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1991-12-31
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Recommendation R.103(R.1xy)
CODE AND SPEED-DEPENDANT TDM 600 BIT/S SYSTEM FOR USE IN
POINT-TO-POINT OR BRANCH-LINE MULDEX CONFIGURATIONS
The CCITT,
considering
(a) that telex subscribers are often geographically located in small
groups;
(b) that TDM multiplexing systems are economical for the transmission of
large numbers of channels;
(c) that certain telex switches handle TDM frames in accordance with
Series-R Recommendations directly and that frame fill should be optimized;
(d) that telex switches handle channels at 50 bauds and a 7.5 unit code;
(e) that a facility for regenerating start-stop signals is used in new
TELEX networks;
(f) that the branch-line multiplexing system should be capable of
accepting and regenerating all the signals of the TELEX signalling system;
(g) that the minimum signal transfer delay through TDM systems is achieved
by the transmission of interleaved elements;
recommends
that, where branch-line remote or low multiplex capacity TDM systems are
to be used for telegraphy, the equipment shall comply with the following
standards:
1. System capacity
The system shall be capable of multiplexing up to 8 channels at 50
bauds (7.5 bits including a stop element of 1.5 units).
2. Start-stop channel inputs
2.1 The modulation rate tolerance that shall be accepted on incoming 50 baud
start-stop signals with a stop element of 1.4 units shall be at least + 1.4%.
2.2 When receiving characters at 50 bauds having nominally 1.5-unit stop elements,
the system shall be capable of transmitting without error isolated incoming characters
that have a 1-unit stop element, occurring at a maximum rate of one per second.
2.3 The minimum interval between start elements of undistorted successive continuous
characters that may be presented at the channel input when the nominal modulation rate
is 50 bauds shall be 145 5/6 ms.
2.4 There shall be no restriction on the continuous transmission of all characters
(including combination No. 32 of International Telegraph Alphabet No. 2) when they are
presented at the maximum permitted rate.
2.5 The effective net margin on all channel inputs when undistorted signals are
received from a transmitter having a nominal character length and rate shall be at least
40%.
2.6 At the nominal modulation rate of 50 bauds, an input character start element
shall be rejected if it is less than 0.4 units duration and shall be accepted if it is
more than 0.6 units duration.
2.7 Elements corresponding to start polarity (at the distant multiplexer output)
shall be inserted in the aggregate stream if the channels are unequipped.
2.8 In the case of an open-circuit line condition at the start-stop channel input, it
shall be possible to choose to transmit elements corresponding to a steady start or stop
polarity in the aggregate bit stream, according to the availability polarity selected.
3. Start-stop channel outputs
3.1 The maximum degree of gross start-stop distortion, produced by the system on a
start-stop channel, shall be 3% for all modulation rates.
3.2 The maximum difference possible between the mean modulation rate of the channel
output signals and the nominal modulation rate shall be 0.2%.
3.3 The minimum stop element duration released at the output shall be 1.25 units,
whatever the distortion, the length of the stop element or the input rate within the
range specified in 2.1 - 2.4 of this Recommendation of the character recognized at the
other end, whether this character is in accordance with this Recommendation or
Recommendations R.101, R.102 or R.112 (for a rate of 50 bauds and a 7.5 unit code).
3.4 Within 6 ms of the recognition of one of the failures described in 8.3 and 8.4 or
carrier loss signalled by the modem, the steady polarity as selected in accordance with
2.8 shall be applied to the channel outputs of the TDM system affected.
3.5 The affected terminal shall signal its synchronization status to the distant
terminal over the signalling channel provided (control channel).
4. Multiplexing details
4.1 Channel interleaving shall be on a bit-by-bit multiplexing basis.
4.2 Both start and stop elements of each input character shall be transmitted through
the aggregate.
