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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) == Unused Reference: '5' is defined on line 1356, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. '1' -- Possible downref: Non-RFC (?) normative reference: ref. '2' -- Possible downref: Non-RFC (?) normative reference: ref. '3' ** Obsolete normative reference: RFC 1638 (ref. '4') (Obsoleted by RFC 2878) -- Possible downref: Non-RFC (?) normative reference: ref. '5' ** Obsolete normative reference: RFC 1700 (ref. '7') (Obsoleted by RFC 3232) -- Possible downref: Non-RFC (?) normative reference: ref. '10' ** Obsolete normative reference: RFC 1293 (ref. '11') (Obsoleted by RFC 2390) -- Possible downref: Non-RFC (?) normative reference: ref. '12' -- Possible downref: Non-RFC (?) normative reference: ref. '13' -- Possible downref: Non-RFC (?) normative reference: ref. '14' Summary: 14 errors (**), 0 flaws (~~), 8 warnings (==), 12 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group C. Brown 2 INTERNET DRAFT Cadia Networks 3 Obsoletes: 1294, 1490 A. Malis 4 Ascom Nexion, Inc. 5 November 14, 1996 6 Expires May 14, 1997 8 Multiprotocol Interconnect over Frame Relay 10 Status of this Memo 12 This document is an Internet-Draft. Internet-Drafts are working 13 documents of the Internet Engineering Task Force (IETF), its areas, 14 and its working groups. Note that other groups may also distribute 15 working documents as Internet-Drafts. 17 Internet-Drafts are draft documents valid for a maximum of six months 18 and may be updated, replaced, or obsoleted by other documents at any 19 time. It is inappropriate to use Internet-Drafts as reference 20 material or to cite them other than as ``work in progress.'' 22 To learn the current status of any Internet-Draft, please check the 23 ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow 24 Directories on ds.internic.net (US East Coast), nic.nordu.net 25 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 26 Rim). 28 This draft specifies an IAB standards track protocol for the Internet 29 community, and requests discussion and suggestions for improvements. 30 Please refer to the current edition of the "IAB Official Protocol 31 Standards" for the standardization state and status of this protocol. 32 Distribution of this memo is unlimited. 34 Abstract 36 This memo describes an encapsulation method for carrying network 37 interconnect traffic over a Frame Relay backbone. It covers aspects 38 of both Bridging and Routing. 40 Systems with the ability to transfer both the encapsulation method 41 described in this document, and others must have a priori knowledge 42 of which virtual circuits will carry which encapsulation method and 43 this encapsulation must only be used over virtual circuits that have 44 been explicitly configured for its use. 46 Acknowledgments 48 This document could not have been completed without the support of 49 Terry Bradley of Starburst Communications. Comments and 50 contributions from many sources, especially those from Ray Samora of 51 Proteon, Ken Rehbehn of Netrix Corporation, Fred Baker and Charles 52 Carvalho of Cisco Systems and Mostafa Sherif of AT&T have been 53 incorporated into this document. Special thanks to Dory Leifer of 54 University of Michigan for his contributions to the resolution of 55 fragmentation issues (though it was deleted in the final version) and 56 Floyd Backes and Laura Bridge of 3Com for their contributions to the 57 bridging descriptions. This document could not have been completed 58 without the expertise of the IP over Large Public Data Networks and 59 the IP over NBMA working groups of the IETF. 61 Modifications from RFC 1490 63 Some language changes were necessary to clarify RFC 1490. None of 64 these changes impacted the technical aspects of this document, but 65 were required to keep diagrams and language specific and consistent. 66 Specifics of these changes will not be listed here. Below are listed 67 those changes which were significant. 69 a) The requirement for stations to accept SNAP encapsulated protocols 70 for which a NLPID was available, was removed. RFC 1490 indicated 71 that, if a protocol, such as IP, had a designated NLPID value, it 72 must be used. Later the document required stations to accept a 73 SNAP encapsulated version of this same protocol. This is clearly 74 inconsistent. A compliant station must send and accept the NLPID 75 encapsulated version of such a protocol. It MAY accept the SNAP 76 encapsulation but should not be required to do so as these frames 77 are noncompliant. 79 b) Fragmentation was removed. To date there are no interoperable 80 implementations of the fragmentation algorithm presented in RFC 81 1490. Additionally, there have been several suggestions that the 82 proposed mechanisms are insufficient for some frame relay 83 applications. To this end, fragmentation was removed from this 84 document. Work will continue elsewhere on the fragmentation 85 issue. 87 c) The address resolution presented in RFC 1490 referred only to 88 PVC environments and is insufficient for SVC environments. 89 Therefore the section title was changed to reflect this. Further 90 work on SVC address resolution will take place in the ION working 91 group. 93 d) The encapsulation for Source Routing BPDUs was added, and the 94 lists in Appendix A were augmented. 96 e) The use of canonical and non-canonical MAC destination addresses 97 in the bridging encapsulations was clarified. 99 f) Explicit support for multiple IP addresses mapped to a single 100 Frame Relay DLCI. 102 1. Conventions and Acronyms 104 The following language conventions are used in the items of 105 specification in this document: 107 o Must, Shall or Mandatory -- the item is an absolute 108 requirement of the specification. 110 o Should or Recommended -- the item should generally be 111 followed for all but exceptional circumstances. 113 o May or Optional -- the item is truly optional and may be 114 followed or ignored according to the needs of the 115 implementor. 117 All drawings in this document are drawn with the left-most bit as the 118 high order bit for transmission. For example, the drawings might be 119 labeled as: 121 0 1 2 3 4 5 6 7 bits 122 +---+---+---+---+---+---+---+ 124 +---------------------------+ 125 | flag (7E hexadecimal) | 126 +---------------------------+ 127 | Q.922 Address* | 128 +-- --+ 129 | | 130 +---------------------------+ 131 : : 132 : : 133 +---------------------------+ 135 Drawings that would be too large to fit onto one page if each octet 136 were presented on a single line are drawn with two octets per line. 137 These are also drawn with the left-most bit as the high order bit for 138 transmission. There will be a "+" to distinguish between octets as 139 in the following example. 