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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 draft-toivanen-sccp-etheric-00.txt Harri Toivanen 4 August 1998 Oy LM Ericsson Ab 5 Expires: March 1999 Petteri Laamo 6 Oy LM Ericsson Ab 7 George Wayne 8 Advanced Computer Communications 9 Paul Harding-Jones 10 Advanced Computer Communications 12 Simplified Call Control Protocol - Etheric 14 Status of this Memo 16 This document is an Internet-Draft. Internet-Drafts are working 17 documents of the Internet Engineering task Force (IETF), its areas, 18 and its working groups. Note that other groups may also distribute 19 working documents as Internet-Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six 22 months and may be updated, replaced, or obsoleted by other 23 documents at any time. It is inappropriate to use Internet-Drafts 24 as reference material or to cite them other than as "work in 25 progress". 27 To learn the current status of any Internet-Draft, please check the 28 "1id-abstract.txt" listing contained in the Internet-Drafts Shadow 29 Directories on ftp.is.co.za (Africa), nic.nordu.net, 30 ftp.nis.garr.it (Europe), munnari.oz.au (Pacific Rim), 31 ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). 33 Abstract 35 This memo describes Simplified Call Control Protocol called Etheric 36 between Signalling System 7 (SS7) controlled Public Switched Telephony 37 Network (PSTN) and Network Access Server (NAS) created by Oy LM 38 Ericsson Ab in co-operation with Advanced Computer Communications inc 39 (ACC). 41 1. General Information 43 1.1 Introduction 45 The Etheric 1.0 is the protocol used to control traffic between Public 46 Switched Telephony Network GateWay (PSTN-GW, initially PSTN exchange) 47 and Network Access Server (NAS) for call setup and release as well as 48 for circuit maintenance. The signalling uses TCP/IP. 50 1.2 Terms and Abbreviations 52 Direction backwards 53 Messages which are sent against the call set-up direction 55 Direction forwards 56 Messages which are sent towards the call set-up direction. 58 GS 59 Group Switch. 61 IP 62 Internet Protocol. 64 Node 65 In this document, one end of the Etheric protocol, i.e. NAS or 66 PSTN-GW. 68 TCP 69 Transmission Control Protocol. 71 TDM 72 Time Division Multiplexed line. 74 2. Function 76 2.1 General 78 PSTN-GW IP-connection 79 --------------------+ 80 I 81 +----------+ I 82 I I I 83 I IP- I I 84 I terminal +------------------+ 85 I I I I 86 +----------+ I I 87 I I 88 TDM interfaces I 89 I I 90 +------+ I +--------+ I 91 I I I I I I 92 I I I I NAS 1 I I 93 I I I I I I 94 I GS +-----------+ +-+ 95 I I I I I I 96 I I I +--------+ I 97 I I I I 98 I I I I 99 I I I I 100 I I I +--------+ I 101 I I I I I I 102 I I I I NAS 2 I I 103 I I I I I I 104 I +-----------+ +-+ 105 I I I I I I 106 I I I +--------+ I 107 I I I I 108 I I I ... I 109 I I I I 110 I I I I 111 I I I I 112 I I I +--------+ I 113 I I I I I I 114 I I I I NAS n +-I 115 I I I I I I 116 I +-----------+ +-+ 117 I I I I I 118 I I I +--------+ 119 I I I 120 +------+ I 121 I 122 --------------------+ 124 The figure above shows the configuration between PSTN-GW and NASs. 126 The Etheric signalling protocol between the PSTN-GW and the NASs is of 127 common channel type. 129 IP-connection is used as the signaling path. TCP is used for reliable 130 transfer of signalling information. 132 As shown in the figure a group of NASs can be connected to the PSTN-GW. 133 The PSTN-GW and NASs connected to the same IP-connection form an IP 134 subnet where the PSTN-GW and each NAS have own IP-addresses. One NAS 135 can be connected to one PSTN-GW only. 137 Each NAS connected to the PSTN-GW with TDM interfaces is considered a 138 'signalling destination' identified by an IP address. While the Etheric 139 signalling is transferred over the IP-connection the data traffic is 140 transferred over the TDM interfaces. 142 The Etheric protocol is a message oriented protocol based on ITU-T 143 Q.767. The protocol identifies the timeslots in TDM interfaces used for 144 traffic by means of a Circuit Identification Code (CIC). CICs are 145 unique per signalling destination, i.e. per NAS. The CICs are numbered 146 so that consecutive timeslots have consecutive CICs within a TDM 147 interface. 149 The Etheric protocol has procedures for automatic recovery from 150 signalling TCP connection failures. 152 The protocol also includes procedures for circuit management which 153 allow the two ends of a signalling connection to align the circuit 154 status after a manual action or an outage situation. 156 2.2 Security Considerations 158 Because of nature of the Etheric protocol it must be secured either by 159 separating IP-connection(s) containing signalling traffic from payload 160 or encrypting IP-connection(s) below Etheric-level. 162 This memo does not contain more about security matters. 164 2.3 Reliability Aspects 166 For increased reliability two parallel IP-connections can be used by the 167 Etheric signalling. The PSTN-GW and each NAS are connected to both 168 IP-connections. The two signalling TCP connections are then set up over 169 the two separate IP-connections. This is also the case when a pair of IP 170 addresses is used to identify the signalling destination. 172 2.4 Message Format 174 The signalling information is transferred by means of signalling 175 messages. A message consists of length indicator and a variable length 176 signalling information field (SIF) which carries the information 177 between PSTN-GW and NAS. 179 +-----+--------+ 180 I I I 181 I I Length I 182 I SIF I Infor- I 183 I I mation I 184 I I I 185 +-----+--------+ 187 2.4.1 LENGTH INFORMATION 189 +---------------------+ 190 I I 191 I byte 0 I 192 I I 193 +---+-----------------+ 194 I I I 195 I F I byte1.B6-B0 I 196 I I I 197 +---+-----------------+ 199 byte0 : not used, coded as 0 201 byte1.B6-B0: message length 203 (number of bytes in the message, 205 the length information part excluded) 207 The F bit is reserved and MUST be set to 0. 209 2.4.2 SIGNALLING INFORMATION FIELD (SIF) 211 +---------------------+ 212 I I 213 I Circuit I 214 I Identification I 215 I Code I 216 I I 217 +---------------------+ 218 I I 219 I Message type I 220 I Code I 221 I I 222 +---------------------+ 223 I I 224 I Mandatory I 225 I fixed part I 226 I I 227 +---------------------+ 228 I I 229 I Mandatory I 230 I variable part I 231 I I 232 +---------------------+ 234 2.4.3 CIRCUIT IDENTIFICATION CODE (CIC) 236 8 7 6 5 4 3 2 1 237 +-------------------------------------------+ 238 I I 239 I CIC least significant bits I 240 I I 241 +---------------------+---------------------+ 242 I I I 243 I spare I CIC most I 244 I I significant bits I 245 I I I 246 +---------------------+---------------------+ 248 The spare bits MUST be set to 0. 250 2.4.4 MESSAGE TYPE CODE 252 The message type code consists of a one octet field and is mandatory 253 for all messages. The message type code uniquely defines the function 254 and format of message. 256 The allocation with reference to the appropriate descriptive section of 257 this specification is found in section 2.5. 259 2.4.5 Formatting Principles 261 Each message consists of a number of parameters listed and described in 262 section 2.6. Each parameter has a name which is coded as a single octet 263 (see section 2.6.2). The length of a parameter may be fixed or 264 variable, and a length indicator of one octet may be included as 265 described in section 2.6.1. 267 2.5 Message Type Codes 269 The abbreviations used in this section are : 271 F mandatory fixed length parameter 272 V mandatory variable length parameter 274 +---------------------------+-----------+-------------+ 275 I I I I 276 I message type I code I reference I 277 I I I I 278 +---------------------------+-----------+-------------+ 279 I I I I 280 I ADDRESS COMPLETE (ACM) I 0000 0110 I 2.5.1 I 281 I I I I 282 I ANSWER (ANM) I 0000 1001 I 2.5.2 I 283 I I I I 284 I BLOCKING (BLO) I 0001 0011 I 2.5.3 I 285 I I I I 286 I BLOCKING I 0001 0101 I 2.5.4 I 287 I ACKNOWLEDGEMENT (BLA) I I I 288 I I I I 289 I CIRCUIT GROUP RESET (GRS) I 0001 0111 I 2.5.5 I 290 I I I I 291 I CIRCUIT GROUP RESET I 0010 1001 I 2.5.6 I 292 I ACKNOWLEDGEMENT (GRA) I I I 293 I I I I 294 I CONNECT (CON) I 0000 0111 I 2.5.7 I 295 I I I I 296 I INITIAL ADDRESS (IAM) I 0000 0001 I 2.5.8 I 297 I I I I 298 I RELEASE (REL) I 0000 1100 I 2.5.9 I 299 I I I I 300 I RELEASE COMPLETE (RLC) I 0001 0000 I 2.5.10 I 301 I I I I 302 I RESET CIRCUIT (RSC) I 0001 0010 I 2.5.11 I 303 I I I I 304 I UNBLOCKING (UBL) I 0001 0100 I 2.5.12 I 305 I I I I 306 I UNBLOCKING I 0001 0110 I 2.5.13 I 307 I ACKNOWLEDGEMENT (UBA) I I I 308 I I I I 309 +---------------------------+-----------+-------------+ 311 2.5.1 ADDRESS COMPLETE (ACM) 313 Indicates that all the address signals required for routing the call to 314 the called party have been received. 