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'12' -- Possible downref: Non-RFC (?) normative reference: ref. '13' -- Possible downref: Non-RFC (?) normative reference: ref. '14' -- Possible downref: Non-RFC (?) normative reference: ref. '15' Summary: 14 errors (**), 0 flaws (~~), 8 warnings (==), 13 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Brown 3 INTERNET DRAFT Fore Systems, Inc. 4 Obsoletes: 1294, 1490 A. Malis 5 Cascade Communications Corp. 6 May 7, 1997 7 Expires November 7, 1997 9 Multiprotocol Interconnect over Frame Relay 11 Status of this Memo 13 This document is an Internet-Draft. Internet-Drafts are working 14 documents of the Internet Engineering Task Force (IETF), its areas, 15 and its working groups. Note that other groups may also distribute 16 working documents as Internet-Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as ``work in progress.'' 23 To learn the current status of any Internet-Draft, please check the 24 ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow 25 Directories on ds.internic.net (US East Coast), nic.nordu.net 26 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 27 Rim). 29 This draft specifies an IAB standards track protocol for the Internet 30 community, and requests discussion and suggestions for improvements. 31 Please refer to the current edition of the "IAB Official Protocol 32 Standards" for the standardization state and status of this protocol. 33 Distribution of this memo is unlimited. 35 Abstract 37 This memo describes an encapsulation method for carrying network 38 interconnect traffic over a Frame Relay backbone. It covers aspects 39 of both Bridging and Routing. 41 Systems with the ability to transfer both the encapsulation method 42 described in this document, and others must have a priori knowledge 43 of which virtual circuits will carry which encapsulation method and 44 this encapsulation must only be used over virtual circuits that have 45 been explicitly configured for its use. 47 Acknowledgments 49 This document could not have been completed without the support of 50 Terry Bradley of Avici Systems, Inc.. Comments and contributions 51 from many sources, especially those from Ray Samora of Proteon, Ken 52 Rehbehn of Visual Networks, Fred Baker and Charles Carvalho of Cisco 53 Systems, and Mostafa Sherif of AT&T have been incorporated into this 54 document. Special thanks to Dory Leifer of University of Michigan for 55 his contributions to the resolution of fragmentation issues (though 56 it was deleted in the final version) and Floyd Backes and Laura 57 Bridge of 3Com for their contributions to the bridging descriptions. 58 This document could not have been completed without the expertise of 59 the IP over Large Public Data Networks and the IP over NBMA working 60 groups of the IETF. 62 Modifications from RFC 1490 64 Some language changes were necessary to clarify RFC 1490. None of 65 these changes impacted the technical aspects of this document, but 66 were required to keep diagrams and language specific and consistent. 67 Specifics of these changes will not be listed here. Below are listed 68 those changes which were significant. 70 a) The requirement for stations to accept SNAP encapsulated protocols 71 for which a NLPID was available, was removed. RFC 1490 indicated 72 that, if a protocol, such as IP, had a designated NLPID value, it 73 must be used. Later the document required stations to accept a 74 SNAP encapsulated version of this same protocol. This is clearly 75 inconsistent. A compliant station must send and accept the NLPID 76 encapsulated version of such a protocol. It MAY accept the SNAP 77 encapsulation but should not be required to do so as these frames 78 are noncompliant. 80 b) Fragmentation was removed. To date there are no interoperable 81 implementations of the fragmentation algorithm presented in RFC 82 1490. Additionally, there have been several suggestions that the 83 proposed mechanisms are insufficient for some frame relay 84 applications. To this end, fragmentation was removed from this 85 document. Work will continue elsewhere on the fragmentation 86 issue. 88 c) The address resolution presented in RFC 1490 referred only to 89 PVC environments and is insufficient for SVC environments. 90 Therefore the section title was changed to reflect this. Further 91 work on SVC address resolution will take place in the ION working 92 group. 94 d) The encapsulation for Source Routing BPDUs was added, and the 95 lists in Appendix A were augmented. 97 e) The use of canonical and non-canonical MAC destination addresses 98 in the bridging encapsulations was clarified. 100 f) Explicit support for multiple IP addresses mapped to a single 101 Frame Relay DLCI. 103 1. Conventions and Acronyms 105 The following language conventions are used in the items of 106 specification in this document: 108 o Must, Shall or Mandatory -- the item is an absolute 109 requirement of the specification. 111 o Should or Recommended -- the item should generally be 112 followed for all but exceptional circumstances. 114 o May or Optional -- the item is truly optional and may be 115 followed or ignored according to the needs of the 116 implementor. 118 All drawings in this document are drawn with the left-most bit as the 119 high order bit for transmission. For example, the drawings might be 120 labeled as: 122 0 1 2 3 4 5 6 7 bits 123 +---+---+---+---+---+---+---+ 125 +---------------------------+ 126 | flag (7E hexadecimal) | 127 +---------------------------+ 128 | Q.922 Address* | 129 +-- --+ 130 | | 131 +---------------------------+ 132 : : 133 : : 134 +---------------------------+ 136 Drawings that would be too large to fit onto one page if each octet 137 were presented on a single line are drawn with two octets per line. 138 These are also drawn with the left-most bit as the high order bit for 139 transmission. There will be a "+" to distinguish between octets as 140 in the following example. 142 |--- octet one ---|--- octet two ---| 143 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 144 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 146 +--------------------------------------------+ 147 | Organizationally Unique | 148 +-- +--------------------+ 149 | Identifier | Protocol | 150 +-----------------------+--------------------+ 151 | Identifier | 152 +-----------------------+ 154 The following are common acronyms used throughout this document. 