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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Engineering Task Force 2 INTERNET-DRAFT Authors 3 Transport Working Group J. Matousek 4 Category: Informational L. Ong 5 June 1998 Bay Networks 6 Expires: January 1999 8 Bay Networks SS7-Internet Access Signaling Protocol 9 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 19 months and may be updated, replaced, or obsoleted by other 20 documents 21 at any time. It is inappropriate to use Internet-Drafts as 22 reference material or to cite them other than as ``work in 23 progress.'' 25 To view the entire list of current Internet-Drafts, please check 26 the "1id-abstracts.txt" listing contained in the Internet-Drafts 27 Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net 28 (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au 29 (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu 30 (US West Coast). 32 Distribution of this document is unlimited. 34 Abstract 36 This memo describes the Bay Networks SS7 Access Signaling Protocol 37 (ASP). This protocol is used between an SS7-Internet Gateway and a 38 Remote Access Server/Network Access Server (NAS). The protocol 39 supports call setup and termination by both Gateway and Access 40 Server, and includes circuit management functions such as circuit 41 blocking and procedures for registration of the Access Server. 43 Table of Contents 45 1. Introduction.................................................2 46 2. References...................................................2 47 3. Basic Principles.............................................3 48 4. Layer 3 Protocol Messages....................................5 49 5. Call Establishment Messages..................................8 50 6. Call Clearing Messages......................................10 51 7. Miscellaneous Q.931 Control Messages........................12 52 8. Q.931 Messages with Global Call Reference...................12 53 9. Maintenance Messages........................................14 54 10.Information Elements........................................20 55 11.Example Message Sequences...................................36 56 12.Error Handling..............................................42 57 13.Timers......................................................42 58 14.State Diagrams..............................................42 59 15.Acknowledgements............................................42 60 16.Contact Information.........................................42 62 1. Introduction 64 This document specifies a protocol that is used between an SS7- 65 Internet Gateway device and a NAS in the Bay Networks' SS7-Internet 66 Gateway Architecture. The Gateway terminates standard Signaling 67 System 7 (SS7) protocol from a PSTN switch or Signal Transfer Point 68 (STP), and uses the Access Signaling Protocol (ASP) to communicate 69 with the NAS. 71 2. References 73 [1] ITU-T Recommendation Q.931 (1993), ISDN user-network interface 74 layer 3 specification for basic control 76 [2] ITU-T Recommendation Q.932 (1993), Generic procedures for the 77 control of ISDN supplementary services. 79 [3] Ulysses Black: ISDN and SS7 (Architecture for Digital Signaling 80 Networks) 82 [4] ITU-T Recommendation H.225.0 Media stream packetization and 83 synchronization on non-guaranteed quality of service LANs. 85 [5] ANSI T1.609-1990: Interworking between the ISDN User-Network 86 Interface Protocol and the SS7 ISUP 88 [6] CCITT Recommendation Q.699: Interworking between Digital 89 Subscriber Signaling System No. 1 and Signaling System No. 7 91 [7] TR 41459: ATT Network ISDN Primary Rate Interface 92 3. Basic Principles 94 The following diagram shows the use of the SS7 Gateway and the ASP 95 for interworking of SS7 and Internet. 97 ........................ ...... 98 . . . 99 . +------+ . . +-------+ 100 . SS7 | / | . SS7 . | SS7 | 101 . Network | STP |------------|Gateway| 102 . /| / | . . +-------+ 103 . / +------+ . . | 104 .........../.../........ . | 105 / / . A| I 106 __________ / / A-link . S| n 107 / / . P| t 108 / / . | e 109 +------+ +------+ . +-----+ r 110 | PSTN | | PSTN |-----TDM---------------| NAS |-------n 111 | SCP | |Switch|-----------------------| |Data e 112 +------+ +------+ Circuits . +-----+ t 113 . 114 . 116 Figure 2: SS7-Internet Interworking for Call Setup 118 The transport of ASP between the Gateway and the NAS uses IP. The 119 messaging defined in this document assumes reliable message 120 delivery between the Gateway and the NAS. 122 The ASP is modeled on the Digital Subscriber Signaling system 1 123 (DSS1) protocol that is defined in ITU-T specification Q.931, with 124 extensions to support additional functions required for the Gateway 125 interface. 127 - Q.931 is well understood and widely used 128 - the mapping from SS7 ISUP to Q.931 is documented in standards 129 - this allows easier standardization for interoperability 131 The protocol is extended using the Protocol Discriminator function 132 in Q.931 to define new messages and information elements, and can 133 be further extended using the same mechanism. 135 Some functions of Q.931, such as the overlap addressing function, 136 are not supported. 138 The ASP supports several maintenance procedures defined in SS7, 139 including: 141 - busying of trunks and channels 142 - graceful and abrupt shutdown of trunks 143 - execution of circuit continuity check requested by either the 144 far-end switch or the SS7 gateway, during call establishment and 145 due to operator request. 146 (NOTE: In the case where an incoming IAM indicates continuity check 147 required on a previous circuit, i.e., previous hop, the SS7 Gateway 148 will delay the SETUP message to the NAS until it receives the COT 149 indicating continuity check successful.) 151 3.1 Mapping of the Circuit Identification Code (CIC) 153 The Access Server will be configured to identify each interface by 154 a number, typically in the range 1-n where n is the number of 155 interfaces supported by the Access Server. The Access Server 157 registers with the Gateway, specifying the number of interfaces it 158 supports, and the Gateway uses internal configuration tables to 159 allow it to translate an interface number specified within the ASP 160 protocol into a Circuit Identification Code (CIC) as defined in 161 SS7. 163 For calls initiated by the NAS, the Gateway is responsible for 164 channel selection. If a Circuit Reservation Message (CRM) is 165 received from the SS7 network reserving a specific circuit, the 166 Gateway will generate the Circuit Reservation Acknowledgement (CRA) 167 and mark that circuit reserved so that it is not selected for 168 outgoing calls until released by the SS7 network. 170 3.2 Security 172 The SS7 gateway acts as a fire-wall between the SS7 networks and 173 the IP signaling network. Access Servers on the IP signaling 174 network do not have direct access to the SS7 network - the gateway 175 must proxy for all the required functionality. 177 Both incoming and outgoing calls (from the NAS perspective) will be 178 supported by the protocol. However, configuration option in the 179 gateway and in the NAS must be provided, which will allow the 180 system administrator to inhibit the placement of outgoing calls 181 (from the NAS into the PSTN network). 183 It is also assumed that the IP signaling network will be physically 184 separate from the NAS user traffic. The NAS needs to support two 185 Ethernet interfaces and must ensure that the IP traffic from the 186 user traffic Ethernet cannot be forwarded to the IP signaling 187 traffic Ethernet and vice versa. 189 3.3 Redundancy 191 The SS7 Gateway will be implemented either using high availability 192 fault tolerant hardware or using standby fully redundant gateways. 193 In the case of hot standby gateways, the gateways must continuously 194 synchronize their internal states on a call by call basis. The 195 NAS, during the registration process, provides information that 196 allows the current active gateway to consolidate its internal 197 states. 199 4. Layer 3 Protocol Messages 201 With reference to the Q.931 specification, the SS7 Gateway will 202 implement the network side and the NAS will implement the user side 203 of the Q.931 protocol. This document specifies when specific 204 messages are used in one direction only, or both directions and 205 when specific information elements are used. Only the Q.931 206 information elements which are applicable to PRI (not BRI), have 207 been specified. Information elements specific to ASP have also been 208 defined. 210 The following notation has been used in the tables below: 211 - Mandatory: the message must be supported by both the gateway and 212 the NAS 213 - Optional: the message must be supported by both gateway and NAS, 214 but the protocol allows that the message not be sent during 215 particular protocol exchange 216 - Not supported: neither the gateway nor the NAS will support the 217 message. 