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2 Network Working Group A. Johnston
3 Internet-Draft Avaya
4 Intended status: Standards Track J. Rafferty
5 Expires: October 11, 2013 Dialogic
6 April 9, 2013
8 A Mechanism for Transporting User to User Call Control Information in
9 SIP
10 draft-ietf-cuss-sip-uui-10
12 Abstract
14 There is a class of applications which benefit from using SIP to
15 exchange User to User Information (UUI) data during session
16 establishment. This information, known as call control UUI data, is
17 a small piece of data inserted by an application initiating the
18 session, and utilized by an application accepting the session. The
19 rules which apply for a specific application are defined by a UUI
20 package. This UUI data is opaque to SIP and its function is
21 unrelated to any basic SIP function. This document defines a new SIP
22 header field, User-to-User, to transport UUI data, along with an
23 extension mechanism.
25 Status of this Memo
27 This Internet-Draft is submitted to IETF in full conformance with the
28 provisions of BCP 78 and BCP 79.
30 Internet-Drafts are working documents of the Internet Engineering
31 Task Force (IETF). Note that other groups may also distribute
32 working documents as Internet-Drafts. The list of current Internet-
33 Drafts is at http://datatracker.ietf.org/drafts/current/.
35 Internet-Drafts are draft documents valid for a maximum of six months
36 and may be updated, replaced, or obsoleted by other documents at any
37 time. It is inappropriate to use Internet-Drafts as reference
38 material or to cite them other than as "work in progress."
40 This Internet-Draft will expire on October 11, 2013.
42 Copyright Notice
44 Copyright (c) 2013 IETF Trust and the persons identified as the
45 document authors. All rights reserved.
47 This document is subject to BCP 78 and the IETF Trust's Legal
48 Provisions Relating to IETF Documents
49 (http://trustee.ietf.org/license-info) in effect on the date of
50 publication of this document. Please review these documents
51 carefully, as they describe your rights and restrictions with respect
52 to this document. Code Components extracted from this document must
53 include Simplified BSD License text as described in Section 4.e of
54 the Trust Legal Provisions and are provided without warranty as
55 described in the Simplified BSD License.
57 Table of Contents
59 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
61 3. Requirements Discussion . . . . . . . . . . . . . . . . . . . 3
62 4. Normative Definition . . . . . . . . . . . . . . . . . . . . . 5
63 4.1. Syntax for UUI Header Field . . . . . . . . . . . . . . . 6
64 4.2. Hex Encoding Definition . . . . . . . . . . . . . . . . . 7
65 4.3. Source Identity of UUI data . . . . . . . . . . . . . . . 7
66 5. Guidelines for UUI Packages . . . . . . . . . . . . . . . . . 8
67 5.1. Extensibility . . . . . . . . . . . . . . . . . . . . . . 10
68 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
69 6.1. Registration of User-to-User Header Field . . . . . . . . 11
70 6.2. Registration of User-to-User Header Field Parameters . . . 11
71 6.3. Registration of UUI Packages . . . . . . . . . . . . . . . 11
72 6.4. Registration of UUI Content Parameters . . . . . . . . . . 12
73 6.5. Registration of UUI Encoding Parameters . . . . . . . . . 12
74 6.6. Registration of SIP Option Tag . . . . . . . . . . . . . . 12
75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
76 8. Appendix - Other Possible Mechanisms . . . . . . . . . . . . . 13
77 8.1. Why INFO is Not Used . . . . . . . . . . . . . . . . . . . 13
78 8.2. Why Other Protocol Encapsulation UUI Mechanisms are
79 Not Used . . . . . . . . . . . . . . . . . . . . . . . . . 14
80 8.3. MIME body Approach . . . . . . . . . . . . . . . . . . . . 14
81 8.4. URI Parameter . . . . . . . . . . . . . . . . . . . . . . 15
82 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
83 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
84 10.1. Informative References . . . . . . . . . . . . . . . . . . 16
85 10.2. Normative References . . . . . . . . . . . . . . . . . . . 17
86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
88 1. Overview
90 This document describes the transport of User to User Information
91 (UUI) data using SIP [RFC3261]. A mechanism is defined for the
92 transport of general application UUI data and for the transport of
93 call control related ITU-T Q.931 User to User Information Element (UU
94 IE) [Q931] and ITU-T Q.763 User to User Information Parameter [Q763]
95 data in SIP. UUI data is widely used in the PSTN today for contact
96 centers and call centers. There is also a trend for the related
97 applications to transition from ISDN to SIP. The UUI extension for
98 SIP may also be used for native SIP UAs implementing similar services
99 and to interwork with ISDN services. Note that in most cases, there
100 is an a priori understanding between the UAs in regard to what to do
101 with received UUI data.