156 BECN - Backward Explicit Congestion Notification 157 BPDU - Bridge Protocol Data Unit 158 C/R - Command/Response bit 159 DCE - Data Communication Equipment 160 DE - Discard Eligibility bit 161 DTE - Data Terminal Equipment 162 FECN - Forward Explicit Congestion Notification 163 PDU - Protocol Data Unit 164 PTT - Postal Telephone & Telegraph 165 SNAP - Subnetwork Access Protocol 167 2. Introduction 169 The following discussion applies to those devices which serve as end 170 stations (DTEs) on a public or private Frame Relay network (for 171 example, provided by a common carrier or PTT. It will not discuss 172 the behavior of those stations that are considered a part of the 173 Frame Relay network (DCEs) other than to explain situations in which 174 the DTE must react. 176 The Frame Relay network provides a number of virtual circuits that 177 form the basis for connections between stations attached to the same 178 Frame Relay network. The resulting set of interconnected devices 179 forms a private Frame Relay group which may be either fully 180 interconnected with a complete "mesh" of virtual circuits, or only 181 partially interconnected. In either case, each virtual circuit is 182 uniquely identified at each Frame Relay interface by a Data Link 183 Connection Identifier (DLCI). In most circumstances, DLCIs have 184 strictly local significance at each Frame Relay interface. 186 The specifications in this document are intended to apply to both 187 switched and permanent virtual circuits. 189 3. Frame Format 191 All protocols must encapsulate their packets within a Q.922 Annex A 192 frame [1]. Additionally, frames shall contain information necessary 193 to identify the protocol carried within the protocol data unit (PDU), 194 thus allowing the receiver to properly process the incoming packet. 195 The format shall be as follows: 197 +---------------------------+ 198 | flag (7E hexadecimal) | 199 +---------------------------+ 200 | Q.922 Address* | 201 +-- --+ 202 | | 203 +---------------------------+ 204 | Control (UI = 0x03) | 205 +---------------------------+ 206 | Pad (when required) (0x00)| 207 +---------------------------+ 208 | NLPID | 209 +---------------------------+ 210 | . | 211 | . | 212 | . | 213 | Data | 214 | . | 215 | . | 216 +---------------------------+ 217 | Frame Check Sequence | 218 +-- . --+ 219 | (two octets) | 220 +---------------------------+ 221 | flag (7E hexadecimal) | 222 +---------------------------+ 224 * Q.922 addresses, as presently defined, are two octets and 225 contain a 10-bit DLCI. In some networks Q.922 addresses 226 may optionally be increased to three or four octets. 228 The control field is the Q.922 control field. The UI (0x03) value is 229 used unless it is negotiated otherwise. The use of XID (0xAF or 230 0xBF) is permitted and is discussed later. 232 The pad field is used to align the data portion (beyond the 233 encapsulation header) of the frame to a two octet boundary. If 234 present, the pad is a single octet and must have a value of zero. 235 Explicit directions of when to use the pad field are discussed later 236 in this document. 238 The Network Level Protocol ID (NLPID) field is administered by ISO 239 and the ITU. It contains values for many different protocols 240 including IP, CLNP, and IEEE Subnetwork Access Protocol (SNAP)[10]. 241 This field tells the receiver what encapsulation or what protocol 242 follows. Values for this field are defined in ISO/IEC TR 9577 [3]. A 243 NLPID value of 0x00 is defined within ISO/IEC TR 9577 as the Null 244 Network Layer or Inactive Set. Since it cannot be distinguished from 245 a pad field, and because it has no significance within the context of 246 this encapsulation scheme, a NLPID value of 0x00 is invalid under the 247 Frame Relay encapsulation. Appendix A contains a list of some of the 248 more commonly used NLPID values. 250 There is no commonly implemented minimum maximum frame size for Frame 251 Relay. A network must, however, support at least a 262 octet 252 maximum. Generally, the maximum will be greater than or equal to 253 1600 octets, but each Frame Relay provider will specify an 254 appropriate value for its network. A Frame Relay DTE, therefore, 255 must allow the maximum acceptable frame size to be configurable. 257 The minimum frame size allowed for Frame Relay is five octets between 258 the opening and closing flags assuming a two octet Q.922 address 259 field. This minimum increases to six octets for three octet Q.922 260 address and seven octets for the four octet Q.922 address format. 262 4. Interconnect Issues 264 There are two basic types of data packets that travel within the 265 Frame Relay network: routed packets and bridged packets. These 266 packets have distinct formats and therefore, must contain an 267 indicator that the destination may use to correctly interpret the 268 contents of the frame. This indicator is embedded within the NLPID 269 and SNAP header information. 271 For those protocols that do not have a NLPID already assigned, it is 272 necessary to provide a mechanism to allow easy protocol 273 identification. There is a NLPID value defined indicating the 274 presence of a SNAP header. 276 A SNAP header is of the form: 278 +--------------------------------------------+ 279 | Organizationally Unique | 280 +-- +--------------------+ 281 | Identifier | Protocol | 282 +-----------------------+--------------------+ 283 | Identifier | 284 +-----------------------+ 286 The three-octet Organizationally Unique Identifier (OUI) identifies 287 an organization which administers the meaning of the Protocol 288 Identifier (PID) which follows. Together they identify a distinct 289 protocol. Note that OUI 0x00-00-00 specifies that the following PID 290 is an Ethertype. 292 4.1. Routed Frames 294 Some protocols will have an assigned NLPID, but because the NLPID 295 numbering space is limited, not all protocols have specific NLPID 296 values assigned to them. When packets of such protocols are routed 297 over Frame Relay networks, they are sent using the NLPID 0x80 (which 298 indicates the presence of a SNAP header) followed by SNAP. If the 299 protocol has an Ethertype assigned, the OUI is 0x00-00-00 (which 300 indicates an Ethertype follows), and PID is the Ethertype of the 301 protocol in use. 303 When a SNAP header is present as described above, a one octet pad is 304 used to align the protocol data on a two octet boundary as shown 305 below. 