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Network Working Group                                       C. AllocchioRequest for Comments: 3601                                    GARR-ItalyCategory: Standards Track                                 September 2003Text String Notation for Dial Sequences andGlobal Switched Telephone Network (GSTN) / E.164 AddressesStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2003).  All Rights Reserved.Abstract   This memo describes the full set of notations needed to represent a   text string in a Dial Sequence.  A Dial Sequence is normally composed   of Dual Tone Multi Frequency (DTMF) elements, plus separators and   additional "actions" (such as "wait for dialtone", "pause for N   secs", etc.) which could be needed to successfully establish the   connection with the target service:  this includes the cases where   subaddresses or DTMF menu navigation apply.1.  Introduction   Since the very first devices interacting with GSTN services appeared,   a need for a unique text string representation of commonly called   telephone numbers, and more generally DTMF sequences and actions, was   foreseen.   This memo describes the full text string representation method.  This   specification was explicitly created to provide an easy, unique and   complete reference which MUST be used by all other specifications   needing a text string representation for a Dial Sequence.   The specification was collected directly from Dial Sequence   definitions which are already described in existing Standard Track   specifications (such as [6] [7] [8] [9]), and is fully synchronized   with them.  Full compatibility is thus assured, and as a consequence,   this specification results in a compendium of existing definitions.Allocchio                   Standards Track                     [Page 1]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 2003   This notation is a fully compatible compendium of existing notations,   and should be used in all specifications needing a text string   representation of a Dial Sequence.   Although the commonly called "telephone numbers" are normally used to   generate a Dial Sequence when establishing a connection, the full   abstract E.164 addresses [2], i.e., the universal addressing on the   Global Switched Telephone Network (GSTN), have further elements which   cannot be dialled.  Thus abstract E.164 addresses cannot be fully   converted into a Dial Sequence or fully represented using this   notation.1.1.  Terminology and Syntax conventions   In this document the formal definitions are described using ABNF   syntax, as defined in [3].  This memo also uses some of the "CORE   DEFINITIONS" defined in "APPENDIX A - CORE" of that document.   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inBCP 14,RFC 2119 [4].   The following terms are also defined in this document:      Dial Sequence:         a series of DTMF elements and human or device "actions";      phone-string:         a text representation of a Dial Sequence;      GSTN address:  a commonly called "telephone number" on the GSTN,         i.e., a diallable subset of an E.164 abstract address or any         private numbering schema diallable address;      gstn-phone:         a text representation of a GSTN address;      subaddr-string:         a text representation of a GSTN subaddress (which includes ISDN         subaddresses [2] and T.33 subaddresses [5]);      post-dial:         a text representation of a post dialling sequence.Allocchio                   Standards Track                     [Page 2]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 20032.  The "Dial Sequence" definition   The possible elements composing a Dial Sequence can vary from a   minimum number, up to a really large and complex collection: in fact,   the sequences already needed to dial a gstn-phone, which is a subset   of the generic Dial Sequence, well represents this variety and   complexity of cases.   In particular, a Dial Sequence is composed by:   -  "DTMF elements": normally available as "keys" on numeric keypads      of dialling devices;   -  "actions": normally performed by the agent (human or device)      composing the Dial Sequence;   -  "separators": used only to improve human readability of a Dial      Sequence.2.1.  The "phone-string" definition   The text representation of the Dial Sequence elements is defined in   the phone-string specification:      phone-string = 1*( DTMF / pause / tonewait / written-sep )      DTMF = ( DIGIT / "#" / "*" / "A" / "B" / "C" / "D" )                     ; special DTMF codes like "*", "#", "A", "B",                     ; "C", "D" are defined in [1].                     ; Important Note: these elements only apply for                     ; alphabetic strings used in DTMF operations.                     ; They are NOT applicable for the alphabetic                     ; characters that are mapped to digits on phone                     ; keypads in some countries.      pause = "p"      tonewait = "w"      written-sep = ( "-" / "." )   Note:      DTMF are the "DTMF elements", pause and tonewait are the "actions"      and written-sep are the "separators".   The "pause" and "tonewait" elements interpretation of the phone-   string depends on the specific devices and implementation using the   specification.  