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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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   This Internet-Draft will expire on November 2, 2016.

Copyright Notice

   Copyright (c) 2016 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
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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













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