SIP Working Group W. Marshall
Internet Draft K. Ramakrishnan
Document: <draft-dcsgroup-sip-privacy-02.txt> AT&T
E. Miller
G. Russell
CableLabs
B. Beser
M. Mannette
K. Steinbrenner
3Com
D. Oran
F. Andreasen
Cisco
J. Pickens
Com21
P. Lalwaney
Nokia
J. Fellows
Motorola
D. Evans
Secure Cable Solutions
K. Kelly
NetSpeak
June, 2000
SIP Extensions for Caller Identity and Privacy
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering
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The list of current Internet-Drafts can be accessed at
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DCS Group Internet Draft - Expiration 12/31/00 1
SIP Extensions for Caller Privacy June 2000
The list of Internet-Draft Shadow Directories can be accessed at
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The distribution of this memo is unlimited. It is filed as <draft-
dcsgroup-sip-privacy-02.txt>, and expires December 31, 2000. Please
send comments to the authors.
1. Abstract
This document describes two extensions to the Session Initiation
Protocol (SIP) [4]. The extensions allow callers and callees to
maintain their privacy in an environment where one or more proxies
serve as intermediaries which can provide the identity of the
parties either directly or indirectly. The extensions allow the
parties to be identified either by name or by type the latter of
which can be used to identify some group of callers and callees.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119 [2].
3. Introduction
In order for SIP to be a viable alternative to the current PSTN, SIP
must support certain popular telephony services as well as some
regulatory and public safety requirements. These include Calling
Identity Delivery services, Calling Identity Delivery Blocking, as
well as the ability to trace the originator of a call. While SIP can
support each of these services independently, certain combinations
cannot be supported. For example, a caller that wants to maintain
privacy and consequently provides unintelligible information in the
From header field will not be identifiable, e.g. for a return call
or call trace, by entities more than a single hop away, since the
contents of the From header cannot be modified. We note that this
problem is not telephony specific but applies to other forms of
session initiation as well. Furthermore, the issue of privacy in an
IP environment is more complicated than in the PSTN, as the caller
and callee will normally exchange IP traffic directly and IP address
information itself may reveal some privacy. The issue of IP address
privacy for both the caller and callee consequently needs to be
addressed as well.
In order to solve the above we assume an architecture as described
in [5] , where a SIP User Agent is associated with a trusted proxy,
and proxies in turn communicate with other proxies and user agents
which may or may not be trusted. Calls utilizing the services of
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this architecture must both be placed and received through the
trusted proxy.
This document defines two extensions to SIP that allow the calling
and called party to be identified by a trusted intermediary while
still being able to maintain their privacy. A new general header,
Remote-Party-ID, identifies each party, and another new general
header, Anonymity, defines the level of privacy requested by the
party. The trusted intermediary verifies the Remote-Party-ID
information supplied and ensures the privacy requested is provided
when forwarding a message across an untrusted boundary.
4. Protocol Overview
UACs that wish to use the extensions defined here MUST include a
Proxy-Require header in the initial INVITE request containing the
option tag "privacy". When such a UAC makes a call, it SHOULD
include a Remote-Party-ID header in the initial INVITE request in
order to identify the originator of the call. The Remote-Party-ID
MUST contain a SIP-URL identifying the UAC and MAY contain a
"display-name" for the UAC as well. Additionally, if privacy is
desired, the UAC MUST include an Anonymity header, which can request
one or more of URI, Name, and IP address privacy.
When a proxy supporting this extension receives an INVITE from an
untrusted entity, it looks for the presence of a Remote-Party-ID
header. If one is found, the proxy determines if the previous hop
was a UA the proxy serves. If so, the Remote-Party-ID information is
verified and modified if needed. If the request instead came from
another untrusted entity, the proxy either removes the Remote-Party-
ID information or marks it as being untrusted. Alternatively, the
proxy MAY reject the request, e.g. with a 403 or 407.
Prior to forwarding the request to an untrusted entity, the proxy
MUST look for the presence of an Anonymity header requesting
privacy. If one is found, the privacy requested MUST be provided
prior to forwarding the request. For URI and Name privacy, this
involves encrypting and possibly removing information provided in
the Remote-Party-ID. For IP Address privacy, it involves providing a
level of indirection for signaling and media through an entity we
refer to as an Anonymizer. The Anonymity header is removed as well.
