Geopriv J. Winterbottom Internet-Draft Andrew Corporation Intended status: Standards Track H. Tschofenig Expires: April 8, 2008 Nokia Siemens Networks M. Thomson Andrew Corporation October 6, 2007 HELD Protocol Context Management Extensions draft-winterbottom-geopriv-held-context-01.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 April 8, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Winterbottom, et al. Expires April 8, 2008 [Page 1] Internet-Draft HELD Context October 2007 Abstract This document describes a protocol extension for the HTTP Enabled Location Delivery (HELD) protocol. It allows a Target to manage their location information on a Location Information Server (LIS) through the application of constraints invoked by accessing a location URI. Constraints described in this memo restrict how often location can be accessed through a location URI, how long the URI is valid for, and the type of location information returned when a location URI is accessed. Extension points are also provided. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. What is a Context? . . . . . . . . . . . . . . . . . . . . . . 5 4. Constraints . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Limited Use URIs . . . . . . . . . . . . . . . . . . . . . 6 4.2. Snapshot URIs . . . . . . . . . . . . . . . . . . . . . . 7 4.3. Location Type URIs . . . . . . . . . . . . . . . . . . . . 7 5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 8 5.1. Create Context Message . . . . . . . . . . . . . . . . . . 8 5.2. Update Context Message . . . . . . . . . . . . . . . . . . 9 5.3. Context Response Message . . . . . . . . . . . . . . . . . 10 5.4. Context Error Messages . . . . . . . . . . . . . . . . . . 12 5.5. Location URI and Context Identifier Generation Rules . . . 12 6. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 8.1. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:geopriv:held:context . . . . . . . 19 8.2. XML Schema Registration . . . . . . . . . . . . . . . . . 19 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21 Appendix A. Context Extensions . . . . . . . . . . . . . . . . . 22 Appendix B. HELD Compliance to IETF Location Configuration Protocol Location Reference Requirements . . . . . . 24 10. Normative References . . . . . . . . . . . . . . . . . . . . . 26 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 Intellectual Property and Copyright Statements . . . . . . . . . . 28 Winterbottom, et al. Expires April 8, 2008 [Page 2] Internet-Draft HELD Context October 2007 1. Introduction The HTTP Enabled Location Delivery (HELD) protocol specification [I-D.ietf-geopriv-http-location-delivery] provides a set of features that can be used by a Target to retrieve location information from a Location Information Server (LIS). The basic HELD specification does this in a more or less stateless manner, and when a location URI is retrieved the Target has no way of controlling how the URI is used; a Location Recipient in pocession of the location URI can get the Target's location until the URI expires. This basic mechanism may be reasonable in a limited set of applications, but is unacceptable in a broader range of applications. This position is highlighted in [I-D.ietf-geopriv-lbyr-requirements] which describes requirements for constraints relating to location URIs. This specification provides support for these requirements in HELD. Winterbottom, et al. Expires April 8, 2008 [Page 3] Internet-Draft HELD Context October 2007 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 [RFC2119]. This document reuses the terms Target, as defined in [RFC3693]. This document uses the term Location Information Server (LIS) as the node in the access network that provides location information about a Target. This term is also used in [I-D.ietf-geopriv-l7-lcp-ps]. Winterbottom, et al. Expires April 8, 2008 [Page 4] Internet-Draft HELD Context October 2007 3. What is a Context? A Location URI points to a LIS that is able to provide the location of a specific Target. The LIS is able to map the URI to the location of the Target inside its administrative domain. We call this mapping a "context". In the basic HELD specification the context is implicitly created with the request for a location URI in the locationRequest message. The Target has no control of the mapping from the URI to the Target's location. This specification provides a degree of control to the Target, allowing it to specify rules to the LIS on how a context should map a URI to location information. A context expires when it reaches a certain age, at which time the mapping between the URI and the Target's location ceases. In the basic HELD specification the exiry time of the context is determined by the LIS when the Target requests a location URI. By allowing the Target to specify and change the life time of a context the Target is able to create URIs for limited periods, or to terminate URIs for which it longer wishes its location to be returned. This specification provides explicit support for this functionality. Winterbottom, et al. Expires April 8, 2008 [Page 5] Internet-Draft HELD Context October 2007 4. Constraints Constraints restrict the ability of a Location Recipient to resolve a location URI to location information. The constraints are selected by the Target and they are provided to the LIS that maintains them along with the context. A LIS, understanding this specification, receives constraints provided by the Target, and returns a set of URIs influenced by the constraints. A single Target may want to place different contraints on different references and hence may have multiple contexts on the LIS. The constraints describe what actions the LIS MUST take when a URI associated with the context is accessed. This document describes three basic constraints that a Target can use in comination for the same context. Once set, these rules remain in force of the life of the context. 