103 This mechanism was designed to meet the use cases, requirements, and
104 call flows for SIP call control UUI detailed in [RFC6567]. All
105 references to requirement numbers (REQ-N) and figure numbers refer to
106 this document.
108 The mechanism is a new SIP header field, along with a new SIP option
109 tag. The header field carries the UUI data, along with parameters
110 indicating the encoding of the UUI data, the UUI package, and
111 optionally the content of the UUI data. The package definition
112 contains details about how a particular application can utilize the
113 UUI mechanism. The header field can be included (sometimes called
114 "escaped") into URIs supporting referral and redirection scenarios.
115 In these scenarios, History-Info is used to indicate the inserter of
116 the UUI data. The SIP option tag can be used to indicate support for
117 the header field. Support for the UUI header field indicates that a
118 UA is able to extract the information in the UUI data and pass it up
119 the protocol stack. Individual packages using the UUI mechanism can
120 utilize SIP media feature tags to indicate that a UA supports a
121 particular UUI package. Guidelines for defining UUI packages are
122 provided.
124 2. Terminology
126 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
127 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
128 "OPTIONAL" in this document are to be interpreted as described in BCP
129 14, RFC 2119 [RFC2119].
131 3. Requirements Discussion
133 This section describes how the User-to-User header field meets the
134 requirements in [RFC6567]. The header field can be included in
135 INVITE requests and responses and BYE requests and responses, meeting
136 REQ-1 and REQ-2.
138 For redirection and referral use cases and REQ-3, the header field
139 shall be included (escaped) into the Contact or Refer-To URI.
140 Currently, UAs that support attended transfer support the ability to
141 include a Replaces header field [RFC3891] into a Refer-To URI, and
142 when acting upon this URI add the Replaces header field to the
143 triggered INVITE. This logic and behavior is identical for the UUI
144 header field. The UA processing the REFER or the 3xx to the INVITE
145 will need to support the UUI mechanism, as UAs in general do not
146 process unknown included header fields.
148 Since SIP proxy forwarding and retargeting does not affect header
149 fields, the header field meets REQ-4.
151 The UUI header field will carry the UUI data and not a pointer to the
152 data, so REQ-5 is met.
154 Since the basic design of the UUI header field is similar to the ISDN
155 UUI service, interworking with PSTN protocols is straightforward and
156 is documented in a separate specification
157 [I-D.ietf-cuss-sip-uui-isdn], meeting REQ-6.
159 Requirements REQ-7, REQ-8, and REQ-10 relate to discovery of the
160 mechanism and supported packages, and hence applications. REQ-7
161 relates to support of the UUI header field, while REQ-8 relates to
162 routing based on support of the UUI header field. REQ-7 is met by
163 defining a new SIP option tag 'uui'. The use of a Require:uui in a
164 request, or Supported:uui in an OPTIONS response could be used to
165 require or discover support of the mechanism. The presence of a
166 Supported:uui or Require:uui header field can be used by proxies to
167 route to an appropriate UA, meeting REQ-8. However, note that only
168 UAs are expected to understand the UUI data - proxies and other
169 intermediaries do not. REQ-10 is met by utilizing SIP feature tags
170 [RFC3840]. For example, the feature tag 'sip.uui-isdn' could be used
171 to indicate support of the ISDN UUI package, or 'sip.uui-pk1' could
172 be used to indicate support for a particular package, pk1.
174 Proxies commonly apply policy to the presence of certain SIP header
175 fields in requests by either passing them or removing them from
176 requests. REQ-9 is met by allowing proxies and other intermediaries
177 to remove UUI header fields in a request or response based on policy.
179 Carrying UUI data elements of at least 129 octets is trivial in the
180 UUI header field, meeting REQ-11. Note that very large UUI data
181 elements should be avoided, as SIP header fields have traditionally
182 not been large.
184 To meet REQ-12 for the redirection and referral use cases, History-
185 Info [I-D.ietf-sipcore-rfc4244bis] can be used. In these retargeting
186 cases, the changed Request-URI will be recorded in the History-Info
187 header field along with the identity of the element that performed
188 the retargeting.
