Internet DRAFT - draft-schwarz-mmusic-sdp-for-gw
draft-schwarz-mmusic-sdp-for-gw
WG MMUSIC Albrecht Schwarz (ed.)
Internet Draft NOKIA
Intended status: Standards track Christian Groves
Expires: November 2016 Huawei
May 2, 2016
SDP codepoints for gateway control
draft-schwarz-mmusic-sdp-for-gw-05.txt
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Abstract
SDP is used in many signalling protocols at call control level (such
as SAP, SIP, BICC), bearer control level (such as RTSP, IPBCP) and
gateway control level (such as H.248/MEGACO, MGCP). Scope of this
RFC is related to gateway control specific SDP usage. Gateway
control protocols do NOT usually define and introduce any new SDP
parameters, however, gateway control protocols need specific SDP
parameter values in addition to those defined at call or bearer
control level. Such SDP codepoints are collected by this RFC with
the purpose of registration with IANA.
Table of Contents
1. Introduction...................................................3
1.1. Motivation................................................3
1.2. Scope.....................................................3
2. Conventions used in this document..............................4
2.1. Prescriptive language.....................................4
2.2. Terminology used..........................................4
2.3. Abbreviations used........................................5
3. Security Considerations........................................6
4. IANA Considerations............................................6
4.1. Registration aspects of "m="-line <proto> element.........6
4.2. SDP codepoints related to "m="-line <proto> element.......7
5. References.....................................................7
5.1. Normative References......................................7
5.2. Informative References....................................9
6. Acknowledgments................................................9
Appendix A. Background - Gateway control protocols in scope...11
A.1. Introduction............................................11
A.2. Background - SDP usage in gateway control protocol(s)...11
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A.3. Motivation - Why gateway control specific SDP?..........12
Appendix B. Decomposed gateways - usage of SDP................13
B.1. SDP for bearer type indication..........................13
B.2. SDP for controlling the mode of operation of a gateway..13
Appendix C. SDP codepoints related to "c="-line...............13
C.1. SDP codepoints related to "c="-line <addrtype> element..13
Appendix D. SDP codepoints related to "m="-line...............13
D.1. SDP codepoints related to "m="-line <proto> element.....13
D.1.1. Purpose...........................................13
D.1.2. Application-agnostic indications..................14
D.1.3. Protocol individual indications...................14
D.1.4. Gateway specific SDP codepoints...................15
D.2. SDP codepoints related to "m="-line <type> element......15
Appendix E. SDP codepoints related to "a="-lines (SDP attrib.)15
E.1. SDP attribute "ITU-T H.248 package".....................15
7. CHANGE LOG....................................................16
7.1. Initial draft name "draft-schwarz-sdp-for-gw"............16
7.1.1. Changes against "-00"...............................16
7.1.2. Changes against "-01"...............................16
7.1.3. Changes against "-02"...............................16
7.2. WG draft name "draft-schwarz-mmusic-sdp-for-gw"..........16
7.2.1. Version "-00".......................................16
7.2.2. Changes against "-00"...............................16
7.2.3. Changes against "-01"...............................17
7.2.4. Changes against "-02"...............................17
7.2.5. Changes against "-03"...............................17
7.2.6. Changes against "-04"...............................17
1. Introduction
1.1. Motivation
There is a gap concerning the registration of some specific SDP
codepoints, which are primarily required for gateway control.
Detailed background information is summarized in Appendix A.
1.2. Scope
The purpose of this document is to collect SDP codepoints, which are
specific to gateway control protocols in order to identify any
additional codepoints that require reqistration with IANA. The focus
is (but not limited to) on SDP codepoints related to the SDP "m="-
line.
These SDP codepoints for gateway control are defined by ITU-T in the
ITU-T H.248.x-series of Recommendations [ITU-T H.248.x]. The
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individual "H.248.x" documents define specific gateway control
applications.
Appendices C, D and E provide SDP line specific considerations
("c="-, "m="- and "a="-lines) from gateway perspective.
