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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Media Gateway Control (Megaco) Gunnar Hellstrom 2 Internet Draft LM Ericsson 3 Document: draft-ietf-megaco-h248f-01.txt Glenn Parsons 4 Category: Standards Track Nortel Networks 5 Expires July 2001 James Rafferty 6 Brooktrout Technology 7 Roy Spitzer 8 Telogy Networks 9 January 14, 2001 11 H.248 Annex F (Fax, Text Conversation, and Call discrimination) 13 Status of this Memo 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026 [1]. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. Internet-Drafts are draft documents valid for a maximum of 22 six 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." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 1. Abstract 33 This document reproduces the content of the ITU-T Study Group 16 34 White Document draft of H.248 Annex F, which was decided in Geneva 35 in November 2000. It also includes minor corrections made in 36 January 2001. 37 This document is submitted for IETF in accordance with 38 procedures currently being negotiated between 39 ITU-T Study Group and ISOC on behalf of the IETF. 41 H.248 Annex F describes packages for fax, text telephone, call type 42 discrimination, and data call detection for use with the 43 H.248 Gateway Control Protocol. As defined in H.248, a "package" is 44 an extension to H.248 that supports specific behavior. 46 The packages are intended for control over gateway functions for 47 transport of facsimile or text conversation between different 48 network environments. Extensions can be made for other kinds of data 49 transport. 51 The Call Type Discrimination package defines control and monitoring 52 of a PSTN line for the signaling protocols used in the beginning of 53 a session of data transmission for fax, text telephony or data. 55 Hellstrom/Parsons/Rafferty/Spitzer Standards track 1 57 H.248 Annex F (Decided and amended) Jan. 2001 59 The Text Telephone package defines control of a PSTN text telephone 60 session in any of the modes supported by the automoding text 61 telephone Recommendation V.18. 63 The Fax package defines control of a PSTN fax transmission. 65 The Fax/Textphone/Modem Tones Detection package defines control over 66 a termination for detection of any signals from a fax, text 67 telephone or data modem during a connection in voice mode. 69 The Text Conversation package defines control over a real time 70 interactive text conversation session using a universal presentation 71 format and transferred with a transport method from a multimedia 72 protocol in any network environment. 74 The IP Fax package defines control over facsimile transmission in a 75 packet network. 77 2. TABLE OF CONTENTS 79 1. Abstract.......................................................1 81 2. TABLE OF CONTENTS..............................................2 83 3. Conventions used in this document..............................5 85 4. Introduction...................................................5 86 4.1 Scope.................................................5 88 5 Definitions...................................................6 89 5.1 Hexadecimal octet coding.................................6 90 5.2 Hexadecimal octet sequence...............................6 92 6. FAX/Textphone/Modem Tones Detection Package....................7 93 6.1 Properties.............................................7 94 6.2 Events.................................................8 95 6.2.1 Additional tone id value.......................8 96 6.3 Signals................................................8 97 6.4 Statistics.............................................8 98 6.5 Procedures.............................................8 100 7 Text Conversation package.....................................9 101 7.1 Properties.............................................9 102 7.1.1 Text buffering time............................9 103 7.1.2 Text termination connection state.............10 104 7.1.3 Text User Identity............................11 105 7.1.4 Text Transport................................11' 106 7.1.5 Text Protocol Version.........................12 107 7.1.6 Redundancy Level..............................12 108 7.1.7 Txc request timer.............................12 110 Hellstrom/Parsons/Rafferty/Spitzer Standards track 2 112 H.248 Annex F (Decided and amended) Jan. 2001 114 7.2 Events................................................13 115 7.2.1 Connection State Change.......................13 116 7.3 Signals...............................................13 117 7.4 Statistics............................................13 118 7.4.1 Characters Transferred........................13 119 7.4.2 Lost Packets..................................13 120 7.5 Procedures............................................13 121 7.5.1 Function......................................14 122 7.5.2 Informative description.......................14 123 7.5.3 Total Conversation............................15 124 7.5.4 Descriptor to use for text conversation.......15 125 8. Text Telephone package......................................16 126 8.1 Properties............................................18 127 8.1.1 Conversation mode.............................18 128 8.1.2 Communication Mode............................19 129 8.1.3 Connection Mode...............................21 130 8.1.4 Action at loss of connection..................22 131 8.1.5 V18 options...................................22 132 8.1.6 Character set.................................22 133 8.2 Events................................................23 134 8.2.1 Connection mode changed.......................23 135 8.3 Signals...............................................23 136 8.4 Statistics............................................23 137 8.4.1 Number of characters transferred..............23 138 8.4.2 Number of alternating turns...................24 139 8.5 Procedures............................................24 140 8.5.1 Basic operation...............................24 141 8.5.2 Informative description.......................24 142 8.5.3 V.18 Modem....................................24 143 8.5.4 Operation with alternating text and voice mode25 144 8.5.5 Alternating text and voice mode with legacy, 145 carrier-less textphones:............................25 146 8.5.6 Alternating voice and text conversation in 147 carrier mode:.......................................26 148 8.5.7 Simultaneous voice and text mode..............26 149 9. Call Type Discrimination package............................27 150 9.1 Properties............................................27 151 9.1.1 Call Types....................................27 152 9.1.2 Text Call Types...............................27 153 9.1.3 V8bissupport..................................28 154 9.1.4 Probe message.................................28 155 9.1.5 Probe order...................................28 156 9.1.6 PhasereversalDetect...........................29 157 9.2 Events................................................29 158 9.2.1 Discriminating tone detected..................29 159 9.3 Signals...............................................32 160 9.3.1 V8Signal......................................32 161 9.3.2 AnswerSignal..................................33 162 9.3.3 CallingSignal.................................34 163 9.3.4 V8bisSignal...................................34 164 9.3.5 V18probe......................................34 166 Hellstrom/Parsons/Rafferty/Spitzer Standards track 3 168 H.248 Annex F (Decided and amended) Jan. 2001 170 9.4 Statistics............................................36 171 9.5 Procedures............................................36 173 9.5.1 Informative description.......................36 174 9.5.2 Operation.....................................37 175 9.5.3 Operation for incoming calls..................37 176 9.5.4 Operation for transit calls, coming from and 177 going to the switched network.......................37 178 9.5.5 Operation for calls having one endpoint in the 179 packet network......................................38 180 9.5.6 Cases when the call type can not be determined 181 from the signals....................................39 182 9.5.7 Scenarios and call flows......................39 183 9.5.8 Initial characters............................39 184 9.5.9 Time critical handling........................39 186 10. Fax package................................................40 187 10.1 Properties...........................................40 188 10.1.1 Fax connection state.........................40 189 10.1.2 Fax Transport................................41 190 10.1.3 TransmissionSpeed............................41 191 10.1.4 PSTN Interface...............................42 192 10.2 Events...............................................42 193 10.2.1 Fax Connection State Change..................42 194 10.3 Signals..............................................42 195 10.4 Statistics...........................................42 196 10.4.1 Pages Transferred............................42 197 10.4.2 Train Downs..................................43 198 10.5 Procedures...........................................43 199 10.5.1 Function.....................................43 200 10.5.2 Process of Adding Fax Capable Terminations...43 201 10.5.3 Process of Ending a Fax Call.................44 202 11. IP Fax package.............................................44 203 11.1 Properties...........................................44 204 11.1.1 Fax connection state.........................44 205 11.1.2 IPFaxTransport...............................45 206 11.1.3 TransmissionSpeed............................45 207 11.1.4 T.38 Capabilities............................45 208 11.1.5 T38MaximumBufferSize.........................46 209 11.1.6 T38MaximumDatagramSize.......................46 210 11.1.7 T38Version...................................46 211 11.2 Events...............................................46 212 11.2.1 Fax Connection State Change..................46 213 11.3 Signals..............................................47 214 11.4 Statistics...........................................47 215 11.4.1 Pages Transferred............................47 216 11.4.2 Train Downs..................................48 218 Hellstrom/Parsons/Rafferty/Spitzer Standards track 4 220 H.248 Annex F (Decided and amended) Jan. 2001 222 11.5 Procedures...........................................48 223 11.5.1 Function.....................................48 224 11.5.2 Process of Adding IP Fax Capable Terminations49 225 11.5.3 Process of Ending a Fax Call.................49 226 11.5.4 Informative Example:.........................49 228 12. Security Considerations......................................50 230 13. References...................................................50 232 14. Acknowledgements.............................................51 234 15. Authors' Addresses...........................................51 236 3. Conventions used in this document 238 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 239 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 240 this document are to be interpreted as described in RFC-2119 [2]. 242 4. Introduction 244 This document gathers together packages for fax, text telephone, 245 call type discrimination and data call detection for use with the 246 Megaco/H.248 gateway control protocol. The packages in this document 247 are in conformance with Megaco/H.248 section 12 package definition 248 guidelines. 250 4.1 Scope 252 H.248 Annex F describes packages for the Megaco/H.248 gateway 253 control protocol related to data or telematic services. With 254 terminations implementing these packages, a gateway is expected to 255 handle initial modem negotiations, and the communication in voice, 256 fax and text telephone call types. 258 It contains: 260 Package "ftmd" for general detection of signals on a fixed telephone 261 line indicating a possible request to enter some data related mode. 263 Package "ctyp" for general call discrimination to sort out if a call 264 should be handled as voice, fax , text telephone or modem data, and 265 perform the initial negotiation. 267 Package "txp" for communicating with text telephones in the 268 telephone network. 