190 The requirement for integrity protection in REQ-13 could be met by
191 the use of an S/MIME signature over a subset of header fields, as
192 defined in Section 23.4 of RFC 3261 "SIP Header Privacy and Integrity
193 using S/MIME: Tunneling SIP". The requirement of REQ-14 for end-to-
194 end privacy could be met using S/MIME or using encryption at the
195 application layer. Note that the use of S/MIME to secure the UUI
196 data will result in an additional body being added to the request.
197 Hop-wise Transport Layer Security (TLS) [RFC5246] allows the header
198 field to meet REQ-15 for hop-by-hop security.
200 4. Normative Definition
202 This document defines a new SIP header field "User-to-User" to
203 transport call control UUI data to meet the requirements in
204 [RFC6567].
206 To help tag and identify the UUI data used with this header field,
207 "purpose", "content", and "encoding" header field parameters are
208 defined. The "purpose" header field parameter identifies the package
209 which defines the generation and usage of the UUI data for a
210 particular application. For the case of interworking with the ISDN
211 UUI Service, the ISDN UUI Service interworking package is used. If
212 the "purpose" header field parameter is not present, interworking
213 with the ISDN UUI Service MUST be assumed. The "content" header
214 field parameter identifies the actual content of the UUI data. If
215 not present, the content MUST be assumed to be the default defined
216 for the package. Newly defined UUI packages MUST define or reference
217 at least a default "content" value. The "encoding" header field
218 parameter indicates the method of encoding the information in the UUI
219 data associated with a particular "content" value. This
220 specification only defines "encoding=hex". If the "encoding" header
221 field parameter is not present, the encoding MUST be assumed to be
222 the default defined for the package.
224 UUI data is considered an opaque series of octets. This mechanism
225 SHOULD NOT be used to convey a URL or URI; the Call-Info header field
226 [RFC3261] is used for this purpose.
228 4.1. Syntax for UUI Header Field
230 The User-to-User (UUI) header field can be present in INVITE requests
231 and responses and in BYE requests and responses. Note that when the
232 UUI header is used in responses, it can only be utilized in end-to-
233 end responses, e.g. 1xx (excluding 100), 2xx, and 3xx responses.
235 The following syntax specification uses the augmented Backus-Naur
236 Form (BNF) as described in RFC 5234 and extends RFC 3261 (where token
237 and quoted-string are defined).
239 UUI = "User-to-User" HCOLON uui-value *(COMMA uui-value)
240 uui-value = uui-data *(SEMI uui-param)
241 uui-data = token / quoted-string
242 uui-param = pkg-param / cont-param / enc-param / generic-param
243 pkg-param = "purpose" EQUAL pkg-param-value
244 pkg-param-value = token
245 cont-param = "content" EQUAL cont-param-value
246 cont-param-value = token
247 enc-param = "content" EQUAL enc-param-value
248 enc-param-value = token / "hex"
250 The rules for how many User-to-User header fields of each package may
251 be present in a request or a response are defined for each package.
252 Multiple User-to-User header fields MAY be present in a request or
253 response. Consistent with the rules of SIP syntax, the syntax
254 defined in this document allows any combination of individual User-
255 to-User header fields or User-to-User header fields with multiple
256 comma separated UUI data elements. Any size limitations on the UUI
257 data for a particular purpose must be defined by the related UUI
258 package.
260 UAs SHOULD ignore UUI data from packages or encoding that they do not
261 understand.
263 If an element supports this specification, it SHOULD include any UUI
264 data included in a redirection URI (if the UUI data and encoding is
265 understood). Note that redirection can occur multiple times to a
266 request.
268 Here is an example of an included User-to-User header field from the
269 redirection response F2 of Figure 2:
271
272 Contact:
275
277 The resulting INVITE F4 would contain:
279 User-to-User: 56a390f3d2b7310023a2;encoding=hex;purpose=foo;content=bar
281 4.2. Hex Encoding Definition
283 This specification defines hex encoding of UUI data. The value of
284 "hex" for the "encoding" header field parameter is normatively
285 defined in this section. It is used to encode binary UUI data with a
286 length that terminates at an octet boundary. Each octet of binary
287 data to be represented in the hex encoding MUST be mapped to two
288 hexadecimal digits (represented by ASCII characters 0-9, A-F and
289 a-f), each representing four bits within the octet. The four bits
290 appearing first in the binary UUI data MUST be mapped to the first
291 hexadecimal digit and the four subsequent bits in the binary UUI data
292 MUST be mapped to the second hexadecimal digit. When mapping 4 bits
293 to a hexadecimal digit, the bit appearing first in the binary UUI
294 data shall be most significant. Thus, Hex encoded UUI data must have
295 an even number of hexadecimal digits, and MUST be considered invalid
296 if it has an odd number. Hex encoding is normally done as a token,
297 although quoted-string is permitted, in which case the quotes MUST be
298 ignored.