316 direction : backward 318 +-----------------+-----------+------+----------+ 319 I I I I I 320 I parameter I reference I type I length I 321 I I I I (octets) I 322 I I I I I 323 +-----------------+-----------+------+----------+ 324 I I I I I 325 I Message type I 2.5 I F I 1 I 326 I I I I I 327 I Backward call I 2.6.9 I F I 1 I 328 I indicators I I I I 329 I I I I I 330 +-----------------+-----------+------+----------+ 332 2.5.2 ANSWER (ANM) 334 Indicates that the call has been answered. 336 This message is used to start metering the charge to the calling 337 subscriber. 339 direction : backward 341 +-----------------+-----------+------+----------+ 342 I I I I I 343 I parameter I reference I type I length I 344 I I I I (octets) I 345 I I I I I 346 +-----------------+-----------+------+----------+ 347 I I I I I 348 I Message type I 2.5 I F I 1 I 349 I I I I I 350 +-----------------+-----------+------+----------+ 352 2.5.3 BLOCKING (BLO) 354 Sent only for maintenance purposes to the node at the other end of a 355 circuit, to cause an engaged condition of that circuit for subsequent 356 calls outgoing from that node. When a circuit is used in the bothway 357 mode of operation a node receiving the blocking message must be capable 358 of accepting incoming calls on the concerned circuit unless it has also 359 sent a blocking message. 361 direction : both 363 +-----------------+-----------+------+----------+ 364 I I I I I 365 I parameter I reference I type I length I 366 I I I I (octets) I 367 I I I I I 368 +-----------------+-----------+------+----------+ 369 I I I I I 370 I Message type I 2.5 I F I 1 I 371 I I I I I 372 +-----------------+-----------+------+----------+ 374 2.5.4 BLOCKING ACKNOWLEDGEMENT (BLA) 376 Sent in response to a blocking message indicating that the circuit has 377 been blocked. 379 direction : both 381 +-----------------+-----------+------+----------+ 382 I I I I I 383 I parameter I reference I type I length I 384 I I I I (octets) I 385 I I I I I 386 +-----------------+-----------+------+----------+ 387 I I I I I 388 I Message type I 2.5 I F I 1 I 389 I I I I I 390 +-----------------+-----------+------+----------+ 392 2.5.5 CIRCUIT GROUP RESET (GRS) 394 Sent to release all circuits connected to one NAS when, due to memory 395 mutilation or other causes, it is unknown whether for example, a 396 release or release complete message is appropriate for each of the 397 circuits in the group. If at the receiving end a circuit is remotely 398 blocked, reception of this message should cause that condition to be 399 removed. 401 direction : both 403 +-----------------+-----------+------+----------+ 404 I I I I I 405 I parameter I reference I type I length I 406 I I I I (octets) I 407 I I I I I 408 +-----------------+-----------+------+----------+ 409 I I I I I 410 I Message type I 2.5 I F I 1 I 411 I I I I I 412 +-----------------+-----------+------+----------+ 414 The CIC in the GRS message is not relevant, and will be coded as 0 when 415 sent. 417 2.5.6 CIRCUIT GROUP RESET ACKNOWLEDGEMENT (GRA) 419 Sent in response to a circuit group reset message and indicating that 420 the requested group of circuits has been reset. 422 direction : both 424 +-----------------+-----------+------+----------+ 425 I I I I I 426 I parameter I reference I type I length I 427 I I I I (octets) I 428 I I I I I 429 +-----------------+-----------+------+----------+ 430 I I I I I 431 I Message type I 2.5 I F I 1 I 432 I I I I I 433 +-----------------+-----------+------+----------+ 435 The CIC in the GRA message is not relevant, and will be coded as 0 when 436 sent. 438 2.5.7 CONNECT (CON) 440 Indicates that all the address signals required for routing the call to 441 the called party have been received and that the call has been 442 answered. 444 This message is used to start metering the charge to the calling 445 subscriber. 447 direction : backward 449 +-----------------+-----------+------+----------+ 450 I I I I I 451 I parameter I reference I type I length I 452 I I I I (octets) I 453 I I I I I 454 +-----------------+-----------+------+----------+ 455 I I I I I 456 I Message type I 2.5 I F I 1 I 457 I I I I I 458 +-----------------+-----------+------+----------+ 460 2.5.8 INITIAL ADDRESS (IAM) 462 Initiates seizure of an outgoing circuit and transmits number and other 463 information relating to the routing and handling of a call. 465 direction : forward 467 +-----------------+-----------+------+----------+ 468 I I I I I 469 I parameter I reference I type I length I 470 I I I I (octets) I 471 I I I I I 472 +-----------------+-----------+------+----------+ 473 I I I I I 474 I Message type I 2.5 I F I 1 I 475 I I I I I 476 I Forward call I 2.6.8 I F I 1 I 477 I indicators I I I I 478 I I I I I 479 I Calling party's I 2.6.6 I F I 1 I 480 I category I I I I 481 I I I I I 482 I Transmission I 2.6.10 I F I 1 I 483 I medium I I I I 484 I requirement I I I I 485 I I I I I 486 I Called party I 2.6.4 I V I 2 - 17 I 487 I number I I I I 488 I I I I I 489 I Calling party I 2.6.5 I V I 2 - 10 I 490 I number I I I I 491 I I I I I 492 +-----------------+-----------+------+----------+ 494 2.5.9 RELEASE (REL) 496 Indicates that the circuit has been released due to the reason (cause) 497 supplied and is ready to be put into the idle state on receipt of the 498 release complete message. 500 direction : both 502 +-----------------+-----------+------+----------+ 503 I I I I I 504 I parameter I reference I type I length I 505 I I I I (octets) I 506 I I I I I 507 +-----------------+-----------+------+----------+ 508 I I I I I 509 I Message type I 2.5 I F I 1 I 510 I I I I I 511 I Cause I 2.6.7 I F I 1 I 512 I indicators I I I I 513 I I I I I 514 +-----------------+-----------+------+----------+ 516 2.5.10 RELEASE COMPLETE (RLC) 518 Is sent in response to the receipt of a release message, or if 519 appropriate, to a reset circuit message, when the circuit concerned has 520 been brought into the idle condition. 522 direction : both 524 +-----------------+-----------+------+----------+ 525 I I I I I 526 I parameter I reference I type I length I 527 I I I I (octets) I 528 I I I I I 529 +-----------------+-----------+------+----------+ 530 I I I I I 531 I Message type I 2.5 I F I 1 I 532 I I I I I 533 +-----------------+-----------+------+----------+ 535 2.5.11 RESET CIRCUIT (RSC) 537 Sent to release a circuit when, due to memory mutilation or other 538 causes, it is unknown whether for example, a released or a release 539 complete message is appropriate. If at the receiving end the circuit is 540 blocked, reception of this message should cause that condition to be 541 removed. 543 direction : both 545 +-----------------+-----------+------+----------+ 546 I I I I I 547 I parameter I reference I type I length I 548 I I I I (octets) I 549 I I I I I 550 +-----------------+-----------+------+----------+ 551 I I I I I 552 I Message type I 2.5 I F I 1 I 553 I I I I I 554 +-----------------+-----------+------+----------+ 556 2.5.12 UNBLOCKING (UBL) 558 Sent to the node at the other end of the circuit to cancel, in that 559 node, the engaged condition of the circuit caused by a previously sent 560 blocking message. 562 direction : both 564 +-----------------+-----------+------+----------+ 565 I I I I I 566 I parameter I reference I type I length I 567 I I I I (octets) I 568 I I I I I 569 +-----------------+-----------+------+----------+ 570 I I I I I 571 I Message type I 2.5 I F I 1 I 572 I I I I I 573 +-----------------+-----------+------+----------+ 575 2.5.13 UNBLOCKING ACKNOWLEDGEMENT (UBA) 577 Sent in response to an unblocking message indicating that the circuit 578 has been unblocked. 580 direction : both 582 +-----------------+-----------+------+----------+ 583 I I I I I 584 I parameter I reference I type I length I 585 I I I I (octets) I 586 I I I I I 587 +-----------------+-----------+------+----------+ 588 I I I I I 589 I Message type I 2.5 I F I 1 I 590 I I I I I 591 +-----------------+-----------+------+----------+ 593 2.6 Parameters 595 2.6.1 FORMAT 597 2.6.1.1 MANDATORY FIXED PART 599 Those parameters that are mandatory and of fixed length for a 600 particular message type will be contained in the mandatory fixed part. 601 The position, length and order of the parameters is uniquely defined by 602 the message type, thus the names of the parameters and the length 603 indicators are not included in the message. 605 +--------------------------+ 606 I I 607 I MANDATORY PARAMETER A I 608 I I 609 +--------------------------+ 610 . . 611 . ... . 612 . . 613 +--------------------------+ 614 I I 615 I MANDATORY PARAMETER F I 616 I I 617 +--------------------------+ 619 2.6.1.2 MANDATORY VARIABLE PART 621 Mandatory parameters of variable length will be included in the 622 mandatory variable part. Pointers are used to indicate the beginning of 623 each parameter. Each pointer is encoded as a single octet. The name of 624 each parameter and the order in which the pointers are sent is implicit 625 in the message type. Parameter names are, therefore, not included in 626 the message. The details of how pointers are encoded is found in 627 section 2.6.1.5. The number of parameters, and thus the number of 628 pointers is uniquely defined by the message type. 630 All the pointers are consecutive at the beginning of the mandatory 631 variable part. Each parameter contains the parameter length indicator 632 followed by the contents of the parameters. 