection algorithm to determine an appropriate set of forwarding nodes. In many cases, it is expected that neighborhood topology discovery functions may be provided by a MANET unicast routing protocol or HELLO protocol implementation running in concurrence with SMF. Or, in other cases, it is possible that the lower link layer or multiple access protocols may provide the necessary neighborhood information through an enhanced interface. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 6] Internet-Draft SMF for MANET March 2006 Different distributed relay set algorithms and associated forwarding decision logic often have differing neighborhood discovery and signaling demands. This document states specific requirements for neighborhood discovery with respect to the forwarding process and relay set selection algorithms described herein and defines an optional SMF Neighborhood Discovery (ND) protocol that can support operation independent of any MANET unicast protocol. Note that Figure 1 provides a notional architecture for _typical_ MANET SMF-capable nodes. However, a goal is that simple end-system (non-forwarding) wireless nodes may also participate in multicast traffic transmission and reception with standard network layer semantics. Also, a multicast border gateway mechanism MUST be used when interoperating with other IP multicast routing in the wired world (e.g., PIM). In present experiments, proxying methods have been used to enable some gateway functionality at MANET border gateways operating with wired multicast routing protocol interfaces. Although SMF may be extended or combined with other protocols to provide increased reliability and group specific forwarding state, the details of those methods will be discussed in other documents. 2.1. Terminology MANET : Mobile Ad hoc Networks SMF : Simplified Multicast Forwarding CF : Classical Flooding CDS : Connected Dominating Set MPR : Multi-point Relay DPD: Duplicate Packet Detection 2.2. Applicability A basic packet forwarding service that reaches all destinations participating within a MANET environment can be a useful generic group communication mechanism for an application layer. While the design requirements for this are similar to those often needed by the control plane of many MANET unicast routing protocol layers, it is desirable to provide a more generic forwarding function for use by other applications. There are a number of application areas that could take advantage of a simple ALL_MANET_NODES delivery service within a MANET routing region (e.g., multimedia streaming, peer-to- peer middleware multicasting, auto-configuration, and multi-hop discovery services). Macker, editor & SMF Design Team Expires September 6, 2006 [Page 7] Internet-Draft SMF for MANET March 2006 3. SMF Design Considerations The simplest design often conceived and adapted for MANET packet flooding is something we designate as the "classical flooding" (CF) algorithm. In CF, each participating forwarder node is required to rebroadcast packets intended for dissemination once and only once. This approach is extremely simple and only requires only some means of duplicate packet detection (DPD) and a basic forwarding mechanism. However, it is well known that using CF, especially within dense networks, results in a significant number of redundant transmissions often referred to as the broadcast storm problem [NTSC99]. Within wireless multi-hop network direct contention and interference is often experienced beyond the single hop interface and reducing unnecessary channel contention within a MANET can also significantly improve network performance. Therefore, minimizing the number of required relay nodes is a heightened design goal in this environment. Unfortunately, reducing the number of relay nodes in a MANET environment may also decrease the robustness of packet delivery in a mobile topology. There exists a design tradeoff between relay efficiency and delivery robustness that is scenario and system dependent and should be considered carefully. If needed, additional reliability mechanisms MAY be considered for use with reduced relay sets (e.g., backup and redundant relay set) but the use of limited hop-by-hop retransmission schemes at the network layer are considered out of scope for this document. If needed by an application, the use of IETF reliable multicast transport layer protocols (e.g., RMT) should be transparently supported by SMF's best effort delivery mechanism. The basic design goal of SMF is support both a simple CF- based forwarding capability and to supplement this with reduced relay set algorithms for increased efficiency. At a theoretic level, work in the area of minimizing packet forwarders, or relay node sets, is often related to basic graph theory problems. In graph theory, a dominating set (DS) for a graph is a set of vertices that, along with their neighbors, constitute all the vertices in the graph. A connected DS (CDS) is a DS where the subgraph induced is connected. A minimum CDS (MCDS) is a set such that the number of vertices is the minimum required to form a CDS. Finding a small dominating set is one of the most fundamental problems of traditional graph theory and is often related to the problem of optimizing flooding algorithms in MANET routing protocols. Finding an MCDS in a given graph is known to be NP-hard [GJ79]. These basic static graph theoretic issues are important to apply in developing efficient relay sets, but in addition MANET relay set designs require distributed and dynamic operation. To better explain the design requirement, we formulated the following characteristics desired of an effective MANET flooding algorithm solution for use in SMF: Macker, editor & SMF Design Team Expires September 6, 2006 [Page 8] Internet-Draft SMF for MANET March 2006 1. A resultant cover set that is small compared to the total number of nodes as the network scales in size and density. 2. A robust approach somewhat resilient to network mobility and link dynamics. 3. A cover set election/maintenance mechanism that is lightweight, distributed, and adaptive in nature. 