Internet Engineering Task Force James M. Polk Internet Draft Cisco Systems Expiration: Dec 23rd, 2003 File: draft-polk-sipping-location-requirements-00.txt Session Initiation Protocol Location Requirements June 23rd, 2003 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Abstract This document presents the requirements for an extension to the Session Initiation Protocol (SIP) [1] for conveyance of user location information from one Session Initiation Protocol (SIP) User Agent to another SIP User Agent. The idea that in some cases the UAC's location could affect proper routing of the SIP message is explored as well. Polk [Page 1]
Internet Draft SIP Location Reqs June 23rd, 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Conventions . . . . . . . . . . . . . . . . . . . . . . . 3 2. In the Body or in a Header . . . . . . . . . . . . . . . . . 3 3. Scope of Location in a Message Body . . . . . . . . . . . . . 4 4. Scope of Location in a Message Header . . . . . . . . . . . . 4 4.1 Location in a Single Header . . . . . . . . . . . . . . . 4 4.2 Location in Separate Message Headers . . . . . . . . . . 5 5. Requirements for UA-to-UA Location Conveyance . . . . . . . . 5 6. Requirements for Proxy-Routed Location Conveyance . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 11. Author Information . . . . . . . . . . . . . . . . . . . . . 8 12. Full Copyright Statement . . . . . . . . . . . . . . . . . . 8 1. Introduction This document presents the requirements for an extension to the Session Initiation Protocol (SIP) [1] for conveyance of user location information from one Session Initiation Protocol (SIP) User Agent to another SIP User Agent. While reasonable people will initially lean strongly towards having any location conveyance in the message body only (where location confidentiality can be maintained), this document examines usage cases where intermediaries must act on the location information in order to determine where the session gets routed. One such example of this is US e911-type emergency sessions (voice or instant messaging). With this in mind, both instances will be looked at here to determine if the requirements are in fact different enough to necessitate two or more solutions. To be clear, the two cases that need to be looked at are the following: 1. one involving a user of a User Agent wanting to transmit his/her location to another user of a user agent for whatever reason (I want to tell you where I am); and 2. a second case involving the UAC including its location in order to allow an appropriate Emergency Response Center (ERC) to be contacted, such as a US e911 Public Safety Answering Point (because that User Agent has signaled for help); Polk [Page 2]
Internet Draft SIP Location Reqs June 23rd, 2003 This document does not discuss how the UAC discovers or is configured with its Location (either coordinate based or civil based). That work is being accomplished in the Geopriv Working Group. 1.1 Conventions used in this 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 in [2]. 2. In the Body or in a Header When one user agent wants to inform another user agent where they are, it seems reasonable to have this accomplished by placing the location information (coordinate or civil) in an S/Mime registered and encoded message body, and sending it as part of a SIP request or response. No routing of the request based on the location information is required in this case; therefore no SIP Proxies between these two UAs need to view the location information contained in the SIP messages. However, it may be infeasible to place the location information in the message body of requests where/when message routing is of particular importance for proper session establishment with the intended party or parties (i.e. calling an ERC). SIP message bodies are not viewed by Proxy Servers [per 1] in order to do proper call routing. The current proposal in front of the SIPPING WG is to use the mechanism described in [3] to universally signal for help. This "sos@example.com" URI is proposed to describe many, if not all ERCs in a region or country - regardless of the original home domain that UA is from. This poses a particular problem when a User Agent is signaling via a Proxy that is not within the civil boundaries of the appropriate PSAP for that user. For example, a large enterprise has a campus that spans more than one PSAP jurisdiction, a UA initiates a session containing the To header "sos@example.com". Where will that Proxy route the SIP Request to? The problem is compounded if a managed domain only has Proxies in one location of a multi site infrastructure - including the possibility of traversing state or country boundaries in cases in which the UA is mobile. Routing a session set-up or instant message, such as SIP MESSAGE from [4], becomes an Achilles Heel for SIP if the user agent is unaware of the correct ERC routing and expects the correct ERC to be selected by the SIP proxy routing machinery.. Polk [Page 3]