219 The following table shows the Q.931 connection control Call 220 Establishment messages and indicates whether ASP supports them. 222 +---------------------+--------------------+---------+---------+ 223 | | Support by the | Q.931 | Section | 224 | | Gateway and NAS | Ref. | | 225 +---------------------+--------------------+---------+---------+ 226 | ALERTING | Not supported (1) | 3.1.1 | N/A | 227 +---------------------+--------------------+---------+---------+ 228 | CALL PROCEEDING | Not supported | 3.1.2 | N/A | 229 +---------------------+--------------------+---------+---------+ 230 | CONNECT | Mandatory | 3.1.3 | 3.1 | 231 +---------------------+--------------------+---------+---------+ 232 | CONNECT ACKNOWLEDGE | Not supported | 3.1.4 | N/A | 233 +---------------------+--------------------+---------+---------+ 234 | PROGRESS | Not supported | 3.1.8 | N/A | 235 +---------------------+--------------------+---------+---------+ 236 | SETUP | Mandatory | 3.1.14 | 3.2 | 237 +---------------------+--------------------+---------+---------+ 238 | SETUP ACKNOWLEDGE | Not supported | 3.1.15 | N/A | 239 +---------------------+--------------------+---------+---------+ 241 Note: (1) It is superfluous because it is assumed that the gateway 242 automatically generates ACM in response to IAM and at the same time 243 forwards SETUP to the NAS. It then only needs CONNECT from the NAS 244 to generate ANM to the SS7 network. 246 Matousek, et al Informational [Page 5] 247 The following table shows the Q.931 Call information phase messages 248 and indicates whether ASP supports them. 250 +---------------------+--------------------+---------+---------+ 251 | | Support by the | Q.931 | Section | 252 | | Gateway and NAS | Ref | | 253 +---------------------+--------------------+---------+---------+ 254 | RESUME | Not supported | 3.1.11 | N/A | 255 +---------------------+--------------------+---------+---------+ 256 | RESUME ACKNOWLEDGE | Not supported | 3.1.12 | N/A | 257 +---------------------+--------------------+---------+---------+ 258 | RESUME REJECT | Not supported | 3.1.13 | N/A | 259 +---------------------+--------------------+---------+---------+ 260 | SUSPEND | Not supported | 3.1.18 | N/A | 261 +---------------------+--------------------+---------+---------+ 262 | SUSPEND ACKNOWLEDGE | Not supported | 3.1.19 | N/A | 263 +---------------------+--------------------+---------+---------+ 264 | SUSPEND REJECT | Not supported | 3.1.20 | N/A | 265 +---------------------+--------------------+---------+---------+ 267 The following table shows the Q.931 Call Clearing messages and 268 indicates whether ASP supports them. 270 +---------------------+--------------------+---------+---------+ 271 | | Support by the | Q.931 | Section | 272 | | Gateway and NAS | Ref | | 273 +---------------------+--------------------+---------+---------+ 274 | DISCONNECT (Note 1) | Optional | 3.1.5 | 6.1 | 275 +---------------------+--------------------+---------+---------+ 276 | RELEASE | Mandatory | 3.1.9 | 6.2 | 277 +---------------------+--------------------+---------+---------+ 278 | RELEASE COMPLETE | Mandatory | 3.1.10 | 6.2 | 279 +---------------------+--------------------+---------+---------+ 281 Note: 1. Both the NAS and the gateway should allow the other side 282 to start the call clearing sequence by using the RELEASE message, 283 and respond with RELEASE COMPLETE. 285 Matousek, et al Informational [Page 6] 286 The following table shows Miscellaneous Q.931 Connection control 287 messages and indicates whether ASP supports them. 289 +---------------------+--------------------+---------+---------+ 290 | | Support by the | Q.931 | Section | 291 | | Gateway and NAS | Ref | | 292 +---------------------+--------------------+---------+---------+ 293 | INFORMATION | Not supported | 3.1.6 | N/A | 294 +---------------------+--------------------+---------+---------+ 295 | NOTIFY | Not supported | 3.1.7 | N/A | 296 +---------------------+--------------------+---------+---------+ 297 | STATUS | Mandatory | 3.1.16 | 7.1 | 298 +---------------------+--------------------+---------+---------+ 299 | STATUS INQUIRY | Mandatory | 3.1.17 | 7.2 | 300 +---------------------+--------------------+---------+---------+ 302 The following table shows the Q.931 messages with global call 303 reference and indicate whether ASP supports them 305 +---------------------+--------------------+---------+---------+ 306 | | Support by the | Q.931 | Section | 307 | | Gateway and NAS | Ref | | 308 +---------------------+--------------------+---------+---------+ 309 | RESTART | Mandatory | 3.4.1 | 8.1 | 310 +---------------------+--------------------+---------+---------+ 311 | RESTART ACKNOWLEDGE | Mandatory | 3.4.2 | 8.2 | 312 +---------------------+--------------------+---------+---------+ 313 | STATUS | Mandatory | 3.4.3 | 8.3 | 314 +---------------------+--------------------+---------+---------+ 316 The following messages are extensions to the standard Q.931 message 317 set. They are sent with a different protocol discriminator (see 318 8.1). They are used to by the NAS to register its capability, its 319 interfaces and the state of each channel after an IP connection 320 between the NAS and the gateway is established. They are also used 321 by the NAS to report on state changes to an interface or a channel, 322 or by the gateway to request a state change of an interface or a 323 channel. 325 Matousek, et al Informational [Page 7] 326 +---------------------+--------------------+---------+---------+ 327 | | Support by the | Q.931 | Section | 328 | | Gateway and NAS | Ref | | 329 +---------------------+--------------------+---------+---------+ 330 | NAS STATUS | Mandatory | N/A | 9.1 | 331 +---------------------+--------------------+---------+---------+ 332 | NAS STATUS ACK | Mandatory | N/A | 9.2 | 333 +---------------------+--------------------+---------+---------+ 334 | INTERFACE STATUS | Mandatory | N/A | 9.3 | 335 +---------------------+--------------------+---------+---------+ 336 | INTERFACE STATUS ACK| Mandatory | N/A | 9.4 | 337 +---------------------+--------------------+---------+---------+ 338 | RESOURCE UPDATE | Mandatory | N/A | 9.5 | 339 +---------------------+--------------------+---------+---------+ 340 | RESOURCE UPDATE ACK | Mandatory | N/A | 9.6 | 341 +---------------------+--------------------+---------+---------+ 342 | SERVICE | Mandatory | N/A | 9.7 | 343 +---------------------+--------------------+---------+---------+ 344 | SERVICE ACK | Mandatory | N/A | 9.8 | 345 +---------------------+--------------------+---------+---------+ 346 | CONT CHECK RESULT | Mandatory | N/A | 9.9 | 347 +---------------------+--------------------+---------+---------+ 349 5. Call Establishment Messages 351 The following messages are used to establish a call. 353 5.1 CONNECT 355 This message is sent by the gateway to the NAS and by the NAS to 356 the gateway, in response to SETUP to indicate the acceptance of the 357 call. 358 +-----------------+----------+--------+-------+--------+ 359 | Information | Refer- | Type | Direc | Length | 360 | element | ence | | tion | | 361 +-----------------+----------+--------+-------+--------+ 362 | Protocol | 10.1 | M | both | 1 | 363 | discriminator | | | | | 364 +-----------------+----------+--------+-------+--------+ 365 | Call Reference | 10.2 | M | both | 3 | 366 +-----------------+----------+--------+-------+--------+ 367 | Message type | 10.3 | M | both | 1 | 368 +-----------------+----------+--------+-------+--------+ 369 | Channel ID | 10.6 | M | both | 2-* | 370 +-----------------+----------+--------+-------+--------+ 372 Matousek, et al Informational [Page 8] 373 3.2 SETUP 375 This message is sent by the gateway to the NAS and by the NAS to 376 the gateway to initiate a call. 377 +-----------------+----------+--------+-------+--------+ 378 | Information | Ref. | Type | Direc | Length | 379 | element | | | tion | | 380 +-----------------+----------+--------+-------+--------+ 381 | Protocol | 10.1 | M | both | 1 | 382 | discriminator | | | | | 383 +-----------------+----------+--------+-------+--------+ 384 | Call Reference | 10.2 | M | both | 3 | 385 +-----------------+----------+--------+-------+--------+ 386 | Message type | 10.3 | M | both | 1 | 387 +-----------------+----------+--------+-------+--------+ 388 | Bearer | 10.7 | M | both | 4-12 | 389 | Capability | | | | | 390 +-----------------+----------+--------+-------+--------+ 391 | Channel ID | 10.6 | O | both | 3-* | 392 | | |(note 1)| | | 393 +-----------------+----------+--------+-------+--------+ 394 | Calling party | 10.8 | O | both | 2-* | 395 | number | | | | | 396 +-----------------+----------+--------+-------+--------+ 397 | Calling party | 10.9 | O | both | 2-23 | 398 | subaddress | | | | | 399 +-----------------+----------+--------+-------+--------+ 400 | Called party | 10.10 | M | both | 2-* | 401 | number | | | | | 402 +-----------------+----------+--------+-------+--------+ 403 | Called party | 10.11 | O | both | 2-23 | 404 | subaddress | | | | | 405 +-----------------+----------+--------+-------+--------+ 406 | Transit network | 10.12 | O | NAS-> | 2-* | 407 | selection | |(note 3)| G/W | | 408 +-----------------+----------+--------+-------+--------+ 409 | Low layer | 10.13 | O | both | 2-18 | 410 | compatibility | |(note 4)| | | 411 +-----------------+----------+--------+-------+--------+ 412 | Shift to | 10.4 | O | G/W-> | 2-* | 413 | codeset 7 | |(note 2)| NAS | | 414 +-----------------+----------+--------+-------+--------+ 415 | Original dialed | 10.18 | O | G/W-> | 2-* | 416 | number | |(note 2)| NAS | | 417 +-----------------+----------+--------+-------+--------+ 419 NOTES 421 1) Mandatory in the gateway-NAS direction. Not included in the NAS 422 to gateway direction - the gateway will select a specific 423 channel and indicate that in the CONNECT message. 425 Matousek, et al Informational [Page 9] 426 2) Including by the gateway if this information was provided in the 427 IAM message, if number translation occurred due to Local Number 428 Portability requirements. 