307 Format of Routed Frames 308 with a SNAP Header 309 +-------------------------------+ 310 | Q.922 Address | 311 +---------------+---------------+ 312 | Control 0x03 | pad 0x00 | 313 +---------------+---------------+ 314 | NLPID 0x80 | Organization- | 315 +---------------+ | 316 | ally Unique Identifier (OUI) | 317 +-------------------------------+ 318 | Protocol Identifier (PID) | 319 +-------------------------------+ 320 | | 321 | Protocol Data | 322 | | 323 +-------------------------------+ 324 | FCS | 325 +-------------------------------+ 327 In the few cases when a protocol has an assigned NLPID (see Appendix 328 A), 48 bits can be saved using the format below: 330 Format of Routed NLPID Protocol 331 +-------------------------------+ 332 | Q.922 Address | 333 +---------------+---------------+ 334 | Control 0x03 | NLPID | 335 +---------------+---------------+ 336 | Protocol Data | 337 +-------------------------------+ 338 | FCS | 339 +-------------------------------+ 341 When using the NLPID encapsulation format as described above, the pad 342 octet is not used. 344 In the case of ISO protocols, the NLPID is considered to be the first 345 octet of the protocol data. It is unnecessary to repeat the NLPID in 346 this case. The single octet serves both as the demultiplexing value 347 and as part of the protocol data (refer to "Other Protocols over 348 Frame Relay for more details). Other protocols, such as IP, have a 349 NLPID defined (0xCC), but it is not part of the protocol itself. 351 Format of Routed IP Datagram 352 +-------------------------------+ 353 | Q.922 Address | 354 +---------------+---------------+ 355 | Control 0x03 | NLPID 0xCC | 356 +---------------+---------------+ 357 | IP Datagram | 358 +-------------------------------+ 359 | FCS | 360 +-------------------------------+ 362 4.2. Bridged Frames 364 The second type of Frame Relay traffic is bridged packets. These 365 packets are encapsulated using the NLPID value of 0x80 indicating 366 SNAP. As with other SNAP encapsulated protocols, there will be one 367 pad octet to align the data portion of the encapsulated frame. The 368 SNAP header which follows the NLPID identifies the format of the 369 bridged packet. The OUI value used for this encapsulation is the 370 802.1 organization code 0x00-80-C2. The PID portion of the SNAP 371 header (the two bytes immediately following the OUI) specifies the 372 form of the MAC header, which immediately follows the SNAP header. 373 Additionally, the PID indicates whether the original FCS is preserved 374 within the bridged frame. 376 As specified in RFC 1638 [4], non-canonical MAC destination addresses 377 are used for encapsulated IEEE 802.5 and FDDI frames, and canonical 378 MAC destination addresses are used for the remaining encapsulations 379 defined in this section. 381 The 802.1 organization has reserved the following values to be used 382 with Frame Relay: 384 PID Values for OUI 0x00-80-C2 386 with preserved FCS w/o preserved FCS Media 387 ------------------ ----------------- ---------------- 388 0x00-01 0x00-07 802.3/Ethernet 389 0x00-02 0x00-08 802.4 390 0x00-03 0x00-09 802.5 391 0x00-04 0x00-0A FDDI 392 0x00-0B 802.6 394 In addition, the PID value 0x00-0E, when used with OUI 0x00-80-C2, 395 identifies Bridge Protocol Data Units (BPDUs) as defined by 396 802.1(d) or 802.1(g) [12], and the PID value 0x00-0F identifies 397 Source Routing BPDUs. 399 A packet bridged over Frame Relay will, therefore, have one of the 400 following formats: 402 Format of Bridged Ethernet/802.3 Frame 403 +-------------------------------+ 404 | Q.922 Address | 405 +---------------+---------------+ 406 | Control 0x03 | pad 0x00 | 407 +---------------+---------------+ 408 | NLPID 0x80 | OUI 0x00 | 409 +---------------+ --+ 410 | OUI 0x80-C2 | 411 +-------------------------------+ 412 | PID 0x00-01 or 0x00-07 | 413 +-------------------------------+ 414 | MAC destination address | 415 : : 416 | | 417 +-------------------------------+ 418 | (remainder of MAC frame) | 419 +-------------------------------+ 420 | LAN FCS (if PID is 0x00-01) | 421 +-------------------------------+ 422 | FCS | 423 +-------------------------------+ 424 Format of Bridged 802.4 Frame 425 +-------------------------------+ 426 | Q.922 Address | 427 +---------------+---------------+ 428 | Control 0x03 | pad 0x00 | 429 +---------------+---------------+ 430 | NLPID 0x80 | OUI 0x00 | 431 +---------------+ --+ 432 | OUI 0x80-C2 | 433 +-------------------------------+ 434 | PID 0x00-02 or 0x00-08 | 435 +---------------+---------------+ 436 | pad 0x00 | Frame Control | 437 +---------------+---------------+ 438 | MAC destination address | 439 : : 440 | | 441 +-------------------------------+ 442 | (remainder of MAC frame) | 443 +-------------------------------+ 444 | LAN FCS (if PID is 0x00-02) | 445 +-------------------------------+ 446 | FCS | 447 +-------------------------------+ 448 Format of Bridged 802.5 Frame 449 +-------------------------------+ 450 | Q.922 Address | 451 +---------------+---------------+ 452 | Control 0x03 | pad 0x00 | 453 +---------------+---------------+ 454 | NLPID 0x80 | OUI 0x00 | 455 +---------------+ --+ 456 | OUI 0x80-C2 | 457 +-------------------------------+ 458 | PID 0x00-03 or 0x00-09 | 459 +---------------+---------------+ 460 | pad 0x00 | Frame Control | 461 +---------------+---------------+ 462 | MAC destination address | 463 : : 464 | | 465 +-------------------------------+ 466 | (remainder of MAC frame) | 467 +-------------------------------+ 468 | LAN FCS (if PID is 0x00-03) | 469 | | 470 +-------------------------------+ 471 | FCS | 472 +-------------------------------+ 473 Format of Bridged FDDI Frame 474 +-------------------------------+ 475 | Q.922 Address | 476 +---------------+---------------+ 477 | Control 0x03 | pad 0x00 | 478 +---------------+---------------+ 479 | NLPID 0x80 | OUI 0x00 | 480 +---------------+ --+ 481 | OUI 0x80-C2 | 482 +-------------------------------+ 483 | PID 0x00-04 or 0x00-0A | 484 +---------------+---------------+ 485 | pad 0x00 | Frame Control | 486 +---------------+---------------+ 487 | MAC destination address | 488 : : 489 | | 490 +-------------------------------+ 491 | (remainder of MAC frame) | 492 +-------------------------------+ 493 | LAN FCS (if PID is 0x00-04) | 494 | | 495 +-------------------------------+ 496 | FCS | 497 +-------------------------------+ 498 Format of Bridged 802.6 Frame 499 +-------------------------------+ 500 | Q.922 Address | 501 +---------------+---------------+ 502 | Control 0x03 | pad 0x00 | 503 +---------------+---------------+ 504 | NLPID 0x80 | OUI 0x00 | 505 +---------------+ --+ 506 | OUI 0x80-C2 | 507 +-------------------------------+ 508 | PID 0x00-0B | 509 +---------------+---------------+ ------- 510 | Reserved | BEtag | Common 511 +---------------+---------------+ PDU 512 | BAsize | Header 513 +-------------------------------+ ------- 514 | MAC destination address | 515 : : 516 | | 517 +-------------------------------+ 518 | (remainder of MAC frame) | 519 +-------------------------------+ 520 | | 521 +- Common PDU Trailer -+ 522 | | 523 +-------------------------------+ 524 | FCS | 525 +-------------------------------+ 527 Note that in bridge 802.6 PDUs, there is only one choice for the PID 528 value, since the presence of a CRC-32 is indicated by the CIB bit in 529 the header of the MAC frame. 531 The Common Protocol Data Unit (CPDU) Header and Trailer are conveyed 532 to allow pipelining at the egress bridge to an 802.6 subnetwork. 