Internet Draft SIP Location Reqs June 23rd, 2003 This document does not address the behavior or configuration of SIP Proxy Servers in these cases in order to accomplish location- sensitive routing. That is out of scope, and left for further (complementary) efforts. 3. Scope of Location in a Message Body If the location information is to be contained within a message body, the rules stated in section 7 of [1] regarding multipart MIME bodies MUST be followed. The format and privacy/security rules of the location information SHOULD be defined within the Geopriv WG. 4. Scope of Location in a Message Header If the location information of the UAC is to be contained within the SIP message header (verses a message body as stated above), one design issue is whether location field(s) are contained within a single header, or multiple headers. The following 2 subsections cover both of these choices for discussion. 4.1 Location in a Single Header Placing location information within a single header of a SIP message has some big advantages: - it is easier to specify the semantics when there are missing fields - it makes readability much easier when reviewing all the location fields contained within the SIP message header ordered as if in a list - an order of the location fields can be specified within this single header (ex: Datum, then Latitude, then Longitude, then Altitude, then... or country, then state/province, then county/region, then city, then district/borough...) This might be important if section 7.3.1 of [1] is still true expedited parsing in Proxies and at the destination. There exist two documents on Location Configuration Information within the Geopriv Working Group, one for Coordinate based location representation (Lat, Long, Alt, Datum, etc) in [5] and one for Civil based Location representation (country, State/province, city, etc) in [6]. Each of these documents should be looked to as a basis for consistency in fields present as well as scope of the fields. If a field is missing, it probably was left out intentionally by the Polk [Page 4]
Internet Draft SIP Location Reqs June 23rd, 2003 UAC (either because that device didn't know what to populate a particular field with, or a policy prevented it from being included within that SIP message). Any location privacy policy of a user agent within a particular domain should allow the most precise location available be presented as an S/MIME body in the SIP Request or response message once a verifiable ERC is determined to be the intended destination of that session. 4.2 Location in Separate Message Headers Creating separate SIP headers for each location field type (latitude, longitude, country, city, etc) does make each header clean and concise. A grouping of these location headers should occur for readability when viewing the location headers within a SIP message header. And since expediting the processing of emergency calls is important, the header placement considerations of section 7.3.1 of [1] apply to these headers when making emergency calls Each of the message headers should be unique in name within a location conveyance type. In providing location information, the UAC should provide as much information as possible within a certain type of location field group (coordinate or civil), and not mix between groups. In other words, a Latitude header should be used if a coordinate location is being provided by the UAC, but is not by itself realistically valuable information if a complete set civil location headers is also present. There exist two documents on Location Configuration Information within the Geopriv Working Group, one for Coordinate based location representation (Lat, Long, Alt, Datum, etc) in [5] and one for Civil based Location representation (country, State/province, city, etc) in [6]. Each of these documents should be looked to as a basis for consistency in fields present as well as scope of the fields. If a desire of the SIP working group is to limit the number of headers that require IANA registration (and coding for), then fulfilling this requirements document will add as little as 2 to that process (1 for coordinate location and 1 for civil location), or as many as 30+ if each location field requires a unique header. 5. Requirements for UA-to-UA Location Conveyance The following are the requirements for UA-to-UA Location Conveyance situations: Polk [Page 5]