4.1. Limited Use URIs A limited use URI can only be accessed a fixed number of times to yield the location of the Target. Each time the URI is used to provide the location of the Target one usage is consumed. Once the limit is reached the URI no longer yields the location of the Target and the URI is deemed spent. By setting the usage limit to 1, the Target is able to create a one- time-URI permitting a Location Recipient to obtain the Target's location only once. Setting the usage limit to something higher than 1 creates functionality analogous to a metro-ticket, where a Location Recipient in possession of the URI can access the Target's location many more times, but not exceeding the imposed limit. Not setting a usage limit provides similar semantics to the URI in the base HELD specification, enabling a Location Recipient to continually obtain the Target's location until the URI expires due to age. When an HTTP URI is assigned to a context, the limit is the number of times that the URI can be accessed before the LIS returns an error. In the case of SIP it is the number of NOTIFY messages that are sent prior to the LIS returning an error. Where a context supports both SIP and HTTP URIs it is the combination of URI accesses and NOTIFY messages that constitutes the usage value, each time the Target's location is provided constitutes a usage. Winterbottom, et al. Expires April 8, 2008 [Page 6] Internet-Draft HELD Context October 2007 4.2. Snapshot URIs A snapshot URI points to the location of the Target at a specific point in time, and no matter how many times the URI is accessed it will always yield the same location. This is useful if, for example, the Target does not want to be tracked. In this specification the location snapshot to which a snapshot URIs points is captured when the context is created on the LIS. 4.3. Location Type URIs A location type URI controls the form of location that can be accessed; This may be geodetic, civic, or both. Winterbottom, et al. Expires April 8, 2008 [Page 7] Internet-Draft HELD Context October 2007 5. Protocol Details This specification introduces four new HELD messages, create context (), update context (), context response (), and context error (). A LIS that does not understand this specification is expected to return a HELD _unsupportedMessage_ error code in a HELD error message. The specification assumes that the LIS was discovered as part of the general HELD LIS discovery process. All messages are sent using the application/held+xml MIME type as defined in [I-D.ietf-geopriv-http-location-delivery]. 5.1. Create Context Message The Target creates a context on the LIS using a create context message. The basic create context message supports the constraints described in Section 4 and consist of three attributes and one element described below: o "uses": an optional attribute instructing the LIS on how many times a URI may yield the location of the Target. This is a positive integer, and has a default value of _unlimited_. The LIS SHOULD support the Target specifying up to at least 100 uses. o "snapshot": an optional attribute instructing the LIS to take a snapshot of the Target's location for use with the context. This a boolean value and has a default of _false_ meaning that a snapshot is not taken, and the Target's location is determined each time the URI is accessed. o "locationType": an optional attribute instructing the LIS on the form of location that URI MUST provide. This is an enumeration and may have a value of _geodetic_, _civic_, or _any_. If unspecified by the Target the LIS will use a value of _any_. If the Target specifies a location type that the LIS cannot provide, then the LIS MUST fail the context creation. o "lifeTime": is a mandatory element that defines the maximum period in seconds that the LIS should keep the context for. The LIS MAY create the context with a shorter life time than was requested, but the life time MUST NOT be longer than was requested. Winterbottom, et al. Expires April 8, 2008 [Page 8] Internet-Draft HELD Context October 2007 7200 Figure 1: createContext Example Figure 1 shows a create context message defining a context which: o may be accessed 10 times o will determine the location of the Target each time it is accessed o will return the location in either geodetic or civic form depending on the request tot he URI o will be valid for 2 hours from the time of context creation 5.2. Update Context Message A Target can change the life time of a context using an update context message. As stated in Section 4 the three attributes used in the context creation, "uses", "snapshot", and "locationType" cannot be changed once a context is created. Since the Target may have more than one context on the LIS, the Target needs to identify the context to be updated. It does this by including a context identifier that is provided to it by the LIS when the context is created. 3600 Figure 2: updateContext Life Time Change Example When a Target includes a life time element in an update context message, the LIS needs to calculate a new context expiry time. The LIS MUST do this by adding the new life time value to the current time on the LIS. This mechanism means the Target can terminate a context at any time. It does this by updating the context with a life time of 0, which results in the LIS setting the context expiry Winterbottom, et al. Expires April 8, 2008 [Page 9] Internet-Draft HELD Context October 2007 time to the present. The LIS MAY also terminate a context if the life time value is set to less than 10 seconds. 