3.1. Previous Related Work Previous novel work on MANET flooding and reduced relay set mechanisms has been done and this document borrows from and builds off previous work accomplished. In [WC02], a taxonomy of flooding algorithms for use in MANET environments was presented and the work examined performance issues related to various approaches. Other important work has developed distributed mechanisms that select and maintain reduced relay node sets. As we have already mentioned, the design tradeoffs are further complicated by wireless contention, topological classes, and the robustness of packet delivery and set election under mobility scenarios. In addition, the actual protocol implementation for IP multicast forwarding based upon these flooding algorithms raises additional design tradeoffs and issues. This includes: 1. protocol state maintenance 2. duplicate packet detection mechanisms 3. packet processing requirements and overhead 4. expected traffic distribution patterns 5. protocol signaling requirements 6. delivery robustness requirements Macker, editor & SMF Design Team Expires September 6, 2006 [Page 9] Internet-Draft SMF for MANET March 2006 4. SMF Packet Processing and Forwarding The SMF Packet Processing and Forwarding actions are conducted with the following packet handling activities: 1. Interception of outbound, locally-generated multicast packets. 2. Reception of inbound packets on a specific network interface(s). In the case that sequence-based DPD as described in Section 5 is used, the purpose of intercepting outbound, locally-generated multicast packets is to apply resequencing of the IPv4 ID header field or add options headers as needed (e.g. IPv6). In the case that resequencing is deemed necessary, it is RECOMMENDED that sequence numbering be applied such that a different sequence number space per duple be used. For initial SMF purposes where no distinct routing path decisions for different IP Multicast address destinations occur, it might appear to be sufficient to use sequence number spaces aggregated across all IP Multicast destinations (or across all IP destinations for a source as is the default implementation of the IPv4 ID field in many operating systems). Future SMF extensions, beyond the present discussion, may contain dynamic forwarding state dependent on the multicast destination address. The future possibility that different destinations may be routed differently suggests "per source/ destination" numbering be used. It should be noted that the default global IPv4 ID sequence space may be sufficient for some SMF deployments and interception of outbound packets may not be required if end systems have numbered the IPv4 ID field in an acceptable manner. In other cases, such as when IPSec headers have been applied to packets, other sequence information (perhaps even "per flow") may be available for the SMF process to make use of in its duplicate table management. Inbound multicast packets will be received by the SMF implementation and processed for possible forwarding. Well-known multicast groups for flooding to all nodes of an ad hoc network are specified for use with the network-layer flooding provided by SMF. These multicast groups are specified to contain all nodes of a contiguous ad hoc network, so that packets transmitted to the multicast address associated with the group will be delivered to all nodes as desired. In other words, any node that is reachable, is automatically granted membership in these multicast groups. For IPv6, the multicast address is specified to be "site-local". The names of the multicast groups are given as "ALL_IPv4_MANET_NODES" (TBD) and "ALL_IPv6_MANET_NODES" (TBD). This document does not support transmissions to any directed broadcast address ranges. Minimally SMF SHALL forward unique (non-duplicate) packets received for these Macker, editor & SMF Design Team Expires September 6, 2006 [Page 10] Internet-Draft SMF for MANET March 2006 well-known group addresses when the TTL or hop count value in the IP header is greater than 1. Optionally, SMF deployments may choose to forward packets for additional "global scope" multicast groups to support application needs or to distribute multicast packets that have ingressed the MANET area via border gateways. Additional addresses will be specified by an a priori list or possible through a dynamic address management interface. In all cases, the following rules SHALL be observed for SMF multicast forwarding: 1. Multicast packets with TTL <= 1 MUST NOT be forwarded*. 2. Link Local multicast packets MUST NOT be forwarded 3. Incoming multicast packets with an IP source address matching one of those of the local host interface(s) MUST NOT be forwarded. 4. Received packet frames with the MAC source address matching the local host interface(s) MUST NOT be forwarded. Note that rule #3 is important because in wireless networks, the local host may receive re-transmissions of its own packets when they are forwarded by neighboring nodes. This rule avoids unnecessary retransmission of locally-generated packets even when other forwarding decision rules would apply. Once these criteria have been met, the implementation should reference a forwarding decision algorithm, possibly in concert with duplicate packet detection, to determine the next step in packet processing. The forwarding decision may be implicit if the SMF implementation is configured to perform classical flooding (CF) of IP multicast packets. Otherwise, the forwarding decision may be controlled by another process. Neighborhood discovery protocols coupled with the source-based multi-point relay (S-MPR) or other CDS selection algorithms described below MAY be used to determine the local host's status with respect to forwarding. For example, some algorithms may control forwarding based on a previous hop indentifier (e.g. S-MPR forwarding), while others may designate the local host as a forwarder of all packets (or at least those generated by known neighbors) based on the neighborhood broadcast topology (e.g. Essential CDS (E-CDS)). DPD is the perhaps the most complex portion of the SMF forwarding process. In general, detection of received duplicate packets is necessary to avoid forwarding the same packet multiple times. However, in some cases (e.g., S-MPR), duplicate detection of some non-forwarded packets is also needed to maintain efficient forwarding. Details on different duplicate packet detection and forwarding rules for the S-MPR, and E-CDS algorithms are given in Macker, editor & SMF Design Team Expires September 6, 2006 [Page 11] Internet-Draft SMF for MANET March 2006 Appendices of his document. The details for these classes of algorithms may also apply to other similar algorithms. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 12] Internet-Draft SMF for MANET March 2006 5. SMF Duplicate Packet Detection One important design difference between routing for MANET interfaces and many wired network interfaces is that forwarding out the same physical interface a packet arrived upon is a normal operation. This operation is often disallowed or discouraged in wired multicast routing designs to avoid possible looping. Similarly, any Reverse Path Forwarding (RPF) logic also used needs to be softened when operating over a single MANET interface. This MANET interface characteristic leads to DPD as a common requirement in MANET packet flooding. While this requires increased per packet processing, it is necessary in MANET-specific multicasting because packets must be potentially be forwarded out the same physical interface they may arrive on and nodes can even receive copies of previously-transmitted packets from other forwarding neighbors. This section describes a basic SMF DPD mechanism and some alternative operational options as considerations. SMF SHOULD implement explicit detection of duplicate multicast packets by a temporal packet identification scheme. This is typically implemented by keeping a history of previous received and forwarded packet identifiers for comparison against recently forwarded multicast packets. There are different possible approaches to packet identification that have been considered. Possibilities include unique markings within packet header fields, such as packet sequence numbering, or application of hash algorithms or similar techniques to compactly and uniquely describe the history of recently received packets. This document RECOMMENDS simple, sequence-based schemes that can be accomplished without additional (non-IP) encapsulation of packets and/or their content. Encapsulation approaches are considered out-of-scope so that non-forwarding edge nodes within a MANET area may easily receive flooded content without any additional software beyond that of a typical IP stack. Packet hashing approaches for DPD may be applicable in some cases, yet early examination of these approaches indicated the computation complexity may be prohibitive for per-packet processing on many candidate MANET platforms (e.g., PDAs). Additionally, the unavoidable "cache-miss" rates, while possibly low for some algorithms, result in the severe penalty of false DPD (and thus packet loss) rather than the more benign penalty of additional computation cycles as associated with most applications of hashing. Implementations will need to age and/or timeout duplicate packet state as new packets are received and forwarded. In the case that sequence-based packet identification is used, implementations SHOULD timeout stale histories for entries where new, non-duplicate packets have not been recently received. The proper duration of any timeout delay is a function of Macker, editor & SMF Design Team Expires September 6, 2006 [Page 13] Internet-Draft SMF for MANET March 2006 expected possible network traversal time, roughly NET_DIAMETER (in hops) times NODE_TRAVERSAL_TIME. NET_DIAMETER measures the maximum possible number of hops given any two nodes in the network. NODE_TRAVERSAL_TIME is a conservative estimate of the average one hop traversal time for packets and should include queueing delays, interrupt processing times, medium access delays, and propagation delays. If the timeout is reset only upon reception of non-duplicate packets, it also limits the time that packets might be incorrectly dropped if a source node is stopped and restarted in the case of sequence-based packet identification. The required size of the duplication detection cache is similarly governed and is also a function of the maximum expected packet rate. Of course, the duplicate packet detection mechanism SHOULD avoid keeping unnecessary state for packet flows such as those that are locally generated or link local destinations that would not be considered for forwarding. 5.1. SMF IPv4 Duplicate Packet Detection IPv4 multicast packets from a particular source are assumed to be marked with a temporally unique identification number in the ID field of the IPv4 packet header that can serve as a "packetIdentifier" for SMF purposes. Unfortunately, in present operating system networking kernels, this IP header field value is not always generated or applied in a consistent manner with respect to SMF needs. In order to build a working implementation without encapsulating packets, an SMF implementation SHOULD provide a sequence generation and marking module that can maintain and set a monotonically increasing IP ID field for locally-generated multicast packets with independent sequence number spaces applied on a basis. When needed this process will also recalculate and replace a proper IP header checksum for the formulated header. For gateways injecting external IPv4 traffic into an SMF MANET area, the gateways SHOULD perform this same IP ID field re-sequencing. Note the presence of IPSec may prevent such resequencing, but does provide its own organic means for duplicate packet detection. The use of IPSec for candidate packet flows presents the opportunity to make use of the additional, perhaps more reliable, sequencing information of the IPSec header for unique packet identification. The IPSec header provides a packet identifier field that can be used on a "per-security assocation" basis. The IP addressing and IPSec Security Parameters Index (SPI) fields are used to identify security associations and, hence, packet flows. So, if the packet is IPSec encapsulated, SMF will check the where the or Macker, editor & SMF Design Team Expires September 6, 2006 [Page 14] Internet-Draft SMF for MANET March 2006 from the IPSec header