Network Working Group M. Munakata Internet-Draft S. Schubert Expires: August 30, 2006 T. Ohba NTT February 26, 2006 ISDN subaddress encoding type for tel URI draft-munakata-iptel-isub-type-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 30, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract Without a tel URI parameter to carry encoding type of Integrated Services Digital Network(ISDN) subaddress, interworking between ISDN User Part(ISUP) network and Session Initiation Protocol(SIP) network is impossible in some cases. To solve the problem, this document specifies a new tel URI parameter to carry encoding type of ISDN subaddress. Munakata, et al. Expires August 30, 2006 [Page 1] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 3.1. SIP-ISDN Interconnection . . . . . . . . . . . . . . . . . 5 3.2. ISDN-SIP-ISDN Interconnection . . . . . . . . . . . . . . 7 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Parameter Definition . . . . . . . . . . . . . . . . . . . . . 9 6. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Gateway behavior . . . . . . . . . . . . . . . . . . . . . 10 6.2. Length and format of isub parameter . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.1. Structure of NSAP Addresses . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.1. Normative Reference . . . . . . . . . . . . . . . . . . . 14 9.2. Informative Reference . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 16 Munakata, et al. Expires August 30, 2006 [Page 2] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 1. Introduction RFC3966[2] defines the tel URI parameter "isub" that is designed to carry Integrated Services Digital Network(ISDN) subaddresses. In a ISDN User Part(ISUP) message, NSAP address[6] or user specified address can be carried as ISDN subaddress. Network Service Access Point(NSAP) address accommodates various types of address information along with an identifier that shows the address type and its encoding type. "isub" parameter can also carry any type of address but RFC3966 doesn't define a solution to carry information of subaddress type (whether the subaddress is NSAP address or not) and an identifier of an encoding type. Most commonly used encoding type for ISDN subaddress is International Alphabet 5(IA5)[5]. RFC 3966 says "ISDN subaddresses typically contain IA5 characters but may contain any octet value". Nevertheless, IA5 is just one of the encoding types among various types of encoding used in NSAP address. Therefore parameter to carry isub value alone is not enough to describe ISDN subaddresses, and additional information is needed. Lack of information describing the encoding type of "isub" parameter will most likely make it difficult for ISDN terminal receiving ISDN subaddress from SIP network(SIP-ISDN Interconnection) to interpret the "isub" parameter value as gateway may translate it using the encoding type not anticipated. It will also make it difficult to recover the original ISDN subaddress value when ISUP message is translated to SIP message and back to ISUP message(ISDN-SIP-ISDN Interconnection), as there is no place holder to carry the encoding type currently in SIP message, the encoding type that was present in the original ISUP message will be lost. To solve the issue, this specification defines "isub-type" parameter to carry information whether the value of "isub" parameter is NSAP address or not and its encoding type. In addition, this document specifies the meaning of the value in "isub" parameter. Munakata, et al. Expires August 30, 2006 [Page 3] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 2. Terminology 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 in RFC 2119[1]. Munakata, et al. Expires August 30, 2006 [Page 4] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 3. Problem Statement Without a tel URI parameter to carry encoding type of ISDN subaddress, such problems shown in 3.1 and 3.2 would happen. 3.1. SIP-ISDN Interconnection The following diagram shows an issue that will be observed when interworking between SIP network and ISDN network addressing an ISDN subaddress. When a SIP equipment sends a request with "isub" parameter to address an ISDN terminal behind Private Branch Exchange(PBX), the encoding type of ISDN subaddress currently can not be specified. Therefore gateway between SIP network and ISDN network can not translate the value of "isub" into ISUP Initial Address Message(IAM) properly because the encoding type information of the ISDN subaddress is missing. Munakata, et al. Expires August 30, 2006 [Page 5] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 ISDN Terminal +-----+ |--->| Bob | SIP Network <---|---> ISDN | |12345| | +-----+ SIP Equipment | +-----+ +-----+ +----+ +-----+ | +-----+ |Alice|----->|Proxy|----->| GW |----->| PBX |----->|Carol| +-----+ +-----+ +----+ +-----+ | +-----+ | | +-----+ |--->|David| +-----+ Alice Proxy GW Switch PBX Bob | | | | | | | INVITE | | | | | |---------->| INVITE | | | | | |------------>| IAM | | | | | |----->|SETUP| | | | | |---->| SETUP | | | | | |---------->| | | | | | | Figure 1: SIP-ISDN Interconnection INVITE tel:+17005554141;isub=12345 SIP/2.0 Note: SETUP is an ISDN message used between ISDN switch and ISDN end terminal. Munakata, et al. Expires August 30, 2006 [Page 6] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 3.2. ISDN-SIP-ISDN Interconnection Following diagram shows the issue that will be observed when interworking message with ISDN subaddress between ISDN network that traverses through SIP network. When an ISDN terminal sends a message that contains ISDN subaddress with its encoding type information, Gateway 1 translates the subaddress into "isub" parameter in SIP message. However, its encoding type is dropped because there is no room for encoding type in SIP message. When Gateway 2 receives "isub", it can not translate "isub" value into IAM message properly because the encoding type information of the ISDN subaddress is missing. ISDN Terminal +-----+ |--->| Bob | ISDN <---|---> SIP Network <---|---> ISDN | |12345| | +-----+ ISDN Terminal | +-----+ +-----+ +-----+ +-----+ +-----+ | +-----+ |Alice|----->| GW1 |---->|Proxy|---->| GW2 |---->| PBX |----->|Carol| +-----+ +-----+ +-----+ +-----+ +-----+ | +-----+ | | +-----+ |--->|David| +-----+ Alice Switch GW1 Proxy GW2 Switch PBX Bob | | | | | | | | | SETUP | | | | | | | |------>| IAM | | | | | | | |---->| INVITE | | | | | | | |---------->| INVITE | | | | | | | |---------->| IAM | | | | | | | |---->|SETUP| | | | | | | |---->| SETUP | | | | | | | |----------->| | | | | | | | | Figure 2: ISDN-SIP-ISDN Interconnection INVITE tel:+17005554141;isub=12345 SIP/2.0 Munakata, et al. Expires August 30, 2006 [Page 7] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 4. Requirements The followings are requirements for a solution to carry ISDN subaddress along with information of subaddress encoding type. Req 1: When "isub" parameter is present in a SIP message, the type of ISDN subaddress (whether it is an NSAP address or not) and its encoding type MUST be identifiable. Req 2: It MUST be possible for entity setting the "isub" parameter in a SIP message, to specify the type of ISDN subaddress(whether it is an NSAP address or not) and the encoding type used. Munakata, et al. Expires August 30, 2006 [Page 8] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 5. Parameter Definition The parameter defined in this draft is represented as a tel URI, which describes the encoding type information of the ISDN subaddress(ISUB Type). It accommodates some of the information that is lacking in the "isub" parameter defined in RFC3966[2]. It is an optional parameter to tel URI. The ABNF[3] syntax is as follows. isub-type = isub-type-tag "=" isub-type-value isub-type-tag = "isub-type" isub-type-value = "nsap-ia5" / "nsap-bcd" / "nsap" / token The semantics of these "isub-type" values are described below: nsap-ia5: Indication that the "isub" parameter value needs to be encoded using IA5(AFI=0x50) when translated to ISUP message. nsap-bcd: Indication that the "isub" parameter value needs to be encoded using Binary Coded Decimal(BCD)(AFI=0x48) when translated to ISUP message. nsap: Indication that the "isub" parameter value needs to be encoded using encoding type defined in ISO8348 other than IA5 (AFI=0x50) or BCD(AFI=0x48). An example of the syntax of the "isub-type" parameter (in a small fragment of a SIP[4] message) is given below: INVITE tel:+17005554141;isub=12345;isub-type=nsap-ia5 SIP/2.0 To: From: "Bob" ;tag=1928301774 Munakata, et al. Expires August 30, 2006 [Page 9] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 6. Usage It is anticipated that this URI parameter will be used along with the "isub" parameter defined in RFC3966[2] when interworking between ISUP networks and SIP network. The URI parameter defined here is an optional parameter to the tel URI. To find out more about the NSAP address, please reference the Appendix in Section 8. If the "isub-type" is absent, and the message is interpreted by an entity on the SIP network, the entity SHOULD assume that the original ISDN subaddress from ISUP message, which was translated to the "isub" parameter, was decoded using IA5(AFI=0x50) and handle the message accordingly. If the "isub-type" is absent, and the message is handled by a gateway translating the SIP message to ISUP message, the gateway SHOULD encode the value in the "isub" parameter using IA5(AFI=0x50) when translating the message into ISUP message. If the "isub-type" value is "nsap", the encoding type is assumed to be in the first two characters of "isub" parameter in hexadecimal format(% HEXDIG HEXDIG). 