634 +--------------------------+ 635 I I 636 I POINTER TO PARAMETER M +--+ 637 I I I 638 +--------------------------+ I 639 . . I 640 . ... . I 641 . . I 642 +--------------------------+ I 643 I I I 644 I POINTER TO PARAMETER P +-----+ 645 I I I I 646 +--------------------------+ I I 647 I I I I 648 I LENGTH OF PARAMETER M I-+ I 649 I I I 650 +--------------------------+ I 651 I I I 652 I PARAMETER M I I 653 I I I 654 +--------------------------+ I 655 . . I 656 . ... . I 657 . . I 658 +--------------------------+ I 659 I I I 660 I LENGTH OF PARAMETER P I----+ 661 I I 662 +--------------------------+ 663 I I 664 I PARAMETER P I 665 I I 666 +--------------------------+ 668 2.6.1.3 FORMAT OF PARAMETER IN MANDATORY VARIABLE PART 670 +--------------------------+ 671 I I 672 I LENGTH OF PARAMETER M I 673 I I 674 +--------------------------+ 675 I I 676 I PARAMETER M CONTENTS I 677 I I 678 +--------------------------+ 680 2.6.1.4 CODING OF THE LENGTH INDICATOR 682 The length indicator field is binary coded to indicate the number of 683 octets in the parameter content field. The length indicated does not 684 include the parameter name octet or the length indicator octet. 686 2.6.1.5 CODING OF THE POINTERS 688 The pointer value (in binary) gives the number of octets between the 689 pointer itself (included) and the first octet (not included) of the 690 parameter associated with that pointer. 692 2.6.2 PARAMETER NAMES 694 +-----------------------+-----------+-------------+ 695 I I I I 696 I parameter name I code I reference I 697 I I I I 698 +-----------------------+-----------+-------------+ 699 I I I I 700 I CALLED PARTY NUMBER I 0000 0100 I 2.6.4 I 701 I I I I 702 I CALLING PARTY NUMBER I 0000 1010 I 2.6.5 I 703 I I I I 704 I CALLING PARTY'S I 0000 1001 I 2.6.6 I 705 I CATEGORY I I I 706 I I I I 707 I CAUSE INDICATORS I 0001 0010 I 2.6.7 I 708 I I I I 709 I FORWARD CALL I 0000 0111 I 2.6.8 I 710 I INDICATORS I I I 711 I I I I 712 I BACKWARD CALL I 0010 1001 I 2.6.9 I 713 I INDICATORS I I I 714 I I I I 715 I TRANSMISSION MEDIUM I 0000 0010 I 2.6.10 I 716 I REQUIREMENT I I I 717 I I I I 718 +-----------------------+-----------+-------------+ 720 2.6.3 PARAMETER NAME VS MESSAGE TABLE 722 +-----------------------+-----------+-------------+ 723 I I I I 724 I parameter name I parameter I messages I 725 I I type I I 726 I I I I 727 +-----------------------+-----------+-------------+ 728 I I I I 729 I CALLED PARTY NUMBER I V I IAM I 730 I I I I 731 I CALLING PARTY NUMBER I V I IAM I 732 I I I I 733 I CALLING PARTY'S I F I IAM I 734 I CATEGORY I I I 735 I I I I 736 I CAUSE INDICATORS I F I REL I 737 I I I I 738 I BACKWARD I F I ACM I 739 I CALL INDICATORS I I I 740 I I I I 741 I FORWARD CALL I F I IAM I 742 I INDICATORS I I I 743 I I I I 744 I TRANSMISSION MEDIUM I F I IAM I 745 I REQUIREMENTS I I I 746 I I I I 747 +-----------------------+-----------+-------------+ 749 2.6.4 CALLED PARTY NUMBER 751 length : 2 - 17 octets 753 8 7 6 5 4 3 2 1 754 +----+----------------------------------+ 755 I I 756 IOdd/I Nature of address I 757 IevenI indicator I 758 I I 759 +----+--------------+-------------------+ 760 I I I 761 I 2nd address I 1st address I 762 I signal I signal I 763 I I I 764 +-------------------+-------------------+ 765 I : I 766 I : I 767 I : I 768 +-------------------+-------------------+ 769 I I I 770 I Filler I nth address I 771 I (if necessary) I signal I 772 I I I 773 +-------------------+-------------------+ 775 Odd/Even Indicator 777 0 Even number of address signals 779 1 Odd number of address signals 781 Nature of Address Indicator 783 0 0 0 0 0 0 0 Spare 784 0 0 0 0 0 0 1 Reserved 785 0 0 0 0 0 1 0 Reserved 786 0 0 0 0 0 1 1 National (significant) number 787 0 0 0 0 1 0 0 International number 788 0 0 0 0 1 0 1 789 to 790 1 1 1 1 1 1 1 Spare 792 Address Signal 794 0 0 0 0 Digit 0 795 0 0 0 1 Digit 1 796 0 0 1 0 Digit 2 797 0 0 1 1 Digit 3 798 0 1 0 0 Digit 4 799 0 1 0 1 Digit 5 800 0 1 1 0 Digit 6 801 0 1 1 1 Digit 7 802 1 0 0 0 Digit 8 803 1 0 0 1 Digit 9 804 1 0 1 0 Spare 805 1 0 1 1 Code 11 806 1 1 0 0 Code 12 807 1 1 0 1 Spare 808 1 1 1 0 Spare 809 1 1 1 1 Reserved 811 The most significant address signal is sent first. Subsequent address 812 signals are sent in successive 4-bit fields. 814 Filler 816 In the case of odd number of address signals, the filler code 0 0 0 0 817 is inserted after the last address signal. 819 2.6.5 CALLING PARTY NUMBER 820 length : 2 - 10 octets 822 8 7 6 5 4 3 2 1 823 +----+----------------------------------+ 824 I I I 825 IOdd/I Nature of address I 826 IevenI indicator I 827 I I I 828 +----+--------------+---------+---------+ 829 I I I I I 830 I NI I Reserved IPresent. I Screen- I 831 I I I ind. I ing I 832 I I I I I 833 +----+--------------+---------+---------+ 834 I I I 835 I 2nd address I 1st address I 836 I signal I signal I 837 I I I 838 +-------------------+-------------------+ 839 I : I 840 I : I 841 I : I 842 +-------------------+-------------------+ 843 I I I 844 I Filler I nth address I 845 I (if necessary) I signal I 846 I I I 847 +-------------------+-------------------+ 849 Odd/Even Indicator 851 0 Even number of address signals 852 1 Odd number of address signals 854 Nature of Address Indicator 856 0 0 0 0 0 0 0 Spare 857 0 0 0 0 0 0 1 Reserved 858 0 0 0 0 0 1 0 Reserved 859 0 0 0 0 0 1 1 National (significant) number 860 0 0 0 0 1 0 0 International number 861 0 0 0 0 1 0 1 862 to 863 1 1 1 1 1 1 1 Spare 865 Screening Indicator 867 0 0 Not available 868 0 1 User provided, verified and passed 869 1 0 Reserved 870 1 1 Network provided 872 When Sreening Indicator is coded 00 the fields: 874 Nature of Address Indicator, Address Presentation Restricted Indicator 875 and Calling Party Number Incomplete Indicator are not used and coded as 876 0. 878 Address Presentation Restricted Indicator 880 0 0 Presentation allowed 881 0 1 Presentation restricted 882 1 0 Reserved 883 1 1 Spare 885 Calling Party Number Incomplete Indicator (NI) 887 0 Complete 888 1 Incomplete 890 Address Signal 892 0 0 0 0 Digit 0 893 0 0 0 1 Digit 1 894 0 0 1 0 Digit 2 895 0 0 1 1 Digit 3 896 0 1 0 0 Digit 4 897 0 1 0 1 Digit 5 898 0 1 1 0 Digit 6 899 0 1 1 1 Digit 7 900 1 0 0 0 Digit 8 901 1 0 0 1 Digit 9 902 1 0 1 0 Spare 903 1 0 1 1 Code 11 904 1 1 0 0 Code 12 905 1 1 0 1 906 to 907 1 1 1 1 Spare 909 The most significant address signal is sent first. Subsequent address 910 signals are sent in successive 4-bit fields. 912 Filler 914 In the case of odd number of address signals, the filler code 0 0 0 0 915 is inserted after the last address signal. 917 The reserved bits are coded as 0. 919 2.6.6 CALLING PARTY'S CATEGORY 921 length : 1 octet 923 8 7 6 5 4 3 2 1 924 +-----------------------------------------+ 925 I I 926 I CALLING PARTY'S CATEGORY I 927 I I 928 +-----------------------------------------+ 930 Categories 932 0 0 0 0 0 0 0 0 Reserved 934 to 936 0 0 0 0 1 0 0 1 Reserved 938 0 0 0 0 1 0 1 0 Normal subscriber (default) 940 0 0 0 0 1 0 1 1 Reserved 942 0 0 0 0 1 1 0 0 Reserved 944 0 0 0 0 1 1 0 1 Test call 946 0 0 0 0 1 1 1 0 Reserved 948 to 950 1 1 1 1 1 1 1 1 Reserved 952 2.6.7 CAUSE INDICATORS 953 length : 1 octet 8 7 6 5 4 3 2 1 955 +---+-----------------------------+ 957 I 1 I Cause Value I 959 IextI I 961 +---+-----------------------------+ 963 Cause value 965 Class 0 0 0 and 0 0 1, normal event: 967 000 0001 (1) Unallocated (unassigned) number 968 000 0011 (3) No route to destination 969 000 0100 (4) Send special information tone 970 001 0000 (16) Normal clearing 971 001 0001 (17) User busy 972 001 0010 (18) No user responding 973 001 0011 (19) No answer from user 974 001 0101 (21) Call reject 975 001 0110 (22) Number changed 976 001 1011 (27) Destination out of order 977 001 1100 (28) Address incomplete 978 001 1111 (31) Normal, unspecified 980 Class 0 1 0, resources unavailable: 982 010 0010 (34) No circuit available 983 010 0110 (38) Network out of order 984 010 1001 (41) Temporary failure 985 010 1010 (42) Switching equipment congestion 986 010 1100 (44) Requested channel not available 987 010 1111 (47) Resource unavailable, unspecified 989 Class 0 1 1, service or option not available: 991 011 1001 (57) Bearer capability not authorized 992 011 1010 (58) Bearer capability not presently 993 available 994 011 1111 (63) Service or option not available, 995 unspecified 997 Class 1 0 0, service or option not implemented: 999 100 0001 (65) Bearer capability not implemented 1000 100 1111 (79) Service or option not implemented, 1001 unspecified 1003 Class 1 0 1, invalid message (e.g. parameter out of 1004 range): 1006 101 1111 (95) Invalid message, unspecified 1008 Class 1 1 0, protocol error (e.g. unknown message): 1010 110 0110 (102) Recover on timer expiry 1011 110 1111 (111) Protocol error, unspecified 1013 Class 1 1 1, interworking: 1015 111 1111 (127) Interworking, unspecified 1017 Extension indicator (ext) 1019 0 Reserved 1020 1 Last octet 1022 2.6.8 FORWARD CALL INDICATORS 1024 length : 1 octet 1026 8 7 6 5 4 3 2 1 1027 +---+---+---+---+---+---+---+---+ 1028 I I I I I I I I I 1029 I H I G I F I E I D I C I B I A I 1030 I I I I I I I I I 1031 +---+---+---+---+---+---+---+---+ 1033 A ISDN access indicator 1035 0 Originating access non-ISDN 1036 1 Originating access ISDN 1038 B to H Reserved 1040 The reserved bits are coded as 0. 