0 Figure 3: updateContext Termination Example 5.3. Context Response Message The LIS informs the Target about the outcome of context operations through the context response message. The LIS MUST always send a context response message to a Target in response to a create context or update context message when the outcome was successful. The context response message contains a "code" attribute indicating the performed operation, and the other attributes and elements indicating the state of the context. The "code" attribute is an enumerated type and has one of the following values: o _created_: The context was successfully created. o _destroyed_: The context was destroyed. o _updated_: The context was successfully updated. The following list details the other attributes are may be returned in a context response message. id: The identifier allocated to the context by the LIS. This identifier is unique in the scope of the LIS. The Target MUST keep this secret and MUST included it in all update requests. The LIS MUST return and "id" in all context response messages. uses: The number of times that the context will yield the Target's location. The LIS MAY report either the original value, or the number of remaining uses. The LIS MUST report this value for all responses pertaining to a known and valid context. This value MAY be ommitted when indicating that a context has been destroyed. Winterbottom, et al. Expires April 8, 2008 [Page 10] Internet-Draft HELD Context October 2007 snapshot: The value of the snapshot attribute in the context. The LIS MUST report this value for all responses pertaining to a known and valid context. This value MAY be ommitted when indicating that a context has been destroyed. locationType: The type of location information that can be acquired through URIs addressing the context. The LIS MUST report this value for all responses pertaining to a known and valid context. This value MAY be omitted when indicating that a context has been destroyed. expiry: The time at which the context will expire. After this time, all location URIs that reference this context no longer work. The LIS MUST report this value for all responses pertaining to a known context. This attribute MUST be provided even when a "code" value of _destroyed_ is included in the context repsonse message. In addition to the above attributes, the LIS also provides a set of URIs that can used to access the Target's location with the surety that the context constraints will be applied. A URI set is returned whenever a context is successfully created on the LIS, and this set remains unchanged for the lifetime of the context. A context response message sent in reply to the create context message in Figure 1 might look like Figure 4. https://lis.example.com:9768/357yc6s64ceyoiuy5ax3o4 sips:357yc6s64ceyoiuy5ax3o4@lis.example.com:9769 Figure 4: contextResponse Example Winterbottom, et al. Expires April 8, 2008 [Page 11] Internet-Draft HELD Context October 2007 5.4. Context Error Messages When the LIS unable to perform the requested context operation it need to inform the Target of this. It does this using a context error message. The context error message consists of a "errorCode" and an optional "message" attribute. The code indicates what went wrong, the message is human-readable text that may provide additional information on what occurred. The "errorCode" attribute is an enumerated type and has one of the following values: o _badMessage_: The LIS was unable to understand the content of the message. o _unknownContext_: The LIS was unable to find the context. o _failed_: The LIS was unable to perform the requested operation. A Target implementing this specification MUST accept a HELD error message as a valid response to a create context or update context message. Figure 5: contextError With Message Example 5.5. Location URI and Context Identifier Generation Rules A primary aim of this specification is to provide a Target a means to cancel a location URI so that it can no longer be used to provide its location. To achieve this, a location URI generated as part of a context creation needs to be unique with in the scope of the LIS, and identify only that context. If the Target destroys a context and subsequently creates a new one, URIs associated the new context MUST be different from those generated for the previous context. [I-D.ietf-geopriv-http-location-delivery] and [I-D.ietf-geopriv-lbyr-requirements] provide guideance on the creation and desired characteristcs of a location URI. The context identifier provided by the LIS to the Target in the context response message MUST be unique and MUST be different from the identifier provided in any location URI. This latter constraint Winterbottom, et al. Expires April 8, 2008 [Page 12] Internet-Draft HELD Context October 2007 ensures that possession of a location URI does not automatically provide access and control over the internals of the context. A context identifier is generated by a LIS to uniquely identify a context. It MUST NOT be feasible for a third-party to easily determine a context identifier by knowing the identity of the Target. This implies that internal correlation (using a hash-table or similar) is the only method that the LIS can use to associate a context id with a particular Target. Winterbottom, et al. Expires April 8, 2008 [Page 13] Internet-Draft HELD Context October 2007 6. XML Schema Winterbottom, et al. Expires April 8, 2008 [Page 14] Internet-Draft HELD Context October 2007 Winterbottom, et al. Expires April 8, 2008 [Page 15] Internet-Draft HELD Context October 2007 Figure 6: Context Management Schema Winterbottom, et al. Expires April 8, 2008 [Page 16] Internet-Draft