141 |--- octet one ---|--- octet two ---| 142 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 143 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 145 +--------------------------------------------+ 146 | Organizationally Unique | 147 +-- +--------------------+ 148 | Identifier | Protocol | 149 +-----------------------+--------------------+ 150 | Identifier | 151 +-----------------------+ 153 The following are common acronyms used throughout this document. 155 BECN - Backward Explicit Congestion Notification 156 BPDU - Bridge Protocol Data Unit 157 C/R - Command/Response bit 158 DCE - Data Communication Equipment 159 DE - Discard Eligibility bit 160 DTE - Data Terminal Equipment 161 FECN - Forward Explicit Congestion Notification 162 PDU - Protocol Data Unit 163 PTT - Postal Telephone & Telegraph 164 SNAP - Subnetwork Access Protocol 166 2. Introduction 168 The following discussion applies to those devices which serve as end 169 stations (DTEs) on a public or private Frame Relay network (for 170 example, provided by a common carrier or PTT. It will not discuss 171 the behavior of those stations that are considered a part of the 172 Frame Relay network (DCEs) other than to explain situations in which 173 the DTE must react. 175 The Frame Relay network provides a number of virtual circuits that 176 form the basis for connections between stations attached to the same 177 Frame Relay network. The resulting set of interconnected devices 178 forms a private Frame Relay group which may be either fully 179 interconnected with a complete "mesh" of virtual circuits, or only 180 partially interconnected. In either case, each virtual circuit is 181 uniquely identified at each Frame Relay interface by a Data Link 182 Connection Identifier (DLCI). In most circumstances, DLCIs have 183 strictly local significance at each Frame Relay interface. 185 The specifications in this document are intended to apply to both 186 switched and permanent virtual circuits. 188 3. Frame Format 190 All protocols must encapsulate their packets within a Q.922 Annex A 191 frame [1,2]. Additionally, frames shall contain information 192 necessary to identify the protocol carried within the protocol data 193 unit (PDU), thus allowing the receiver to properly process the 194 incoming packet. The format shall be as follows: 196 +---------------------------+ 197 | flag (7E hexadecimal) | 198 +---------------------------+ 199 | Q.922 Address* | 200 +-- --+ 201 | | 202 +---------------------------+ 203 | Control (UI = 0x03) | 204 +---------------------------+ 205 | Pad (when required) (0x00)| 206 +---------------------------+ 207 | NLPID | 208 +---------------------------+ 209 | . | 210 | . | 211 | . | 212 | Data | 213 | . | 214 | . | 215 +---------------------------+ 216 | Frame Check Sequence | 217 +-- . --+ 218 | (two octets) | 219 +---------------------------+ 220 | flag (7E hexadecimal) | 221 +---------------------------+ 223 * Q.922 addresses, as presently defined, are two octets and 224 contain a 10-bit DLCI. In some networks Q.922 addresses 225 may optionally be increased to three or four octets. 227 The control field is the Q.922 control field. The UI (0x03) value is 228 used unless it is negotiated otherwise. The use of XID (0xAF or 229 0xBF) is permitted and is discussed later. 231 The pad field is used to align the data portion (beyond the 232 encapsulation header) of the frame to a two octet boundary. If 233 present, the pad is a single octet and must have a value of zero. 234 Explicit directions of when to use the pad field are discussed later 235 in this document. 237 The Network Level Protocol ID (NLPID) field is administered by ISO 238 and the ITU. It contains values for many different protocols 239 including IP, CLNP, and IEEE Subnetwork Access Protocol (SNAP)[10]. 240 This field tells the receiver what encapsulation or what protocol 241 follows. Values for this field are defined in ISO/IEC TR 9577 [3]. A 242 NLPID value of 0x00 is defined within ISO/IEC TR 9577 as the Null 243 Network Layer or Inactive Set. Since it cannot be distinguished from 244 a pad field, and because it has no significance within the context of 245 this encapsulation scheme, a NLPID value of 0x00 is invalid under the 246 Frame Relay encapsulation. Appendix A contains a list of some of the 247 more commonly used NLPID values. 249 There is no commonly implemented minimum maximum frame size for Frame 250 Relay. A network must, however, support at least a 262 octet 251 maximum. Generally, the maximum will be greater than or equal to 252 1600 octets, but each Frame Relay provider will specify an 253 appropriate value for its network. A Frame Relay DTE, therefore, 254 must allow the maximum acceptable frame size to be configurable. 256 The minimum frame size allowed for Frame Relay is five octets between 257 the opening and closing flags assuming a two octet Q.922 address 258 field. This minimum increases to six octets for three octet Q.922 259 address and seven octets for the four octet Q.922 address format. 261 4. Interconnect Issues 263 There are two basic types of data packets that travel within the 264 Frame Relay network: routed packets and bridged packets. These 265 packets have distinct formats and therefore, must contain an 266 indicator that the destination may use to correctly interpret the 267 contents of the frame. This indicator is embedded within the NLPID 268 and SNAP header information. 270 For those protocols that do not have a NLPID already assigned, it is 271 necessary to provide a mechanism to allow easy protocol 272 identification. There is a NLPID value defined indicating the 273 presence of a SNAP header. 275 A SNAP header is of the form: 277 +--------------------------------------------+ 278 | Organizationally Unique | 279 +-- +--------------------+ 280 | Identifier | Protocol | 281 +-----------------------+--------------------+ 282 | Identifier | 283 +-----------------------+ 285 The three-octet Organizationally Unique Identifier (OUI) identifies 286 an organization which administers the meaning of the Protocol 287 Identifier (PID) which follows. Together they identify a distinct 288 protocol. Note that OUI 0x00-00-00 specifies that the following PID 289 is an Ethertype. 291 4.1. Routed Frames 293 Some protocols will have an assigned NLPID, but because the NLPID 294 numbering space is limited, not all protocols have specific NLPID 295 values assigned to them. When packets of such protocols are routed 296 over Frame Relay networks, they are sent using the NLPID 0x80 (which 297 indicates the presence of a SNAP header) followed by SNAP. If the 298 protocol has an Ethertype assigned, the OUI is 0x00-00-00 (which 299 indicates an Ethertype follows), and PID is the Ethertype of the 300 protocol in use. 302 When a SNAP header is present as described above, a one octet pad is 303 used to align the protocol data on a two octet boundary as shown 304 below. 