Thus their exact meaning is not mandated in thisAllocchio                   Standards Track                     [Page 3]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 2003   document.  The next section provides some examples drawn from common   practice.  Both "pause" and "tonewait" are case insensitive.   Implementation of "pause" and "tonewait":      -  one instance of a "pause" SHOULD be interpreted as a pause of         one second between the preceding and succeeding dial string         elements;      -  a "tonewait" SHOULD be interpreted as a pause that will last         until the calling party hears a dial tone or another indication         that more dial string characters may be processed.  An off-hook         indication MAY also be interpreted as this kind of indication         (meaning that the audio channel has been opened to the         receiving party);      -  because these characters are not a part of the GSTN subscriber         address (telephone number) per se, any dial string characters         that succeed either a "pause" or "tonewait" SHOULD be sent         using DTMF signalling.   The use of written-sep elements is allowed in order to improve human   readability of the phone-string.  The written-sep are elements which   can be placed between dial elements, such as digits etc.  Any   occurrences of written-sep elements in a phone-string MUST NOT result   in any action.  Conformant implementations MAY drop or insert   written-sep into the phone-string they handle.   The phone-string definition is used in the following sections to   explicitly describe the encoding of some specific subcases where it   applies.3.  The "gstn-phone" definition   In order to access a GSTN address, a human or a device must perform a   Dial Sequence.  Thus, a GSTN address can be represented using the   phone-string elements.  In particular, diallable E.164 numeric   addresses [2] represent a limited subset of all possible GSTN   addresses, while the complete complex case needs a full encoding   schema, as it also includes a local or private addressing schema.   In order to describe this distinction and provide anyhow a complete   encoding schema, the following definition of "gstn-phone" is   provided:      gstn-phone = ( global-phone / local-phone )Allocchio                   Standards Track                     [Page 4]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 20033.1.  The "global-phone" definition   The purpose of the global-phone element is to represent diallable   E.164 numeric addresses.  As such, it uses a subset of a phone-string   definition only.   The syntax for a global-phone element is as follows:      global-phone = "+" 1*( DIGIT / written-sep )   Any other dialling schemes MUST NOT use the leading "+" defined here.   The "+" sign is strictly reserved for the standard "global-phone"   syntax, and, even if not specifically part of the phone-string   definition, it is needed to uniquely label a global-phone.3.2.  The "local-phone" definition   The local-phone element is intended to represent the set of possible   cases where the global-phone numbering schema does not apply.  Given   the different and complex conventions currently being used in the   GSTN system, the local-phone definition supports a large number of   elements.   The detailed syntax for local-phone elements is as follows:      local-phone =  [ exit-code ] dial-number      local-phone =/ exit-code [ dial-number ]      exit-code = phone-string                  ; this will include elements such as the digit to                  ; access outside line, the long distance carrier                  ; access code, the access password to the service,                  ; etc...      dial-number = phone-string                  ; this is in many cases composed of different elements                  ; such as the local phone number, the area code                  ; (if needed), the international country code                  ; (if needed), etc...   Notes:      The "+" character is reserved for use in a global-phone and MUST      NOT be used in a local-phone string;      Please note that a local-phone string MUST NOT be a null string,      i.e., at least an exit-code, or a dial-number or both MUST be      present.Allocchio                   Standards Track                     [Page 5]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 20034.  The "subaddr-string" definition   In GSTN service, there are cases where a subaddress is required to   specify the final destination.  To specify these subaddresses, a Dial   Sequence is also used, and thus the "subaddr-string" can be encoded   as:      subaddr-string = phone-string   Note:      Within actual uses of subaddresses, some specific services can      limit the possible set of phone-string elements allowed.  In      particular, there are ISDN subaddresses [2] [8], which restrict      the phone-string elements to 1*( DIGIT / written-sep ) and service      specific subaddresses, like the fax service T.33 subaddress [5]      [7], which restrict phone-string elements to 1*( DIGIT ).5.  The "post-dial" definition   In some cases, after the connection with the destination GSTN device   has been established, a further dialling sequence is required to   access further services.  