DISPATCH Working Group J. van Elburg
Internet-Draft Ericsson Telecommunicatie B.V.
Intended status: Informational K. Drage
Expires: January 7, 2010 Alcatel-Lucent
July 6, 2009
The Session Initiation Protocol (SIP) P-Private-Network-Indication
Private-Header (P-Header)
draft-vanelburg-dispatch-private-network-ind-00
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Abstract
This document specifies the SIP P-Private-Network-Indication
P-header. The use of this private network indication extension is
only applicable inside an administrative domain with previously
agreed-upon policies for generation, transport and usage of such
information. A private network indication allows nodes in such a
domain to treat private network traffic according to a different set
of rules than the set applicable to public network traffic. The
indication also distinguishes traffic from one private network from
another private network.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Business communication . . . . . . . . . . . . . . . . . . 5
1.4. Indication types . . . . . . . . . . . . . . . . . . . . . 6
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Traffic . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Public network traffic . . . . . . . . . . . . . . . . . . 7
3.3. Private network traffic . . . . . . . . . . . . . . . . . 8
3.4. Trust domain . . . . . . . . . . . . . . . . . . . . . . . 8
4. Application of terminology . . . . . . . . . . . . . . . . . . 8
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Overview of solution . . . . . . . . . . . . . . . . . . . . . 12
7. Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. UA behaviour . . . . . . . . . . . . . . . . . . . . . . . 13
7.2. Proxy behaviour . . . . . . . . . . . . . . . . . . . . . 13
7.2.1. Private-Network-Indication generation . . . . . . . . 13
7.2.2. Private-Network-Indication consumption . . . . . . . . 13
7.2.3. Private-Network-Indication removal . . . . . . . . . . 13
8. P-Private-Network-Indication header field definition . . . . . 13
9. Security considerations . . . . . . . . . . . . . . . . . . . 14
10. IANA considerations . . . . . . . . . . . . . . . . . . . . . 15
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
12.1. Normative references . . . . . . . . . . . . . . . . . . . 15
12.2. Informative references . . . . . . . . . . . . . . . . . . 15
Appendix A. Alternative solutions discussed . . . . . . . . . . . 16
A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 16
A.2. Attribute on existing header field . . . . . . . . . . . . 17
A.3. Token value on existing header field . . . . . . . . . . . 17
A.4. Resource-Priority header field . . . . . . . . . . . . . . 17
A.5. P-Asserted-Service header field . . . . . . . . . . . . . 17
A.6. Request-Disposition header field . . . . . . . . . . . . . 17
A.7. P-Access-Network-Information . . . . . . . . . . . . . . . 18
A.8. URI parameter . . . . . . . . . . . . . . . . . . . . . . 18
A.9. New header field . . . . . . . . . . . . . . . . . . . . . 18
A.9.1. General . . . . . . . . . . . . . . . . . . . . . . . 18
A.9.2. Full SIP header field . . . . . . . . . . . . . . . . 18
A.9.3. New P-header field . . . . . . . . . . . . . . . . . . 18
Appendix B. Revision Information . . . . . . . . . . . . . . . . 18
B.1. version 00, SIPPING . . . . . . . . . . . . . . . . . . . 18
B.2. version 01, SIPPING . . . . . . . . . . . . . . . . . . . 19
B.3. version 02, SIPPING . . . . . . . . . . . . . . . . . . . 19
B.4. version 03, SIPPING . . . . . . . . . . . . . . . . . . . 19
B.5. version 00, DISPATCH . . . . . . . . . . . . . . . . . . . 19
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
1.1. General
ETSI TISPAN defines Next Generation Networks (NGN) which uses the
3rd-Generqation Partnership Project (3GPP) IMS (IP Multimedia
Subsystem) which in turn uses SIP (RFC3261 [RFC3261]) as its main
signalling protocol. (For more information on the IMS, a detailed
description can be found in 3GPP TS 23.228 [3GPP.23.228] and 3GPP TS
24.229 [3GPP.24.229].) 3GPP and ETSI TISPAN have identified a set of
requirements that can be met by defining a new SIP P-header,
according to the procedures in RFC 3427 [RFC3427].
