💾 Archived View for gmi.noulin.net › rfc › rfc5503.gmi captured on 2022-06-04 at 06:41:53. Gemini links have been rewritten to link to archived content
⬅️ Previous capture (2022-01-08)
-=-=-=-=-=-=-
Obsoletes:
Keywords: P-DCS-TRACE-PARTY-ID, P-DCS-OSPS, P-DCS-BILLING-INFO, P-DCS-LAES, P-DCS-Redirect, P-DCS-INFO
Network Working Group F. Andreasen
Request for Comments: 5503 Cisco
Obsoletes: 3603 B. McKibben
Category: Informational CableLabs
B. Marshall
AT&T
March 2009
Private Session Initiation Protocol (SIP) Proxy-to-Proxy Extensions for
Supporting the PacketCable Distributed Call Signaling Architecture
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Andreasen, et al. Informational [Page 1]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
Abstract
In order to deploy a residential telephone service at a very large
scale across different domains, it is necessary for trusted elements
owned by different service providers to exchange trusted information
that conveys customer-specific information and expectations about the
parties involved in the call. This document describes private
extensions to the Session Initiation Protocol, RFC 3261, for
supporting the exchange of customer information and billing
information between trusted entities in the PacketCable Distributed
Call Signaling Architecture. These extensions provide mechanisms for
access network coordination to prevent theft of service, customer
originated trace of harassing calls, support for operator services
and emergency services, and support for various other regulatory
issues. The use of the extensions is only applicable within closed
administrative domains, or among federations of administrative
domains with previously agreed-upon policies where coordination of
charging and other functions is required.
Andreasen, et al. Informational [Page 2]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
Table of Contents
1. Applicability Statement .........................................4
2. Introduction ....................................................4
3. Trust Boundary ..................................................6
4. Conventions Used in This Document ...............................7
5. P-DCS-TRACE-PARTY-ID ............................................7
5.1. Syntax .....................................................8
5.2. Procedures at an Untrusted User Agent Client (UAC) .........9
5.3. Procedures at a Trusted User Agent Client (UAC) ............9
5.4. Procedures at an Untrusted User Agent Server (UAS) .........9
5.5. Procedures at a Trusted User Agent Server (UAS) ............9
5.6. Procedures at Proxy .......................................10
5.6.1. Procedures at Originating Proxy ....................10
5.6.2. Procedures at Terminating Proxy ....................11
6. P-DCS-OSPS .....................................................11
6.1. Syntax ....................................................11
6.2. Procedures at an Untrusted User Agent Client (UAC) ........12
6.3. Procedures at a Trusted User Agent Client (UAC) ...........12
6.4. Procedures at an Untrusted User Agent Server (UAS) ........13
6.5. Procedures at a Trusted User Agent Server (UAS) ...........13
6.6. Procedures at Proxy .......................................14
7. P-DCS-BILLING-INFO .............................................14
7.1. Syntax ....................................................16
7.2. Procedures at an Untrusted User Agent Client (UAC) ........18
7.3. Procedures at a Trusted User Agent Client (UAC) ...........18
7.4. Procedures at an Untrusted User Agent Server (UAS) ........18
7.5. Procedures at a Trusted User Agent Server (UAS) ...........18
7.6. Procedures at Proxy .......................................19
7.6.1. Procedures at Originating Proxy ....................19
7.6.2. Procedures at Terminating Proxy ....................20
7.6.3. Procedures at Tandem Proxy .........................21
8. P-DCS-LAES and P-DCS-Redirect ..................................21
8.1. Syntax ....................................................23
8.2. Procedures at an Untrusted User Agent Client (UAC) ........24
8.3. Procedures at a Trusted User Agent Client (UAC) ...........24
8.4. Procedures at an Untrusted User Agent Server (UAS) ........25
8.5. Procedures at a Trusted User Agent Server (UAS) ...........25
8.6. Procedures at Proxy .......................................26
8.6.1. Procedures at Originating Proxy ....................26
8.6.2. Procedures at Terminating Proxy ....................28
9. Security Considerations ........................................29
10. IANA Considerations ...........................................29
11. Changes since RFC 3603 ........................................31
12. Acknowledgments ...............................................32
13. References ....................................................32
13.1. Normative References .....................................32
13.2. Informative References ...................................33
Andreasen, et al. Informational [Page 3]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
1. Applicability Statement
The Session Initiation Protocol (SIP) [RFC3261] extensions described
in this document make certain assumptions regarding network topology,
linkage between SIP and lower layers, and the availability of
transitive trust. These assumptions are generally not applicable in
the Internet as a whole. The use of these headers is only applicable
within closed administrative domains, or among federations of
administrative domains with previously agreed-upon policies where
coordination of charging and other functions is required, as in, for
example, the architecture presented in [DCSARCH]. Use outside such a
domain could result in the leakage of potentially sensitive or
private information. User consent to the privacy implications of the
policies in [DCSARCH] is strongly encouraged in those domains as
well.
Although [RFC2119] language is used in this document, the scope of
the normative language is only for the area of applicability of the
document and, like the technology, it does not apply to the general
Internet.
2. Introduction
In order to deploy a SIP based residential telephone service at very
large scale across different domains, it is necessary for trusted
elements owned by different service providers to exchange trusted
information that conveys billing information and expectations about
the parties involved in the call.
There are many billing models used in deriving revenue from telephony
services today. Charging for telephony services is tightly coupled
to the use of network resources. It is outside the scope of this
document to discuss the details of these numerous and varying
methods.
A key motivating principle of the Distributed Call Signaling (DCS)
architecture described in [DCSARCH] is the need for network service
providers to be able to control and monitor network resources;
revenue may be derived from the usage of these resources as well as
from the delivery of enhanced services such as telephony.
Furthermore, the DCS architecture recognizes the need for
coordination between call signaling and resource management. This
coordination ensures that users are authenticated and authorized
before receiving access to network resources and billable enhanced
services.
Andreasen, et al. Informational [Page 4]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
DCS Proxies, as defined in [DCSARCH], have access to subscriber
information and act as policy decision points and trusted
intermediaries along the call signaling path. Edge routers provide
the network connectivity and resource policy enforcement mechanism
and also capture and report network connectivity and resource usage
information. Edge routers need to be given billing information that
can be logged with Record-Keeping or Billing servers. The DCS Proxy,
as a central point of coordination between call signaling and
resource management, can provide this information based on the
authenticated identity of the calling and called parties. Since
there is a trust relationship among DCS Proxies, they can be relied
upon to exchange trusted billing information pertaining to the
parties involved in a call. See [DCSARCH] for a description of the
trust boundary and trusted versus untrusted entities.
For these reasons, it is appropriate to consider defining SIP header
extensions to allow DCS Proxies to exchange information during call
setup. The extensions only appear on trusted network segments, are
inserted upon entering a trusted network region, and are removed
before leaving trusted network segments.
Significant amounts of information are retrieved by an originating
DCS Proxy in its handling of a connection setup request from a user
agent. Such information includes location information about the
subscriber (essential for emergency services calls), billing
information, and station information (e.g., coin-operated phone). In
addition, while translating the destination number, information such
as the local-number-portability office code is obtained and will be
needed by all other proxies handling this call.
For Usage Accounting records, it is necessary to have an identifier
that can be associated with all the event records produced for the
call. The SIP Call-ID header field cannot be used as such an
identifier since it is selected by the originating user agent, and it
may not be unique among all past calls as well as current calls.
Further, since this identifier is to be used by the service provider,
it should be chosen in a manner and in a format that meets the
service provider's needs.