Clause 4 on "IANA consideration" addresses the SDP information as in
scope of this document ("which is inter alia the result of such
gateway control aspect as discussed in above referred Appendices).
2. Conventions used in this document
2.1. Prescriptive language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
2.2. Terminology used
APPLICATION:
This term, when used in the context of "application-agnostic" or
"application-aware", refers to the IP application protocol on top
of a "L4 transport protocol" (e.g., "TCP", "UDP") with or without
a "transport security protocol" (e.g., "TLS", "DTLS").
NOTE - The notion of application includes (if present) also the
associated protocol layer of "application level framing protocol"
(e.g., "RTP").
BORDER GATEWAY:
A H.248 packet-to-packet (media) gateway, such as an IP-to-IP
gateway, with scope on two-party communication services.
NOTE: not to be confused with border gateway entities in the
native IP router space, such as a border router with support of
border gateway protocols (such as BGP, e.g. [RFC1163]).
CODEPOINT:
The combination of a "signalling parameter" plus assigned "value"
in protocol engineering. The "value" represents a codepoint (or
code position) in the code space.
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X-AGNOSTIC / X-AWARE:
Placeholder 'X' denotes a protocol layer, a protocol stack or an
abstracted model such as "application", "media", "transport", etc.
This term indicates whether the controlled entity (here: H.248 MG)
is aware or not about information concerning 'X'.
2.3. Abbreviations used
B2BUA Back-to-Back User Agent
BGF Bearer Gateway Function
BGP Border Gateway Protocol
BICC Bearer Independent Call Control
DTLS Datagram Transport Layer Security
GCP Gateway Control Protocol
IPBCP (ITU-T) IP Bearer Control Protocol
ITU-T International Telecommunication Union Telecommunication
Standardization Sector
IWF Interworking Function
MEGACO Media Gateway Control
MG (H.248) Media Gateway
MGC (H.248) Media Gateway Controller
RTP Real-time Transport Protocol
RTSP Real-Time Streaming Protocol
SAP Session Announcement Protocol
SCTP Stream Control Transmission Protocol
SDP Session Description Protocol
SIP Session Initiation Protocol
TCP Transmission Control Protocol
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TLS Transport Layer Security
UA User Agent
UDP User Datagram Protocol
3. Security Considerations
This RFC is related to the registration of protocol codepoints, thus
outside any security aspects.
4. IANA Considerations
4.1. Registration aspects of "m="-line <proto> element
The usual registration process is described in Section 8.2.2 of
[RFC4566]. Usage of such SDP codepoints for gateway control is
specific (as outlined in Appendix B and section D.1), therefore
leads to following considerations related to the registration
process:
a) [RFC4566], 8.2.2: The "proto" field describes the transport
protocol used.
Comment from gateway control: the notion of "transport protocol"
translates to either single protocol layer or protocol stack segment
(see section D.1).
b) [RFC4566], 8.2.2: New transport protocols SHOULD be registered
with IANA. Registrations MUST reference an RFC describing the
protocol.
Comment from gateway control: there are not any new IP transport
protocols defined by ITU-T for gateway control, hence, there will be
not any correspondent RFC. There will be rather a reference to an
ITU-T document which specifies the usage of that SDP codepoint in
the application-specific context of gateway control.
c) [RFC4566], 8.2.2: Registrations MUST also define the rules by
which their "fmt" namespace is managed.
Comment from gateway control: not applicable because there are not
any new IP transport protocols defined by ITU-T for gateway control,
hence existing rules are used.
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4.2. SDP codepoints related to "m="-line <proto> element
This document updates the "Session Description Protocol (SDP)
Parameters" registry as specified in Section 8.2.2 of [RFC4566].
Specifically, it adds the values in Table 1 to the table for the SDP
"proto" field registry.