533 Specifically, the CPDU Header contains the BAsize field, which 534 contains the length of the PDU. If this field is not available to 535 the egress 802.6 bridge, then that bridge cannot begin to transmit 536 the segmented PDU until it has received the entire PDU, calculated 537 the length, and inserted the length into the BAsize field. If the 538 field is available, the egress 802.6 bridge can extract the length 539 from the BAsize field of the Common PDU Header, insert it into the 540 corresponding field of the first segment, and immediately transmit 541 the segment onto the 802.6 subnetwork. Thus, the bridge can begin 542 transmitting the 802.6 PDU before it has received the complete PDU. 544 One should note that the Common PDU Header and Trailer of the 545 encapsulated frame should not be simply copied to the outgoing 802.6 546 subnetwork because the encapsulated BEtag value may conflict with the 547 previous BEtag value transmitted by that bridge. 549 Format of BPDU Frame 550 +-------------------------------+ 551 | Q.922 Address | 552 +-------------------------------+ 553 | Control 0x03 | 554 +-------------------------------+ 555 | PAD 0x00 | 556 +-------------------------------+ 557 | NLPID 0x80 | 558 +-------------------------------+ 559 | OUI 0x00-80-C2 | 560 +-------------------------------+ 561 | PID 0x00-0E | 562 +-------------------------------+ 563 | | 564 | BPDU as defined by | 565 | 802.1(d) or 802.1(g)[12] | 566 | | 567 +-------------------------------+ 568 | FCS | 569 +-------------------------------+ 571 Format of Source Routing BPDU Frame 572 +-------------------------------+ 573 | Q.922 Address | 574 +-------------------------------+ 575 | Control 0x03 | 576 +-------------------------------+ 577 | PAD 0x00 | 578 +-------------------------------+ 579 | NLPID 0x80 | 580 +-------------------------------+ 581 | OUI 0x00-80-C2 | 582 +-------------------------------+ 583 | PID 0x00-0F | 584 +-------------------------------+ 585 | | 586 | Source Routing BPDU | 587 | | 588 | | 589 +-------------------------------+ 590 | FCS | 591 +-------------------------------+ 593 5. Data Link Layer Parameter Negotiation 595 Frame Relay stations may choose to support the Exchange 596 Identification (XID) specified in Appendix III of Q.922 [1]. This 597 XID exchange allows the following parameters to be negotiated at the 598 initialization of a Frame Relay circuit: maximum frame size N201, 599 retransmission timer T200, and the maximum number of outstanding 600 Information (I) frames K. 602 A station may indicate its unwillingness to support acknowledged mode 603 multiple frame operation by specifying a value of zero for the 604 maximum window size, K. 606 If this exchange is not used, these values must be statically 607 configured by mutual agreement of Data Link Connection (DLC) 608 endpoints, or must be defaulted to the values specified in Section 609 5.9 of Q.922: 611 N201: 260 octets 613 K: 3 for a 16 Kbps link, 614 7 for a 64 Kbps link, 615 32 for a 384 Kbps link, 616 40 for a 1.536 Mbps or above link 618 T200: 1.5 seconds [see Q.922 for further details] 620 If a station supporting XID receives an XID frame, it shall respond 621 with an XID response. In processing an XID, if the remote maximum 622 frame size is smaller than the local maximum, the local system shall 623 reduce the maximum size it uses over this DLC to the remotely 624 specified value. Note that this shall be done before generating a 625 response XID. 627 The following diagram describes the use of XID to specify non-use of 628 acknowledged mode multiple frame operation. 630 Non-use of Acknowledged Mode Multiple Frame Operation 631 +---------------+ 632 | Address | (2,3 or 4 octets) 633 | | 634 +---------------+ 635 | Control 0xAF | 636 +---------------+ 637 | format 0x82 | 638 +---------------+ 639 | Group ID 0x80 | 640 +---------------+ 641 | Group Length | (2 octets) 642 | 0x00-0E | 643 +---------------+ 644 | 0x05 | PI = Frame Size (transmit) 645 +---------------+ 646 | 0x02 | PL = 2 647 +---------------+ 648 | Maximum | (2 octets) 649 | Frame Size | 650 +---------------+ 651 | 0x06 | PI = Frame Size (receive) 652 +---------------+ 653 | 0x02 | PL = 2 654 +---------------+ 655 | Maximum | (2 octets) 656 | Frame Size | 657 +---------------+ 658 | 0x07 | PI = Window Size 659 +---------------+ 660 | 0x01 | PL = 1 661 +---------------+ 662 | 0x00 | 663 +---------------+ 664 | 0x09 | PI = Retransmission Timer 665 +---------------+ 666 | 0x01 | PL = 1 667 +---------------+ 668 | 0x00 | 669 +---------------+ 670 | FCS | (2 octets) 671 | | 672 +---------------+ 674 6. Address Resolution for PVCs 676 Though address resolution is required in both PVC and SVC environments, this 677 document will only describe address resolution as it applies to PVCs. SVC 678 operation will be discussed in future documents. 680 There are situations in which a Frame Relay station may wish to 681 dynamically resolve a protocol address over PVCs. This may be 682 accomplished using the standard Address Resolution Protocol (ARP) [6] 683 encapsulated within a SNAP encoded Frame Relay packet as follows: 685 +-----------------------+-----------------------+ 686 | Q.922 Address | 687 +-----------------------+-----------------------+ 688 | Control (UI) 0x03 | pad 0x00 | 689 +-----------------------+-----------------------+ 690 | NLPID 0x80 | | SNAP Header 691 +-----------------------+ OUI 0x00-00-00 + Indicating 692 | | ARP 693 +-----------------------+-----------------------+ 694 | PID 0x0806 | 695 +-----------------------+-----------------------+ 696 | ARP packet | 697 | . | 698 | . | 699 | . | 700 +-----------------------+-----------------------+ 702 Where the ARP packet has the following format and values: 704 Data: 705 ar$hrd 16 bits Hardware type 706 ar$pro 16 bits Protocol type 707 ar$hln 8 bits Octet length of hardware address (n) 708 ar$pln 8 bits Octet length of protocol address (m) 709 ar$op 16 bits Operation code (request or reply) 710 ar$sha noctets source hardware address 711 ar$spa moctets source protocol address 712 ar$tha noctets target hardware address 713 ar$tpa moctets target protocol address 715 ar$hrd - assigned to Frame Relay is 15 decimal 716 (0x000F) [7]. 718 ar$pro - see assigned numbers for protocol ID number for 719 the protocol using ARP. (IP is 0x0800). 721 ar$hln - length in bytes of the address field (2, 3, or 4) 723 ar$pln - protocol address length is dependent on the 724 protocol (ar$pro) (for IP ar$pln is 4). 726 ar$op - 1 for request and 2 for reply. 