306 Format of Routed Frames 307 with a SNAP Header 308 +-------------------------------+ 309 | Q.922 Address | 310 +---------------+---------------+ 311 | Control 0x03 | pad 0x00 | 312 +---------------+---------------+ 313 | NLPID 0x80 | Organization- | 314 +---------------+ | 315 | ally Unique Identifier (OUI) | 316 +-------------------------------+ 317 | Protocol Identifier (PID) | 318 +-------------------------------+ 319 | | 320 | Protocol Data | 321 | | 322 +-------------------------------+ 323 | FCS | 324 +-------------------------------+ 326 In the few cases when a protocol has an assigned NLPID (see Appendix 327 A), 48 bits can be saved using the format below: 329 Format of Routed NLPID Protocol 330 +-------------------------------+ 331 | Q.922 Address | 332 +---------------+---------------+ 333 | Control 0x03 | NLPID | 334 +---------------+---------------+ 335 | Protocol Data | 336 +-------------------------------+ 337 | FCS | 338 +-------------------------------+ 340 When using the NLPID encapsulation format as described above, the pad 341 octet is not used. 343 In the case of ISO protocols, the NLPID is considered to be the first 344 octet of the protocol data. It is unnecessary to repeat the NLPID in 345 this case. The single octet serves both as the demultiplexing value 346 and as part of the protocol data (refer to "Other Protocols over 347 Frame Relay for more details). Other protocols, such as IP, have a 348 NLPID defined (0xCC), but it is not part of the protocol itself. 350 Format of Routed IP Datagram 351 +-------------------------------+ 352 | Q.922 Address | 353 +---------------+---------------+ 354 | Control 0x03 | NLPID 0xCC | 355 +---------------+---------------+ 356 | IP Datagram | 357 +-------------------------------+ 358 | FCS | 359 +-------------------------------+ 361 4.2. Bridged Frames 363 The second type of Frame Relay traffic is bridged packets. These 364 packets are encapsulated using the NLPID value of 0x80 indicating 365 SNAP. As with other SNAP encapsulated protocols, there will be one 366 pad octet to align the data portion of the encapsulated frame. The 367 SNAP header which follows the NLPID identifies the format of the 368 bridged packet. The OUI value used for this encapsulation is the 369 802.1 organization code 0x00-80-C2. The PID portion of the SNAP 370 header (the two bytes immediately following the OUI) specifies the 371 form of the MAC header, which immediately follows the SNAP header. 372 Additionally, the PID indicates whether the original FCS is preserved 373 within the bridged frame. 375 As specified in RFC 1638 [4], non-canonical MAC destination addresses 376 are used for encapsulated IEEE 802.5 and FDDI frames, and canonical 377 MAC destination addresses are used for the remaining encapsulations 378 defined in this section. 380 The 802.1 organization has reserved the following values to be used 381 with Frame Relay: 383 PID Values for OUI 0x00-80-C2 385 with preserved FCS w/o preserved FCS Media 386 ------------------ ----------------- ---------------- 387 0x00-01 0x00-07 802.3/Ethernet 388 0x00-02 0x00-08 802.4 389 0x00-03 0x00-09 802.5 390 0x00-04 0x00-0A FDDI 391 0x00-0B 802.6 393 In addition, the PID value 0x00-0E, when used with OUI 0x00-80-C2, 394 identifies Bridge Protocol Data Units (BPDUs) as defined by 395 802.1(d) or 802.1(g) [12], and the PID value 0x00-0F identifies 396 Source Routing BPDUs. 398 A packet bridged over Frame Relay will, therefore, have one of the 399 following formats: 401 Format of Bridged Ethernet/802.3 Frame 402 +-------------------------------+ 403 | Q.922 Address | 404 +---------------+---------------+ 405 | Control 0x03 | pad 0x00 | 406 +---------------+---------------+ 407 | NLPID 0x80 | OUI 0x00 | 408 +---------------+ --+ 409 | OUI 0x80-C2 | 410 +-------------------------------+ 411 | PID 0x00-01 or 0x00-07 | 412 +-------------------------------+ 413 | MAC destination address | 414 : : 415 | | 416 +-------------------------------+ 417 | (remainder of MAC frame) | 418 +-------------------------------+ 419 | LAN FCS (if PID is 0x00-01) | 420 +-------------------------------+ 421 | FCS | 422 +-------------------------------+ 423 Format of Bridged 802.4 Frame 424 +-------------------------------+ 425 | Q.922 Address | 426 +---------------+---------------+ 427 | Control 0x03 | pad 0x00 | 428 +---------------+---------------+ 429 | NLPID 0x80 | OUI 0x00 | 430 +---------------+ --+ 431 | OUI 0x80-C2 | 432 +-------------------------------+ 433 | PID 0x00-02 or 0x00-08 | 434 +---------------+---------------+ 435 | pad 0x00 | Frame Control | 436 +---------------+---------------+ 437 | MAC destination address | 438 : : 439 | | 440 +-------------------------------+ 441 | (remainder of MAC frame) | 442 +-------------------------------+ 443 | LAN FCS (if PID is 0x00-02) | 444 +-------------------------------+ 445 | FCS | 446 +-------------------------------+ 447 Format of Bridged 802.5 Frame 448 +-------------------------------+ 449 | Q.922 Address | 450 +---------------+---------------+ 451 | Control 0x03 | pad 0x00 | 452 +---------------+---------------+ 453 | NLPID 0x80 | OUI 0x00 | 454 +---------------+ --+ 455 | OUI 0x80-C2 | 456 +-------------------------------+ 457 | PID 0x00-03 or 0x00-09 | 458 +---------------+---------------+ 459 | pad 0x00 | Frame Control | 460 +---------------+---------------+ 461 | MAC destination address | 462 : : 463 | | 464 +-------------------------------+ 465 | (remainder of MAC frame) | 466 +-------------------------------+ 467 | LAN FCS (if PID is 0x00-03) | 468 | | 469 +-------------------------------+ 470 | FCS | 471 +-------------------------------+ 472 Format of Bridged FDDI Frame 473 +-------------------------------+ 474 | Q.922 Address | 475 +---------------+---------------+ 476 | Control 0x03 | pad 0x00 | 477 +---------------+---------------+ 478 | NLPID 0x80 | OUI 0x00 | 479 +---------------+ --+ 480 | OUI 0x80-C2 | 481 +-------------------------------+ 482 | PID 0x00-04 or 0x00-0A | 483 +---------------+---------------+ 484 | pad 0x00 | Frame Control | 485 +---------------+---------------+ 486 | MAC destination address | 487 : : 488 | | 489 +-------------------------------+ 490 | (remainder of MAC frame) | 491 +-------------------------------+ 492 | LAN FCS (if PID is 0x00-04) | 493 | | 494 +-------------------------------+ 495 | FCS | 496 +-------------------------------+ 497 Format of Bridged 802.6 Frame 498 +-------------------------------+ 499 | Q.922 Address | 500 +---------------+---------------+ 501 | Control 0x03 | pad 0x00 | 502 +---------------+---------------+ 503 | NLPID 0x80 | OUI 0x00 | 504 +---------------+ --+ 505 | OUI 0x80-C2 | 506 +-------------------------------+ 507 | PID 0x00-0B | 508 +---------------+---------------+ ------- 509 | Reserved | BEtag | Common 510 +---------------+---------------+ PDU 511 | BAsize | Header 512 +-------------------------------+ ------- 513 | MAC destination address | 514 : : 515 | | 516 +-------------------------------+ 517 | (remainder of MAC frame) | 518 +-------------------------------+ 519 | | 520 +- Common PDU Trailer -+ 521 | | 522 +-------------------------------+ 523 | FCS | 524 +-------------------------------+ 526 Note that in bridge 802.6 PDUs, there is only one choice for the PID 527 value, since the presence of a CRC-32 is indicated by the CIB bit in 528 the header of the MAC frame. 