Once a UAS supporting this extension receives the INVITE, it can use
the Remote-Party-ID information provided to identify the originator
of the call, unless the originator had requested privacy. If the
INVITE contained a Proxy-Require with an option tag of "privacy",
the UAS SHOULD include a Remote-Party-ID identifying it in the first
non-100 response. Irrespective, the UAS MUST include an Anonymity
header if it desires any privacy.
When a proxy supporting this extension receives a non-100 response
to the initial INVITE, it looks for a Remote-Party-ID header field
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and applies similar processing as for the initial INVITE with one
difference. If the INVITE did not contain a Proxy-Require with an
option tag of "privacy", the proxy MUST ensure that any privacy
requested in the response is provided prior to forwarding it,
irrespective of whether the previous hop is trusted or not.
Finally, when the UAC receives the first non-100 response from the
UAS, it can use Remote-Party-ID information provided to identify the
terminating party, unless the terminator had requested privacy.
5. Header Field Definitions
Table 1 below is an extension of tables 4 and 5 in [4] for the new
headers defined here:
where enc. e-e ACK BYE CAN INV OPT REG
Anonymity g n h - - - o - -
Remote-Party-ID g n h - - - o - -
Table 1: Summary of header fields.
The headers can be used in an INVITE as well as any response to an
INVITE.
5.1 Remote-Party-ID Header Field Definitions
The Remote-Party-ID header field provides the identity of the remote
party. At the called party it contains the identity of the caller,
and at the calling party, it contains the translated identity of the
called party. Remote-Party-ID is defined by the following ABNF [3]:
Remote-Party-ID = "Remote-Party-ID" ":" [display-name]
"<" addr-spec ">" *(";" rpi-token)
rpi-token = rpi-screen | rpi-type | other-rpi-token
rpi-screen = "rpi-screen" "=" ("no" | "yes" )
rpi-type = "rpi-type" "=" 1#token
other-rpi-token = token ["=" (token | quoted-string)]
Furthermore, we define the value "private" for "other-user" in an
"addr-spec", to indicate that the user part of an "addr-spec" is in
a non-intelligible form. The syntax for "other-user" is therefore
refined to:
other-user = token | "private"
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Comparisons follow the case-sensitivity rules defined by SIP [4].
The "display-name" in Remote-Party-ID is a text string that
identifies the name of the party. The "addr-spec" contains
information identifying the party either in clear-text or encrypted
form. In the latter case, the "user" part of the "addr-spec"
contains the encrypted party information, whereas the "hostport"
identifies the entity that can decrypt the information. Furthermore,
an "other-user" value of "private" will then be present to indicate
that the "addr-spec" is encrypted.
The "rpi-screen" describes what verification the Remote-Party-ID
information has undergone. The value "yes" (assumed by default)
indicates the Remote-Party-ID was verified successfully by the proxy
itself or the proxy received the INVITE from a trusted proxy with
this indication. The value "no" indicates the Remote-Party-ID was
either not verified successfully by the proxy or the proxy received
the message from an untrusted entity.
The "rpi-type" allows a group of users to be identified by some
common denominator. The denominator(s) used as well as the semantics
associated with these are a local issue and hence outside the scope
of this document. One example use might be to define an "rpi-type"
of "operator". An "operator" caller type might request special
privileges, e.g. performing an emergency interrupt on a voice call,
that the UA might not normally allow. Again, we purposely do not
define any particular rpi-types or semantics here.
Finally, the "other-rpi-token" parameter allows Remote-Party-ID to
be extended.
5.2 Anonymity Header Field Definition
The Anonymity header field allows an originating SIP user agent to
indicate the degree of privacy that should be provided to its
session.
The ABNF for the proposed header field follows:
Anonymity = "Anonymity" ":" 1#privacy-tag
privacy-tag = "full" | "uri" | "name" | "ipaddr" | "off"
Comparisons follow the case-sensitivity rules defined by SIP [4].
If privacy is requested, it MUST be one or more of "full", "uri",
"name", or "ipaddr". The value "off" indicates that no privacy is
requested, and MUST be the only value if present.
The value "uri" requests the party's identity not be provided to the
destination. The value "name" requests the party's name not be
provided. The value "ipaddr" requests IP privacy such that the
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other party does not learn the IP address of this party. The value
"full" requests both URI, Name, and IP address privacy.
It should be noted, that the header field allows both the
originating and terminating user agent to indicate its desire for
privacy.
6. Protocol Semantics
Below, we provide the protocol semantics for a UAC, a UAS, and a
proxy.