serves as the "packetIdentifier" value. Although it would be possible to support IP layer fragmentation , SMF traffic sources or gateways SHOULD set the don't fragment bit for traffic intended to be carried by SMF. This is recommended to avoid the additional complexity and inefficiencies arising from supporting IP layer fragmentation. To perform duplicate detection, SMF will check the combination against a cache history of received packet identifiers. Some forwarding algorithms may require that unique packets are only noted when received from certain neighbor nodes. Multiple interface semantics may also add some additional considerations to the forwarding process depending upon the specific relay set selection forwarding rules. Although its use is demonstrated in working prototype code, the adoption of the IPv4 ID field for widespread packet duplication detection has some disadvantages that should be discussed. The main disadvantage is that, as mentioned, the use and interpretation of the field is known to be non-consistent across operating systems. The ID field is also limited and may provide less robust detection for high bandwidth applications since sequence wrap-around may occur relatively frequently if it is not possible to achieve "per source/ destination" sequencing. As an alternative, the use of a header option or encapsulation header in future implementations may provide more flexibility and consistency (see IPv6 DPD). Another advantage of using a header option (or other encapsulation, if determined absolutely necessary) is that it would be possible for MANET gateway nodes to assess whether packets ingressing a MANET area have already been properly sequenced to avoid unnecessary re-injection of packets. We leave these design alternatives to be further defined and discussed in future work or later revisions of this ID. A basic sequencing and marking design similar to the one we formulate here can be easily adapted to work with future approaches or can be bypassed when not needed. 5.2. SMF IPv6 Duplicate Packet Detection The following section describes the mechanism and options for SMF IPv6 DPD. The core IPv6 header does not provide an explicit identification header field that we can exploit for DPD. SMF defines two methods for IPv6 use: a hop-by-hop DPD options header and the use of IPSec sequencing when an IPSec header is detected. SMF MUST provide a DPD marking module that can insert the hop-by-hop IPv6 header option defined for locally generated MANET multicast. If the packet is _not_ IPSec encapsulated, SMF will use the IPv6 packet header and IPv6 DPD option to form that is checked against a cache history of received IPv6 packet identifiers. Similarly to the case for IPv4, the presence of IPSec may prevent the intermediate addition of a hop-by-hop options header. Fortunately, the IPSec header provides a packet identifier field that can be used on a "per- security assocation" basis. The IP addressing fields and IPSec Security Parameters Index (SPI) fields are used to identify security associations and, hence, packet flows. So, if the packet is IPSec encapsulated, SMF will check the where the or from the IPv6 IPSec header serves as a "packetIdentifier" value. 5.2.1. IPv6 SMF-DPD Header Option Format Figure 2 illustrates the format of the IPv6 SMF Duplication Packet Detection (SMF-DPD) hop-by-hop header option. (Discussion: Is there any value in specifying this as a "destination" option instead?). If this is the only hop-by-hop option present, this will result in the addition of 8 bytes to the IPv6 packet header including the "Next Header", "Header Extension Length", SMF-DPD option fields, and padding. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | Option Type | Opt. Data Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DPD packet identifier | ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fig. 2 - IPv6 SMF-DPD Hop-by-hop Header Option Option Type = (TBD) Opt. Data Len = 2 DPD packet identifier = monotonically increasing 16-bit sequence number assigned on a per basis. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 16] Internet-Draft SMF for MANET March 2006 6. Relay Set Selection As mentioned SMF MUST support CF-based forwarding as a basic forwarding mechanism when optimized relay set information is not available or not selected. In CF mode, each node transmits a locally generated or newly received packet exactly once. The DPD technique mentioned in the previous section is critical to proper operation and avoids any duplicate packet retransmissions. In the requirements sections, it was stated that SMF MUST support the ability to modify forwarding rules based upon relay set information that is received dynamically during operation. In this way, SMF can operate more efficiently within the MANET multicast area. In the section we define the interface and processing semantics to allow SMF to support a variety of different relay set algorithms and approaches. Some recommended criteria for relay set selection algorithm candidates: 1. Robust with respect to mobility or other network dynamics 2. Require minimal signaling for neighbor discovery and/or control 3. Allow nodes to express preference for/against selection as relay Some relay set algorithms that meet this criteria are described in the Appendices of this document. Different algorithms may be more suitable for different MANET routing types or deployments. Additional relay set selection algorithms may be specified in separate documents in the future. The Appendices in this document can serve as a template for the content of such potential future specifications. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 17] Internet-Draft SMF for MANET March 2006 7. Baseline SMF Neighborhood Discovery Protocol (NDP) In absence of a compatible, coexisting unicast routing protocol or MAC layer protocol that provides neighborhood toplogy information sufficient for relay set selection, this section defines a basline SMF neighborhood discovery protocol (NDP) that MAY be run between SMF nodes. With respect to neighborhood topology knowledge and/or discovery, there are three basic modes of SMF operation: 1. Classical Flooding (CF) mode with no requirement for discovery or knowledge of neighborhood topology, 2. External control mode where an external process dynamically sets the local SMF relay status (e.g., Early SMF prototypes have leveraged neighborhood toplogy information collected by MANET unicast routing protocols such as OLSRv2 or Manet-OSPF ), and 3. Independent operating mode using a neighborhood discovery ("hello") protocol to collect the local topology information required for the various CDS algorithm modes discussed in the Appendices. We have previously discussed modes 1 and 2. This section will specify a baseline, stand-alone NDP that can be used to operate SMF independent of any MANET unicast routing protocol and still provide optimized relay set functionality. The intention of this protocol design is to be consistent with the Generalized MANET Packet/Message Format work [PacketBB] in progress within the MANET WG and the SMF protocol design is closely related to and borrows from the HELLO protocol being specified by OLSRv2 [OLSRv2] but separates out specific CDS algorithm support. 7.1. SMF NDP Description SMF NDP messages are exchanged between local interface neighbor nodes and SMF NDP messages are transmitted to a well-known link-local multicast address, ALL_SMF_NEIGHBORS (TBD), on a well-known UDP port number , SMF_NDP_PORT (TBD). The SMF NDP protocol provides the following functions: 1. 1-hop neighbor link sensing: maintaining neighbor lists and performing a basic bidirectionality check of neighbor links 2. 2-hop Neighborhood Discovery: collecting 2-hop symmetric neighborhood information and any information relevant to relay set election Macker, editor & SMF Design Team Expires September 6, 2006 [Page 18] Internet-Draft SMF for MANET March 2006 3. Relay Set Signaling: signal relay set selection to neighbor nodes if the relay set algorithm requires such information SMF NDP messages are exchanged between link local neighbor nodes only and are not forwarded. 7.2. SMF NDP Messaging SMF-NDP nodes periodically generate a single message type, SMF_HELLO, conforming to the Generalized MANET Packet/Message Format work [PacketBB] in progress within the MANET WG. This generalized packet/ message format provides a standard message header convention and a standard format for messages containing sets of type-length-value (TLV) content and blocks of network addresses with associated TLV content. This supports the needs of SMF-NDP and typical MANET routing protocol messaging. _(TBD - Differential NDP messages may be defined in future revisions on this specification)_ SMF NDP messages are generated and transmitted per interface, i.e. different SMF NDP messages are generated and transmitted per SMF interface of a node. SMF NDP messages are generated and transmitted periodically, with a default interval between two SMF NDP messages of SMF_HELLO_INTERVAL. The transmission of SMF_HELLO messages are also randomly jittered by a value establish by SMF_JITTER to decrease the likelihood of increased contention caused by synchronized SMF_HELLO intervals within a wireless network. The default value for SMF_JITTER is 0.5, specified by valued between 0 and 1, and represents a percentage of SMF_HELLO_INTERVAL around which to jitter transmissions. The SMF_HELLO message contains a header, a set of message TLVs describing general properties of originating node (e.g., CDS algorithm id, SMF_HELLO transmission interval, relay "willingness", etc), and an address block of detected one-hop neighbors with an associated TLV block indicating the status and other attributes of connectivity to those neighbors. Thus, by exchanging these messages with neighbors (via broadcast), SMF nodes gain knowledge of two-hop neighborhood connectivity. This information can be used to execute the different relay set selection algorithms described in the Appendices of this document. It is also possible that the SMF_HELLO message could be extended with additional address blocks and TLV sets as needed to support other relay set selection algorithms outside of the scope of this document. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 19] Internet-Draft SMF for MANET March 2006 7.2.1. SMF_HELLO Message Header The SMF_HELLO message has a value of SMF_HELLO (TBD). The field SHALL have set to indicate a reduced with _no_ or elements since the SMF_HELLO message is implicitly a one-hop message. Thus, the content shall consist of only the and elements. The SHALL correspond to the interface address on which the SMF_HELLO message was transmitted and the will be incremented monotonically and receivers will use this field to track SMF_HELLO message loss. 7.2.2. SMF_HELLO Message TLVs *Relay Set Algorithm Identifier*: type=SMF_RELAY_ALGORITHM, length 1, values = {CF, S-MPR, E-CDS, MPR-CDS} *Hello Transmission Interval*: type=SMF_HELLO_INTERVAL, length = 1, value = time* Note: The four highest bits of the 8-bit TLV value represent the mantissa (a) and the four lowest bits represent the exponent (b), yielding a time value equal to: time = (1+a/16)*2^b seconds. Thus, values in the range from 62.5 msec to 32,768 seconds can be represented. *Relay "Willingness"*: type=SMF_RELAY_WILLING, length =1, value "willingness" Note: If this message TLV is omitted, a default willingess value is assumed. Also note that this particular TLV may be also be carried in the address block portion(s) of the message to convey "willingness" values learned from neighboring nodes. 7.2.3. SMF_HELLO Address Block TLVs The first of a SMF_HELLO message is comprised of a list of the message originator's neighbors. The associated set of TLVs for the describe the status and other attributes for the given list of neighbors. In general, the TLVs will be "multivalue" TLVs that index the subset range of addresses to which they apply. In some cases, a given TLV type may be provided for each address in the block, while in other cases, some TLVs may apply only to a subset of addresses. Where possible, it is RECOMMENDED that implementations group address subsets within the accordingly to preserve message compactness and minimize message processing demands. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 20] Internet-Draft SMF for MANET March 2006 There are two TLV types that can be applied to convey the status of neighbors to the originating node. At least one of these One of these "Link Status" is applied for neighbor nodes detected via the same interface on which the SMF_HELLO message is transmitted, while the other "Other Neighbor Status" conveys the status of neighbors on other interfaces. For initial applications of SMF, it is expected that the "Link Neighbor Status" TLV will be most applicable and the "Other Neighbor Status" TLV will allow support when forwarding across an SMF domain comprised of multiple interfaces is required. *Link Neighbor Status*: type=SMF_LINK_STATUS, length=1, values {HEARD, SYMMETRIC, LOST} *Other Neighbor Status*: type = SMF_OTHER_STATUS, length=1, value {SYMMETRIC, LOST} The following table summarizes the use of these neighbor TLVs for different cases: +-------------------------------------------+-----------------------+ | Set of neighbor addresses | TLV (type=value) | +-------------------------------------------+-----------------------+ | HEARD over the interface which the | (Link Status=HEARD) | | SMF_HELLO was transmitted on | | | | | | SYMMETRIC over the interface which the | (Link | | SMF_HELLO was transmitted on | Status=SYMMETRIC) | | | | | LOST over the interface which the | (Link Status=LOST) | | SMF_HELLO was transmitted on | | | | | | SYMMETRIC over any other interface than | (Other Neighbor | | the one transmitted on | Status=SYMMETRIC) | | | | | LOST node on any other interface that the | (Other Neighbor | | one transmitte on | Status=LOST) | +-------------------------------------------+-----------------------+ _(TBD - We plan to define an optional "link quality" TLV (or a pair to convey quality))_ Other TLV types are required to support the relay set selection algorithms described in the Appendices of this document. For example, the S-MPR and MPR-CDS algorithms require a TLV type to indicate which address (if any) have been selected as MPRs for the originating node. And the E-CDS algorithm requires a "Router Priority" value for each symmetric neighbor in the address list to enable its relay set selection mechanism. Those TLVs are described Macker, editor & SMF Design Team Expires September 6, 2006 [Page 21] Internet-Draft SMF for MANET March 2006 in the corresponding appendices where applicable. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 22] Internet-Draft SMF for MANET March 2006 8. SMF Multicast Border Gateway Considerations Typically, it is expected that SMF will be used to distribute multicast traffic within a MANET area. However, it is also envisioned to allow interconnection of SMF operation with networks using other multicast routing protocols if appropriate conditions are met. Some primary considerations for further defintion (TBD) include: 1. Determining which multicast groups should transit the gateway whether entering or exiting the attached MANET area(s). 2. TTL threshold or other scoping policies. 3. Any marking or labeling to enable DPD on ingressing packets. 4. Interface with exterior multicast routing protocols. 5. Possible operation with multiple gateways. The behavior of gateway nodes is the same as that of non-gateway nodes when forwarding packets to interfaces within the MANET area. Packets that are passed to interfaces operating typical multicast routing protocols SHOULD be evaluated for duplicate packet status since standard multicast forwarding for wired interfaces do not usually perform this function. 8.1. Forwarded Multicast Groups Determining which groups should be forwarded to or from a MANET SMF area presents challenges. Ideally, only groups for which there is active group membership should be injected into the SMF domain. This might be accomplished by providing an IPv4 Internet Group Membership Protocol (IGMP) or IPV6 Multicast Listener Discovery (MLD) proxy function so that MANET SMF nodes can inform attached gateways (and hence multicast networks) of their current group membership status. 8.2. Multicast Group Scoping (TBD) 8.3. Duplicate Packet Detection Marking Packets sourced external to an SMF area may not have duplicate packet sequencing properly applied and the gateway may need to provide that sequencing information upon entry to the network. In the case of IPv6, the gateway can apply the SMF DPD Hop-by-Hop options header to packets forwarded into the MANET area for those packets that do not Macker, editor & SMF Design Team Expires September 6, 2006 [Page 23] Internet-Draft SMF for MANET March 2006 already have the option applied. This header option provides the side benefit that the gateway can explicitly determine if the packet has already been marked and can use the packet identification field to determine that it is not re-injecting a duplicate packet. For IPv4, it is RECOMMENDED that gateway nodes re-sequence the ID field of packets injected into the area. However, the IPv4 ID field does not provide the gateway with explicit information on whether the field has been previously set for SMF purposes. Thus, the potential exists that duplicate IPv4 packets may be re-injected by a gateway into an SMF area. Further discussion and experimentation is recommended in this area. _(If multiple gateways are injecting packets, how do we make sure that dups are sequenced the same way? )_ 8.4. Interface with Exterior Multicast Routing Protocols (TBD) 8.5. Multiple Gateways (TBD) Macker, editor & SMF Design Team Expires September 6, 2006 [Page 24] Internet-Draft SMF for MANET March 2006 9. Security Considerations Gratuitous use of option headers can cause problems in routers. Routers outside of MANET routing areas should ignore SMF header options if encountered. Authentication mechanisms to identify the source of an option header should be considered to reduce vulnerability to a variety of attacks. Additional security consideration TBD. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 25] Internet-Draft SMF for MANET March 2006 10. IANA Considerations There are number of discussions within this SMF specification that will be subject to IANA registration. The IP Header Extensions being defined within this document MUST have an IANA registry established for them upon publication of the first RFC. Additionally, the well- known multicast addresses intended for default use by the SMF forwarding process should be registered and defined by the first RFC published. These IANA considerations may in common or may be handed in comjunction with other MANET protocol efforts including the General Message Format specification and potentially common neighborhood discovery protocol considerations. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 26] Internet-Draft SMF for MANET March 2006 11. Acknowledgments Many of the concepts and mechanisms used and adopted by SMF resulted from many years of discussion of related work within the MANET WG. There are obviously many people that have contributed to past discussions and related draft documents within the WG that have influenced the development of SMF concepts that deserve acknowledgment. In particular, the document is largely a direct product of the SMF design team within the IETF MANET WG and borrows text and implementation ideas from these individuals. SMF Design Team Contributors Thomas Clausen Charles Perkins Brian Adamson Justin Dean Brian Haberman Ian Chakeres Maoyu Wang Et al The RFC text was produced using Marshall Rose's xml2rfc tool. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 27] Internet-Draft SMF for MANET March 2006 12. References 12.1. Normative References [E-CDS] Ogier, R., "MANET Extension of OSPF Using CDS Flooding", Proceedings of the 62nd IETF , March 2005. [MPR-CDS] Adjih, C., Jacquet, P., and L. Viennot, "Computing Connected Dominating Sets with Multipoint Relays", Ad Hoc and Sensor Wireless Networks , January 2005. [OLSRv2] Clausen, T. and et al, "Optimized Link State Routing Protocol version 2", draft-ietf-manet-olsrv2-00, Work in progress , March 2006. [PacketBB] Clausen, T. and et al, "Generalized MANET Packet/Message Format", draft-ietf-manet-packetbb-00, Work in progress , March 2006. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing Protocol", 2003. 12.2. Informative References [GJ79] Garey, M. and D. Johnson, "Computers and Intractability: A Guide to the Theory of NP-Completeness.", Freeman and Company , 1979. [JLMV02] Jacquet, P., Laouiti, V., Minet, P., and L. Viennot, "Performance of multipoint relaying in ad hoc mobile routing protocols", Networking , 2002. [MDC04] Macker, J., Dean, J., and W. Chao, "Simplified Multicast Forwarding in Mobile Ad hoc Networks", IEEE MILCOM 2004 Proceedings , 2004. [NTSC99] Ni, S., Tseng, Y., Chen, Y., and J. Sheu, "The Broadcast Storm Problem in Mobile Ad hoc Networks", Proceedings Of ACM Mobicom 99 , 1999. [RFC2901] Macker, JP. and MS. Corson, "Mobile Ad hoc Networking Macker, editor & SMF Design Team Expires September 6, 2006 [Page 28] Internet-Draft SMF for MANET March 2006 (MANET): Routing Protocol Performance Issues and Evaluation Considerations", 1999. [RFC3684] Ogier, R., Templin, F., and M. Lewis, "Topology Dissemination Based on Reverse-Path Forwarding", 2003. [WC02] Williams, B. and T. Camp, "Comparison of Broadcasting Techniques for Mobile Ad hoc Networks", Proceedings of ACM Mobihoc 2002 , 2002. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 29] Internet-Draft SMF for MANET March 2006 Appendix A. Source-based Multipoint Relay (S-MPR) The source-based multipoint relay (S-MPR) set selection algorithm enables individual nodes, using two-hop topology information to select a minimum set of neighboring nodes that can provide relay to all nodes within a two-hop radius. This distributed technique has been shown to approximate selection of a MCDS in [JLMV02]. Individual nodes must collect two-hop neighborhood information from neighbors, determine an appropriate current relay set, and then inform the resultant selected neighbors of their relay status. The Optimized Link State Routing (OLSR) protocol has used this algorithm and protocol for relay of link state updates and other control information[RFC3626] and has been shown to operate well even in dynamic network environments. Because a node's status as a relay is with respect to neighboring nodes who have selected it (i.e., its "selectors"), the relaying node must know the previous-hop transmitter of packets it receives in order to make an appropriate forwarding decision. Additionally, it is important that relay nodes forward packets only for those nodes currently identified as symmetric, one-hop neighbors to maintain correctness. Also, because the selection of relays does not result in a common set among neighboring nodes, relays MUST mark in their duplicate table any transmissions from non-selector, symmetric, one- hop neighbors (for a given interface) and not forward subsequent received copies of that packet even if received from a selector neighbor. Deviation here may result in unecessary, even excessive, repeat transmission of packets throughout the network. Or incorrect duplicate table recording of packets received from non-symmetric neighbors may result in incomplete flooding. In these respects, flooding based on the S-MPR algorithm is more complex than that based upon some other relay set selection algorithms. When multiple interfaces are present, the S-MPR SMF forwarded must keep some independent state for each interface with regards to duplicate packets. For example, when a packet is received from a non-selector, one-hop symmetric neighbor, an SMF forwarder using the S-MPR algorithm must update its duplicate packet state with respect to the interface on which the packet was received. If the SMF forwarder receives that same packet from a selector neighbor on a different interface, it MUST still forward that packet on all interfaces it has not received that packet from a one-hop symmetric neighbor. Once a packet has been forwarded in this fashion, subsequent duplicates received on any interface are ignored. A.1. S-MPR Relay Set Selection If SMF is operating S-MPR relay set election independent of Macker, editor & SMF Design Team Expires September 6, 2006 [Page 30] Internet-Draft SMF for MANET March 2006 coexistent OLSR operation, based upon SMF ND mechanisms, the election algorithm defined within RFC3626 [RFC3626] should be used. A.2. Neighborhood Discovery Requirements S-MPR election operation