300 4.3. Source Identity of UUI data
302 It is important for the recipient of UUI data to know the identity of
303 the UA that inserted the UUI data. In a request without a History-
304 Info [I-D.ietf-sipcore-rfc4244bis] header field, the identity of the
305 entity which inserted the UUI data will be assumed to be the source
306 of the SIP message. For a SIP request, typically this is the UA
307 identified by the URI in the From header field or a P-Asserted-
308 Identity [RFC3325] header field. In a request with a History-Info
309 header field, the recipient needs to parse the Targeted-to-URIs
310 present (hi-targeted-to-uri) to see if any included User-to-User
311 header fields are present. If an included User-to-User header field
312 is present and matches the UUI data in the request, this indicates
313 that redirection has taken place, resulting in the inclusion of UUI
314 data in the request. The inserter of the UUI data will be the UA
315 identified by the Targeted-to-URI of the History-Info element prior
316 to the element with the included UUI data. In a response, the
317 inserter of the UUI data will be the identity of the UA that
318 generated the response. Typically, this is the UA identified in the
319 To header field of the response. Note that any updates to this
320 identity by use of the SIP Connected Identity extension [RFC4916] or
321 others will update this information.
323 For an example of History-Info and redirection, consider Figure 2
324 from [RFC6567] where the Originating UA is Carol, the Redirector Bob,
325 and the Terminating UA Alice. The INVITE F4 containing UUI data
326 could be:
328 INVITE sips:alice@example.com SIP/2.0
329 Via: SIP/2.0/TLS lab.example.com:5061
330 ;branch=z9hG4bKnashds9
331 To: Bob
332 From: Carol ;tag=323sf33k2
333 Call-ID: dfaosidfoiwe83ifkdf
334 Max-Forwards: 70
335 Contact:
336 Supported: histinfo
337 User-to-User: 342342ef34;encoding=hex
338 History-Info: ;index=1
339
340 History-Info: ;index=1.1;rc=1
342
344 Without the redirection captured in the History-Info, Alice would
345 conclude the UUI data was inserted by Carol. However, the History-
346 Info containing UUI data (index=1.1) indicates that the inserter was
347 Bob (index=1).
349 Note that the tag convention from SIP Torture Test
350 Messages [RFC4475] is used to show that there are no line breaks in
351 the actual message syntax.
353 To enable maintaining a record of the inserter identity of UUI data,
354 UAs supporting this mechanism SHOULD support History-Info
355 [I-D.ietf-sipcore-rfc4244bis] and include Supported: histinfo in all
356 requests and responses.
358 Border elements such as proxies or Back-to-Back User Agents (B2BUAs)
359 which anonymize a SIP URI in a History-Info header field SHOULD leave
360 the corresponding User-to-User parameter, if present, and the
361 corresponding User-to-User header field unchanged. Border elements
362 removing a History-Info header containing a User-to-User parameter
363 SHOULD NOT drop the corresponding User-to-User header. Otherwise,
364 the UA consuming the UUI data may not be able at SIP level to
365 identify the source of the UUI data.
367 5. Guidelines for UUI Packages
369 UUI packages defined using this SIP UUI mechanism MUST follow the
370 "RFC Required" guideline as defined in [RFC5226] and publish a
371 standards track RFC which describes the usage. Note that this
372 mechanism is not suitable for the transport of arbitrary data between
373 UAs. The following guidelines are provided to help determine if this
374 mechanism is appropriate or some other SIP mechanism should be used.
375 The SIP UUI mechanism is applicable when all of the following
376 conditions be met:
378 1. The information is generated and consumed by an application
379 during session setup using SIP, but the application is not
380 necessarily SIP aware.
382 2. The behavior of SIP entities that support it is not
383 significantly changed (as discussed in Section 4 of [RFC5727]).