Billing information may not necessarily be unique for each user
(consider the case of calls from an office all billed to the same
account). Billing information may not necessarily be identical for
all calls made by a single user (consider prepaid calls, credit card
calls, collect calls, etc). It is therefore necessary to carry
billing information separate from the calling and called party
identification. Furthermore, some billing models call for split-
charging where multiple entities are billed for portions of the call.
Andreasen, et al. Informational [Page 5]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
The addition of a SIP General Header Field allows for the capture of
billing information and billing identification for the duration of
the call.
The billing extensions only appear on trusted network segments and
MAY be inserted by a DCS Proxy in INVITE and REFER requests and
INVITE responses in a trusted network segment, and removed before
leaving trusted network segments.
In addition to support for billing, current residential telephone
service includes the need for customer-originated trace (of harassing
or obscene calls), for operator services such as busy line
verification and emergency interrupt (initiated by an operator from
an Operator Services Position System (OSPS)), for emergency services
such as 9-1-1 calls to a Public Service Access Point (PSAP) and the
subsequent call handling, and for support of Electronic Surveillance
and Law Enforcement access as required by applicable legislation and
court orders. In all of these cases, additional information about
the call and about the subscribers involved in the call needs to be
exchanged between the proxies.
3. Trust Boundary
The DCS architecture [DCSARCH] defines a trust boundary around the
various systems and servers that are owned, operated by, and/or
controlled by the service provider. These trusted systems include
the proxies and various servers such as bridge servers, voicemail
servers, announcement servers, etc. Outside of the trust boundary
lie the customer premises equipment and various application and media
servers operated by third-party service providers.
Certain subscriber-specific information, such as billing and
accounting information, stays within the trust boundary. Other
subscriber-specific information, such as endpoint identity, may be
presented to untrusted endpoints or may be withheld based on
subscriber profiles.
The User Agent (UA) may be either within the trust boundary or
outside the trust boundary, depending on exactly what function is
being performed and exactly how it is being performed. Accordingly,
the procedures followed by a user agent are different depending on
whether the UA is within the trust boundary or outside the trust
boundary.
Andreasen, et al. Informational [Page 6]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
The following sections giving procedures for user agents therefore
are subdivided into trusted user agents and untrusted user agents.
Since UAs may support client and server functions, the UA sections
include procedures for the User Agent Client (UAC) and User Agent
Server (UAS).
4. 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 BCP 14, [RFC2119].
The term "private-URL" used in this document refers to a SIP URI that
is generated by a proxy, contains a "hostport" that identifies the
proxy, and contains a "userinfo" string that is generated by the
proxy. The userinfo typically contains (or points to) information
that is not to be disclosed outside the trusted domain of the
proxies, such as billing account numbers, electronic surveillance
indication, electronic surveillance parameters, and call redirection
information. Consequently, the information is either stored locally
by the proxy, or encrypted with a private key known only to the proxy
and encoded in a character string in the userinfo portion of the URL.
A checksum is included in the userinfo data to detect tampering. The
mechanism by which a proxy recognizes a userinfo as a private-URL and
decodes and recovers the original information is local to the proxy
and is not subject to standardization. Some possible implementations
include an initial magic cookie (e.g., z9hG4Bk followed by the
pointer/information), or use of a reserved "user" name (e.g.,
"private") with the optional "password" containing the pointer/
information.
5. P-DCS-TRACE-PARTY-ID
In the telephone network, calling identity information is used to
support regulatory requirements such as the Customer Originated Trace
service, which provide the called party with the ability to report
obscene or harassing phone calls to law enforcement. This service is
provided independently of caller-id, and works even if the caller
requested anonymity. The calling party is here identified as the
station originating the call. In order for this service to be
dependable, the called party must be able to trust that the calling
identity information being presented is valid. One way to achieve
this is described in [RFC3325].
To initiate a customer-originated-trace from an untrusted User Agent
Client (UAC), an additional header is defined for the INVITE request.
This header is called P-DCS-Trace-Party-ID, and does not appear in
any other request or response. The untrusted UAC also includes the
Andreasen, et al. Informational [Page 7]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
Target-Dialog header field, defined in [RFC4538], in the INVITE
request in order to explicitly identify the call to be traced. The
entity addressed by the Request-URI performs the service-provider-
specific functions of recording and reporting the caller identity in
the P-DCS-Trace-Party-ID for law enforcement action. It then
forwards the call to either an announcement server or to the service
provider's business office to collect further information about the
complaint. A trusted UAC does not use this header, as it initiates
this action locally.
5.1. Syntax
The ABNF description of this header is (some terms used in this ABNF
are defined in [RFC3261]):
P-DCS-Trace-Party-ID = "P-DCS-Trace-Party-ID" HCOLON name-addr
*1(SEMI timestamp-param) *(SEMI trace-param)
timestamp-param = "timestamp=" 1*DIGIT ["." 1*DIGIT]
trace-param = generic-param ; defined in RFC 3261
This document adds the following entry to Table 2 of [RFC3261]:
Header field where proxy ACK BYE CAN INV OPT REG PUB
------------ ----- ----- --- --- --- --- --- --- ---
P-DCS-Trace-Party-ID R dmr - - - o - - -
SUB NOT REF INF UPD PRA MSG
--- --- --- --- --- --- ---
- - - - - - -
The addr-spec contained in name-addr contains a URL that identifies
the remote endpoint. Addr-spec typically contains a tel URL or SIP
URI giving the identity of the remote endpoint, as provided in the
signaling messages that established the session to be traced.
The timestamp-param contains the value of the time the UA determines
it received the session initiation request of the call requested to
be traced. The timestamp-param is populated using the Network Time
Protocol timestamp format defined in RFC 1305 [RFC1305] and used by
the Simple Network Time Protocol [RFC4330]. The timestamp SHOULD be
encoded in UTF-8 Format per [RFC3629]. The trace-param is a generic
parameter for future extensions.
An example of the P-DCS-Trace-Party-ID header is shown as follows:
P-DCS-Trace-Party-ID: <sip:+12345678912@domain.com;user=phone>;
timestamp=3434688831.2327
Andreasen, et al. Informational [Page 8]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
5.2. Procedures at an Untrusted User Agent Client (UAC)
The UAC MUST insert a P-DCS-Trace-Party-ID header into the initial
INVITE message for a customer-originated-trace request. The trace
request from the Untrusted User Agent Client is able to be initiated
during the dialog or after the release of the dialog or call that is
requested to be traced. The UAC MUST use a SIP URI in the Request-
URI with userinfo set to "call-trace" and hostport identifying the
call tracing entity for the untrusted UA. The [RFC3603] version of
the P-DCS-Trace-Party-ID did not include the timestamp-param
parameter; however, the syntax is backwards compatible with
[RFC3603]. A UAC compliant to this updated specification MUST insert
the timestamp and the Target-Dialog header field defined in [RFC4538]
if known to the UAC.
In case of an anonymous malicious call, where the remote party is not
known to the Untrusted UAC, the Untrusted UAC SHOULD indicate the
user as anonymous in the P-DCS-Trace-Party-ID, for example, as
follows: sip:anonymous@anonymous.invalid.
5.3. Procedures at a Trusted User Agent Client (UAC)
A trusted UAC performs the customer-originated-trace in a manner
similar to the trusted User Agent Server (UAS), described below. A
trusted UAC MUST NOT include this header in any request.
5.4. Procedures at an Untrusted User Agent Server (UAS)
This header MUST NOT appear in any response sent by a UAS.
