Liaison statement
Response to Liaison Statement to IETF MMUSIC concerning 'Improved end-to-end QoS Enhancements for MTSI'

State Posted
Posted Date 2016-06-10
From Group mmusic
From Contact Bo Burman
To Contacts
CcFlemming Andreasen
Ben Campbell
Alissa Cooper
Bo Burman
Alexey Melnikov
Multiparty Multimedia Session Control Discussion List
Response Contact Flemming Andreasen
Bo Burman
Purpose In response
Attachments (None)
Liaisons referred by this one LS on Improved end-to-end QoS Enhancements for MTSI
IETF MMUSIC Working Group thanks 3GPP TSG SA WG4 for informing about their work in <>.

It is understandable that SDP attribute-based approaches, such as solutions D and F in 3GPP TR 26.924, are being considered for further development. Of the alternatives proposed, use of an SDP attribute (i.e., an "a=" line) is to be preferred over use of further extensions to SDP "b=" lines. Attributes are the natural extension point for SDP, and offer flexibility that is not present in "b=" lines. This is compatible with the solutions proposed by 3GPP TR 26.924.

Whether any new attribute is signalled per RTP payload type, as in solution D, or per "m=" line, as in solution F, is a more complex issue. Neither seems unreasonable on the surface, and a QoS attribute per "m=" line is natural if each "m=" line represents a single media sent on a single port, with the SDP offer/answer exchange being used only to select what encoding is used for that media.

However, with the definition and widespread adoption of the SDP BUNDLE extension <>, the assumption that a single "m=" line represents a single type of media being sent on a single UDP port is becoming less tenable.

IETF MMUSIC urges 3GPP TSG SA4 to consider the impact of the SDP BUNDLE extension on their choice, and to further coordinate with IETF to ensure that whatever is developed is compatible with SDP sessions where multiple "m=" lines, representing several different types of media, are sent on a single UDP port.

Next IETF meetings:
- IETF 96, July 17-22, 2016, Berlin, Germany
- IETF 97, November 13-18, 2016, Seoul, South Korea

Bo Burman
MMUSIC WG co-chair