385 3. User Agents (UAs) are the generators and consumers of the UUI
386 data. Proxies and other intermediaries may route based on the
387 presence of a User-to-User header field or a particular package
388 tag but do not otherwise consume or generate the UUI data.
390 4. There are no overriding privacy issues associated with the
391 information being transported (e.g., geolocation or emergency-
392 related information are examples of inappropriate UUI data).
394 5. The UUI data is not being utilized for user-to-user Remote
395 Procedure Call (RPC) calls.
397 UUI packages define the semantics for a particular application usage
398 of UUI data. The content defines the syntax of the UUI data, while
399 the encoding defines the encoding of the UUI data for the content.
400 Each content is defined as a stream of octets, which allows multiple
401 encodings of that content. For example, packages may define:
403 1. The SIP methods and responses in which the UUI data may be
404 present.
406 2. The maximum number of UUI data elements that may be inserted
407 into a request or response. (The default is one per encoding.)
408 Note that a UA may still receive a request with more than this
409 maximum number due to redirection. The package must define how to
410 handle this situation.
412 3. The default values for content and encoding if they are not
413 present. If the same UUI data may be inserted multiple times with
414 different encodings, the packages must state this. A package may
415 support and define multiple contents and their associated
416 encodings, and reuse contents defined by other packages.
418 4. Any size limitations on the UUI data. Size should be
419 specified in terms of the octet stream output of the content,
420 since the size of the resulting uui-data element will vary
421 depending on the encoding scheme.
423 A package MUST define a "purpose" header field value to identify the
424 package in the coding. A package MUST describe the new application
425 which is utilizing the UUI data and provide some use case examples.
426 The default "content" value MUST be defined or referenced in another
427 document for the package. Additional allowed contents MAY also be
428 defined or referenced. Any restrictions on the size of the UUI data
429 MUST be described. In addition, a package MAY define a Media Feature
430 tag per RFC 3840 [RFC3840] to indicate support for this UUI package.
431 For example, the media feature tag sip.uui-pk1 could be defined to
432 indicate support for a UUI package named pk1. The definition of a
433 new SIP option tag solely to identify support for a UUI package is
434 NOT RECOMMENDED unless there are additional SIP behaviors needed to
435 implement this feature.
437 For an example UUI package definition, see
438 [I-D.ietf-cuss-sip-uui-isdn].
440 5.1. Extensibility
442 New "content" values MUST describe the semantics of the UUI data,
443 valid encodings, and give some example use cases. A previously
444 defined UUI content value can be used in a new package. In this
445 case, the semantics and usage of the content by the new package is
446 defined within the new package. New UUI content types cannot be
447 added to existing packages - instead, a new package would need to be
448 defined. New content values defined are added to the IANA registry
449 with a standards track RFC, which needs to discuss the issues in this
450 section. If no new encoding value is defined for a content, the
451 encoding defaults to "hex" as defined in this document. In this
452 case, the "hex" value will be explicitly stated via the encoding
453 parameter as the encoding for the content.
455 New "encoding" values associated with a new content MUST reference a
456 specific encoding scheme (such as "hex" which is defined in this
457 specification) or define the new encoding scheme. A previously
458 defined UUI encoding value can be used with a newly defined content.
459 In this case, the usage of the encoding is defined by the content
460 definition. New UUI encodings cannot be added to existing contents -
461 instead, a new content would need to be defined. Newly defined
462 encoding values are added to the IANA registry with a standards track
463 RFC, which needs to discuss the issues in this section.
465 6. IANA Considerations
467 6.1. Registration of User-to-User Header Field
469 This document defines a new SIP header field named "User-to-User".
471 The following row shall be added to the "Header Fields" section of
472 the SIP parameter registry:
474 +------------------+--------------+-----------+
475 | Header Name | Compact Form | Reference |
476 +------------------+--------------+-----------+
477 | User-to-User | | [RFCXXXX] |
478 +------------------+--------------+-----------+
480 Editor's Note: [RFCXXXX] should be replaced with the designation of
481 this document.
483 6.2. Registration of User-to-User Header Field Parameters
485 This document defines the parameters for the header field defined in
486 the preceding section. The header field "User-to-User" can contain
487 the parameters "encoding", "content", and "purpose".
