Internet Engineering Task Force (IETF) C. Holmberg

Internet Engineering Task Force (IETF) C. Holmberg
Request for Comments: 7549 J. Holm
Category: Standards Track Ericsson
ISSN: 2070-1721 R. Jesske
Deutsche Telekom
M. Dolly
AT&T
May 2015

3GPP SIP URI Inter-Operator Traffic Leg Parameter

Abstract

In 3GPP networks, the signaling path between a calling user and a
called user can be partitioned into segments, referred to as traffic
legs. Each traffic leg may span networks belonging to different
operators and will have its own characteristics that can be different
from other traffic legs in the same call. A traffic leg might be
associated with multiple SIP dialogs, e.g., in case a Back-to-Back
User Agent (B2BUA) that modifies the SIP dialog identifier is located
within the traffic leg.

This document defines a new SIP URI parameter, 'iotl' (an
abbreviation for Inter-Operator Traffic Leg). The parameter can be
used in a SIP URI to indicate that the entity associated with the
address, or an entity responsible for the host part of the address,
represents the end of a specific traffic leg (or multiple traffic
legs).

The SIP URI 'iotl' parameter defined in this document has known uses
in 3GPP networks. Usage in other networks is also possible.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7549.

Holmberg, et al. Standards Track [Page 1]

RFC 7549 3GPP 'iotl' May 2015

Copyright Notice

Copyright (c) 2015 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Holmberg, et al. Standards Track [Page 2]

RFC 7549 3GPP 'iotl' May 2015

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Traffic Leg Examples . . . . . . . . . . . . . . . . . . . . 6
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Originating Roaming Call . . . . . . . . . . . . . . . . 6
4.3. Terminating Roaming Call . . . . . . . . . . . . . . . . 7
4.4. Call from Originating Home to Terminating Home . . . . . 7
5. 'iotl' SIP URI Parameter . . . . . . . . . . . . . . . . . . 7
5.1. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Parameter Values . . . . . . . . . . . . . . . . . . . . 8
5.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 8
5.2.2. homea-homeb . . . . . . . . . . . . . . . . . . . . . 8
5.2.3. homeb-visitedb . . . . . . . . . . . . . . . . . . . 8
5.2.4. visiteda-homea . . . . . . . . . . . . . . . . . . . 9
5.2.5. homea-visiteda . . . . . . . . . . . . . . . . . . . 9
5.2.6. visiteda-homeb . . . . . . . . . . . . . . . . . . . 9
6. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. 3GPP Examples . . . . . . . . . . . . . . . . . . . 12
A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 12
A.2. The UE Registers via P-CSCF . . . . . . . . . . . . . . . 12
A.3. Originating IMS Call . . . . . . . . . . . . . . . . . . 14
A.4. Terminating IMS Call . . . . . . . . . . . . . . . . . . 15
A.5. Call between Originating Home and Terminating Home
Network . . . . . . . . . . . . . . . . . . . . . . . . . 16
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17

Holmberg, et al. Standards Track [Page 3]

RFC 7549 3GPP 'iotl' May 2015

1. Introduction

In a 3GPP network, an end-user device can be attached (e.g., using a
radio access network) to its own operator network (home network)
[TS.3GPP.24.229] or to another operator's network (visited network)
[TS.3GPP.24.229]. In the latter case, the user is referred to as a
roaming user.

3GPP operator networks are often not connected directly to each
other. Instead, there might be intermediate networks, referred to as
3GPP transit networks, between them. Such transit networks act on
the SIP level or the IP level.

In 3GPP networks, the signaling path between a calling user and a
called user can be partitioned into segments, referred to as traffic
legs. Each traffic leg may span networks belonging to different
operators and will have its own characteristics that can be different
from other traffic legs in the same call. A traffic leg might be
associated with multiple SIP dialogs, e.g., in case a B2BUA [RFC3261]
that modifies the SIP dialog identifier is located within the traffic
leg.

The traffic leg information can be used by intermediary entities to
make policy decisions related to, e.g., media anchoring, signaling
policy, insertion of media functions (e.g., transcoder), and
charging.