1.2. Applicability
According to RFC 3427 [RFC3427], P-headers have a limited
applicability. Specifications of P-headers such as this RFC need to
clearly document the useful scope of the proposal, and explain its
limitations and why it is not suitable for the general use of SIP on
the Internet.
The P-Private-Network-Indication header field is intended to be used
in controlled closed networks like 3GPP IMS and ETSI TISPAN NGN
networks. The P-Private-Network-Indication header field does not
seem useful in a general internet environment.
1.3. Business communication
In the context of its work on business communiction support in public
next generation networks, ETSI TISPAN has identified a framework
[ETSI.181.019] for the support of business communication capabilities
by the NGN. As well as the direct attachment of Next Generation
Corporate Network (NGCN) equipment, this includes the capability to
"host" functionality relating to an enterprise within the NGN itself.
These hosting arrangements are:
a) virtual leased line, where NGCN sites are interconnected through
the NGN;
b) business trunking application, where the NGN hosts transit
capabilities between NGCN's, break-in capabilities where the NGN
converts public network traffic to private network traffic for
delivery at a served NGCN and break-out capabilities where the
NGN converts private network traffic from a served NGCN to public
network traffic; and
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c) hosted enterprise services, where an NGN hosts originating and/or
terminating business communication capabilities for business
communication users that are directly attached to an NGN.
ETSI TISPAN has requirements that can be met by the introduction of
an explicit indication for private network traffic.
The traffic generated or received by a public NGN on behalf of a
private network can be either:
o public network traffic: traffic sent to or received from an NGN
for processing according to the rules for ordinary subscribers of
a public telecommunication network. This type of traffic is known
as public network traffic;
o private network traffic: traffic sent to the NGN for processing
according to an agreed set of rules specific to an enterprise.
This type of traffic is known as private network traffic. Private
network traffic is normally within a single enterprise, but
private network traffic can also exist between two different
enterprises if not precluded for regulatory reasons.
1.4. Indication types
A private network indication as proposed by this document is an
indication to each and every network element traversed that this is
private network traffic as opposed to public network traffic. This
indication does not identify an end user on a private network and is
not for delivery to an end user on the private network. It is an
indication that special service arrangements apply for an enterprise,
and therefore it is an indication of service on behalf of an
enterprise, not an indication of service to a private network end
user.
In order to allow NGN IMS nodes to perform different processing ETSI
TISPAN formulated the following requirements on NGN:
1. The NGN shall distinguish public network traffic from private
network traffic.
2. The NGN shall distinguish private network traffic belonging to
one enterprise from that belonging to another enterprise.
To summarize a few example reasons for a public NGN to make the
distinction between the two types of traffic:
o Different regulations apply to the two types of traffic, most
notably lawful intercept requirements. Another example is
emergency calls may be handled differently depending on the type
of traffic.
o Different charging regimes may apply.
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o Call recording for business reasons (e.g. quality control,
training, non-repudiation) might apply only to a specific type of
traffic.
o Different levels of signalling and/or media transparency may apply
to the different types of traffic.
There are several reasons why there is a need for an explicit
indication in the signalling:
1. As calling and target addresses can not in all cases be used to
determine whether a certain call is to be treated as private or
public network traffic.
2. Separate nodes in the network need to be able to act on the type
of traffic being handled, when implicit schemes would be used it
would require distribution of such enterprise specific logic over
multiple nodes of multiple operators. That is clearly not a
manageable architecture.
3. There may be cases where treating the call as a public network
call although both participants are from the same enterprise is
advantageous to the enterprise.
Given the above background this document will formulate requirements
on SIP for support of an explicit private network indication.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
3. Definitions
3.1. Traffic
In the context of this document the term traffic is understood as all
communication pertaining to and/or controlled by a SIP transaction or
dialog.
3.2. Public network traffic
Traffic sent to or received from a public telecommunication network
for processing according to the rules for ordinary subscribers of a
public telecommunication network.
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3.3. Private network traffic
Traffic sent to or received from a public telecommunication network
for processing according to an agreed set of rules specific to an
enterprise or a community of closely related enterprises.
