Network & Mobility
Integration
Technical Reference - Analogue Supplementary Services,
Telstra
DC.002
Data Transmission to CPE for Presentation Features
Issue Number 4
Issue Date: 24 July, 1997
1. GENERAL
This Technical Reference describes CPE. requirements for the reception of
data for presentation services (e.g Calling Number Display) from the exchange
on analogue customer lines.
These requirements are based on Bellcore Specification GR-30-CORE "LSSGR:
Voiceband Data Transmission Interface, Section 6.6" A Module of LSSGR,
FR-NWT-000064 [1], with the minimum adaptation required for operation
within the Australian telephone network.
2. DIFFERENCES BETWEEN BELLCORE GR-30-CORE AND TELSTRA REQUIREMENTS
Whilst Telstra requirements are modeled closely on the Bellcore document,
some minor modifications are necessary for satisfactory operation
within the Australian network.
2.1 Ring Cadences
The standard (default) Telstra ring cadence is two bursts of ring 400 ms off 200 ms off and
400 ms on followed by 2 s of silence- (The US ring cadences consist of a 2 s burst
offing followed by a 4 s silent interval. The first silent interval is used for data transmission).
Other Telstra (distinctive) ring cadences shorten the silent period to as little as 1.4 s.
This would severely limit the amount of tine available for the sending of data via the modem.
In order to allow up to 3.5 s of time for transmission of data, the requirements in this
Technical Reference provide for an initial burst of ring in the range 200 ms to 650 ms.
This is followed by a silent interval of sufficient duration as will allow for the transmission
of data When this has been completed, the particular ring cadence appropriate to the
call to the customer's service is then applied.
2.2. Message Format
Bellcore specifies two message formats - Single Messages and Multiple Messages.
Telstra will use the Multiple Message format only.
3. DESCRIPTION
3.1. General Description
This section describes the CPE requirements for the reception of data
(e.g. Calling Number) Sent by a terminating exchange for CPE in either
the on-book or off-hook states. The data transmission technique used is
asynchronous frequency shift keying at 1200 bit/s, consistent with Bellcore
Specification GR-30-CORE "LSSGR: Voiceband Data Transmission Interface7
Section 6.6" A Module of LSSGR FR-NWT-000064 [1]. Note that the frequencies
used are identical with Bellcore 202 modem frequencies, and are therefore
not compatible with ITU-T Rec. V.23.
The signalling interface is arranged to allow simplex data transmission from
the terminating exchange to the CPE when a voice path has been established.
There are four modes of data transmission, these are the on-hook data
transmission with ring, prior to ring, without ring and the data transmission
during the off-hook state It is assumed that the CPE will be ready to receive
data at the time the PSTN exchange sends it, Section 4 details the requirements
on timing and tolerances for data reception.
The CPE should be capable of supporting alphanumeric display of received data messages.
3.2. On-Hook Data Transmission with Ring
This signalling case is intended for transfer of data associated with a
call in the process of being set up (e.g Calling Line Identification Presentation
[2] and Calling Name Presentation [4]).
Data is transmitted during the period between the initial burst of the ringing
signal and the cadenced ringing The silent interval between the initial burst
of ring and the commencement of the cadenced ring will be of sufficient duration
to allow the PSTN exchange to transmit the necessary data to the CPE.
a) The initial burst of ring will be in the range 200 ms to 650 ms.
b) The pause TI immediately after the initial burst of ring will be between 500 ms and 1000 ms.
c) The duration of the data transmission Will be a function of ale amount of data to be
transmitted, but it will be limited to a maximum of 3.5 s.
d) The pause Th between the cessation of data transmission and the first bunt of
cadenced ring will be in the range 200 ms to 1000 ms.
If the customer answers prior to or during data transmission, the transmission will
cease within the time necessary for the PSTN exchange to detect the off-hook
state (less than 500 ms) and the line placed into a state to allow the incoming
call to proceed In these circumstances, the CPE should discard any resultant
incomplete data messages received.