728 ar$sha - Q.922 source hardware address, with C/R, FECN, 729 BECN, and DE set to zero. 731 ar$tha - Q.922 target hardware address, with C/R, FECN, 732 BECN, and DE set to zero. 734 Because DLCIs within most Frame Relay networks have only local 735 significance, an end station will not have a specific DLCI assigned 736 to itself. Therefore, such a station does not have an address to put 737 into the ARP request or reply. Fortunately, the Frame Relay network 738 does provide a method for obtaining the correct DLCIs. The solution 739 proposed for the locally addressed Frame Relay network below will 740 work equally well for a network where DLCIs have global significance. 742 The DLCI carried within the Frame Relay header is modified as it 743 traverses the network. When the packet arrives at its destination, 744 the DLCI has been set to the value that, from the standpoint of the 745 receiving station, corresponds to the sending station. For example, 746 in figure 1 below, if station A were to send a message to station B, 747 it would place DLCI 50 in the Frame Relay header. When station B 748 received this message, however, the DLCI would have been modified by 749 the network and would appear to B as DLCI 70. 751 ~~~~~~~~~~~~~~~ 752 ( ) 753 +-----+ ( ) +-----+ 754 | |-50------(--------------------)---------70-| | 755 | A | ( ) | B | 756 | |-60-----(---------+ ) | | 757 +-----+ ( | ) +-----+ 758 ( | ) 759 ( | ) <---Frame Relay 760 ~~~~~~~~~~~~~~~~ network 761 80 762 | 763 +-----+ 764 | | 765 | C | 766 | | 767 +-----+ 768 Figure 1 770 Lines between stations represent data link connections (DLCs). 771 The numbers indicate the local DLCI associated with each 772 connection. 774 DLCI to Q.922 Address Table for Figure 1 776 DLCI (decimal) Q.922 address (hex) 777 50 0x0C21 778 60 0x0CC1 779 70 0x1061 780 80 0x1401 782 For authoritative description of the correlation between DLCI and 783 Q.922 [1] addresses, the reader should consult Q.922. A summary 784 of the correlation is included here for convenience. The 785 translation between DLCI and Q.922 address is based on a two byte 786 address length using the Q.922 encoding format. The format is: 788 8 7 6 5 4 3 2 1 789 +------------------------+---+--+ 790 | DLCI (high order) |c/r|ea| 791 +--------------+----+----+---+--+ 792 | DLCI (lower) |FECN|BECN|DE |EA| 793 +--------------+----+----+---+--+ 795 For ARP and its variants, the FECN, BECN, C/R and DE bits are 796 assumed to be 0. 798 When an ARP message reaches a destination, all hardware addresses 799 will be invalid. The address found in the frame header will, 800 however, be correct. Though it does violate the purity of layering, 801 Frame Relay may use the address in the header as the sender hardware 802 address. It should also be noted that the target hardware address, 803 in both ARP request and reply, will also be invalid. This should not 804 cause problems since ARP does not rely on these fields and in fact, 805 an implementation may zero fill or ignore the target hardware address 806 field entirely. 808 As an example of how this address replacement scheme may work, refer 809 to figure 1. If station A (protocol address pA) wished to resolve 810 the address of station B (protocol address pB), it would format an 811 ARP request with the following values: 813 ARP request from A 814 ar$op 1 (request) 815 ar$sha unknown 816 ar$spa pA 817 ar$tha undefined 818 ar$tpa pB 820 Because station A will not have a source address associated with it, 821 the source hardware address field is not valid. Therefore, when the 822 ARP packet is received, it must extract the correct address from the 823 Frame Relay header and place it in the source hardware address field. 824 This way, the ARP request from A will become: 826 ARP request from A as modified by B 827 ar$op 1 (request) 828 ar$sha 0x1061 (DLCI 70) from Frame Relay header 829 ar$spa pA 830 ar$tha undefined 831 ar$tpa pB 833 Station B's ARP will then be able to store station A's protocol 834 address and Q.922 address association correctly. Next, station B 835 will form a reply message. Many implementations simply place the 836 source addresses from the ARP request into the target addresses and 837 then fills in the source addresses with its addresses. In this case, 838 the ARP response would be: 840 ARP response from B 841 ar$op 2 (response) 842 ar$sha unknown 843 ar$spa pB 844 ar$tha 0x1061 (DLCI 70) 845 ar$tpa pA 847 Again, the source hardware address is unknown and when the request is 848 received, station A will extract the address from the Frame Relay 849 header and place it in the source hardware address field. Therefore, 850 the response will become: 852 ARP response from B as modified by A 853 ar$op 2 (response) 854 ar$sha 0x0C21 (DLCI 50) 855 ar$spa pB 856 ar$tha 0x1061 (DLCI 70) 857 ar$tpa pA 859 Station A will now correctly recognize station B having protocol 860 address pB associated with Q.922 address 0x0C21 (DLCI 50). 862 Reverse ARP (RARP) [8] will work in exactly the same way. Still 863 using figure 1, if we assume station C is an address server, the 864 following RARP exchanges will occur: 866 RARP request from A RARP request as modified by C 867 ar$op 3 (RARP request) ar$op 3 (RARP request) 868 ar$sha unknown ar$sha 0x1401 (DLCI 80) 869 ar$spa undefined ar$spa undefined 870 ar$tha 0x0CC1 (DLCI 60) ar$tha 0x0CC1 (DLCI 60) 871 ar$tpa pC ar$tpa pC 873 Station C will then look up the protocol address corresponding to 874 Q.922 address 0x1401 (DLCI 80) and send the RARP response. 876 RARP response from C RARP response as modified by A 877 ar$op 4 (RARP response) ar$op 4 (RARP response) 878 ar$sha unknown ar$sha 0x0CC1 (DLCI 60) 879 ar$spa pC ar$spa pC 880 ar$tha 0x1401 (DLCI 80) ar$tha 0x1401 (DLCI 80) 881 ar$tpa pA ar$tpa pA 883 This means that the Frame Relay interface must only intervene in the 884 processing of incoming packets. 886 In the absence of suitable multicast, ARP may still be implemented. 887 To do this, the end station simply sends a copy of the ARP request 888 through each relevant DLC, thereby simulating a broadcast. 890 The use of multicast addresses in a Frame Relay environment is 891 presently under study by Frame Relay providers. At such time that 892 the issues surrounding multicasting are resolved, multicast 893 addressing may become useful in sending ARP requests and other 894 "broadcast" messages. 896 Because of the inefficiencies of broadcasting in a Frame Relay 897 environment, a new address resolution variation was developed. It is 898 called Inverse ARP [11] and describes a method for resolving a 899 protocol address when the hardware address is already known. In 900 Frame Relay's case, the known hardware address is the DLCI. Using 901 Inverse ARP for Frame Relay follows the same pattern as ARP and RARP 902 use. That is the source hardware address is inserted at the 903 receiving station. 