3.4. Trust domain
The term Trust Domain in this document is taken from RFC3324
[RFC3324]. A trust domain applies to the private network indication.
The rules for specifying such a trust domain are specified in RFC3324
[RFC3324] which require the filling out a Spec (T).
The Spec (T) need not specify the same contents and trust domain
boundaries that are used for other header fields like for example the
P-Asserted-Identity.
4. Application of terminology
Figure 1 shows the interconnection of sites belonging to two private
networks using the public network. Traffic in the public network
relating to the interconnection of the two sites of enterprise 1 are
tagged as private network traffic relating to enterprise 1. In
certain cases an enterprise can also choose to send traffic from one
enterprise site to another enterprise site as public network traffic
when this is beneficial to the enterprise. Traffic in the public
network relating to the interconnection of the two sites of
enterprise 2 are tagged as private network traffic relating to
enterprise 2. Enterprise 1 also generates traffic to public phones
and this is public network traffic (untagged in the public network).
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+------------------------------+
| private network |
+------------+ |<===========traffic==========>| +------------+
| enterprise | | (enterprise 1) | | enterprise |
| 1 +-----+------------------------------+-----+ 1 !
| site 1 | | | | site 2 |
+------------+ | +---+-----| |
| public | | | |
/--\ |<=========network========>| | +------------+
o /\ o | traffic | |
/ \----------+--------------------------+ |
+----+ | |
public | |
phone | |
| private network |
+------------+ |<===========traffic==========>| +------------+
| enterprise | | (enterprise 2) | | enterprise |
| 2 +-----+------------------------------+-----+ 2 !
| site 1 | | | | site 2 |
+------------+ | | +------------+
| |
+------------------------------+
Figure 1
Figure 2 shows the interconnection of sites belonging to a private
network using the public network, and supported in the public network
by a server providing a business trunking application. The business
trunking application providing routeing capabilities for the
enterprise traffic, and supports the identification of calls to and
from public network users, break-in and break out of that traffic.
(Note that the business trunking application may consist of a
concatenation of application logic provided to the originating
enterprise site and application logic that is provided to the
terminatig enterprise site.) Traffic in the public network relating
to the interconnection of the two sites of enterprise 1 are tagged as
private network traffic relating to enterprise 1. The business
trunking application also routes traffic to public phones and this is
public network traffic (untagged in the public network).
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+-------------------------------------------------+
| private network |
+------------+ |<===========traffic============>+------------+ |
| enterprise | | (enterprise 1) | | |
| 1 +-----+--------------------------------+ | |
| site 1 | | | business | |
+------------+ | +-----+ trunking | |
| public | | application| |
/--\ |<=========network========>| +--+ | |
o /\ o | traffic | | | | |
/ \----------+--------------------------+ | | | |
+----+ | | +------------+ |
public | | |
phone | | |
| private network | |
+------------+ |<===========traffic=========>| |
| enterprise | | (enterprise 1) | |
| 1 +-----+-----------------------------+ |
| site 2 | | |
+------------+ | |
| |
+-------------------------------------------------+
Figure 2
Figure 3 shows the interconnection of a site belonging to an private
network to a server providing a hosted enterprise service application
(also known as Centrex). The hosted enterprise service application
supports phones belonging to the enterprise and is also able to route
traffic to or from public network phones using break-in or break-out
functionality. Traffic in the public network relating to the
interconnection of the site of enterprise 1 and the hosted enterprise
service belonging to enterprise 1 are tagged as private network
traffic relating to enterprise 1. The hosted enterprise service
application also routes traffic to public phones and this is public
network traffic (untagged in the public network). Traffic from the
enterprise phones would not normally be tagged (such a tag is added
at the server providing the hosted enterprise services application.
(Note that the hosted enterprise service logic may be preceded or
subseded by a business trunking application that offers services on
behalf of an enterprise site.)