+-------+----------------------+-------------------------+
| Type | SDP Name | Reference |
+-------+----------------------+-------------------------+
| proto | "TLS" | [ITU-T H.248.90] |
+-------+----------------------+-------------------------+
| proto | "TCP/TLS" | [ITU-T H.248.90] Note 1 |
+-------+----------------------+-------------------------+
| proto | "SCTP/TLS" | [ITU-T H.248.90] |
+-------+----------------------+-------------------------+
| proto | "DTLS" | [ITU-T H.248.93] |
+-------+----------------------+-------------------------+
| proto | "UDP/DTLS" | [ITU-T H.248.93] |
+-------+----------------------+-------------------------+
| proto | "DCCP/DTLS" | [ITU-T H.248.93] |
+-------+----------------------+-------------------------+
| proto | "SCTP" | [ITU-T H.248.97] Note2 |
+-------+----------------------+-------------------------+
| proto | "SCTP/DTLS" | [ITU-T H.248.97] Note2 |
+-------+----------------------+-------------------------+
| proto | "DTLS/SCTP" | [ITU-T H.248.97] Note2 |
+-------+----------------------+-------------------------+
Table 1: SDP "proto" field values
Note 1 - Codepoint "TCP/TLS" already registered [RFC4572].
Note 2 - Table entry may be deleted again dependent on progress of
IETF draft "draft-ietf-mmusic-sctp-sdp"
(http://tools.ietf.org/wg/mmusic/draft-ietf-mmusic-sctp-sdp/).
5. References
5.1. Normative References
[RFC2119] RFC 2119 (03/1997), "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14.
[RFC2885] RFC 2885 (08/2000), "Megaco Protocol version 0.8".
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[RFC3015] RFC 3015 (11/2000), "Megaco Protocol Version 1.0".
[RFC3525] RFC 3525 (06/2003), "Gateway Control Protocol Version 1".
[RFC4566] RFC 4566 (07/2006), "SDP: Session Description Protocol".
[RFC4572] RFC 4572 (07/2006), "Connection-Oriented Media Transport
over the Transport Layer Security (TLS) Protocol in the
Session Description Protocol (SDP)".
[RFC5125] RFC 5125 (02/2008), "Reclassification of RFC 3525 to
Historic".
[ITU-T H.248.x] The ITU-T H.248.x-series of Recommendations
(Gateway Control Protocol).
Website: http://www.itu.int/rec/T-REC-H/e
[ITU-T H.248.1] Recommendation ITU-T H.248.1 (03/2013), "Gateway
control protocol: Version 3".
Free copy via: http://www.itu.int/rec/T-REC-H.248.1-
201303-I/en
[ITU-T H.248.15] Recommendation ITU-T H.248.15 (03/2013), "Gateway
control protocol: SDP ITU-T H.248 package attribute".
Free copy via: http://www.itu.int/rec/T-REC-H.248.15-
201303-I/en
[ITU-T H.248.39] Recommendation ITU-T H.248.39 (10/2014), "Gateway
control protocol: H.248 SDP parameter identification and
wildcarding".
Free copy via: http://www.itu.int/rec/T-REC-H.248.39/en
[ITU-T H.248.49] Recommendation ITU-T H.248.49 (08/2007), "Gateway
control protocol: Session description protocol RFC and
capabilities packages".
Free copy via: http://www.itu.int/rec/T-REC-H.248.49/en
[ITU-T H.248.80] Recommendation ITU-T H.248.80 (01/2014), "Usage of
the revised SDP offer / answer model with H.248".
Free copy via: http://www.itu.int/rec/T-REC-H.248.80/en
[ITU-T H.248.90] Recommendation ITU-T H.248.90 (10/2014), "Gateway
control protocol: H.248 packages for control of transport
security using TLS".
Free copy via: http://www.itu.int/rec/T-REC-H.248.90/en
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[ITU-T H.248.92] Recommendation ITU-T H.248.92 (10/2014), "Gateway
control protocol: Stream endpoint interlinkage package".
Free copy via: http://www.itu.int/rec/T-REC-H.248.92/en
[ITU-T H.248.93] Recommendation ITU-T H.248.93 (10/2014), "Gateway
control protocol: H.248 packages for control of transport
security using DTLS".