6.1 UAC Behavior
When a UAC supporting this extension initiates a call through its
trusted proxy, it SHOULD include a Remote-Party-ID header in the
initial INVITE request in order to identify the originator of the
call. The Remote-Party-ID header MUST at a minimum contain an "addr-
spec" to uniquely identify the calling party. The "addr-spec" SHOULD
be the same string as appears in the Request-URI for incoming call
attempts. The Remote-Party-ID may optionally include a "display-
name" and an "rpi-type". The "display-name" SHOULD be a name that
the proxy has associated with the calling party, e.g. the
subscribers full name. The "rpi-type" can be used as a convenience
to identify some group of users.
If the UAC desires privacy for the call, it MUST include an
Anonymity header specifying the desired level of privacy, e.g. "uri"
to maintain privacy of the "addr-spec". As honoring the privacy
requested depends on the proxy, the UAC MUST furthermore include a
Proxy-Require header with an option-tag of "privacy".
If the UAC desires "name" or "full" privacy, the UAC MUST NOT reveal
the originating subscriber's name in the "display-name" portion of
the From header. This can be achieved by, e.g., not providing a
"display-name" or setting the "display-name" to "anonymous".
If the UAC desires "uri" or "full" privacy, the UAC MUST NOT reveal
the originating subscriber's identity in the SIP-URL in the From
header field. The UAC SHOULD instead supply a cryptographically
random identifier for the userinfo, and a non-identifying hostname,
e.g. "localhost", for the hostport.
If the UAC desires "ipaddr" or "full" privacy, the UAC MUST NOT base
the Call-ID on the originator's IP address.
The first non-100 response received by the UAC MAY also contain a
Remote-Party-ID identifying the called party. If the Remote-Party-ID
contains an "rpi-screen" parameter with a value of "no", the UAC
SHOULD NOT trust the validity of the information provided.
Otherwise, the UAC SHOULD use the information provided to identify
the called-party rather than any information originally put in the
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To header field. The "addr-spec" contained in this Remote-Party-ID
can be used as the Request-URI by the UAC to initiate certain call
control functions or subsequent calls that are required to reference
the party reached. Examples of these include call transfer and
repeat call.
6.2 UAS Behavior
A UAS supporting this extension and receiving an INVITE from its
trusted proxy looks for a Remote-Party-ID header field to identify
the originator of the request. If the Remote-Party-ID contains an
"rpi-screen" parameter with a value of "no", the UAS SHOULD NOT
trust the validity of the information provided. Otherwise, the UAS
SHOULD use the information provided to identify the caller rather
than any information provided in the From header field.
The "addr-spec" contained in the Remote-Party-ID received can be
used as the Request-URI by the UAS to initiate certain call control
functions or subsequent calls that are required to reference the
party reached. Examples of these include call transfer and return
call.
If the initial INVITE contained a Proxy-Require header field with an
option tag of "privacy", the UAS SHOULD insert a Remote-Party-ID
header field identifying itself into the first non-100 response it
sends. The rules for the Remote-Party-ID are similar to those for
the initial INVITE for a UAC.
Regardless of whether the UAS provides a Remote-Party-ID in the
first non-100 response, the UAS MAY insert an Anonymity header in
that response to request any desired called party privacy. It should
be noted though, that the UAS can not depend on this privacy being
honored, if the original INVITE did not contain a Proxy-Require with
an option tag of "privacy".
6.3 Proxy Behavior
When a proxy supporting this extension receives an INVITE from an
untrusted entity, the proxy first determines if the request came
from a UAC that it serves. If so, it examines the INVITE for the
presence of a Remote-Party-ID header field. If a Remote-Party-ID
header field is present, the information supplied is verified and,
if needed, rewritten. The proxy MUST verify that the "addr-spec"
provided is a valid "addr-spec" for that UAC; if not, the proxy MUST
rewrite the "addr-spec" with a valid "addr-spec" for that UAC. If
"display-name" is provided in Remote-Party-ID, the proxy MUST verify
that the "display-name" is a valid string for the UAC; if not or if
the "display-name" is omitted, the proxy MUST rewrite the "display-
name" with a valid string for the UAC or remove the "display-name".
Note, that the proxy does not check a "display-name" provided in the
From header field. If "rpi-type" is provided, the proxy MUST verify
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that the UAC is of the indicated "rpi-type"(s); if not, the proxy
MUST remove the offending "rpi-type"(s) - this includes removing
unrecognized "rpi-type"(s).
