idnits 2.17.1 draft-ietf-atm-multipro-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Cannot find the required boilerplate sections (Copyright, IPR, etc.) in this document. Expected boilerplate is as follows today (2024-04-23) according to https://trustee.ietf.org/license-info : IETF Trust Legal Provisions of 28-dec-2009, Section 6.a: This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. IETF Trust Legal Provisions of 28-dec-2009, Section 6.b(i), paragraph 2: Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. IETF Trust Legal Provisions of 28-dec-2009, Section 6.b(i), paragraph 3: This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- ** Missing document type: Expected "INTERNET-DRAFT" in the upper left hand corner of the first page ** Missing expiration date. The document expiration date should appear on the first and last page. ** The document seems to lack a 1id_guidelines paragraph about Internet-Drafts being working documents. ** The document seems to lack a 1id_guidelines paragraph about 6 months document validity. ** The document seems to lack a 1id_guidelines paragraph about the list of current Internet-Drafts. ** The document seems to lack a 1id_guidelines paragraph about the list of Shadow Directories. ** Expected the document's filename to be given on the first page, but didn't find any == No 'Intended status' indicated for this document; assuming Proposed Standard == It seems as if not all pages are separated by form feeds - found 0 form feeds but 16 pages Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) ** The document seems to lack separate sections for Informative/Normative References. All references will be assumed normative when checking for downward references. ** There are 21 instances of too long lines in the document, the longest one being 6 characters in excess of 72. Miscellaneous warnings: ---------------------------------------------------------------------------- == Couldn't figure out when the document was first submitted -- there may comments or warnings related to the use of a disclaimer for pre-RFC5378 work that could not be issued because of this. Please check the Legal Provisions document at https://trustee.ietf.org/license-info to determine if you need the pre-RFC5378 disclaimer. -- The document date (December 17, 1992) is 11450 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. '2' -- Possible downref: Non-RFC (?) normative reference: ref. '3' ** Obsolete normative reference: RFC 1294 (ref. '4') (Obsoleted by RFC 1490, RFC 2427) -- Possible downref: Non-RFC (?) normative reference: ref. '5' -- Possible downref: Non-RFC (?) normative reference: ref. '6' -- Possible downref: Non-RFC (?) normative reference: ref. '8' -- Possible downref: Non-RFC (?) normative reference: ref. '9' Summary: 12 errors (**), 0 flaws (~~), 3 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Juha Heinanen 3 Reguest for Comments: DRAFT Telecom Finland 4 Expires June 17, 1993 December 17, 1992 6 Multiprotocol Interconnect over ATM Adaptation Layer 5 8 Status of this Memo 10 This document is an Internet Draft. Internet Drafts are working 11 documents of the Internet Engineering Task Force (IETF), its Areas, 12 and its Working Groups. Note that other groups may also distribute 13 working documents as Internet Drafts. 15 Internet Drafts are draft documents valid for a maximum of six 16 months. Internet Drafts may be updated, replaced, or obsoleted by 17 other documents at any time. It is not appropriate to use Internet 18 Drafts as reference material or to cite them other than as a 19 ``working draft'' or ``work in progress.'' Please check the 1id- 20 abstracts.txt listing contained in the internet-drafts Shadow 21 Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, 22 ftp.nisc.sri.com, or munnari.oz.au to learn the current status of any 23 Internet Draft. 25 Abstract 27 This memo describes two encapsulations methods for carrying network 28 interconnect traffic over ATM AAL5. The first method allows 29 multiplexing of multiple protocols over a single ATM virtual circuit 30 whereas the second method assumes that each protocol is carried over 31 a separate ATM virtual circuit. 