6.1. Gateway behavior Gateway receiving message/signal from ISDN network containing ISDN subaddress SHOULD check the encoding used for the subaddress, and set the equivalent "isub" parameter and "isub-type" parameter to the SIP message in a form of tel URI parameter. Following text is a recommended guideline when translating ISUP message containing ISDN subaddress. If the ISDN subaddress is encoded using IA5(AFI=0x50), the entity translating the message SHOULD set "nsap-ia5" to the "isub-type" and value after 5th octet of the subaddress information element in original ISUP message as "isub" value in ASCII characters. If the ISDN subaddress is encoded using BCD(AFI=0x48), the entity translating the message SHOULD set "nsap-bcd" to the "isub-type" and decode the value after 5th octet of the subaddress information element in original ISUP message using BCD and set it as the "isub" value in ASCII characters(numbers). If the ISDN subaddress is an NSAP address but neither encoded by IA5(AFI=0x50) nor BCD(AFI=0x48), the entity translating the message SHOULD set "nsap" to the "isub-type" and value after 4th octet of the subaddress information element in original ISUP message as "isub" value in hexadecimal format(% HEXDIG HEXDIG). Munakata, et al. Expires August 30, 2006 [Page 10] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 If the ISDN subaddress is not an NSAP address, the entity translating the message MAY set any value as a token. 6.2. Length and format of isub parameter An entity setting an "isub" parameter is RECOMMENDED to set the "isub-type" value with the encoding type used. Following text is a recommended guideline when setting the "isub" parameter. If the "isub-type" is "nsap-ia5", the "isub" parameter value SHOULD NOT exceed 19 ASCII characters. If the "isub-type" is "nsap-bcd", the "isub" parameter value SHOULD NOT exceed 38 ASCII characters(numbers). If the "isub-type" is "nsap", the "isub" parameter value SHOULD NOT exceed 40 ASCII characters and it SHOULD be in hexadecimal format(% HEXDIG HEXDIG). Entity MAY define other type of "isub-type" as a token. Munakata, et al. Expires August 30, 2006 [Page 11] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 7. Security Considerations The parameter defined here adds no new security considerations to those discussed in [2] Munakata, et al. Expires August 30, 2006 [Page 12] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 8. Appendix 8.1. Structure of NSAP Addresses In ISUP messages, ISDN subaddress is represented as NSAP address. NSAP address is defined as follows in ISO8348. NSAP address consists of Initial Domain Part(IDP) and Domain Specific Part(DSP). Then IDP consists of two fields, Authority and Format Identifier(AFI) and Initial Domain Identifier(IDI). The maximum length of NSAP address is 20 octets. <----------------- NSAP Address -----------------> +------------------------------------------------+ | I D P | | |-----------| D S P | | AFI | IDI | | +------------------------------------------------+ Figure 3 AFI value is two hexadecimal digits(00-FF), and it identifies IDI format and DSP syntax. IDI value is decimal digits, and it identifies a network addressing domain or authority responsible for allocating values of the DSP. Typical encoding type of ISDN subaddress, IA5, is identified with AFI=0x50. When AFI value is 0x50, IDI is null, and the length of IDP is 2 digits(1 octet). In this case, DSP value is a subaddress encoded by IA5 and its maximum length is 19 octets. Munakata, et al. Expires August 30, 2006 [Page 13] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 9. References 9.1. Normative Reference [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966, December 2004. [3] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. 9.2. Informative Reference [4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [5] International Telecommunications Union, "International Reference Alphabet (IRA) (Formerly International Alphabet No. 5 or IA5) - Information technology - 7-bit coded character set for information interchange", Recommendation T.50, 1992. [6] INTERNATIONAL STANDARD, "Information technology - Open Systems Interconnection - Network service definition", ISO/IEC 8348. Munakata, et al. Expires August 30, 2006 [Page 14] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 Authors' Addresses Mayumi Munakata NTT Corporation Phone: +81 422 36 7565 Email: munakata.mayumi@lab.ntt.co.jp Shida Schubert NTT Corporation Phone: +1 604 762 5606 Takumi Ohba NTT Corporation 9-11, Midori-cho 3-Chome Musashino-shi, Tokyo 180-8585 Japan Phone: +81 422 59 7748 Email: ohba.takumi@lab.ntt.co.jp URI: http://www.ntt.co.jp Munakata, et al. Expires August 30, 2006 [Page 15] Internet-Draft ISDN subaddress encoding type for tel URI February 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Munakata, et al. Expires August 30, 2006 [Page 16]