270 Package "fax" for communication with facsimile in the telephone 271 network.Hellstrom/Parsons/Rafferty/Spitzer Standards track 5 273 H.248 Annex F (Decided and amended) Jan. 2001 275 Package "txc" for general text conversation in other environments. 277 Package "ipfax" for fax transmission in IP networks. 279 5 Definitions 281 5.1 Hexadecimal octet coding 283 Hexadecimal octet coding is a means for representing a string of 284 octets as a string of hexadecimal digits, with two digits 285 representing each octet. 287 Each octet is issued by the DTE or DCE in the same time sequence as 288 transmitted on the GSTN line, with no intervening characters. 289 For each octet, the 8-bit sequence is encoded as two hexadecimal 290 digits. Bit 0 is the first transmitted; bit 7 is the last. 292 Bits 7-4 are encoded as the first hexadecimal digit, with Bit 7 as 293 MSB and Bit 4 as LSB. Bits 3-0 are encoded as the second hexadecimal 294 digit, with Bit 3 as MSB and Bit 0 as LSB. 296 Examples: 298 Octet bit pattern Hexadecimal T.50 codes 299 (time order as coding 300 specified in V.8 and 301 V.8 bis) 303 00011011 D8 4/4, 3/8 305 11100100 27 3/2, 3/7 307 10000011 10100010 C1451390 4/3, 3/1, 3/4, 308 11001000 00001001 3/5, 3/1, 3/3, 309 3/9, 3/0 311 5.2 Hexadecimal octet sequence 313 A hexadecimal octet sequence is an even number of hexadecimal 314 digits, terminated by a (T.50 0/13) character. 316 6. FAX/Textphone/Modem Tones Detection Package 318 PackageID: ftmd, 0x000E 319 Version: 1 320 Extends: tonedet version 1 322 Hellstrom/Parsons/Rafferty/Spitzer Standards track 6 324 H.248 Annex F (Decided and amended) Jan. 2001 326 This package defines an event to detect the presence of data traffic 327 (fax, textphone or modem) on a line. The main intention of this 328 event may be used to effect the compression option on the line so 329 that an audio codec capable of transmitting modem signals can be 330 invoked to handle the connection when needed. This Package extends 331 the possible values of tone id in the "start tone detected" event. 332 Note that there is no discrimination between tones from this 333 package. If discrimination is desired, the Call Type Discrimination 334 package should be invoked. 336 6.1 Properties 338 None 340 6.2 Events 342 Events are defined as for the tone detection package. 344 6.2.1 Additional tone id value 346 dtfm, 0x0039 347 This tone id is generated when any of the following tones are 348 detected: 350 "Tone" Description Applicable to 352 CNG a T.30 fax calling Fax 354 V21flag a V21 tone and flags Fax 356 CIV18 a V.8 CI with V.18 call Textphone 357 function 359 XCI a V.18 XCI Textphone 361 V18txp a V.18 "txp" Textphone 363 Belltone a Bell 103 carrier, either the Textphone 364 high or the low frequency 365 channel (as defined in V.18) 367 Baudot a Baudot initial tone and Textphone 368 character (as def. in V.18) 370 Edt an EDT initial tone and Textphone 371 character (as def. in V.18) 373 CIdata a V.8 CI with any data call Data 374 function 375 Hellstrom/Parsons/Rafferty/Spitzer Standards track 7 377 H.248 Annex F (Decided and amended) Jan. 2001 379 CT a V.25 calling tone Text and Data 381 CIfax a V.8 CI with facsimile call Fax 382 function 384 V21tone a V.21 carrier, either the high Text and Data 385 or the low frequency channel 387 V23tone a V.23 carrier, either the high Text and data 388 or the low frequency channel 390 V8bis a V.8 bis modem handshaking Fax, Text and 391 signal Data 393 ANS V.25 ANS, equivalent to T.30 Fax, Text and 394 CED from answering terminal Data 396 ANSAM V.8 ANSam Fax, Text and 397 Data 398 6.3 Signals 400 None 402 6.4 Statistics 404 None 406 6.5 Procedures 408 None 410 7 Text Conversation package 412 PackageID: txc (0x00F) 413 Version: 1 414 Extends: None 416 Description: 417 The Text Conversation package is intended for enabling real time 418 text conversation between terminals in different networks or 419 multimedia environments. This package includes the mechanisms needed 420 to transport T.140 text conversation streams [11] in multimedia 421 environments. The transport mechanism will be different for each 422 environment where the package is used. 424 Hellstrom/Parsons/Rafferty/Spitzer Standards track 8 426 H.248 Annex F (Decided and amended) Jan. 2001 428 7.1 Properties 430 7.1.1 Text buffering time 432 PropertyID: bufftime (0x0001) 433 Type: Integer 434 Possible values: 0-500 435 Defined in: LocalControl 436 Characteristics: Read/Write 438 Description: 439 This property indicates the time in ms that T.140 [8] data shall be 440 collected before transmission in order to keep overhead from text 441 low. In low bitrate IP networks, a value of 500 ms is recommended. 442 In environments with low overhead or high bitrates this property 443 should have the value 0 enabling immediate transmission of entered 444 characters. 446 7.1.2 Text termination connection state 448 PropertyID: connstate (0x0002) 449 Type: Enumeration 450 Possible values: 452 Idle (0x0001) for no 453 connection 454 efforts 456 Prepare (0x0002) for being known 457 in the 458 termination and 459 ready to accept 460 connections. 461 (The text 462 capability is 463 offered in 464 session 465 requests.) 467 Initiate (0x0003) for taking the 468 initiative to 469 establish a text 470 connection 471 opening a text 472 channel 474 Accept (0x0004) for accepting an 475 incoming request 476 for a text 477 session 479 Hellstrom/Parsons/Rafferty/Spitzer Standards track 9 481 H.248 Annex F (Decided and amended) Jan. 2001 483 Deny (0x0005) for denying an 484 incoming text 485 connect request 487 Connected (0x0006) for established 488 connection in 489 text mode 490 Defined in: TerminationState 491 Characteristics: Read/Write 493 Description: 494 The connection state property is used to register text capability, 495 request a text connection, and reflect details of the achieved text 496 connection. For transport methods having separate channel control 497 procedures, managed by the MGC, only a subset of the values is 498 used: Idle, Prepare, Connected. 500 7.1.3 Text User Identity 502 PropertyID: txuserid (0x0003) 503 Type: String 504 Possible value: String of up to 64 characters in Unicode 505 UTF-8 [23]. 506 Defined in: LocalControl 507 Characteristics: Read/Write 508 Description: 509 This parameter holds the optional remote User Identity parameter of 510 a T.140 [11] text conversation session, retrieved from the session. 512 7.1.4 Text Transport 514 PropertyID: trpt (0x0004) 515 Type: Enumeration 516 Possible values: 518 H224 (0x0001) for H.224 Client 519 ID=2 in H.320 521 AL1 (0x0002) for AL1 in H.324 523 TCP (0x0003) for TCP as in 524 H.323 Annex G 525 [12] 527 Hellstrom/Parsons/Rafferty/Spitzer Standards track 10 529 H.248 Annex F (Decided and amended) Jan. 2001 531 RTP/T140 (0x0004) for RTP with 532 T140 [11] as in 533 H323 Annex G 534 [12] or IETF SIP 536 RTP/RED/T140 (0X0005) for RTP with 537 T140 and 538 redundancy 539 coding RED as 540 in H323 Annex G 541 or IETF SIP 543 T134 (0X0006) for T.134 in the 544 T.120 545 environment [14] 547 Unassigned (0X0007) When no 548 transport 549 protocol is 550 assigned 551 Defined in: LocalControl 552 Characteristics: Read/Write 554 Description: 555 The Transport parameter reflects the transport mechanism selected 556 for the Text Conversation termination. When the media description 557 has the full capability of describing sessions including the 558 transport mechanism, this parameter is implied by the media 559 descriptor. 561 7.1.5 Text Protocol Version 563 PropertyID: TextProto (0x0005) 564 Type: Integer 565 Possible values: Any integer 566 corresponding to a 567 T.140 version number. 568 (currently 1) 569 Defined in: LocalControl 570 Characteristics: Read/Write 571 Description: 572 The version of the T.140 protocol used in the connection. 574 7.1.6 Redundancy Level 576 PropertyID: red (0x0006) 577 Type: Integer 579 Hellstrom/Parsons/Rafferty/Spitzer Standards track 11 581 H.248 Annex F (Decided and amended) Jan. 2001 583 Possible values: 0-6 584 0=use default or automatic decision on redundancy level 585 (default) 586 1=Use no redundancy 587 2-6=use specified number of generations of data. 589 Defined in: LocalControl 590 Characteristics: Read/Write 592 Description: 593 The number of generations to use in RTP redundancy coding including 594 the Primary. 596 7.1.7 Txc request timer 598 PropertyID: txctim (0x0007) 599 Type: integer 600 Possible values: 0-6000 601 Default: 0 602 Defined in: LocalControl 603 Characteristics: Read/Write 605 Description: 606 The txctim property is a timer value in tenths of seconds for the 607 requested operation. If the requested operation is not completed 608 within this time, the state is returned to Idle and the result 609 reported in the connchange event. An initial timer value of 0 610 indicates that no timer control is requested. 612 7.2 Events 614 7.2.1 Connection State Change 616 Event Id: connchange (0x0001) 618 EventDescriptorParameters: none 620 ObservedEventDescriptorParameters: 622 ParameterName: Connection Change 623 ParameterID: connchng (0X0001) 624 Type: Enumeration 625 Possible Value: As property txc/connstate 627 Description: 628 This event will occur when the text connection state for the 629 termination has changed. Its parameter is the new contents of the 630 Connection State property. 632 If a request timed out, the state is returned to Idle. 634 Hellstrom/Parsons/Rafferty/Spitzer Standards track 12 636 H.248 Annex F (Decided and amended) Jan. 2001 638 7.3 Signals 640 None 642 7.4 Statistics 644 7.4.1 Characters Transferred 646 StatisticsID: chartrans (0x0001) 647 Units: count 649 Description: 650 No of bytes of T140 data transferred through the termination. 652 7.4.2 Lost Packets 654 StatisticsID: packlost (0x0002) 655 Units: count 657 Description: 658 Number of T140 packets lost as counted by the receiving T.140 659 termination. 661 7.5 Procedures 663 The following are standard transport mechanisms for text 664 conversation in different environments. 665 * In H.320: H.224 with Client ID=2 666 * In H.324: AL1 channel connected with H.245 procedures 667 * In T.120. T.134 transport in T.125 communication channel 668 environment. 669 * In H.323. RTP/T140 or TCP as selected with H.245 messages. 670 * In IETF SIP: RTP/T140 as initiated with SDP. 671 Note that the T140 text media is also used together with V.18 [9] 672 modems for text telephony, specified in a separate package: 673 Text_Telephone (txp). 675 The Text Conversation package is intended to be added to a 676 multimedia termination, handling appropriate multiplexing and 677 control. 679 7.5.1 Function 681 A termination with Text Conversation adds capability declaration for 682 a text conversation channel in the call setup according to 683 procedures defined for each environment. When matching capabilities 684 exist, a T140 channel can be established according to the transport 685 protocol used in the current environment. T140 text stream contents 686 received from one termination is transferred for transmission to 687 other t140 capable terminations in the context. The T140 contents 688 may be buffered for a short moment for possible collection of more 689 text in the same transmission according to the buffer time property. 690 Hellstrom/Parsons/Rafferty/Spitzer Standards track 13 692 H.248 Annex F (Decided and amended) Jan. 2001 694 7.5.2 Informative description 696 Real time text conversation allows telecom users to carry out a 697 written conversation. The presentation and coding aspects of 698 standardised text conversation are defined in ITU-T T.140. Text is 699 transmitted character by character (or in small blocks ) so that the 700 users experience a close interaction. The text and basic editing 701 control is ISO 10 646-1, UTF-8 [23] coded. The figure gives an 702 example of how a text conversation can be displayed to the user. 704 -------------------------------------------------------------------- 705 |ANNE |EVE | 706 | | | 707 |Hi, this is Anne. |Oh, hello Anne, I am glad you | 708 | |are calling! It was long | 709 |Yes, have you heard that I will |since we met! | 710 |come to Paris in November? | | 711 | |No, that was new to me. What | 712 | |brings you here? | 713 -------------------------------------------------------------------- 714 Figure: Possible display of a one to one text conversation. 