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 gonzalo.camarillo@ericsson.com
Cchannu.hietalahti@nokia.com
Purpose For action
Deadline 2009-11-13 Action Taken
Attachments (None)
Body
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
To:     IESG, IETF-RAI
Cc:

Contact Person:
                Name: Stefan Bruhn
        E-mail Address: Stefan.Bruhn@ericsson.com

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