33 1. Introduction 35 Asynchronous Transfer Mode (ATM) based networks are of increasing 36 interest for both local and wide area applications. This memo 37 describes two different methods for carrying connectionless network 38 interconnect traffic (routed and bridged PDUs) over an ATM network. 39 The first method allows multiplexing of multiple protocols over a 40 single ATM virtual circuit. The protocol of a carried PDU is 41 identified by prefixing the PDU by an IEEE 802.2 Logical Link Control 42 (LLC) header. This method is in the following called "LLC 43 Encapsulation" and a subset of it has been earlier defined for SMDS 44 [1]. The second method does higher-layer protocol multiplexing 45 implicitly by ATM Virtual Circuits (VCs). It is in the following 46 called "VC Based Multiplexing". 48 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 50 ATM is a cell based transfer mode that requires variable length user 51 information to be segmented and reassembled to/from short, fixed 52 length cells. This memo doesn't specify a new Segmentation And 53 Reassembly (SAR) method for bridged and routed PDUs. Instead, the 54 PDUs are carried in the Payload field of Common Part Convergence 55 Sublayer (CPCS) PDU of AAL5 [2]. AAL5 is a new simple and efficient 56 ATM Adaptation Layer currently being standardized both in ANSI and 57 CCITT. 59 Note that this memo only describes how routed and bridged PDUs are 60 carried directly over the CPCS of AAL5, i.e., when the Service 61 Specific Convergence Sublayer (SSCS) of AAL5 is empty. If Frame 62 Relay Specific Convergence Sublayer (FRCS), as defined in I.555 [3], 63 is used over the CPCS of AAL5, then routed and bridged PDUs are 64 carried using the NLPID multiplexing method described in RFC 1294 65 [4]. Appendix A (which is for information only) shows the format of 66 the FRCS-PDU as well as how IP and CLNP PDUs are encapsulated over 67 FRCS according to RFC 1294. 69 2. Selection of the Multiplexing Method 71 It is envisioned that VC Based Multiplexing will be dominant in 72 environments where dynamic creation of large numbers of ATM VCs is 73 fast and economical. These conditions are likely to first prevail in 74 ATM LANs. LLC Encapsulation, on the other hand, may be desirable 75 when it is not practical for one reason or another to have a separate 76 VC for each carried protocol. This is the case, for example, if the 77 ATM network only supports (semi) Permanent Virtual Circuits (PVCs) or 78 if charging depends heavily on the number of simultaneous VCs. 80 When two ATM stations wish to exchange connectionless network 81 interconnect traffic, selection of the multiplexing method is done 82 either by manual configuration (in case of PVCs) or by B-ISDN 83 signalling procedures (in case of Switched VCs). The details of B- 84 ISDN signalling are still under study in CCITT [5]. It can, however, 85 be assumed that B-ISDN signalling messages include a "Low layer 86 compatibility" information element, which will allow negotiation of 87 AAL5 and the carried (encapsulation) protocol. 89 3. AAL5 Frame Format 91 No matter which multiplexing method is selected, routed and bridged 92 PDUs shall be encapsulated within the Payload field of AAL5 CPCS-PDU. 93 The format of the AAL5 CPCS-PDU is given below: 95 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 97 AAL5 CPCS-PDU Format 98 +-------------------------------+ 99 | . | 100 | . | 101 | CPCS-PDU Payload | 102 | (up to 2^16 - 1 octets) | 103 | . | 104 | . | 105 +-------------------------------+ 106 | PAD ( 0 - 47 octets) | 107 +-------------------------------+ ------- 108 | Reserved (2 octets) | 109 +-------------------------------+ 110 | Length (2 octets) | CPCS-PDU Trailer 111 +-------------------------------| 112 | CRC (4 octets) | 113 +-------------------------------+ ------- 115 The Payload field contains user information up to 2^16 - 1 octets. 