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+-------------------------------------------------+
| private network |
+------------+ |<===========traffic============>+------------+ |
| enterprise | | (enterprise 1) | | |
| 1 +-----+--------------------------------+ hosted | |
| site 1 | | | enterprise | |
+------------+ | +-----+ service | |
| public | | enterprise | |
/--\ |<=========network========>| +--+ 1 | |
o /\ o | traffic | | | | |
/ \----------+--------------------------+ | | | |
+----+ | | +------------+ |
public | | |
phone | | |
| private network | |
/--\ |<===========traffic=========>| |
o /\ o | (enterprise 1) | |
/ \----------+-----------------------------+ |
+----+ | |
enterprise | |
phone | |
+-------------------------------------------------+
Figure 3
5. Requirements
This section lists the requirements on SIP derived from consideration
in Section 1:
R1: It is REQUIRED that an indication can be send in SIP initial
requests for a dialog or SIP standalone requests that indicates
that the request or associated session is to be treated
according to the rules of private network traffic.
R2: The indication from R1 can be inserted by a SIP proxy belonging
to an administrative entity where for onward routeing, the
traffic within that administrative entity needs to be so
distinguished. The indication is not needed where the traffic
is assumed to be all public, or where the traffic is assumed to
be all private.
R3: The indication from R1 can be removed by a SIP proxy belonging
to an administrative entity where for onward routeing, the
traffic no longer needs to be so distinguished. An example
exists where the traffic reaches an NGCN site where the traffic
is now assumed to all private network traffic. Another example
is on the final hop to the UA.
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R4: It is REQUIRED that the indication from R1 allows entities to
determine the set of rules that are applicable, these rules may
be enterprise specific.
R5: It is REQUIRED that the indication from R1 allows entities
receiving it to distinguish private network traffic from
different enterprises.
R6: The identifier to distinguish private network traffic belonging
to one enterprise from that belonging to another enterprise must
be globally unique. Business communication arrangements for any
particular enterprise can be expected to span multiple NGN
operators potentially in multiple countries.
R7: The indication from R1 relates primarily to the SIP signaling.
Applying the same concept to media may be possible, but is not
necessarily meaningful where media is routed differently from
signalling.
6. Overview of solution
The mechanism proposed in this document relies on a new header field
called 'Private-Network-Indication' that contains an private network
identifier expressed as a domain name, for example:
P-Private-Network-Indication: ericsson.com
A proxy server which handles a message can, based on authentication
of the source of a message and configuration or local policy, insert
such a Private-Network-Indication header field into the message and
forward it to other trusted proxies to be handled as private network
traffic. A proxy that is about to forward a message to a proxy
server or UA that it does not trust MUST remove the Private-Network-
Indication header field.
The private network identifier expressed as a domain name allows it
to be globally unique identifier associated with the enterprise.
Domain name is used as it allows reuse of a company owned internet
domain name, without requiring an additional private network
identifier registry. When the enterprise needs more then one
identifier it can freely add subdomains that it has under its own
control.
The formal syntax for the Private-Network-Indication header is
presented in Section 8.
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7. Behaviour
7.1. UA behaviour
Use of this extension by UA's is not foreseen. Therefore there is no
particular UA behaviour specified in connection to the Private-
Network-Indication header field.
7.2. Proxy behaviour
7.2.1. Private-Network-Indication generation
Proxies that are responsible for determining certain traffic is to be
treated as private network traffic or contain a breakin function that
converts incoming public network traffic to private network traffic
MUST insert a Private-Network-Indication header field in to requests
for a dialog or requests for a standalone transaction where the value
MUST be set to the private network identifier corresponding to the
enterprise to which the traffic belongs.
7.2.2. Private-Network-Indication consumption
Proxies that are responsible for applying different processing
behaviours to specific private network traffic as to public network
traffic MUST support this extension. The Private-Network-Indication
header field MUST NOT be used by a proxy in case it is received on a
request it received from an entity that it does not trust, in such
case it MUST be removed before the request is forwarded.
7.2.3. Private-Network-Indication removal
Proxies that are at the edge of the trustdomain or contain a breakout
function that converts incoming private network traffic to public
network traffic MUST remove the Private-Network-Indication header
field before forwarding a request that contains such a header field
with a value.
