Network Working Group A. Johnston
Internet-Draft Avaya
Intended status: Standards Track J. McMillen
Expires: August 11, 2011 Unaffiliated
J. Rafferty
Dialogic
February 7, 2011
A Mechanism for Transporting User to User Call Control Information in
SIP
draft-ietf-cuss-sip-uui-00
Abstract
There is a need for applications using SIP to exchange User to User
Information (UUI) data during session establishment. This
information, known as call control UUI, is a small piece of data
inserted by an application initiating the session, and utilized by an
application accepting the session. This data is opaque to SIP and
its function is unrelated to any basic SIP function. This document
defines a new SIP header field, User-to-User, to transport UUI, along
with an extension mechanism.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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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."
This Internet-Draft will expire on August 11, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements Discussion . . . . . . . . . . . . . . . . . . . 3
4. Normative Definition . . . . . . . . . . . . . . . . . . . . . 5
4.1. Syntax for UUI Header Field . . . . . . . . . . . . . . . 5
4.2. Definition of New Parameter Values . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. Registration of Header Field . . . . . . . . . . . . . . . 6
5.2. Registration of Header Field Parameters . . . . . . . . . 7
5.3. Registration of SIP Option Tag . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Appendix - Other Possible Mechanisms . . . . . . . . . . . . . 8
7.1. Why INFO is Not Used . . . . . . . . . . . . . . . . . . . 8
7.2. Why Other Protocol Encapsulation UUI Mechanisms are
Not Used . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.3. MIME body Approach . . . . . . . . . . . . . . . . . . . . 9
7.4. URI Parameter . . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Informative References . . . . . . . . . . . . . . . . . . 10
9.2. Normative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Overview
This document describes the transport of User to User Information
(UUI) using SIP [RFC3261]. Specifically, we discuss a mechanism for
the transport of general application UUI and also for the transport
of call control related ITU-T Q.931 User to User Information Element
(UU IE) [Q931] and ITU-T Q.763 User to User Information Parameter
[Q763] data in SIP. UUI is widely used in the PSTN today in contact
centers and call centers which are transitioning away from ISDN to
SIP. This extension will also be used for native SIP endpoints
implementing similar services and interworking with ISDN services.
This mechanism was designed to meet the use cases, requirements, and
call flows for SIP call control UUI detailed in
[I-D.ietf-cuss-sip-uui-reqs]. All references to requirement numbers
(REQ-N) and figure numbers refer to this document.
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 BCP 14, RFC 2119
[RFC2119].
3. Requirements Discussion
This section describes how the User-to-User header field can meet the
requirements in [I-D.ietf-cuss-sip-uui-reqs]. The header field would
be included in INVITE requests and responses and BYE requests and
responses, and would pass transparently through proxies.
Requirements REQ-8 and REQ-10 relate to discovery of the mechanism
and supported applications. REQ-8 could be met by defining a new SIP
option tag 'uui'. The use of a 'Require: uui' in a request, or
'Supported: uui' in an OPTIONS response could be used to require or
discover support of the mechanism. REQ-10 could be met by creating a
new class of SIP feature tags. For example, the feature tag
'sip.uui.isdn' could be used to indicate support of the ISDN UUI
service, or 'sip.uui.app1' could be used to indicate support for a
particular application.
For redirection and referral use cases and REQ-3, the header field
would be escaped into the Contact or Refer-To URI. Currently, UAs
that support attended transfer support the ability to escape a
Replaces header field into a Refer-To URI, and when acting upon this
URI add the Replaces header field to the triggered INVITE. This
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logic and behavior is identical for the proposed UUI header field.
To meet REQ-12 in redirection and referral use cases, a History-Info
[I-D.ietf-sipcore-rfc4244bis] extension could be used. During
redirection or retargeting, History-Info captures the history and the
identity of the entity performing the redirection or referral. A new
History-Info parameter could be defined to indicate that the UUI was
inserted during this operation. The source of UUI inserted during
redirection or referral could then be determined by examination of
the History-Info header field.
OPEN ISSUE: How important is it to meet this requirement? Is
History-Info the right way?
The requirement for integrity protection in REQ-13 could be met by
the use of an S/MIME signature over a subset of header fields, as
defined in Section 23.4 of RFC 3261 "SIP Header Privacy and Integrity
using S/MIME: Tunneling SIP". It could not be achieved using RFC
4474 without some sort of extension. The requirement for end-to-end
privacy could be met using S/MIME or using encryption at the
application layer. Note that the use of S/MIME to secure the UUI
will result in an additional body being added to the request.