716 For each transport environment, a suitable transport protocol must 717 be selected to carry the text. Currently defined and Recommended 718 transport environments for T.140 text media streams that can be 719 supported by this package are: 721 1. Packet networks, where the procedures described in H.323 Annex G 722 [12] can be used for setting up and conducting text conversation 723 sessions, using TCP or RTP/T140 for the transport of T.140. 725 2. Packet networks, where the IETF Session Initiation Protocol SIP 726 can be used for setting up and conducting text conversation sessions 727 using RTP/T140 for the transport of T.140. 729 3. The H.324 multimedia environment in PSTN, ISDN and Mobile 730 networks, where an AL1 channel connected by H.245 procedures is used 731 for T.140. 733 4. The H.320 multimedia environment, where a H.224 channel with 734 client ID=2 is specified for transport of T.140. 736 5. The T.120 data conferencing environment, that can be used alone 737 or in conjunction with any of the environments above, where T.134 738 specifies the application entity and T.125 the data channel for 739 T.140. 741 Hellstrom/Parsons/Rafferty/Spitzer Standards track 14 743 H.248 Annex F (Decided and amended) Jan. 2001 745 A separate Text Telephone package (txp) supports text telephony in 746 the PSTN using the ITU-T V.18 modem in native and legacy modes and 747 T.140 for communication with terminations using this package. 748 Interworking between these forms of Text Conversation can be 749 achieved through the use of gateways with packages defined here. 751 7.5.3 Total Conversation 753 Most text conversation transport environments are part of multimedia 754 communication systems. With the introduction of text, they enable 755 conversation in video, text and voice simultaneously, called Total 756 Conversation. The total set of communication modes that people tend 757 to use locally can be offered on a distance through Total 758 Conversation. Since the text part is built on the unified 759 presentation level T.140, the task to arrange interoperability of 760 Total Conversation in different network environments through a 761 gateway is simplified. 763 Video is optional in the multimedia systems. Therefore compatible 764 text-and-voice conversation can also be established within the same 765 framework. 767 7.5.4 Descriptor to use for text conversation. 769 One descriptor value is of specific interest for the Text 770 Conversation and Text Telephone packages. That is the text 771 conversation media stream. It is described here for information. 773 Text conversation stream 775 This descriptor is used for the text conversation stream, according 776 to ITU-T T.140 [11]. T.140 gives a general presentation level 777 description for a termination supporting real time text 778 conversation. The text and basic editing control is UTF-8 coded 779 [23]. For each transport environment, a suitable transport protocol 780 must be selected to carry the text. 782 T140 is a registered MIME text stream name, that can be specified to 783 be used as it is or in RTP embedding of RFC 2793 [13]. 785 Examples: 787 From MGC to MG in an ADD command, the T140 stream could be specified 788 as this example shows: 789 Media { Stream = 4 { LocalControl { 790 Mode = ReceiveOnly, 791 g/NetworkType = RTP/IP4, 792 g/PreferredCodecs=T140}}} 794 Hellstrom/Parsons/Rafferty/Spitzer Standards track 15 796 H.248 Annex F (Decided and amended) Jan. 2001 798 The MG would return the SDP specification for the media stream: 799 Media { Stream = 4 {Local = SDP { 800 v=0 801 c=IN IP4 125.125.125.111 802 m=text 1111 RTP/AVP 98 803 a=rtpmap:96 red 804 a=fmtp: 98 96/96 805 a=rtpmap: 96 t140}}} 807 8. Text Telephone package 809 PackageID : txp (0x0010) 810 Version: 1 811 Extends: None 813 Description 815 The text telephone package is used on a line termination in a Media 816 Gateway, to handle text telephone calls. It includes V.18 [9] text 817 telephone modem functionality that adapts to different legacy text 818 telephone systems in the PSTN as well as it provides communication 819 with V.18 equipped text telephones. The text media stream is UTF-8 820 coded [23] with a few editing functions as specified in ITU-T T.140 821 [11]. The text telephone package is intended to be operated together 822 with the Call Type Discrimination package (ctyp) to perform V.18 823 automoding functions. 825 Text Telephony 827 Text Telephony offers a real time conversation in text between two 828 parties. It may be combined with voice conversation. Text telephony 829 in PSTN existed in at least 6 incompatible legacy modes before the 830 automoding modem Recommendation for text telephony V.18 was 831 introduced by the ITU. V.18 is suitable for use in PSTN text 832 telephones, but also in gateways for connection to the PSTN text 833 telephones. When connected, it can operate in one of its native V.18 834 modes, or in any of the 6 legacy modes described in V.18 annexes. 835 The legacy modes are Baudot, EDT, DTMF, V.21, Minitel and Bell103. 836 The mode detection and adjustment of the transmission to the 837 selected mode is automatic. 839 The native modes use ITU-T T.140 for the text coding and control and 840 V.21 [17] or optionally V.61[22] for the modulation. The legacy 841 modes use different character coding schemes, but when used in a 842 gateway, the text stream to and from the textphone termination is 843 T.140 coded for all modes. The text telephone package described here 844 includes character conversion, filtering and other adaptation needed 845 for conversation with the legacy mode text telephones. 847 Hellstrom/Parsons/Rafferty/Spitzer Standards track 16 849 H.248 Annex F (Decided and amended) Jan. 2001 851 Carrier modes and carrier-less modes. 853 Three of the legacy textphone modes are carrier-less. This means 854 that they do not send any signal at all when there are no characters 855 to transmit. Three legacy modes and the native V.18 modes use a 856 carrier tone transmitted as long as the connection is maintained. If 857 the carrier stops, it is detected but the line is not disconnected, 858 because this is normal behaviour during call transfer and 859 alternating voice and text usage. 861 Text telephone package considerations above the V.18 modem level. 863 V.18 only specifies an automoding modem and the requirement to use 864 T.140 when V.18 native mode is achieved in a connection. When used 865 in a gateway, there are some general issues that must be handled 866 above the V.18 level. 868 Character set. 870 The legacy modes have limited character sets. For all legacy modes, 871 appropriate character conversion, filtering and control interception 872 is included in the package functionality, so that the communication 873 with other T140 text terminations in the context is equalized to a 874 T140 text stream. 876 Embedded termination functionality 878 There is no need to open all details of the use of V.18 and T.140 to 879 be accessible from the MGC in a gateway. V.18, T.140, character 880 conversion methods and other automated methods are therefore 881 combined in the text telephone package that can be added to suitable 882 terminations of a gateway. 884 Hellstrom/Parsons/Rafferty/Spitzer Standards track 17 886 H.248 Annex F (Decided and amended) Jan. 2001 888 This figure describes the text telephone 889 package components. 891 Control Text stream Audio stream 892 | | | 893 | | | 894 | | | 895 | |_____________________| | 896 | | | | 897 |-----> | T.140 | | 898 | | | | 899 | |_____________________| | 900 | | | | 901 | | | | 902 | |___________________| |___________________| | 903 | | | | | | 904 |->| Transparent text | | T.140 conversion | | 905 | | transmission for | | for legacy | | 906 | | native V.18 modes | | textphone modes | | 907 | | | | | | 908 | |___________________| |___________________| | 909 | | | | 910 | | | | 911 | |_____________________| | 912 | | | Simultaneous audio | 913 |-----> | V.18 |---------------------| 914 | | Modem | | 915 | | | | 916 | |_____________________| | 917 | | | 918 | | | 919 | / \ | 920 | / \ Alternating audio | 921 |-------------------->/ \-----------------------------| 922 \ / 923 \ / 924 \ / 925 | 926 | 927 Line interface 929 Figure : Text telephone package functional view 931 8.1 Properties 933 8.1.1 Conversation mode 935 PropertyID: convmode (0x0001) 936 Type: Sub-list 938 Possible values: 940 Hellstrom/Parsons/Rafferty/Spitzer Standards track 18 942 H.248 Annex F (Decided and amended) Jan. 2001 944 Text-only (0x0001) Basic text only mode, not 945 possible to combine with voice. 946 Alternating (0x0002) Text and voice may be 947 alternating. 948 Simultaneous (0x0003) Simultaneous text and voice 949 mode. 950 Defined in: Termination state 951 Characteristics: Read/Write 953 Description: 955 The behaviour of the termination is influenced by this property. By 956 setting the property to a selection of the possible values, the 957 number of ways that the conversation can be conducted can be 958 defined. After connection the property contains the actual 959 conversation mode used in the call. 961 The basic text only mode shall always be supported. 963 The alternating text and voice mode is most often used to enable one 964 user to speak and read and the other to listen and type. It is used 965 because there was no technology support for simultaneous voice and 966 text when text telephony was introduced. It is only supported for 967 compatibility with the legacy mode text telephone habits. 969 The simultaneous text and voice mode enables the users to 970 communicate in any combination and order of the two media. No legacy 971 mode terminals operate in this mode. V.18 equipped terminals with 972 V.61 [21] modulation can operate in this mode. 974 8.1.2 Communication Mode 976 PropertyID: commode (0x0002) 977 Type: Enumeration 978 Possible values: 980 V18-V21Hi (0x0001) native V.18 mode transmitting 981 on the high channel for text 982 only or text and voice 983 alternatively. 985 V18-V21Lo (0x0002) native V.18 mode transmitting 986 on the low channel for text 987 only or text and voice 988 alternatively. 990 V18-V61C (0x0003) native V.18 mode for text and 991 voice simultaneously, 993 transmitting in the caller's 994 channel. 996 Hellstrom/Parsons/Rafferty/Spitzer Standards track 19 998 H.248 Annex F (Decided and amended) Jan. 2001 1000 V18-V61A (0x0004) native V.18 mode for text and 1001 voice simultaneously, 1002 transmitting in the answering 1003 part's channel. 1005 V21Hi (0x0005) legacy V.21 mode transmitting 1006 on the high channel 1008 V21Lo (0x0006) legacy V.21 mode transmitting 1009 on the low channel. 1011 DTMF (0x0007) DTMF text telephone mode. 1013 EDT (0x0008) EDT ("European Deaf Telephone") 1015 Baudot 45 (0x0009) Baudot 45.45 bits / s 1017 Baudot 47 (0x000A) Baudot undetermined bitrate 1019 Baudot 50 (0x000B) Baudot 50 bits/s 1021 V23Hi (0x000C) V.23 modulation and Minitel 1022 coding transmitting on the high 1023 channel 1025 V23Lo (0x000D) V.23 modulation and Minitel 1026 coding, transmitting on the low 1027 channel. 1029 BellHi (0x000E) Bell 103, transmitting on the 1030 high channel 1032 BellLo (0x000F) Bell 103, transmittion on the 1033 low channel 1035 None (0x0010) No mode achieved 1036 Defined in: LocalControl 1037 Characteristics: Read/Write 1039 Description: 1041 This property indicates what modulation and mode the V.18 modem is 1042 operating in, reflecting what type of text telephone it is in 1043 connection with. For an explanation of the different modes, see 1044 ITU-T V.18 [9]. 1046 If specific mode operation is wanted, this property is set before 1047 the text connection is made. Normally it is set with the outcome of 1048 the V.18 automoding procedure performed with the Call Type 1049 Discrimination package. 1051 Hellstrom/Parsons/Rafferty/Spitzer Standards track 20 1053 H.248 Annex F (Decided and amended) Jan. 2001 1055 When a legacy mode textphone signal is detected by the Call Type 1056 Discrimination package, the connection result is only reported, but 1057 V.18 does not transmit any signal until ordered to do so by setting 1058 this property or when probing is invoked from this package. 1060 8.1.3 Connection Mode 1062 PropertyID: connmode (0x0003) 1063 Type: Enumeration 1064 Possible values: 1066 Idle (0x0001) No connection established and no efforts 1067 to connect 1069 Connecting (0x0002) For request of the native or legacy mode 1070 indicated in the Communication Mode 1071 property. 