430 3) Included by the NAS to select a particular transit network (see 431 Annex C of Q.931). This Information Element will not be used in 432 the first release. 434 4) Included in the NAS to gateway direction when the NAS wants to 435 pass low layer compatibility information to the called user. 436 Included in the gateway to NAS direction if the calling user 437 included a Low layer compatibility information element in the 438 SETUP message 440 6. Call Clearing Messages 442 The following messages are used to tear down calls either in the 443 process of being established or already established. 445 6.1 DISCONNECT 447 The NAS or the gateway sends this message to indicate that the 448 equipment sending the message (the gateway or the NAS) wishes to 449 disconnect a particular call. 450 +-----------------+----------+--------+-------+--------+ 451 | Information | Refer- | Type | Direc | Length | 452 | element | ence | | tion | | 453 +-----------------+----------+--------+-------+--------+ 454 | Protocol | 10.1 | M | both | 1 | 455 | discriminator | | | | | 456 +-----------------+----------+--------+-------+--------+ 457 | Call Reference | 10.2 | M | both | 3 | 458 +-----------------+----------+--------+-------+--------+ 459 | Message type | 10.3 | M | both | 1 | 460 +-----------------+----------+--------+-------+--------+ 461 | Cause | 10.14 | M | both | 2-32 | 462 +-----------------+----------+--------+-------+--------+ 464 Matousek, et al Informational [Page 10] 465 6.2 RELEASE 467 The NAS or the gateway sends this message to indicate the receipt 468 of the DISCONNECT, has disconnected the channel (if any) and 469 intends to release the call reference when it receives RELEASE 470 COMPLETE. 472 +-----------------+----------+--------+-------+--------+ 473 | Information | Refer- | Type | Direc | Length | 474 | element | ence | | tion | | 475 +-----------------+----------+--------+-------+--------+ 476 | Protocol | 10.1 | M | both | 1 | 477 | discriminator | | | | | 478 +-----------------+----------+--------+-------+--------+ 479 | Call Reference | 10.2 | M | both | 3 | 480 +-----------------+----------+--------+-------+--------+ 481 | Message type | 10.3 | M | both | 1 | 482 +-----------------+----------+--------+-------+--------+ 483 | Cause | 10.14 | O | both | 2-32 | 484 | | |(note 1)| | | 485 +-----------------+----------+--------+-------+--------+ 487 Note 1: Mandatory if this is the first message when call clearing. 489 6.3 RELEASE COMPLETE 491 The NAS or the gateway sends this message to indicate that the 492 equipment sending the message (the gateway or the NAS) has released 493 the channel (if any) and call reference. The channel becomes 494 available for reuse and the receiving equipment shall release the 495 reference number. 496 +-----------------+----------+--------+-------+--------+ 497 | Information | Refer- | Type | Direc | Length | 498 | element | ence | | tion | | 499 +-----------------+----------+--------+-------+--------+ 500 | Protocol | 10.1 | M | both | 1 | 501 | discriminator | | | | | 502 +-----------------+----------+--------+-------+--------+ 503 | Call Reference | 10.2 | M | both | 3 | 504 +-----------------+----------+--------+-------+--------+ 505 | Message type | 10.3 | M | both | 1 | 506 +-----------------+----------+--------+-------+--------+ 507 | Cause | 10.14 | O | both | 2-32 | 508 | | |(note 1)| | | 509 +-----------------+----------+--------+-------+--------+ 511 Note 1: Mandatory if this is the first message when call clearing. 513 Matousek, et al Informational [Page 11] 514 7. Miscellaneous Q.931 Connection Control Messages 516 7.1 STATUS 518 The gateway or the NAS sends this message in response to the STATUS 519 ENQUIRY. This message is sent with the Call Reference specific to 520 the call. 521 +-----------------+----------+--------+-------+--------+ 522 | Information | Refer- | Type | Direc | Length | 523 | element | ence | | tion | | 524 +-----------------+----------+--------+-------+--------+ 525 | Protocol | 10.1 | M | both | 1 | 526 | discriminator | | | | | 527 +-----------------+----------+--------+-------+--------+ 528 | Call Reference | 10.2 | M | both | 3 | 529 +-----------------+----------+--------+-------+--------+ 530 | Message type | 10.3 | M | both | 1 | 531 +-----------------+----------+--------+-------+--------+ 532 | Cause | 10.14 | M | both | 4-32 | 533 +-----------------+----------+--------+-------+--------+ 534 | Call state | 10.15 | M | both | 3 | 535 +-----------------+----------+--------+-------+--------+ 537 7.2 STATUS ENQUIRY 539 In order to determine the state of a specific call the STATUS 540 ENQUIRY message may be sent at any time. It will solicit a STATUS 541 message from the peer. It is mandatory to respond to STATUS 542 ENQUIRY with STATUS. This message is sent with the Call Reference 543 specific to the call. 544 +-----------------+----------+--------+-------+--------+ 545 | Information | Refer- | Type | Direc | Length | 546 | element | ence | | tion | | 547 +-----------------+----------+--------+-------+--------+ 548 | Protocol | 10.1 | M | both | 1 | 549 | discriminator | | | | | 550 +-----------------+----------+--------+-------+--------+ 551 | Call Reference | 10.2 | M | both | 3 | 552 +-----------------+----------+--------+-------+--------+ 553 | Message type | 10.3 | M | both | 1 | 554 +-----------------+----------+--------+-------+--------+ 556 8. Q.931 Messages with Global Call Reference 558 The following messages with global call reference will be 559 supported. 561 8.1 RESTART 563 This message is sent by the NAS or by the gateway to request the 564 recipient to restart (i.e. return to an idle condition) the 565 indicated channel(s) or interface. Any calls established on this 566 channel or interface will be disconnected. 568 +-------------------+----------+--------+-------+--------+ 569 | Information | Refer- | Type | Direc | Length | 570 | element | ence | | tion | | 571 +-------------------+----------+--------+-------+--------+ 572 | Protocol | 10.1 | M | both | 1 | 573 | discriminator | | | | | 574 +-------------------+----------+--------+-------+--------+ 575 | Call Reference | 10.2 | M | both | 3 | 576 +-------------------+----------+--------+-------+--------+ 577 | Message type | 10.3 | M | both | 1 | 578 +-------------------+----------+--------+-------+--------+ 579 | Channel ID | 10.6 | M | both | 2-* | 580 +-------------------+----------+--------+-------+--------+ 581 | Restart Indicator | 10.16 | M | both | 3 | 582 +-------------------+----------+--------+-------+--------+ 584 8.2 RESTART ACKNOWLEDGE 586 This message is sent to acknowledge the receipt of the RESTART 587 message and to indicate that the requested restart is complete. 589 +-------------------+----------+--------+-------+--------+ 590 | Information | Refer- | Type | Direc | Length | 591 | element | ence | | tion | | 592 +-------------------+----------+--------+-------+--------+ 593 | Protocol | 10.1 | M | both | 1 | 594 | discriminator | | | | | 595 +-------------------+----------+--------+-------+--------+ 596 | Call Reference | 10.2 | M | both | 3 | 597 +-------------------+----------+--------+-------+--------+ 598 | Message type | 10.3 | M | both | 1 | 599 +-------------------+----------+--------+-------+--------+ 600 | Channel ID | 10.6 | M | both | 2-* | 601 +-------------------+----------+--------+-------+--------+ 602 | Restart Indicator | 10.16 | M | both | 3 | 603 +-------------------+----------+--------+-------+--------+ 605 8.3 STATUS 607 The NAS or the gateway sends this message at any time to 608 report certain error conditions listed in 10.14. In particular, 609 this message will be sent if the NAS or the gateway receives an 610 incorrectly formatted message, or a message which is not permitted 611 in a given state. 613 +-----------------+----------+--------+-------+--------+ 614 | Information | Refer- | Type | Direc | Length | 615 | element | ence | | tion | | 616 +-----------------+----------+--------+-------+--------+ 617 | Protocol | 10.1 | M | both | 1 | 618 | discriminator | | | | | 619 +-----------------+----------+--------+-------+--------+ 620 | Call Reference | 10.2 | M | both | 3 | 621 +-----------------+----------+--------+-------+--------+ 622 | Message type | 10.3 | M | both | 1 | 623 +-----------------+----------+--------+-------+--------+ 624 | Cause | 10.14 | M | both | 4-32 | 625 +-----------------+----------+--------+-------+--------+ 626 | Call state | 10.15 | M | both | 3 | 627 +-----------------+----------+--------+-------+--------+ 629 9. Maintenance Messages 631 The following messages were defined as an extension to the standard 632 Q.931 based messages. The protocol discriminator is used to 633 distinguish them from the standard set. 635 9.1 NAS STATUS 637 This message is sent by the NAS to register the fact that it is 638 operational and whether it is coming out of a cold or warm start. 639 It can also be used to indicate by the NAS that it wishes to close 640 the connection with the gateway. 641 The message will be sent using non-global Call Reference. 