UK SG16
Title: Proposed UK Response to questions regarding contribution D.223
The attached is a proposed draft contribution to the March 2003 meeting of SG16.
It provides the response to several questions regarding contribution D.223 (Simultaneous
Voice and Data Transmission for V.18) that were raised during the Feb 2002 Study Group
16 Question H/16 meeting. See attached document PL-064 Annex 1 for detailed description of questions.
.
Contact: George Skorkowski
Tel: 0208 9640774
Email: info@dspg.co.uk
UIT - Secteur de la normalisation des télécommunications
ITU - Telecommunication Standardization Sector
UIT - Sector de Normalización de las Telecomunicaciones
Study Period 2001-2004
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Geneva, 20-39 May 2003
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Question(s): H/16
SOURCE*: BT
TITLE: Response to questions regarding contribution D.223
Contact: George Skorkowski, DSPG
Tel: 0208 9640774
Email: info@dspg.co.uk

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Introduction
During the Feb 2002 Study Group 16 Question H/16 meeting, several questions were raised regarding contribution D.223.
The following is a draft response to these questions:
Q 1. Transmission of Simultaneous Voice and Data through different kind of networks
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The modulation technique used for SVD is modified V.21 FSK. Since it is a standard inband modulation its performance is very similar to other FSK modems such as V.21,
V.23 etc. A number of comparative tests with SVD and V.21 have been performed over the PSTN and Network Emulator with no difference in results between the two modulation techniques.
Q 2. Start-up method
It is proposed to implement the start-up using in-band tone detection as a part of V.18 automoding.
The alternative start-up procedure using new code points in V.8 and V.8bis was rejected due to a shortage of new code points especially for such a low volume product.
Q 3. Collision with signalling system 5
The following is a list of in-band signalling frequencies:
System 5
2400

15 Hz
2600
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15 Hz
System 6
2000

30Hz
2000

30 Hz
The proposed SVD FSK modem carrier frequencies shown below do not collide with any of the in-band signalling methods.
FSK Modem Specification
The communication circuit for data transmission is a duplex circuit whereby data transmission in both directions simultaneously is possible at 300 bit/s or less.
The modulation is a binary modulation obtained by frequency shift, resulting in a modulation rate equal to the data signalling rate.
For channel No. 1, the nominal mean frequency is 3000 Hz.
For channel No. 2, it is 3300 Hz.
The frequency deviation is ± 50 Hz. In each channel, the higher characteristic frequency (F
A
) corresponds to a binary 0.

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Signalling rate
Carrier frequency Channel 1
Channel 2
100 baud
Fz = 2950 Hz => binary 1
Fa = 3050 Hz => binary 0
Fz = 3250 Hz => binary 1
Fa = 3350 Hz => binary 0
Table V.1 Modem summary
The characteristic frequencies (see table V.1) as measured at the modulator output must not differ by more than ± 6 Hz from the nominal figures.
A maximum drift f requency of ± 6 Hz is assumed for the line. Hence the demodulation equipment must tolerate drifts of ± 12 Hz between the frequencies received and their nominal values.
Data may be transmitted by asynchronous procedures.
Echo control devices will be disabled due to use of V.8 procedures.
The maximum power output of the modem into the line shall not exceed 1 mW.
The power level of the modem should be adjusted to make allowance for loss between this equipment and the point of entry to an international circuit, so that the corresponding nominal level of the signal at the international circuit input shall not exceed - 13 dBm0 (see
Recommendation V.2, § 2).
When both channels are used for simultaneous both-way data transmission, channel No. 1 is used for transmission of the caller's data (i.e. the person making the telephone call) towards the called station, while channel No. 2 is used for transmission in the other direction.