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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-14) exists of draft-ietf-rolc-nhrp-10 Summary: 8 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet-Draft Grenville Armitage 3 Bellcore 4 November 26th, 1996 6 Using the MARS model in non-ATM NBMA networks. 7 9 Status of this Memo 11 This document was submitted to the IETF Internetworking over NBMA 12 (ION) Working Group. Publication of this document does not imply 13 acceptance by the ION WG of any ideas expressed within. Comments 14 should be submitted to the ion@nexen.com mailing list. 16 Distribution of this memo is unlimited. 18 This memo is an internet draft. Internet Drafts are working documents 19 of the Internet Engineering Task Force (IETF), its Areas, and its 20 Working Groups. Note that other groups may also distribute working 21 documents as Internet Drafts. 23 Internet Drafts are draft documents valid for a maximum of six 24 months. Internet Drafts may be updated, replaced, or obsoleted by 25 other documents at any time. It is not appropriate to use Internet 26 Drafts as reference material or to cite them other than as a "working 27 draft" or "work in progress". 29 Please check the lid-abstracts.txt listing contained in the 30 internet-drafts shadow directories on ds.internic.net (US East 31 Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or 32 munnari.oz.au (Pacific Rim) to learn the current status of any 33 Internet Draft. 35 Abstract 37 The MARS model developed by the IP over ATM working group is also 38 applicable to other NBMA networks that provide the equivalent of 39 switched, point to multipoint connections. This short document is 40 intended to state the obvious equivalences, and explain the less 41 obvious implications. No changes to the MARS model per se are 42 suggested or required. The MARS model is not required for NBMA 43 networks that offer a link level group addressing service that maps 44 directly onto the IP multicast model. 46 This document is informational, and may influence the development of 47 MARSv2/NHRPv2 in line with the new ION charter and 'goals and 48 milestones' timeline. 50 1. Introduction. 52 Most network layer models, like the one described in RFC 1112 [1] for 53 IP multicasting, assume sources may send their packets to an abstract 54 'multicast group addresses'. Link layer support for such an 55 abstraction is assumed to exist, and is provided by technologies such 56 as Ethernet. 58 Some NBMA networks (e.g. ATM) do not support a multicast (or group) 59 address abstraction. In these environments multicasting is usually 60 supported through point to multipoint calls (or emulated with 61 multiple point to point calls). The MARS model [2] was originally 62 developed by the IP over ATM working group. For completeness this 63 memo explains how the MARS model and protocol can be applied to other 64 NBMA technologies that offer similar, limited multicast support. 66 2. The MARS model's basic assumptions. 68 Section 3 of [2] describes the basic assumptions that the MARS model 69 makes about the services available from the link layer network (using 70 ATM as the specific case). In summary (from the intro to section 3), 71 these are: 73 The ATM model broadly describes an 'AAL User' as any entity that 74 establishes and manages VCs and underlying AAL services to 75 exchange data. An IP over ATM interface is a form of 'AAL User' 76 (although the default LLC/SNAP encapsulation mode specified in 77 RFC1755 really requires that an 'LLC entity' is the AAL User, 78 which in turn supports the IP/ATM interface). 80 The most fundamental limitations of UNI 3.0/3.1's multicast 81 support are: 83 Only point to multipoint, unidirectional VCs may be 84 established. 86 Only the root (source) node of a given VC may add or remove 87 leaf nodes. 89 Leaf nodes are identified by their unicast ATM addresses. 91 Given this point to multipoint call service, the MARS document goes 92 on to describe two architectures for emulating multipoint to 93 multipoint IP multicasting - the VC Mesh, and the Multicast Server. 94 In either case it was assumed that IP/ATM interfaces (whether in 95 routers or hosts) are allowed to originate and manage outgoing point 96 to multipoint calls without network operator intervention or manual 97 provisioning. 99 The MARS document also specifies that AAL5 be used for all SVCs, 100 implying a requirement that the underlying link service supports the 101 atomic exchange of PDUs. 103 3. Generalising the MARS model. 105 Any NBMA service that offers an equivalent to (or superset of) the 106 ATM point to multipoint call service can use the MARS model directly. 107 It must be possible to transmit atomic data units bi-directionally 108 with point to point calls, and unidirectionally (from root to leaves) 109 on point to multipoint calls. 111 A MARS is simply an entity with an NBMA address. 113 A MARS Client is simply an entity with an NBMA address. 115 An MCS (where needed) is simply an entity with an NBMA address. 