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1991-12-31
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Recommendation S.22
Replace by the following:
"CONVERSATION IMPOSSIBLE" AND OR PRE-RECORDED MESSAGE IN RESPONSE TO
J/BELL SIGNALS FROM A TELEX TERMINAL
(Geneva, 1980; amended at Melbourne, 1988)
The CCITT,
considering
(a) that conventional telex terminals incorporate a facility that
allows an operator at one end of an established connection to attract the
attention of an operator at the other end, this being achieved by
transmitting J/BELL (combination No. 10 in International Telegraph Alphabet No. 2) in
figure-case;
(b) that technological developments and changing customer requirements have
led to the introduction of the page-printing, receive-only, telex terminal, which,
because of the absence of a keyboard, makes any conversational mode of operation
impossible;
(c) that this limitation is not indicated to a calling station at the time
the connection is established and may well result in wasted circuit time through
attempts to establish contact with the called station via the J/BELL facility;
(d) that automatic calling and/or answering terminals employing data
terminal equipment (DTE) and data circuit terminating equipment (DCE), in accordance
with Recommendation S.16, are unlikely to have a conversational mode of operation;
(e) that technological developments and changing operational requirements
may lead to the retention of messages in storage until a suitable opportunity to
print-out arises;
(f) that it may be useful for called subscribers, who do not anticipate
conversing with the calling subscriber, either because conversation is impossible or
for any other reason, to answer by a pre-recorded message,
unanimously declares the following views
1. Where a telex terminal is incapable of a conversational mode of operation,
either through the absence of a keyboard or for local operational reasons, or if the
subscriber wishes to deliver a pre-recorded message, then it is highly desirable, at
least in new equipment, that such a terminal be able to automatically return an
appropriate service signal sequence and/or the pre-recorded message on
receipt of one or more ITA2 combination No. 10 characters (i.e. BELL signals) when
preceded by ITA2 combination No. 30 (i.e. figure-shift).
2. The recommended sequence of signals to be returned in such circumstances
should incorporate the code expression.
CI Conversation Impossible
in conformity with the Recommendation cited in [1].
3. The complete sequence incorporating the code expression CI should have a
format that corresponds with the Recommendation cited in [2], concerning service
signals for ineffective calls, except that it should not be followed by the clearing
signal.
4. Where a pre-recorded message is to be returned, then it should follow the
rules established in the Note of this Recommendation, and should not be followed by
the clearing signal.
If conversation is impossible after the pre-recorded message is delivered,
this message should start with the CI conversation impossible sequence of signals as
specified in 2 and 3.
5. As operators often key several repetitions of J/BELL (in figure-case) when
attempting to contact a distant operator, a delay of 0.5 - 1.0 second should precede
the transmission of the sequence described in 2, 3 and 4 above, the delay to be
measured from the stop element of the last J/BELL combination detected.
Note - The length of the pre-recorded message should be unlimited provided that a
pause of 1 sec. minimum is included within the message after every (x) characters,
(the number of characters are to be decided).
- When conversation is impossible, the mandatory code expression CI should
precede and follow the pre-recorded message.
- No "WRU" signals should be contained within the pre-recorded message up to
the last code expression CI. Triggering of the calling party's answerback could be
initiated after the end of the pre-recorded message.
- No combination 32 signals should be contained within the pre-recorded
message.
The terminal and/or the network emitting the pre-recorded message should
interrupt transmission immediately, when detecting modulation in the opposite
direction.
Every pre-recorded message is not necessarily sent to the calling party upon
simple reception of the triggering signal provided in 1 above. Measures can be
taken at the called party to reserve it to some special correspondents. The callers
that are not qualified to receive it will then receive only the CI signal provided
for in 2."
REFERENCES
[1] CCITT Recommendation Operational provisions for the international telex
service, Recommendation F.60, 4.1.
[2] CCITT Recommendation Signalling conditions to be applied in the
international telex service, Recommendation U.1, 10.1.2.