1073 Connected (0x0003) Connection established in one of the 1074 communication modes 1075 Defined in: Termination State. 1076 Characteristics: Read/Write 1078 Description: 1079 This property indicates in what connection phase and mode the V.18 1080 modem is operating. A connection effort is initiated by setting this 1081 property to connecting, with the desired mode in the Communication 1082 Mode property. 1084 A V.18 modem can be controlled to operate in one of a set of modes 1085 for seeking contact with a counterpart. The modes available are 1086 listed as values of this property. Determination of the mode is made 1087 by the ctype package, possibly combined with the probing action of 1088 thatis package. 1090 Once connected, the termination operates in the selected mode until 1091 the text connection is lost or it is ordered to disconnect. If text 1092 connection is lost for a certain time, the automoding procedure can 1093 be restarted through the ctyp package, or the modem can stay in the 1094 achieved mode trying to reconnect. 1096 The ctyp package may be used on a connected voice line to detect if 1097 the remote user want to enter text mode. It must be noted that for 1098 some of the legacy modes (EDT, DTMF and Baudot), the user has to 1099 push some keys on the textphone to make the connection when V.18 is 1100 set in the automode monitor mode. This is slightly unusual for a 1101 textphone user, who normally waits for the answering side to start 1102 the conversation. Therefore, the explicit automoding modes should be 1103 used when possible, probing as answering and sending V.18 signals as 1104 calling. 1106 Hellstrom/Parsons/Rafferty/Spitzer Standards track 21 1108 H.248 Annex F (Decided and amended) Jan. 2001 1110 If a connection request fails, the property returns to Idle state. 1111 If the connection request succeeds, the property changes value to 1112 Connected. 1114 8.1.4 Action at loss of connection 1116 PropertyID: lossconnection (0x0006) 1117 Type: Enumeration 1118 Possible values: 1119 Keep: (0x0001) keep selected communication mode 1120 Return: (0x0002) return to automoding. 1121 Defined in: Termination State 1122 Characteristics: Read/Write 1124 Description: 1125 This property tells how the V.18 modem handles loss of text 1126 connection. When "Keep" is selected, the conversation is optimised 1127 for the alternating text - voice mode.When "Return" is selected, the 1128 communication is optimised for call forwarding between different 1129 types of text telephones. For that case, ctyp must be invoked for 1130 reconnection. 1132 8.1.5 V18 options 1134 PropertyID: v18opt (0x0007) 1135 Type: Enumeration 1136 Possible values: List of: 1137 V.61 capability (0x0001): indicates the ability to use V.61 1138 modulation[22] 1139 Defined in: Termination state 1140 Charateristics: Read/Write 1142 Description: 1143 This property indicates what optional capabilities the V.18 modem 1144 implementation has and is allowed to use. 1146 8.1.6 Character set 1148 PropertyID: characterset (0x0008) 1149 Type: String 1150 Possible values: ISO registered name for a character set. 1151 Defined in: Termination State 1152 Characteristics: Read/Write 1154 Description: 1155 The legacy modes have limited character sets. For all legacy modes, 1156 appropriate character conversion, filtering and control interception 1157 is included in the package functionality, so that the communication 1158 with other T140 text terminations in the context is equalized to a 1159 T140 text stream. 1161 Hellstrom/Parsons/Rafferty/Spitzer Standards track 22 1163 H.248 Annex F (Decided and amended) Jan. 2001 1165 For a user friendly conversion of received 1166 national characters in the limited character sets to ISO 10 646-1 1167 used in T.140, there is a need to specify what national translation 1168 table to use. This is valid for EDT, DTMF, V.21 and Baudot modes. 1169 The Character set parameter is the the registered ISO code for the 1170 national variant of the ITU-T T.50 [24] character set used. Default 1171 is: 1172 * German for EDT, 1173 * Danish for DTMF (suitable also for the Netherlands), 1174 * Swedish/Finnish for V.21 (suitable also for UK), 1175 * International Reference Version for Baudot. 1177 Example: In Norway, the letter "A" (A and E together) is used in the 1178 same location of the 7-bit character table as used for letter "A" (A 1179 with umlaut) in Finland and Sweden. The international reference 1180 version has the character "[" (left bracket) in the same position. 1181 In T140 these characters have unique positions. 1183 8.2 Events 1185 8.2.1 Connection mode changed 1187 EventID: connchng (0x0001) 1189 EventDescriptorParameters: none 1191 ObservedEventDescriptorParameters: 1193 Same as the property txp/commode 1195 Description: 1196 This event reports the change of communication mode, as result of a 1197 connection effort, or a disconnection. 1199 8.3 Signals 1201 None. 1203 8.4 Statistics 1205 8.4.1 Number of characters transferred 1207 StatisticsID: chartrans (0x0001) 1208 Units: count 1209 Description: 1210 Number of bytes of T140 data transferred.(sent and received) 1212 8.4.2 Number of alternating turns. 1214 StatisticsID: altturns (0x0002) 1215 Units: count 1216 Hellstrom/Parsons/Rafferty/Spitzer Standards track 23 1218 H.248 Annex F (Decided and amended) Jan. 2001 1220 Description: 1221 Number of alternating turns when using alternating conversation 1222 mode. 1224 8.5 Procedures 1226 8.5.1 Basic operation 1228 After line connection, the termination where the Text Telephone 1229 package is implemented should be requested to try a text telephone 1230 connection using the functionality of the Call Type Discrimination 1231 Package for the modem signalling according to ITU-T V.18 in a 1232 selected mode. Once the connection is established, the text 1233 telephone package is used for the text communication in the 1234 established mode. 1236 After connection in text mode, the result is a gateway context with 1237 one textphone termination and one voice line termination connected 1238 to the same line. In the same context, the normal case is to have 1239 other terminations with audio and text conversation media. 1240 In the most simple text-only case, the audio streams are not used 1241 and may be released. 1243 Text received through the V.18 modem is converted if necessary to 1244 T.140 [11]. It is embedded in the RTP/T140 format according to the 1245 rules in T.140 and RFC 2793 [13], specifying RTP/T140. Text received 1246 from other text conversation terminations is transmitted through the 1247 text telephone termination after extraction from the RTP packets. 1248 This process continues until any end disconnects. 1250 8.5.2 Informative description 1252 Descriptors to use for text telephony: 1253 Two descriptor values are of specific interest for the Text 1254 Telephone package. That is the text conversation media stream and 1255 the V.18 modem. The text conversation media stream is described in 1256 the Text Conversation package. The V.18 modem descriptor is 1257 described here for information. 1259 8.5.3 V.18 Modem 1261 Modem name V18. 1263 This modem type is intended for communication with text telephones 1264 in the PSTN. Its operational modes are implemented in the textphone 1265 package. The logic for setting and detecting the mode according to 1266 V.18 is handled by the ctyp package. Some properties of the text 1267 telephone package and the Call Type Discrimination package directly 1268 reflect parameters for control of the V.18 modem. V.18 modem 1269 implementations may have different capabilities reflected in the 1270 property values. 1272 Hellstrom/Parsons/Rafferty/Spitzer Standards track 24 1274 H.248 Annex F (Decided and amended) Jan. 2001 1276 A V.18 modem may be operated in automode monitor mode, when it 1277 listens on a voice line for text telephone signals. This mode can be 1278 used to detect that the user wish to transit from voice to text 1279 during a voice call. That is done entirely with the ctyp package. 1280 Alternatively, a V.18 modem may be operated in modes where it 1281 actively tries to establish a text telephone connection. The 1282 procedure includes transmission of text telephone specific signals 1283 on the line. For calling modems, it is done by the CI signal in the 1284 ctyp package. For an answering modem it is done with the ctyp 1285 package combined with probing from the textphone package by setting 1286 the commode property to the probing mode. 1288 When the mode is discriminated, the commode property should be set 1289 to request communication in that mode. 1291 After successful connection in a text telephone mode, the text 1292 session is conducted in the specific mode as controlled with the 1293 commmode property, and the text stream is made available in T.140 1294 format for other text terminations in the context. 1296 The text telephone package only contains the text connection and 1297 text media aspects of the termination. It is supposed to be combined 1298 with appropriate call control packages, line interface packages and 1299 voice channel packages. 1301 8.5.4 Operation with alternating text and voice mode 1303 If the involved gateways have the alternating text and voice 1304 capability, the following procedure can be applied to give the users 1305 a possibility to go back and forth between using text and voice. 1306 Between the terminals in the context, two streams are members of the 1307 context during the call, the text stream and the audio stream.The 1308 procedure is slightly dependent on the terminal type as described in 1309 the following section. 1311 8.5.5 Alternating text and voice mode with legacy, carrier-less 1312 textphones: 1314 For the carrierless types Baudot, DTMF and EDT the following way to 1315 operate should be used: When V.18 detects text, the textphone 1316 termination stops feeding the audio stream into the audio- stream of 1317 the context, and instead inserts the detected and T140 converted 1318 characters into the text-stream. This mode is continued as long as 1319 characters keep coming from the PSTN textphone. 1321 Hellstrom/Parsons/Rafferty/Spitzer Standards track 25 1323 H.248 Annex F (Decided and amended) Jan. 2001 1325 When no more characters arrive, and no textphone signal is received 1326 within 1 second, the audio channel is again fed to the Audio-stream 1327 channel. If new text comes from the V.18 side, the process is 1328 repeated. 1330 It is important that the implementation of V.18 can retrieve 1331 characters from the first detected text telephone signals after each 1332 mode shift. The leading tones before the characters can be as short 1333 as 150 ms. 1335 If text is received from the context through the Text stream, when 1336 V.18 is not active receiving text, the voice path is muted, and the 1337 characters are sent to the V.18 modem for transmission. When all 1338 text is transmitted and no more is received for two seconds, the 1339 audio channels are enabled again. 1341 Since the carrier-less systems are one way alternate transmission 1342 systems, transmission of characters is possible only in one 1343 direction at a time. Once started, reception is given priority. 1345 In the Context, two way simultaneous transmission is possible. 1346 Therefore, characters received from the context while V.18 is busy 1347 receiving should be buffered (up to a reasonable limit). 1349 All these actions after the initial connections are automatic and 1350 are handled within the textphone termination. 1352 8.5.6 Alternating voice and text conversation in carrier mode: 1354 After a carrier mode text connection is established, loss of 1355 carrier can be taken as the indication that the audio stream shall 1356 be connected with audio interface of the line. When the remote end 1357 is a V.21, Bell or V.18 device, the text communication can be full 1358 duplex, so the gateway can just let the text streams flow between 1359 the terminations. 1361 When carrier reappear, or text is received through the text system, 1362 the audio stream shall be muted, and text transmission noted. 