8. P-Private-Network-Indication header field definition
This document defines the SIP P-Private-Network-Indication header
field. This header field can be added by a proxy to initial requests
for a dialog or standalone requests. The presence of the P-Private-
Network-Indication header field signifies to proxies that understand
this header field that the request is to be treated as private
network traffic. The P-Private-Network-Indication header field
contains a domain name value that allows the private network traffic
to be associated with an enterprise to which it belongs and that
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allow proxies that understand this header field to process the
request according to the request processing behaviours configured for
a specific enterprise.
The augmented Backus-Naur Form (BNF) (RFC5234 [RFC5234]) syntax of
the P-Private-Network-Indication header field is the following:
P-Private-Network-Indication =
"P-Private-Network-Indication" HCOLON PNI-value
*(SEMI PNI-param)
PNI-param = generic-param
PNI-value = hostname
EQUAL, HCOLON, SEMI, hostname and generic-param are defined in
RFC3261 [RFC3261].
The following is an example of a P-Private-Network-Indication header
field:
P-Private-Network-Indication: ericsson.com
9. Security considerations
The private network indication being defined in this document is to
be used in an environment where elements are trusted and where
attackers are not supposed to have access to the protocol messages
between those elements. Traffic protection between network elements
is sometimes achieved by using IPsec and sometimes by physically
protecting the network. In any case, the environment where the
private network indication will be used ensures the integrity and the
confidentiality of the contents of this header field.
A private network indication received from an untrusted node MUST NOT
be used and the information MUST be removed from a request or
response before it is forwarded to entities in the trust domain.
There is a security risk if a private network indication is allowed
to propagate out of the trust domain where it was generated. In that
case sensitive information would be revealed by such a breach. To
prevent such a breach from happening: Proxies MUST NOT insert the
information when forwarding requests to a next hop located outside
the trust domain. When forwarding the request to a trusted node,
proxies MUST NOT insert the header field unless they have sufficient
knowledge that the route set includes another proxy in the trust
domain that understands the header field, such as the own proxy.
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There is no automatic mechanism to learn the support for this
specification. Proxies MUST remove the information when forwarding
requests to untrusted nodes or when the proxy does not have knowledge
of any other proxy in the route set that is able to understand the
header field.
10. IANA considerations
This document defines a new SIP header field: P-Private-Network-
Indication. This header field needs to be registered by the IANA in
the SIP Parameters registry under the Header Fields subregistry.
11. Acknowledgments
The authors thank Bruno Chatras, John Elwell and Salvatore Loreto for
providing comments on an early version of this draft. Further we
thank John Elwell for performing the expert review.
12. References
12.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, November 2002.
[RFC3427] Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J.,
and B. Rosen, "Change Process for the Session Initiation
Protocol (SIP)", BCP 67, RFC 3427, December 2002.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
12.2. Informative references
[ETSI.181.019]
ETSI, "Telecommunication and Internet converged Services
and Protocols for Advanced Networking (TISPAN); Business
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Communication Requirements", ETSI TS 181 019 V2,
July 2007.
[3GPP.23.228]
3GPP, "IP Multimedia Subsystem (IMS); Stage 2", 3GPP
TS 23.228 V8.
[3GPP.24.229]
3GPP, "Internet Protocol (IP) multimedia call control
protocol based on Session Initiation Protocol (SIP) and
Session Description Protocol (SDP); Stage 3", 3GPP
TS 24.229 V8.
[RFC3455] Garcia-Martin, M., Henrikson, E., and D. Mills, "Private
Header (P-Header) Extensions to the Session Initiation
Protocol (SIP) for the 3rd-Generation Partnership Project
(3GPP)", RFC 3455, January 2003.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[I-D.drage-sipping-service-identification]
Drage, K., "A Session Initiation Protocol (SIP) Extension
for the Identification of Services",
draft-drage-sipping-service-identification-03 (work in
progress), March 2009.
Appendix A. Alternative solutions discussed
A.1. General
It would be technical possible, but extremely complex to perform this
function without an explicit indication. For example, a logical
distinction of proxies to handle private network traffic relating to
enterprise 1, enterprise 2 and the public network traffic could be
made by assigning different SIP URIs to these logical entities. This
is not regarded as a viable solution.
