Subject: RE: Re: [Sipping] Use cases of multi-transcoding

From: "Kang Tae-Gyu" <[email-masked]>
Date: Wed, 22 Feb 2006 10:30:34 +0900

Hi, Albrecht

Thank you for your good comments.

- -> in line

Kang
----------------------------------
From: "[email-masked]" <[email-masked]>
From Date: 2006-02-21 PM 4:29:12
To: "Kang Tae-Gyu" <[email-masked]>
Cc: "[email-masked]" <[email-masked]>
Subject: Re: [Sipping] Use cases of multi-transcoding

Hi Kang,

just a comment to the transcoding scenario between two different WB codecs
(WB1<->WB2).

Transcoding as such should be avoided because it is inherently decreasing
the audio/speech quality ("adds e.g., delay impairments and Ie, equipment
impairment factors") and an "expensive" network function.
There must be therefore an agreed justifaction, particularly for WB1<->WB2
transcoding scenarios!

Transcoding between two different NB codecs (NB1<->NB2) is often
inevitable.

- -> You are right. So, I would like to minimize the number of transcoding to keep the quality at my internet draft. http://www.ietf.org/internet-drafts/draft-kang-sipping-transc-scenario-00.txt

- -> Transcoding between two different WB codecs (WB1<->WB2) is also inevitable.

The difference with WB codecs is that terminals "should support a fallback
mode to a NB codec" in my opinion. There are two possibilities:
NB mode is part of the WB codec modes of operation (e.g., G.729EV
with G.729A as NB mode), or
separate NB codec (e.g., terminal concept according G.725).

- -> The transmission modes, mode 1, 2, 3, at G.725 are for WB.

- -> If terminals do not connect Type 0 or Mode 0(switching using G.711), we can do it without the fallback.

The inconsistent "WB1<->WB2" E2E scenario might then lead to fallbacks to
(default) NB codecs. In case of a then "NB1<->NB2" inconsistency to NB
transcoding in the network.

- -> The fallbacks to [default] NB codecs is the most convenient way between WB and WB.

- -> But, it will be lost WB quality. "WB1<->WB2" E2E transcoding is higher quality than fallback[NB] transcoding.

Comments?

Albrecht

"Kang Tae-Gyu"
<[email-masked].         To:      <[email-masked]>
kr>                      cc:      [email-masked], [email-masked], [email-masked],
[email-masked]
21.02.2006 03:12         Subject: [Sipping] Use cases of multi-transcoding
Please respond
to Kang Tae-Gyu

Hello,

I would like to discuss about the use case of multi-transcoding. First of
all, I am sorry for that I could not answer about its use case when I
received the question from the floor, IETF 64 Vancouver meeting, because of
poor English. Also, thank you for the minutes(chairmen and note takers).

There are three kinds of use cases of multi-transcoding.
-    one or two more heterogeneous networks
-    one or two more ITSPs
-    one or two more wideband speech codecs

There are one or two more heterogeneous networks: enterprise networks using
IP-PBX, ITSP(Internet Telephony Service Provider), IMS in 3GPP2,
PacketCable, and Wibro. They will not use a common codec. So, they need
multi transcoding such as;
-    use case 1: A(a) - IP PBX T1(a-b) - ITSP T2(b-c, b-d) - IMS T3(a-d,
d-e) - D(d)
-    use case 2: A(a) - IP PBX T1(a-b) - ITSP T2(b-c, b-d) - PacketCable
T4(c-d) - F(d)
-    use case 3: E(e) - IMS T3(a-d, e-d) - ITSP T2(b-c, b-d) - Wibro
T4(a-d, d-c) - G(c)

There are one or two more ITSPs or SBC because all of internet telephony
subscribers will not subscribe only one ITSP. There are a lot of domestic
ITSPs and international ITSPs or ITXP. Internet telephony should be
supported any kind of terminal vendor even though it supports any specific
codec. It also supports multi call forwarding service. So, they need multi
transcoding such as;
-    use case 4: C(c) - ITSP T2(c-b, b-d) - ITSP T6(b-a, b-d) - ITSP7
T7(a-d, d-e) - G(d)

There are one or two more wideband speech codecs. There has been developing
one or two more wideband speech codecs for internet telephony: AMR-WB in
3GPP, VMR-WB in 3GPP2, G.729EV in ITU-T SG 16 Question 10, a wideband codec
in ITU-T SG 16 Question 9, and AAC in ISO/IEC. In this convention, Capital
letter means a node and lowercase(a, b, c, d, and e) means a codec.

A wideband codec encodes voice using 16,000 samples per second (50 ~
7,000Hz), as opposed to the 8,000 samples per second (300 ~ 3,400Hz) by
narrowband codec. A voice quality of wideband codec is better than one of
narrowband codec due to support wider band. A tandem transcoding means to
encode narrowband codec such as G.711. So, it makes down sampling and worse
the voice quality. If two parties(calling party and called party) have two
different wideband codecs, transcoders should transcode a wideband codec to
another wideband codec without tandem transcoding. If we use a common codec
with G.711(tandem), there is no more need multi-transcoding. But, we need a
multi-transcoding for supplying a wideband speech high quality to each
sides.
-    use case 5: wideband codec to wideband codec without tandem
transcoding

Multi transcoding signaling can be useful for internet telephony
environments supported by standard; an example VoIP network in quality of
service for next generation Voice over IP networks, MSF-TR-QoS-001.final,
2003 Feb, and Telecommunications and Internet Protocol Harmonization over
Networks (TIPHON) Release 3; End-to-End Quality of Service in TIPHON
Systems; Part 3: Signalling and Control of End-to-End Quality of Service
(QoS)-V2.1.2, 2002.

Multi trascoder can cover the use case using one or two more conference
bridge transcoding model.

We would like to discuss open these use cases or another use case. Comments
are welcome.

Thanks,
Kang

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_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip
Use [email-masked] for new developments of core SIP