Question 22/XVII - Digital performance of data transmission services
using V-Series modems over the telephone network
(Continuation of Question 22/XVII, 1985-1988)
(Concerns Study Groups IV, VII and XII)

Considering

(a) that the existing Recommendations V.50 and V.53 only provide signal
quality and maintenance limits for modulation rates up to 1200 bauds;

(b) that existing Recommendation V.52 describes the "Characteristics of
distortion and error rate measuring apparatus for data transmission" at
modulation rates up to 4800 bauds;

(c) that the existing Recommendations V.50, V.52 and V.53 are based upon
the use of the Recommendation V.28 electrical characteristics however,
certain V-Series modems may also use the optional Recommendation
V.10/V.11 electrical characteristics;

(d) that Administrations offer data transmission service using
V-Series modems on voice-band telephone-type circuits at data signalling
rates up to 9600 bit/s per second (see Recommendation V.5 and V.6),

there is an urgent need to study:

How should Recommendations V.50, V.52 and V.53 be revised and/or
updated?

This study should include, inter alia, the following points:

1. Should the study of asynchronous and synchronous data transmission be
separated, possibly into separate Recommendations?

2. Should the revised Recommendation(s) refer to both signal quality of
interchange circuits and error-rate performance specifications, or
should these characteristics be described in separate Recommendations?

Note - It is expected that the primary study of the signal quality
characteristics will be under Question 13/XVII.

3. Should the "V.50-Series" be reorganized better to reflect the
organization of the performance and maintenance Recommendations?

4. What characteristics of asynchronous transmission systems require
study? For example:

a) further study of the limits of telegraph distortion expressed as
degree of isochronous distortion at the DTE/DCE interface for various
data signalling rates (expressed in bit/s) is required;

b) further study of the limits for bit and block error rates at the
DTE/DCE interface for various data signalling rates (expressed in
bit/s).

Note - As the bit error rate is dependent on the telegraph margin of the
receiving apparatus, this margin may need to be specified at various
values to take account of the different performance to be expected of
mechanical and electrical apparatus. Similarly various values of block
length appropriate to the system under test may need to be defined.

5. What characteristics of synchronous data transmission systems require
study? For example:

a) further study of the merits of measuring bit error vs. block error
vs. error free seconds is required;

b) further study of various test patterns, such as the 2047 or the
220-1 patterns is required;

c) further study of isochronous jitter especially on the timing leads
for tandem digital links is required.

6. What should be the duration of error rate performance tests to
achieve a high degree of confidence in the test results?

Note 1 - The study of this Question should take into account the work of
Study Group VII in connection with their Questions 32, 33 and 34/VII.