117 The PAD field pads the CPCS-PDU to fit exactly into the ATM cells 118 such that the last 48 octet cell payload created by the SAR sublayer 119 will have the CPCS-PDU Trailer right justified in the cell. 121 The Reserved field is coded 0x00-00 and is used to achieve 32 bit 122 alignment in the CPCS-PDU trailer. Additional functions besides the 123 32 bit alignment are for further study in CCITT. 125 The Length field indicates the length, in octets, of the Payload 126 field. The maximum value for the Length field is 65535 octets. A 127 Length field coded as zero is used for the abort function. 129 The CRC field protects the CPCS-PDU Header (if included) + the 130 Payload field + the PAD field + the Reserved field + the Length 131 field. 133 4. LLC Encapsulation 135 LLC Encapsulation is needed when several protocols are carried over 136 the same VC. In order to allow the receiver to properly process the 137 incoming AAL5 CPCS-PDU, the Payload Field must contain information 138 necessary to identify the protocol of the routed or bridged PDU. In 139 LLC Encapsulation this information is encoded in an LLC header placed 140 in front of the carried PDU. 142 Although this memo only deals with protocols that operate over LLC 143 Type 1 (unacknowledged connectionless mode) service, the same 144 encapsulation principle applies also to protocols operating over LLC 146 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 148 Type 2 (connection-mode) service. In the latter case the format 149 and/or contents of the LLC header would differ from what is shown 150 below. 152 4.1. LLC Encapsulation for Routed Protocols 154 In LLC Encapsulation the protocol of the routed PDU is identified by 155 prefixing the PDU by an IEEE 802.2 LLC header, which is possibly 156 followed by an IEEE 802.1a SubNetwork Attachment Point (SNAP) header. 157 In LLC Type 1 operation, the LLC header consists of three one octet 158 fields: 160 +------+------+------+ 161 | DSAP | SSAP | Ctrl | 162 +------+------+------+ 164 In LLC Encapsulation for routed protocols, the Control field has 165 always value 0x03 specifying Unnumbered Information Command PDU. 167 The LLC header value 0xFE-FE-03 identifies that a routed ISO PDU (see 168 [6] and Appendix B) follows. The Control field value 0x03 specifies 169 Unnumbered Information Command PDU. For routed ISO PDUs the format 170 of the AAL5 CPCS-PDU Payload field shall thus be as follows: 172 Payload Format for Routed ISO PDUs 173 +-------------------------------+ 174 | LLC 0xFE-FE-03 | 175 +-------------------------------+ 176 | . | 177 | ISO PDU | 178 | (up to 2^16 - 4 octets) | 179 | . | 180 +-------------------------------+ 182 The routed ISO protocol is identified by a one octet NLPID field that is 183 part of Protocol Data. NLPID values are administered by ISO and CCITT. 184 They are defined in ISO/IEC TR 9577 [6] and some of the currently 185 defined ones are listed in Appendix C. 187 An NLPID value of 0x00 is defined in ISO/IEC TR 9577 as the Null Network 188 Layer or Inactive Set. Since it has no significance within the context 189 of this encapsulation scheme, a NLPID value of 0x00 is invalid under the 190 ATM encapsulation. 192 It would also be possible to use the above encapsulation for IP, since, 193 although not an ISO protocol, IP has an NLPID value 0xCC defined for it. 194 This format must not be used. Instead, IP is encapsulated like all 195 other routed non-ISO protocols by identifying it in the SNAP header that 197 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 199 immediately follows the LLC header. 201 The presence of a SNAP header is indicated by the LLC header value 202 0xAA-AA-03. A SNAP header is of the form 204 +------+------+------+------+------+ 205 | OUI | PID | 206 +------+------+------+------+------+ 208 The three-octet Organizationally Unique Identifier (OUI) identifies an 209 organization which administers the meaning of the following two octet 210 Protocol Identifier (PID). Together they identify a distinct routed or 211 bridged protocol. The OUI value 0x00-00-00 specifies that the following 212 PID is an EtherType. 