530 The Common Protocol Data Unit (CPDU) Header and Trailer are conveyed 531 to allow pipelining at the egress bridge to an 802.6 subnetwork. 532 Specifically, the CPDU Header contains the BAsize field, which 533 contains the length of the PDU. If this field is not available to 534 the egress 802.6 bridge, then that bridge cannot begin to transmit 535 the segmented PDU until it has received the entire PDU, calculated 536 the length, and inserted the length into the BAsize field. If the 537 field is available, the egress 802.6 bridge can extract the length 538 from the BAsize field of the Common PDU Header, insert it into the 539 corresponding field of the first segment, and immediately transmit 540 the segment onto the 802.6 subnetwork. Thus, the bridge can begin 541 transmitting the 802.6 PDU before it has received the complete PDU. 543 One should note that the Common PDU Header and Trailer of the 544 encapsulated frame should not be simply copied to the outgoing 802.6 545 subnetwork because the encapsulated BEtag value may conflict with the 546 previous BEtag value transmitted by that bridge. 548 Format of BPDU Frame 549 +-------------------------------+ 550 | Q.922 Address | 551 +-------------------------------+ 552 | Control 0x03 | 553 +-------------------------------+ 554 | PAD 0x00 | 555 +-------------------------------+ 556 | NLPID 0x80 | 557 +-------------------------------+ 558 | OUI 0x00-80-C2 | 559 +-------------------------------+ 560 | PID 0x00-0E | 561 +-------------------------------+ 562 | | 563 | BPDU as defined by | 564 | 802.1(d) or 802.1(g)[12] | 565 | | 566 +-------------------------------+ 567 | FCS | 568 +-------------------------------+ 570 Format of Source Routing BPDU Frame 571 +-------------------------------+ 572 | Q.922 Address | 573 +-------------------------------+ 574 | Control 0x03 | 575 +-------------------------------+ 576 | PAD 0x00 | 577 +-------------------------------+ 578 | NLPID 0x80 | 579 +-------------------------------+ 580 | OUI 0x00-80-C2 | 581 +-------------------------------+ 582 | PID 0x00-0F | 583 +-------------------------------+ 584 | | 585 | Source Routing BPDU | 586 | | 587 | | 588 +-------------------------------+ 589 | FCS | 590 +-------------------------------+ 592 5. Data Link Layer Parameter Negotiation 594 Frame Relay stations may choose to support the Exchange 595 Identification (XID) specified in Appendix III of Q.922 [1]. This 596 XID exchange allows the following parameters to be negotiated at the 597 initialization of a Frame Relay circuit: maximum frame size N201, 598 retransmission timer T200, and the maximum number of outstanding 599 Information (I) frames K. 601 A station may indicate its unwillingness to support acknowledged mode 602 multiple frame operation by specifying a value of zero for the 603 maximum window size, K. 605 If this exchange is not used, these values must be statically 606 configured by mutual agreement of Data Link Connection (DLC) 607 endpoints, or must be defaulted to the values specified in Section 608 5.9 of Q.922: 610 N201: 260 octets 612 K: 3 for a 16 Kbps link, 613 7 for a 64 Kbps link, 614 32 for a 384 Kbps link, 615 40 for a 1.536 Mbps or above link 617 T200: 1.5 seconds [see Q.922 for further details] 619 If a station supporting XID receives an XID frame, it shall respond 620 with an XID response. In processing an XID, if the remote maximum 621 frame size is smaller than the local maximum, the local system shall 622 reduce the maximum size it uses over this DLC to the remotely 623 specified value. Note that this shall be done before generating a 624 response XID. 626 The following diagram describes the use of XID to specify non-use of 627 acknowledged mode multiple frame operation. 629 Non-use of Acknowledged Mode Multiple Frame Operation 630 +---------------+ 631 | Address | (2,3 or 4 octets) 632 | | 633 +---------------+ 634 | Control 0xAF | 635 +---------------+ 636 | format 0x82 | 637 +---------------+ 638 | Group ID 0x80 | 639 +---------------+ 640 | Group Length | (2 octets) 641 | 0x00-0E | 642 +---------------+ 643 | 0x05 | PI = Frame Size (transmit) 644 +---------------+ 645 | 0x02 | PL = 2 646 +---------------+ 647 | Maximum | (2 octets) 648 | Frame Size | 649 +---------------+ 650 | 0x06 | PI = Frame Size (receive) 651 +---------------+ 652 | 0x02 | PL = 2 653 +---------------+ 654 | Maximum | (2 octets) 655 | Frame Size | 656 +---------------+ 657 | 0x07 | PI = Window Size 658 +---------------+ 659 | 0x01 | PL = 1 660 +---------------+ 661 | 0x00 | 662 +---------------+ 663 | 0x09 | PI = Retransmission Timer 664 +---------------+ 665 | 0x01 | PL = 1 666 +---------------+ 667 | 0x00 | 668 +---------------+ 669 | FCS | (2 octets) 670 | | 671 +---------------+ 673 6. Address Resolution for PVCs 675 Though address resolution is required in both PVC and SVC environments, this 676 document will only describe address resolution as it applies to PVCs. SVC 677 operation will be discussed in future documents. 679 There are situations in which a Frame Relay station may wish to 680 dynamically resolve a protocol address over PVCs. This may be 681 accomplished using the standard Address Resolution Protocol (ARP) [6] 682 encapsulated within a SNAP encoded Frame Relay packet as follows: 684 +-----------------------+-----------------------+ 685 | Q.922 Address | 686 +-----------------------+-----------------------+ 687 | Control (UI) 0x03 | pad 0x00 | 688 +-----------------------+-----------------------+ 689 | NLPID 0x80 | | SNAP Header 690 +-----------------------+ OUI 0x00-00-00 + Indicating 691 | | ARP 692 +-----------------------+-----------------------+ 693 | PID 0x0806 | 694 +-----------------------+-----------------------+ 695 | ARP packet | 696 | . | 697 | . | 698 | . | 699 +-----------------------+-----------------------+ 701 Where the ARP packet has the following format and values: 703 Data: 704 ar$hrd 16 bits Hardware type 705 ar$pro 16 bits Protocol type 706 ar$hln 8 bits Octet length of hardware address (n) 707 ar$pln 8 bits Octet length of protocol address (m) 708 ar$op 16 bits Operation code (request or reply) 709 ar$sha noctets source hardware address 710 ar$spa moctets source protocol address 711 ar$tha noctets target hardware address 712 ar$tpa moctets target protocol address 714 ar$hrd - assigned to Frame Relay is 15 decimal 715 (0x000F) [7]. 