HELD Context October 2007 7. Security Considerations There are several security concerns associated with the details in this specification. The first is to do with the nature of the sensitivity of any data passed from the Target to the LIS for inclusion in a context. The second is the ability of the LIS to contain the number of contexts that it will permit to exist for a given Target address. Finally, there is a threat of Targets performing DoS attacks on the LIS by trying to create large numbers of short-lived contexts that result in the LIS expending resources in message processing. HELD [I-D.ietf-geopriv-http-location-delivery] mandates the use of TLS for exchanges between a Target and the LIS. This is deemed adequate to provide confidentiality to any contextual data in transit. The LIS implementation and the operator of the LIS need to take sufficient steps to ensure that active contextual data on the LIS is not readily available to anyone other than the Target. The Target MUST NOT provide any information to the LIS that it does not want the LIS to know or be able to use in some capacity associated with determination or providing of the Target's location. It is quite conceivable that a LIS will be required to provide location to Targets residing behind a NAT; a DSL home router with 5 PCs attached is a good example this situation. In this case it is reasonable for each device to create its own context on the LIS, and for the LIS to treat each context individually even though the LIS cannot make any other distinction between the end hosts; that is, they share a common IP address/identity from the LIS perspective. Given the constraints that can be added to a context and the way that a Target might want to manage expiry separately, a Target may use multiple contexts as a way to isolate applications from each other. For instance, a Target can create a context for each application so that it can revoke access to its location information for each without affecting other applications' access. This environment, however, opens the LIS to a type of denial of service attack through an overload of contexts. It is RECOMMENDED that an implementer of this specification include mechanisms to restrict to the maximum number of contexts that can be created on the LIS by an individual Target. Using short-term location URIs in a carefully controlled manner may obviate the need for individual location authorization policies on the LIS. This leads to reduced LIS complexity and the amount of private information that the Target need share with the LIS. This specification provides the ability for a Target to cancel a location URI which extends the Target's ability to enforce its entitlement to Winterbottom, et al. Expires April 8, 2008 [Page 17] Internet-Draft HELD Context October 2007 privacy. Using the mechanisms described in this memo a target can create URIs with short validity periods; this restricts how long a third-party is able to obtain the location of the Target while still allowing the Target the convenience of using a location reference. The generation of context identifiers by the LIS is a critical component to supporting the functionality described in this memo. The LIS MUST follow the rules described in Section 5.5 for generating context identifiers. Winterbottom, et al. Expires April 8, 2008 [Page 18] Internet-Draft HELD Context October 2007 8. IANA Considerations This document registers the schema and associated namespace with IANA. 8.1. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:geopriv:held:context This section registers a new XML namespace, "urn:ietf:params:xml:ns:geopriv:held:context", as per the guidelines in [RFC3688]. URI: urn:ietf:params:xml:ns:geopriv:held:context Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), James Winterbottom (james.winterbottom@andrew.com). XML: BEGIN HELD Context Management Messages

Namespace for HELD Context Management Messages

urn:ietf:params:xml:ns:geopriv:held:context

[[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX with the RFC number for this specification.]]

See RFCXXXX.

END 8.2. XML Schema Registration This section registers an XML schema as per the guidelines in [RFC3688]. URI: urn:ietf:params:xml:schema:geopriv:held:context Winterbottom, et al. Expires April 8, 2008 [Page 19] Internet-Draft HELD Context October 2007 Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), James Winterbottom (james.winterbottom@andrew.com). Schema: The XML for this schema can be found as the entirety of Figure 6 of this document. Winterbottom, et al. Expires April 8, 2008 [Page 20] Internet-Draft HELD Context October 2007 9. Acknowledgements Thanks to Adam Muhlbauer and Neil Justusson for their comments on the pre-version of this draft. Winterbottom, et al. Expires April 8, 2008 [Page 21] Internet-Draft HELD Context October 2007 Appendix A. Context Extensions A context contains specific information about a Target and is stored on the LIS. As with other protocols it is necessary to consider extensibility. When defining context data extensions it is necessary to consider how they will be used; this includes not only how to provide the information from the Target to the LIS, but also acceptance and error indications from the LIS back to the Target. For example, a context may be created with several extensions included, how does the LIS indicate that extensions 1 and 3 were successful but that extension 2 had a problem in its formatting? Guidelines for designing context extensions that provide functionality are described below. Two basic types of context data extension are envisioned. The first consist of data provided by the Target to be consumed by the LIS; for example information pertaining to PIDF-LO construction, usage-rules, and authorization policies. The second type of data consists of a two way exchange between the Target and the LIS; for example exchanging location determination capabilities. Extensibility to the context scheme is to allow additional elements to be added to the context easily. The general idea is shown in Figure 8. 