214 The format of the AAL5 CPCS-PDU Payload field for routed non-ISO PDUs 215 shall thus be as follows: 217 Payload Format for Routed non-ISO PDUs 218 +-------------------------------+ 219 | LLC 0xAA-AA-03 | 220 +-------------------------------+ 221 | OUI 0x00-00-00 | 222 +-------------------------------+ 223 | EtherType (2 octets) | 224 +-------------------------------+ 225 | . | 226 | Non-ISO PDU | 227 | (up to 2^16 - 9 octets) | 228 | . | 229 +-------------------------------+ 231 In the particular case of an Internet IP PDU, the Ethertype value is 232 0x08-00: 234 Payload Format for Routed IP PDUs 235 +-------------------------------+ 236 | LLC 0xAA-AA-03 | 237 +-------------------------------+ 238 | OUI 0x00-00-00 | 239 +-------------------------------+ 240 | EtherType 0x08-00 | 241 +-------------------------------+ 242 | . | 243 | IP PDU | 244 | (up to 2^16 - 9 octets) | 245 | . | 246 +-------------------------------+ 248 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 250 4.2. LLC Encapsulation for Bridged Protocols 252 In LLC Encapsulation bridged PDUs are encapsulated by identifying the 253 type of the bridged media in the SNAP header. As with routed non-ISO 254 protocols, the presence of the SNAP header is indicated by the LLC 255 header value 0xAA-AA-03. With bridged protocols the OUI value in the 256 SNAP header is the 802.1 organization code 0x00-80-C2 and the actual 257 type of the bridged media is specified by the two octet PID. 258 Additionally, the PID indicates whether the original Frame Check 259 Sequence (FCS) is preserved within the bridged PDU. The media type 260 (PID) values that can be used in ATM encapsulation are listed in 261 Appendix B. 263 The AAL5 CPCS-PDU Payload field carrying a bridged PDU shall, therefore, 264 have one of the following formats. Padding is added after the PID field 265 if necessary in order to align the user information field of the bridged 266 PDU at a four octet boundary. 268 Payload Format for Bridged Ethernet/802.3 PDUs 269 +-------------------------------+ 270 | LLC 0xAA-AA-03 | 271 +-------------------------------+ 272 | OUI 0x00-80-C2 | 273 +-------------------------------+ 274 | PID 0x00-01 or 0x00-07 | 275 +-------------------------------+ 276 | PAD 0x00-00 | 277 +-------------------------------+ 278 | MAC destination address | 279 +-------------------------------+ 280 | | 281 | (remainder of MAC frame) | 282 | | 283 +-------------------------------+ 284 | LAN FCS (if PID is 0x00-01) | 285 +-------------------------------+ 287 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 289 Payload Format for Bridged 802.4 PDUs 290 +-------------------------------+ 291 | LLC 0xAA-AA-03 | 292 +-------------------------------+ 293 | OUI 0x00-80-C2 | 294 +-------------------------------+ 295 | PID 0x00-02 or 0x00-08 | 296 +-------------------------------+ 297 | PAD 0x00-00-00 | 298 +-------------------------------+ 299 | Frame Control (1 octet) | 300 +-------------------------------+ 301 | MAC destination address | 302 +-------------------------------+ 303 | | 304 | (remainder of MAC frame) | 305 | | 306 +-------------------------------+ 307 | LAN FCS (if PID is 0x00-02) | 308 +-------------------------------+ 310 Payload Format for Bridged 802.5 PDUs 311 +-------------------------------+ 312 | LLC 0xAA-AA-03 | 313 +-------------------------------+ 314 | OUI 0x00-80-C2 | 315 +-------------------------------+ 316 | PID 0x00-03 or 0x00-09 | 317 +-------------------------------+ 318 | PAD 0x00-00-XX | 319 +-------------------------------+ 320 | Frame Control (1 octet) | 321 +-------------------------------+ 322 | MAC destination address | 323 +-------------------------------+ 324 | | 325 | (remainder of MAC frame) | 326 | | 327 +-------------------------------+ 328 | LAN FCS (if PID is 0x00-03) | 329 +-------------------------------+ 331 Note that the 802.5 Access Control (AC) field has no significance 332 outside the local 802.5 subnetwork. It can thus be regarded as 333 the last octet of the three octet PAD field, which can be set to 334 any value (XX). 