5.5. Procedures at a Trusted User Agent Server (UAS)
If the P-DCS-Trace-Party-ID header is present in the initial INVITE
request from a UAC, and the Request-URI of the INVITE has userinfo
set to "call-trace" and hostport set to the UAS, the UAS MUST perform
the service-provider-specific functions of recording and reporting
the caller identity and associated trace parameters (if any) from the
Target-Dialog header field for law enforcement action. The UAS then
MUST redirect the call, via a 3xx response, to either an announcement
server or to the service provider's business office to collect
further information about the complaint.
This header MUST NOT appear in any response sent by a UAS.
If the P-DCS-Trace-Party-ID header is not present in the initial
INVITE request from a UAC, and the Request-URI of the INVITE has
userinfo set to "call-trace" the UAS MUST reject the request.
Andreasen, et al. Informational [Page 9]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
5.6. Procedures at Proxy
Two sets of proxy procedures are defined: (1) the procedures at an
originating proxy, and (2) the procedures at a terminating proxy.
The originating proxy is a proxy that received the INVITE request
from an untrusted endpoint.
The terminating proxy is a proxy that sends the INVITE request to an
untrusted endpoint.
A proxy that both receives the INVITE request from an untrusted
endpoint, and sends the INVITE request to an untrusted endpoint,
performs both sets of procedures.
5.6.1. Procedures at Originating Proxy
If the P-DCS-Trace-Party-ID header is present in the initial INVITE
request from the UAC, and the Request-URI of the INVITE has userinfo
other than "call-trace" and hostport set to other than a potentially
provisioned call tracing entity, then the proxy MAY reject the
request, or it MAY remove the P-DCS-Trace-Party-ID header from the
request. If the header is present in a valid request, and contains a
private-URL that identifies the proxy in the hostport, then the
originating proxy SHOULD replace the private-URL with its original
contents (i.e., the verified identity of the caller of the session
that is being traced and trace parameters from the Target-Dialog
header fields defined in [RFC4538]).
The proxy records the caller URL and target dialog IDs on sessions
directed toward the untrusted UAC if provisioned to do so by the
network operator. If the is P-DCS-Trace-Party-ID header is present
in a valid request, and contains an anonymous caller indication in
the name-addr parameter, the originating proxy MUST replace the
anonymous URL with the verified identity of the caller of the session
that is being traced if available and recorded by the proxy.
Otherwise, the proxy does not replace the anonymous URL.
If the origination proxy is provisioned to store URLs and target
dialog IDs for incoming calls, and if the proxy detects that the URL
and target dialog ID in a trace request does not match a recorded
incoming dialog request, then the proxy MUST reject the trace call
request.
The origination proxy does not add the P-DCS-Trace-Party-ID header
from a request that does not already contain the header.
Andreasen, et al. Informational [Page 10]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
5.6.2. Procedures at Terminating Proxy
This header MUST NOT appear in any request or response sent by a
terminating proxy to an untrusted endpoint.
6. P-DCS-OSPS
Some calls have special call processing requirements that may not be
satisfied by normal user agent call processing. For example, when a
user is engaged in a call and another call arrives, such a call might
be rejected with a busy indication. However, some Public Switched
Telephone Network (PSTN) operator services require special call
processing. In particular, the Busy Line Verification (BLV) and
Emergency Interrupt (EI) services initiated by an operator from an
Operator Services Position System (OSPS) on the PSTN network have
such a need. Similarly, emergency calls to a 9-1-1 Public Service
Access Point (PSAP) may result in trunk signaling causing operator
ringback using a howling tone or sustained ring on the originating
line (country-specific variations may exist).
In order to inform the SIP user agent that special treatment should
be given to a call, we use a new P-DCS-OSPS header, with a field that
may be set to a value indicating when a special type of call
processing is requested. We define three values in this header
field, namely "BLV" for busy line verification, "EI" for emergency
interrupt, and "RING" for operator ringback (e.g., howling/sustained
tone ring in the US).
If the user agent decides to honor such a request, the response of
the user agent to an INVITE with either "BLV" or "EI" will not be a
busy indication. Since "EI" and "RING" only occur on established
dialogs, they may also appear in UPDATE requests.
6.1. Syntax
The ABNF description of the P-DCS-OSPS header is as follows (some
terms used in this ABNF are defined in [RFC3261]):
P-DCS-OSPS = "P-DCS-OSPS" HCOLON OSPS-Tag
OSPS-Tag = "BLV" / "EI" / "RING" / token
Andreasen, et al. Informational [Page 11]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
This document adds the following entry to Table 2 of [RFC3261]:
Header field where proxy ACK BYE CAN INV OPT REG PUB
------------ ----- ----- --- --- --- --- --- --- ---
P-DCS-OSPS R dr - - - o - - -
SUB NOT REF INF UPD PRA MSG
--- --- --- --- --- --- ---
- - - - o - -
The OSPS-Tag value of "token" is defined for extensibility, and is
reserved for future use.
6.2. Procedures at an Untrusted User Agent Client (UAC)
The P-DCS-OSPS header MUST NOT be sent in a request from an untrusted
UAC.
6.3. Procedures at a Trusted User Agent Client (UAC)
This header is typically only inserted by a Media Gateway Controller
[DCSARCH] that is controlling a Media Gateway with special trunks to
a PSTN OSPS system or PSAP. This trunk group is usually referred to
as a BLV-trunk group and employs special signaling procedures that
prevent inadvertent use. Calls originating at the PSTN OSPS system
are sent over this trunk group, and result in an INVITE request with
the P-DCS-OSPS header.
This header MAY be sent in an INVITE request, and MUST NOT appear in
any message other than those listed below.
OSPS-Tag value "BLV" MUST NOT appear in any request other than an
initial INVITE request establishing a new dialog.
OSPS-Tag value "EI" MUST NOT appear in any request or response other
than (1) a subsequent INVITE within a preexisting dialog established
with the OSPS-Tag value of "BLV", or (2) an UPDATE request within a
preexisting dialog established with the OSPS-Tag value of "BLV".
OSPS-Tag value "RING" MUST NOT appear in any request or response
other than (1) a subsequent INVITE within a preexisting dialog
established by a UAC to an operator or PSAP, or (2) an UPDATE request
within a preexisting dialog established by a UAC to an operator or
PSAP.
Andreasen, et al. Informational [Page 12]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
6.4. Procedures at an Untrusted User Agent Server (UAS)
If the UAS receives an INVITE request with an OSPS-Tag of "BLV",
dialog identification that matches an existing dialog, it MUST reject
the request with a 403 (Forbidden) response.
If the UAS receives an INVITE/UPDATE request with an OSPS-Tag value
of "EI" or "RING", with dialog identification that does not match an
existing dialog that was established with the OSPS-Tag value of
"BLV", it MUST reject the request with a 403 (Forbidden) response.
If the UAS receives an INVITE that contains an OSPS-Tag value of
"BLV" and is not willing to cooperate in offering this service, it
MUST reject the request with a 403 (Forbidden) response.
The UAS SHOULD NOT reject an INVITE with a "BLV" OSPS-Tag due to a
busy condition. The UAS MUST NOT respond with a 3xx-Redirect
response code to an INVITE with a "BLV" OSPS-Tag. The UAS SHOULD NOT
alert the user of the incoming call attempt if the "BLV" OSPS-Tag is
present in the INVITE.
If an INVITE with OSPS-Tag of "BLV" is accepted (e.g., meeting all
quality-of-service (QoS) pre-conditions, etc.), the UAS MUST send an
audio stream on this connection to the address and port given in the
Session Description Protocol (SDP) of the INVITE. The UAS MAY
perform a mixing operation between the two ends of an existing active
call and send the resulting media stream to the address and port
indicated. Alternatively, the UAS MAY send a copy of the local voice
stream, and (if there is no activity on the local voice stream) send
a copy of the received voice stream of an existing call. If the
state of the UAS is idle, the UAS SHOULD send a stream of silence
packets to OSPS. If the state of the UAS is ringing or ringback, the
UAS SHOULD send a ringback stream to OSPS.