1042 2.6.9 BACKWARD CALL INDICATORS 1044 length : 1 octet 1046 8 7 6 5 4 3 2 1 1047 +---+---+---+---+---+---+---+---+ 1048 I I I I I I I I I 1049 I H I G I F I E I D I C I B I A I 1050 I I I I I I I I I 1051 +---+---+---+---+---+---+---+---+ 1053 A In-band information indicator 1055 0 no-indication 1056 1 in-band information or an appropriate pattern 1057 is now available 1059 B to H Reserved 1061 The reserved bits are coded as 0. 1063 2.6.10 TRANSMISSION MEDIUM REQUIREMENT 1065 length : 1 octet 1067 8 7 6 5 4 3 2 1 1068 +---------------------------------+ 1069 I I 1070 +---------------------------------+ 1072 Transmission medium requirement 1074 0000 0000 speech 1075 0000 0001 64 kbit/s restricted 1076 0000 0010 64 kbit/s unrestricted 1077 0000 0011 3.1 khz audio 1078 0000 0100 reserved 1079 0000 0101 reserved 1080 0000 0110 spare 1081 0000 0111 reserved 1082 0000 1000 reserved 1083 0000 1001 reserved 1084 0000 1010 reserved 1085 0000 1011 1086 to 1087 1111 1111 spare 1089 2.7 Message Sequences for Different Traffic Cases 1091 2.7.1 Succsessful Call Set-up and Release 1093 2.7.1.1 Non-auto answer 1095 Alerting Indication with Address Complete Indication 1097 (A) (B) 1099 IAM includes I IAM I 1100 all address I --------------------> I 1101 signals I I 1102 I ACM I 1103 Inform A-user I <-------------------- I B user sends ALERT. 1104 with ALERT. I I 1105 I I 1106 I I 1107 I I 1108 I ANM I The B-user answers, 1109 I <-------------------- I ring tone removed. 1110 I I 1111 ... 1112 I I 1113 I REL I cause = normal clearing 1114 I --------------------> I 1115 I RLC I 1116 I <-------------------- I 1118 Note that NAS will not generate tones. 1120 2.7.1.2 Auto Answer 1121 (A) (B) 1123 IAM includes I IAM I 1124 all address I --------------------> I 1125 signals I I 1126 I CON I Routing is 1127 I <-------------------- I completed, the 1128 I I B-user has answered 1129 ... 1130 I I 1131 I REL I cause = normal clearing 1132 I --------------------> I 1133 I RLC I 1134 I <-------------------- I 1136 2.7.2 Signalling in Relation to Blocking 1138 2.7.2.1 Blocking, Single Circuit, Maintenance or Hardware Failure 1139 Oriented 1141 (A) (B) 1143 I I 1144 I BLO I 1145 I --------------------> I 1146 I I 1147 I BLA I 1148 I <-------------------- I 1149 I I 1151 2.7.2.2 Unblocking, Single Circuit, Maintenance or Hardware Failure 1152 Oriented 1154 (A) (B) 1156 I I 1157 I UBL I 1158 I --------------------> I 1159 I I 1160 I UBA I 1161 I <-------------------- I 1162 I I 1164 2.7.3 Interworking Cases 1166 2.7.3.1 ISUP-Etheric, non-auto answer 1168 ISUP Etheric 1170 (A) ---------------> (B) ---------------> (C) 1172 I IAM I I 1173 I ------------------> I IAM I 1174 I I ------------------> I 1175 I I ACM I 1176 I ACM I <------------------ I 1177 I <------------------ I I 1178 I I ANM I 1179 I ANM I <------------------ I 1180 I <------------------ I I 1181 I I I 1182 ... 1183 I I I 1184 I *) REL I I 1185 I ------------------> I REL I 1186 I RLC I ------------------> I 1187 I <------------------ I RLC I 1188 I I <------------------ I 1190 *) cause = normal clearing 1192 2.7.3.2 ISUP-Etheric, auto answer 1194 ISUP Etheric 1196 (A) ----------------> (B) ----------------> (C) 1198 I IAM I I 1199 I ------------------> I IAM I 1200 I I ------------------> I 1201 I I CON I 1202 I ACM I <------------------ I 1203 I <------------------ I I 1204 I ANM I I 1205 I <------------------ I I 1206 I I I 1207 ... 1208 I I I 1209 I *) REL I I 1210 I ------------------> I REL I 1211 I RLC I ------------------> I 1212 I <------------------ I RLC I 1213 I I <------------------ I 1215 *) cause = normal clearing 1217 2.7.3.3 DSS1-Etheric 1219 DSS1 Etheric 1221 (A) ----------------> (B) ----------------> (C) 1223 I SETUP I I 1224 I ------------------> I I 1225 I CALL PROC I I 1226 I <------------------ I IAM I 1227 I I ------------------> I 1228 I I ACM I 1229 I ALERTING I <------------------ I 1230 I <------------------ I I 1231 I I I 1232 I I ANM I 1233 I CONNECT I <------------------ I 1234 I <------------------ I I 1235 I I I 1236 I CONN ACK I I 1237 I ------------------> I I 1238 ... 1239 I I I 1240 I *) DISCONNECT I I 1241 I ------------------> I REL I 1242 I RELEASE I ------------------> I 1243 I <------------------ I RLC I 1244 I REL COM I <------------------ I 1245 I ------------------> I I 1247 *) cause = normal clearing 1249 2.8 Basic Call Control and Signalling Procedures 1251 2.8.1 Basic Procedures 1253 The basic call control procedure is divided into three phases; call 1254 set-up, the data/conversation phase and call clear-down. Messages are 1255 used to establish and terminate the different phases of a call. 1256 Standard inband supervisory tones are returned to the caller to provide 1257 information on call progress. 1259 2.8.2 Successful Call Set-up from PSTN-GW to NAS 1261 2.8.2.1 Forward address signalling 1263 a) Circuit selection 1265 When the originating exchange has received the complete selection 1266 information from the calling party (or an intermediate exchange has 1267 received the information via ISUP or other inter-exchange signalling), 1268 and has determined that the call is to be routed to target 1269 organisation, selection of a suitable, free circuit takes place and an 1270 Initial Address Message is sent to NAS. 1272 The selection of the route will depend on the called party number and 1273 connection type required. 1275 In addition, in the case of a subscriber with digital access, the 1276 set-up message contains bearer capability information which is analyzed 1277 by the originating exchange to determine the correct connection type. 1278 The information received from the access interface is used to set the 1279 value of the Transmission Medium Requirement parameter. 1281 At an intermediate exchange the connection type is set according to the 1282 signalling information received via inter-exchange signalling. 1284 The connection types allowed are: 1286 - speech. 1287 - 64 kbit/s restricted. 1288 - 64 kbit/s unrestricted. 1289 - 3.1 kHz audio. 1291 The connection type will be included in the Initial Address Message, 1292 (as Transmission Medium Requirement). The Initial Address Message 1293 conveys implicitly the meaning that the indicated circuit has been 1294 seized. 1296 b) Initial Address Message 1298 The Initial Address Message contains all the information that is 1299 required to route the call to the correct target organisation. 1301 All Initial Address Messages will include a Calling Party Category 1302 Parameter, a Called Party Number Parameter (minimum of 1 address 1303 signal), a Calling Party Number Parameter (can have an indicator that 1304 calling party number is not included) and a Transmission Medium 1305 Requirement Parameter. 1307 The Transmission Medium Requirement Parameter contains the connection 1308 type e.g. 64 kbit/s unrestricted. 1310 c) Completion of transmission path 1312 Through connection of the transmission path will be completed in the 1313 backward direction immediately after the reception of the Address 1314 Complete Message (the transmission path is completed in the forward 1315 direction on receipt of a Connect or Answer Message). 1317 d) Await address complete 1319 When the PSTN-GW has sent the Initial Address Message the awaiting 1320 address complete timer T7 is started. If timer T7 expires the 1321 connection is released and an indication is returned to the calling 1322 subscriber. 1324 2.8.2.2 Address Complete Message and Connect Message 1326 Return of Address Complete Message from NAS 1328 An Address Complete Message will be sent from the NAS as soon as it has 1329 reserved all necessary resources to handle the incoming call (connected 1330 the modem etc.). 1332 Return of Connect Message from NAS 1334 The Connect Message signifies both address complete and answer 1335 conditions. 1337 Receipt of Address Complete/Connect Message at PSTN-GW 1339 Intermediate exchange 1341 Upon receipt of an Address Complete Message an intermediate exchange 1342 will send the corresponding Address Complete Message to the preceding 1343 exchange. If this is the controlling exchange the awaiting answer 1344 timer(T9) is started. If timer(T9) expires the connection is released 1345 and an indication is sent to the calling subscriber. 