336 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 338 Payload Format for Bridged FDDI PDUs 339 +-------------------------------+ 340 | LLC 0xAA-AA-03 | 341 +-------------------------------+ 342 | OUI 0x00-80-C2 | 343 +-------------------------------+ 344 | PID 0x00-04 or 0x00-0A | 345 +-------------------------------+ 346 | PAD 0x00-00-00 | 347 +-------------------------------+ 348 | Frame Control (1 octet) | 349 +-------------------------------+ 350 | MAC destination address | 351 +-------------------------------+ 352 | | 353 | (remainder of MAC frame) | 354 | | 355 +-------------------------------+ 356 | LAN FCS (if PID is 0x00-04) | 357 +-------------------------------+ 359 Payload Format for Bridged 802.6 PDUs 360 +-------------------------------+ 361 | LLC 0xAA-AA-03 | 362 +-------------------------------+ 363 | OUI 0x00-80-C2 | 364 +-------------------------------+ 365 | PID 0x00-0B | 366 +---------------+---------------+ ------ 367 | Reserved | BEtag | Common 368 +---------------+---------------+ PDU 369 | BAsize | Header 370 +-------------------------------+ ------- 371 | MAC destination address | 372 +-------------------------------+ 373 | | 374 | (remainder of MAC frame) | 375 | | 376 +-------------------------------+ 377 | | 378 | Common PDU Trailer | 379 | | 380 +-------------------------------+ 382 Note that in bridged 802.6 PDUs, there is only one choice for the 383 PID value, since the presence of a CRC-32 is indicated by the CIB 384 bit in the header of the MAC frame. 386 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 388 The Common Protocol Data Unit (PDU) Header and Trailer are 389 conveyed to allow pipelining at the egress bridge to an 802.6 390 subnetwork. Specifically, the Common PDU Header contains the 391 BAsize field, which contains the length of the PDU. If this field 392 is not available to the egress 802.6 bridge, then that bridge 393 cannot begin to transmit the segmented PDU until it has received 394 the entire PDU, calculated the length, and inserted the length 395 into the BAsize field. If the field is available, the egress 396 802.6 bridge can extract the length from the BAsize field of the 397 Common PDU Header, insert it into the corresponding field of the 398 first segment, and immediately transmit the segment onto the 802.6 399 subnetwork. Thus, the bridge can begin transmitting the 802.6 PDU 400 before it has received the complete PDU. 402 Note that the Common PDU Header and Trailer of the encapsulated 403 frame should not be simply copied to the outgoing 802.6 subnetwork 404 because the encapsulated BEtag value may conflict with the 405 previous BEtag value transmitted by that bridge. 407 Payload Format for BPDUs 408 +-------------------------------+ 409 | LLC 0xAA-AA-03 | 410 +-------------------------------+ 411 | OUI 0x00-80-C2 | 412 +-------------------------------+ 413 | PID 0x00-0E | 414 +-------------------------------+ 415 | | 416 | BPDU as defined by | 417 | 802.1(d) or 802.1(g) | 418 | | 419 +-------------------------------+ 421 5. VC Based Multiplexing 423 In VC Based Multiplexing, the carried network interconnect protocol is 424 identified implicitly by the VC connecting the two ATM stations, i.e. 425 each protocol must be carried over a separate VC. There is therefore no 426 need to include explicit multiplexing information in the Payload of the 427 AAL5 CPCS-PDU. This results in minimal bandwidth and processing overhead. 429 As indicated above, the carried protocol can be either manually 430 configured or negotiated dynamically during call establishment using 431 signalling procedures. The signalling details will be defined later in 432 other RFCs when the relevant standards have become available. 