Free copy via: http://www.itu.int/rec/T-REC-H.248.93/en
[ITU-T H.248.97] Recommendation ITU-T H.248.97 (11/2015), "Gateway
control protocol: H.248 support for control of SCTP bearer
connections".
Free copy via: http://www.itu.int/rec/T-REC-H.248.97-
201511-P/en
[ITU-T H.Sup14] Supplement ITU-T H.Sup14 (10/2015), "Gateway
Control Protocol: ITU-T H.248.x-series - SDP codepoints
for gateway control - Release 2".
Free copy via: http://www.itu.int/rec/T-REC-H.Sup14-
201510-I/en
[ETSI 183046] ETSI TR 183 046 V3.3.1 (2009-08), "Telecommunications
and Internet converged Services and Protocols for Advanced
Networking (TISPAN); SDP Interworking between Call/Session
Control Protocols (SIP/SDP, RTSP/SDP; etc.) and the
Gateway Control Protocol (H.248/SDP)".
[ETSI 183068] ETSI TR 183 068 V3.1.1 (2009-08), "Telecommunications
and Internet converged Services and Protocols for Advanced
Networking (TISPAN); Guidelines on using Ia H.248 profile
for control of Border Gateway Functions (BGF); Border
Gateway Guidelines".
5.2. Informative References
[RFC1163] RFC 1163 (06/1990), "A Border Gateway Protocol (BGP)".
[RFC7092] RFC 7092 (12/2013), "A Taxonomy of Session Initiation
Protocol (SIP) Back-to-Back User Agents".
6. Acknowledgments
The work origins in ITU-T Study Group 16 Question 3 "Multimedia
gateway control architectures and protocols" in cooperation with
3GPP CT4 (Technical Specification Group "Core Network and
Terminals", Working Group 4). The authors like to thank all
delegates for comments, review and contributions.
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Authors' Addresses
Dr. Albrecht Schwarz (editor)
NOKIA
Lorenzstrasse 10
D-70435 Stuttgart
GERMANY
Email: Albrecht.Schwarz@nokia.com
Christian Groves
Huawei
Melbourne
AUSTRALIA
Email: Christian.Groves@nteczone.com
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Appendix A. Background - Gateway control protocols in scope
A.1. Introduction
Gateway control protocols are required for decomposed network
elements which separate media plane and signalling plane related
network functions (see e.g., [RFC7092] concerning a decomposed B2BUA
with a SIP specific signalling B2BUA plus a media plane B2BUA
entity).
The gateway control interface between the controlling entity (known
as media gateway controller, MGC) and controlled entity (known as
media gateway) follows a disclosed, open, standardized protocol.
This RFC considers such gateway control protocols which use the SDP
[RFC4566] as embedded signalling for media-related characteristics.
This RFC focuses on following gateway control protocol, known as
"H.248", as standardized within the ITU-T H.248.x-series of
Recommendations [ITU-T H.248.x]. The core protocol is defined by
H.248.1 [ITU-T H.248.1], which actually originates in the IETF,
known as MEGACO (media gateway control):
IETF history:
o Closed working group "MEGACO" (since technology was transferred
to ITU-T);
o IETF MEGACO protocol versions: see [RFC2885], [RFC3015],
[RFC3525];
o Transfer IETF to ITU-T: "Reclassification of RFC 3525 to
Historic", [RFC5125].
A.2. Background - SDP usage in gateway control protocol(s)
Gateway control protocol H.248 supports two message encoding modes:
binary and text. Gateway deployments in IP network environments use
primarily H.248 text encoding mode in order to benefit from SDP
usage at call control signalling level. For instance, the SIP level
SDP information is mapped by the H.248 MGC entity to SDP information
as used in H.248 gateway control signaling. The following list
indicates areas where SDP is used in H.248 gateway control:
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o SDP in H.248: clause 7.1.8 "Local and Remote Descriptors" and
particularly clause 7.1.8.1.1.2 "Summary - ITU-T H.248 usage of
SDP" in [ITU-T H.248.1];
o Wildcarding in SDP: "H.248 SDP parameter identification and
wildcarding" [ITU-T H.248.39];
o SDP versioning: "SDP RFC and capabilities packages", [ITU-T
H.248.49];
o SDP profiling: the allowed SDP elements and codespace could be
limited by H.248 profile specifications, see "ITU-T H.248 profile
definition template" in Appendix III/[ITU-T H.248.1] (profile
template clauses 6.15 and 6.16 are related to SDP);
o SDP offer/answer models: "Usage of the revised SDP offer / answer
model with H.248", [ITU-T H.248.80];
o SDP mapping between call control and H.248: "SDP Interworking
between Call/Session Control Protocols (SIP/SDP, RTSP/SDP; etc.)