If a Remote-Party-ID header was not present in the INVITE, but the
proxy is able to identify the originating UAC anyway, the proxy
inserts a Remote-Party-ID header with the correct information.
If the request instead came from an untrusted entity, and it was not
a UAC the proxy serves or the proxy is unable to identify the
entity, the proxy MUST either remove any Remote-Party-ID header or
add "rpi-screen=no" before the request is forwarded. Alternatively,
the proxy MAY reject the request, e.g. with a 403 or 407.
The proxy furthermore looks for the presence of an Anonymity header.
If an Anonymity header is present and the next hop is trusted, the
proxy MUST ensure that a Proxy-Require header with an option-tag of
"privacy" is present.
If the proxy forwards the request to an untrusted entity, and the
Anonymity header is present, the proxy MUST remove the Anonymity
header and ensure the privacy requested will be honored.
For non IP-address privacy, the proxy MUST do the following: If the
Anonymity header contains the value "full" or "uri", the proxy MUST
replace the "addr-spec" in the Remote-Party-ID header in the initial
INVITE with a private "addr-spec" and add a "user=private"
parameter. If the Anonymity header contains the value "full" or
"name", the proxy MUST delete the "display-name" in the Remote-
Party-ID header field in the initial INVITE. To generate the user
part of a private "addr-spec", the proxy MUST include (1) the
initial "addr-spec", (2) the value of Anonymity, and (3) sufficient
checksum information to prevent tampering by the untrusted party. It
MAY contain any other information the proxy desires as well. This
information MUST be encoded or encrypted such that the next hop is
unable to discern the initial "addr-spec". It is RECOMMENDED that
the string be encrypted with a symmetric privately-held key, and
converted to a printable string using Base64 encoding. The proxy
MUST identify itself in the hostname of the private "addr-spec".
For IP-address privacy, the proxy MUST rewrite the request to ensure
that the IP-address of the originating UAC will not be revealed.
This implies that neither SIP signaling nor IP media streams are
exchanged directly between the UAC and UAS. A level of indirection
which we call an Anonymizer MUST be provided.
Prior to forwarding the request, the proxy SHOULD remove any
"privacy" option tag present in a Proxy-Require header field to
prevent unnecessary failure of the request if downstream proxies do
not support this extension.
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When receiving the first non-100 response to the initial INVITE from
an untrusted entity, the proxy first determines if the response came
from a UAS that it serves.
If it did, the proxy examines the response for the presence of a
Remote-Party-ID and Anonymity header and applies similar processing
as for an INVITE received from a UAC served by the proxy.
Furthermore, if the original INVITE did not contain a Proxy-Require
header field with an option tag of "privacy", the proxy can not
determine if the previous hop supports the extension or not.
Consequently, if the response contains a request for privacy, the
privacy MUST be applied by this proxy, irrespective of whether the
upstream hop is trusted or not.
If the response came from an untrusted entity, and it was not a UAS
the proxy serves, the proxy MUST either remove any Remote-Party-ID
header provided or set "rpi-screen=no" before the response is
forwarded upstream. The same action MUST be taken when the initial
INVITE did not contain a Proxy-Require with an option tag of
"private", irrespective of whether the downstream hop was trusted or
not.
6.4 Additional proxy behavior
A proxy supporting this extension SHOULD be prepared to receive a
request containing a SIP-URL with a user parameter of "private". If
the "hostport" part of the SIP-URL identifies the proxy handling the
request, the proxy MUST decrypt the "user" portion of the SIP-URL
and replace it with the decrypted SIP-URL that was contained in the
"user" portion as well as any other information included, e.g.
Anonymity. Note that the decrypted SIP-URL may itself contain a
"private" SIP-URL. If the proxy is unable to decrypt and recover
such a "private" SIP-URL, it MUST fail the request with a 4xx error
code.
7 Example of Use
In this Section, we will illustrate how the request for privacy may
work in practice. It should be noted that the privacy service
described can be implemented in a number of ways; we merely describe
one possible solution in this section.