requires 2-hop neighbor knowledge as provided by the SMF NDP process or as available from external sources. MPRs are dynamically selected by each node and selections MUST be advertised and dynamically updated within the SMF NDP or equivalent protocol. For SMF NDP, the following TLV is specified to indicate MPR selection status. *MPR Designation*: type=SMF_MPR_SELECT, length=0, value = [no value] Note this is a "no value" TLV, and the presence of this TLV implies that the corresponding address(es) have been selected by the SMF_HELLO message originator as MPR(s). Macker, editor & SMF Design Team Expires September 6, 2006 [Page 31] Internet-Draft SMF for MANET March 2006 Appendix B. Essential Connecting Dominating Set (E-CDS) Algorithm The "Essential connecting dominating set" (E-CDS) algorithm [E-CDS] allows nodes to use two-hop topology information to appropriately elect _themselves_ as relay nodes to form an efficient (for flooding) CDS. While this algorithm does not tend to produce as small a set of relay nodes (per forwarded packet) as the previously-described S-MPR algorithm, it is not dependent upon previous-hop information to make a forwarding decision; it simply forwards any received non-duplicate packets. This property also allows relay nodes using the E-CDS algorithm to be intermixed with nodes performing only classical flooding. Additionally, the semantics for multiple interface support are simplified as compared to S-MPR and even packets that are received from non-symmetric neighbors may be forwarded without compromising flooding efficiency or correctness. B.1. E-CDS Relay Set Selection This section provides a short description of the E-CDS based relay set selection algorithm and is based upon Richard Ogier's original summary within [E-CDS]. This was originally discussed in the context of forming partial adjacencies and efficient flooding for MANET-OSPF work but its core algorithm is applied here. E-CDS requires two-hop neighbor information collected through the SMF-NDP or other process. Each router has a Router Identifier (may be represented by an interface address) and Router Priority value. The Router Priority value may be dynamic and represent such metrics as node degree. The fundamental election steps are as follows: 1. If an SMF node has a higher (Router Priority, Router ID) than all of its symmetric neighbors, it elects itself to the relay set. 2. Else, if there does not exist a path from neighbor j with largest (Router Priority, Router ID) to some other neighbor, via neighbors with larger values of (Router Priority, Router ID), then it elects itself to the relay set. The basic form of E-CDS described and applied within this specification does not at present define redundant relay set election but such capability is supported by the E-CDS design. B.2. E-CDS Forwarding Rules E-CDS forwarding are quite simple and straightforward. As mentioned, there is no need to check previous hop information during forwarding. Upon electing itself as an E-CDS relay set forwarder, SMF nodes perform DPD functions and forward all ranges of multicast traffic Macker, editor & SMF Design Team Expires September 6, 2006 [Page 32] Internet-Draft SMF for MANET March 2006 allowed. B.3. Neighborhood Discovery Requirements To support functions required by the core E_CDS relay set algorithm the following TLV is required to be transmitted by each node within a SMF_HELLO message: *Router Priority*: type=SMF_ROUTER_PRIORITY, length=1, value priority* For E-CDS operation, some value of SMF_ROUTER_PRIORITY must be given or assumed for each address in the portion of the SMF_HELLO message. If a SMF_HELLO message originator does not provide a SMF_ROUTER_PRIORITY value for given address(es), a default value SMF_RPRI_DEFAULT=(TBD) should be assumed. Local determination of a node SMF_ROUTER_PRIORITY value can be done in multiple ways as described in the [E-CDS]. An early implementation of SMF and E-CDS has used node degree computed during neighbor discovery, yet it is still unclear if this is the best method. Unlike the MPR method, the E-CDS is a self-electing algorithm. SMF_ROUTER_PRIORITY needs to be shared with all immediate neighbor nodes and 2-hop neighbor knowledge is needed during the self election process. Further algorithm examples and details are covered in the Appendices. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 33] Internet-Draft SMF for MANET March 2006 Appendix C. Multipoint Relay Connected Dominating Set (MPR-CDS) Algorithm The MPR-CDS algorithm is an extension to the basic MPR election algorithm and results in a shared relay set that forms a CDS. Its forwarding rules within SMF are non-dependent upon previous hop information similar to E-CDS. C.1. MPR-CDS Relay Set Selection An overview of the the MPR-CDS selection algorithm is provided in [MPR-CDS]. The basic requirements for election are similar to the basic MPR algorithm with the addtion that some node ordering knowledge is required. This is similar to the E-CDS requirement and can be based upon node IP address or some other unique router identifier. The rules for election are as follows: A node decides it is in the relay set if: 1. the node is smaller than all its neighbors (Rule 1) 2. or the node is an MPR of its smallest neighbor (Rule 2) C.2. MPR-CDS Forwarding Rules MPR-CDS forwarding are quite simple and straightforward. As with E-CDS, there is no need to check previous hop information during forwarding. Upon electing itself as a MPR-CDS relay set forwarder, SMF nodes perform DPD functions and forward all ranges of multicast traffic allowed. C.3. Neighborhood Discovery Requirements No additional discovery requirements are needed beyond the basic Hello and MPR-related TLVs already discussed. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 34] Internet-Draft SMF for MANET March 2006 Authors' Addresses Joseph Macker NRL Washington, DC 20375 USA Email: macker@itd.nrl.navy.mil SMF Design Team IETF MANET WG Email: manet@ietf.org Macker, editor & SMF Design Team Expires September 6, 2006 [Page 35] Internet-Draft SMF for MANET March 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Macker, editor & SMF Design Team Expires September 6, 2006 [Page 36]