OPEN ISSUE: Is there interest in developing this mechanism?
For example, here is an example User-to-User header field from
message F1 in Figure 1 of [I-D.ietf-cuss-sip-uui-reqs]:
User-to-User: 56a390f3d2b7310023a;encoding=hex;purpose=isdn-interwork
;content=isdn-uui
As another example, here is an escaped User-to-User header field from
the redirection response F2 of Figure 3:
<allOneLine>
Contact: <sip:+12125551212@gateway.example.com?User-to-User=
56a390f3d2b7310023a%3Bencoding%3Dhex%3Bpurpose%3Disdn-interwork%3B
content%3Disdn-uui>
</allOneLine>
The resulting INVITE F5 would contain:
User-to-User: 56a390f3d2b7310023a;encoding=hex;purpose=isdn-interwork
;content=isdn-uui
An escaped User-to-User header field from the REFER message response
F1 of Figure 4:
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<allOneLine>
Refer-To: <sip:+12125551212@gateway.example.com?User-to-User=
56a390f3d2b7310023a%3Bencoding%3Dhex%3Bpurpose%3Disdn-interwork%3B
content%3Disdn-uui>
</allOneLine>
This would result in the INVITE F4 containing:
User-to-User: 56a390f3d2b7310023a;encoding=hex;purpose=isdn-interwork
;content=isdn-uui
The header field approach meets REQ-1, REQ-2, REQ-3, REQ-4, REQ-5,
REQ-7, REQ-9, REQ-11, REQ-13, and REQ-14. The mechanism can likely
meet REQ-12 with a History-Info extension.
4. Normative Definition
This document defines a new SIP header field "User-to-User" to
transport call control UUI to meet the requirements in
[I-D.ietf-cuss-sip-uui-reqs].
To help tag and identify the UUI used with this header field,
"purpose", "content", and "encoding" parameters are defined. This
specification only defines "encoding=hex". Other specifications can
define other purposes and contents for this header field per the
requirements of this document.
4.1. Syntax for UUI Header Field
The User-to-User header field can be present in INVITE requests and
responses only and in BYE requests and responses.
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC 2234 and extends RFC 3261.
UUI = "User-to-User" HCOLON uui-data *(SEMI uui-param)
uui-data = token
uui-param = enc-param | cont-param | purp-param | generic-param
enc-param = "encoding="("hex" | token)
cont-param = "content=" token
purp-param = "purpose=" token
If the encoding parameter is not present, the default value of "hex"
MUST be assumed. Other encoding methods of encoding MAY also be
standardized.
OPEN ISSUE: Is this encoding the encoding used by SIP, or the
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encoding used by the application? For interworking with ISDN, these
are not necessarily the same thing. For example, the data coming
from ISDN may be encoded as IA5. However, this data may then be
encoded in SIP as hex. Earlier versions have defined an
"encoding=ia5" parameter, but do we need this? Or do we actually
have UUI data that is encoded and transported over SIP using IA5?
User-to-User header fields with different purpose parameters may be
present in a request or response. The number of User-to-User header
fields which may be present in a request or response is defined for a
particular purpose (application). Any size limitations on the UUI
for a particular purpose must be defined by that purpose.
4.2. Definition of New Parameter Values
This specification defines only the values of "hex" for the
"encoding" parameter. New values can be defined and added to the
IANA registry with a standards track RFC, which needs to discuss the
issues in this section.
New "encoding" values must reference a common encoding scheme or
define the exact new encoding scheme.
New "content" values must describe the content of the UUI and give
some example use cases. The default "encoding" and other allowed
encoding methods must be defined for this new content.
New "purpose" values must describe the new purpose and give some
example use cases. The default "content" value and other allowed
contents must be defined for this new purpose. Any restrictions on
the size of the UUI data must be described for the new purpose.
5. IANA Considerations
5.1. Registration of Header Field
This document defines a new SIP header field named "User-to-User".
The following row shall be added to the "Header Fields" section of
the SIP parameter registry:
+------------------+--------------+-----------+
| Header Name | Compact Form | Reference |
+------------------+--------------+-----------+
| User-to-User | | [RFCXXXX] |
+------------------+--------------+-----------+
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Editor's Note: [RFCXXXX] should be replaced with the designation of
this document.
5.2. Registration of Header Field Parameters
This document defines the parameters for the header field defined in
the preceding section. The header field "User-to-User" can contain
the parameters "encoding", "content", and "purpose".