643 +-------------------+----------+--------+-------+--------+ 644 | Information | Refer- | Type | Direc | Length | 645 | element | ence | | tion | | 646 +-------------------+----------+--------+-------+--------+ 647 | Protocol | 10.1 | M | NAS-> | 1 | 648 | discriminator | | | G/W | | 649 +-------------------+----------+--------+-------+--------+ 650 | Call Reference | 10.2 | M | NAS-> | 3 | 651 | | | | G/W | | 652 +-------------------+----------+--------+-------+--------+ 653 | Message type | 10.3 | M | NAS-> | 1 | 654 | | | | G/W | | 655 +-------------------+----------+--------+-------+--------+ 656 | Shift to Codeset 7| 10.4 | M | NAS-> | 1 | 657 | | | | G/W | | 658 +-------------------+----------+--------+-------+--------+ 659 | NAS status info | 10.19 | M | NAS-> | 3 | 660 | | | | G/W | | 661 +-------------------+----------+--------+-------+--------+ 663 9.2 NAS STATUS ACK 665 This message is sent by the gateway to NAS in response to NAS 666 STATUS. It will also indicate whether the gateway will allow the 667 NAS to receive only or also generate calls using the Cause 668 Information Element. 670 This message will be sent using non-global Call Reference. 672 +-----------------+----------+--------+-------+--------+ 673 | Information | Refer- | Type | Direc | Length | 674 | element | ence | | tion | | 675 +-----------------+----------+--------+-------+--------+ 676 | Protocol | 10.1 | M | G/W-> | 1 | 677 | discriminator | | | NAS | | 678 +-----------------+----------+--------+-------+--------+ 679 | Call Reference | 10.2 | M | G/W-> | 3 | 680 | | | | NAS | | 681 +-----------------+----------+--------+-------+--------+ 682 | Message type | 10.3 | M | G/W-> | 1 | 683 | | | | NAS | | 684 +-----------------+----------+--------+-------+--------+ 685 | Cause | 10.14 | M | G/W-> | 2-32 | 686 | | | | NAS | | 687 +-----------------+----------+--------+-------+--------+ 689 9.3 INTERFACE STATUS 691 This message is sent by the NAS to the gateway to register the 692 available interfaces and to indicate the status of each channel on 693 that interface. Changes in the state of any interface or any 694 channel must be reported to the gateway using the SERVICE message. 695 Also, any call tear-down originated by NAS must be reported to the 696 gateway. 698 The gateway must process and respond to the INTERFACE STATUS 699 message before requesting any interface or channel state changes 700 using the SERVICE message. Once it responds to the INTERFACE STATUS 701 message, the gateway can also start originating and terminating 702 calls. 704 This message will use non-global Call Reference. 706 +-------------------+----------+--------+-------+--------+ 707 | Information | Refer- | Type | Direc | Length | 708 | element | ence | | tion | | 709 +-------------------+----------+--------+-------+--------+ 710 | Protocol | 10.1 | M | NAS-> | 1 | 711 | discriminator | | | G/W | | 712 +-------------------+----------+--------+-------+--------+ 713 | Call Reference | 10.2 | M | NAS-> | 3 | 714 | | | | G/W | | 715 +-------------------+----------+--------+-------+--------+ 716 | Message type | 10.3 | M | NAS-> | 1 | 717 | | | | G/W | | 718 +-------------------+----------+--------+-------+--------+ 719 | Shift to Codeset 7| 10.4 | M | NAS-> | 1 | 720 | | | | G/W | | 721 +-------------------+----------+--------+-------+--------+ 722 | Interface status | 10.21 | M | NAS-> | 17-21 | 723 | info | | | G/W | | 724 +-------------------+----------+--------+-------+--------+ 726 9.4 INTERFACE STATUS ACK 728 This message is sent by the Gateway in response to INTERFACE STATUS 729 message. The Cause Information Element indicates the 730 success/failure of the interface registration operation. 732 This response will use non-global Call Reference. 734 +-----------------+----------+--------+-------+--------+ 735 | Information | Refer- | Type | Direc | Length | 736 | element | ence | | tion | | 737 +-----------------+----------+--------+-------+--------+ 738 | Protocol | 10.1 | M | G/W-> | 1 | 739 | discriminator | | | NAS | | 740 +-----------------+----------+--------+-------+--------+ 741 | Call Reference | 10.2 | M | G/W-> | 3 | 742 | | | | NAS | | 743 +-----------------+----------+--------+-------+--------+ 744 | Message type | 10.3 | M | G/W-> | 1 | 745 | | | | NAS | | 746 +-----------------+----------+--------+-------+--------+ 747 | Cause | 10.14 | M | G/W-> | 2-32 | 748 | | | | NAS | | 749 +-----------------+----------+--------+-------+--------+ 751 9.5 RESOURCE UPDATE 753 This message is sent by the NAS to register the resources it 754 controls. The NAS will also send this message whenever the number 755 of resources has changed as a result of failure or administrator 756 action (e.g. modem failure). 758 The message will be sent using non-global Call Reference. 759 +-------------------+----------+--------+-------+--------+ 760 | Information | Refer- | Type | Direc | Length | 761 | element | ence | | tion | | 762 +-------------------+----------+--------+-------+--------+ 763 | Protocol | 10.1 | M | NAS-> | 1 | 764 | discriminator | | | G/W | | 765 +-------------------+----------+--------+-------+--------+ 766 | Call Reference | 10.2 | M | NAS-> | 3 | 767 | | | | G/W | | 768 +-------------------+----------+--------+-------+--------+ 769 | Message type | 10.3 | M | NAS-> | 1 | 770 | | | | G/W | | 771 +-------------------+----------+--------+-------+--------+ 772 | Shift to Codeset 7| 10.4 | M | NAS-> | 1 | 773 | | | | G/W | | 774 +-------------------+----------+--------+-------+--------+ 775 | NAS resource 1 | 10.20 | M | NAS-> | | 776 | (note 1) | | | G/W | | 777 +-------------------+----------+--------+-------+--------+ 778 | ... | | | | | 779 +-------------------+----------+--------+-------+--------+ 780 | NAS resource n | 10.20 | O | NAS-> | | 781 | | | | G/W | | 782 +-------------------+----------+--------+-------+--------+ 784 (1) This information element can be repeated 1 to n times. 786 9.6 RESOURCE UPDATE ACK 788 This message is sent by the gateway to NAS in response to RESOURCE 789 UPDATE. This message will be sent using non-global Call Reference. 791 +-----------------+----------+--------+-------+--------+ 792 | Information | Refer- | Type | Direc | Length | 793 | element | ence | | tion | | 794 +-----------------+----------+--------+-------+--------+ 795 | Protocol | 10.1 | M | G/W-> | 1 | 796 | discriminator | | | NAS | | 797 +-----------------+----------+--------+-------+--------+ 798 | Call Reference | 10.2 | M | G/W-> | 3 | 799 | | | | NAS | | 800 +-----------------+----------+--------+-------+--------+ 801 | Message type | 10.3 | M | G/W-> | 1 | 802 | | | | NAS | | 803 +-----------------+----------+--------+-------+--------+ 804 | Cause | 10.14 | M | G/W-> | 2-32 | 805 | | | | NAS | | 806 +-----------------+----------+--------+-------+--------+ 808 9.7 SERVICE 810 The gateway sends this message to request a change of the current 811 status of an interface or channel. The NAS sends this message to 812 report to the gateway the change in status of a particular 813 interface or channel. 815 This message might result in SS7 Blocking or Unblocking messages 816 to be sent to the switch. 818 +-----------------+----------+--------+-------+--------+ 819 | Information | Refer- | Type | Direc | Length | 820 | element | ence | | tion | | 821 +-----------------+----------+--------+-------+--------+ 822 | Protocol | 10.1 | M | both | 1 | 823 | discriminator | | | | | 824 +-----------------+----------+--------+-------+--------+ 825 | Call Reference | 10.2 | M | both | 3 | 826 +-----------------+----------+--------+-------+--------+ 827 | Message type | 10.3 | M | both | 1 | 828 +-----------------+----------+--------+-------+--------+ 829 | Channel ID | 10.6 | M | both | 3-6 | 830 +-----------------+----------+--------+-------+--------+ 831 | Shift to | 10.4 | M | both | 1 | 832 | Codeset 7 | | | | | 833 +-----------------+----------+--------+-------+--------+ 834 | Change status | 10.17 | M | both | 3 | 835 +-----------------+----------+--------+-------+--------+ 837 9.8 SERVICE ACK 839 This message is sent as an acknowledgment to the SERVICE message. 840 If sent be the NAS, it indicates that the NAS is processing the 841 SERVICE request. If sent by the gateway, it indicates that the 842 gateway has recorded the change in status. 844 +-----------------+----------+--------+-------+--------+ 845 | Information | Refer- | Type | Direc | Length | 846 | element | ence | | tion | | 847 +-----------------+----------+--------+-------+--------+ 848 | Protocol | 10.1 | M | both | 1 | 849 | discriminator | | | | | 850 +-----------------+----------+--------+-------+--------+ 851 | Call Reference | 10.2 | M | both | 3 | 852 +-----------------+----------+--------+-------+--------+ 853 | Message type | 10.3 | M | both | 1 | 854 +-----------------+----------+--------+-------+--------+ 855 | Channel ID | 10.6 | M | both | 3-6 | 856 +-----------------+----------+--------+-------+--------+ 857 | Shift to | 10.4 | M | both | 1 | 858 | Codeset 7 | | | | | 859 +-----------------+----------+--------+-------+--------+ 860 | Change status | 10.17 | M | both | 3 | 861 +-----------------+----------+--------+-------+--------+ 863 9.9 CONTINUITY CHECK RESULT 865 The NAS sends this message to report to the gateway the result of 866 continuity check for a particular channel. 868 +-------------------+----------+--------+----------+--------+ 869 | Information | Refer- | Type | Direc | Length | 870 | element | ence | | tion | | 871 +-------------------+----------+--------+----------+--------+ 872 | Protocol | 10.1 | M | NAS->G/W | 1 | 873 | discriminator | | | | | 874 +-------------------+----------+--------+----------+--------+ 875 | Call Reference | 10.2 | M | NAS->G/W | 3 | 876 +-------------------+----------+--------+----------+--------+ 877 | Message type | 10.3 | M | NAS->G/W | 1 | 878 +-------------------+----------+--------+----------+--------+ 879 | Channel ID | 10.6 | M | NAS->G/W | 3-6 | 880 +-------------------+----------+--------+----------+--------+ 881 | Shift to Codeset 7| 10.4 | M | NAS->G/W | 1 | 882 +-------------------+----------+--------+----------+--------+ 883 | Continuity result | 10.22 | M | NAS->G/W | 3 | 884 +-------------------+----------+--------+----------+--------+ 886 10. Information Elements 888 10.1 Protocol Discriminator 890 The protocol discriminator is the first field (1 byte) of every 891 message. Two protocol discriminator values will be supported: 892 - Q.931 user-network call control messages. The value used will 893 be hex 08. 