434 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 436 5.1. VC Based Multiplexing of Routed Protocols 438 PDUs of routed protocols shall be carried as such in the Payload of the 439 AAL5 CPCS-PDU. The format of the AAL5 CPCS-PDU Payload field thus becomes: 441 Payload Format for Routed PDUs 442 +-------------------------------+ 443 | . | 444 | Carried PDU | 445 | (up to 2^16 - 1 octets) | 446 | . | 447 | . | 448 +-------------------------------+ 450 5.2. VC Based Multiplexing of Bridged Protocols 452 PDUs of bridged protocols shall be carried in the Payload of the AAL5 453 CPCS-PDU exactly as described in section 4.2 except that only the 454 fields after the PID field are included. The AAL5 CPCS-PDU Payload 455 field carrying a bridged PDU shall, therefore, have one of the 456 following formats. 458 Payload Format for Bridged Ethernet/802.3 PDUs 459 +-------------------------------+ 460 | PAD 0x00-00 | 461 +-------------------------------+ 462 | MAC destination address | 463 +-------------------------------+ 464 | | 465 | (remainder of MAC frame) | 466 | | 467 +-------------------------------+ 468 | LAN FCS (VC dependent option) | 469 +-------------------------------+ 471 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 473 Payload Format for Bridged 802.4/802.5/FDDI PDUs 474 +-------------------------------+ 475 | PAD 0x00-00-00 or 0x00-00-XX | 476 +-------------------------------+ 477 | Frame Control (1 octet) | 478 +-------------------------------+ 479 | MAC destination address | 480 +-------------------------------+ 481 | | 482 | (remainder of MAC frame) | 483 | | 484 +-------------------------------+ 485 | LAN FCS (VC dependent option) | 486 +-------------------------------+ 488 Note that the 802.5 Access Control (AC) field has no significance 489 outside the local 802.5 subnetwork. It can thus be regarded as 490 the last octet of the three octet PAD field, which in case of 491 802.5 can be set to any value (XX). 493 Payload Format for Bridged 802.6 PDUs 494 +---------------+---------------+ ------- 495 | Reserved | BEtag | Common 496 +---------------+---------------+ PDU 497 | BAsize | Header 498 +-------------------------------+ ------- 499 | MAC destination address | 500 +-------------------------------+ 501 | | 502 | (remainder of MAC frame) | 503 | | 504 +-------------------------------+ 505 | | 506 | Common PDU Trailer | 507 | | 508 +-------------------------------+ 510 Payload Format for BPDUs 511 +-------------------------------+ 512 | | 513 | BPDU as defined by | 514 | 802.1(d) or 802.1(g) | 515 | | 516 +-------------------------------+ 518 In case of Ethernet, 802.3, 802.4, 802.5, and FDDI PDUs the presense 519 or absence of the trailing LAN FCS shall be identified implicitly by 521 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 523 the VC, since the PID field is not included. PDUs with the LAN FCS 524 and PDUs without the LAN FCS are thus considered to belong to 525 different protocols even if the bridged media type would be the same. 527 6. Address Resolution 529 An ATM network provides VCs that form the basis for connections 530 between stations attached to it. A VC may also span over several ATM 531 networks in an "ATM internet" consisting of an arbitrary 532 concatenation of private ATM and public ATM networks. ATM VCs can be 533 establish either (semi)permanently by the operator of the ATM network 534 or dynamically by an ATM signalling protocol being defined by CCITT. 535 In either case, each VC is identified by a Virtual Path Identifier 536 (VPI) and a Virtual Channel Identifier (VCI). These identifiers have 537 only local significance at each ATM interface. 539 The support of multicasting in ATM networks is also presently under 540 study in CCITT. If an ATM network supports multicasting, a special 541 VPI/VCI pair can be used to indicate the sending of ATM cells to all 542 stations in a particular multicast group. An ATM station may use the 543 multicasting capability to dynamically resolve a protocol address to 544 a hardware address using the standard Address Resolution Protocol 545 (ARP) [7]. ARP packets are encapsulated within an LLC encoded CPCS- 546 PDU Payload field as described in section 4. The details of 547 multicast based address resolution will be described in a future RFC 548 when more information is available on the ATM multicast mechanism. 