717 ar$pro - see assigned numbers for protocol ID number for 718 the protocol using ARP. (IP is 0x0800). 720 ar$hln - length in bytes of the address field (2, 3, or 4) 722 ar$pln - protocol address length is dependent on the 723 protocol (ar$pro) (for IP ar$pln is 4). 725 ar$op - 1 for request and 2 for reply. 727 ar$sha - Q.922 source hardware address, with C/R, FECN, 728 BECN, and DE set to zero. 730 ar$tha - Q.922 target hardware address, with C/R, FECN, 731 BECN, and DE set to zero. 733 Because DLCIs within most Frame Relay networks have only local 734 significance, an end station will not have a specific DLCI assigned 735 to itself. Therefore, such a station does not have an address to put 736 into the ARP request or reply. Fortunately, the Frame Relay network 737 does provide a method for obtaining the correct DLCIs. The solution 738 proposed for the locally addressed Frame Relay network below will 739 work equally well for a network where DLCIs have global significance. 741 The DLCI carried within the Frame Relay header is modified as it 742 traverses the network. When the packet arrives at its destination, 743 the DLCI has been set to the value that, from the standpoint of the 744 receiving station, corresponds to the sending station. For example, 745 in figure 1 below, if station A were to send a message to station B, 746 it would place DLCI 50 in the Frame Relay header. When station B 747 received this message, however, the DLCI would have been modified by 748 the network and would appear to B as DLCI 70. 750 ~~~~~~~~~~~~~~~ 751 ( ) 752 +-----+ ( ) +-----+ 753 | |-50------(--------------------)---------70-| | 754 | A | ( ) | B | 755 | |-60-----(---------+ ) | | 756 +-----+ ( | ) +-----+ 757 ( | ) 758 ( | ) <---Frame Relay 759 ~~~~~~~~~~~~~~~~ network 760 80 761 | 762 +-----+ 763 | | 764 | C | 765 | | 766 +-----+ 767 Figure 1 769 Lines between stations represent data link connections (DLCs). 770 The numbers indicate the local DLCI associated with each 771 connection. 773 DLCI to Q.922 Address Table for Figure 1 775 DLCI (decimal) Q.922 address (hex) 776 50 0x0C21 777 60 0x0CC1 778 70 0x1061 779 80 0x1401 781 For authoritative description of the correlation between DLCI and 782 Q.922 [1] addresses, the reader should consult Q.922. A summary 783 of the correlation is included here for convenience. The 784 translation between DLCI and Q.922 address is based on a two byte 785 address length using the Q.922 encoding format. The format is: 787 8 7 6 5 4 3 2 1 788 +------------------------+---+--+ 789 | DLCI (high order) |c/r|ea| 790 +--------------+----+----+---+--+ 791 | DLCI (lower) |FECN|BECN|DE |EA| 792 +--------------+----+----+---+--+ 794 For ARP and its variants, the FECN, BECN, C/R and DE bits are 795 assumed to be 0. 797 When an ARP message reaches a destination, all hardware addresses 798 will be invalid. The address found in the frame header will, 799 however, be correct. Though it does violate the purity of layering, 800 Frame Relay may use the address in the header as the sender hardware 801 address. It should also be noted that the target hardware address, 802 in both ARP request and reply, will also be invalid. This should not 803 cause problems since ARP does not rely on these fields and in fact, 804 an implementation may zero fill or ignore the target hardware address 805 field entirely. 807 As an example of how this address replacement scheme may work, refer 808 to figure 1. If station A (protocol address pA) wished to resolve 809 the address of station B (protocol address pB), it would format an 810 ARP request with the following values: 812 ARP request from A 813 ar$op 1 (request) 814 ar$sha unknown 815 ar$spa pA 816 ar$tha undefined 817 ar$tpa pB 819 Because station A will not have a source address associated with it, 820 the source hardware address field is not valid. Therefore, when the 821 ARP packet is received, it must extract the correct address from the 822 Frame Relay header and place it in the source hardware address field. 823 This way, the ARP request from A will become: 825 ARP request from A as modified by B 826 ar$op 1 (request) 827 ar$sha 0x1061 (DLCI 70) from Frame Relay header 828 ar$spa pA 829 ar$tha undefined 830 ar$tpa pB 832 Station B's ARP will then be able to store station A's protocol 833 address and Q.922 address association correctly. Next, station B 834 will form a reply message. Many implementations simply place the 835 source addresses from the ARP request into the target addresses and 836 then fills in the source addresses with its addresses. In this case, 837 the ARP response would be: 839 ARP response from B 840 ar$op 2 (response) 841 ar$sha unknown 842 ar$spa pB 843 ar$tha 0x1061 (DLCI 70) 844 ar$tpa pA 846 Again, the source hardware address is unknown and when the request is 847 received, station A will extract the address from the Frame Relay 848 header and place it in the source hardware address field. Therefore, 849 the response will become: 851 ARP response from B as modified by A 852 ar$op 2 (response) 853 ar$sha 0x0C21 (DLCI 50) 854 ar$spa pB 855 ar$tha 0x1061 (DLCI 70) 856 ar$tpa pA 858 Station A will now correctly recognize station B having protocol 859 address pB associated with Q.922 address 0x0C21 (DLCI 50). 861 Reverse ARP (RARP) [8] will work in exactly the same way. Still 862 using figure 1, if we assume station C is an address server, the 863 following RARP exchanges will occur: 865 RARP request from A RARP request as modified by C 866 ar$op 3 (RARP request) ar$op 3 (RARP request) 867 ar$sha unknown ar$sha 0x1401 (DLCI 80) 868 ar$spa undefined ar$spa undefined 869 ar$tha 0x0CC1 (DLCI 60) ar$tha 0x0CC1 (DLCI 60) 870 ar$tpa pC ar$tpa pC 872 Station C will then look up the protocol address corresponding to 873 Q.922 address 0x1401 (DLCI 80) and send the RARP response. 875 RARP response from C RARP response as modified by A 876 ar$op 4 (RARP response) ar$op 4 (RARP response) 877 ar$sha unknown ar$sha 0x0CC1 (DLCI 60) 878 ar$spa pC ar$spa pC 879 ar$tha 0x1401 (DLCI 80) ar$tha 0x1401 (DLCI 80) 880 ar$tpa pA ar$tpa pA 882 This means that the Frame Relay interface must only intervene in the 883 processing of incoming packets. 885 In the absence of suitable multicast, ARP may still be implemented. 886 To do this, the end station simply sends a copy of the ARP request 887 through each relevant DLC, thereby simulating a broadcast. 889 The use of multicast addresses in a Frame Relay environment is 890 presently under study by Frame Relay providers. At such time that 891 the issues surrounding multicasting are resolved, multicast 892 addressing may become useful in sending ARP requests and other 893 "broadcast" messages. 