1363 Minitel does not support any voice interworking mode. 1365 8.5.7 Simultaneous voice and text mode 1367 In case the simultaneous voice and text method is enabled, the 1368 handling of the voice and text channels is trivial. Once connected, 1369 the text stream can stay connected with the remote text stream all 1370 the time to serve a two way simultaneous text conversation, and the 1371 audio channel can be connected with the remote audio stream to 1372 support a two way simultaneous audio channel. This mode can be 1373 supported by V.18 with V.61 modulation. 1375 Hellstrom/Parsons/Rafferty/Spitzer Standards track 26 1377 H.248 Annex F (Decided and amended) Jan. 2001 1379 9. Call Type Discrimination package 1381 PackageID : ctyp (0x0011) 1382 Version: 1 1383 Extends: none 1385 Description: 1386 This package monitors the termination for signals indicating 1387 presence of a T.30 telefax terminal [5], a V.18 or legacy mode text 1388 telephone [9] or data modem. In co-operation with the MGC and the 1390 remote MG or endpoint, it can perform exchange of signals until the 1391 call type is determined and an appropriate mode for the call can be 1392 established. 1394 The package contain modem negotiation functions of ITU-T V.25 [10], 1395 V.8[7], v.8 bis[8], V.18[9] and T.30[5] 1397 9.1 Properties 1399 9.1.1 Call Types 1401 PropertyID: calltyp (0x0001) 1402 Type: sub-list 1403 Possible values: 1404 FAX (0x0001) 1405 TEXT (0x0002) 1406 DATA (0x0003) 1407 Defined in: Termination State 1408 Characteristics: Read/Write 1410 Description: 1411 The Call Types property selects the types of calls for which the 1412 termination is monitored. Note that the connection is by default 1413 regarded to be capable of handling audio and therefore no specific 1414 value is included for that. 1416 9.1.2 Text Call Types 1418 PropertyID: ttyp (0x0002) 1419 Type: Sub-list 1420 Possible values: 1421 V21 (0x0001) 1422 DTMF (0x0002) 1423 Baudot45 (0x0003) 1424 Baudot50 (0x0004) 1425 Bell (0x0005) 1426 EDT (0x0006) 1427 Minitel (0x0007) 1428 V18 (0x0008) 1430 Hellstrom/Parsons/Rafferty/Spitzer Standards track 27 1432 H.248 Annex F (Decided and amended) Jan. 2001 1434 Description: 1435 This parameter indicates for what text telephone modes the 1436 termination is monitored, used in TEXT mode 1438 9.1.3 V8bissupport 1440 PropertyID: v8bsup (0x0003) 1441 Type Boolean 1443 Possible values: 1444 True V.8 bis is supported by the package 1445 False V.8 bis is not supported by the package 1446 Defined in: Termination State 1447 Characteristics: Read 1449 Description: 1450 Support of the V.8 bis [8]modem negotiating procedure is optional. 1451 The V8bissupport property indicates if V.8 bis is supported. It can 1452 be used in TEXT,FAX and DATA modes. 1454 9.1.4 Probe message 1456 PropertyID: probemsg (0x0004) 1457 Type: String 1458 Possible Value: Any string, not more than 20 characters long. 1459 Defined in: Termination State 1460 Characteristics: Read/Write 1462 Description: 1463 This property holds a short string that the termination transmits as 1464 a stimulating probe message for the carrierless communication modes 1465 in the answering modes. The far end user will see this message when 1466 it is transmitted in the mode matching the counterpart's textphone, 1467 and type a response back, enabling the V.18 modem to detect the type 1468 of carrierless text telephone in the connection. 1470 When issued, it is automatically followed by " GA" in Baudot 1471 probing, and with "+" in EDT and DTMF probing to reflect the 1472 turntaking signal habit in the different user communities. The 1473 string could be customised to briefly inform the called user about 1474 what service that is reached. 1476 Note that the string is not issued in the carrier modes. 1478 9.1.5 Probe order 1480 PropertyID: probeorder (0x0005) 1481 Type: Sub-List 1482 Possible values: (for recommended orders, see V.18) 1483 Any combination of none to six of the type indicators 1484 V21 (0x0001) 1486 Hellstrom/Parsons/Rafferty/Spitzer Standards track 28 1488 H.248 Annex F (Decided and amended) Jan. 2001 1490 DTMF (0x0002) 1491 Baudot (0x0003) 1492 EDT (0x0004) 1493 MINITEL (0x0005) 1494 BELL (0x0006) 1495 in any desired order. 1496 Defined in: Termination state 1497 Characteristics: Read/Write 1499 Description: 1500 This property holds an indication on what modes to probe for, and 1501 the order the probes will be transmitted. Probing is a time 1502 consuming procedure and it is important that the most likely modes 1503 are probed first. The order to select depends on if any legacy mode 1504 textphones are on the market in the area where the gateway is 1505 installed. An optimised order can be composed by enumerating the 1506 desired specific type indicators. Note that leaving out a type from 1507 probing may cause connection problems for connection with textphones 1508 of that type. 1510 9.1.6 PhasereversalDetect 1512 PropertyID: v8bsup (0x0006) 1513 Type Boolean 1514 Possible values: 1515 True Phase reversal detection is supported 1516 False Phase reversal detection is not supported 1517 Defined in: Termination State 1518 Characteristics: Read 1520 Description: 1521 This property indicates support of detection of the phase reversals 1522 within ANS or ANSam signals. If this property has the value "False", 1523 ANS with phase reversals (ANSBAR) will be reported as ANS and ANSam 1524 with phase reversals (ANSAMBAR) will be reported as ANSam in the 1525 dtone event. 1527 9.2 Events 1529 9.2.1 Discriminating tone detected 1531 EventID: dtone (0x0001) 1533 Description: 1534 This event indicates that a signal valid for detection and 1535 discrimination of mode was detected. The signal name is given as a 1536 parameter. Further logic is needed in some cases to discriminate the 1537 call type from this information. The V.8 bis related parameters are 1538 returned only when V.8 bis is supported [8]. 1540 Note that some textphones operate with DTMF tones. This package 1541 decodes initial DTMF signals according to the specification for text 1543 Hellstrom/Parsons/Rafferty/Spitzer Standards track 29 1545 H.248 Annex F (Decided and amended) Jan. 2001 1547 telephones in V.18 [9]. DTMF detection may be indicated also from 1548 the "dd" package if that is active. 1550 EventsDescriptor parameters: none 1552 ObservedEventDescriptor parameters: 1554 Discriminating Tone Type 1556 ParameterID: dtt (0x0001) 1557 Type: Enumeration 1558 Possible values: 1560 For FAX 1561 CNG (0x0001) a T.30 fax calling tone 1562 V21flag (0x0002) V21 tone and flags for fax answering 1564 For TEXT 1565 XCI (0x0003) a V.18 XCI 1566 V18txp1 (0x0004) a V.18 txp signal in channel V.21(1) 1567 V18txp2 (0x0005) a V.18 txp signal in channel V.21(2) 1568 BellHi (0x0006) a Bell 103 carrier on the high 1569 channel 1570 BellLo (0x0007) a Bell 103 low channel 1571 Baudot45(0x0008) a Baudot45 initial carrier and 1572 characters 1573 Baudot50(0x0009) a Baudot50 initial carrier and 1574 characters 1575 Edt (0x000A) an EDT initial tone and characters 1576 DTMF (0x000B) DTMF signals 1578 For DATA 1579 Sig (0x000C) Modulation signal from a mode 1580 only used for data. I.e.. not 1581 V.21, V.23 nor Bell 103. 1583 Common to TEXT and DATA: 1584 CT (0x000D) a V.25 calling tone 1585 V21hi (0x000E) a V.21 carrier on the higher 1586 frequency channel 1587 V21lo (0x000F) a V.21 carrier on the low 1588 frequency channel 1589 V23hi (0x0010) a V.23 high carrier 1590 V23lo (0x0011) a V.23 low carrier 1591 CI (0x0012) a V.8 CI with contents in 1592 "dtvalue" 1594 Common to FAX, TEXT and DATA: 1595 ANS (0x0013) V.25 ANS, equivalent to T.30 1596 CED from answering terminal 1598 Hellstrom/Parsons/Rafferty/Spitzer Standards track 30 1600 H.248 Annex F (Decided and amended) Jan. 2001 1602 ANSbar (0x0014) V.25 ANS with phase reversals 1603 ANSAM (0x0015) V.8 ANSam 1604 ANSAMbar(0x0016) V.8 ANSam with phase reversals 1605 CM (0x0017) V.8 CM with contents in 1606 "dtvalue" 1607 CJ (0x0018 V.8 CJ 1608 JM (0x0019) V.8 JM with contents in 1609 "dtvalue" 1610 ENDOFSIG(0x001A) End of reported signal detected 1611 reported for continous or repeated 1612 signals 1613 V8BIS (0x001B) V.8bis signal, with signal type in 1614 parameter V8bistype and value in 1615 "dtvalue" 1617 Discriminating Tone Value 1619 ParameterID dtvalue (0x0002) 1620 Type: string 1621 Possible values: 1622 When used for V.8 and V.8 bis related messages, the following coding 1623 rules applies: 1624 . The transmitted V.8 message is specified as hexadecimal octet 1625 coded string 1626 . The transmitted V.8 bis message frame(s) is specified as 1627 hexadecimal octet coded string (F.3.1.). Additional messages 1628 are delimited by comma characters. Flag generation, flag 1629 transparency 0-bit insertion and FCS generation are performed 1630 by the MG. If no data is provided by the MGC, no V.21 carrier 1631 is generated beyond that used in segment 2. For two 1632 concatenated messages, the MG shall insert the required 1633 preamble between the first and second messages. 1635 If a V.8 bis message is detected without a preceding V.8 bis signal, 1636 the preamble is reported as a 0 value. 1638 The contents of valid V.8 bis message(s), if detected, are reported 1639 using hexadecimal octet coded string(s) (5.1). Flag detection and 1640 consumption, flag transparency 0-bit deletion and FCS checking are 1641 performed by the MG. The MG shall not report invalid messages (e.g. 1642 bad FCS). If two consecutive messages are detected but the first is 1643 invalid, the MG shall indicate this with a comma in front of the 1644 second message (e.g. ,<2nd message>). Two concatenated V.8 bis 1645 messages are reported with two consecutive indications. 1647 V8bis type 1649 ParameterID v8bist (0x0004) 1650 Type enumeration 1651 Possible values: 1653 Hellstrom/Parsons/Rafferty/Spitzer Standards track 31 1655 H.248 Annex F (Decided and amended) Jan. 2001 1657 ESi (0x0001) V.8bis signal ESi 1659 ESr (0x0002) V.8bis signal ESr 1661 MRe (0x0003) V.8bis signal MRe 1663 MRdi (0x0004) V.8bis signal MRd from initiator 1665 MRdr (0x0005) V.8bis signal MRd from responder 1667 CRe (0x0006) V.8bis signal CRe 1669 CRdi (0x0007) V.8bis signal CRd from initiator 1671 CRdr (0x0008) V.8bis signal CRd from responder 1673 MS (0x0009) V.8 bis message MS with contents 1674 in "dtvalue" 1676 CL (0x000A) V.8 bis message CL with contents 1677 in "dtvalue" 1679 CLR (0x000B) V.8 bis message CLR with 1680 contents in "dtvalue" 1682 ACK (0x000C) V.8 bis message ACK with 1683 contents in "dtvalue" 1685 NAK (0x000D) V.8 bis message NAK with 1686 contents in "dtvalue" 1688 Description: A detected V.8 bis [8] signal. V.8 bis can be used for 1689 all modes. 1691 Initial Characters 1693 ParameterID: ichar (0x0005) 1694 Type: String 1695 Possible values: characters received in the detection process in the 1696 carrierless textphone modes EDT, Baudot and DTMF, intended to be 1697 inserted in txp. 1699 9.3 Signals 1701 9.3.1 V8Signal 1703 SignalID: v8sig (0x0001) 1704 SignalType: OO 1706 Parameters: 1708 Hellstrom/Parsons/Rafferty/Spitzer Standards track 32 1710 H.248 Annex F (Decided and amended) Jan. 2001 1712 V.8 Signal Type 1714 Parameter ID: v8styp (0x0001) 1715 Type: Enumeration 1716 Possible values 1717 CM (0x0001) 1718 CJ (0x0002) 1719 JM (0x0003) 1720 CI (0x0004) 1721 v8nosig (0x0005) no signal _ used to stop the V.8 signal 1722 Default may be provisioned 1724 V8SigCont 1726 Parameter ID: v8scont (0x0002) 1727 Type: string 1728 Possible values: Allowed contents of the signals, coded as 1729 hexadecimal octet coded string. 1730 Default is empty. 1732 Description The V.8 [7] signals carry data for call type and 1733 modulation modes. These parameters can be supplied through the 1734 v8cont parameter. V.8 can be used for FAX, TEXT and DATA modes. 