894 - Maintenance messages defined in section 7. The value used will 895 be hex 03. 897 10.2 Call Reference 899 Call reference is always the second field of every message. 900 The purpose of the call reference is to identify the call or 901 facility registration/cancellation request at the local gateway to 902 NAS interface to which the particular message applies. A sequence 903 of Call reference values will be allocated for each TCP/IP 904 connection. For the detail format of the information element refer 905 to Q.931 specification 907 Global Call Reference values will be supported. 909 The protocol between the gateway and NAS will always use Call 910 reference with length of 2. 912 10.3 Message Type 914 The message type is the third field. For the individual values of 915 Q.931 defined fields refer to section 4.4 of the Q.931 916 specification. 918 In the case when the protocol discriminator indicates Maintenance 919 message, the value of the message type will be: 921 +------------------------------+--------+ 922 | Message | Hex | 923 | | Value | 924 +------------------------------+--------+ 925 | NAS STATUS | 01 | 926 +------------------------------+--------+ 927 | NAS STATUS ACK | 02 | 928 +------------------------------+--------+ 929 | INTERFACE STATUS | 03 | 930 +------------------------------+--------+ 931 | INTERFACE STATUS ACK | 04 | 932 +------------------------------+--------+ 933 | RESOURCE UPDATE | 05 | 934 +------------------------------+--------+ 935 | RESOURCE UPDATE ACK | 06 | 936 +------------------------------+--------+ 937 | SERVICE | 0F | 938 +------------------------------+--------+ 939 | SERVICE ACK | 07 | 940 +------------------------------+--------+ 941 | CONTINUITY CHECK RESULT | 08 | 942 +------------------------------+--------+ 944 10.4 Extension to Codesets 946 Refer to section 4.5.2 of the Q.931 for the definition of codeset 947 change procedures. The ASP will use the locking procedure to 948 codeset 7 (user defined) to define the Information Elements 949 specific to the 950 ASP. 952 10.5 Coding of Other Information Elements 954 All other Information Elements will be coded using the coding 955 rules for variable length information elements defined in section 956 4.5.1 of the Q.931 specification. The Information Element 957 Identifier values for standard Q.931 elements are defined in 958 section 4 of the Q.931 specification. 960 The values of Information Elements identifiers defined specifically 961 in this document will be specified using locking shift into codeset 962 7. They are: 964 +------------------------------+--------+ 965 | Information Element | Hex | 966 | | Value | 967 +------------------------------+--------+ 968 | Original Dialed Number | 01 | 969 +------------------------------+--------+ 970 | NAS Status Info | 02 | 971 +------------------------------+--------+ 972 | NAS Resources | 03 | 973 +------------------------------+--------+ 974 | Interface Status Info | 04 | 975 +------------------------------+--------+ 976 | Change Status | 05 | 977 +------------------------------+--------+ 978 | Continuity Result | 07 | 979 +------------------------------+--------+ 981 10.6 Channel Identification 983 This information element will be coded according to the general 984 coding rules defined in section 4.5.1 of the Q.931 specification. 985 The specific definition of the coding of this element is in section 986 4.5.13 of the Q.931 specification. The information element will be 987 coded as follows: 989 +-----+----------+----+---------+-------------------------+ 990 |Octet| Field |Bits| Value | Explanation | 991 +-----+----------+----+---------+-------------------------+ 992 | 1 |Extension | 8 | 0 | Multiple octets in | 993 | | | | | element | 994 | +----------+----+---------+-------------------------+ 995 | |IE Iden- |7-1 | 0011000 | Channel Identification | 996 +-----+----------+----+---------+-------------------------+ 997 | 2 |Length |8-1 | Binary | Length of IE | 998 +-----+----------+----+---------+-------------------------+ 999 | 3 |Extension | 8 | 1 |Last octet of description| 1000 | +----------+----+---------+-------------------------+ 1001 | |Interface | 7 | 1 |Interface explicitly | 1002 | |ID present| | |defined by this IE | 1003 | +----------+----+---------+-------------------------+ 1004 | |Interface | 6 | 1 |Primary rate | 1005 | |type | | | | 1006 | +----------+----+---------+-------------------------+ 1007 | |Spare | 5 | 0 |Spare | 1008 | +----------+----+---------+-------------------------+ 1009 | |Preferred/| 4 | 1 |Exclusive; only the | 1010 | |exclusive | | |indicated channel is | 1011 | | | | |acceptable | 1012 | +----------+----+---------+-------------------------+ 1013 | |D-channel | 3 | 0 |This is not D-channel | 1014 | +----------+----+---------+-------------------------+ 1015 | |Info |2-1 | 00 |No channel specified - | 1016 | |channel | | |the message applies to | 1017 | |selection | | | whole interface (1) | 1018 | | | +---------+-------------------------+ 1019 | | | | 01 |Channel defined in the | 1020 | | | | |following octets | 1021 +-----+----------+----+---------+-------------------------+ 1022 | 4 |Extension | 8 | 1 |Last octet of description| 1023 | +----------+----+---------+-------------------------+ 1024 | |Interface |7-1 | Binary |Number assigned to | 1025 | | | | |interface (note 2) | 1026 +-----+----------+----+---------+-------------------------+ 1027 | 5 |Extension | 8 | 1 |Last octet of description| 1028 | +----------+----+---------+-------------------------+ 1029 | |Coding std|7-6 | 00 |ITU standardized | 1030 | +----------+----+---------+-------------------------+ 1031 | |Number/map| 5 | 0 |Channel is indicated | 1032 | | | | |by number | 1033 | | | +---------+-------------------------+ 1034 | | | | 1 |Channel is indicated by | 1035 | | | | |by slot map | 1036 | +----------+----+---------+-------------------------+ 1037 | |Channel |4-1 | 0011 |B channel units | 1038 | |type | | | | 1039 continued 1041 +-----+----------+----+---------+-------------------------+ 1042 | 6-n |Channel |8-1 | Binary |Binary number assigned to| 1043 | |number/ | | |the channel (note 3) | 1044 | |slot map | | | | 1045 | | | +---------+-------------------------+ 1046 | | | | Binary |Bit position in slot map | 1047 | | | | |corresponding to the time| 1048 | | | | |slots used by the channels| 1049 | | | | |are set to 1 (note 4) | 1050 +-----+----------+----+---------+-------------------------+ 1052 Note: 1053 (1) If the Info Channel Selection field is set to 00 (no channel 1054 specified), the information element will end with octet 4. If 1055 the field is set to 01, octets 5 onwards will be present. 1056 (2) Interface identifier will be agreed between the gateway and 1057 the NAS and configured on both. The gateway will be configured 1058 to map interface numbers (with local meaning) to CICs. 1059 (3) If the channel is indicated by number, the bit 8 will be used 1060 as an extension bit and will be set to 1 to indicate that this 1061 is the last octet of description. 1062 (4) Refer to the Q.931 time-slot map definition for T1 and E1. 1063 Bit map will not be implemented in the first release. 1065 10.7 Bearer Capability 1067 This information element will be coded according to the coding 1068 rules defined in section 4.5.1 of the Q.931 specification. The 1069 specific definition of the coding of this element is in section 1070 4.5.5 of the Q.931 specification. 1072 This information element will be coded as follows. 1074 +-----+----------+----+---------+-------------------------+ 1075 |Octet| Field |Bits| Value | Explanation | 1076 +-----+----------+----+---------+-------------------------+ 1077 | 1 |Extension | 8 | 0 | Multiple octets in | 1078 | | | | | element | 1079 | +----------+----+---------+-------------------------+ 1080 | |IE Iden- |7-1 | 0000100 | Bearer Capability | 1081 | |tifier | | | | 1082 +-----+----------+----+---------+-------------------------+ 1083 | 2 |Length |8-1 | Binary | Length of IE | 1084 +-----+----------+----+---------+-------------------------+ 1085 | 3 |Extension | 8 | 1 |Last octet | 1086 | +----------+----+---------+-------------------------+ 1087 | |Coding |7-6 | 00 |ITU-T standardized | 1088 | |standard | | | | 1089 | +----------+----+---------+-------------------------+ 1090 | |Inform. |5-1 | 00000 |Speech | 1091 | |transfer | +---------+-------------------------+ 1092 | |capability| | 01000 |Unrestricted digital info| 1093 | | | +---------+-------------------------+ 1094 | | | | 01001 |Restricted digital info | 1095 | | | +---------+-------------------------+ 1096 | | | | 10000 |3.1 khz audio | 1097 +-----+----------+----+---------+-------------------------+ 1098 | 4 |Extension | 8 | 1 |Last octet | 1099 | +----------+----+---------+-------------------------+ 1100 | |Transfer |7-6 | 00 |Circuit mode | 1101 | |mode | | | | 1102 | +----------+----+---------+-------------------------+ 1103 | |Info |5-1 | 10000 |64 kbit/s - circuit mode | 1104 | |transfer | | | | 1105 | |rate | | | | 1106 +-----+----------+----+---------+-------------------------+ 1107 | 5 |Extension | 8 | 1 |Last octet | 1108 | +----------+----+---------+-------------------------+ 1109 | |Layer 1 |7-6 | 01 |Layer 1 identification | 1110 | |identif. | | |coding | 1111 | +----------+----+---------+-------------------------+ 1112 | |Layer 1 |5-1 | 00001 |rate adaption | 1113 | |protocol | +---------+-------------------------+ 1114 | | | | 00010 |u-law encoding | 1115 | | | +---------+-------------------------+ 1116 | | | | 00011 |a-law encoding | 1117 +-----+----------+----+---------+-------------------------+ 1119 Note: 1121 (1) additional octets will be required to support V.110 rate 1122 adaption, including the 56 K rate. For details refer to the 1123 Q.931 specification. 