489 The following rows shall be added to the "Header Field Parameters and
490 Parameter Values" section of the SIP parameter registry:
492 +------------------+----------------+-------------------+-----------+
493 | Header Field | Parameter Name | Predefined Values | Reference |
494 +------------------+----------------+-------------------+-----------+
495 | User-to-User | encoding | hex | [RFCXXXX] |
496 +------------------+----------------+-------------------+-----------+
497 | User-to-User | content | | [RFCXXXX] |
498 +------------------+----------------+-------------------+-----------+
499 | User-to-User | purpose | | [RFCXXXX] |
500 +------------------+----------------+-------------------+-----------+
502 Editor's Note: [RFCXXXX] should be replaced with the designation of
503 this document.
505 6.3. Registration of UUI Packages
507 This specification establishes the uui-packages sub-registry under
508 http://www.iana.org/assignments/sip-parameters. New uui-packages
509 MUST follow the "Specification Required" guideline as defined in
510 [RFC5226].
512 The descriptive text for the table of uui-content is:
514 UUI Packages provides information about the usage of the UUI data in
515 a User-to-User header field [RFCXXXX].
517 +------------+------------------------------------------+-----------+
518 | Package | Description | Reference |
519 +------------+------------------------------------------+-----------+
521 6.4. Registration of UUI Content Parameters
523 This specification establishes the uui-content sub-registry under
524 http://www.iana.org/assignments/sip-parameters. New uui-content
525 values MUST follow the "Specification Required" guideline as defined
526 in [RFC5226].
528 The descriptive text for the table of uui-content is:
530 UUI Content provides information about the content of the UUI data in
531 a User-to-User header field [RFCXXXX].
533 +------------+------------------------------------------+-----------+
534 | Content | Description | Reference |
535 +------------+------------------------------------------+-----------+
537 6.5. Registration of UUI Encoding Parameters
539 This specification establishes the uui-encoding sub-registry under
540 http://www.iana.org/assignments/sip-parameters and initiates its
541 population with the table below. Additional uui-encoding values MUST
542 follow the "Specification Required" guideline as defined in
543 [RFC5226].
545 The descriptive text for the table of uui-encoding is:
547 UUI Encoding provides information about the encoding of the UUI data
548 in a User-to-User header field [RFCXXXX].
550 +-----------+-------------------------------------------+-----------+
551 | Encoding | Description | Reference |
552 +-----------+-------------------------------------------+-----------+
553 | hex | The UUI data is encoded using hexadecimal | [RFCXXXX] |
554 +-----------+-------------------------------------------+-----------+
556 6.6. Registration of SIP Option Tag
558 This specification registers a new SIP option tag, as per the
559 guidelines in Section 27.1 of [RFC3261].
561 This document defines the SIP option tag "uui".
563 The following row has been added to the "Option Tags" section of the
564 SIP Parameter Registry:
566 +------------+------------------------------------------+-----------+
567 | Name | Description | Reference |
568 +------------+------------------------------------------+-----------+
569 | uui | This option tag is used to indicate that | [RFCXXXX] |
570 | | a UA supports and understands the | |
571 | | User-to-User header field. | |
572 +------------+------------------------------------------+-----------+
574 Editor's Note: [RFCXXXX] should be replaced with the designation of
575 this document.
577 7. Security Considerations
579 User to user information can potentially carry sensitive information
580 that might require privacy or integrity protection. Standard
581 deployed SIP security mechanisms such as TLS transport, offer these
582 properties on a hop-by-hop basis. To preserve multi-hop or end-to-
583 end confidentiality and integrity of UUI data, approaches using
584 S/MIME or IPSec can be used, as discussed in the draft. However, the
585 lack of deployment of these mechanisms means that applications can
586 not in general rely on them. As such, applications are encouraged to
587 utilize their own security mechanisms.
589 If the UUI data was included by the UA originator of the SIP request
590 or response, normal SIP mechanisms can be used to determine the
591 identity of the inserter of the UUI data. If the UUI data was
592 included by a UA that was not the originator of the request, History-
593 Info can be used to determine the identity of the inserter of the UUI
594 data. UAs can apply policy based on the origin of the UUI data using
595 this information.
597 8. Appendix - Other Possible Mechanisms
599 Two other possible mechanisms for transporting UUI data will be
600 described: MIME body and URI parameter transport.