If an INVITE/UPDATE with OSPS-Tag of "EI" is accepted, the UAS MUST
enable communication between the UAC and the local user. The UAS MAY
put any existing call on hold, or initiate an ad hoc conference.
If an INVITE/UPDATE with OSPS-Tag of "RING" is accepted, the UAS MUST
perform operator ringback in accordance with local procedures, e.g.,
generate a 3-second howling tone or a sustained ring, depending on
the state of the user equipment.
6.5. Procedures at a Trusted User Agent Server (UAS)
The procedures at a trusted UAS MUST be identical to those described
in 6.4.
Andreasen, et al. Informational [Page 13]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
6.6. Procedures at Proxy
In the DCS architecture, the OSPS is considered a trusted UAC. If a
proxy receives a P-DCS-OSPS header in a request from an untrusted
source, it MUST either remove the header or reject the request with a
403 (Forbidden) response.
A proxy that implements a call-forwarding service MUST NOT respond to
an INVITE request with a 3xx response, if the request contained the
P-DCS-OSPS header.
7. P-DCS-BILLING-INFO
There are many billing models used in deriving revenue from telephony
services today. Charging for telephony services is tightly coupled
to the use of network resources. It is outside the scope of this
document to discuss the details of these numerous and varying
methods.
Proxies have access to subscriber information and act as policy
decision points and trusted intermediaries along the call signaling
path. Edge routers provide the network connection and resource
policy enforcement mechanism and also capture and report network
connection and resource usage information. Edge routers need to be
given billing information that can be logged with Record-Keeping or
Billing servers. The proxy, as a central point of coordination
between call signaling and resource management, can provide this
information based on the authenticated identity of the calling and
called parties. Since there is a trust relationship among proxies,
they can be relied upon to exchange trusted billing information
pertaining to the parties involved in a call.
For Usage Accounting records, it is necessary to have an identifier
that can be associated with all the event records produced for the
call. The SIP Call-ID header field cannot be used as such an
identifier since it is selected by the originating user agent, and
may not be unique among all past calls as well as current calls.
Further, since this identifier is to be used by the service provider,
it should be chosen in a manner and in a format that meets the
service provider's needs.
Billing information may not necessarily be unique for each user
(consider the case of calls from an office all billed to the same
account). Billing information may not necessarily be identical for
all calls made by a single user (consider prepaid calls, credit card
calls, collect calls, etc). It is therefore necessary to carry
Andreasen, et al. Informational [Page 14]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
billing information separate from the calling and called party
identification. Furthermore, some billing models call for
split-charging where multiple entities are billed for portions of the
call.
The addition of a SIP General Header Field allows for the capture of
billing information and billing identification for the duration of
the call.
The billing extensions only appear on trusted network segments, and
MAY be inserted by a proxy or trusted UA in INVITE and SUBSCRIBE
requests in a trusted network segment, and removed before leaving
trusted network segments. The P-DCS-Billing-Info header extension is
used only on requests and responses between proxies and trusted UAs.
It is never sent to an untrusted UA. It is expected that untrusted
UAs do not send this header.
Andreasen, et al. Informational [Page 15]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
7.1. Syntax
The DCS-Billing-Info header is defined by the following ABNF (some
terms used in this ABNF are defined in [RFC3261]):
P-DCS-Billing-Info = "P-DCS-Billing-Info" HCOLON
Billing-Correlation-ID "/" FEID
*(SEMI Billing-Info-param)
Billing-Correlation-ID = 1*48(HEXDIG)
FEID = 1*16(HEXDIG) "@" host
Billing-Info-param = RKS-Group-ID-param / Charge-param /
Calling-param / Called-param /
Routing-param / Loc-Routing-param /
JIP-param / generic-param
RKS-Group-ID-param = "rksgroup" EQUAL RKS-Group-ID
RKS-Group-ID = token
Charge-param = "charge" EQUAL Acct-Charge-URI
Acct-Charge-URI = LDQUOT addr-spec RDQUOT
Calling-param = "calling" EQUAL Acct-Calling-URI
Acct-Calling-URI = LDQUOT addr-spec RDQUOT
Called-param = "called" EQUAL Acct-Called-URI
Acct-Called-URI = LDQUOT addr-spec RDQUOT
Routing-param = "routing" EQUAL Acct-Routing-URI
Acct-Routing-URI = LDQUOT addr-spec RDQUOT
Loc-Routing-param = "locroute" EQUAL Acct-Loc-Routing-URI
Acct-Loc-Routing-URI = LDQUOT addr-spec RDQUOT
JIP-param = "jip" EQUAL jip
jip = LDQUOT 1*phonedigit-hex jip-context RDQUOT
jip-context = ";jip-context=" jip-descriptor
jip-descriptor = global-hex-digits
global-hex-digits = "+" 1*3(phonedigit) *phonedigit-hex
phonedigit = DIGIT / [ visual-separator ]
phonedigit-hex = HEXDIG / "*" / "#" / [ visual-separator ]
visual-separator = "-" / "." / "(" / ")"
This document adds the following entry to Table 2 of [RFC3261]:
Header field where proxy ACK BYE CAN INV OPT REG PUB
------------ ----- ----- --- --- --- --- --- --- ---
P-DCS-Billing-Info admr - - - o - - -
SUB NOT REF INF UPD PRA MSG
--- --- --- --- --- --- ---
- - - - - - -
Andreasen, et al. Informational [Page 16]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
The P-DCS-Billing-Info extension contains an identifier that can be
used by an event recorder to associate multiple usage records,
possibly from different sources, with a billable account. It further
contains the subscriber account information, and other information
necessary for accurate billing of the service. This header is only
used between proxies and trusted UAs.
The Billing-Correlation-ID, BCID, is specified in [PCEM] as a 24-byte
binary structure, containing 4 bytes of NTP timestamp, 8 bytes of the
unique identifier of the network element that generated the ID, 8
bytes giving the time zone, and 4 bytes of monotonically increasing
sequence number at that network element. This identifier is chosen
to be globally unique within the system for a window of several
months. This MUST be encoded in the P-DCS-Billing-Info header as a
hexadecimal string of up to 48 characters. Leading zeroes MAY be
suppressed.
The Financial-Entity-ID (FEID) is specified in [PCEM] as an 8-byte
structure, containing the financial identifier for that domain,
followed by a domain name. FEID can be associated with a type of
service and could be assigned to multiple domains by the same
provider. A domain could contain multiple assigned FEIDs. This
8-byte structure MUST be encoded in the P-DCS-Billing-Info header as
a hexadecimal string of up to 16 characters. Trailing zeroes MAY be
suppressed. "Host" contains the domain name.
The RKS-Group-ID specifies a Record-Keeping server (or group of
cooperating servers) for event messages relating to this call. It is
used to control certain optimizations of procedures when multiple
event message streams are being sent to the same Record-Keeping
server.
Additional parameters contain the information needed for generation
of event message records. Acct-Charge-URI, Acct-Calling-URI, Acct-
Called-URI, Acct-Routing-URI, and Acct-Loc-Routing-URI are each
defined as URLs; they should all contain tel URLs with E.164
formatted addresses. These fields are further defined in [PCEM]
under the element identifiers "Charge_Number" (element ID 16),
"Calling_Party_Number" (element ID 4), "Called_Party_Number" (element
ID 5), "Routing Number" (element ID 25), and
"Location_Routing_Number" (element ID 22).