1125 10.8 Calling Party Number 1127 This information element will be coded according to the coding 1128 rules defined in section 4.5.1 of the Q.931 specification. The 1129 specific definition of the coding of this element is in section 1130 4.5.10 of the Q.931 specification. 1132 10.9 Calling Party Subaddress 1134 This information element will be coded according to the coding 1135 rules defined in section 4.5.1 of the Q.931 specification. The 1136 specific definition of the coding of this element is in section 1137 4.5.11 of the Q.931 specification. 1139 10.10 Called Party Number 1141 This information element will be coded according to the coding 1142 rules defined in section 4.5.1 of the Q.931 specification. The 1143 specific definition of the coding of this element is in section 1144 4.5.8 of the Q.931 specification. 1146 10.11 Called Party Subaddress 1148 This information element will be coded according to the coding 1149 rules defined in section 4.5.1 of the Q.931 specification. The 1150 specific definition of the coding of this element is in section 1151 4.5.9 of the Q.931 specification. 1153 10.12 Transit Network Selection 1155 This information element will be coded according to the coding 1156 rules defined in section 4.5.1 of the Q.931 specification. The 1157 specific definition of the coding of this element is in section 1158 4.5.29 of the Q.931 specification. 1160 10.13 Low Layer Compatibility 1162 This information element will be coded according to the coding 1163 rules defined in section 4.5.1 of the Q.931 specification. The 1164 specific definition of the coding of this element is in section 1165 4.5.19 of the Q.931 specification. 1167 10.14 Cause 1169 This information element will be coded as follows: 1171 +-----+----------+----+---------+-------------------------+ 1172 |Octet| Field |Bits| Value | Explanation | 1173 +-----+----------+----+---------+-------------------------+ 1174 | 1 |Extension | 8 | 0 | Multiple octets in | 1175 | | | | | element | 1176 | +----------+----+---------+-------------------------+ 1177 | |IE Iden- |7-1 | 0001000 | Cause | 1178 | |tifier | | | | 1179 +-----+----------+----+---------+-------------------------+ 1180 | 2 |Length |8-1 | Binary | Length of IE | 1181 +-----+----------+----+---------+-------------------------+ 1182 | 3 |Extension | 8 | 1 |Last octet | 1183 | +----------+----+---------+-------------------------+ 1184 | |Coding |7-6 | 11 |Standard specific to | 1185 | |standard | | |location | 1186 | +----------+----+---------+-------------------------+ 1187 | |Spare | 5 | 0 |Spare | 1188 | |----------+----+---------+-------------------------+ 1189 | |Location |4-1 | 0001 |Private network serving | 1190 | | | | |local user | 1191 +-----+----------+----+---------+-------------------------+ 1192 | 4 |Extension | 8 | 1 |Last octet of description| 1193 | +----------+----+---------+-------------------------+ 1194 | |Cause |7-1 | Binary |See table below | 1195 | |value | | | | 1196 +-----+----------+----+---------+-------------------------+ 1197 | 5 |Diagnostic|8-1 | Binary |See table below | 1198 | etc | | | | | 1199 +-----+----------+----+---------+-------------------------+ 1200 The following cause values will be used: 1201 +--------+--------------------------------+--------------+ 1202 | Number | Explanation | Diagnostics | 1203 +--------+--------------------------------+--------------+ 1204 | 01 | Unallocated (unassigned) number| None | 1205 +--------+--------------------------------+--------------+ 1206 | 06 | Channel unacceptable | None | 1207 +--------+--------------------------------+--------------+ 1208 | 16 | Normal Call clearing | None | 1209 +--------+--------------------------------+--------------+ 1210 | 17 | User busy | None | 1211 +--------+--------------------------------+--------------+ 1212 | 18 | No user responding | None | 1213 +--------+--------------------------------+--------------+ 1214 | 21 | Call rejected | None | 1215 +--------+--------------------------------+--------------+ 1216 | 28 | Invalid number format | Number IE | 1217 +--------+--------------------------------+--------------+ 1218 | 44 | Requested circuit/channel | None | 1219 | | not available | | 1220 +--------+--------------------------------+--------------+ 1221 | 52 | Outgoing call barred | None | 1222 +--------+--------------------------------+--------------+ 1223 | 54 | Incoming call barred | None | 1224 +--------+--------------------------------+--------------+ 1225 | 65 | Bearer capability not implem. | None | 1226 +--------+--------------------------------+--------------+ 1227 | 69 | Channel type not implemented | None | 1228 +--------+--------------------------------+--------------+ 1229 | 81 | Invalid call reference | None | 1230 +--------+--------------------------------+--------------+ 1231 | 96 | Mandatory Info Element missing | IE identifier| 1232 +--------+--------------------------------+--------------+ 1233 | 97 | Message type non-existent or | Message type | 1234 | | not implemented | | 1235 +--------+--------------------------------+--------------+ 1236 | 98 | Message not compatible with the| Message type | 1237 | | call state or message type not | | 1238 | | existent or not implemented | | 1239 +--------+--------------------------------+--------------+ 1240 | 99 | Information element non- | IE identifier| 1241 | | existent or not implemented | | 1242 +--------+--------------------------------+--------------+ 1243 | 100 | Invalid IE Contents | IE identifier| 1244 +--------+--------------------------------+--------------+ 1245 | 125 | NAS registered for incoming | None | 1246 | |calls only | | 1247 +--------+--------------------------------+--------------+ 1248 | 126 | NAS registered for incoming | None | 1249 | | and outgoing calls | | 1250 +--------+--------------------------------+--------------+ 1251 | 127 | NAS registration rejected | None | 1252 +--------+--------------------------------+--------------+ 1253 10.15 Call State 1255 This information element will be coded according to the coding 1256 rules defined in section 4.5.1 of the Q.931 specification. The 1257 specific definition of the coding of this element is in section 1258 4.5.7 of the Q.931 specification. 1260 10.16 Restart Indicator 1262 This information element will be coded according to the coding 1263 rules defined in section 4.5.1 of the Q.931 specification. The 1264 specific definition of the coding of this element is in section 1265 4.5.25 of the Q.931 specification. 1267 All the specified values (indicated channel, single interface, all 1268 interfaces) will be supported. 1270 10.17 Change Status 1272 This information element will be coded as follows. 1274 +-----+----------+----+---------+-------------------------+ 1275 |Octet| Field |Bits| Value | Explanation | 1276 +-----+----------+----+---------+-------------------------+ 1277 | 1 |Extension | 8 | 0 | Multiple octets in | 1278 | | | | | element | 1279 | +----------+----+---------+-------------------------+ 1280 | |IE Iden- |7-1 | | Change Status | 1281 | |tifier | | | | 1282 +-----+----------+----+---------+-------------------------+ 1283 | 2 |Length |8-1 | Binary | Length of IE | 1284 +-----+----------+----+---------+-------------------------+ 1285 | 3 |Extension | 8 | 1 |Last octet | 1286 | +----------+----+---------+-------------------------+ 1287 | |Preference| 7 | 0 |Interface specified by | 1288 | | | | |Channel Identification IE| 1289 | | | +---------+-------------------------+ 1290 | | | | 1 |Specific Channel speci- | 1291 | | | | |fied by | 1292 | | | | |Channel Identification IE| 1293 | +----------+----+---------+-------------------------+ 1294 | |Spare |6-4 | 0000 |Spare | 1295 | +----------+----+---------+-------------------------+ 1296 | |New Status|3-1 | 000 |In service | 1297 | | | +---------+-------------------------+ 1298 | | | | 001 |Loop back | 1299 | | | +---------+-------------------------+ 1300 | | | | 010 |Out of service | 1301 | | | +---------+-------------------------+ 1302 | | | | 011 |Request continuity check | 1303 | | | +---------+-------------------------+ 1304 | | | | 100 |Graceful shutdown | 1305 +-----+----------+----+---------+-------------------------+ 1306 The following table shows the relationship between the 'Preference" 1307 field and the 'New Status' field when the request is originated by 1308 the SS7 Gateway. 