550 Multicast based address resolution will not be practical over large 551 public or private ATM networks. In such cases it might be possible 552 to apply a technique similar to "shortcut routing" [8] to augment the 553 address resolution process. Address resolution could also work using 554 a "well known" VC that connects to one or more address resolution 555 servers. Another possibility might be to use DNS to store both the 556 internet address and the physical ATM address of the destination. 557 Finally, as proposed in [9], an ATM network could support signalling 558 based on internet addresses in which case no address resolution would 559 be needed. Further elaboration of address resolution mechanisms is 560 outside the scope of this memo. 562 7. Bridging in an ATM Network 564 An ATM interface acting as a bridge must be able to flood, forward, 565 and filter bridged PDUs. 567 Flooding is performed by sending the PDU to all possible appropriate 568 destinations. In the ATM environment this means sending the PDU 569 through each relevant VC. This may be accomplished by explicitly 570 copying it to each VC or by using a multicast VC. 572 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 574 To forward a PDU, a bridge must be able to associate a destination 575 MAC address with a VC. It is unreasonable and perhaps impossible to 576 require bridges to statically configure an association of every 577 possible destination MAC address with a VC. Therefore, ATM bridges 578 must provide enough information to allow an ATM interface to 579 dynamically learn about foreign destinations beyond the set of ATM 580 stations. 582 To accomplish dynamic learning, a bridged PDU shall conform to the 583 encapsulation described within section 4. In this way, the receiving 584 ATM interface will know to look into the bridged PDU and learn the 585 association between foreign destination and an ATM station. 587 8. For Further Study 589 Due to incomplete standardization of ATM multicasting, addressing, 590 and signalling mechanisms, details related to the negotiation of the 591 multiplexing method as well as address resolution had to be left for 592 further study. 594 Acknowledgements 596 This document has evolved from RFCs [1] and [4] from which much of 597 the material has been adopted. Thanks to their authors T. Bradley, 598 C. Brown, A. Malis, D. Piscitello, and C. Lawrence. In addition, 599 the expertise of the ATM working group of the IETF has been 600 invaluable in completing the document. Special thanks Brian 601 Carpenter of CERN, Rao Cherukuri of IBM, Dan Grossman of Motorola, 602 Joel Halpern of Network Systems, Bob Hinden of Sun Mircosystems, and 603 Gary Kessler of MAN Technology Corporation for their detailed 604 contributions. 606 Security Considerations 608 Security issues are not addressed in this memo. 610 References 612 [1] Piscitello, D. and Lawrence, C., "The Transmission of IP 613 Datagrams over the SMDS Service". RFC 1209, Bell Communications 614 Research, March 1991. 616 [2] CCITT, "AAL Type 5, Draft Recommendation text for section 6 of 617 I.363". CCITT Study Group XVIII/8-5, Report of Rapporteur's 618 Meeting on AAL type 5, Annex 2, Copenhagen, 19-21 October, 1992. 620 [3] CCITT, "Draft Recommendation I.555". CCITT Study Group XVIII, 621 Working Party 2, TD 36, Annex 4, Geneva 8-19 June, 1992. 623 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 625 [4] Bradley, T., Brown, C., and Malis, A., "Multiprotocol 626 Interconnect over Frame Relay". RFC 1294, Wellfleet 627 Communications, Inc. and BBN Communications, January 1992. 629 [5] CCITT, "Draft text for Q.93B". CCITT Study Group XI, Working 630 Party XI/6, 23 September - 2 October, 1992. 632 [6] Information technology - Telecommunications and Information 633 Exchange Between Systems, "Protocol Identification in the 634 Network Layer". ISO/IEC TR 9577, October 1990. 636 [7] Plummer, David C., "An Ethernet Address Resolution Protocol". 637 RFC 826, Symbolics, Inc., November 1982. 639 [8] Tsuchiya, Paul, "Discovery and Routing over Large Public Data 640 Networks". Internet Draft, Bellcore, July 1992. 