The JIP-param contains the calling jurisdiction information, or
numbering plan area, of the network in which the call originated.
The field is further defined in [PCEM] under the element identifier
"Jurisdiction_Information_Parameter" (element ID 82). An older
[RFC3603] compliant implementation may not use the JIP-param.
Andreasen, et al. Informational [Page 17]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
7.2. Procedures at an Untrusted User Agent Client (UAC)
This header is never sent to an untrusted UA. It is expected that
untrusted UAs do not send this header.
7.3. Procedures at a Trusted User Agent Client (UAC)
The UAC MUST generate the Billing-Correlation-ID for the call, and
insert it into the P-DCS-Billing-Info header in the initial INVITE or
SUBSCRIBE message sent to the terminating entity, along with the
charging information for the call. The UAC MUST include its FEID,
and the RKS-Group-ID for the Record-Keeping server being used by the
UAC. If the UAC performed a Local Number Portability (LNP) query, it
MUST include the Routing Number and Location Routing Number returned
by the query. If available to the UAC, the UAC MUST include the JIP-
param.
If the response to the initial INVITE is a 3xx-Redirect, the UAC
generates a new initial INVITE request to the destination specified
in the Contact header field, as per standard SIP. If a UAC receives
a 3xx-Redirect response to an initial INVITE, the new INVITE
generated by the UAC MUST contain the P-DCS-Billing-Info header field
values from the 3xx-Redirect response. If the UAC is acting as a
back-to-back user agent (B2BUA), instead of generating a new INVITE
it MAY generate a private-URL and place it in the Contact header
field of a 3xx-Redirect response sent to the originating endpoint.
This private-URL MUST contain (or contain a pointer to) the P-DCS-
Billing-Info value, which indicates the charging arrangement for the
new call, and an expiration time very shortly in the future, to limit
the ability of the originator to re-use this private-URL for multiple
calls.
A UAC that includes a Refer-To header in a REFER request MUST include
a P-DCS-Billing-Info header in the Refer-To's URL. This P-DCS-
Billing-Info header MUST include the accounting information of the
initiator of the REFER.
7.4. Procedures at an Untrusted User Agent Server (UAS)
This header is never sent to an untrusted UAS, and is never sent by
an untrusted UAS.
7.5. Procedures at a Trusted User Agent Server (UAS)
The UAS MUST include a P-DCS-Billing-Info header in the first
reliable 1xx (except 100) or 2xx response to an initial INVITE or
SUBSCRIBE message. This P-DCS-Billing-Info header MUST include the
Billing-Correlation-ID generated by the UAS, the FEID of the UAS, and
Andreasen, et al. Informational [Page 18]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
the RKS-Group-ID of the Record-Keeping server being used by the UAS.
The UAS MAY change the values of Acct-Charge-URI if it wishes to
override the billing information that was present in the INVITE
(e.g., for a toll-free call). The decision to do this and the
contents of the new Acct-Charge-URI MUST be determined by service
provider policy provisioned in the UAS. If the UAS performed an LNP
query, it MUST include the Routing Number and Location Routing Number
returned by the query.
The UAS MUST add a P-DCS-Billing-Info header to a 3xx-Redirect
response to an initial INVITE, giving the accounting information for
the call forwarder, for the call segment from the destination to the
forwarded-to destination.
7.6. Procedures at Proxy
Three sets of proxy procedures are defined: (1) the procedures at an
originating proxy, (2) the procedures at a terminating proxy, and (3)
the procedures at a tandem proxy.
The originating proxy is a proxy that received the INVITE or
SUBSCRIBE request from an untrusted endpoint.
The terminating proxy is a proxy that sends the INVITE or SUBSCRIBE
request to an untrusted endpoint.
A proxy that is neither an originating proxy nor a terminating proxy
is a tandem proxy.
For purposes of mid-call changes, such as call transfers, the proxy
that receives the request from an untrusted endpoint is considered
the initiating proxy; the proxy that sends the request to a non-
trusted endpoint is considered the recipient proxy. Procedures for
the initiating proxy are included below with those for originating
proxies, while procedures for the recipient proxy are included with
those for terminating proxies.
A proxy that both receives the request from an untrusted endpoint,
and sends the request to an untrusted endpoint, performs both sets of
procedures.
7.6.1. Procedures at Originating Proxy
The originating proxy MUST generate the Billing-Correlation-ID for
the call, and insert it into the P-DCS-Billing-Info header in the
initial INVITE or SUBSCRIBE message sent to the terminating entity,
along with the charging information for the call. The originating
proxy MUST include its FEID and the RKS-Group-ID for the
Andreasen, et al. Informational [Page 19]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
Record-Keeping server being used by the originating proxy. If the
originating proxy performed an LNP query, it MUST include the Routing
Number, Location Routing Number, and JIP-param returned by the query.
Any P-DCS-Billing-Info header present from an untrusted UA MUST be
removed.
If the Request-URI contains a private-URL, and the decoded username
contains billing information, the originating proxy MUST generate a
P-DCS-Billing-Info header with that decrypted information.
Otherwise, the originating proxy MUST determine the accounting
information for the call originator and insert a P-DCS-Billing-Info
header including that information.
If the response to the initial INVITE is a 3xx-Redirect, received
prior to a non-100 provisional response, the originating proxy
generates a new initial INVITE request to the destination specified
in the Contact header field, as per standard SIP. If an originating
proxy receives a 3xx-Redirect response to an initial INVITE prior to
a non-100 provisional response, the INVITE generated by the proxy
MUST contain the P-DCS-Billing-Info header from the 3xx-Redirect
response.
If the response to the initial INVITE is a 3xx-Redirect, received
after a non-100 provisional response, the originating proxy generates
a private-URL and places it in the Contact header of a 3xx-Redirect
response sent to the originating endpoint. This private-URL MUST
contain (or contain a pointer to) the P-DCS-Billing-Info value, which
indicates the charging arrangement for the new call, and an
expiration time very shortly in the future, to limit the ability of
the originator to re-use this private-URL for multiple calls.
An originating proxy that processes a REFER request from an untrusted
UA MUST include a P-DCS-Billing-Info header in the Refer-To's URL.
This P-DCS-Billing-Info header MUST include the accounting
information of the initiator.
7.6.2. Procedures at Terminating Proxy
The terminating proxy MUST NOT send the P-DCS-Billing-Info header to
an untrusted destination.
The terminating proxy MUST include a P-DCS-Billing-Info header in the
first reliable 1xx (except 100) or 2xx response to an initial INVITE
or SUBSCRIBE message. This P-DCS-Billing-Info header MUST include
the Billing-Correlation-ID generated by the terminating proxy, the
FEID of the terminating proxy, and the RKS-Group-ID of the Record-
Keeping server being used by the terminating proxy. The terminating
proxy MAY change the values of Acct-Charge-URI if it wishes to
Andreasen, et al. Informational [Page 20]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
override the billing information that was present in the INVITE
(e.g., for a toll-free call). The decision to do this and the
contents of the resulting P-DCS-Billing-Info header MUST be
determined by service provider policy provisioned in the terminating
proxy. If the terminating proxy performed an LNP query, it MUST
include the Routing Number and Location Routing Number returned by
the query.
The terminating proxy MUST add P-DCS-Billing-Info headers to a 3xx-
Redirect response to an initial INVITE, giving the accounting
information for the call forwarder, for the call segment from the
destination to the forwarded-to destination.