602 8.1. Why INFO is Not Used
604 Since the INFO method [RFC6086], was developed for ISUP interworking
605 of user-to-user information, it might seem to be the logical choice
606 here. For non-call control user-to-user information, INFO can be
607 utilized for end to end transport. However, for transport of call
608 control user-to-user information, INFO can not be used. As the call
609 flows in [RFC6567] show, the information is related to an attempt to
610 establish a session and must be passed with the session setup request
611 (INVITE), responses to that INVITE, or session termination requests.
612 As a result, it is not possible to use INFO in these cases.
614 8.2. Why Other Protocol Encapsulation UUI Mechanisms are Not Used
616 Other protocols have the ability to transport UUI data. For example,
617 consider the ITU-T Q.931 User to User Information Element (UU IE)
618 [Q931] and the ITU-T Q.763 User to User Information Parameter [Q763].
619 In addition, NSS (Narrowband Signaling System) [Q1980] is also able
620 to transport UUI data. Should one of these protocols be in use, and
621 present in both User Agents, then utilizing these other protocols to
622 transport UUI data might be a logical solution. Essentially, this is
623 just adding an additional layer in the protocol stack. In these
624 cases, SIP is not transporting the UUI data; it is encapsulating
625 another protocol, and that protocol is transporting the UUI data.
626 Once a mechanism to transport that other protocol using SIP exists,
627 the UUI data transport function is essentially obtained without any
628 additional effort or work.
630 However, the authors believe that SIP needs to have its own native
631 UUI data transport mechanism. It is not reasonable for a SIP UA to
632 have to implement another entire protocol (either ISDN or NSS, for
633 example) just to get the very simple UUI data transport service. Of
634 course, this work does not preclude anyone from using other protocols
635 with SIP to transport UUI data.
637 8.3. MIME body Approach
639 One method of transport is to use a MIME body. This is in keeping
640 with the SIP-T architecture [RFC3372] in which MIME bodies are used
641 to transport ISUP information. Since the INVITE will normally have
642 an SDP message body, the resulting INVITE with SDP and UUI data will
643 be multipart MIME. This is not ideal as many SIP UAs do not support
644 multipart MIME INVITEs.
646 A bigger problem is the insertion of a UUI message body by a redirect
647 server or in a REFER. The body would need to be encoded in the
648 Contact URI of the 3xx response or the Refer-To URI of a REFER.
649 Currently, the authors are not aware of any UAs that support this
650 capability today for any body type. As such, the complete set of
651 semantics for this operation would need to be determined and defined.
652 Some issues will need to be resolved, such as, do all the Content-*
653 header fields have to be included as well? And, what if the included
654 Content-Length does not agree with the included body?
655 Since proxies cannot remove a body from a request or response, it is
656 not clear how this mechanism could meet REQ-9.
658 The requirement for integrity protection could be met by the use of
659 an S/MIME signature over the body, as defined in Section 23.3 of RFC
660 3261 "Securing MIME bodies". Alternatively, this could be achieved
661 using RFC 4474 [RFC4474]. The requirement for end-to-end privacy
662 could be met using S/MIME encryption or using encryption at the
663 application layer. However, note that neither S/MIME or RFC 4474
664 enjoys deployment in SIP today.
666 An example:
668
669 Contact:
671
673 As such, the MIME body approach meets REQ-1, REQ-2, REQ-4, REQ-5,
674 REQ-7, REQ-11, REQ-13, and REQ-14. Meeting REQ-12 seems possible,
675 although the authors do not have a specific mechanism to propose.
676 Meeting REQ-3 is problematic, but not impossible for this mechanism.
677 However, this mechanism does not seem to be able to meet REQ-9.
679 8.4. URI Parameter
681 Another proposed approach is to encode the UUI data as a URI
682 parameter. This UUI parameter could be included in a Request-URI or
683 in the Contact URI or Refer-To URI. It is not clear how it could be
684 transported in a responses which does not have a Request-URI, or in
685 BYE requests or responses.
687
688 Contact:
690
692 An INVITE sent to this Contact URI would contain UUI data in the
693 Request-URI of the INVITE. The URI parameter has a drawback in that
694 a URI parameter carried in a Request-URI will not survive retargeting
695 by a proxy as shown in Figure 2 of [RFC6567]. That is, if the URI is
696 included with an Address of Record instead of a Contact URI, the URI
697 parameter in the Reqeuest-URI will not be copied over to the Contact
698 URI, resulting in the loss of the information. Note that if this
699 same URI was present in a Refer-To header field, the same loss of
700 information would occur.