The figure below shows two users (Alice and Bob) and the different
type of networks that the signaling might traverse. The signaling
path can be divided into multiple traffic legs, and the type of
traffic legs depends on how the signaling is routed.

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RFC 7549 3GPP 'iotl' May 2015

Alice -- ORIG HNW +++++ TRANSIT NW +++++ TERM HNW -- Bob
Home + + + + + Home
+ ++++++++++++++++++ + +
+ + +
+ + +
+ +++++++++++++++++++++++ +
+ + + +
Alice -- ORIG VNW +++++ TRANSIT NW ++ TERM VNW -- Bob
Visited Visited

ORIG HNW = Originating 3GPP Home Network
TERM HNW = Terminating 3GPP Home Network
ORIG VNW = Originating 3GPP Visited Network
TERM VNW = Terminating 3GPP Visited Network
TRANSIT NW = 3GPP Transit Network

Figure 1: 3GPP Operator Network Roaming Roles

In Figure 1, Alice is a user initiating communication with Bob. Also,
consider the following information:

Alice is attached to an originating network, which is either the home
network of Alice or a visited network (in case Alice is roaming). In
both cases, any originating service is provided by the home network
of Alice.

Bob is attached to a terminating network, which is either the home
network of Bob or a visited network (in case Bob is roaming). In
both cases, any terminating service is provided by the home network
of Bob.

A transit network providing transit functions (e.g., translation of
free phone numbers) may be included between the originating and
terminating networks and between visited and home networks.

This document defines a new SIP URI parameter [RFC3261], 'iotl' (an
abbreviation for Inter-Operator Traffic Leg). The parameter can be
used in a SIP URI to indicate that the entity associated with the
address, or an entity responsible for the host part of the address,
represents the end of a specific traffic leg (or multiple traffic
legs).

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RFC 7549 3GPP 'iotl' May 2015

This document defines the following 'iotl' parameter values:

o homea-homeb

o homeb-visitedb

o visiteda-homea

o homea-visiteda

o visiteda-homeb

SIP entities that do not support the SIP URI 'iotl' parameter will
simply ignore it, if received, as defined in [RFC3261].

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 [RFC2119].

3. Applicability

The SIP URI 'iotl' parameter defined in this document has known uses
in 3GPP networks. Usage in other networks is also possible.

4. Traffic Leg Examples

4.1. General

This section describes examples of different types of traffic legs in
3GPP networks.

4.2. Originating Roaming Call

In this case, Alice is located in a visited network. When Alice
sends the initial SIP INVITE request for a call, one traffic leg
(referred to as the 'visiteda-homea' traffic leg) represents the
signaling path between the User Agent (UA) of Alice and the home
Serving Call Session Control Function (S-CSCF) [TS.3GPP.24.229] of
Alice.

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RFC 7549 3GPP 'iotl' May 2015

4.3. Terminating Roaming Call

In this case, Bob is located in a visited network. When the home
S-CSCF of Bob forwards the initial SIP INVITE request for a call
towards Bob, one traffic leg (referred to as the 'homeb-visitedb'
traffic leg) represents the signaling path between the home S-CSCF of
Bob and the UA of Bob.

4.4. Call from Originating Home to Terminating Home

In this case, the home S-CSCF of Alice forwards the initial SIP
INVITE request towards the home S-CSCF of Bob. The signaling path
between the S-CSCFs represents one traffic leg (referred to as the
'homea-homeb' traffic leg).

5. 'iotl' SIP URI Parameter

5.1. Usage

As specified in [RFC3261], when a SIP entity inserts a SIP URI in an
initial request for a dialog, or in a stand-alone request, the SIP
URI will be used to route the request to another SIP entity,
addressed by the SIP URI, or to a SIP entity responsible for the host
part of the SIP URI (e.g., a SIP registrar). If such an entity
represents the end of one or more traffic legs, the SIP entity
inserting the SIP URI can add a SIP URI 'iotl' parameter to the SIP
URI to indicate the type(s) of traffic leg. Each parameter value
indicates a type of traffic leg.