117 The MARS control messages defined in sections 4 onwards of the MARS 118 document are shown carrying ATM addresses. Using different mar$afn 119 (Address Family) values in the fixed header of MARS control messages 120 allows MARS entities to indicate they are carrying other types of 121 NBMA addresses (as for NHRP[3]). As for NHRP, the interpretation of 122 the 'sub-address' fields shall be in the context of the address 123 family selected (which means it will often simply be null). 125 In all cases where {IP, ATM.1, ATM.2, ...} mappings are referred to, 126 they may be interpreted as {IP, NBMA.1, NBMA.2, ...} in the context 127 of whatever NBMA network you are deploying MARS. 129 The MARS Cluster is defined in [2] as: 131 The set of ATM interfaces chosing to participate in direct ATM 132 connections to achieve multicasting of AAL_SDUs between 133 themselves. 135 It is trivial to observe that the cluster definition is independent 136 of the underlying link layer technology. A revised definition 137 becomes: 139 The set of NBMA interfaces chosing to participate in direct NBMA 140 connections to achieve multicasting of packets between themselves. 142 This document does not provide any additional information on how to 143 safely build a cluster that spans IP unicast subnet boundaries. The 144 existing caveat that a Cluster == a LIS remains unchanged. 146 The term 'Cluster Member' continues to refer to an endpoint that is 147 currently using a MARS for multicast support. The potential scope of 148 a cluster may be the entire membership of a LIS, while the actual 149 scope of a cluster depends on which endpoints are actually cluster 150 members at any given time. 152 Section 3.4 of [2] provided a somewhat stylised set of mneumonics for 153 the signalling functions available to AAL Users. These mneumonics are 154 then used in the remainder of [2] to indicate link layer events to 155 which MARS entities might react. Recast from the perspective of an 156 NBMA based MARS entity, the descriptions would now read: 158 The following generic signalling functions are presumed to be 159 available to local MARS entities: 161 L_CALL_RQ Establish a pt-pt call to a specific endpoint. 162 L_MULTI_RQ Establish pt-mpt call to a specific endpoint. 163 L_MULTI_ADD Add new leaf node to previously established pt-mpt 164 call. 165 L_MULTI_DROP Remove specific leaf node from established pt-mpt 166 call. 167 L_RELEASE Release pt-pt call, or all Leaves of a pt-mpt call. 169 The signalling exchanges and local information passed between MARS 170 entity and NBMA signalling entity with these functions are outside 171 the scope of this document. 173 The following indications are assumed to be available to MARS 174 entities, generated by by the local NBMA signalling entity: 176 L_ACK Succesful completion of a local request. 177 L_REMOTE_CALL A new call has been established to the MARS 178 entity. 179 ERR_L_RQFAILED A remote NBMA endpoint rejected an L_CALL_RQ, 180 L_MULTI_RQ, or L_MULTI_ADD. 181 ERR_L_DROP A remote NBMA endpoint dropped off an existing 182 call. 183 ERR_L_RELEASE An existing call was terminated. 185 The signalling exchanges and local information passed between MARS 186 entity and NBMA signalling entity with these functions are outside 187 the scope of this document. 189 4. Open Issues. 191 The trade offs between VC Mesh and Multicast Server modes may look 192 quite different for each NBMA technology. This will be especially 193 true in the area of VC (or equivalent) resource consumption in the 194 NICs of hosts, routers, and endpoints supporting MARSs or MCSs. The 195 use of VC mesh mode is most vulnerable to NBMA technologies that are 196 signalling intensive or resource challenged. 198 Sizing of Clusters (and hence LISes) will also be affected by a given 199 NBMA network's ability to support lots of pt-mpt calls. 200 Additionally, you cannot have more members in a cluster than you can 201 have leaf nodes on a pt-mpt call, without hacking the MARS model 202 (e.g. because of ClusterControlVC). 204 On going developments in server synchronisation protocols for 205 redundant MARS and MCS entities are expected to be applicable to 206 non-ATM NBMA networks. 208 Quality of service considerations are outside the scope of this 209 document. They will be very specific to each NBMA technology's 210 capabilities. Look to the ISSLL working group for answers here. 212 If the NBMA network offers some sort of native multipoint to 213 multipoint service then use of the MARS model may not be optimal. 214 Such situations require further analysis. 216 Use of NBMA networks other than ATM does not imply that the problems 217 associated with multicast 'short cuts' have been solved. This is 218 still an open issue. 220 Security Consideration 222 Security consideration are not addressed in this document. 224 Acknowledgments 226 Author's Address 228 Grenville Armitage 229 Bellcore, 445 South Street 230 Morristown, NJ, 07960 231 USA 232 Email: gja@bellcore.com 234 References 235 [1] S. Deering, "Host Extensions for IP Multicasting", RFC 1112, 236 Stanford University, August 1989. 238 [2] G.J. Armitage, "Support for Multicast over UNI 3.0/3.1 based ATM 239 Networks.", Bellcore, RFC 2022, Bellcore, November 1996. 241 [3] J. Luciani, et al, "NBMA Next Hop Resolution Protocol (NHRP)", 242 INTERNET DRAFT, draft-ietf-rolc-nhrp-10.txt, October 1996.