7.1 Basic Privacy Example
The Figure below illustrates a basic privacy example scenario
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SIP Extensions for Caller Privacy June 2000
+---------+ +--------+
1: INVITE | Proxy-o | 2: INVITE | Proxy-t| 3: INVITE
+------->| |------------>| |---------+
| +---------+ +--------+ |
| |
| trust boundary |
. . |. . . . . . . . . . . . . . . . . . . . . . .. . . | . . .
| |
| \/
+------+ RTP/RTCP +------+
| UA-o |<------------------------------------------->| UA-t |
+------+ +------+
Figure 1 - Basic Privacy Example
The originating user agent (UA-o) sends an INVITE (1) to Proxy-o
where it identifies itself and requests URI and Name privacy. Since
the From header field contains calling identity information, UA-o
supplies a cryptographically random identifier for the user info,
and a non-identifying hostname, e.g. "localhost" rather than its
true identity:
INVITE
From: sip:xyz@localhost
Remote-Party-ID: "John Doe" <sip:jdoe@foo.com>
Anonymity: uri, name
Proxy-Require: privacy
Proxy-o verifies the calling identity information before it sends
INVITE (2) to Proxy-t, which in this case is trusted. Proxy-t
examines the Anonymity header field included in the INVITE and sees
that URI and Name privacy is requested. Proxy-t therefore removes
the "display-name" from Remote-Party-ID, encrypts the "addr-spec"
ID, puts the result in the "user" part, inserts itself as the "host"
and adds a "user=private" parameter. Also, Proxy-t removes the
Anonymity header:
INVITE
From: sip:xyz@localhost
Remote-Party-ID: <sip:e(<sip:jdoe@foo.com>)@proxy-t.foo.com;
user=private>
Proxy-Require: privacy
UA-o notes the presence of the Remote-Party-ID, but since a
"user=private" parameter is provided, it can only identify the
calling party as private. UA-o decides to accept the call, and
responds with a 180 Ringing. In this case, there is no request for
Anonymity, so only the Remote-Party-ID of the called party is added:
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SIP Extensions for Caller Privacy June 2000
180
Remote-Party-ID: <sip:mdoe@foo.com>
Proxy-t verifies the information provided and adds the omitted
"display-name" to the Remote-Party-ID. Since no Anonymity was
requested, proxy-t can provide the Remote-Party-ID information to
proxy-o in clear:
180
Remote-Party-ID: "Mary Doe" <sip:mdoe@foo.com>
Proxy-o forwards the response to UA-o as is.
While this illustrates the basic operation of the service, there are
additional issues that need to be considered. In SIP, there are
several fields that can reveal the identity of the calling party,
either in part or completely. Other protocols used, e.g. SDP and RTP
may reveal identity information as well. A user agent wishing to not
reveal its identity should consider each of these. Our next example
looks more closely at this.
7.2 Full Privacy Example
The second example we look at is one where full privacy is
requested, i.e. both calling name and number privacy, as well as IP
address privacy. The Figure below illustrates how IP address privacy
can be achieved by inserting a trusted intermediary, an anonymizer,
for the media streams between UA-o and UA-t.
+---------+ +--------+
1: INVITE | Proxy-o | 2: INVITE | Proxy-t| 3: INVITE
+------->| |------------>| |----------+
| +---------+ +--------+ |
| \ / |
| \ / |
| SIP +--------+ SIP |
| +----------------->| anony- |-------------------+ |
| | +------>| mizer |--------+ | |
| | | +--------+ | | |
| | | | | |
| | | | | |
| | | trust boundary | | |
. . |.|. . . . . | . . . . . . . . . . . . | . . .. . |..| . . .
| | | | | |
| | | | \/ \/
+------+ RTP/RTCP| |RTP/RTCP +------+
| UA-o |<--------+ +-------->| UA-t |
+------+ +------+
Figure 2 - Full Privacy Example
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For all signaling and media exchange purposes, the anonymizer adds a
level of indirection thereby hiding the IP address(es) of UA-o from
UA-t. This indirection is used both for the media streams and SIP
signaling, beyond the initial INVITE, exchanged directly between UA-
o and UA-t.
Also, the following commonly used header fields may reveal privacy
information, which can be remedied as described:
@ The From header field must not reveal any calling identity
information in the SIP-URL. This can be remedied, e.g. by
supplying a cryptographically random identifier for the userinfo,
and a non-identifying hostname, e.g. "localhost". The "display-
name" can either be omitted or provided as "anonymous".
@ A Contact header field must be set to point to the anonymizer to
prevent any direct signaling between UA-o and UA-t
@ Via header fields identifying either UA-o or Proxy-o must be
hidden, e.g. by encryption or simple stateful removal and re-
insertion by Proxy-t.
