Liaison statement
LS on Codec Discussion in IETF

Submission date 2009-08-24
From 3GPP (Susanna Kooistra)
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 item. 
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 IETF.  
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