For routing of an initial SIP request for a dialog, or a stand-alone
SIP request, a SIP entity can add the 'iotl' parameter to (a) the SIP
URI of the Request-URI [RFC3261] or (b) the SIP URI of a Route header
field [RFC3261] of the SIP request. SIP entities can add the 'iotl'
parameter to the SIP URI of a Path header field [RFC3327] or a
Service-Route header field [RFC3608] in order for the parameter to
later occur in a Route header field.

When a SIP entity receives an initial request for a dialog or a
stand-alone request, which contains one or more SIP URI 'iotl'
parameters, it identifies the type of traffic leg in the following
way:

o if the SIP request contains a single Route header field containing
a SIP URI with an 'iotl' parameter, that parameter identifies the
type of traffic leg;

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RFC 7549 3GPP 'iotl' May 2015

o if the SIP request contains multiple Route header fields
containing a SIP URI with an 'iotl' parameter, the 'iotl'
parameter associated with the SIP URI of the topmost Route header
field (or, if the SIP URI of the topmost Route header field does
not contain an 'iotl' parameter, the SIP URI of the Route header
field closest to the topmost) identifies the type of traffic leg;
or

o if a SIP request contains an 'iotl' parameter only in the Request-
URI SIP URI, the 'iotl' parameter identifies the type of traffic
leg.

During SIP registration [RFC3261], entities can add the 'iotl'
parameter to the SIP URI of a Path or Service-Route header field if
the entity is aware that the SIP URI will be used to indicate the end
of a specific traffic leg for initial requests for dialogs or stand-
alone requests sent on the registration path.

As defined in [RFC3261], a SIP proxy must not modify or remove URI
parameters from SIP URIs associated with other entities. This also
applies to the 'iotl' parameter.

5.2. Parameter Values

5.2.1. General

This section describes the SIP URI 'iotl' parameter values defined in
this specification.

Note that, when a request is routed between different networks, the
request might traverse one or more IBCFs (Interconnection Border
Control Functions) acting as network border entities.

5.2.2. homea-homeb

This value indicates that a SIP entity responsible for the host part
of the SIP URI associated with the parameter represents the end of a
traffic leg between the home network (originating) of the calling
user and the home network (terminating) of the called user.

In 3GPP, this traffic leg is between two S-CSCFs.

5.2.3. homeb-visitedb

This value indicates that the SIP entity addressed by the SIP URI
associated with the parameter represents the end of a traffic leg
between the home network (terminating) of the called user and the
visited network (terminating) in which the called user is located.

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RFC 7549 3GPP 'iotl' May 2015

In 3GPP, this traffic leg is between the home S-CSCF and the User
Equipment (UE) of the called user or between the Service
Centralization and Continuity Application Server (SCC AS) in the home
network of the called user and Access Transfer Control Function
(ATCF) in the visited network of the called user.

5.2.4. visiteda-homea

This value indicates that a SIP entity responsible for the host part
of the SIP URI associated with the parameter represents the end of a
traffic leg between the visited network (originating) in which the
calling user is located and the home network (originating) of the
calling user.

In 3GPP, this traffic leg is between the UE and the home S-CSCF of
the calling user or between the Proxy Call Session Control Function
(P-CSCF) in the visited network, serving the calling user and the
home S-CSCF of the calling user.

5.2.5. homea-visiteda

This value indicates that the SIP entity addressed by the SIP URI
associated with the parameter represents the end of a traffic leg
between the home network (originating) and the visited network
(originating) in which the calling user is located.

In 3GPP, this traffic leg is between the home S-CSCF of the calling
user and the Transit and Roaming Function (TRF) [TS.3GPP.24.229]
serving the calling user and exists in scenarios where the home
S-CSCF of the calling user forwards a request back to the visited
network where the UE of the calling user is located. An example of
this is when the Roaming Architecture for Voice over IMS with Local
Breakout (RAVEL) [TS.3GPP.24.229] feature is enabled.