The following rows shall be added to the "Header Field Parameters and
Parameter Values" section of the SIP parameter registry:
+------------------+----------------+-------------------+-----------+
| Header Field | Parameter Name | Predefined Values | Reference |
+------------------+----------------+-------------------+-----------+
| User-to-User | encoding | hex | [RFCXXXX] |
+------------------+----------------+-------------------+-----------+
Editor's Note: [RFCXXXX] should be replaced with the designation of
this document.
5.3. Registration of SIP Option Tag
This specification registers a new SIP option tag, as per the
guidelines in Section 27.1 of [RFC3261].
This document defines the SIP option tag "uui".
The following row has been added to the "Option Tags" section of the
SIP Parameter Registry:
+------------+------------------------------------------+-----------+
| Name | Description | Reference |
+------------+------------------------------------------+-----------+
| uui | This option tag is used to indicate that | [RFCXXXX] |
| | a UA supports and understands the | |
| | User-to-User header field. | |
+------------+------------------------------------------+-----------+
Editor's Note: [RFCXXXX] should be replaced with the designation of
this document.
6. Security Considerations
User to user information can potentially carry sensitive information
that might require privacy or integrity protection. Standard
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deployed SIP security mechanisms such as TLS transport, offer these
properties on a hop-by-hop basis. To preserve multi-hop or end-to-
end confidentiality and integrity of UUI, approaches using S/MIME or
RFC 4474 can be used, as discussed in the draft. However, the lack
of deployment of these mechanisms means that applications can not in
general rely on them. As such, applications are encouraged to
utilize their own security mechanisms.
7. Appendix - Other Possible Mechanisms
Two other possible mechanisms for transporting UUI will be described:
MIME body and URI parameter transport.
7.1. Why INFO is Not Used
Since the INFO method [RFC2976], was developed for ISUP interworking
of user-to-user information, it might seem to be the logical choice
here. For non-call control user-to-user information, INFO can be
utilized for end to end transport. However, for transport of call
control user-to-user information, INFO can not be used. As the call
flows in [I-D.ietf-cuss-sip-uui-reqs] show, the information is
related to an attempt to establish a session and must be passed with
the session setup request (INVITE), responses to that INVITE, or
session termination requests. As a result, it is not possible to use
INFO in these cases.
7.2. Why Other Protocol Encapsulation UUI Mechanisms are Not Used
Other protocols have the ability to transport UUI information. For
example, consider the ITU-T Q.931 User to User Information Element
(UU IE) [Q931] and the ITU-T Q.763 User to User Information Parameter
[Q763]. In addition, NSS (Narrowband Signaling System) [Q1980] is
also able to transport UUI information. Should one of these
protocols be in use, and present in both User Agents, then utilizing
these other protocols to transport UUI might be a logical solution.
Essentially, this is just adding an additional layer in the protocol
stack. In these cases, SIP is not transporting the UUI; it is
encapsulating another protocol, and that protocol is transporting the
UUI. Once a mechanism to transport that other protocol using SIP
exists, the UUI transport function is essentially obtained without
any additional effort or work.
However, the authors believe that SIP needs to have its own native
UUI transport mechanism. It is not reasonable for a SIP UA to have
to implement another entire protocol (either ISDN or NSS, for
example) just to get the very simple UUI transport service. Of
course, this work does not preclude anyone from using other protocols
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with SIP to transport UUI information.
7.3. MIME body Approach
One method of transport is to use a MIME body. This is in keeping
with the SIP-T architecture [RFC3372] in which MIME bodies are used
to transport ISUP information. Since the INVITE will normally have
an SDP message body, the resulting INVITE with SDP and UUI will be
multipart MIME. This is not ideal as many SIP UAs do not support
multipart MIME INVITEs.
A bigger problem is the insertion of a UUI message body by a redirect
server or in a REFER. The body would need to be encoded in the
Contact URI of the 3xx response or the Refer-To URI of a REFER.
Currently, the authors are not aware of any UAs that support this
capability today for any body type. As such, the complete set of
semantics for this operation would need to be determined and defined.
Some issues will need to be resolved, such as, do all the Content-*
header fields have to be escaped as well? And, what if the escaped
Content-Length does not agree with the escaped body?
Since proxies cannot remove a body from a request or response, it is
not at all clear how this mechanism could meet REQ-9.
The requirement for integrity protection could be met by the use of
an S/MIME signature over the body, as defined in Section 23.3 of RFC
3261 "Securing MIME bodies". Alternatively, this could be achieved
using RFC 4474 [RFC4474]. The requirement for end-to-end privacy
could be met using S/MIME encryption or using encryption at the
application layer. However, note that neither S/MIME or RFC 4474
enjoys deployment in SIP today.