905 In our example, station A may use Inverse ARP to discover the 906 protocol address of the station associated with its DLCI 50. The 907 Inverse ARP request would be as follows: 909 InARP Request from A (DLCI 50) 910 ar$op 8 (InARP request) 911 ar$sha unknown 912 ar$spa pA 913 ar$tha 0x0C21 (DLCI 50) 914 ar$tpa unknown 916 When Station B receives this packet, it will modify the source 917 hardware address with the Q.922 address from the Frame Relay header. 918 This way, the InARP request from A will become: 920 ar$op 8 (InARP request) 921 ar$sha 0x1061 922 ar$spa pA 923 ar$tha 0x0C21 924 ar$tpa unknown. 926 Station B will format an Inverse ARP response and send it to station 927 A as it would for any ARP message. 929 Stations must be able to map more than one IP address in the same IP 930 subnet (CIDR address prefix) to a particular DLCI on a Frame Relay 931 interface. This need arises from applications such as remote access, 932 where servers must act as ARP proxies for many dial-in clients, each 933 assigned a unique IP address while sharing bandwidth on the same DLC. 934 The dynamic nature of such applications result in frequent address 935 association changes with no affect on the DLC's status as reported by 936 Frame Relay PVC Status Signaling. 938 As with any other interface that utilizes ARP, stations may learn the 939 associations between IP addresses and DLCIs by processing unsolicited 940 ("gratuitous") ARP requests that arrive on the DLC. If one station 941 (perhaps a terminal server or remote access server) wishes to inform 942 its peer station on the other end of a Frame Relay DLC of a new 943 association between an IP address and that PVC, it should send an 944 unsolicited ARP request with the source IP address equal to the 945 destination IP address, and both set to the new IP address being used 946 on the DLC. This allows a station to "announce" new client 947 connections on a particular DLCI. The receiving station must store 948 the new association, and remove any old existing association, if 949 necessary, from any other DLCI on the interface. 951 7. IP over Frame Relay 953 Internet Protocol [9] (IP) datagrams sent over a Frame Relay network 954 conform to the encapsulation described previously. Within this 955 context, IP could be encapsulated in two different ways. 957 1. NLPID value indicating IP 959 +-----------------------+-----------------------+ 960 | Q.922 Address | 961 +-----------------------+-----------------------+ 962 | Control (UI) 0x03 | NLPID 0xCC | 963 +-----------------------+-----------------------+ 964 | IP packet | 965 | . | 966 | . | 967 | . | 968 +-----------------------+-----------------------+ 970 2. NLPID value indicating SNAP 972 +-----------------------+-----------------------+ 973 | Q.922 Address | 974 +-----------------------+-----------------------+ 975 | Control (UI) 0x03 | pad 0x00 | 976 +-----------------------+-----------------------+ 977 | NLPID 0x80 | | SNAP Header 978 +-----------------------+ OUI = 0x00-00-00 + Indicating 979 | | IP 980 +-----------------------+-----------------------+ 981 | PID 0x0800 | 982 +-----------------------+-----------------------+ 983 | IP packet | 984 | . | 985 | . | 986 | . | 987 +-----------------------+-----------------------+ 989 Although both of these encapsulations are supported under the given 990 definitions, it is advantageous to select only one method as the 991 appropriate mechanism for encapsulating IP data. Therefore, IP data 992 shall be encapsulated using the NLPID value of 0xCC indicating IP as 993 shown in option 1 above. This (option 1) is more efficient in 994 transmission (48 fewer bits), and is consistent with the 995 encapsulation of IP in X.25. 997 8. Other Protocols over Frame Relay 999 As with IP encapsulation, there are alternate ways to transmit 1000 various protocols within the scope of this definition. To eliminate 1001 the conflicts, the SNAP encapsulation is only used if no NLPID value 1002 is defined for the given protocol. 1004 As an example of how this works, ISO CLNP has a NLPID defined (0x81). 1005 Therefore, the NLPID field will indicate ISO CLNP and the data packet 1006 will follow immediately. The frame would be as follows: 1008 +---------------------------------------------+ 1009 | Q.922 Address | 1010 +----------------------+----------------------+ 1011 | Control (UI) 0x03 | NLPID 0x81 (CLNP) | 1012 +----------------------+----------------------+ 1013 | remainder of CLNP packet | 1014 | . | 1015 | . | 1016 +---------------------------------------------+ 1018 In this example, the NLPID is used to identify the data packet as 1019 CLNP. It is also considered part of the CLNP packet and as such, the 1020 NLPID should not be removed before being sent to the upper layers for 1021 processing. The NLPID is not duplicated. 1023 Other protocols, such as IPX, do not have a NLPID value defined. As 1024 mentioned above, IPX would be encapsulated using the SNAP header. In 1025 this case, the frame would be as follows: 1027 +---------------------------------------------+ 1028 | Q.922 Address | 1029 +----------------------+----------------------+ 1030 | Control (UI) 0x03 | pad 0x00 | 1031 +----------------------+----------------------+ 1032 | NLPID 0x80 (SNAP) | OUI - 0x00 00 00 | 1033 +----------------------+ | 1034 | | 1035 +---------------------------------------------+ 1036 | PID 0x8137 | 1037 +---------------------------------------------+ 1038 | IPX packet | 1039 | . | 1040 | . | 1041 +---------------------------------------------+ 1043 9. Bridging Model for Frame Relay 1045 The model for bridging in a Frame Relay network is identical to the 1046 model for remote bridging as described in IEEE P802.1g "Remote MAC 1047 Bridging" [13] and supports the concept of "Virtual Ports". Remote 1048 bridges with LAN ports receive and transmit MAC frames to and from 1049 the LANs to which they are attached. They may also receive and 1050 transmit MAC frames through virtual ports to and from other remote 1051 bridges. A virtual port may represent an abstraction of a remote 1052 bridge's point of access to one, two or more other remote bridges. 1054 Remote Bridges are statically configured as members of a remote 1055 bridge group by management. All members of a remote bridge group are 1056 connected by one or more virtual ports. The set of remote MAC bridges 1057 in a remote bridge group provides actual or *potential* MAC layer 1058 interconnection between a set of LANs and other remote bridge groups 1059 to which the remote bridges attach. 1061 In a Frame Relay network there must be a full mesh of Frame Relay VCs 1062 between bridges of a remote bridge group. If the frame relay network 1063 is not a full mesh, then the bridge network must be divided into 1064 multiple remote bridge groups. 