A proxy receiving a mid-call REFER request that includes a Refer-To
header generates a private-URL and places it in the Refer-To header
sent to the endpoint. This private-URL MUST contain the P-DCS-
Billing-Info value, which indicates the charging arrangement for the
new call, and an expiration time very shortly in the future, to limit
the ability of the endpoint to re-use this private-URL for multiple
calls.
7.6.3. Procedures at Tandem Proxy
If the tandem proxy performed an LNP query, it MUST insert the
Routing Number and Location Routing Number returned by the query into
the P-DCS-Billing-Info header in the first reliable 1xx/2xx/3xx
(except 100) response.
8. P-DCS-LAES and P-DCS-Redirect
NOTE: According to RFC 2804 [RFC2804], the IETF supports
documentation of lawful intercept technology if it is necessary to
develop it. The following section provides such documentation. The
[RFC2119] language, as stated above, describes the requirements of
the specification only if implemented, and strictly within the
applicability domain described above. See RFC 2804 for description
of issues regarding privacy, security, and complexity in relation to
this technology.
The P-DCS-LAES extension contains the information needed to support
Lawfully Authorized Electronic Surveillance. This header contains
the address and port of an Electronic Surveillance Delivery Function
for delivery of a duplicate stream of event messages related to this
call. The header fields MAY also contain the associated BCID for the
event stream as well as additional address and port for delivery of
call content and associated cccid. The BCID is used to correlate a
series of events associated with a single call or session. The cccid
is used to identify an intercepted call content to an intercepted
Andreasen, et al. Informational [Page 21]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
call. The P-DCS-LAES header is only used between proxies and trusted
UAs. The P-DCS-LAES header defined here is not backwards compatible
with that defined in [RFC3603], which is deprecated by the document.
This version of the P-DCS-LAES header adds a cccid parameter to
support the intercept of content, and deletes security key
information. This version does not mandate the use of the BCID.
The P-DCS-Redirect extension contains call identifying information
needed to support the requirements of Lawfully Authorized Electronic
Surveillance of redirected calls. This header is only used between
proxies and trusted UAs.
Note that there is overlap in function between the P-DCS-Redirect
header and the History-Info header specified in RFC 4244. The
original P-DCS-Redirect came to existence in RFC 3603 before the
History-Info. Therefore, the P-DCS-Redirect header is continued here
for backwards compatibility with existing implementations.
Use of P-DCS-LAES and P-DCS-Redirect is controlled by a combination
of legislation, regulation, and court orders, which MUST be followed.
In certain cases, inclusion of these headers will be mandated, and
therefore MUST be present in the requests and responses indicated.
In other cases, inclusion of these headers will be forbidden, and
therefore MUST NOT be present in the request and responses indicated.
In the sub-sections that follow, use of "SHOULD" is intended to
capture these conflicting situations, e.g., a P-DCS-LAES header
SHOULD be included in an initial INVITE means either that it MUST be
included or that it MUST NOT be included, based on the applicable
court orders.
Andreasen, et al. Informational [Page 22]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
8.1. Syntax
The formats of the P-DCS-LAES and P-DCS-Redirect headers are given by
the following ABNF (some terms used in this ABNF are defined in
[RFC3261] and [RFC5234]):
P-DCS-LAES = "P-DCS-LAES" HCOLON Laes-sig
*(SEMI Laes-param)
Laes-sig = hostport
Laes-param = Laes-content / Laes-cccid
Laes-bcid / generic-param
Laes-content = "content" EQUAL hostport
Laes-bcid = "bcid" EQUAL 1*48(HEXDIG)
Laes-cccid = "cccid" EQUAL 1*8(HEXDIG)
P-DCS-Redirect = "P-DCS-Redirect" HCOLON Called-ID
*(SEMI redir-params)
Called-ID = LDQUOT addr-spec RDQUOT
redir-params = redir-uri-param / redir-count-param /
generic-param
redir-uri-param = "redirector-uri" EQUAL Redirector
Redirector = LDQUOT addr-spec RDQUOT
redir-count-param = "count" EQUAL Redir-count
Redir-count = 1*DIGIT
This document adds the following entry to Table 2 of [RFC3261]:
Header field where proxy ACK BYE CAN INV OPT REG PUB
------------ ----- ----- --- --- --- --- --- --- ---
P-DCS-LAES adr - - - o - - -
P-DCS-Redirect adr - - - o - - -
SUB NOT REF INF UPD PRA MSG
--- --- --- --- --- --- ---
- - - - - - -
- - - - - - -
The values of Laes-sig and Laes-content are addresses of the
Electronic Surveillance Delivery Function, and used as the
destination address for call-identifying information and call-
content, respectively. Laes-bcid contains a correlation ID that is
used to link a sequence of intercepted call processing events related
to a single call. Laes-cccid contains an identifier of the
intercepted call content. The Laes-bcid field MAY be present. The
BCID is included per network operator configuration to support events
reported as defined in [PCEM]. The Laes-cccid field MAY be present
when the Laes-content field is present. The Laes-cccid is included
Andreasen, et al. Informational [Page 23]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
per network operator configuration for networks where entities
receiving the intercepted contents may act a media relay functions to
other surveillance functions that are the source of the content
surveillance request. The design of multiple surveillance entities
that receive call content is beyond the scope of this document.
The P-DCS-Redirect header contains redirection information. The
Called-ID indicates the original destination requested by the user
(e.g., number dialed originally), the redir-uri-param indicates the
entity performing the redirection, and the Redir-count indicates the
number of redirections that have occurred. For example, if A calls
B, who forwards to C, who forwards to D, then, when C forwards to D,
the Called-ID will be A, redir-uri-param will be C, and count will be
2.
8.2. Procedures at an Untrusted User Agent Client (UAC)
This header MUST NOT be sent to an untrusted UAC, and MUST NOT be
sent by an untrusted UAC.
8.3. Procedures at a Trusted User Agent Client (UAC)
The UAC checks for an outstanding lawfully authorized surveillance
order for the originating subscriber, and, if present, MAY include
this information in the Authorization for Quality of Service [PCDQOS]
or MAY signal this information to the device performing the intercept
(e.g., a Media Gateway). Otherwise, intercept access points are
instructed to perform call content and/or call data intercept by
mechanisms that are outside the scope of this document.
If the P-DCS-LAES header is present in the first reliable 1xx (except
100), 2xx, or 3xx response (indicating surveillance is required on
the terminating subscriber, but that the terminating equipment is
unable to perform that function), the UAC MAY include this
information in the Authorization for Quality of Service, or MAY
signal this information to the device performing the intercept (e.g.,
a Media Gateway). Otherwise, intercept access points are instructed
to perform call content and/or call data intercept by mechanisms that
are outside the scope of this document.
If a 3xx-Redirect response to the initial INVITE request is received,
and if a P-DCS-LAES header is present in the 3xx response, the UAC
SHOULD include that header unchanged in the reissued INVITE. The UAC
SHOULD also include a P-DCS-Redirect header containing the original
dialed number, the most recent redirecting party, and the number of
redirections that have occurred. Although it is technically possible
for the originating equipment to perform this surveillance (or add to
its existing surveillance of the call), the design of the
Andreasen, et al. Informational [Page 24]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
surveillance system has the terminating equipment performing the
surveillance for all the intermediate forwardings.
A UAC that includes a Refer-To header in a REFER request, when the
originating subscriber has an outstanding lawfully authorized
surveillance order, SHOULD include a P-DCS-LAES header attached to
the Refer-To. The UAC MAY also include a P-DCS-Redirect header. The
P-DCS-LAES header MAY include the Laes-bcid parameter set to a value
that uniquely identifies the call, SHOULD include the address and
port of the local Electronic Surveillance Delivery Function for a
copy of the call's event messages, SHOULD include the address and
port of the local Electronic Surveillance Delivery Function for the
copy of call content if call content is to be intercepted, and MAY
include the Laes-cccid parameter set to a value that uniquely
identifies the intercepted audio stream if call content is to be
intercepted.