and the Gateway Control Protocol (H.248/SDP)" [ETSI 183046].
o SDP for mode control in border gateways: see Annex G
"Illustration of BGF modes of operation" and particularily Annex
G.2 "BGF modes driven by particular SDP lines" [ETSI 183068].
A.3. Motivation - Why gateway control specific SDP?
Gateway control protocol (GCP) specific SDP codepoints are primarily
required in two areas:
1. SDP for bearer type indication
2. SDP for controlling the mode of operation of a gateway
Clause 3 provides detailed background and [ETSI 183068], Annex G
illustrates several examples in the area of IP-to-IP gateways (also
known as border gateways).
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Appendix B. Decomposed gateways - usage of SDP
Gateway control protocol (GCP) specific SDP codepoints are primarily
required in two areas:
B.1. SDP for bearer type indication
The bearer connection endpoint at media gateway level needs to be
specified concerning the required bearer protocol or protocol stack
segment respectively. This relates essentially to the SDP "m="line
<proto> element. However, media gateways require in addition so
called "agnostic" type of SDP codepoints, which is in contrast to
the so called application-aware, transport protocol type aware SDP
codepoints used by communication endpoints (such as a SIP UA located
in an IP host entity).
B.2. SDP for controlling the mode of operation of a gateway
A media gateway (MG) typically internally interconnects multiple
bearer connection endpoints. A plethora of interworking functions
(IWF) may be supported in the media plane by the MG. The type of IWF
is known as mode of operation. The mode of operation is typically
controlled via SDP. The semantic is actually the result of the SDP
information of ALL involved bearer connection endpoints (in H.248:
terminations / stream endpoints). The operation may be traffic
directions specific.
Appendix C. SDP codepoints related to "c="-line
C.1. SDP codepoints related to "c="-line <addrtype> element
H.248 may utilise the existing <addrtype> elements as defined in the
IANA registry "http://www.iana.org/assignments/sdp-parameters/sdp-
parameters.xhtml#sdp-parameters-5". No additional registrations are
required.
Appendix D. SDP codepoints related to "m="-line
D.1. SDP codepoints related to "m="-line <proto> element
D.1.1. Purpose
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The SDP "m=" line <proto> element allows the indication of
a) a single protocol (layer) or
b) a protocol stack (i.e., multiple, consecutive protocol layers).
The protocol stack based value is inherently ambiguous in case of
the requirement in indicating a particular protocol layer out of the
stack. This is a well-known issue of this element.
Example: <proto> = "x/y/z", i.e., indicates a protocol stack segment
with protocol layering "z-over-y-over-x". The MGC wants to trigger a
bearer control procedure for protocol 'y' at MG level and uses such
an SDP codepoint. However, there are also the options of bearer
control procedures at protocol layers 'x' or 'z'. Consequently, the
SDP codepoint "x/y/z" can't be used because semantically ambigous.
What would be required here are separate SDP codepoints "x", "y" and
"z".
The example illustrates that there are not any new IP transport
protocols invented for gateway control.
D.1.2. Application-agnostic indications
Application-agnostic, - or X-agnostic in general -, indications are
typically realized by using character "-" instead of a concrete
value in SDP fields (see [ITU-T H.248.39]). Such an SDP value is
basically out of scope of IANA registration.