1736 V18XCIEnable 1738 Parameter ID: v18xcien (x0003) 1739 Type: Boolean 1740 Possible values: 1741 True XCI transmission enabled during V.18 CI transmission 1742 False XCI transmission disabled 1743 Default is True 1745 Description: XCI can be sent intermixed with CI transmission as 1746 specified in V.18 to stimulate plainMinitel terminals to respond as 1747 text telephones. Used in TEXT mode. 1749 9.3.2 AnswerSignal 1751 SignalID: ans (0x0002) 1752 Signal Type OO 1754 Parameters: 1756 AnsType 1758 ParameterID: AnsType (0x0001) 1759 Type: Enumeration 1761 Possible values: 1763 Hellstrom/Parsons/Rafferty/Spitzer Standards track 33 1765 H.248 Annex F (Decided and amended) Jan. 2001 1767 ANS (0x0001) V.25 ANS (equivalent to T.30 1768 CED) for all modes 1769 ANSBAR (0x0002) V.25 ANS with phase reversals 1770 for all modes 1771 ANSAM (0x0003) V.8 ANSam for all modes 1772 ANSAMBAR (0x0004) V.8 ANSam with phase reversals 1773 for all modes 1774 V18txp1 (0x0005) a V.18 txp signal played in V.21 1775 channel(1) for TEXT 1776 V18txp2 (0x0006) a V.18 txp signal played in V.21 1777 channel(2) for TEXT 1778 ansnosig (0x0007) no signal _ used to turn off the 1779 signal 1780 Default may be provisioned 1782 9.3.3 CallingSignal 1784 SignalID: callsig (0x0003) 1785 SignalType OO 1786 Parameters 1788 callSigname 1789 Parameter ID cSn (0x0001) 1790 Type Enumeration 1791 Possible values: 1793 CT (0x0001) V.25 Calling Tone used for TEXT and DATA 1794 CNG (0x0002) T.30 Calling tone used for FAX with defined 1795 cadence 1796 callnosig (0x0003) no signal _ used to turn off the signal 1798 Default may be provisioned 1800 9.3.4 V8bisSignal 1802 SignalID: v8bs (0x0004) 1803 Signaltype BR 1805 Parameters: 1807 V8bisSigname 1809 ParameterID: V8bsn (0x0001) 1810 Type: Enumeration 1811 Possible values: 1812 ESi (0x0001) V.8bis signal ESi 1813 ESr (0x0002) V.8bis signal ESr 1814 MRe (0x0003) V.8bis signal MRe 1816 Hellstrom/Parsons/Rafferty/Spitzer Standards track 34 1818 H.248 Annex F (Decided and amended) Jan. 2001 1820 MRdi (0x0004) V.8bis signal MRd from initiator 1821 MRdrl (0x0005) V.8bis signal MRd from responder on 1822 low power 1824 CRel (0x0006) V.8bis signal CRe on low power 1825 CRdi (0x0007) V.8bis signal CRd from initiator 1826 CRdr (0x0008) V.8bis signal CRd from responder 1827 MS (0x0009) V.8 bis message MS with contents 1828 in signalvalue 1829 CL (0x000A) V.8 bis message CL with contents 1830 in signalvalue 1831 CLR (0x000B) V.8 bis message CLR with contents 1832 in signalvalue 1833 ACK (0x000C) V.8 bis message ACK with contents 1834 in signalvalue 1835 NAK (0x000D) V.8 bis message NAK with contents 1836 in signalvalue 1837 MRdrh (0x000E) V.8bis signal MRd from responder on 1838 high power 1839 CReh (0x000F) V.8bis signal CRe on high power 1840 Default may be provisioned 1842 Description: 1843 V.8 bis [8] signals can be used in all modes. Some V.8 bis signals 1844 contain data messages, supplied in V8bisSigContents. 1846 V8bisSigContents 1848 ParameterID: V8bscont (0x0002) 1849 Type: string 1850 Possible values: Valid contents for the V.8 bis signals 1851 Default is empty. 1853 Description: 1854 Some of the V.8 bis signals are messages. Their contents can be 1855 defined with theV8biscont parameter. V.8bis can be used in TEXT, 1856 FAX and DATA modes. 1858 The transmitted V.8 bis message frame(s) is specified as hexadecimal 1859 octet coded string (see section 5). Additional messages are 1860 delimited by comma characters. Flag generation, flag transparency 0- 1861 bit insertion and FCS generation are performed by the MG. If no data 1862 is provided by the MGC, no V.21 carrier is generated beyond that 1863 used in segment 2. For two concatenated messages, the MG shall 1864 insert the required preamble between the first and second messages. 1866 If a V.8 bis message is detected without a preceding V.8 bis signal, 1867 the preamble is reported as a 0 value. 1869 Hellstrom/Parsons/Rafferty/Spitzer Standards track 35 1871 H.248 Annex F (Decided and amended) Jan. 2001 1873 The contents of valid V.8 bis message(s), if detected, are reported 1874 using hexadecimal octet coded string(s) (see section 5). Flag 1875 detection and consumption, flag transparency 0-bit deletion and FCS 1876 checking are performed by the MG. The MG shall not report invalid 1877 messages (e.g. bad FCS). If two consecutive messages are detected 1878 but the first is invalid, the MG shall indicate this with a comma in 1879 front of the second message (e.g. ,<2nd message>). Two concatenated 1880 V.8 bis messages are reported with two consecutive 1881 indications. 1883 9.3.1.5 V18probe 1885 SignalID: v18prob (0x0005) 1886 SignalType: OO 1887 Parameters: none 1889 Description: This signal transmits the v18 probes in order to 1890 stimulate possible text telephones to transmit connect establishing 1891 signals. The probes are sent according to the specification in 1892 Recommendation V.18. For carrierless probes, the string in the 1893 "probemsg" property is transmitted. The probes are sent in the order 1894 specified in the property "probeorder". 1896 9.4 Statistics 1898 none 1900 9.5 Procedures 1902 The Call Type Discrimination package is invoked for cases when the 1903 network connection is established and the call may enter one of the 1904 types of voice, fax, text telephone and modem. The package contains 1905 functionality to support the decision and connection processes. Once 1906 discriminated and the modem handshaking completed, an appropriate 1907 specific call type package should be invoked to complete the 1908 connection establishment on the modulation level and perform the 1909 session. 1911 When used for active modem negotiation, by means of commands from 1912 the MGC, the termination shall be made to operate according to the 1913 Recommendations for modem negotiation; V.25[10], V.8[7], V.8 bis[8], 1914 V.18[9] and T.30[5]. For probing according to V.18 during the 1915 negotiating process, the probing mechanism may be applied as 1916 defined in this package by turning the signal v18prob ON. 1917 The package may also be used for monitoring and reporting on data 1918 activity on the termination. 1920 9.5.1 Informative description 1922 If the desired call type is known from the beginning, the call type 1923 discrimination package should be invoked in order to actively try 1924 to establish a connection by sending out stimulating signals. By 1926 Hellstrom/Parsons/Rafferty/Spitzer Standards track 36 1928 H.248 Annex F (Decided and amended) Jan. 2001 1930 contrast this package is also used to monitor the line to detect 1931 signals which are to be relayed to the Media Gateway Controller as 1932 input to a discrimination decision. In principle, when tones are 1933 reported to the MGC as events by an MG, the MG should avoid passing 1934 these tones via the media stream where possible, to reduce the 1935 possibility of unwanted duplicate tones. Since the Call Type 1936 Discrimination package can be invoked to initially only monitor the 1937 line, it can be invoked on lines where voice calls are the most 1938 common mode of operation. There may be situations where this 1939 passive way of working results in less efficient or less reliable 1940 connection in fax/text/data mode. 1942 9.5.2 Operation 1944 The package is activated on a termination of a line in an outgoing 1945 or incoming call where fax, text or data mode may be wanted. The 1946 properties are set to the enabled call types. 1948 9.5.3 Operation for incoming calls 1950 The call is answered, the destination is evaluated and the remote 1951 call initiated using packages and gateway functions outside the 1952 scope of this package. 1954 The MGC may order stimulating signals defined in this package to be 1955 sent on the line. 1957 The line is monitored for signals for the selected modes as defined 1958 in the "dtone" event descriptor. 1960 The MGC is expected to evaluate call type indications of all types; 1961 registered type of the destination, offered capabilities of the 1962 endpoint, invoked connection efforts of specific types from the 1963 endpoint and discriminating events from a call type discriminating 1964 package active in setting up the connection with the other endpoint. 1965 As soon as the modem handshaking is complete and a condition is 1966 reached that is valid for only one call type, a package for handling 1967 that call type should be invoked by the MGC, thus placing the MG 1968 into the desired mode of operation. 1970 The package contains components for conducting a negotiation 1971 procedure according to the different connection procedures defined 1972 in recommendations V.25 [10], V.8 [7], V.8 bis [8], T.30 [5], T.38 1973 [6] and V.18 [9]. (V.8 bis support is optional and its availability 1974 can be interrogated through the property V8bissupport). 1976 9.5.4 Operation for transit calls, coming from and going to the 1977 switched network 1979 If no fax/text/data indication is present in the incoming call, the 1980 outgoing call is placed in voice mode, with the Call Type 1981 Discrimination package active. 1983 Hellstrom/Parsons/Rafferty/Spitzer Standards track 37 1985 H.248 Annex F (Decided and amended) Jan. 2001 1987 If a valid tone is detected, it is reported to the MGC as an event. 1988 By actions of the MGC it can be signalled to be replayed at the 1989 other end. 1991 The process continues according to the rules of the connection 1992 procedures until the call type can be determined and the mode of 1993 operation can be established. 1995 9.5.5 Operation for calls having one endpoint in the packet network 1997 If no fax/text/data indication is present in the incoming call, the 1998 outgoing call in the packet network is placed in voice mode. 1999 If a request to open a text channel, a fax channel or a data channel 2000 is made from the packet endpoint, the corresponding call type is 2001 tried on the switched network connection. 2003 If a signal indicating presence of a fax, textphone or a modem is 2004 received from the circuit switched network, and the call type can be 2005 evaluated, a corresponding channel is requested to the remote packet 2006 endpoint. If that request is acknowledged, the connection in the 2007 fax/text/data mode is completed on the switched side. 2009 If the call type can not be evaluated, further signal exchange is 2010 performed on the switched interface until the call type is 2011 determined, and then the channel establishment continues on the 2012 packet side. 2014 9.5.6 Cases when the call type can not be determined from the signals 2016 For cases when the call type can not be determined by the signal 2017 exchange, a decision must be taken by other means, or a transparent 2018 transport can be selected. 2020 The other means to make the decision may be a number analysis and 2021 comparison to registered user preferences or network defaults. 2023 Cases when the decision is not possible by signal analysis but need 2024 to be taken by external means: 2026 V.21: Used both for text telephony and for credit card 2027 transactions. The decision is recommended to be based on 2028 regional preferences and registering preference for data per 2029 destination number in regions where the default preference is 2030 for text telephony. 2032 V.23: Used both for Minitel-based text telephones and for the 2033 Minitel information retrieval system. The conflict is only when 2034 an answering endpoint transmits the v23hi signal. A transparent 2035 data transport is recommended for this case. 2037 Hellstrom/Parsons/Rafferty/Spitzer Standards track 38 2039 H.248 Annex F (Decided and amended) Jan. 2001 2041 9.5.7 Scenarios and call flows 2043 Signal sequence scenarios can be derived from the different 2044 connection protocols, with T.38 being the main protocol for fax, 2045 V.18 for text telephony and V.8 / V.25 for data. 2047 The typical fax scenario is discriminated when CNG is detected from 2048 the calling end and a corresponding CED (ANS) and/or V.21flags are 2049 detected at the answering end. For instances when either a CNG or 2050 ANS is not reported to the MGC, V21flags detection is sufficient for 2051 fax discrimination. Alternatively, a V.8 CM or JM signal with a fax 2052 call type may be detected at either end. 2054 The text telephone scenario is discriminated when a text telephone 2055 call type is detected in V.8, a text telephone function is 2056 negotiated in V.8 bis, or a signal valid for text only is detected. 2057 The data scenario is discriminated when a data call type is detected 2058 in V.8, a data function is negotiated in V.8 bis, or a data mode 2059 (not text) is entered by any part. 2061 In all cases the handshaking protocol should be completed using the 2062 Call Type Discrimination package, before entering the selected data 2063 mode. 2065 9.5.8 Initial characters 2067 For carrierless text telephones of the Baudot, EDT and DTMF types 2068 the text transmission itself is needed for mode determination, and 2069 therefore the characters received during determination shall be 2070 stored. They shall be made available by local actions in the MGto be 2071 used by the txp package as initially received text for a seamless 2072 takeover of a connection. 