3.3. On-Hook Data transmission prior to Ring
This signalling case is intended for specialised applications for the transfer
of data associated with a call in the process of being set up (e.g. calls from
special category CPE for telemetry applications).
There may or may not be a Pre-Data Transmission signal sent prior to data
transmission if a pre-data signal is sent it will be either a Line Polarity Reversal
or an Open Switching Interval (OSI). The OSI is a short removal of battery feed
in the range of 150 ms to 350 ms if a Line Polarity Reversal is sent, the line will
return to normal polarity when the B-party answers or the A-party clears or the
PSTN clears the call due to a no answer time expiry.
The timing for On-Hook Data Transmission prior to Ring as follows:
3.4. On-Hook Data Transmission without Ring
This signalling case is intended for transfer of data for applications
not associated with a call (e.g. to indicate the presence of a message
in a message storage system [3], or a requirement for telemetry applications).
There may or may not be a Pre-Data Transmission signal sent prior
to data transmission, if a pre-data signal is sent, it will be either a Line
Polarity reversal or an Open Switching Interval (OSI). If Line Polarity
Reversal is sent, the Post-Data Transmission signal will be a Line
Polarity Restoration to normal polarity. There is no Post-Data Transmission
signal if an OSI is applied as a Pre-Data Transmission signal.
The timing for On-Hook Data Transmission without Ring as follows:
3.5. Data Transmission During Off-Hook State
This signalling case is intended for transfer of data associated with a
Current call (e.g. Calling Line Identification Presentation [2] for a waiting call).
For data transmission to occur while the customer is in an off-hook state. the voice
path must be disabled within the CPE to allow the exchange to communicate
with the modem contained therein. This is achieved by using the CPE Alerting
Signal to initiate a modem Session and control of the voice connection. The
CPE internal voice path must he disabled during data transmission in order
to preclude both the audible reception of tones and the injection of any signal
from the associated telephone, by the customer to whom the name number or
other data will be presented.
The sequence of events for data transmission to take place in the off-hook state as follows:
a) The PSTN disables the voice path to me distant CPE.
b) The PSTN applies a Subscriber Alerting Signal (SAS) to the local CPE.
c) The PSTN applies a CPE Alerting Signal (CAS) to the local CPE.
d) The OPE sends acknowledgment (AC K) in response to the CAS.
e) The PSTN applies the data sequence.
f) The PSTN enables the voice path to the distant CPE.
The SAS is a signal to alert the customer of the service (e.g Call Waiting
tone in the case of a waiting call).
The CAS is a machine-recognisable signal used to alert the OPE to prepare for data reception .
The ACK signal sent by the CPE will be:
a) ADSI CPE ACK signal- DTMF digit 'A' (697 Hz and 1633 Hz) as specified
in Austel/ACA Technical Standard 002 [5] and with a duration in the range 55 to 65 ms.
b) Non-ADSI CPE ACK signal DTMF digit 'D' (941 Hz and 1633 Hz as specified
in Austel/ACA Technical Standard 002 [5] and with a duration in the range 55 to 55 ms.
The timing for off-Hook Data Transmission is as follows:
Legend:
| T1 | 0-60 ms | Pre-Subscriber Alerting Signal (SAS) |
| T2 | 250 ms-1 sec | Duration of Subscribe Alerting Signal (SAS) |
| T3 | 0-80 ms | Pause between Subscriber Alerting Signal (SAS) and CPE Alerting Signal (CAS). |
| T4 | 80-85 ms | Duration of CPE Alerting Signal (CAS). |
| T5 | 0-100 ms | Acknowledgement (ACK) delay from CPE. |
| T6 | 50-100 ms | Pre-data transmission pause. |
| T7 | feature specific | Data transmission time is feature dependent. |
| T8 | 0-120 ms | Enable voice path time to distant CPE. |
Figure 3.5 Off-Hook Data Transmission Timing
If the CPE sends an ACK signal outside the range of T5 the PSTN will abort
the data transmission and re-establish the voice path to the distant CPE,
For Reversal On Seizure lines, the above data transmission sequence will
occur while the line polarity is reversed.