@ Call-ID should not be based on UA-o's IP-address
Furthermore, when SDP is used to describe the media in the session,
the session descriptions exchanged by the user agents need to be
modified to direct the media streams to the anonymizer. The use of
SDP fields revealing calling identity information needs to be
considered as well. Similar concerns apply to the use of RTCP.
8. Security Considerations
A user requesting complete privacy must still authenticate himself
to the proxy, and therefore the SIP messages between the UA and the
proxy MUST be protected. Likewise, it is necessary that the proxies
take precautions to protect the user identification information from
eavesdropping and interception. Use of IPSec between the UA and
proxy as well as between proxies is recommended.
9. Notice Regarding Intellectual Property Rights
AT&T may seek patent or other intellectual property protection for
some or all of the technologies disclosed in the document. If any
standards arising from this disclosure are or become protected by
one or more patents assigned to AT&T, AT&T intends to disclose those
patents and license them on reasonable and non-discriminatory terms.
Future revisions of this draft may contain additional information
regarding specific intellectual property protection sought or
received.
3COM may seek patent or other intellectual property protection for
some or all of the technologies disclosed in the document. If any
DCS Group Internet Draft - Expiration 12/31/00 12
SIP Extensions for Caller Privacy June 2000
standards arising from this disclosure are or become protected by
one or more patents assigned to 3COM, 3COM intends to disclose those
patents and license them on reasonable and non-discriminatory terms.
Future revisions of this draft may contain additional information
regarding specific intellectual property protection sought or
received.
10. References
1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
2 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
3 Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, Internet Mail Consortium and
Demon Internet Ltd., November 1997
4 M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg,"SIP:
session initiation protocol," Request for Comments (Proposed
Standard) 2543, Internet Engineering Task Force, Mar. 1999.
5 Marshall, W. et. al, "Architectural Considerations for Providing
Carrier Class Telephony Services Utilizing SIP-based Distributed
Call Control Mechanisms", Internet Draft, Internet Engineering
Task Force, draft-dcsgroup-sip-arch-02, June 2000, Work In
Progress
11. Acknowledgments
The Distributed Call Signaling work in the PacketCable project is
the work of a large number of people, representing many different
companies. The authors would like to recognize and thank the
following for their assistance: John Wheeler, Motorola; David
Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jon Fellows,
Jay Strater, Jeff Ollis, Clive Holborow, Motorola; Doug Newlin,
Guido Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks;
Farzi Khazai, Nortel; John Chapman, Bill Guckel, Michael Ramalho,
Cisco; Chuck Kalmanek, Doug Nortz, John Lawser, James Cheng, Tung-
Hai Hsiao, Partho Mishra, AT&T; Telcordia Technologies; and Lucent
Cable Communications.
12. Author's Addresses
Bill Marshall
AT&T
Florham Park, NJ 07932
Email: wtm@research.att.com
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K. K. Ramakrishnan
AT&T
Florham Park, NJ 07932
Email: kkrama@research.att.com
Ed Miller
CableLabs
Louisville, CO 80027
Email: E.Miller@Cablelabs.com
Glenn Russell
CableLabs
Louisville, CO 80027
Email: G.Russell@Cablelabs.com
Burcak Beser
3Com
Rolling Meadows, IL 60008
Email: Burcak_Beser@3com.com
Mike Mannette
3Com
Rolling Meadows, IL 60008
Email: Michael_Mannette@3com.com
Kurt Steinbrenner
3Com
Rolling Meadows, IL 60008
Email: Kurt_Steinbrenner@3com.com
Dave Oran
Cisco
Acton, MA 01720
Email: oran@cisco.com
Flemming Andreasen
Cisco
Edison, NJ
Email: fandreas@cisco.com
John Pickens
Com21
San Jose, CA
Email: jpickens@com21.com
Poornima Lalwaney
Nokia
San Diego, CA 92121
Email: poornima.lalwaney@nokia.com
Jon Fellows
Motorola
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San Diego, CA 92121
Email: jfellows@gi.com
Doc Evans
Secure Cable Solutions
Westminster, CO 30120
Email: drevans@securecable.com
Keith Kelly
NetSpeak
Boca Raton, FL 33587
Email: keith@netspeak.com
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SIP Extensions for Caller Privacy June 2000
Full Copyright Statement
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or assist in its implementation may be prepared, copied, published
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Expiration Date This memo is filed as <draft-dcsgroup-sip-privacy-
02.txt>, and expires December 31, 2000.
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