1347 If a Connect Message is received at an intermediate exchange instead of 1348 an Address Complete Message, a Connect Message will be sent to the 1349 preceding exchange. 1351 Originating exchange 1353 a) On receipt of an Address Complete Message an alerting indication is 1354 passed to the calling party if possible. 1356 b) On receipt of the Address Complete Message the awaiting address 1357 complete timer (T7) is stopped and the awaiting answer timer (T9) is 1358 started if this is the controlling exchange. If timer (T9) expires 1359 the connection is released and an indication is sent to the calling 1360 subscriber. 1362 c) If the Connect Message is received then, the awaiting address 1363 complete timer(T7) is stopped. 1365 2.8.2.3 Answer Message 1367 On detection of answer the controlling exchange will stop timer (T9). 1369 Return of Answer Message from NAS 1371 When the call is connected to the target organisation the NAS 1372 terminates the transmission path and the ringing tone is removed if 1373 applicable. An Answer Message to the PSTN-GW is sent. 1375 Receipt of Answer Message at PSTN-GW 1377 When the PSTN-GW receives an Answer Message indicating the required 1378 connection has been completed, the transmission path is connected 1379 through in the forward direction, if not already connected. 1381 The calling party is informed (originating exchange) or a corresponding 1382 Answer Message is sent to the preceding exchange (intermediate 1383 exchange). 1385 Return of answer from automatic terminals 1387 When connections are set-up to terminals having an automatic answer 1388 feature, the alerting indication may not be received. When the 1389 connection from NAS to target organisation is set up an Answer Message 1390 is sent provided that an Address Complete Message has been sent, 1391 otherwise the Connect Message is sent. 1393 2.8.3 Successful Call Set-up from NAS to PSTN-GW 1395 2.8.3.1 Forward address signalling 1397 a) Selection of called party 1399 Upon receipt of an Initial Address Message the destination exchange 1400 will analyze the called party number to determine to which party the 1401 call should be connected. It will also check the called party's line 1402 condition. If the connection is allowed the destination exchange will 1403 setup a connection to the called party. 1405 An intermediate exchange, on receipt of an Initial Address Message, 1406 will analyze the called party number and the other routing information 1407 (TMR) to determine the routing of the call. If the intermediate 1408 exchange can route the call using the connection type specified in the 1409 Transmission Medium Requirement Parameter, a free inter-exchange 1410 circuit is seized and an Initial Address Message (or corresponding 1411 signalling information in other signalling systems) is sent to the 1412 succeeding exchange. 1414 2.8.3.2 Address Complete Message and Connect Message 1416 Return of Address Complete Message from destination exchange 1418 An Address Complete Message will be sent from the destination exchange 1419 as soon as it has been determined that the complete called party number 1420 has been received, or an alerting indication is received from the 1421 called party. However there is no direct mapping from alerting, 1422 received from the access signalling system, to address complete. 1424 Return of Connect Message from the destination exchange 1426 If a connect indication is received from the ISDN access under the 1427 following conditions, 1429 - no alerting indication received from the ISDN access, and 1430 - an Address Complete Message has not yet been sent by the destination 1431 exchange, 1433 a Connect Message is sent by the destination exchange. This Connect 1434 Message signifies both address complete and answer conditions. 1436 The destination exchange will through connect before the Connect 1437 Message is sent. 1439 Receipt of Address Complete/Connect Message at an intermediate exchange 1441 Upon receipt of an Address Complete/Connect Message an intermediate 1442 exchange will send an Address Complete/Connect Message to NAS. 1444 2.8.3.3 Answer Message 1446 Return of Answer Message 1448 When the called party answers (destination exchange), or if Answer 1449 Message (or corresponding signalling information) is received 1450 (intermediate exchange), PSTN-GW connects through the transmission path 1451 and the ringing tone is removed if applicable. An Answer Message to 1452 NAS is sent. 1454 2.8.4 Unsuccessful Call Set-up 1456 If at any time in the call set-up the connection cannot be completed a 1457 Release Message is returned. This message contains the reason (cause 1458 code). 1460 2.8.4.1 Actions at the node initiating a Release Message 1462 The initiating node (PSTN-GW or NAS) immediately starts the release of 1463 the switched path (if established). The node sends a Release Message to 1464 the other node and timers T1 and T5 are started to ensure that a 1465 Release Complete Message is received. (Expiration of timers T1 and T5 1466 are covered in section 2.8). 1468 2.8.4.2 Actions at the node receiving a Release Message 1470 On receipt of a Release Message, the release of the switched path is 1471 started. 1473 In addition, the receiving node will (if applicable) attempt to re-route the call. 1475 When the switched path is released, a Release Complete Message is sent. 1477 2.8.5 Normal Call Release 1479 The release procedures are based on a two message (Release, Release 1480 Complete) approach whereby the Release Message initiates release of the 1481 circuit switched connection. 1483 The same procedures are used irrespective of whether the release is 1484 initiated from PSTN-GW or NAS. 1486 Actions at the release initiating node 1488 On receipt of a request to release the call, the node immediately 1489 starts the release of the switched path. A Release Message is sent to 1490 the other node and timers T1 and T5 are started to ensure that a 1491 Release Complete Message is received. 1493 Actions at the release receiving node 1495 On receipt of a Release Message, the node will start the release of the 1496 switched path. When the switched path is released a Release Complete 1497 Message is returned to the other node. 1499 2.8.5.1 Collision of Release Messages 1501 In the case when two points in the connection both initiate the release 1502 of a call, a Release Message may be received after the release of the 1503 switched path is initiated. In this case, a Release Complete Message is 1504 returned to the node from which the concerned Release Message was 1505 received. The Release Complete Message will be sent when the switched 1506 path is released. 1508 2.8.6 Network Features 1510 2.8.6.1 Automatic repeat attempt 1512 Automatic repeat attempt, as defined in Recommendation Q.12 is 1513 provided: 1515 i) on detection of dual seizure (at the non-control node); 1517 ii) on receipt of a Blocking Message after sending an Initial 1518 Address Message and before any backward message has been 1519 received; 1521 iii) on receipt of a Reset Circuit Message after sending an Initial 1522 Address Message and before a backward message has been 1523 received; 1525 iv) on receipt of an unreasonable message during call set up. 1527 2.8.6.2 Blocking and unblocking of circuits 1529 The Blocking and Unblocking Messages are provided to permit the 1530 switching equipment or maintenance system to remove from (and return 1531 to) traffic, circuits because of a fault or to permit testing. 1533 Since the circuits have bothway capability, the Blocking Message can be 1534 originated by either node. The receipt of a Blocking Message, will have 1535 the effect of, prohibiting non test calls on the relevant circuit 1536 outgoing from the PSTN-GW and all calls from NAS (Test calls are only 1537 initiated from PSTN-GW to NAS). This condition will remain until an 1538 Unblocking Message is received, but will not prohibit test calls 1539 incoming to the NAS. Test calls generated in the outgoing direction 1540 from the PSTN-GW that sent the Blocking Message will also be processed. 1541 Non-test Initial Address Messages will result in an abnormal case. 1543 An acknowledgement sequence is always required for the Blocking and 1544 Unblocking Message. This is performed using the Blocking 1545 Acknowledgement Message or the Unblocking Acknowledgement Message. The 1546 acknowledgement is not sent until the appropriate action, either 1547 blocking or unblocking has been taken. The Release Message should not 1548 override a blocking message and return circuits to service which might 1549 be faulty. 1551 The blocked circuit will be returned to service: 1552 - on transmission of the Unblocking Acknowledgement Message at one end, 1553 - on reception of the Unblocking Acknowledgement Message at the other 1554 end. 1556 Other actions on receipt of a Blocking Message 1558 In the event of a Blocking Message being received, after an Initial 1559 Address Message has been sent in the opposite direction on that 1560 circuit, and before a backward message relating to that call has been 1561 received, an automatic repeat attempt will be made on another circuit. 