Several solutions have been raised and whether or not they are
suitable and fulfill the requirements need to be discussed:
o Attribute on existing header?
o Token on some existing header?
o Resource-Priority header?
o P-Asserted-Service header?
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o Request-Disposition header?
o P-Access-Network-Information header?
o URI parameter?
o New P-header?
o New header?
A.2. Attribute on existing header field
A.3. Token value on existing header field
A.4. Resource-Priority header field
Some of the distinctive functions are already provided for in this
header field. A potential mechanism would be to define a namespace
for private network traffic. It would however be impossible to
define a namespace for each enterprise, and therefore some additional
parameter would need to be defined to carry the unique identifier of
the particular enterprise to which the private network traffic
relates. Successful usage may also require a tightening of the
procedures for use of the Resource-Priority header field (much at the
moment is left to the particular application of this header field).
Private network traffic may, but is not necessarily handled with a
different priority then public network traffic. Use of the Resource-
Priority header field however seems to imply that the main focus of
the indication is on prioritizing private network traffic. This may
render use of the Resource-Priority header field as less appropriate
for our particular purpose.
A.5. P-Asserted-Service header field
The services envisaged by the P-Asserted-Service header field
(draft-drage-sipping-service-identification
[I-D.drage-sipping-service-identification]) are those applied to the
end user. The end user in these cases is the end user of the
enterprise or NGCN, not the enterprise itself. Therefore this header
field is not considered suitable for this problem.
A.6. Request-Disposition header field
The Request-Disposition header field (RFC3841 [RFC3841]) specifies
caller preferences for how a server should process a request. The
caller in these cases is the end user of the enterprise or NGCN, not
the enterprise itself. Therefore this header field is not considered
suitable for this problem. Further RFC3841 explicitly states that
the set of request disposition directives is not extensible.
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A.7. P-Access-Network-Information
The P-Access-Network-Info header field (RFC3455 [RFC3455]) contains
information about the access network that a UA uses to get IP
connectivity. However the access that one uses does not define the
private network that a call that one sets up is to be part of.
Particular examples that illustrate this:
o A Hosted Enterprise Services user (i.e. Centrex) uses the access
of the operator while still being able to setup calls that will
turn out to be private network traffic.
o A corporate network UE that attaches to an operator network, but
receives services from its home corporate network.
A.8. URI parameter
A marking on the entities within the Via header field that are
treating this as private network traffic. Potential marking on the
route header field of entities that are expected to treat it as
private network traffic.
A.9. New header field
If none of the existing header fields is appropriate a logical step
is to define a new header field for the private network indication.
A.9.2. Full SIP header field
A full SIP header field is appropriate when the usage of this
information element is more general then closed networks like ETSI
TISPAN NGN or 3GPP IMS.
A.9.3. New P-header field
In case no general usage is foreseen other then usage in closed
networks like those specified by ETSI TISPAN NGN or 3GPP IMS a
P-header field seems the appropriate choice.
Appendix B. Revision Information
B.1. version 00, SIPPING
1. 2008-02-18, Initial version
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B.2. version 01, SIPPING
1. 2008-02-23, Added a solution based on a new header field. Added
Overview, Behaviour and Header Definition sections. Updated the
trust domain definition. Improved some of the existing text
based on comments from John Elwell.
B.3. version 02, SIPPING
1. 2008-07-11, Changed to a P-header field. Changed title. Added
Terminology application and Applicability sections. Moved the
Potential solutions section to appendix Alternative solutions
discussed.
B.4. version 03, SIPPING
1. 2009-02-19, Updated boilerplate.
B.5. version 00, DISPATCH
1. 2009-07-06, Updates as result of Expert review. Moved to
DISPATCH.
Authors' Addresses
Hans Erik van Elburg
Ericsson Telecommunicatie B.V.
Ericssonstraat 2
Rijen 5121 ML
The Netherlands
Email: ietf.hanserik@gmail.com
Keith Drage
Alcatel-Lucent
The Quadrant, Stonehill Green, Westlea
Swindon SN5 7DJ
UK
Email: drage@alcatel-lucent.com
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