7200 7200 . . . Figure 8: Create Context with Extensions When defining a context data extension it is necessary to ensure that the LIS can provide an adequate response to the Target indicating acceptance or rejection of the data provided. This may be an explicit OK or FAIL message within the extension namespace, it may be an attribute associated with part of a larger data exchange, or it may result in the LIS failing to create the context at all. Regardless, it is mandatory for a context data extension to provide Winterbottom, et al. Expires April 8, 2008 [Page 22] Internet-Draft HELD Context October 2007 an indication of success or failure. https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o sips:357yc6s64ceyoiuy5ax3o@ls.example.com:9769 data guff in here for extension Figure 9: LIS response to createContext When defining information to be included in a context data extension consideration should be given to how that data can be removed from the context. In some cases it may be necessary to void the context on the LIS in order to remove information, but this SHOULD be treated as a last resort and not used as the primary mechanism for removing data from the context. Winterbottom, et al. Expires April 8, 2008 [Page 23] Internet-Draft HELD Context October 2007 Appendix B. HELD Compliance to IETF Location Configuration Protocol Location Reference Requirements This section describes how HELD and this specification comply to the LCP location reference requirements stipulated in [I-D.ietf-geopriv-lbyr-requirements]. High-level requirements for a location configuration protocol. C1. "Location URI support - LCP: The configuration protocol MUST support a location reference in URI form." COMPLY. HELD only provides location references in URI form. C2. "Location URI expiration: The LCP MUST support the ability to specify to the server, the length of time that a location URI will be valid." COMPLY. HELD with the context management extensions described in this document provide the Target the ability to specify expiry times for location URIs. C3. "Location URI cancellation: The LCP MUST support the ability to request a cancellation of a specific location URI." COMPLY. HELD with the context management extensions described in this document provide the Target the ability to void location URIs when required. C4. "Random Generated: The location URI MUST be hard to guess, i.e., it MUST contain a cryptographically random component." COMPLY. The HELD specification and this document provide specific guidance on the security surrounding location URI generation. C5. "Identity Protection - LCP: The location URI MUST NOT contain any information that identifies the user, device or address of record within the URI form." Winterbottom, et al. Expires April 8, 2008 [Page 24] Internet-Draft HELD Context October 2007 COMPLY. The HELD specification and this document provide specific guidance on the anonymity of the Target with regards to the generation of location URIs. C6. "Reuse flag default: The LCP MUST support the default condition of a requested location URI being repeatedly reused." COMPLY. HELD with the context management extensions described in this document provide the Target the ability to specify how many times a location URI may yield the location of Target. C7. "One-time-use: The LCP MUST support the ability for the client to request a 'one-time-use' location URI (e.g., via a reuse flag setting)." COMPLY. HELD with the context management extensions described in this document provide the Target the ability to specify how many times a location URI may yield the location of Target. This value may be set to 1 to create a one-time URI. Winterbottom, et al. Expires April 8, 2008 [Page 25] Internet-Draft HELD Context October 2007 10. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [I-D.ietf-geopriv-http-location-delivery] Barnes, M., Winterbottom, J., Thomson, M., and B. Stark, "HTTP Enabled Location Delivery (HELD)", draft-ietf-geopriv-http-location-delivery-02 (work in progress), September 2007. [I-D.ietf-geopriv-l7-lcp-ps] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and Requirements", draft-ietf-geopriv-l7-lcp-ps-05 (work in progress), September 2007. [I-D.ietf-geopriv-lbyr-requirements] Marshall, R., "Requirements for a Location-by-Reference Mechanism", draft-ietf-geopriv-lbyr-requirements-00 (work in progress), September 2007. Winterbottom, et al. Expires April 8, 2008 [Page 26] Internet-Draft HELD Context October 2007 Authors' Addresses James Winterbottom Andrew Corporation PO Box U40 University of Wollongong, NSW 2500 AU Phone: +61 242 212938 Email: james.winterbottom@andrew.com URI: http://www.andrew.com/products/geometrix Hannes Tschofenig Nokia Siemens Networks Otto-Hahn-Ring 6 Munich, Bavaria 81739 Germany Phone: +49 89 636 40390 Email: Hannes.Tschofenig@nsn.com URI: http://www.tschofenig.com Martin Thomson Andrew Corporation PO Box U40 University of Wollongong, NSW 2500 AU Phone: +61 242 212915 Email: martin.thomson@andrew.com URI: http://www.andrew.com/products/geometrix Winterbottom, et al. Expires April 8, 2008 [Page 27] Internet-Draft HELD Context October 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Intellectual Property 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. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Winterbottom, et al. Expires April 8, 2008 [Page 28]