1562 The node receiving the Blocking Message releases the original call 1563 attempt in the normal manner after sending the Blocking Acknowledgement 1564 Message and will not seize that circuit for subsequent calls. 1566 If the Blocking Message is received 1568 - after an Initial Address Message has been sent for that circuit in 1569 the opposite direction and after at least one backward message 1570 relating to that call has been received, or 1572 - after an Initial Address Message has been received for that circuit 1573 beforehand, the node will not seize that circuit for subsequent 1574 calls. 1576 The fact that the circuit is engaged on a call will not delay 1577 transmission of the Blocking (Unblocking) Acknowledgement Message. 1579 If a Blocking Message is sent and subsequently an Initial Address 1580 Message is received in the opposite direction, the following action is 1581 taken; 1583 - for test calls, the call should be accepted in NAS, if possible. In 1584 the case where the test call cannot be accepted, the Blocking Message 1585 must be repeated; 1586 - for calls other than test calls, the Blocking Message must be 1587 repeated and the Initial Address Message discarded. 1589 When a circuit is blocked by use of the Blocking Message the 1590 maintenance system should be informed at both ends of the circuit. 1592 Abnormal blocking procedures 1594 The following procedures are designed to cover abnormal cases which may 1595 occur in the blocking/unblocking procedures. 1597 i) if a Blocking Message is received for a blocked circuit, a 1598 Blocking Acknowledgement Message will be sent; 1599 ii) if an Unblocking Message is received for an unblocked circuit, 1600 an Unblocking Acknowledgement Message will be sent. 1601 iii) if a Blocking Acknowledgement Message, which is not expected as 1602 an acknowledgement for a Blocking Message, is received; 1604 - relating to a circuit which is locally blocked, the Blocking 1605 Acknowledgement Message is discarded; 1607 - relating to a circuit which is not locally blocked, then the 1608 maintenance system is notified. 1610 iv) if an Unblocking Acknowledgement Message, which is not an 1611 expected response to an Unblocking Message, is received; 1613 - relating to a circuit which is not locally blocked, the received 1614 Unblocking Acknowledgement Message is discarded; 1616 - relating to a circuit which is locally blocked then the maintenance 1617 system is notified. 1619 v) If a non test Initial Address Message is received on a remotely 1620 blocked circuit, the remotely blocked state of the circuit is 1621 removed and the Initial Address Message is processed normally 1622 unless the circuit is also locally blocked in which case the 1623 Initial Address Message is discarded. However it should not be 1624 the preferred method of unblocking a circuit. 1626 2.8.7 Abnormal Conditions 1628 2.8.7.1 Dual seizure 1630 Because circuits have the capability of bothway operation, it is 1631 possible that the two nodes will attempt to seize the same circuit at 1632 approximately the same time. 1634 Detection of dual seizure 1636 A dual seizure is detected by a node from the fact that it receives an 1637 Initial Address Message for a circuit for which it has sent an Initial 1638 Address Message, but before it receives a valid backwards message. 1640 Preventive Action 1642 An opposite order of selection is used at each node of a bothway 1643 circuit group. PSTN-GW will always select circuits from the lowest 1644 device (CIC) number end and NAS from the highest device number of a 1645 circuit group. 1647 Actions to Be Taken on Detection of Dual Seizure 1649 The PSTN-GW will control all circuits. On detection of a dual seizure, 1650 the call being processed by the controlling node (PSTN-GW) for that 1651 circuit will be completed and the received Initial Address Message will 1652 be disregarded. 1654 Under these conditions, the call being processed by the controlling 1655 node will be allowed to continue. The call being processed by the 1656 non-controlling node will be dropped and the switch-path released. A 1657 Release Message will not be sent. The non-controlling node will make an 1658 automatic repeat attempt on the same or on an alternative route. 1660 2.8.7.2 Reset of circuits 1662 In systems which maintain circuit status in memory there may be 1663 occasions when the memory becomes mutilated. In such a case the 1664 circuits must be reset to the idle condition at both nodes to make them 1665 available for new traffic. Since the system with the mutilated memory 1666 does not know whether the circuits are idle, busy outgoing, busy 1667 incoming, blocked, etc., Reset Circuit Messages or a Circuit Group 1668 Reset Message should be sent as appropriate for the affected circuits. 1670 Reset Circuit Message 1672 On receipt of a Reset Circuit Message the receiving (unaffected) node 1673 will; 1675 a) if it is the incoming or outgoing node on a connection in any state 1676 of call set-up or during a call, accept the message as a Release 1677 Message and respond by sending a Release Complete Message, after the 1678 circuit has been made idle; 1680 b) if the circuit is in the idle condition, accept the message as a 1681 Release Message and respond by sending a Release Complete Message; 1683 c) if it has previously sent a Blocking Message, or if it is unable to 1684 release the circuit as described above, respond with a Blocking 1685 Message. If an incoming or outgoing call is in progress, this call 1686 should be released and the circuit returned to the blocked 1687 condition. A Release Complete Message is sent following the Blocking 1688 Message. The Blocking Message should be acknowledged by the affected 1689 exchange. If the acknowledgement is not received, the repetition 1690 procedure should be followed; 1692 d) if it has previously received a Blocking Message, respond by 1693 releasing a possible outgoing call or call attempt on the circuit, 1694 remove the blocked condition, restore the circuit to the idle state, 1695 and respond with a Release Complete Message; 1697 e) if the message is received after the sending of an Initial Address 1698 Message but before receipt of a backward message relating to that 1699 call, clear the circuit and make an automatic repeat attempt on 1700 another circuit if appropriate; 1702 f) if the message is received after having sent a Reset Circuit 1703 Message, respond by a Release Complete Message. After receipt of the 1704 appropriate acknowledgement message, the circuit should be made 1705 available for service. 1707 g) clear any interconnected circuits by the appropriate method (e.g. 1708 release). 1710 The affected node will then reconstruct its memory according to the 1711 received response(s) to the Reset Circuit Message, and respond to the 1712 message(s) in the normal way i.e. send Blocking Acknowledgement Message 1713 in response to a Blocking Message. If the circuit is in a blocked 1714 condition, blocking procedures should be re-initiated. 1716 If no Release Complete Message is received in acknowledgement to the 1717 Reset Circuit Message within time T16, the Reset Circuit Message should 1718 be repeated. If an acknowledgement for the message is not received 1719 within time T17 after the initial Reset Circuit Message, the 1720 maintenance system should be notified. However, the sending of the 1721 Reset Circuit Message should continue at time T17 intervals until 1722 maintenance intervention occurs. 1724 Circuit Group Reset Message 1726 If all circuits at either node are affected by a memory mutilation, 1727 Circuit Group Reset Message should be used to make them available for 1728 new traffic. 1730 On receipt of a Circuit Group Reset Message the receiving (unaffected) 1731 node will; 1733 a) restore the circuits to the idle state; 1734 b) send the appropriate Blocking Message(s) if it had previously sent 1735 Blocking Message(s); 1736 c) respond by a Circuit Group Reset Acknowledgement Message; 1737 d) if it had previously received (a) Blocking Message(s) for one or 1738 more of the circuit(s) involved, the blocked condition will be 1739 removed and the circuits will be made available for service; 1740 e) if a Circuit Group Reset Message is received after having sent a 1741 Circuit Group Reset Message or a Reset Circuit Message the concerned 1742 circuits, are made available for service after receipt of the 1743 appropriate acknowledgement message; 1744 f) appropriate messages should be sent on interconnected circuits to 1745 release them. 1747 The affected node will then reconstruct its memory according to the 1748 possibly received Blocking Messages and the received Circuit Group 1749 Reset Acknowledgement Message. It will respond to the possibly received 1750 Blocking Messages in the normal way. If the circuit is in a blocked 1751 condition, blocking procedures should be re-initiated. 