5.2.6. visiteda-homeb

This value indicates that a SIP entity responsible for the host part
of the SIP URI associated with the parameter represents the end of a
traffic leg between the visited network (originating) of the calling
user and the home network (terminating) of the called user.

In 3GPP, this traffic leg is between the TRF [TS.3GPP.24.229] serving
the calling user and the home S-CSCF of the called user and exists in
scenarios where a request is forwarded from the visited network where
the calling user is located directly to the home S-CSCF of the called
user. An example of this is when the RAVEL [TS.3GPP.24.229] feature
is enabled.

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RFC 7549 3GPP 'iotl' May 2015

6. Syntax

6.1. General

This section defines the ABNF for the 'iotl' SIP URI parameter. The
ABNF defined in this specification is conformant to RFC 5234
[RFC5234].

This specification does not create an IANA registry for 'iotl'
parameter values. A registry should be considered if new parameter
values are defined in the future.

6.2. ABNF

The ABNF [RFC5234] grammar for this SIP URI parameter is:

uri-parameter =/ iotl-param
iotl-param = iotl-tag "=" iotl-value ["." iotl-value]
iotl-tag = "iotl"
iotl-value = "homea-homeb" / "homeb-visitedb" / "visiteda-homea"
/ "homea-visiteda" / "visiteda-homeb" / other-iotl
other-iotl = 1*iotl-char
iotl-char = alphanum / "-"
;; alphanum defined in RFC 3261

7. Security Considerations

The information in the 'iotl' parameter is used for making policy
decisions. Such policies can be related to charging and triggering
of services. In order to prevent abuse, which could cause user
billing or service failure, the parameter SHOULD only be used for
making policy decisions based on the role by nodes within the same
trust domain [RFC3325], and network boundary entities MUST NOT
forward information received from untrusted entities. In addition,
an agreement MUST exist between the operators for usage of the
roaming role information.

General security considerations for SIP are defined in [RFC3261]

8. IANA Considerations

Per this specification, IANA has added one new value to the "SIP/SIPS
URI Parameters" registry as defined in [RFC3969].

Parameter Name Predefined Values Reference
____________________________________________
iotl Yes RFC 7549

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RFC 7549 3GPP 'iotl' May 2015

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.

[RFC3327] Willis, D. and B. Hoeneisen, "Session Initiation Protocol
(SIP) Extension Header Field for Registering Non-Adjacent
Contacts", RFC 3327, DOI 10.17487/RFC3327, December 2002,
<http://www.rfc-editor.org/info/rfc3327>.

[RFC3608] Willis, D. and B. Hoeneisen, "Session Initiation Protocol
(SIP) Extension Header Field for Service Route Discovery
During Registration", RFC 3608, DOI 10.17487/RFC3608,
October 2003, <http://www.rfc-editor.org/info/rfc3608>.

[RFC3969] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)", BCP
99, RFC 3969, DOI 10.17487/RFC3969, December 2004,
<http://www.rfc-editor.org/info/rfc3969>.

[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.

[TS.3GPP.24.229]
3GPP, "Vocabulary for 3GPP Specifications", 3GPP TS 24.229
12.6.0, September 2014.

9.2. Informative References

[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
DOI 10.17487/RFC3325, November 2002,
<http://www.rfc-editor.org/info/rfc3325>.

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RFC 7549 3GPP 'iotl' May 2015

Appendix A. 3GPP Examples

A.1. General

This section contains example call flows based on 3GPP usage of the
SIP URI 'iotl' parameter.

A.2. The UE Registers via P-CSCF

The Visited Proxy (P-CSCF) adds the 'iotl' value 'homeb-visitedb' to
the Path header field of the REGISTER request to be used for
terminating routing towards Alice. The Home Proxy (S-CSCF) adds the
'iotl' value 'visiteda-homea' to the Service-Route header field to be
used for originating initial/stand-alone requests from Alice.