2074 9.5.9 Time critical handling 2076 The default way of handling connection requests should be to 2077 propagate the connection request to the remote endpoint, and verify 2078 capabilities before positively responding to an incoming connection 2079 request for fax, text or data mode. It can however be very time 2080 consuming to verify the endpoint capabilities, and connect 2081 appropriate channels. The caller may timeout between detection of 2082 off-hook, and receiving a positive signal. Similar time critical 2083 steps exist in the V.8, V.8 bis, V.18, T.30 and V.25 procedures. The 2084 MGC must take action to compromise between the risk of one party 2085 timing out because of long waiting for a signal, and the risk of 2086 connecting a fax/text/data call before the capabilities of the 2087 endpoints are verified and the appropriate channels connected. One 2088 possible way to handle this risk is to define default actions to 2089 take before any party in the call times out. The ctyp package gives 2090 the MGC all necessary control to handle the connection process 2091 including such actions. 2092 Hellstrom/Parsons/Rafferty/Spitzer Standards track 39 2094 H.248 Annex F (Decided and amended) Jan. 2001 2096 10. Fax package 2098 Package Name: Fax 2099 PackageID: fax (0x0012) 2100 Version: 1 2101 Extends: None 2103 Description: 2104 The fax package is intended for enabling fax communication between 2105 terminals/applications in different networks or messaging 2106 environments. This package includes the mechanisms needed to 2107 identify T.30 [5] fax sessions (signals and data). 2109 10.1 Properties 2111 10.1.1 Fax connection state 2113 PropertyID: faxstate (0x0001) 2114 Type: Enumeration 2115 Possible values: 2116 Idle (0x0001) no connection efforts 2117 Prepare (0x0002) known in the termination and 2118 ready to accept connections 2119 Negotiating (0x0003) taking the initiative to 2120 establish a fax connection 2121 TrainR (0x0004) Fax Phase B or later training 2122 as Receiver 2123 TrainT (0x0005) Fax Phase B or later training 2124 as Transmitting 2125 Connected (0x0006) completed connection 2126 EOP (0x0007) Procedures Complete 2127 ProcInterrupt (0x0008) Procedure Interrupt Processing 2128 Disconnect (0x0009) Premature Disconnect 2130 Characteristics: Read/Write 2131 Defined in: TerminationState 2133 Description: 2134 After successful phase A connection with the ctyp package, the 2135 connection state property is used to request a fax connection. 2136 When placing a termination into a fax mode, the initial state shall 2137 be set to "Negotiating". 2139 When this property is interrogated, it shall reflect the state of 2140 the achieved fax connection. 2142 A connection effort can be cancelled by setting the faxstate 2143 property to Idle. 2145 Hellstrom/Parsons/Rafferty/Spitzer Standards track 40 2147 H.248 Annex F (Decided and amended) Jan. 2001 2149 10.1.2 Fax Transport 2151 PropertyID: ftrpt (0x0001) 2152 Type: Enumeration 2153 Possible values: 2154 T30 (0x0001) for T.30 PSTN sessions without ECM 2155 T30ECM (0x0002) for T.30 PSTN sessions with ECM 2156 (non-V.34) 2157 T.30V34 (0x0003) for T.30 PSTN sessions with V.34 2158 (half-duplex) 2160 Characteristics: Read/Write 2161 Defined in: Termination State 2163 Description: 2164 The Transport parameter reflects the transport mechanism selected 2165 for the fax termination. 2167 10.1.3 TransmissionSpeed 2169 PropertyID: trspd (0x0002) 2170 Type: Integer 2171 Possible values: 1200-33600 2172 Defined in: Termination State 2173 Characteristics: Read/Write 2175 Description: 2176 The Transport parameter reflects the transmission speed seen at the 2177 analog interface for the fax relay or the transmission speed used by 2178 the FAX termination (T.30 PSTN). 2180 10.1.4 PSTN Interface 2182 PropertyID: pstnif (0x0003) 2183 Type: Enumeration 2184 Possible values: 2185 NA (0x0001) not applicable 2186 V17 (0x0002) 2187 V27TER (0x0003) 2188 V29 (0x0004) 2189 V21 (0x0005) 2190 V34 (0x0006) 2192 Defined in: Termination State 2193 Characteristics: Read/Write 2195 Description: 2196 The PSTN Interface parameter reflects the interface used to connect 2197 to a physical FAX machine. 2199 Hellstrom/Parsons/Rafferty/Spitzer Standards track 41 2201 H.248 Annex F (Decided and amended) Jan. 2001 2203 10.2 Events 2205 10.2.1 Fax Connection State Change 2207 Event ID: faxconnchange (0x0001) 2209 EventDescriptor Parameters: none 2211 ObservedEventDescriptorParameters: 2213 Fax Connection Change 2215 ParameterID: faxconnchng (0x0001) 2216 Type: Enumeration 2217 Possible Value: 2218 Idle (0x0001) no connection efforts 2219 Prepare (0x0002) known in the termination and 2220 ready to accept connections 2221 Negotiating (0x0003) taking the initiative to 2222 establish a fax connection 2223 TrainR (0x0004) Fax Phase B or later training 2224 as Receiver 2225 TrainT (0x0005) Fax Phase B or later training 2226 as Transmitting 2227 Connected (0x0006) completed connection 2228 EOP (0x0007) Procedures Complete 2229 ProcInterrupt (0x0008) Procedure Interrupt Processing 2230 EOF (0x0009) end of fax session, call 2231 terminating 2232 PI (0x000A) Priority Interrupt ; Switch to 2233 Voice 2234 Disconnect (0x000B) Premature Disconnect 2236 Description: 2237 This event will occur when the fax connection state for the 2238 termination has changed. Its parameter is the new Fax Connection 2239 State. A connection effort that timed out returns the termination to 2240 the Idle state. 2242 10.3 Signals 2244 None 2246 10.4 Statistics 2248 10.4.1 Pages Transferred 2250 StatisticsID: pagestrans (0x0001) 2251 Type: integer 2252 Description: 2253 No of pages of fax image data transferred through the termination. 2255 Hellstrom/Parsons/Rafferty/Spitzer Standards track 42 2257 H.248 Annex F (Decided and amended) Jan. 2001 2259 10.4.2 Train Downs 2261 StatisticsID: traindowns (0x0002) 2262 Units: count 2264 Description: 2265 Number of times FAX trained down during tramsmission. 2267 10.5 Procedures 2269 The following are standard transport mechanisms for fax in different 2270 environments. 2272 * In T.30: Use T.30 [5] procedures with and without ECM 2273 * In T.30 Annex C/F: Use T.30 procedures selected via V.8 (Used for 2274 V.34 fax) 2276 10.5.1 Function 2278 A termination with Fax provides a method for transfer of fax pages 2279 preceded by negotiations in the call setup according to procedures 2280 defined for each environment. When matching capabilities exist, the 2281 appropriate sessions can be established in order to transfer pages 2282 of image or binary data. 2284 Real time fax allows telecom users to transfer fax pages in real 2285 time. The procedural aspects of GSTN fax are defined in ITU-T T.30. 2286 [5] The compression methods used in transporting fax images are 2287 defined in T.4, T.6, T.81, T.82, T.85 and T.44. In traditional 2288 T.30 without error correction, images are transferred in a stream 2289 one page at a time. In T.30 with error correction, images are 2290 transferred in blocks that are also known as partial pages. 2291 Numerous examples of fax sessions are contained in Appendix IV to 2292 T.30. 2294 For each transport environment, a suitable transport protocol must 2295 be selected to carry the image. Currently defined and Recommended 2296 transport environments for T.30 media streams that can be supported 2297 by this package are GSTN networks, where the procedures are defined 2298 in T.30, T.30 Annex A (for error correction), T.30 Annex C (duplex 2299 protocol) and Annex F (half duplex V.34 protocol). 2301 10.5.2 Process of Adding Fax Capable Terminations 2303 The MGs are responsible for detecting fax tones and relaying the 2304 related events to the MGC. The MGC should conduct Call 2305 Discrimination as defined within the Call Type Discrimination 2306 Package in order to determine whether a fax or other mode is 2307 applicable. The MGC may choose to skip this if the MG is not 2309 Hellstrom/Parsons/Rafferty/Spitzer Standards track 43 2311 H.248 Annex F (Decided and amended) Jan. 2001 2313 capable of the Call Type Discrimination Package. Once the MGC 2314 evaluates the tones and determines that the incoming call is fax, 2315 the MGC shall execute appropriate Modify commands to place the 2316 termination into a "Negotiating" state. 2318 10.5.3 Process of Ending a Fax Call 2320 The MGs are responsible for detecting events that would cause the 2321 interruption of a fax call. The MGC is responsible for making the 2322 determination if this switch can be made and instruct the MGs to 2323 switch. It also responsible for switching it back to fax. The MGC 2324 should receive indication that the fax call ends from the MG before 2325 receiving typical call termination indications. 2327 11. IP Fax package 2329 Package Name: IPFax 2330 PackageID: ipfax (0x0013) 2331 Version: 1 2332 Extends: None 2334 Description: 2335 The fax package is intended for enabling real time or store and 2336 forward fax communication between terminals/applications in 2337 different networks or messaging environments. This package includes 2338 the mechanisms needed to transport T.30 fax sessions (signals and 2339 data) in a real time IP environment. The transport mechanism will 2340 be different for each environment where the package is used. 2342 11.1 Properties 2344 11.1.1 Fax connection state 2346 PropertyID: faxstate (0x0001) 2347 Type: Enumeration 2348 Possible values: 2349 Idle (0x0001) no connection efforts 2350 Prepare (0x0002) known in the termination and 2351 ready to accept connections 2352 Negotiating (0x0003) taking the initiative to 2353 establish a fax connection 2354 TrainR (0x0004) Fax Phase B or later training 2355 as Receiver 2356 TrainT (0x0005) Fax Phase B or later training 2357 as Transmitter 2358 Connected (0x0006) for completed connection 2359 EOP (0x0007) Procedures Complete 2360 ProcInterrupt (0x0008) Procedure Interrupt Processing 2361 Disconnect (0x0009) Premature Disconnect 2363 Hellstrom/Parsons/Rafferty/Spitzer Standards track 44 2365 H.248 Annex F (Decided and amended) Jan. 2001 2367 Characteristics: Read/Write 2368 Defined in: Termination State 2370 Description: 2371 After successful phase A connection with the ctyp package, 2372 the connection state property is used to request a fax connection. 2373 When placing a termination into a fax mode, the initial state shall 2374 be set to "Negotiating". 2376 When this property is interrogated, it shall reflect the state of 2377 the achieved fax connection. 2379 11.1.2 IPFaxTransport 2381 PropertyID: ipftrpt (0x0001) 2382 Type: Enumeration 2383 Possible values: 2384 T38UDPTL (0x0001) for T.38 [6]using UDPTL 2385 T38TCP (0x0002) for T.38 using TCP 2386 T37 (0x0003) for T.37 [22] 2387 AUDIO (0x0004) for audio codec (e.g., G.711 over RTP [4]) 2389 Characteristics: Read/Write 2390 Defined in: Termination State 2392 Description: 2393 The IP Fax Transport parameter reflects the transport mechanism 2394 selected for the fax termination. 2396 11.1.3 TransmissionSpeed 2398 PropertyID: trspd (0x0002) 2399 Type: Integer 2400 Possible values: 0-33600 2401 Characteristics: Read/Write 2402 Defined in: Termination State 2404 Description: 2405 The Transport property reflects the transmission speed seen at the 2406 IP interface for the fax relay. A value of zero (0) indicates that 2407 there is no speed set. 2409 11.1.4 T.38 Capabilities 2411 PropertyID: T38Capabilities (0x0003) 2412 Type: sub-list 2413 Possible values: 2414 FaxFillBitRemoval (0x0001) indication of fill bit removal 2415 FaxTranscodingMMR (0x0002) for MMR transcoding 2416 availability 2417 FaxTranscodingJBIG (0x0003) for JBIG transcoding 2418 availability 2419 Hellstrom/Parsons/Rafferty/Spitzer Standards track 45 2421 H.248 Annex F (Decided and amended) Jan. 2001 2423 UDPFEC (0x0004) UDP Forward Error Correction 2424 UDPRedundancy (0x0005) UDP Redundancy Error Correction 2426 Characteristics: Read/Write 2427 Defined in: Termination State 2429 Description: 2430 These capabilities describe the T.38 [6] fax termination. They are 2431 defined in Rec T.38 Annex B. Their SDP equivalents are defined in 2432 Rec. T.38 Annex D. 2434 11.1.5 T38MaximumBufferSize 2436 PropertyID: T38MaxBufferSize (0x0004) 2437 Type: Integer 2438 Possible values: 0- 2439 Characteristics: Read/Write 2440 Defined in: Termination State 2442 Description: 2443 This capability describes the T.38 fax termination. They are 2444 defined in Rec T.38 Annex B. Their SDP equivalents are defined in 2445 Rec. T.38 Annex D. 2447 11.1.6 T38MaximumDatagramSize 2449 PropertyID: T38MaxDatagramSize (0x0005) 2450 Type: Integer 2451 Possible values: 0- 2452 Characteristics: Read/Write 2453 Defined in: Termination State 2455 Description: 2456 This capability describes the T.38 fax termination. They are 2457 defined in Rec T.38 Annex B. Their SDP equivalents are defined in 2458 Rec. T.38 Annex D. 2460 11.1.7 T38Version 2462 PropertyID: T38Version (0x0006) 2463 Type: Integer 2464 Possible values: 0- 2465 Characteristics: Read/Write 2466 Defined in: Termination State 2468 Description: 2469 This is the T.38 version number. 