1753 If no acknowledgement to a Circuit Group Reset Message is received 1754 within time T22, the Circuit Group Reset Message should be repeated. If 1755 an acknowledgement for the Circuit Group Reset Message is not received 1756 within time T23 after sending the initial Circuit Group Reset Message 1757 the maintenance system should be notified. However, the sending of the 1758 Circuit Group Reset Message should continue at time T23 intervals until 1759 maintenance intervention occurs. 1761 Abnormal circuit group reset message procedures 1763 i) if a Circuit Group Reset Acknowledgement Message is received which 1764 is not a correct response to a sent Circuit Group Reset Message, it 1765 is discarded. 1767 2.8.7.3 Failure in the blocking/unblocking sequence 1769 A node will repeat the Blocking (Unblocking) Message on failure to 1770 receive the appropriate acknowledgement in response to one of these 1771 messages before the respective timer T12 (T14) expires. 1773 If the appropriate acknowledgement is not received within time T13 1774 (T15) after sending the initial Blocking (Unblocking) Message, the 1775 maintenance system should be alerted, the repetition of the Blocking 1776 (Unblocking) Message should be continued at time T13 (T15) intervals 1777 until maintenance intervention occurs and the circuit is taken out of 1778 (returned to) service as appropriate. 1780 2.8.7.4 Receipt of unreasonable/unrecognized signalling information 1781 Messages 1783 Undetected errors at the TCP/IP level and exchange malfunctions may 1784 produce signalling information Messages that are either ambiguous or 1785 inappropriate. 1787 The following are considered message format errors: 1789 a) The message length is less than the number of octets required for 1790 the fixed mandatory part and the mandatory variable pointers. 1791 b) A mandatory variable pointer points beyond the message length. 1792 c) A mandatory variable causes the overall message length to be 1793 exceeded. 1795 When a message format error is detected the message shall be discarded. 1797 Note : A format error can only be detected when the message is 1798 recognized. For the purposes of format error detection, the 1799 message length is interpreted as the received message length. 1801 Message format error checks are performed on all messages. 1803 The procedures listed below do not include the procedures for blocking, 1804 unblocking and reset, these are covered in separate sections. 1806 Handling of unrecognized information 1808 Unrecognized messages and parameters should be discarded without 1809 disrupting normal call handling. 1811 Unrecognized parameter values should be handled according to the Table 1812 1. 1814 The following actions are defined 1816 Default : Handle as if default value was 1817 received 1819 Discard Parameter : Entire parameter is discarded 1821 Release : Call is released with appropriate 1822 cause value 1824 Table 1 Required Actions for Unrecognised Parameter Values 1826 +----------------------------------+--------------------------------+ 1827 I I I 1828 I Parameter Field Name I Required Action I 1829 I I I 1830 +----------------------------------+--------------------------------+ 1831 I I I 1832 I Called Party Number I I 1833 I . Nature of address indicator I Send release with cause 28 I 1834 I . Address signals I Send release with cause 28 I 1835 I . Filler I Default: 0000 I 1836 I I I 1837 +----------------------------------+--------------------------------+ 1838 I I I 1839 I Calling Party Number I I 1840 I . Nature of address indicator I Discard parameter I 1841 I . Address presentation I Default: 01 'presentation I 1842 I restricted indicator I restricted' I 1843 I . Screening indicator I Discard parameter I 1844 I . Address signals I Discard parameter I 1845 I . Filler I Default: 0000 I 1846 I I I 1847 +----------------------------------+--------------------------------+ 1848 I I I 1849 I Calling Party's Category I I 1850 I . Categories I Default: 0000 1010 'ordinary I 1851 I I subscriber'I 1852 I I I 1853 +----------------------------------+--------------------------------+ 1854 I I I 1855 I Cause Indicators I I 1856 I . Cause value I Default: 'Unspecified within I 1857 I I class xxx' I 1858 I I I 1859 +----------------------------------+--------------------------------+ 1860 I I I 1861 I Transmission Medium Requirement I I 1862 I . Transmission medium requirementI Send release with cause 65 I 1863 I I I 1864 +----------------------------------+--------------------------------+ 1866 2.8.7.5 Handling of Unexpected Messages 1868 An unexpected message is one which contains a valid message type code 1869 but has been received in the wrong phase of the call. 1871 In order to resolve possible ambiguities in the state of a circuit when 1872 unexpected messages are received the following will apply; 1874 a) if a Release Message is received relating to an idle circuit it will 1875 be acknowledged with a Release Complete Message; 1876 b) if a Release Complete Message is received relating to an idle 1877 circuit it will be discarded; 1878 c) if a Release Complete Message is received relating to a busy circuit 1879 for which a Release Message has not been sent, the circuit will be 1880 released and a Release Message will be sent. 1881 d) if other unexpected messages are received, the following actions 1882 will be undertaken; 1884 - if the circuit is idle, the Reset Circuit Message is sent; 1885 - if the circuit has been seized by a call, after receipt of a backward 1886 message required for the call set-up, the unreasonable signalling 1887 information is discarded; 1888 - if the circuit has been seized by a call, before receipt of a 1889 backward message required for the call set-up, the Reset Circuit 1890 Message is sent. If the circuit is seized by an incoming call, the 1891 call will be released. If the circuit is seized by an outgoing call, 1892 an automatic repeat attempt is provided on another circuit. 1894 2.8.7.6 Failure to receive a "Release Complete" Message - Time T1 and 1895 T5 1897 If a Release Complete Message is not received in response to a Release 1898 Message before time T1, the Release Message is retransmitted. 1900 If no Release Complete Message is received on the expiry of timer T5, 1901 the node shall; 1903 i) send a Reset Circuit Message; 1904 ii) alert the maintenance system; 1905 iii) remove the circuit from traffic; 1906 iv) continue the sending of the Reset Circuit Message at time T17 1907 intervals until maintenance action occurs. 1909 2.8.7.7 Other Failure Conditions 1911 Call-failure 1913 The call-failure indication (cause #31) is sent in a Release Message 1914 whenever a call attempt fails and other specific signals do not apply. 1915 Reception of the Release Message at intermediate exchange will cause 1916 the Release Message to be sent to preceding exchanges. If the 1917 signalling does not permit theRelease Message to be sent, the 1918 appropriate signal, tone or announcement is sent to the preceding 1919 exchange. 1921 2.8.8 Start-up Procedures 1923 The start-up procedure between PSTN-GW and NAS is a manually controlled 1924 procedure. It is initiated by PSTN-GW for each circuit. After the 1925 start-up procedure the circuits are in manually blocked condition. 1927 During the process of placing circuits into service, unacknowledged 1928 circuit supervision messages will most likely be reported to 1929 maintenance system. In order to minimize this impact, it is 1930 recommended that coordination takes place between PSTN-GW and NAS and 1931 established procedures for placing circuits into service be followed 1932 (Circuits are first taken into service in NAS and then in PSTN-GW). 1933 Lack of coordination may result in inefficient use of exchange and 1934 maintenance resources. 1936 2.8.8.1 Initial procedure for putting circuits into service 1938 PSTN-GW ----> NAS 1940 -----RSC----> 1942 <----RLC----- 1944 * <----BLO----- 1946 -----BLA----> 1948 -----BLO----> ** 1950 <----BLA----- 1952 *) PSTN-GW updates the remote blocking condition (Circuit blocked in 1953 NAS) 1955 **) NAS updates the remote blocking condition (Circuit blocked in 1956 PSTN-GW) 1958 Circuits are deblocked 1960 PSTN-GW ----> NAS 1962 -----UBL----> (1) 1964 <----UBA----- 1966 <----UBL----- (2) 1968 -----UBA----> 1970 (1) Circuit is deblocked in PSTN-GW. 1972 (2) Circuit is deblcoked in NAS. (The circuits can be deblocked first 1973 either in NAS or PSTN-GW.) 1975 The Circuits are now ready for traffic. 1977 2.8.9 Loadsharing 1979 The signalling is loadshared between the two TCP connections. 1981 The messages with even CIC use one TCP connection, and the messages 1982 with odd CIC the other connection. Following conditions are exceptions 1983 to that principle: 1985 All messages are then sent on the working TCP connection, if the other 1986 connection is not working. 