1310 +------------+--------------------------+-------------------------+ 1311 | | Interface Specified | Channel Specified | 1312 +------------+--------------------------+-------------------------+ 1313 | In Service | The NAS will attempt to | The NAS will mark the | 1314 | | bring the T1/E1 into ser-| channel as available. | 1315 | | vice. The NAS will | Established calls will | 1316 | | respond with 'Out of | not be affected. | 1317 | | Service' if the T1/E1 is | | 1318 | | down (not framing). | | 1319 +------------+--------------------------+-------------------------+ 1320 | Loop Back | The T1/E1 will be placed | The NAS will place the | 1321 | | into loopback. All esta-| DS0 into loopback state | 1322 | | blished calls will be | if there is no esta- | 1323 | | torn down. | blished call. The NAS | 1324 | | | will respond with 'In | 1325 | | | Service' if a call is | 1326 | | | in progress. | 1327 +------------+--------------------------+-------------------------+ 1328 | Out of | The NAS will place the | The NAS will mark the | 1329 | Service | T1/E1 into this state. | DS0 and tear down any | 1330 | | All established calls | if there is no esta- | 1331 | | will be torn down. | established calls. | 1332 +------------+--------------------------+-------------------------+ 1333 | Request | The NAS will reject this | The NAS will execute the| 1334 | Continuity | message and send STATUS | continuity check if | 1335 | Check | message. | there is no established | 1336 | | | call. The NAS will res-| 1337 | | | pond with 'In Service' | 1338 | | | if a call is in progress| 1339 +------------+--------------------------+-------------------------+ 1340 | Graceful | The NAS will mark the | The NAS will mark the | 1341 | Shutdown | T1/E1. It will not tear | DS0, but will not tear | 1342 | | down any established | down any established | 1343 | | calls. | calls. | 1344 +------------+--------------------------+-------------------------+ 1345 The following shows the relationship between the "Preference" field 1346 and "New Status" field when the request is originated by the NAS. 1348 +------------+--------------------------+-------------------------+ 1349 | | Interface Specified | Channel Specified | 1350 +------------+--------------------------+-------------------------+ 1351 | In Service | The NAS will send this | The NAS can send this | 1352 | | message when the T1/E1 | request for Channels it | 1353 | | framing is achieved. The | previously took "Out of | 1354 | | Gateway should not change| Service". The Gateway | 1355 | | the state of any esta- | should not change the | 1356 | | blished call. | state of any | 1357 | | | established call. | 1358 +------------+--------------------------+-------------------------+ 1359 | Loop Back | The NAS will not generate| The NAS will not gene- | 1360 | | this request. The Gate- | rate this request. The | 1361 | | way should respond with | Gateway should respond | 1362 | | STATUS. | with STATUS. | 1363 +------------+--------------------------+-------------------------+ 1364 | Out of | The NAS will place the | The NAS will send this | 1365 | Service | T1/E1 into this state if | message in the case of | 1366 | | T1/E1 framing is lost or | modem failure. Any | 1367 | | if requested by the | established call will | 1368 | | operator. All esta- | be torn down. | 1369 | | blished calls will be | | 1370 | | torn down. | | 1371 +------------+--------------------------+-------------------------+ 1372 | Request | The NAS will not send | The NAS will use this | 1373 | Continuity | this message. The Gate- | request as a result of | 1374 | Check | way should respond with | an operator request. | 1375 | | STATUS. | | 1376 +------------+--------------------------+-------------------------+ 1377 | Graceful | The NAS will issue this | The NAS will not issue | 1378 | Shutdown | request as a result of an| this message. The Gate-| 1379 | | operator request. Any | way should reject this | 1380 | | call in progress should | message using the | 1381 | | not be affected. | STATUS message. | 1382 +------------+--------------------------+-------------------------+ 1384 10.18 Original Dialed Number 1386 The format of this Information Element will be the same as for the 1387 Called Party Number Information Element specified in section 4.5.8 1388 of the Q.931. 1390 10.19 NAS Status Info 1392 The format of this information element will be as follows: 1394 +-----+----------+----+---------+-----------------------+ 1395 |Octet| Field |Bits| Value | Explanation | 1396 +-----+----------+----+---------+-----------------------+ 1397 | 1 |Extension | 8 | 0 | Multiple octets in | 1398 | | | | | element | 1399 | +----------+----+---------+-----------------------+ 1400 | |IE Iden- |7-1 | | NAS Status Info | 1401 | |tifier | | | | 1402 +-----+----------+----+---------+-----------------------+ 1403 | 2 |Length |8-1 | 1 | Length of IE | 1404 +-----+----------+----+---------+-----------------------+ 1405 | 3 |Extension | 8 | 1 |Last octet | 1406 | +----------+----+---------+-----------------------+ 1407 | |Spare |7-3 | 00000 |Spare | 1408 | +----------+----+---------+-----------------------+ 1409 | |Status |2-1 | 00 |Cold start: NAS coming | 1410 | | | | | up after booting | 1411 | | | +---------+-----------------------+ 1412 | | | | 01 |Warm start: NAS is | 1413 | | | | | reestablishing gateway| 1414 | | | | | connectivity | 1415 | | | +---------+-----------------------+ 1416 | | | | 10 |Hot shutdown: NAS will | 1417 | | | | | disconnect abruptly. | 1418 | | | | | All calls should be | 1419 | | | | | terminated. | 1420 | | | +---------+-----------------------+ 1421 | | | | 11 |Soft shutdown: NAS will| 1422 | | | | |shutdown when all calls| 1423 | | | | | have terminated. | 1424 +-----+----------+----+---------+-----------------------+ 1425 10.20 NAS Resource 1427 This information provides information regarding the NAS available 1428 resources. 1430 +-----+----------+----+---------+----------------------+ 1431 |Octet| Field |Bits| Value | Explanation | 1432 +-----+----------+----+---------+----------------------+ 1433 | 1 |Extension | 8 | 0 | Multiple octets in | 1434 | | | | | element | 1435 | +----------+----+---------+----------------------+ 1436 | |IE Iden- |7-1 | | NAS Resources | 1437 | |tifier | | | | 1438 +-----+----------+----+---------+----------------------+ 1439 | 2 |Length |8-1 | 2 | Length of IE | 1440 +-----+----------+----+---------+----------------------+ 1441 | 3 |Extension | 8 | 1 |Last octet | 1442 | +----------+----+---------+----------------------+ 1443 | |Category |7-5 | 001 |Modems | 1444 | | | +---------+----------------------+ 1445 | | | | 010 | HDLC channels | 1446 | +----------+----+---------+----------------------+ 1447 | |State |4-1 | 0001 |Available | 1448 +-----+----------+----+---------+----------------------+ 1449 | 4 |Extension | 8 | 1 |Last octet | 1450 | +----------+----+---------+----------------------+ 1451 | |Capacity |7-1 | Binary |Count of resources in | 1452 | | | | | that category | 1453 +-----+----------+----+---------+----------------------+ 1454 10.21 Interface Status Info 1456 This information element is used to specify the status of a given 1457 interface and the status of all the associated channels. 1458 +-----+----------+----+---------+-------------------------+ 1459 |Octet| Field |Bits| Value | Explanation | 1460 +-----+----------+----+---------+-------------------------+ 1461 | 1 |Extension | 8 | 0 | Multiple octets in | 1462 | | | | | element | 1463 | +----------+----+---------+-------------------------+ 1464 | |IE Iden- |7-1 | | Interface Status Info | 1465 | |tifier | | | | 1466 +-----+----------+----+---------+-------------------------+ 1467 | 2 |Length |8-1 | Binary | Length of IE | 1468 +-----+----------+----+---------+-------------------------+ 1469 | 3 |Extension | 8 | 1 |Last octet of description| 1470 | +----------+----+---------+-------------------------+ 1471 | |Interface |7-1 | Binary |Interface number | 1472 +-----+----------+----+---------+-------------------------+ 1473 | 4 |Extension | 8 | 1 |Last octet of description| 1474 | +----------+----+---------+-------------------------+ 1475 | |Spare |7-3 | 00000 |Spare | 1476 | +----------+----+---------+-------------------------+ 1477 | |Interface |2-1 | 00 |In Service (up) | 1478 | | status | +---------+-------------------------+ 1479 | | | | 01 |Maintenance (loopback)(1)| 1480 | | | +---------+-------------------------+ 1481 | | | | 10 |Out of Service (down)(1) | 1482 +-----+----------+----+---------+-------------------------+ 1483 | 5 |Extension | 8 | 1 |Last octet | 1484 | +----------+----+---------+-------------------------+ 1485 | |Chan Count|7-1 | Binary |Count of channels sup- | 1486 | | | | |ported by interface | 1487 +-----+----------+----+---------+-------------------------+ 1488 | 6 |Chan 1 |8-5 | 0000 |Idle - no existing calls | 1489 | |Status | +---------+-------------------------+ 1490 | | | | 0001 |Unavailable/blocked | 1491 | | | +---------+-------------------------+ 1492 | | | | 0010 |Call in progress | 1493 | +----------+----+---------+-------------------------+ 1494 | |Chan 2 |4-1 | 0000 |Idle - no existing calls | 1495 | |Status | +---------+-------------------------+ 1496 | | | | 0001 |Unavailable/blocked | 1497 | | | +---------+-------------------------+ 1498 | | | | 0010 |Call in progress | 1499 +-----+----------+----+---------+-------------------------+ 1501 Octet 6 is repeated until all channels defined by octet 5 are 1502 specified. 1504 Note 1:If the interface status is either Maintenance or Out of 1505 Service, octets 6 onwards are not provided. Their state is implied 1506 from the state of the interface. 