1066 The frame relay VCs that interconnect the bridges of a remote bridge 1067 group may be combined or used individually to form one or more 1068 virtual bridge ports. This gives flexibility to treat the Frame 1069 Relay interface either as a single virtual bridge port, with all VCs 1070 in a group, or as a collection of bridge ports (individual or grouped 1071 VCs). 1073 When a single virtual bridge port provides the interconnectivity for 1074 all bridges of a given remote bridge group (i.e. all VCs are combined 1075 into a single virtual port), the standard Spanning Tree Algorithm may 1076 be used to determine the state of the virtual port. When more than 1077 one virtual port is configured within a given remote bridge group 1078 then an "extended" Spanning Tree Algorithm is required. Such an 1079 extended algorithm is defined in IEEE 802.1g [13]. The operation of 1080 this algorithm is such that a virtual port is only put into backup if 1081 there is a loop in the network external to the remote bridge group. 1083 The simplest bridge configuration for a Frame Relay network is the 1084 LAN view where all VCs are combined into a single virtual port. 1085 Frames, such as BPDUs, which would be broadcast on a LAN, must be 1086 flooded to each VC (or multicast if the service is developed for 1087 Frame Relay services). Flooding is performed by sending the packet to 1088 each relevant DLC associated with the Frame Relay interface. The VCs 1089 in this environment are generally invisible to the bridge. That is, 1090 the bridge sends a flooded frame to the frame relay interface and 1091 does not "see" that the frame is being forwarded to each VC 1092 individually. If all participating bridges are fully connected (full 1093 mesh) the standard Spanning Tree Algorithm will suffice in this 1094 configuration. 1096 Typically LAN bridges learn which interface a particular end station 1097 may be reached on by associating a MAC address with a bridge port. 1098 In a Frame Relay network configured for the LAN-like single bridge 1099 port (or any set of VCs grouped together to form a single bridge 1100 port), however, the bridge must not only associated a MAC address 1101 with a bridge port, but it must also associate it with a connection 1102 identifier. For Frame Relay networks, this connection identifier is 1103 a DLCI. It is unreasonable and perhaps impossible to require bridges 1104 to statically configure an association of every possible destination 1105 MAC address with a DLC. Therefore, Frame Relay LAN-modeled bridges 1106 must provide a mechanism to allow the Frame Relay bridge port to 1107 dynamically learn the associations. To accomplish this dynamic 1108 learning, a bridged packet shall conform to the encapsulation 1109 described within section 4.2. In this way, the receiving Frame Relay 1110 interface will know to look into the bridged packet to gather the 1111 appropriate information. 1113 A second Frame Relay bridging approach, the point-to-point view, 1114 treats each Frame Relay VC as a separate bridge port. Flooding and 1115 forwarding packets are significantly less complicated using the 1116 point-to-point approach because each bridge port has only one 1117 destination. There is no need to perform artificial flooding or to 1118 associate DLCIs with destination MAC addresses. Depending upon the 1119 interconnection of the VCs, an extended Spanning Tree algorithm may 1120 be required to permit all virtual ports to remain active as long as 1121 there are no true loops in the topology external to the remote bridge 1122 group. 1124 It is also possible to combine the LAN view and the point-to-point 1125 view on a single Frame Relay interface. To do this, certain VCs are 1126 combined to form a single virtual bridge port while other VCs are 1127 independent bridge ports. 1129 The following drawing illustrates the different possible bridging 1130 configurations. The dashed lines between boxes represent virtual 1131 circuits. 1133 +-------+ 1134 -------------------| B | 1135 / -------| | 1136 / / +-------+ 1137 / | 1138 +-------+/ \ +-------+ 1139 | A | -------| C | 1140 | |-----------------------| | 1141 +-------+\ +-------+ 1142 \ 1143 \ +-------+ 1144 \ | D | 1145 -------------------| | 1146 +-------+ 1148 Since there is less than a full mesh of VCs between the bridges in 1149 this example, the network must be divided into more than one remote 1150 bridge group. A reasonable configuration is to have bridges A, B, 1151 and C in one group, and have bridges A and D in a second. 1153 Configuration of the first bridge group combines the VCs 1154 interconnection the three bridges (A, B, and C) into a single virtual 1155 port. This is an example of the LAN view configuration. The second 1156 group would also be a single virtual port which simply connects 1157 bridges A and D. In this configuration the standard Spanning Tree 1158 Algorithm is sufficient to detect loops. 1160 An alternative configuration has three individual virtual ports in 1161 the first group corresponding to the VCs interconnecting bridges A, B 1162 and C. Since the application of the standard Spanning Tree Algorithm 1163 to this configuration would detect a loop in the topology, an 1164 extended Spanning Tree Algorithm would have to be used in order for 1165 all virtual ports to be kept active. Note that the second group 1166 would still consist of a single virtual port and the standard 1167 Spanning Tree Algorithm could be used in this group. 1169 Using the same drawing, one could construct a remote bridge scenario 1170 with three bridge groups. This would be an example of the point-to- 1171 point case. Here, the VC connecting A and B, the VC connecting A and 1172 C, and the VC connecting A and D are all bridge groups with a single 1173 virtual port. 1175 10. Appendix A 1177 List of Commonly Used NLPIDs 1179 0x00 Null Network Layer or Inactive Set 1180 (not used with Frame Relay) 1181 0x08 Q.933 [2] 1182 0x80 SNAP 1183 0x81 ISO CLNP 1184 0x82 ISO ESIS 1185 0x83 ISO ISIS 1186 0xB0 FRF.9 Data Compression [14] 1187 0xCC Internet IP 1189 List of PIDs of OUI 00-80-C2 1191 with preserved FCS w/o preserved FCS Media 1192 ------------------ ----------------- -------------- 1193 0x00-01 0x00-07 802.3/Ethernet 1194 0x00-02 0x00-08 802.4 1195 0x00-03 0x00-09 802.5 1196 0x00-04 0x00-0A FDDI 1197 0x00-0B 802.6 1198 0x00-0D Fragments 1199 0x00-0E BPDUs as defined by 1200 802.1(d) or 1201 802.1(g)[12]. 1202 0x00-0F Source Routing BPDUs 1204 11. Appendix B - Connection Oriented Procedures 1206 This Appendix contains additional information and instructions for 1207 using ITU Recommendation Q.933 [2] and other ITU standards for 1208 encapsulating data over frame relay. The information contained here 1209 is similar (and in some cases identical) to that found in Annex E to 1210 ITU Q.933. The authoritative source for this information is in Annex 1211 E and is repeated here only for convenience. 