1988 Group Reset Message is always acknowledged using the same TCP 1989 connection upon which it was received. 1991 Blocking messages are always acknowledged using the same TCP connection 1992 upon which it was received. The reason for this is the exchange of 1993 blocking messages after restart situations when one TCP connection may 1994 not be started yet. 1996 2.8.10 TCP/IP Connection Break 1998 If the TCP/IP connection (or both connections in case of duplicated 1999 Ethernet) between PSTN-GW and NAS goes down, the following actions take 2000 place: 2002 - All circuits are blocked for new calls. 2003 - Calls in set-up phase are released without exchanging release 2004 messages. 2005 - Calls in Active state are kept. 2007 PSTN-GW tries to open the TCP/IP connection after a supervised time. If 2008 the opening does not succeed, PSTN-GW retries to open the connection 2009 until it succeeds. The time, after which PSTN-GW tries to open the 2010 connection, is 2 - 3 seconds at the first try. After that the 2011 supervision time is increased at each try, until the maximum time limit 2012 is reached. After that the a new try is done with an interval of the 2013 maximum time. 2015 The timeout values are: 2017 - Increase step 1 - 120 seconds, default value 15 seconds 2018 - Maximum interval 4 - 300 seconds, default value 120 seconds 2020 When the TCP/IP connection (at least one connection in case of 2021 duplicated Ethernet) comes up, the following actions take place: 2023 - All circuits are deblocked. 2024 - A Reset Circuit Message is sent for the calls that were released 2025 during the time the TCP/IP connections were down. 2027 2.9 Timers 2029 +--------+--------------+----------------------------+ 2030 I I I I 2031 I SYMBOL I TIME-OUT I CAUSE FOR INITIATION I 2032 I I VALUE I I 2033 I I I I 2034 +--------+--------------+----------------------------+ 2035 I I I I 2036 I T 1 I4-60 IWhen Release Message is I 2037 I ISeconds Isent I 2038 I I I I 2039 +--------+--------------+----------------------------+ 2040 I I I I 2041 I T 5 I1-15 IWhen initial Release I 2042 I IMinutes IMessage is sent I 2043 I I I I 2044 +--------+--------------+----------------------------+ 2045 I I I I 2046 I T 7 I20-30 IWhen Initial Address I 2047 I ISeconds IMessage is sent I 2048 I I I I 2049 +--------+--------------+----------------------------+ 2050 I I I I 2051 I T 9 I1-4 IWhen Address Complete I 2052 I IMinutes IMessage is received I 2053 I I I I 2054 +--------+--------------+----------------------------+ 2055 I I I I 2056 I T 12 I4-60 IWhen Blocking Message is I 2057 I ISeconds Isent I 2058 I I I I 2059 +--------+--------------+----------------------------+ 2060 I I I I 2061 I T 13 I1-15 IWhen initial Blocking I 2062 I IMinutes IMessage is sent I 2063 I I I I 2064 +--------+--------------+----------------------------+ 2065 I I I I 2066 I T 14 I4-60 IWhen Unblocking Message is I 2067 I ISeconds Isent I 2068 I I I I 2069 +--------+--------------+----------------------------+ 2070 I I I I 2071 I T 15 I1-15 IWhen initial Unblocking I 2072 I IMinutes IMessage is sent I 2073 I I I I 2074 +--------+--------------+----------------------------+ 2075 I I I I 2076 I T 16 I4-60 IWhen Reset Circuit Message I 2077 I ISeconds Iis sent not due to expiry I 2078 I I Iof T5 I 2079 I I I I 2080 +--------+--------------+----------------------------+ 2081 I I I I 2082 I T 17 I1-15 IWhen initial Reset Circuit I 2083 I IMinutes IMessage is sent I 2084 I I I I 2085 +--------+--------------+----------------------------+ 2086 I I I I 2087 I T 22 I4-60 IWhen Circuit Group Reset I 2088 I ISeconds IMessage is sent I 2089 I I I I 2090 +--------+--------------+----------------------------+ 2091 I I I I 2092 I T 23 I1-15 IWhen initial Circuit Group I 2093 I IMinutes IReset Message is sent I 2094 I I I I 2095 +--------+--------------+----------------------------+ 2097 +--------+--------------------------+---------------------------------+ 2098 I I I I 2099 I SYMBOL I NORMAL TERMINATION I AT EXPIRY I 2100 I I I I 2101 +--------+--------------------------+---------------------------------+ 2102 I I I I 2103 I T 1 I At receipt of the I Retransmit Release Message and I 2104 I I Release Complete message I start timer T1 I 2105 I I I I 2106 +--------+--------------------------+---------------------------------+ 2107 I I I I 2108 I T 5 I At receipt of the I Send Reset Circuit Message, I 2109 I I Release Complete message I alert maintenance personnel and I 2110 I I I remove the circuit from I 2111 I I I service, stop T1, start T17. I 2112 I I I Procedure continues until I 2113 I I I maintenance intervention I 2114 I I I occurs. I 2115 I I I I 2116 +--------+--------------------------+---------------------------------+ 2117 I I I I 2118 I T 7 I When the condition for I Release all equipment and I 2119 I I normal release of I connection I 2120 I I address and routing I (Send Release Message) I 2121 I I information is met ( I I 2122 I I receipt of ACM, CON, I I 2123 I I messages) I I 2124 I I I I 2125 +--------+--------------------------+---------------------------------+ 2126 I I I I 2127 I T 9 I At the receipt of Answer I Release connection I 2128 I I Message I send back Release Message I 2129 I I I I 2130 +--------+--------------------------+---------------------------------+ 2132 +--------+--------------------------+---------------------------------+ 2133 I I I I 2134 I SYMBOL I NORMAL TERMINATION I AT EXPIRY I 2135 I I I I 2136 +--------+--------------------------+---------------------------------+ 2137 I T 12 I At receipt of Blocking I Retransmit Blocking Message I 2138 I I Acknowledgement Message I and restart T12 I 2139 +--------+--------------------------+---------------------------------+ 2140 I T 13 I At receipt of Blocking I Retransmit Blocking Message, I 2141 I I Acknowledgement Message I alert maintenance personnel, I 2142 I I I restart T13 and stop T12. I 2143 I I I Procedure continues until I 2144 I I I maintenance intervention I 2145 I I I occurs. I 2146 +--------+--------------------------+---------------------------------+ 2147 I T 14 I At receipt of Unblocking I Retransmit Unblocking Message I 2148 I I Acknowledgement Message I and restart T14 I 2149 +--------+--------------------------+---------------------------------+ 2150 I T 15 I At receipt of Unblocking I Retransmit Unblocking Message I 2151 I I Acknowledgement Message I alert maintenance personnel, I 2152 I I I restart T15 and stop T14. I 2153 I I I Procedure continues until I 2154 I I I maintenance intervention I 2155 I I I occurs. I 2156 +--------+--------------------------+---------------------------------+ 2157 I T 16 I At the receipt of the I Retransmit Reset Circuit I 2158 I I Release Complete Message I Message and restart T16 I 2159 I I (acknowledgement) I I 2160 +--------+--------------------------+---------------------------------+ 2161 I T 17 I At the receipt of the I Alert maintenance personnel, I 2162 I I Release Complete Message I retransmit Reset Circuit I 2163 I I (acknowledgement) I Message, restart T17, stop T16. I 2164 I I I Procedure continues until I 2165 I I I maintenance intervention I 2166 I I I occurs. I 2167 +--------+--------------------------+---------------------------------+ 2168 I T 22 I At the receipt of the I Retransmit Circuit Group Reset I 2169 I I Circuit Group Reset I Message and restart T22 I 2170 I I Acknowledgement Message I I 2171 +--------+--------------------------+---------------------------------+ 2172 I T 23 I At the receipt of the I Alert maintenance personnel, I 2173 I I Circuit Group Reset I retransmit Circuit Group Reset I 2174 I I Acknowledgement Message I Message, restart T23, stop T22. I 2175 I I I Procedure continues until I 2176 I I I maintenance intervention I 2177 I I I occurs. I 2178 +--------+--------------------------+---------------------------------+ 2180 3. References 2182 [1] ITU-T Recomendation Q.767. Specifications of Signalling system 2183 No. 7. Applications of the ISDN User Part of CCITT Signalling 2184 System No. 7 for international ISDN connections. 2186 4. Intellectual property rights 2188 Authors are not aware of any IPR issues covering this draft. However, 2189 we have not done a proper screening on this and it may be that there 2190 are some patents, even inside Ericsson, covering all or part of this 2191 internet draft. 2193 5. Authors 2195 Harri Toivanen 2196 Oy LM Ericsson Ab 2197 02420 JORVAS 2198 Finland 2199 Phone: +358-9-299 2247 2200 Email: Harri.Toivanen@ericsson.com 2202 Petteri Laamo 2203 Oy LM Ericsson Ab 2204 02420 JORVAS 2205 Finland 2206 Phone: +358-9-299 2747 2207 Email: Petteri.Laamo@lmf.ericsson.se 2209 George Wayne 2210 Advanced Computer Communications 2211 340 Storke Road 2212 Santa Barbara, CA 93117 2213 U.S.A. 2214 Email: gwayne@acc.com 2216 Paul Harding-Jones 2217 Advanced Computer Communications 2218 340 Storke Road 2219 Santa Barbara, CA 93117 2220 U.S.A. 2221 Email: phj@acc.com