Liaison statement
LS on Codec Discussion in IETF

State Posted
Posted Date 2009-08-24
From Group 3GPP
From Contact Susanna Kooistra
To Groups IESG, RAI
To Contacts
Purpose For action
Deadline 2009-11-13 Action Taken
Attachments (None)
3GPP TSG-SA WG4 Meeting #55 	S4-090767
Stockholm, Sweden, August 17-21, 2009
Title:	LS on Codec Discussion in IETF

Source:	3GPP SA WG4

Contact Person:
        	Name: Stefan Bruhn
 	E-mail Address: 

Attachments:	none

1. Abstract
3GPP SA WG4 (SA4) is aware of the ongoing discussion within IETF about
creating a new working group with the objective of standardizing new speech
codecs. The discussion is taking place via an IETF mailing list and there was
also a wideband audio codec BOF at IETF#75 essentially addressing that same
SA4 would like to provide some clarifications on possible misconceptions about
the capabilities of 3GPP speech codecs expressed during the discussion. In
addition, SA4 would like to provide an update of the ongoing codec
standardization work in SA4 and invite IETF to contribute to this process in
order to make use of the codec standardization expertise of SA4. SA4 would
further like to express concerns about the idea that IETF would open its own
codec standardization working group. 
2. 3GPP codecs
3GPP has a long history and extensive experience in the standardization of
speech and audio codecs. SA 4 is the permanent codec expert group that, among
other tasks, is responsible for 3GPP codec standardization and related
aspects, including requirement definition, test and processing plan design,
testing, codec selection, codec characterization and maintenance, etc. 3GPP
standardized a multitude of speech and audio codecs for both conversational
and streaming applications. Among them are AMR and AMR-WB that have a
mandatory status in 3GPP specifications. AMR and AMR-WB were originally
standardized for CS GSM voice service. However, the performance of these
codecs was carefully characterized even for PS transmissions and found
suitable for 3GPP VoIP applications over 3GPP radio accesses which are very
demanding both in terms of the limited and costly transmission resources and
the non-perfect transmission conditions of mobile radio channels. 3GPP
technical specifications 26.114 and 26.235 mandate the use of these codecs for
VoIP transmissions that are part of the 3GPP multimedia telephony service for
IMS and, respectively, 3GPP PS conversational multimedia services. In
particular 3GPP TS 26.114 specifies the powerful instrument of codec rate
adaptation that builds upon the multi-rate property of AMR and, respectively
AMR-WB, which together with redundancy transmission allows for extremely
robust VoIP service operation under severe packet loss conditions. Also worth
noting is that 3GPP fully specifies their codecs with open encoder and decoder
source code (both fixed-point and floating-point), the open source code is
publicly available for download, and so are all 3GPP specifications. TS 26.114
specifies the full VoIP framework including delay jitter buffer, packet loss
handling, etc. 
3GPP regards their AMR and AMR-WB codecs as efficient “internet” codecs that
are suitable for VoIP applications. 
3. Licensing aspects
The licensing of possible IPRs that are part of 3GPP specifications complies
with the IPR obligation valid for all 3GPP members, and is very similar to the
rules in IETF and results in FRAND (Fair Reasonable and Non Discriminatory)
licensing terms which do not exclude royalty-free licensing. 
4. Ongoing codec work in 3GPP
At present SA4 has no active speech or audio codec development work item.
However, there is a study item ongoing called Enhanced Voice Service for the
Evolved Packet System (EPS) that intends to identify potential new codec
requirements for new use cases in the environment of the EPS. As a result SA4
may start a new standardization work with the target to develop and
standardize a new codec meeting these requirements. SA4 would like to invite
interested parties in IETF to contribute to the definition of requirements
such that a potential future new codec for EPS could also address IETF needs.
It will be possible to accomodate requirements brought forward by IETF to the
extent they also meet 3GPP needs.  
5. Concerns
SA4 would further like to express concern about ideas to open a working group
in IETF intending to standardize a new speech or audio codec. SA4 believes
that codec standardizations for all media including video are properly
addressed in the established codec expert groups in 3GPP, ITU-T and MPEG and
that the codecs developed by these groups address the needs for efficient
media compression in the various conceivable systems and application contexts.
There may always emerge new requirements for new systems or applications or
changing user expectations, however, typically the existing codec expert
groups are open to requests to address such requirements in their work. SA4
has the opinion that such new requirements possibly leading to new codecs are
more efficiently handled in these groups than in a potential new group in
SA4 would also like to point out that there is a well established
collaboration between IETF and codec expert groups in e.g. 3GPP, ITU-T and
MPEG. As an example, RTP payload formats or network aspects are typically
defined in IETF and referred to in 3GPP specifications, while codec
standardizations are done by the codec groups outside IETF. The creation of a
new codec group in IETF could be viewed as redundant since it would create
overlap of working areas and ultimately be counterproductive for our
established collaboration.
SA4 also sees the risk that opening a new codec standardization and a new
codec standardization group could lead to proliferation of coding formats with
undesirable consequences like interoperability issues among different systems
and increased costs both for implementation and equipment, and quality
degradations due to the need for transcoding between these formats. Also,
standardizing codecs without addressing the specific requirements of existing
transmissions systems (and 3GPP systems in particular for the case of 3GPP)
bears the risk that such codecs would be unattractive since not optimal for
such systems.
Finally, SA4 is concerned by the fact that starting a new codec expert group
in IETF would either not attract the right expertise to make the resulting
work relevant or result in dilution of codec expertise in the existing codec
groups. A participation of all codec experts in all codec expert groups is
necessary to ensure that codecs are well designed and thought through. 
6. Conclusion
SA4 would be happy to provide more detailed information to IETF about its
speech and audio codec specifications. 3GPP SA4 invites IETF to an open dialog
about their specific codec requirements and offers its codec expertise to
serve the needs of the internet community.
7. Date of Upcoming TSG-SA WG4 Meetings:

SA4#56	09 – 13 November 2009, Sophia Antipolis, France