The trusted UAC MUST NOT send the P-DCS-LAES and P-DCS-Redirect
headers to an untrusted entity.
8.4. Procedures at an Untrusted User Agent Server (UAS)
This header MUST NOT be sent to an untrusted UAS, and MUST NOT be
sent by an untrusted UAS.
8.5. Procedures at a Trusted User Agent Server (UAS)
The UAS checks for an outstanding lawfully authorized surveillance
order for the terminating subscriber, or presence of the P-DCS-LAES
header in the INVITE request. If either is present, the UAS MAY
include this information in the authorization for Quality of Service
[PCDQOS]. Otherwise, intercept access points are instructed to
perform call content and/or call data intercept by mechanisms that
are outside the scope of this document.
If the terminating equipment is unable to perform the required
surveillance (e.g., if the destination is a voicemail server), the
UAS SHOULD include a P-DCS-LAES header in the first reliable 1xx
(except 100), 2xx, or 3xx response requesting the originating proxy
to perform the surveillance. The P-DCS-LAES header MAY include the
Laes-bcid parameter with a value that uniquely identifies the call,
SHOULD include the address and port of the local Electronic
Surveillance Delivery Function for a copy of the call's event
messages, SHOULD include the address and port of the local Electronic
Surveillance Delivery Function for the copy of call content if call
Andreasen, et al. Informational [Page 25]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
content is to be intercepted, and MAY include the Laes-cccid
parameter set to a value that uniquely identifies the intercepted
audio stream if call content is to be intercepted.
If the response to the initial INVITE request is a 3xx-Redirect
response, and there is an outstanding lawfully authorized
surveillance order for the terminating subscriber, the UAS SHOULD
include a P-DCS-LAES header in the 3xx-Redirect response, with
contents as described above.
The trusted UAS MUST NOT send the P-DCS-LAES and P-DCS-Redirect
headers to an untrusted entity.
8.6. Procedures at Proxy
Two sets of proxy procedures are defined: (1) the procedures at an
originating proxy, and (2) the procedures at a terminating proxy.
The originating proxy is a proxy that receives the INVITE request
from an untrusted endpoint.
The terminating proxy is a proxy that sends the INVITE request to an
untrusted endpoint.
For purposes of mid-call changes, such as call transfers, the proxy
that receives the request from an untrusted endpoint is considered
the initiating proxy; the proxy that sends the request to an
untrusted endpoint is considered the recipient proxy. Procedures for
the initiating proxy are included below with those for originating
proxies, while procedures for the recipient proxy are included with
those for terminating proxies.
A proxy that both receives the INVITE request from an untrusted
endpoint, and sends the INVITE request to an untrusted endpoint, MUST
NOT generate P-DCS-LAES nor P-DCS-Redirect headers.
A proxy that is neither an originating proxy nor a terminating proxy
SHOULD pass the P-DCS-Laes and P-DCS-Redirect headers in requests and
responses.
8.6.1. Procedures at Originating Proxy
The originating proxy MUST remove any P-DCS-LAES and P-DCS-Redirect
headers in requests or responses to or from an untrusted proxy or
untrusted UA.
The originating proxy checks for an outstanding lawfully authorized
surveillance order for the originating subscriber, and, if present,
MAY include this information in the Authorization for Quality of
Andreasen, et al. Informational [Page 26]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
Service [PCDQOS] or MAY signal this information to the device
performing the intercept (e.g., a Media Gateway). Otherwise,
intercept access points are instructed to perform call content and/or
call data intercept by mechanisms that are outside the scope of this
document.
If the P-DCS-LAES header is present in the first reliable 1xx (except
100), 2xx, or 3xx response (indicating surveillance is required on
the terminating subscriber, but that the terminating equipment is
unable to perform that function), the originating proxy MAY include
this information in the Authorization for Quality of Service, or MAY
signal this information to the device performing the intercept (e.g.,
a Media Gateway). Otherwise, intercept access points are instructed
to perform call content and/or call data intercept by mechanisms that
are outside the scope of this document.
If the Request-URI in an initial INVITE request contains a private-
URL, the originating proxy MUST decrypt the userinfo information to
find the real destination for the call, and other special processing
information. If electronic surveillance information is contained in
the decrypted userinfo, the originating proxy SHOULD generate a P-
DCS-LAES and (if necessary) a P-DCS-REDIRECT header with the
surveillance information.
If a 3xx-Redirect response to the initial INVITE request is received
prior to a non-100 provisional response, and if a P-DCS-LAES header
is present in the 3xx response, the originating proxy SHOULD include
that header unchanged in the reissued INVITE. The originating proxy
SHOULD also include a P-DCS-Redirect header containing the original
dialed number, the most recent redirecting party, and the number of
redirections that have occurred.
If a 3xx-Redirect response to the initial INVITE request is received
after a non-100 provisional response, the originating proxy generates
a private-URL and places it in the Contact header of a 3xx-Redirect
response sent to the originating endpoint. If a P-DCS-LAES header is
present in the 3xx response, this private-URL MUST contain (1) the
electronic surveillance information from the 3xx-Redirect response,
(2) the original destination number, (3) the identity of the
redirecting party, and (4) the number of redirections of this call.
An originating proxy that processes a REFER request [RFC3515] from an
untrusted UA, when the originating subscriber has an outstanding
lawfully authorized surveillance order, becomes a B2BUA for that
request. It SHOULD reissue the request with a P-DCS-LAES header
added to the Refer-To's URL. It MAY also include a P-DCS-Redirect
header. The P-DCS-LAES header SHOULD include (1) the address and
port of the local Electronic Surveillance Delivery Function for a
Andreasen, et al. Informational [Page 27]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
copy of the call's event messages, (2) the address and port of the
local Electronic Surveillance Delivery Function for the copy of call
content if call content is to be intercepted. The P-DCS-LAES header
MAY include (1) the Laes-bcid parameter set to a value that uniquely
identifies the call, and (2) the Laes-cccid parameter set to a value
that uniquely identifies the intercepted audio stream if call content
is to be intercepted.
An initiating proxy that sends a mid-call REFER request including a
Refer-To header, when the initiating subscriber has an outstanding
lawfully authorized surveillance order, SHOULD include a P-DCS-LAES
header in the Refer-To's URL.
The originating proxy MUST NOT send the P-DCS-LAES and P-DCS-Redirect
headers to an untrusted entity.
8.6.2. Procedures at Terminating Proxy
The terminating proxy MUST remove any P-DCS-LAES and P-DCS-Redirect
headers in requests or responses to or from an untrusted proxy or UA.
The terminating proxy checks for an outstanding lawfully authorized
surveillance order for the terminating subscriber. If present, the
terminating proxy MAY include this information in the authorization
for Quality of Service [PCDQOS]. Otherwise, intercept access points
are instructed to perform call content and/or call data intercept by
mechanisms that are outside the scope of this document.
The terminating proxy MUST NOT send the P-DCS-LAES and P-DCS-Redirect
headers to an untrusted entity, either as headers in the request or
response, or as headers attached to URIs in the request or response.
If the terminating equipment is unable to perform the required
surveillance (e.g., if the destination is a voicemail server), the
terminating proxy SHOULD include a P-DCS-LAES header in the first
reliable 1xx/2xx/3xx (except 100) response requesting the originating
proxy to perform the surveillance. The P-DCS-LAES header MAY include
the Laes-bcid parameter set to a value that uniquely identifies the
call, SHOULD include the address and port of the local Electronic
Surveillance Delivery Function for a copy of the call's event
messages, SHOULD include the address and port of the local Electronic
Surveillance Delivery Function for the copy of call content if call
content is to be intercepted, and MAY include the Laes-cccid
parameter set to a value that uniquely identifies the audio stream if
call content is to be intercepted.