Internet Draft SIP Location Reqs June 23rd, 2003 REQ UU1 - MUST work with dialog-initiating SIP Requests and responses, as well as the SIP MESSAGE method[4] REQ UU2 - the precision of resolution of the location given by the UAC is determined by the UAC, and SHOULD be based on who the UAC is sending this location information to (most likely via local policy) REQ UU3 - UAC Location information SHOULD remain confidential in route to the destination UA REQ UU4 - The privacy and security rules established within the Geopriv Working Group which would categorize SIP as a 'using protocol' MUST be followed [7] REQ UU5 - The first sub-field must be what type of location information it is (coordinate, civil, GPS, other) 6. Requirements for Proxy-Routed Location Conveyance The following are the requirements for Proxy-Routed Location Conveyance situations: REQ PR1 - MUST work with dialog-initiating SIP Requests and responses, as well as the SIP MESSAGE method[4] REQ PR2 - a mechanism SHOULD be in place to hide this location header from unwanted observation while in transit to, form, and among SIP intermediaries; but MUST NOT be mandatory for successful conveyance of location (don't want the SIP Request to fail without this mechanism used during emergencies) REQ PR3 - any mechanism used to prevent unwanted observation of this Location Header(s) CANNOT fail the SIP Request if not understood by intermediary SIP entities or the destination UAS REQ PR4 - There SHOULD be a mechanism for the ERC to request the UAC's location information (perhaps more precise location information) after the original SIP Request has been received without failing the original SIP Request (which is the most important aspect of this document: that the session is received by the proper ERC) It is possible for a Proxy to determine the proper ERC to route the SIP Request to (based on the included location information within supplied by the UAC), yet create the situation where the ERC does not know enough location information for personnel response to the emergency. Polk [Page 6]
Internet Draft SIP Location Reqs June 23rd, 2003 REQ PR5 - A SIP location Header field (probably the first if there is an order established to the headers) MUST be what type of location information type it is (coordinate, civil, GPS, other) REQ PR6 - SHOULD have the complete location (coordinate or civil) contained within a single header REQ PR7 - the most precise resolution (defined in [5])SHOULD be given by the UAC when sending its location to an ERC (or equivalent facility) REQ PR8 - proxies SHOULD NOT partially remove location information, but MAY remove it in its entirety when crossing a trust boundary to preserve privacy REQ PR9 - proxies MAY add location information unknown to the UAC if known to the proxy REQ PR10 - if section 7.3.1 of [1] needs to be followed, the Location Header SHOULD be near the top of the SIP message header for rapid parsing purposes REQ PR11 - mixed or additional location fields CAN be present providing more precise location information, but MUST be uniquely identifiable and SHOULD be relevant An example of this might be using the coordinate location header and adding an identifiable cube or office number field at the end of the coordinate header. 7. Security Considerations Conveyance of geo-location of a UAC is problematic for many reasons. This document calls for that conveyance to normally be accomplished through secure message body means (like S/MIME). In cases where a session set-up is routed based on the location of the UAC initiating the session or SIP MESSAGE, containing the location in a message body does no good. At the same time, securing the location in a header might fail in certain times that is detrimental to that session (user). These times are those of emergency sessions (like to a US e911-like service). Although not advocated, this document therefore requires that location conveyance in deterministic times of emergency not be bound to being confidential universally, as that process might fail and could cost lives. Polk [Page 7]
Internet Draft SIP Location Reqs June 23rd, 2003 8. IANA Considerations There are no IANA considerations within this document at this time. 9. Acknowledgements To Dave Oran for helping to shape this idea 10. References - Normative [1] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, E. Schooler, "SIP: Session Initiation Protocol ", RFC 3261, June 2002 [2] S. Bradner, "Key words for use in RFCs to indicate requirement levels," RFC 2119, Mar. 1997. [3] H. Schulzrinne, "draft-schulzrinne-sipping-sos-04.txt", Internet Draft, Jan 03, Work in progress [4] B. Campbell, Ed., J. Rosenberg, H. Schulzrinne, C. Huitema, D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging" , RFC 3428, December 2002 [5] J. Polk, J. Schnizlein, M. Linsner, " draft-ietf-geopriv-dhcp-lci- option-01.txt", Internet Draft, June 2003, Work in progress [6] H. Schulzrinne, "draft-schulzrinne-geopriv-dhcp-civil-01.txt", Internet Draft, Feb 03, Work in progress [7] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk, "draft- ietf-geopriv-reqs-03.txt", Internet Draft, Mar 03, Work in progress 11. Author Information James M. Polk Cisco Systems 2200 East President George Bush Turnpike Richardson, Texas 75082 USA jmpolk@cisco.com Polk [Page 8]
Internet Draft SIP Location Reqs June 23rd, 2003 12. Full Copyright Statement "Copyright (C) The Internet Society (February 23rd, 2001). 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 assigns. 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." The Expiration date for this Internet Draft is: Dec 23rd, 2003 Polk [Page 9]