702 The URI parameter approach would meet REQ-3, REQ-5, REQ-7, REQ-9, and
703 REQ-11. It is possible the approach could meet REQ-12 and REQ-13.
704 The mechanism does not appear to meet REQ-1, REQ-2, REQ-4, and
705 REQ-14.
707 9. Acknowledgements
709 Joanne McMillen was a major contributor and co-author of earlier
710 versions of this document. Thanks to Paul Kyzivat for his
711 contribution of hex encoding rules. Thanks to Spencer Dawkins, Keith
712 Drage, Vijay Gurbani, and Laura Liess for their review of the
713 document. The authors wish to thank Roland Jesske, Celine Serrut-
714 Valette, Francois Audet, Denis Alexeitsev, Paul Kyzivat, Cullen
715 Jennings, and Mahalingam Mani for their comments.
717 10. References
719 10.1. Informative References
721 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part
722 formats and codes",
723 http://www.itu.int/rec/T-REC-Q.931-199805-I/en .
725 [Q931] "ITU-T Q.931 User to User Information Element (UU IE)",
726 http://www.itu.int/rec/T-REC-Q.931-199805-I/en .
728 [RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol
729 for Telephones (SIP-T): Context and Architectures",
730 BCP 63, RFC 3372, September 2002.
732 [RFC6086] Holmberg, C., Burger, E., and H. Kaplan, "Session
733 Initiation Protocol (SIP) INFO Method and Package
734 Framework", RFC 6086, January 2011.
736 [RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J.,
737 and H. Schulzrinne, "Session Initiation Protocol (SIP)
738 Torture Test Messages", RFC 4475, May 2006.
740 [RFC5727] Peterson, J., Jennings, C., and R. Sparks, "Change Process
741 for the Session Initiation Protocol (SIP) and the Real-
742 time Applications and Infrastructure Area", BCP 67,
743 RFC 5727, March 2010.
745 [I-D.ietf-cuss-sip-uui-isdn]
746 Drage, K. and A. Johnston, "Interworking ISDN Call Control
747 User Information with SIP",
748 draft-ietf-cuss-sip-uui-isdn-04 (work in progress),
749 May 2012.
751 [Q1980] "ITU-T Q.1980.1 The Narrowband Signalling Syntax (NSS) -
752 Syntax Definition", http://www.itu.int/itudoc/itu-t/aap/
753 sg11aap/history/q1980.1/q1980.1.html .
755 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
756 Extensions to the Session Initiation Protocol (SIP) for
757 Asserted Identity within Trusted Networks", RFC 3325,
758 November 2002.
760 [RFC6567] Johnston, A. and L. Liess, "Problem Statement and
761 Requirements for Transporting User-to-User Call Control
762 Information in SIP", RFC 6567, April 2012.
764 10.2. Normative References
766 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
767 Requirement Levels", BCP 14, RFC 2119, March 1997.
769 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
770 A., Peterson, J., Sparks, R., Handley, M., and E.
771 Schooler, "SIP: Session Initiation Protocol", RFC 3261,
772 June 2002.
774 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for
775 Authenticated Identity Management in the Session
776 Initiation Protocol (SIP)", RFC 4474, August 2006.
778 [I-D.ietf-sipcore-rfc4244bis]
779 Barnes, M., Audet, F., Schubert, S., Elburg, H., and C.
780 Holmberg, "An Extension to the Session Initiation Protocol
781 (SIP) for Request History Information",
782 draft-ietf-sipcore-rfc4244bis-11 (work in progress),
783 January 2013.
785 [RFC4916] Elwell, J., "Connected Identity in the Session Initiation
786 Protocol (SIP)", RFC 4916, June 2007.
788 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
789 "Indicating User Agent Capabilities in the Session
790 Initiation Protocol (SIP)", RFC 3840, August 2004.
792 [RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation
793 Protocol (SIP) "Replaces" Header", RFC 3891,
794 September 2004.
796 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
797 (TLS) Protocol Version 1.2", RFC 5246, August 2008.
799 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
800 IANA Considerations Section in RFCs", BCP 26, RFC 5226,
801 May 2008.
803 Authors' Addresses
805 Alan Johnston
806 Avaya
807 St. Louis, MO 63124
809 Email: alan.b.johnston@gmail.com
811 James Rafferty
812 Dialogic
813 Needham, MA 02494
815 Email: james.rafferty@dialogic.com