Andreasen, et al. Informational [Page 28]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
If the response to the initial INVITE request is a 3xx-Redirect
response, and there is an outstanding lawfully authorized
surveillance order for the terminating subscriber, the terminating
proxy SHOULD include a P-DCS-LAES header in the 3xx-Redirect
response, with contents as described above.
A proxy receiving a mid-call REFER request [RFC3515] that includes a
Refer-To header with a P-DCS-LAES header attached becomes a B2BUA for
this request. It MUST generate a private-URL and place it in the
Refer-To header sent to the endpoint. This private-URL MUST contain
the P-DCS-LAES and P-DCS-Redirect information from the attached
header fields.
9. Security Considerations
QoS gate coordination, billing information, and electronic
surveillance information are all considered to be sensitive
information that MUST be protected from eavesdropping and furthermore
require integrity checking. It is therefore necessary that the
trusted UAs and proxies take precautions to protect this information
from eavesdropping and tampering. Use of IPsec or TLS between
proxies and trusted UAs is REQUIRED. A minimum mandatory-to-
implement IPsec configuration for the DCS architecture is given by
[PCSEC]. Also REQUIRED is mutual authentication (1) between Proxies
and (2) between trusted UAs and Proxies, both of which MAY be
implemented with administratively pre-shared keys, or through
consultation with another trusted third party. If IPsec is to be
used, the specification of the security policies and procedures of
the administrative domain where these headers are applicable (and all
connections between administrative domains in the federation) MUST
define an interoperable set of options.
10. IANA Considerations
The following changes to the Session Initiation Protocol (SIP)
Parameters registry have been made by IANA.
The Header Fields registry has been updated as follows:
Header Name compact Reference
----------------- ------- ---------
P-DCS-Trace-Party-ID [RFC5503]
P-DCS-OSPS [RFC5503]
P-DCS-Billing-Info [RFC5503]
P-DCS-LAES [RFC5503]
P-DCS-Redirect [RFC5503]
Andreasen, et al. Informational [Page 29]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
The following entries in the Header Field Parameters and Parameter
Values registry have been updated:
Header Field Parameter Name Values
Reference
---------------------------- --------------------------- ----------
P-DCS-Billing-Info called No
[RFC5503]
P-DCS-Billing-Info calling No
[RFC5503]
P-DCS-Billing-Info charge No
[RFC5503]
P-DCS-Billing-Info locroute No
[RFC5503]
P-DCS-Billing-Info rksgroup No
[RFC5503]
P-DCS-Billing-Info routing No
[RFC3603]
P-DCS-LAES content No
[RFC5503]
P-DCS-Redirect count No
[RFC5503]
P-DCS-Redirect redirector-uri No
[RFC5503]
The following entry in the Header Field Parameters and Parameter
Values registry has been marked "OBSOLETED":
Header Field Parameter Name Values
Reference
---------------------------- --------------------------- ----------
P-DCS-LAES key (OBSOLETED) No
[RFC3603][RFC5503]
Andreasen, et al. Informational [Page 30]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
The following entries in the Header Field Parameters and Parameter
Values registry have been created:
Header Field Parameter Name Values
Reference
---------------------------- --------------------------- ----------
P-DCS-Billing-Info jip No
[RFC5503]
P-DCS-LAES bcid No
[RFC5503]
P-DCS-LAES cccid No
[RFC5503]
P-DCS-Trace-Party-ID timestamp No
[RFC5503]
11. Changes since RFC 3603
o A timestamp parameter is added to the P-DCS-Trace-Party-ID header
when available. Procedures on the use of the Target-Dialog header
used together with the P-DCS-Trace-Party-ID are added.
o The JIP parameter is added to the P-DCS-Billing-Info header when
available.
o The BCID billing correlation identifier and cccid (call content
channel identifier) are added to the P-DCS-LAES header.
o P-DCS-Billing-Info header is applied to the SUBSCRIBE method.
o P-DCS-REDIRECT header is applied to the REFER method.
o The use of QoS authorization to establish content intercept is
made optional in order not to preclude alternative content
intercept provisioning mechanisms.
o PUBLISH and MESSAGE methods are added to the SIP method
applicability matrices throughout.
o Correction is made to Table 2 to add m=modify.
o IANA considerations are updated.
o Corrections are made to timestamp format, and references are
updated.
Andreasen, et al. Informational [Page 31]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
12. 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, Brian Lindsay. 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; Lucent
Cable Communications; and Miguel Garcia, Ericsson.
Previous versions further acknowledged, as co-authors, several people
for providing the text of this document. They are:
Bill Marshall (wtm@research.att.com) and K. K. Ramakrishnan
(kkrama@research.att.com), AT&T; Ed Miller
(edward.miller@terayon.com), Terayon; David Hancock (D.Hancock@
Cablelabs.com) and Glenn Russell (G.Russell@Cablelabs.com),
CableLabs; Burcak Beser (burcak@juniper.net) Juniper Networks; Mike
Mannette (Michael_Mannette@3com.com) and Kurt Steinbrenner
(Kurt_Steinbrenner@3com.com), 3Com; Dave Oran (oran@cisco.com) and
Flemming Andreasen (fandreas@cisco.com), Cisco Systems; John Pickens
(jpickens@com21.com), Com21; Poornima Lalwaney
(poornima.lalwaney@nokia.com), Nokia; Jon Fellows
(jfellows@coppermountain.com), Copper Mountain Networks; Doc Evans
(n7dr@arrisi.com) Arris, and Keith Kelly (keith@netspeak.com),
NetSpeak.
13. References
13.1. Normative References
[RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992.
[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.
[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
Andreasen, et al. Informational [Page 32]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
for IPv4, IPv6 and OSI", RFC 4330, January 2006.
[RFC4538] Rosenberg, J., "Request Authorization through Dialog
Identification in the Session Initiation Protocol (SIP)",
RFC 4538, June 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
13.2. Informative References
[DCSARCH] Marshall, W., Osman, M., Andreasen, F., and D. Evans,
"Architectural Considerations for Providing Carrier Class
Telephony Services Utilizing SIP-based Distributed Call
Control Mechanisms", January 2003.
[PCDQOS] Cable Television Laboratories, Inc., "PacketCable 1.5
Specifications, Dynamic Quality of Service", August 2005.
[PCEM] Cable Television Laboratories, Inc., "PacketCable 1.5
Specifications, Event Messages", December 2005.
[PCSEC] Cable Television Laboratories, Inc., "PacketCable 1.5
Specifications, Security", January 2005.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
May 2000.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
November 2002.
[RFC3603] Marshall, W. and F. Andreasen, "Private Session Initiation
Protocol (SIP) Proxy-to-Proxy Extensions for Supporting
the PacketCable Distributed Call Signaling Architecture",
RFC 3603, October 2003.
Andreasen, et al. Informational [Page 33]
RFC 5503 SIP Proxy-to-Proxy Extensions March 2009
Authors' Addresses
Flemming Andreasen
Cisco
Edison, NJ
USA
EMail: fandreas@cisco.com
Bernie McKibben
CableLabs
Louisville, CO
USA
EMail: B.McKibben@cablelabs.com
Bill Marshall
AT&T
Florham Park, NJ
USA
EMail: wtm@research.att.com
Andreasen, et al. Informational [Page 34]