1508 10.22 Continuity Result 1510 This Information element is used to report the result of continuity 1511 check performed by the NAS. The format will be as follows: 1513 +-----+----------+----+---------+-----------------------+ 1514 |Octet| Field |Bits| Value | Explanation | 1515 +-----+----------+----+---------+-----------------------+ 1516 | 1 |Extension | 8 | 0 | Multiple octets in | 1517 | | | | | element | 1518 | +----------+----+---------+-----------------------+ 1519 | |IE Iden- |7-1 | | Continuity Result | 1520 | |tifier | | | | 1521 +-----+----------+----+---------+-----------------------+ 1522 | 2 |Length |8-1 | 1 | Length of IE | 1523 +-----+----------+----+---------+-----------------------+ 1524 | 3 |Extension | 8 | 1 |Last octet | 1525 | +----------+----+---------+-----------------------+ 1526 | |Spare |7-2 | 0000000 |Spare | 1527 | +----------+----+---------+-----------------------+ 1528 | |Result | 1 | 0 |Continuity Check failed| 1529 | | | +---------+-----------------------+ 1530 | | | | 1 |Continuity Check suc- | 1531 | | | | |ceeded | 1532 +-----+----------+----+---------+-----------------------+ 1533 11. Examples of Timing Diagrams 1535 11.1 NAS Registers with Gateway for Service 1537 The following timing diagram shows that the NAS is responsible for 1538 the registration of the interfaces under its control. 1540 NAS Gateway 1541 | | 1542 | NAS STATUS (cold start) | 1543 |------------------------------>| 1544 | NAS STATUS ACK | 1545 |<------------------------------| 1546 | | 1547 | INTERFACE STATUS (i/f 1 up) | 1548 |------------------------------>| 1549 | INTERFACE STATUS ACK | 1550 |<------------------------------| 1551 | | 1552 | INTERFACE STATUS (i/f 2 down) | 1553 |------------------------------>| 1554 | INTERFACE STATUS ACK | 1555 |<------------------------------| 1556 | | 1557 | RESOURCE UPDATE | 1558 |------------------------------>| 1559 | RESOURCE UPDATE ACK | 1560 |<------------------------------| 1562 11.2 Gateway Originated Normal Call Setup and Release 1564 The following diagram shows successful Call establishment 1565 for gateway originated calls. 1567 NAS Gateway 1568 | | 1569 | SETUP (Channel ID = n) | 1570 |<------------------------------| 1571 | CONNECT | 1572 |------------------------------>| 1573 | | 1574 | DISCONNECT | 1575 |------------------------------>| 1576 | RELEASE | 1577 |<------------------------------| 1578 | RELEASE COMPLETE | 1579 |------------------------------>| 1581 Note: The disconnect sequence can be initiated by either the NAS or 1582 by the gateway to hang-up the call. 1584 11.3 Call Setup with Alternative Call Clearing 1586 The following diagram shows successful Call establishment 1587 for gateway originated calls, using an alternative call clearing 1588 sequence that is also allowed in the protocol. 1590 NAS Gateway 1591 | | 1592 | SETUP (Channel ID = n) | 1593 |<------------------------------| 1594 | CONNECT | 1595 |------------------------------>| 1596 | | 1597 | RELEASE | 1598 |<------------------------------| 1599 | RELEASE COMPLETE | 1600 |------------------------------>| 1602 11.4 NAS Originated Normal Call Setup 1604 The following diagram shows successful Call establishment 1605 for NAS originated calls. For NAS originated calls, the Gateway 1606 selects the channel to be used in the call. 1608 NAS Gateway 1609 | | 1610 | SETUP(channel not specified) | 1611 |------------------------------>| 1612 | CONNECT ( Channel ID = n ) | 1613 |<------------------------------| 1614 | | 1615 | DISCONNECT | 1616 |------------------------------>| 1617 | RELEASE | 1618 |<------------------------------| 1619 | RELEASE COMPLETE | 1620 |------------------------------>| 1622 Note: The disconnect sequence can be initiated by either the NAS or 1623 by the gateway to hang-up the call. Disconnection can be initiated 1624 by either the DISCONNECT or RELEASE message. 1626 11.5 Unsuccessful Call Establishment Sequence 1628 The following sequence illustrates when a call is rejected by the 1629 NAS. 1631 NAS Gateway 1632 | | 1633 | SETUP | 1634 |<------------------------------| 1635 | RELEASE COMPLETE | 1636 |------------------------------>| 1638 11.6 Continuity check test as part of Incoming Call Setup - Success 1640 The following sequence illustrates when the gateway receives an IAM 1641 message indicating that a continuity test should be performed on 1642 the circuit prior to the call establishment. 1644 NAS Gateway 1645 | | 1646 | SERVICE (chan n loop back) | 1647 |<------------------------------| 1648 | SERVICE ACK | 1649 |------------------------------>| 1650 | | 1651 | SETUP | 1652 |<------------------------------| 1653 | CONNECT | 1654 |------------------------------>| 1656 Per Q.699 (3.1.18) continuity checking should be performed before 1657 the SETUP is sent to the terminating end-point. SERVICE message 1658 from the gateway to the NAS is used to initiate the loopback. If 1659 the remote end-point indicates to the gateway that the continuity 1660 check succeeded, the gateway proceeds with SETUP. 1662 11.6 Continuity check test as part of Incoming Call Setup - Failure 1664 If the remote end indicates failure, the gateway will send SERVICE 1665 message to the NAS requesting that the channel be placed into the 1666 in service state. 1668 NAS Gateway 1669 | | 1670 | SERVICE (chan n loop back) | 1671 |<------------------------------| 1672 | SERVICE ACK | 1673 |------------------------------>| 1674 | | 1675 | SERVICE (chan n in service) | 1676 |<------------------------------| 1677 | SERVICE ACK | 1678 |------------------------------>| 1680 11.7 Continuity check test as part of Outgoing Call Setup - Success 1682 The following sequence illustrates when the NAS initiates call 1683 setup and the SS7 Gateway determines that continuity test should be 1684 performed on the circuit prior to the call establishment. 1686 NAS Gateway 1687 | | 1688 | SETUP (channel not specified) | 1689 |------------------------------>| 1690 | | 1691 | SERVICE (chan n request | 1692 | continuity check) | 1693 |<------------------------------| 1694 | SERVICE ACK | 1695 |------------------------------>| 1696 | CONTINUITY CHECK RESULT | 1697 |------------------------------>| 1698 | | 1699 | CONNECT (Channel ID = n) | 1700 |<------------------------------| 1701 11.8 Continuity check test initiated by the SS7 gateway operator 1703 The gateway sends a SERVICE message to initiate the continuity 1704 check. The NAS performs continuity check and reports the result 1705 using the CONTINUITY CHECK RESULT. 1707 NAS Gateway 1708 | | 1709 | SERVICE (chan n request | 1710 | continuity check) | 1711 |<------------------------------| 1712 | SERVICE ACK | 1713 |------------------------------>| 1714 | | 1715 | CONTINUITY CHECK RESULT | 1716 |------------------------------>| 1718 11.7 NAS detects bearer T1/E1 line down (LOS, Red Alarm) 1720 If the NAS detects that a particular T1/E1 line failed, it sends a 1721 SERVICE message to the gateway. Established calls will be torn down 1722 as part of normal processing - i.e the NAS modems will detect loss 1723 of connection and the NAS will disconnect the call. The gateway 1724 will request blocking of CICs associated with the particular T1/E1 1725 using an SS7 Blocking or Circuit Group Blocking Message. 1727 NAS Gateway 1728 | | 1729 | SERVICE (i/f 1 out-of-service)| 1730 |------------------------------>| 1731 | SERVICE ACK | 1732 |<------------------------------| 1734 11.8 Individual bearer channel taken out-of-service by NAS 1736 NAS Gateway 1737 | | 1738 | SERVICE(chan n out-of-service)| 1739 |------------------------------>| 1740 | SERVICE ACK | 1741 |<------------------------------| 1742 11.9 Individual bearer channel taken out-of-service by Gateway 1743 operator 1745 NAS Gateway 1746 | | 1747 | SERVICE(chan n out-of-service)| 1748 |<------------------------------| 1749 | SERVICE ACK | 1750 |------------------------------>| 1752 11.10 Bearer T1/E1 trunk abrupt shutdown initiated by Gateway 1753 operator 1755 NAS Gateway 1756 | | 1757 | SERVICE (i/f n out-of-service)| 1758 |<------------------------------| 1759 | SERVICE ACK | 1760 |------------------------------>| 1762 11.11 Bearer T1/E1 trunk abrupt shutdown initiated by NAS 1764 NAS Gateway 1765 | | 1766 | SERVICE (i/f n out-of-service)| 1767 |------------------------------>| 1769 | SERVICE ACK | 1770 |<------------------------------| 1772 11.12 Bearer T1/E1 trunk graceful shutdown initiated by Gateway 1773 operator 1775 NAS Gateway 1776 | | 1777 | SERVICE (i/f n graceful shutdown) | 1778 |<----------------------------------| 1779 | SERVICE ACK | 1780 |---------------------------------->| 1782 11.13 Bearer T1/E1 trunk graceful shutdown initiated by NAS 1784 NAS Gateway 1785 | | 1787 | SERVICE (i/f n graceful shutdown) | 1788 |---------------------------------->| 1789 | SERVICE ACK | 1790 |<----------------------------------| 1791 10. Error Handling 1793 Refer to section 3.7.8 of TR 41459 ATT Network ISDN Primary Rate 1794 Interface. This section defines how to handle error conditions such 1795 as Call reference errors, message type errors , etc. The ASP will 1796 use the error procedures. 1798 11. Timers 1800 To be provided. 1802 12. State Diagrams 1804 To be provided. 1806 13. Acknowledgements 1808 The authors would like to acknowledge Mehdi Ghasem, Wan Man and Ki 1809 Suh of Stratus Computer, as well as Miguel Sasson of Bay Networks 1810 for their helpful review and comments on this protocol specification. 1812 14. Contact Information 1814 Jiri Matousek Lyndon Ong 1815 Bay Networks, Inc. Bay Networks, Inc. 1816 5 Federal Street 4401 Gt America Pkwy 1817 Billerica, MA 01821 Santa Clara, CA 95052 1819 jiri@baynetworks.com long@baynetworks.com 1821 EXPIRES JANUARY 1999