4.3 The transfer delay shall not exceed 60 ms.
5. Frame structure
5.1 A unique frame of 12 bits, of duration 20 ms, equivalent to an aggregate signal
rate of 600 bit/s shall be used, as shown in Table 1/R.1xy:
TABLE 1/R.1xy
Frame details
5.2 The frame may be considered as a 600 bit/s start/stop character, time slot "12"
being the start element of polarity A, slots 10 and 11 forming the stop element of
polarity Z, as shown in Figure 1/R.1xy.
FIGURE 1/R.1xy
Branch-line muldex frame
6. Aggregate signal details
6.1 The aggregate signal rate shall be 600 bit/s. The tolerance on the modulation
rate of the receive aggregate signals of the TDM system shall be between +2.3% and -
0.5%.
6.2 The effective net margin of the aggregate signal receiver of the TDM system shall
be at least 40%.
6.3 The maximum degree of isochronous distortion of the send aggregate signals of the
TDM system shall be 5%.
6.4 When the TDM system is operated over an international telephone-type circuit, a
modem complying with the appropriate aspects of the Series-V Recommendations (in
particular Recommendation V.23) should preferably be employed.
7. Control channel encoding
7.1 The 50 bit/s control channel, the position of which in the frame described in 5
is accurately known, enables all risk of imitation to be eliminated.
7.2 The structure of the control channel shall be in accordance with Figure 2/R.1xy.
It corresponds to an anisochronous character with a recurrence of 240 ms, formed from a
one unit start element of polarity Z, five information elements and a six unit stop
element of polarity A.
FIGURE 2/R.1.xy
Branch-line muldex control channel
7.3 The control channel information provides for the transmission of information in
accordance with Table 2/R.1xy.
TABLE 2/R.1xy
Information transmitted by the control channel
Note - The least significant bits are sent first.
8. Synchronizing
8.1 The maximum average synchronization time in the absence of error and imitation
shall be 600 ms.
8.2 Synchronism shall be considered achieved after recognition of the frame
positioning pattern (sequence of two elements of polarity Z followed by an element of
polarity A) as described in 5 and at least two successive recognitions of the control
channel (6 elements of polarity A followed by one element of polarity Z modulo 12) in
compliance with 7.
8.3 The maximum time loss of sychronization due to a steady polarity signal shall be
120 ms.
8.4 The maximum time loss of synchronization for repeated error on the
synchronization pattern in the control channel shall be 380 ms.
9. Telex signalling
9.1 Specifications for the signals used to establish, to clear and to control telex
calls are laid down in Recommendation U.1 (types A and B), U.11 (type C) and U.12
(type D). Recommendation U.25 lists the modes of both-way telex signalling on a single
circuit and the signalling combinations on a given aggregate that a TDM terminal shall
be capable of handling.
9.2 Recommendation U.25 also lays down the tolerances on the control signals from a
TDM terminal to telex and vice versa.
10. Maintenance
The branch looping facilities shall remain in accordance with
Recommendation R.115.
11. Numbering of channels
The numbering of channels for the branch line telegraph muldex is given in
Tables 1/R.114 and 4/R.114 in accordance with the numbering scheme concerning
Recommendations R.101 and R.102.
12. Channel selection
Remote channels shall be grouped so as to provide maximum ease of use of
heterogeneous frames, a time slot allocation involving little variation in the sampling
rate being retained.
The selection of channel grouping and the method used shall be based on bilateral
agreement, particularly when the channels of an existing system have to be branched
without there being any possibility of a reconfiguration of the whole.
Tables 3 and 4/R.1xy give an example of remote channel grouping on the basis of
muldexes in conformity with Recommendation R.101 or R.102.
TABLE 3/R.1xy
Example of grouping of remote channels for an R.101 muldex
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1) Although incomplete, a sixth remote channel could be implemented with the
remaining 50 baud channels.
2) Channel 0516 may not be remoted when the corresponding TS is used to transmit the
maintenance channel in the R.101 multiplexer.
TABLE 4/R.1xy
Example of grouping of remote channels for an R.102 muldex