Re: [MMUSIC] Last Call: <draft-ietf-mmusic-rfc4566bis-34.txt> (SDP: Session Description Protocol) to Proposed Standard

Magnus Westerlund <> Fri, 12 April 2019 08:59 UTC

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From: Magnus Westerlund <>
To: "Roni Even (A)" <>, "" <>
CC: "" <>, "" <>, "" <>
Thread-Topic: [MMUSIC] Last Call: <draft-ietf-mmusic-rfc4566bis-34.txt> (SDP: Session Description Protocol) to Proposed Standard
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Subject: Re: [MMUSIC] Last Call: <draft-ietf-mmusic-rfc4566bis-34.txt> (SDP: Session Description Protocol) to Proposed Standard
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To be clear, I am not proposing that any existing attribute would be forced to suddenly accept UTF-8 strings with no charset restriction. Simply that new attribute's values can be defined to be UTF-8 in general. I think the important distinction here is that a parser must be ready to accept any UTF-8 character as the sender can't know if a particular charset limitation applies to a specific consumer. However, in form I don't see a problem of the SDP itself informing the consumer that there is a charset limitation applied in this document.

My interpretation of the current situation is that it we hesitate to use UTF-8 fields due to the uncertainty in the requirements on consumers of SDP.


Magnus Westerlund
(As Individual)

On 2019-04-11 12:05, Roni Even (A) wrote:
Hi Magnus,
I think it will affect the IANA registries where values may be shared with non SDP attribute. For example the sub-protocol in the IANA WebSocket Subprotocol name registry

Roni Even

From: mmusic [] On Behalf Of Magnus Westerlund
Sent: Thursday, April 11, 2019 11:14 AM
Subject: Re: [MMUSIC] Last Call: <draft-ietf-mmusic-rfc4566bis-34.txt> (SDP: Session Description Protocol) to Proposed Standard

MMUSIC WG, Document Editors

In the processing of draft-ietf-mmusic-data-channel-sdpneg-25 an interesting question arose regarding text strings in SDP attribute values.

Currently the document says:

4.5.  Internationalization

   The SDP specification recommends the use of the ISO 10646 character

   set in the UTF-8 encoding [RFC3629] to allow many different languages

   to be represented.  However, to assist in compact representations,

   SDP also allows other character sets such as ISO 8859-1 to be used

   when desired.  Internationalization only applies to free-text sub-

   fields (session name and background information), and not to SDP as a


If one like to include UTF-8 field for attributes it would be good if

the requirement would be clear going forward that there is an expectancy

that at least parser can process any UTF-8 strings that may occur in any


That would allow future SDP field values to use UTF-8 strings without risks

and simplify processing. Like in the case of the data channel SDP mapping

where the extra step of encoding lable characters not visually safe as escaped

characters could be avoided.

Does anyone have input if making such a change would have significant impact on

the interoperability?



On 2019-03-22 15:46, The IESG wrote:

The IESG has received a request from the Multiparty Multimedia Session

Control WG (mmusic) to consider the following document: - 'SDP: Session

Description Protocol'

  <draft-ietf-mmusic-rfc4566bis-34.txt> as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final

comments on this action. Please send substantive comments to the<> mailing lists by 2019-04-12. Exceptionally, comments may be

sent to<> instead. In either case, please retain the beginning of

the Subject line to allow automated sorting.


   This memo defines the Session Description Protocol (SDP).  SDP is

   intended for describing multimedia sessions for the purposes of

   session announcement, session invitation, and other forms of

   multimedia session initiation.  This document obsoletes RFC 4566.

The file can be obtained via

IESG discussion can be tracked via

No IPR declarations have been submitted directly on this I-D.


mmusic mailing list<>


Magnus Westerlund


Network Architecture & Protocols, Ericsson Research


Ericsson AB                 | Phone  +46 10 7148287

Torshamnsgatan 23           | Mobile +46 73 0949079

SE-164 80 Stockholm, Sweden | mailto:<>



Magnus Westerlund

Network Architecture & Protocols, Ericsson Research
Ericsson AB                 | Phone  +46 10 7148287
Torshamnsgatan 23           | Mobile +46 73 0949079
SE-164 80 Stockholm, Sweden | mailto:<>