D.1.3. Protocol individual indications
There is the so-called "interlinkage" capability defined for gateway
control, see [ITU-T H.248.92]. This functionality allows to
interlink connection/session oriented transport protocol endpoints
within a media gateway. If two transport protocol endpoints are
interlinked the establishment and/or release of a connection/session
at the source transport protocol endpoint will trigger an MG-
autonomous establishment and/or release of the interlinked transport
protocol endpoint.
The configuration of the gateway internal interlinkage topology is
defined in section 7.1.1/[ITU-T H.248.92] and uses the SDP <proto>
element for the indication of interlinked protocol layers. However,
the SDP codepoints are limited to single protocol layers only.
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Reference: [ITU-T H.248.92] section 7.1.1: "Value proto is as per
clause 9/[IETF RFC 4566], with the restriction that a single
transport protocol value should be selected when the IANA proto
codepoint represents a protocol stack segment (format e.g. "x/y/z"),
rather than a single individual protocol layer (format "x")."
D.1.4. Gateway specific SDP codepoints
See [ITU-T H.Sup14].
D.2. SDP codepoints related to "m="-line <type> element
No specific from H.248 perspective.
Appendix E. SDP codepoints related to "a="-lines (SDP attrib.)
E.1. SDP attribute "ITU-T H.248 package"
ITU-T Recommendation [ITU-T H.248.15] defines an ITU-T specific
extension for SDP. The SDP attribute "a=h248item:" allows for the
carriage of general ITU-T H.248 properties in the local and remote
descriptor in the textual ITU-T H.248 protocol encoding mode. This
attribute has already been registered with IANA (see:
http://www.iana.org/assignments/sdp-parameters/sdp-
parameters.xhtml#sdp-parameters-5).
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7. CHANGE LOG
7.1. Initial draft name "draft-schwarz-sdp-for-gw"
7.1.1. Changes against "-00"
o Replace Draft ITU-T Recommandation work item name by "H.248.x"
number (H.248.90 (TLS), H.248.92 (SEPLINK))
o Correction of clause 5: addition of ITU-T specific SDP attribute
"a=h248item:"
o Editorial: update of abbreviation list
7.1.2. Changes against "-01"
o addition of SDP "c=" line information
o complementary information on registration status (clauses 4.1 and
6.1)
o Missing reference (RFC 4572) to codepoint "TCP/TLS" added.
o Editorial: review & update of abbreviation list
7.1.3. Changes against "-02"
o correction of draft name from "draft-schwarz-sdp-for-gw-..." to
"draft-schwarz-mmusic-sdp-for-gw-...", i.e., a restart with
version number 00 required
o update of references
7.2. WG draft name "draft-schwarz-mmusic-sdp-for-gw"
7.2.1. Version "-00"
The June 2014 draft.
7.2.2. Changes against "-00"
o clause 1.4 'scope': addition of complementary information
o clause 5.1.1: there was still information solicited, which is
added here
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o clause 5.1.3: there was still information solicited, dependent on
progress of H.248.92, which is added here
o clause 8.1: clarification of registration aspects related to RFC
4566
o editorials: update of references due to recent approval of
Recommendations (rev.) H.248.39, H.248.90, H.248.92 and H.248.93,
and Supplement H.Sup14 by ITU-T.
7.2.3. Changes against "-01"
o nearly all informative text of the main body was moved in
Appendices in order to narrow and limit the normative text on the
prime subject of this draft, thus, "-02" does provide only
editorial updates, - in more detail:
new Appendix A = old sections 1.1, 1.2 and 1.3;
new Appendix B = old section 3;
new Appendix C = old section 4;
new Appendix D = old section 5;
new Appendix E = old section 6.
7.2.4. Changes against "-02"
o editorial error corrected: section 1.1 was splitted again in
sections 1.1 "Motivation" and "Scope".
7.2.5. Changes against "-03"
o Reference update I: ITU-T H.248.SCTP => H.248.97
o Reference update II: ITU-T H.Sup14 Release 1 => H.Sup14 Release 2
7.2.6. Changes against "-04"
o missing URLs inserted in two ITU-T references
Schwarz Expires November 2, 2016 [Page 17]