A typical example is an automated menu-   driven service using DTMF sequences. These cases may be represented   using the "post-dial" definition below:      post-dial = phone-string6.  Examples   In order to clarify the specification we present, here are a limited   set of examples.  Please note that all the examples are for   illustration purposes only.   A GSTN address in Italy, dialled from U.S.A., using local-phone,   without written-sep:      01139040226338   A GSTN address in Germany, using global-phone and written-sep ".":      +49.81.7856345   A GSTN address in U.S.A. using global-phone and written-sep "-":      +1-202-455-7622Allocchio                   Standards Track                     [Page 6]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 2003   A post-dial sequence, pausing, dialling 1, waiting for dial tone,   dialling 7005393, waiting again for dial tone and dialling 373; note   the use of four "p" elements (pppp) to specify a longer initial   pause:      pppp1w7005393w373   A Dial Sequence in Italy (long distance call), using local-phone,   with exit-code "9", long distance access "0", area code "40", pause   "p" and written-sep ".":      9p040p22.63.38   A Dial Sequence using exit-code "0", a wait for dial tone, local-   phone for an International "800" toll-free number dialled from   Belgium (international prefix "00"), and a post-dial sequence to   access a voice mailbox with userID "334422" and Personal   Identification Number (PIN) code "1234":      0w00800-39380023pp334422p12347.  Conclusions   This proposal creates a full standard text encoding for Dial   Sequences, including GSTN and diallable E.164 addresses, and thus   provides a unique common representation method both for standard   protocols and applications.   Some definitions, like these corresponding to an alias of the generic   phone-string element, are somewhat a theoretical distinction; however   they are useful to provide a more subtle distinction, allowing other   specifications to be more exact in a consistent way.   The proposal is consistent with existing standard specifications.8.  Security Considerations   This document specifies a means to represent Dial Sequences, which   could include GSTN addresses and private codes sequences, like   Personal Identification Numbers, to access special services.  As   these text strings could be transmitted without encoding inside   protocols or applications services, this could allow unauthorized   people to gain access to these codes.  Users SHOULD be provided   methods to prevent this disclosure, like code encryption, or   masquerading techniques: out-of-band communication of authorization   information or use of encrypted data in special fields are the   available non-standard techniques.Allocchio                   Standards Track                     [Page 7]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 20039.  Collected ABNF Syntax   In this section we provide a summary of ABNF specifications.      phone-string = 1*( DTMF / pause / tonewait / written-sep )      DTMF = ( DIGIT / "#" / "*" / "A" / "B" / "C" / "D" )      written-sep = ( "-" / "." )      pause = "p"      tonewait = "w"      gstn-phone = ( global-phone / local-phone )      global-phone = "+" 1*( DIGIT / written-sep )      local-phone =  [ exit-code ] dial-number      local-phone =/ exit-code [ dial-number ]      exit-code = phone-string      dial-number = phone-string      subaddr-string = phone-string      post-dial = phone-string10.  References10.1.  Normative References   [1] ETSI I-ETS 300,380 - Universal Personal Telecommunication (UPT):       Access Devices Dual Tone Multi Frequency (DTMF) sender for       acoustical coupling to the microphone of a handset telephone       (March 1995).   [2] ITU E.164 - The International Public Telecommunication Numbering       Plan E.164/I.331 (May 1997).   [3] Crocker, D. Ed. and P. Overell, "Augmented BNF for Syntax       Specifications: ABNF",RFC 2234, November 1997.   [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement       Levels",BCP 14,RFC 2119, March 1997.Allocchio                   Standards Track                     [Page 8]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 2003   [5] ITU T.33 - Facsimile routing utilizing the subaddress;       recommendation T.33 (July, 1996).10.2.  Informative References   [6] Allocchio, C., "Minimal GSTN address format in Internet Mail",RFC 3191, October 2001.   [7] Allocchio, C., "Minimal FAX address format in Internet Mail",RFC3192, October 2001.   [8] Allocchio, C., "GSTN Address Element Extensions in E-mail       Services",RFC 2846, June 2000.   [9] Vaha-Sipila, A., "URLs for Telephone Calls",RFC 2806, April       2000.11.  Author's Address   Claudio Allocchio   GARR   c/o Sincrotrone Trieste   SS 14 Km 163.5 Basovizza   I 34012 Trieste   Italy   Phone: +39 040 3758523   Fax:   +39 040 3758565   X.400: C=it;A=garr;P=garr;S=Allocchio;G=Claudio;   EMail: Claudio.Allocchio@garr.itAllocchio                   Standards Track                     [Page 9]

RFC 3601       Dial Sequences and GSTN / E.164 Addresses  September 200312.  Full Copyright Statement   Copyright (C) The Internet Society (2003).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assignees.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Allocchio                   Standards Track                    [Page 10]