An example:
<allOneLine>
Contact: <sip:+12125551212@gateway.example.com?Content-Type=
application/uui&body=ZeGl9i2icVqaNVailT6F5iJ90m6mvuTS4OK05M0vDk0Q4Xs>
</allOneLine>
Note that the <allOneLine> tag convention from SIP Torture Test
Messages [RFC4475] is used to show that there are no line breaks in
the actual message syntax.
As such, the MIME body approach meets REQ-1, REQ-2, REQ-4, REQ-5,
REQ-7, REQ-11, REQ-13, and REQ-14. Meeting REQ-12 seems possible,
although the authors do not have a specific mechanism to propose.
Meeting REQ-3 is problematic, but not impossible for this mechanism.
However, this mechanism does not seem to be able to meet REQ-9.
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7.4. URI Parameter
Another proposed approach is to encode the UUI as a URI parameter.
This UUI parameter could be included in a Request-URI or in the
Contact URI or Refer-To URI. It is not clear how it could be
transported in a responses which does not have a Request-URI, or in
BYE requests or responses.
<allOneLine>
Contact: <sip:+12125551212@gateway.example.com;uui=ZeGl9i2icVqaNVailT6
F5iJ90m6mvuTS4OK05M0vDk0Q4Xs>
</allOneLine>
An INVITE sent to this Contact URI would contain UUI in the Request-
URI of the INVITE. The URI parameter has a drawback in that a URI
parameter carried in a Request-URI will not survive retargeting by a
proxy as shown in Figure 2 of [I-D.ietf-cuss-sip-uui-reqs]. That is,
if the URI is included with an Address of Record instead of a Contact
URI, the URI parameter in the Reqeuest-URI will not be copied over to
the Contact URI, resulting in the loss of the information. Note that
if this same URI was present in a Refer-To header field, the same
loss of information would occur.
The URI parameter approach would meet REQ-3, REQ-5, REQ-7, REQ-9, and
REQ-11. It is possible the approach could meet REQ-12 and REQ-13.
The mechanism does not appear to meet REQ-1, REQ-2, REQ-4, and
REQ-14.
8. Acknowledgements
Thanks to Spencer Dawkins, Keith Drage, Vijay Gurbani, and Laura
Liess for their review of the document. The authors wish to thank
Francois Audet, Denis Alexeitsev, Paul Kyzivat, Cullen Jennings, and
Mahalingam Mani for their comments.
9. References
9.1. Informative References
[Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part
formats and codes",
http://www.itu.int/rec/T-REC-Q.931-199805-I/en .
[Q931] "ITU-T Q.931 User to User Information Element (UU IE)",
http://www.itu.int/rec/T-REC-Q.931-199805-I/en .
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[ETSI] "ETSI ETS 300 207-1 Ed.1 (1994), Integrated Services
Digital Network (ISDN); Diversion supplementary
services".
[RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol
for Telephones (SIP-T): Context and Architectures",
BCP 63, RFC 3372, September 2002.
[RFC2976] Donovan, S., "The SIP INFO Method", RFC 2976,
October 2000.
[RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J.,
and H. Schulzrinne, "Session Initiation Protocol (SIP)
Torture Test Messages", RFC 4475, May 2006.
[Q1980] "ITU-T Q.1980.1 The Narrowband Signalling Syntax (NSS) -
Syntax Definition", http://www.itu.int/itudoc/itu-t/aap/
sg11aap/history/q1980.1/q1980.1.html .
9.2. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] 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.
[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, November 2002.
[I-D.ietf-cuss-sip-uui-reqs]
Johnston, A., McMillen, J., and L. Liess, "Problem
Statement and Requirements for Transporting User to User
Call Control Information in SIP",
draft-ietf-cuss-sip-uui-reqs-01 (work in progress),
December 2010.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[I-D.ietf-sipcore-rfc4244bis]
Barnes, M., Audet, F., Schubert, S., Netherlands, T., and
C. Holmberg, "An Extension to the Session Initiation
Protocol (SIP) for Request History Information",
draft-ietf-sipcore-rfc4244bis-02 (work in progress),
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October 2010.
Authors' Addresses
Alan Johnston
Avaya
St. Louis, MO 63124
Email: alan.b.johnston@gmail.com
Joanne McMillen
Unaffiliated
Email: c.joanne.mcmillen@gmail.com
James Rafferty
Dialogic
Email: james.rafferty@dialogic.com
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