2471 11.2 Events 2473 11.2.1 Fax Connection State Change 2475 Hellstrom/Parsons/Rafferty/Spitzer Standards track 46 2477 H.248 Annex F (Decided and amended) Jan. 2001 2479 Event ID: faxconnchange (0x0001) 2481 EventDescriptor Parameters: none 2483 ObservedEventDescriptorParameters: 2485 Fax Connection Change 2487 ParameterID: faxconnchng (0x0001) 2488 Type: Enumeration 2489 Possible Values: 2490 Idle (0x0001) no connection efforts 2491 Prepare (0x0002) known in the termination and 2492 ready to accept connections 2493 Negotiating (0x0003) taking the initiative to 2494 establish a fax connection 2495 TrainR (0x0004) Fax Phase B or later training 2496 as Receiver 2497 TrainT (0x0005) Fax Phase B or later training 2498 as Transmitter 2499 Connected (0x0006) for completed connection 2500 EOP (0x0007) Procedures Complete 2501 ProcInterrupt (0x0008) Procedure Interrupt Processing 2502 EOF (0x0009) - end of fax session, call 2503 terminating 2504 PI (0x000A) - Priority Interrupt ; Switch 2505 to Voice 2506 Disconnect (0x000B) Premature Disconnect 2508 Description: 2509 This event will occur when the fax connection state for the 2510 termination has changed. Its parameter reflects the new state. If a 2511 connection effort times out, it is reported in this event, with the 2512 faxconnchng parameter set to Idle. 2514 11.3 Signals 2516 None 2518 11.4 Statistics 2520 11.4.1 Pages Transferred 2522 StatisticsID: pagestrans (0x0001) 2523 Type: integer 2525 Description: 2526 No of pages of fax image data transferred through the termination. 2528 Hellstrom/Parsons/Rafferty/Spitzer Standards track 47 2530 H.248 Annex F (Decided and amended) Jan. 2001 2531 11.4.2 Train Downs 2533 StatisticsID: traindowns (0x0002) 2534 Units: count 2536 Description: 2537 Number of times FAX trained down during tramsmission. 2539 11.5 Procedures 2541 The following are standard transport mechanisms for fax in different 2542 environments. 2544 * In T.38 Annex B: UDPTL or TCP in T.38 fax only 2545 communication channel environment. 2546 * In H.323 Annex D[25]: UDPTL or TCP as selected with H.245 2547 messages. 2548 * In T.38 Annex D (SIP): UDPTL or TCP as initiated with SDP 2549 * In T.38 Annex E: UDPTL or TCP as initiated with H.248 2550 * In T.37: SMTP (MIME) /TCP 2552 11.5.1 Function 2554 A termination with Fax provides a method for transfer of fax pages 2555 preceded by negotiations in the call setup according to procedures 2556 defined for each environment. When matching capabilities exist, the 2557 appropriate sessions can be established in order to transfer pages 2558 of image or binary data. 2560 Real time fax allows telecom users to transfer fax pages in real 2561 time. For each transport environment, a suitable transport protocol 2562 must be selected to carry the image. Currently defined and 2563 Recommended transport environments for T.30 media streams that can 2564 be supported by this package are: 2566 1. Packet networks, where the procedures described in T.38 Annex B 2567 [6] can be used for setting up and conducting fax sessions, using 2568 TCP or UDPTL for the transport of T.30 signals and data. 2570 2. Packet networks, where the procedures described in H.323 Annex D 2571 [25] can be used for setting up and conducting fax and voice 2572 sessions, using TCP or UDPTL as negotiated via H.245. 2574 3. Packet networks, where the IETF Session Initiation Protocol SIP 2575 can be used for setting up and conducting fax sessions as defined in 2576 T.38 Annex D using UDPTL or TCP for the transport of T.30 signals 2577 and data. 2579 4. Packet networks, where H.248 can be used for setting up and 2580 conducting fax sessions as defined in T.38 Annex E using UDPTL or 2581 TCP for the transport of T.30 signals and data. 2583 Hellstrom/Parsons/Rafferty/Spitzer Standards track 48 2585 H.248 Annex F (Decided and amended) Jan. 2001 2587 5. Packet networks, where the packets of G.711 coded data (with T.30 2588 signals and data embedded) can be transported via RTP. 2590 The Extended Simple Mail Transport Protocol messaging environment 2591 over packet, that can be used alone or in conjunction with any of 2592 the environments above, where T.37 [22] specify the methods for 2593 transporting image/tiff files using the same compression methods 2594 as specified for use in T.30. 2595 Interworking between these forms of fax can be achieved through the 2596 use of gateways with packages defined here. For information it can 2597 be noted that RFC 2301-2305 and RFCs 2530-2532 specify these 2598 transport mechanisms. 2600 11.5.2 Process of Adding IP Fax Capable Terminations 2602 The MGs are responsible for detecting fax tones and relaying the 2603 related events to the MGC. The MGC should conduct Call 2604 Discrimination as defined within the Call Type Discrimination 2605 Package in order to determine whether a fax or other mode is 2606 applicable. The MGC may choose to skip this if the MG is not 2607 capable of the Call Type Discrimination Package. Once the MGC 2608 evaluates the tones and determines that the incoming call is fax, 2609 the MGC shall execute appropriate Modify commands to place the IP 2610 fax capable termination into a "Negotiating" state. 2612 11.5.3 Process of Ending a Fax Call 2614 The MGs are responsible for detecting events that would cause the 2615 interruption of a fax call. The MGC is responsible for making the 2616 determination if this switch can be made and instruct the MGs to 2617 switch. It also responsible for switching it back to fax. 2618 The MGC should receive indication that the fax call ends from the MG 2619 before receiving typical call termination indications. 2621 11.5.4 Informative Example: 2623 One possible instruction from an MGC to an MG to modify an existing 2624 context to a T.38 media stream: 2626 MGC to MG: 2627 MEGACO/1.0 [123.123.123.4]:55555 2628 Transaction = 14 { 2629 Context = 2000 { 2630 Modify = RTP/1 { 2631 Media { 2632 Stream = 1 { 2633 Local { 2634 v=0 2635 c=IN IP4 124.124.124.222 2636 m=image 1111 udptl t38 2637 a=T38FaxRateManagement:transferredTCF 2638 a=T38UdpEC:t38UDPFEC 2640 Hellstrom/Parsons/Rafferty/Spitzer Standards track 49 2642 H.248 Annex F (Decided and amended) Jan. 2001 2644 } 2645 } 2646 } 2647 } 2648 } 2649 } 2651 12. Security Considerations 2653 Security considerations regarding media gateway control are 2654 discussed in section 10 of [3]. 2656 13. References 2658 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 2659 9, RFC 2026, October 1996. 2661 2 Bradner, S., "Key words for use in RFCs to Indicate Requirement 2662 Levels", BCP 14, RFC 2119, March 1997. 2664 3 ITU-T Recommendation H.248, "Gateway Control Protocol", Geneva, 2665 June 2000. Also to appear as RFC xxxx (currently draft-ietf- 2666 megaco-merged-01.txt). 2668 4 Schulzrinne, H., et al, RTP: A Transport Protocol for Real-Time 2669 Applications, IETF RFC 1889, January 1996. 2671 5 ITU-T Recommendation T.30 (7/96) Procedures for document 2672 facsimile transmission in the general switched telephone network. 2674 6 ITU-T Recommendation T.38 (6/98) Procedures for real-time Group 3 2675 facsimile communication over IP networks. 2677 7 ITU-T Recommendation V.8 (2000) Procedures for starting sessions 2678 of data transmission over the public switched telephone network. 2680 8 ITU-T Recommendation V.8 bis (2000) Procedures for the 2681 identification and selection of common modes of operation between 2682 data circuit-termination equipments (DCEs). 2684 9 ITU-T Recommendation V.18 (2000) Operational and interworking 2685 requirements for DCES operating in the text telephone mode. 2687 10 ITU-T Recommendation V.25 (1996) Automatic answering equipment 2688 and/or parallel automatic calling equipment on the general 2689 switched telephone network. 2691 11 ITU-T Recommendation T.140 (1998) _ Text conversation protocol 2692 for multimedia application. With amendment 1 (2000). 2694 Hellstrom/Parsons/Rafferty/Spitzer Standards track 50 2696 H.248 Annex F (Decided and amended) Jan. 2001 2698 12 ITU-T Recommendation H.323 Annex G(2000); Text Conversation and 2699 Text SET (2000). 2701 13 G. Hellstrom, "RTP Payload for Text Conversation", Internet 2702 Engineering Task Force, RFC 2793. (2000) 2704 14 ITU-T Recommendation T.134 (1998) Text Chat Application Entity. 2706 15 ITU-T Recommendation V.17 (02/91) Recommendation V.17 (02/91) - A 2707 2-wire modem for facsimile applications with rates up to 14 400 2708 bit/s. 2710 16 ITU-T Recommendation V.27 ter (11/88) - 4800/2400 bits per second 2711 modem standardized for use in the general switched telephone 2712 network. 2714 17 ITU-T Recommendation V.21 (11/88) - 300 bits per second duplex 2715 modem standardized for use in the general switched telephone 2716 network. 2718 18 ITU-T Recommendation V.23 (11/88) - 600/1200-baud modem 2719 standardized for use in the general switched telephone network. 2721 19 ITU-T Recommendation V.34 (02/91) - A duplex modem operating at 2722 data signalling rates of up to 14 400 bit/s for use on the 2723 general switched telephone network and on leased point-to-point 2724 2-wire telephone-type circuit. 2726 20 ITU-T Recommendation V.90 (09/98) - A digital modem and analogue 2727 modem pair for use on the Public Switched Telephone Network 2728 (PSTN) at data signalling rates of up to 56 000 bit/s downstream 2729 and up to 33 600 bit/s upstream. 2731 21 ITU-T Recommendation V.61 (08/96) - A simultaneous voice plus 2732 data modem, operating at a voice plus data signalling rate of 2733 4800 bit/s, with optional automatic switching to data-only 2734 signalling rates of up to 14 400 bit/s, for use on the General 2735 Switched . 2737 22 ITU-T Recommendation T.37 (6/98) Procedures for the transfer of 2738 facsimile data via store and forward on the internet. 2740 23 ISO/IEC 10646-1: (1993), Universal Multiple Octet Coded Character 2741 Set. 2743 24 ITU-T T.50 (1992), International Reference Alphabet (IRA) 2744 (formerly International Alphabet No. 5 or IA5) _ Information 2745 technology _ 7-bit coded character set for information 2746 interchange. 2748 25 ITU-T H.323 Annex D. (1998) Facsimile. 2750 Hellstrom/Parsons/Rafferty/Spitzer Standards track 51 2752 H.248 Annex F (Decided and amended) Jan. 2001 2754 13.1 Non-normative references 2756 - RFC 2532, Extended Facsimile Using Internet Mail., IETF 2757 - RFC 2530, Indicating Supported Media Features Using Extensions to 2758 DSN and MDN., IETF 2759 - RFC 2531, Content Feature Schema for Internet Fax., IETF 2760 - RFC 2301, File Format for Internet Fax., IETF 2761 - RFC 2302, Tag Image File Format (TIFF) - image/tiff MIME Sub-type 2762 Registration, IETF 2763 - RFC 2303, Minimal PSTN address format in Internet Mail., IETF 2764 - RFC 2304, Minimal FAX address format in Internet Mail., IETF 2765 - RFC 2305, A Simple Mode of Facsimile Using Internet Mail., IETF 2767 14. Acknowledgements 2769 The authors wishes to recognize important support in the creation of this 2770 document given by Nancy Greene, Nortel Networks. 2772 15. Authors' Addresses 2774 Gunnar Hellstrom 2775 L M Ericsson 2776 Tel +46 708 204 288 2777 E-mail: gunnar.hellstrom@era.ericsson.se 2779 Glenn Parsons 2780 Nortel Networks 2781 Tel: +1 613-763-7582 2782 Fax: +1-613-763-4461 2783 E-mail: gparsons@nortelnetworks.com 2785 James Rafferty 2786 Brooktrout Technology 2787 410 First Avenue 2788 Needham, MA 02494 USA 2789 Phone: +1-781-433-9462 2790 Fax: 781-433-9268 2791 E-mail: jraff@brooktrout.com 2793 Roy Spitzer 2794 Telogy Networks, Inc. 2795 20250 Century Blvd. 2796 Germantown, MD 20874 USA 2797 Phone: +1 301 515-6531 2798 Fax: +1 301 515-7954 2799 Email: rspitzer@telogy.com 2801 Hellstrom/Parsons/Rafferty/Spitzer Standards track 52