Visited Proxy Visited Proxy Home Proxy Home Proxy
Alice's . . . . P-CSCF . . . . . IBCF-V . . . . . IBCF-H . . . . S-CSCF
| | | | |
| REGISTER F1 | | | |
|--------------->| REGISTER F2 | | |
| |--------------->| REGISTER F3 | |
| | |--------------->| REGISTER F4 |
| | | |--------------->|
| | | | |
| | | | 200 (OK) F5 |
| | | |<---------------|
| | | 200 (OK) F6 | |
| | |<---------------| |
| | 200 (OK) F7 | | |
| |<---------------| | |
| 200 (OK) F8 | | | |
|<---------------| | | |

F1 REGISTER Alice -> P-CSCF
REGISTER sip:registrar.home1.net SIP/2.0

F2 REGISTER P-CSCF -> IBCF-V
REGISTER sip:registrar.home1.net SIP/2.0
Path: <p-cscf URI;iotl=homeb-visitedb>

F3 REGISTER IBCF-V -> IBCF-H
REGISTER sip:registrar.home1.net SIP/2.0
Path: <p-cscf URI;iotl=homeb-visitedb>

F4 REGISTER IBCF-H -> S-CSCF
REGISTER sip:registrar.home1.net SIP/2.0
Path: <p-cscf URI;iotl=homeb-visitedb>

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RFC 7549 3GPP 'iotl' May 2015

F5 200 OK S-CSCF -> IBCF-H
200 OK
Path: <p-cscf URI;iotl=homeb-visitedb>
Service-Route: <s-cscf URI;iotl=visiteda-homea>

F6 200 OK IBCF-H -> IBCF-V
200 OK
Path: <p-cscf URI;iotl=homeb-visitedb>
Service-Route: <s-cscf URI;iotl=visiteda-homea>

F7 200 OK IBCF-V -> P-CSCF
200 OK
Path: <p-cscf URI;iotl=homeb-visitedb>
Service-Route: <s-cscf URI;iotl=visiteda-homea>

F8 200 OK P-CSCF -> Alice
200 OK
Path: <p-cscf URI;iotl=homeb-visitedb>
Service-Route: <s-cscf URI;iotl=visiteda-homea>

Figure 2: The UE Registers via P-CSCF

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RFC 7549 3GPP 'iotl' May 2015

A.3. Originating IMS Call

In the originating INVITE request from Alice, the 'iotl' value
'visiteda-homea', received in the Service-Route header field during
registration, is added to the Route header field representing the
Home Proxy (S-CSCF) to indicate the traffic leg type between the
Visited Proxy (P-CSCF) and the Home Proxy (S-CSCF).

Visited Proxy Visited Proxy Home Proxy Home Proxy
Alice's . . . . P-CSCF . . . . . IBCF-V . . . . . IBCF-H . . . . S-CSCF
| | | | |
| INVITE F1 | | | |
|--------------->| INVITE F2 | | |
| |--------------->| INVITE F3 | |
| | |--------------->| INVITE F4 |
| | | |--------------->|
| | | | |
| | | | 180 F5 |
| | | 180 F6 |<---------------|
| | 180 F7 |<---------------| |
| 180 F8 |<---------------| | |
|<---------------| | | |
| | | | |

F1 INVITE Alice -> P-CSCF
INVITE sip:[email protected] SIP/2.0
Route: <p-cscf URI>,<s-cscf URI;iotl=visiteda-homea>

F2 INVITE P-CSCF -> IBCF-V
INVITE sip:[email protected] SIP/2.0
Route: <ibcf-v URI>,<s-cscf URI;iotl=visiteda-homea>

F3 INVITE IBCF-V -> IBCF-H
INVITE sip:[email protected] SIP/2.0
Route: <ibcf-h URI>,<s-cscf URI;iotl=visiteda-homea>

F4 INVITE IBCF-H -> S-CSCF
INVITE sip:[email protected] SIP/2.0
Route: <s-cscf URI;iotl=visiteda-homea>

Figure 3: Originating IP Multimedia Subsystem (IMS) Call

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RFC 7549 3GPP 'iotl' May 2015

A.4. Terminating IMS Call

In the terminating INVITE request towards Alice, the 'iotl' value
'homeb-visitedb' provided to the Home Proxy (S-CSCF) during
registration is added to the Route header field representing the
Visited Proxy (P-CSCF) to indicate the traffic leg type between the
Home Proxy (S-CSCF) and the Visited Proxy (P-CSCF).