895 Because of the inefficiencies of broadcasting in a Frame Relay 896 environment, a new address resolution variation was developed. It is 897 called Inverse ARP [11] and describes a method for resolving a 898 protocol address when the hardware address is already known. In 899 Frame Relay's case, the known hardware address is the DLCI. Using 900 Inverse ARP for Frame Relay follows the same pattern as ARP and RARP 901 use. That is the source hardware address is inserted at the 902 receiving station. 904 In our example, station A may use Inverse ARP to discover the 905 protocol address of the station associated with its DLCI 50. The 906 Inverse ARP request would be as follows: 908 InARP Request from A (DLCI 50) 909 ar$op 8 (InARP request) 910 ar$sha unknown 911 ar$spa pA 912 ar$tha 0x0C21 (DLCI 50) 913 ar$tpa unknown 915 When Station B receives this packet, it will modify the source 916 hardware address with the Q.922 address from the Frame Relay header. 917 This way, the InARP request from A will become: 919 ar$op 8 (InARP request) 920 ar$sha 0x1061 921 ar$spa pA 922 ar$tha 0x0C21 923 ar$tpa unknown. 925 Station B will format an Inverse ARP response and send it to station 926 A as it would for any ARP message. 928 Stations must be able to map more than one IP address in the same IP 929 subnet (CIDR address prefix) to a particular DLCI on a Frame Relay 930 interface. This need arises from applications such as remote access, 931 where servers must act as ARP proxies for many dial-in clients, each 932 assigned a unique IP address while sharing bandwidth on the same DLC. 933 The dynamic nature of such applications result in frequent address 934 association changes with no affect on the DLC's status as reported by 935 Frame Relay PVC Status Signaling. 937 As with any other interface that utilizes ARP, stations may learn the 938 associations between IP addresses and DLCIs by processing unsolicited 939 ("gratuitous") ARP requests that arrive on the DLC. If one station 940 (perhaps a terminal server or remote access server) wishes to inform 941 its peer station on the other end of a Frame Relay DLC of a new 942 association between an IP address and that PVC, it should send an 943 unsolicited ARP request with the source IP address equal to the 944 destination IP address, and both set to the new IP address being used 945 on the DLC. This allows a station to "announce" new client 946 connections on a particular DLCI. The receiving station must store 947 the new association, and remove any old existing association, if 948 necessary, from any other DLCI on the interface. 950 7. IP over Frame Relay 952 Internet Protocol [9] (IP) datagrams sent over a Frame Relay network 953 conform to the encapsulation described previously. Within this 954 context, IP could be encapsulated in two different ways. 956 1. NLPID value indicating IP 958 +-----------------------+-----------------------+ 959 | Q.922 Address | 960 +-----------------------+-----------------------+ 961 | Control (UI) 0x03 | NLPID 0xCC | 962 +-----------------------+-----------------------+ 963 | IP packet | 964 | . | 965 | . | 966 | . | 967 +-----------------------+-----------------------+ 969 2. NLPID value indicating SNAP 971 +-----------------------+-----------------------+ 972 | Q.922 Address | 973 +-----------------------+-----------------------+ 974 | Control (UI) 0x03 | pad 0x00 | 975 +-----------------------+-----------------------+ 976 | NLPID 0x80 | | SNAP Header 977 +-----------------------+ OUI = 0x00-00-00 + Indicating 978 | | IP 979 +-----------------------+-----------------------+ 980 | PID 0x0800 | 981 +-----------------------+-----------------------+ 982 | IP packet | 983 | . | 984 | . | 985 | . | 986 +-----------------------+-----------------------+ 988 Although both of these encapsulations are supported under the given 989 definitions, it is advantageous to select only one method as the 990 appropriate mechanism for encapsulating IP data. Therefore, IP data 991 shall be encapsulated using the NLPID value of 0xCC indicating IP as 992 shown in option 1 above. This (option 1) is more efficient in 993 transmission (48 fewer bits), and is consistent with the 994 encapsulation of IP in X.25. 996 8. Other Protocols over Frame Relay 998 As with IP encapsulation, there are alternate ways to transmit 999 various protocols within the scope of this definition. To eliminate 1000 the conflicts, the SNAP encapsulation is only used if no NLPID value 1001 is defined for the given protocol. 1003 As an example of how this works, ISO CLNP has a NLPID defined (0x81). 1004 Therefore, the NLPID field will indicate ISO CLNP and the data packet 1005 will follow immediately. The frame would be as follows: 1007 +---------------------------------------------+ 1008 | Q.922 Address | 1009 +----------------------+----------------------+ 1010 | Control (UI) 0x03 | NLPID 0x81 (CLNP) | 1011 +----------------------+----------------------+ 1012 | remainder of CLNP packet | 1013 | . | 1014 | . | 1015 +---------------------------------------------+ 1017 In this example, the NLPID is used to identify the data packet as 1018 CLNP. It is also considered part of the CLNP packet and as such, the 1019 NLPID should not be removed before being sent to the upper layers for 1020 processing. The NLPID is not duplicated. 1022 Other protocols, such as IPX, do not have a NLPID value defined. As 1023 mentioned above, IPX would be encapsulated using the SNAP header. In 1024 this case, the frame would be as follows: 1026 +---------------------------------------------+ 1027 | Q.922 Address | 1028 +----------------------+----------------------+ 1029 | Control (UI) 0x03 | pad 0x00 | 1030 +----------------------+----------------------+ 1031 | NLPID 0x80 (SNAP) | OUI - 0x00 00 00 | 1032 +----------------------+ | 1033 | | 1034 +---------------------------------------------+ 1035 | PID 0x8137 | 1036 +---------------------------------------------+ 1037 | IPX packet | 1038 | . | 1039 | . | 1040 +---------------------------------------------+ 1042 9. Bridging Model for Frame Relay 1044 The model for bridging in a Frame Relay network is identical to the 1045 model for remote bridging as described in IEEE P802.1g "Remote MAC 1046 Bridging" [13] and supports the concept of "Virtual Ports". Remote 1047 bridges with LAN ports receive and transmit MAC frames to and from 1048 the LANs to which they are attached. They may also receive and 1049 transmit MAC frames through virtual ports to and from other remote 1050 bridges. A virtual port may represent an abstraction of a remote 1051 bridge's point of access to one, two or more other remote bridges. 1053 Remote Bridges are statically configured as members of a remote 1054 bridge group by management. All members of a remote bridge group are 1055 connected by one or more virtual ports. The set of remote MAC bridges 1056 in a remote bridge group provides actual or *potential* MAC layer 1057 interconnection between a set of LANs and other remote bridge groups 1058 to which the remote bridges attach. 