1213 The Network Level Protocol ID (NLPID) field is administered by ISO 1214 and the ITU. It contains values for many different protocols 1215 including IP, CLNP (ISO 8473), ITU Q.933, and ISO 8208. A figure 1216 summarizing a generic encapsulation technique over frame relay 1217 networks follows. The scheme's flexibility consists in the 1218 identification of multiple alternative to identify different 1219 protocols used either by 1221 - end-to-end systems or 1222 - LAN to LAN bride and routers or 1223 - a combination of the above. 1225 over frame relay networks. 1227 Q.922 control 1228 | 1229 | 1230 -------------------------------------------- 1231 | | 1232 UI I Frame 1233 | | 1234 --------------------------------- -------------- 1235 | 0x08 | 0x81 |0xCC | 0x80 |..01.... |..10.... 1236 | | | | | | 1237 Q.933 CLNP IP SNAP ISO 8208 ISO 8208 1238 | | Modulo 8 Modulo 128 1239 | | 1240 -------------------- OUI 1241 | | | 1242 L2 ID L3 ID ------- 1243 | User | | 1244 | Specified | | 1245 | 0x70 802.3 802.6 1246 | 1247 --------------------------- 1248 |0x51 |0x4E | |0x4C |0x50 1249 | | | | | 1250 7776 Q.922 Others 802.2 User 1251 Specified 1253 For those protocols which do not have a NLPID assigned or do not have 1254 a SNAP encapsulation, the NLPID value of 0x08, indicating ITU 1255 Recommendation Q.933 should be used. The four octets following the 1256 NLPID include both layer 2 and layer 3 protocol identification. The 1257 code points for most protocols are currently defined in ITU Q.933 low 1258 layer compatibility information element. The code points for "User 1259 Specified" are described in Frame Relay Forum FRF.3.1 [15]. There is 1260 also an escape for defining non-standard protocols. 1262 Format of Other Protocols 1263 using Q.933 NLPID 1264 +-------------------------------+ 1265 | Q.922 Address | 1266 +---------------+---------------+ 1267 | Control 0x03 | NLPID 0x08 | 1268 +---------------+---------------+ 1269 | L2 Protocol ID | 1270 | octet 1 | octet 2 | 1271 +---------------+---------------+ 1272 | L3 Protocol ID | 1273 | octet 1 | octet 2 | 1274 +---------------+---------------+ 1275 | Protocol Data | 1276 +-------------------------------+ 1277 | FCS | 1278 +-------------------------------+ 1280 ISO 8802/2 with user specified 1281 layer 3 1282 +-------------------------------+ 1283 | Q.922 Address | 1284 +---------------+---------------+ 1285 | Control 0x03 | NLPID 0x08 | 1286 +---------------+---------------+ 1287 | 802/2 0x4C | 0x80 | 1288 +---------------+---------------+ 1289 |User Spec. 0x70| Note 1 | 1290 +---------------+---------------+ 1291 | DSAP | SSAP | 1292 +---------------+---------------+ 1293 | Control (Note 2) | 1294 +-------------------------------+ 1295 | Remainder of PDU | 1296 +-------------------------------+ 1297 | FCS | 1298 +-------------------------------+ 1300 Note 1: Indicates the code point for user specified 1301 layer 3 protocol. 1303 Note 2: Control field is two octets for I-format and 1304 S-format frames (see 88002/2) 1306 Encapsulations using I frame (layer 2) 1307 The Q.922 I frame is for supporting layer 3 protocols which require 1308 acknowledged data link layer (e.g., ISO 8208). The C/R bit will be 1309 used for command and response indications. 1311 Format of ISO 8208 frame 1312 Modulo 8 1313 +-------------------------------+ 1314 | Q.922 Address | 1315 +---------------+---------------+ 1316 | ....Control I frame | 1317 +---------------+---------------+ 1318 | 8208 packet (modulo 8) Note 3 | 1319 | | 1320 +-------------------------------+ 1321 | FCS | 1322 +-------------------------------+ 1324 Note 3: First octet of 8208 packet also identifies the 1325 NLPID which is "..01....". 1327 Format of ISO 8208 frame 1328 Modulo 128 1329 +-------------------------------+ 1330 | Q.922 Address | 1331 +---------------+---------------+ 1332 | ....Control I frame | 1333 +---------------+---------------+ 1334 | 8208 packet (modulo 128) | 1335 | Note 4 | 1336 +-------------------------------+ 1337 | FCS | 1338 +-------------------------------+ 1340 Note 4: First octet of 8208 packet also identifies the 1341 NLPID which is "..10....". 1343 12. References 1345 [1] International Telecommunication Union, "ISDN Data Link Layer 1346 Specification for Frame Mode Bearer Services", ITU-T 1347 Recommendation Q.922, 1992. 1349 [2] International Telecommunication Union, "Signalling Specifications 1350 for Frame Mode Switched and Permanent Virtual Connection Control 1351 and Status Monitoring", ITU-T Recommendation Q.933, 1995. 1353 [3] Information technology - Telecommunications and Information 1354 Exchange between systems - Protocol Identification in the Network 1355 Layer, ISO/IEC TR 9577: 1992. 1357 [4] F. Baker, R. Bowen, "PPP Bridging Control Protocol (BCP)", RFC 1358 1638, ACC, June 1994. 1360 [5] International Standard, Information Processing Systems - Local 1361 Area Networks - Logical Link Control, ISO 8802-2, ANSI/IEEE, 1362 Second Edition, 1994-12-30. 1364 [6] Plummer, D., "An Ethernet Address Resolution Protocol - or - 1365 Converting Network Protocol Addresses to 48.bit Ethernet Address 1366 for Transmission on Ethernet Hardware", STD 37, RFC 826, MIT, 1367 November 1982. 1369 [7] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700, 1370 USC/Information Sciences Institute, October 1994 1372 [8] Finlayson, R., Mann, R., Mogul, J., and M. Theimer, "A Reverse 1373 Address Resolution Protocol", STD 38, RFC 903, Stanford 1374 University, June 1984. 1376 [9] Postel, J. and Reynolds, J., "A Standard for the Transmission of 1377 IP Datagrams over IEEE 802 Networks", RFC 1042, USC/Information 1378 Sciences Institute, February 1988. 1380 [10] IEEE, "IEEE Standard for Local and Metropolitan Area Networks: 1381 Overview and architecture", IEEE Standard 802-1990. 1383 [11] Bradley, T., and C. Brown, "Inverse Address Resolution Protocol", 1384 RFC 1293, Wellfleet Communications, Inc., January 1992. 1386 [12] IEEE, "IEEE Standard for Local and Metropolitan Networks: Media 1387 Access Control (MAC) Bridges", IEEE Standard 802.1D-1990. 1389 [13] PROJECT 802 - LOCAL AND METROPOLITAN AREA NETWORKS, Draft 1390 Standard 802.1G: Remote MAC Bridging, Draft 13, May 22, 1995. 1392 [14] Frame Relay Forum, "Data Compression Over Frame Relay 1393 Implementation Agreement", FRF.9, January 22, 1996. 1395 [15] Frame Relay Forum, "Multiprotocol Encapsulation Implementation 1396 Agreement", FRF.3.1, June 22, 1995. 1398 13. Security Considerations 1400 Security issues are not discussed in this memo. 1402 14. Authors' Addresses 1404 Caralyn Brown 1405 FORE Systems, Inc. 1406 1 Corporate Drive 1407 Andover, MA 01810 1408 Phone: (508) 689-2400 x133 1409 Email: cbrown@fore.com 1411 Andrew Malis 1412 Cascade Communications Corp. 1413 5 Carlisle Road 1414 Westford, MA 01886 1415 Phone: (508) 952-7414 1416 Email: malis@casc.com