Home Proxy Home Proxy Visited Proxy Visited Proxy
S-CSCF . . . . IBCF-H . . . . . IBCF-V . . . . . P-CSCF . . . . . Bob
| | | | |
| INVITE F1 | | | |
|--------------->| INVITE F2 | | |
| |--------------->| INVITE F3 | |
| | |--------------->| INVITE F4 |
| | | |--------------->|
| | | | |
| | | | 180 F5 |
| | | 180 F6 |<---------------|
| | 180 F7 |<---------------| |
| 180 F8 |<---------------| | |
|<---------------| | | |
| | | | |

F1 INVITE S-CSCF -> IBCF-H
INVITE sip:[email protected] SIP/2.0
Route: <ibcf-h URI>,<p-cscf-v URI;iotl=homeb-visitedb

F2 INVITE IBCF-H -> IBCF-V
INVITE sip:[email protected] SIP/2.0
Route: <ibcf-v URI>,<p-cscf-v URI;iotl=homeb-visitedb

F3 INVITE IBCF-V -> P-CSCF
INVITE sip:[email protected] SIP/2.0
Route: <p-cscf-v URI;iotl=homeb-visitedb

F4 INVITE P-CSCF -> Bob
INVITE sip:[email protected] SIP/2.0

Figure 4: Terminating IMS Call

Holmberg, et al. Standards Track [Page 15]

RFC 7549 3GPP 'iotl' May 2015

A.5. Call between Originating Home and Terminating Home Network

The S-CSCF of the originating home network adds the 'iotl' value
'homea-homeb' in the Request-URI of the INVITE, sent towards the
S-CSCF of the terminating network to indicate the traffic leg type
between the S-CSCFs.

Home-A Proxy Home-A Proxy Home-B Proxy Home-B Proxy Home-B Proxy
S-CSCF-A . . . . IBCF-A . . . . .IBCF-B . . . . .I-CSCF-B . . .S-CSCF-B
| | | | |
| INVITE F1 | | | |
|--------------->| INVITE F2 | | |
| |--------------->| INVITE F3 | |
| | |--------------->| INVITE F4 |
| | | |--------------->|
| | | | |
| | | | 180 F5 |
| | | 180 F6 |<---------------|
| | 180 F7 |<---------------| |
| 180 F8 |<---------------| | |
|<---------------| | | |
| | | | |

F1 INVITE S-CSCF-A -> IBCF-A
INVITE sip:[email protected];iotl=homea-homeb SIP/2.0

F2 INVITE IBCF-a -> IBCF-B
INVITE sip:[email protected];iotl=homea-homeb SIP/2.0

F3 INVITE IBCF-B -> I-CSCF-B
INVITE sip:[email protected];iotl=homea-homeb SIP/2.0

F4 INVITE I-CSCF-B -> S-CSCF-B
INVITE sip:[email protected];iotl=homea-homeb SIP/2.0

Figure 5: Call between Originating Home and Terminating Home Network

Holmberg, et al. Standards Track [Page 16]

RFC 7549 3GPP 'iotl' May 2015

Acknowledgements

The authors wish to thank everyone in the 3GPP community that gave
comments on the initial version of this document and contributed with
comments and suggestions during the work. A special thanks to Paul
Kyziwat, Dale Worley, and Michael Hammer. Robert Sparks performed
the Gen-ART review of the document.

Authors' Addresses

Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland

EMail: [email protected]

Jan Holm
Ericsson
Kistavagen 25
Stockholm16480
Sweden

EMail: [email protected]

Roland Jesske
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
Darmstadt 64307
Germany

Phone: +4961515812766
EMail: [email protected]

Martin Dolly
AT&T
718 Clairmore Ave
Lanoka Harbor 08734
United States

EMail: [email protected]

Holmberg, et al. Standards Track [Page 17]