1060 In a Frame Relay network there must be a full mesh of Frame Relay VCs 1061 between bridges of a remote bridge group. If the frame relay network 1062 is not a full mesh, then the bridge network must be divided into 1063 multiple remote bridge groups. 1065 The frame relay VCs that interconnect the bridges of a remote bridge 1066 group may be combined or used individually to form one or more 1067 virtual bridge ports. This gives flexibility to treat the Frame 1068 Relay interface either as a single virtual bridge port, with all VCs 1069 in a group, or as a collection of bridge ports (individual or grouped 1070 VCs). 1072 When a single virtual bridge port provides the interconnectivity for 1073 all bridges of a given remote bridge group (i.e. all VCs are combined 1074 into a single virtual port), the standard Spanning Tree Algorithm may 1075 be used to determine the state of the virtual port. When more than 1076 one virtual port is configured within a given remote bridge group 1077 then an "extended" Spanning Tree Algorithm is required. Such an 1078 extended algorithm is defined in IEEE 802.1g [13]. The operation of 1079 this algorithm is such that a virtual port is only put into backup if 1080 there is a loop in the network external to the remote bridge group. 1082 The simplest bridge configuration for a Frame Relay network is the 1083 LAN view where all VCs are combined into a single virtual port. 1084 Frames, such as BPDUs, which would be broadcast on a LAN, must be 1085 flooded to each VC (or multicast if the service is developed for 1086 Frame Relay services). Flooding is performed by sending the packet to 1087 each relevant DLC associated with the Frame Relay interface. The VCs 1088 in this environment are generally invisible to the bridge. That is, 1089 the bridge sends a flooded frame to the frame relay interface and 1090 does not "see" that the frame is being forwarded to each VC 1091 individually. If all participating bridges are fully connected (full 1092 mesh) the standard Spanning Tree Algorithm will suffice in this 1093 configuration. 1095 Typically LAN bridges learn which interface a particular end station 1096 may be reached on by associating a MAC address with a bridge port. 1097 In a Frame Relay network configured for the LAN-like single bridge 1098 port (or any set of VCs grouped together to form a single bridge 1099 port), however, the bridge must not only associated a MAC address 1100 with a bridge port, but it must also associate it with a connection 1101 identifier. For Frame Relay networks, this connection identifier is 1102 a DLCI. It is unreasonable and perhaps impossible to require bridges 1103 to statically configure an association of every possible destination 1104 MAC address with a DLC. Therefore, Frame Relay LAN-modeled bridges 1105 must provide a mechanism to allow the Frame Relay bridge port to 1106 dynamically learn the associations. To accomplish this dynamic 1107 learning, a bridged packet shall conform to the encapsulation 1108 described within section 7. In this way, the receiving Frame Relay 1109 interface will know to look into the bridged packet to gather the 1110 appropriate information. 1112 A second Frame Relay bridging approach, the point-to-point view, 1113 treats each Frame Relay VC as a separate bridge port. Flooding and 1114 forwarding packets are significantly less complicated using the 1115 point-to-point approach because each bridge port has only one 1116 destination. There is no need to perform artificial flooding or to 1117 associate DLCIs with destination MAC addresses. Depending upon the 1118 interconnection of the VCs, an extended Spanning Tree algorithm may 1119 be required to permit all virtual ports to remain active as long as 1120 there are no true loops in the topology external to the remote bridge 1121 group. 1123 It is also possible to combine the LAN view and the point-to-point 1124 view on a single Frame Relay interface. To do this, certain VCs are 1125 combined to form a single virtual bridge port while other VCs are 1126 independent bridge ports. 1128 The following drawing illustrates the different possible bridging 1129 configurations. The dashed lines between boxes represent virtual 1130 circuits. 1132 +-------+ 1133 -------------------| B | 1134 / -------| | 1135 / / +-------+ 1136 / | 1137 +-------+/ \ +-------+ 1138 | A | -------| C | 1139 | |-----------------------| | 1140 +-------+\ +-------+ 1141 \ 1142 \ +-------+ 1143 \ | D | 1144 -------------------| | 1145 +-------+ 1147 Since there is less than a full mesh of VCs between the bridges in 1148 this example, the network must be divided into more than one remote 1149 bridge group. A reasonable configuration is to have bridges A, B, 1150 and C in one group, and have bridges A and D in a second. 1152 Configuration of the first bridge group combines the VCs 1153 interconnection the three bridges (A, B, and C) into a single virtual 1154 port. This is an example of the LAN view configuration. The second 1155 group would also be a single virtual port which simply connects 1156 bridges A and D. In this configuration the standard Spanning Tree 1157 Algorithm is sufficient to detect loops. 1159 An alternative configuration has three individual virtual ports in 1160 the first group corresponding to the VCs interconnecting bridges A, B 1161 and C. Since the application of the standard Spanning Tree Algorithm 1162 to this configuration would detect a loop in the topology, an 1163 extended Spanning Tree Algorithm would have to be used in order for 1164 all virtual ports to be kept active. Note that the second group 1165 would still consist of a single virtual port and the standard 1166 Spanning Tree Algorithm could be used in this group. 1168 Using the same drawing, one could construct a remote bridge scenario 1169 with three bridge groups. This would be an example of the point-to- 1170 point case. Here, the VC connecting A and B, the VC connecting A and 1171 C, and the VC connecting A and D are all bridge groups with a single 1172 virtual port. 1174 10. Appendix A 1176 List of Commonly Used NLPIDs 1178 0x00 Null Network Layer or Inactive Set 1179 (not used with Frame Relay) 1180 0x80 SNAP 1181 0x81 ISO CLNP 1182 0x82 ISO ESIS 1183 0x83 ISO ISIS 1184 0xB0 FRF.9 Data Compression [14] 1185 0xCC Internet IP 1187 List of PIDs of OUI 00-80-C2 1189 with preserved FCS w/o preserved FCS Media 1190 ------------------ ----------------- -------------- 1191 0x00-01 0x00-07 802.3/Ethernet 1192 0x00-02 0x00-08 802.4 1193 0x00-03 0x00-09 802.5 1194 0x00-04 0x00-0A FDDI 1195 0x00-0B 802.6 1196 0x00-0D Fragments 1197 0x00-0E BPDUs as defined by 1198 802.1(d) or 1199 802.1(g)[12]. 