642 [9] Lyon, T., Liaw, F., and Romanow, A., "Network Layer Architecture 643 for ATM Networks". Internet Draft, Sun Microsystems, July 1992. 645 Appendix A. Multiprotocol Encapsulation over FRCS 647 I.555 defines a Frame Relaying Specific Convergence Sublayer (FRCS) 648 to be used on the top of the Common Part of the AAL for Frame 649 Relay/ATM interworking. The service offered by FRCS corresponds to 650 the Core service for Frame Relaying as described in I.233. 652 An FRCS-PDU consists of Q.922 Address field followed by Q.922 653 Information field. The Q.922 flags and the FCS are omitted, since 654 the corresponding functions are provided by the AAL. The figure 655 below shows an FRCS-PDU embedded in the Payload of an AAL5 CPCS-PDU. 657 FRCS-PDU in Payload of AAL5 CPCS-PDU 658 +-------------------------------+ ------- 659 | Q.922 Address Field | FRCS-PDU Header 660 | (2-4 octets) | 661 +-------------------------------+ ------- 662 | . | 663 | . | 664 | Q.922 Information field | FRCS-PDU Payload 665 | . | 666 | . | 667 +-------------------------------+ ------- 668 | AAL5 CPCS-PDU Trailer | 669 +-------------------------------+ 671 Routed and bridged PDUs are encapsulated inside the FRCS-PDU as 672 defined in RFC 1294. The Q.922 Information field starts with a Q.922 674 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 676 Control field followed by an optional Pad octet that is used to align 677 the remainder of the frame to a convenient boundary for the sender. 678 The protocol of the carried PDU is then identified by prefixing the 679 PDU by an ISO/CCITT Network Layer Protocol ID (NLPID). 681 In the particular case of an IP PDU, the NLPID is 0xCC and the FRCS- 682 PDU has the following format: 684 FRCS-PDU Format for Routed IP PDUs 685 +-------------------------------+ 686 | Q.922 Addr Field | 687 | (2 or 4 octets) | 688 +-------------------------------+ 689 | 0x03 (Q.922 Control) | 690 +-------------------------------+ 691 | NLPID 0xCC | 692 +-------------------------------+ 693 | . | 694 | IP PDU | 695 | (up to 2^16 - 5 octets) | 696 | . | 697 +-------------------------------+ 699 Note that according to RFC 1294 the Q.922 Address field shall be 700 either 2 or 4 octets, i.e., a 3 octet Address field is not supported. 702 In the particular case of a CLNP PDU, the NLPID is 0x81 and the 703 FRCS-PDU has the following format: 705 FRCS-PDU Format for Routed CLNP PDUs 706 +-------------------------------+ 707 | Q.922 Addr Field | 708 | (2 or 4 octets) | 709 +-------------------------------+ 710 | 0x03 (Q.922 Control) | 711 +-------------------------------+ 712 | NLPID 0x81 | 713 +-------------------------------+ 714 | . | 715 | Rest of CLNP PDU | 716 | (up to 2^16 - 5 octets) | 717 | . | 718 +-------------------------------+ 720 Note that in case of ISO protocols the NLPID field forms the first 721 octet of the PDU itself and shall thus not be repeated. 723 The above encapsulation applies only to those routed protocols that 725 RFC DRAFT Multiprotocol Interconnect over ATM AAL5 December 1992 727 have a unique NLPID assigned. For other routed protocols (and for 728 bridged protocols), it is necessary to provide another mechanism for 729 easy protocol identification. This can be achieved by using an NLPID 730 value 0x80 to indicate that an IEEE 802.1a SubNetwork Attachment 731 Point (SNAP) header follows. 733 See RFC 1294 for more details related to multiprotocol encapsulation 734 over FRCS. 736 Appendix B. List of Locally Assigned values of OUI 00-80-C2 738 with preserved FCS w/o preserved FCS Media 739 ------------------ ----------------- -------------- 740 0x00-01 0x00-07 802.3/Ethernet 741 0x00-02 0x00-08 802.4 742 0x00-03 0x00-09 802.5 743 0x00-04 0x00-0A FDDI 744 0x00-05 0x00-0B 802.6 745 0x00-0D Fragments 746 0x00-0E BPDUs 748 Appendix C. Partial List of NLPIDs 750 0x00 Null Network Layer or Inactive Set (not used with ATM) 751 0x80 SNAP 752 0x81 ISO CLNP 753 0x82 ISO ESIS 754 0x83 ISO ISIS 755 0xCC Internet IP 757 Author's Address 759 Juha Heinanen Telecom Finland, PO Box 228, SF-33101 Tampere, Finland 761 Phone: +358 49 500 958 763 Email: Juha.Heinanen@datanet.tele.fi