1200 0x00-0F Source Routing BPDUs 1202 11. Appendix B - Connection Oriented Procedures 1204 This Appendix contains additional information and instructions for 1205 using ITU Q.933 and other ITU standards for encapsulating data over 1206 frame relay. The information contained here is similar (and in some 1207 cases identical) to that found in Annex F to ANSI T1.617A. The 1208 authoritative source for this information is in Annex F and is 1209 repeated here only for convenience. 1211 The Network Level Protocol ID (NLPID) field is administered by ISO 1212 and the ITU. It contains values for many different protocols 1213 including IP, CLNP (ISO 8473), ITU Q.933, and ISO 8208. A figure 1214 summarizing a generic encapsulation technique over frame relay 1215 networks follows. The scheme's flexibility consists in the 1216 identification of multiple alternative to identify different 1217 protocols used either by 1219 - end-to-end systems or 1220 - LAN to LAN bride and routers or 1221 - a combination of the above. 1223 over frame relay networks. 1225 Q.922 control 1226 | 1227 | 1228 -------------------------------------------- 1229 | | 1230 UI I Frame 1231 | | 1232 --------------------------------- -------------- 1233 | 0x08 | 0x81 |0xCC | 0x80 |..01.... |..10.... 1234 | | | | | | 1235 Q.933 CLNP IP SNAP ISO 8208 ISO 8208 1236 | | Modulo 8 Modulo 128 1237 | | 1238 -------------------- OUI 1239 | | | 1240 L2 ID L3 ID ------- 1241 | User | | 1242 | specified | | 1243 | 0x70 802.3 802.6 1244 | 1245 ------------------- 1246 |0x51 |0x4E | |0x4C 1247 | | | | 1248 7776 Q.922 Others 802.2 1250 For those protocols which do not have a NLPID assigned or do not have 1251 a SNAP encapsulation, the NLPID value of 0x08, indicating ITU 1252 Recommendation Q.933 should be used. The four octets following the 1253 NLPID include both layer 2 and layer 3 protocol identification. The 1254 code points for most protocols are currently defined in ANSI T1.617 1255 low layer compatibility information element. There is also an escape 1256 for defining non-standard protocols. 1258 Format of Other Protocols 1259 using Q.933 NLPID 1260 +-------------------------------+ 1261 | Q.922 Address | 1262 +---------------+---------------+ 1263 | Control 0x03 | NLPID 0x08 | 1264 +---------------+---------------+ 1265 | L2 Protocol ID | 1266 | octet 1 | octet 2 | 1267 +---------------+---------------+ 1268 | L3 Protocol ID | 1269 | octet 1 | octet 2 | 1270 +---------------+---------------+ 1271 | Protocol Data | 1272 +-------------------------------+ 1273 | FCS | 1274 +-------------------------------+ 1276 ISO 8802/2 with user specified 1277 layer 3 1278 +-------------------------------+ 1279 | Q.922 Address | 1280 +---------------+---------------+ 1281 | Control 0x03 | NLPID 0x08 | 1282 +---------------+---------------+ 1283 | 802/2 0x4C | 0x80 | 1284 +---------------+---------------+ 1285 |User Spec. 0x70| Note 1 | 1286 +---------------+---------------+ 1287 | DSAP | SSAP | 1288 +---------------+---------------+ 1289 | Control (Note 2) | 1290 +-------------------------------+ 1291 | Remainder of PDU | 1292 +-------------------------------+ 1293 | FCS | 1294 +-------------------------------+ 1296 Note 1: Indicates the code point for user specified 1297 layer 3 protocol. 1299 Note 2: Control field is two octets for I-format and 1300 S-format frames (see 88002/2) 1302 Encapsulations using I frame (layer 2) 1303 The Q.922 I frame is for supporting layer 3 protocols which require 1304 acknowledged data link layer (e.g., ISO 8208). The C/R bit will be 1305 used for command and response indications. 1307 Format of ISO 8208 frame 1308 Modulo 8 1309 +-------------------------------+ 1310 | Q.922 Address | 1311 +---------------+---------------+ 1312 | ....Control I frame | 1313 +---------------+---------------+ 1314 | 8208 packet (modulo 8) Note 3 | 1315 | | 1316 +-------------------------------+ 1317 | FCS | 1318 +-------------------------------+ 1320 Note 3: First octet of 8208 packet also identifies the 1321 NLPID which is "..01....". 1323 Format of ISO 8208 frame 1324 Modulo 128 1325 +-------------------------------+ 1326 | Q.922 Address | 1327 +---------------+---------------+ 1328 | ....Control I frame | 1329 +---------------+---------------+ 1330 | 8208 packet (modulo 128) | 1331 | Note 4 | 1332 +-------------------------------+ 1333 | FCS | 1334 +-------------------------------+ 1336 Note 4: First octet of 8208 packet also identifies the 1337 NLPID which is "..10....". 1339 12. References 1341 [1] International Telecommunication Union, "ISDN Data Link Layer 1342 Specification for Frame Mode Bearer Services", ITU-T 1343 Recommendation Q.922, 1992. 1345 [2] American National Standard For Telecommunications - Integrated 1346 Services Digital Network - Signaling Specification for Frame 1347 Relay Bearer Service for DSS 1, ANSI T1.617a, 1994. 1349 [3] Information technology - Telecommunications and Information 1350 Exchange between systems - Protocol Identification in the Network 1351 Layer, ISO/IEC TR 9577: 1992. 1353 [4] F. Baker, R. Bowen, "PPP Bridging Control Protocol (BCP)", RFC 1354 1638, ACC, June 1994. 1356 [5] International Standard, Information Processing Systems - Local 1357 Area Networks - Logical Link Control, ISO 8802-2, ANSI/IEEE, 1358 Second Edition, 1994-12-30. 1360 [6] Plummer, D., "An Ethernet Address Resolution Protocol - or - 1361 Converting Network Protocol Addresses to 48.bit Ethernet Address 1362 for Transmission on Ethernet Hardware", STD 37, RFC 826, MIT, 1363 November 1982. 1365 [7] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700, 1366 USC/Information Sciences Institute, October 1994 1368 [8] Finlayson, R., Mann, R., Mogul, J., and M. Theimer, "A Reverse 1369 Address Resolution Protocol", STD 38, RFC 903, Stanford 1370 University, June 1984. 1372 [9] Postel, J. and Reynolds, J., "A Standard for the Transmission of 1373 IP Datagrams over IEEE 802 Networks", RFC 1042, USC/Information 1374 Sciences Institute, February 1988. 1376 [10] IEEE, "IEEE Standard for Local and Metropolitan Area Networks: 1377 Overview and architecture", IEEE Standard 802-1990. 1379 [11] Bradley, T., and C. Brown, "Inverse Address Resolution Protocol", 1380 RFC 1293, Wellfleet Communications, Inc., January 1992. 1382 [12] IEEE, "IEEE Standard for Local and Metropolitan Networks: Media 1383 Access Control (MAC) Bridges", IEEE Standard 802.1D-1990. 1385 [13] PROJECT 802 - LOCAL AND METROPOLITAN AREA NETWORKS, Draft 1386 Standard 802.1G: Remote MAC Bridging, Draft 13, May 22, 1995. 1388 [14] Frame Relay Forum, "Data Compression Over Frame Relay 1389 Implementation Agreement", FRF.9, January 22, 1996. 1391 13. Security Considerations 1393 Security issues are not discussed in this memo. 1395 14. Authors' Addresses 1397 Caralyn Brown 1398 Cadia Networks 1399 One Corporate Drive 1400 Andover, MA 01810 1401 USA 1403 Phone: +1 508 689 2400 x133 1404 Email: cbrown@cadia.com 1406 Andrew G. Malis 1407 Ascom Nexion, Inc. 1408 289 Great Road 1409 Acton, MA 01720 1410 USA 1412 Phone: +1 508 266 4522 1413 Email: malis@nexen.com