3.6. Outgoing Calls
Presence of the data interface facility must not affect the ability to originate calls.
However, outgoing calls may be impacted by the services that use this interface.
For example, off-hook data transfer as described above may be initiated by the
exchange during outgoing calls made from the CPE.
4. INTERFACE REQUIREMENTS
4.1 Physical Interface
4.1.1 Data Transmission
| Link Type | Two wire, Simplex |
| Transmission scheme | Analogue Frequency Shifting Keying |
| Logic 1 (Mark) | 1200 +/- 12 Hz |
| Logic 0 (Space) | 2200 +/- 22 Hz |
| Transmission Rate | 1200 +/- 12 bits per second |
| Application of data | Serial, Binary, Asynchronous, Least Significant Bit first |
Maximum gap between
two successive bytes | 16.7 ms (20 bits) |
| Bit Error Rate | < 10^-5 |
| Phase Continuity of Message | Maintained from inital service to end |
| Transmission Level | -13.5 +/- 1 dBm into a resistive termination of 600 ohm at the
PSTN exchange MDF. The level at the Service Delivery Point
may be up to 20 dB lower than this for on-hook an up to 8 dB lower for off-hook data transmission.
|
| Character Format | 1 start bit, 8 data bits, 1 stop bit |
| Character Set | ASCII 7 bit, 8 bits is transmitted with the most significant bit
set to zero. |
The 600 ohm resistive termination is a reference value for measurement purposes only.
Table 4.1.1 Data Transmission Parameters
Optimal interworking using this facility will be achieved by compliance with the following
recommendations:
· During the on-hook state, the VF impedance of the CPE during reception of presentation
data he as high as practicable, preferably not less than 15 k ohm, which will allow parallel
connection of CPE using presentation features.
· Passband filtering of the data signalling frequencies be employed within the CPE to eliminate
low and high frequency interference.
· CPE designs should allow for up to 10 dB of twist between the data signalling frequencies.
Other technical requirements for CPE connected to the PSTN are described in Austel/ACA
Technical Standards 002 [5], TS 004 [6] and TS 030 [7].
The time that elapses between the transmission of individual data bytes within
data messages win not exceed the time period associated with the transmission
of two bytes. If this timing interval is exceeded, the received data should be
treated as erroneous. Furthermore, the mark signal (which is transmitted between
data bytes) should be monitored for continuity. An interruption that exceeds 8 ms
should cause the received data to be treated as erroneous. An interruption of the
mark signal for 8 ms or less (i.e., less than one byte period) may be ignored by
the data receiver.
4.1.2 Signalling
The dual tone CPE Alerting Signal (CAS) will conform to the following standards:
| Dual Tone Frequencies | 2130 +/- Hz and 2750 +/- 14 Hz |
| Transmission Level | -15+/-1 dBm per frequency measured into a 600-ohm
at the PSTN exchange MDF. The level at the
Service Delivery Point may be up to 8 dB lower than this.
|
| Duration | 80 - 85 ms |
Table 4.1.2 CPE Alerting Signal Parameters
4.2. Protocol
The asynchronous protocol used for this interface provides efficient
use of the available bit rare, reliable error detection, and flexibility for future expansion.
The protocol involves the transmission of a series of 8-bit data bytes that are each bounded
by a start bit (space) and a stop bit (mark). The data is sent in the order of the least significant
bit (bit 0) first.
The format of the data message is shown below The message type byte indicates that the
data consists of one or more parameters. This is known as the multiple message format.
Each parameter Consists of a parameter type byte parameter length byte, and up to a
maximum of 20 data bytes.
Messages that are not recognised by the CPE should be ignored (i.e. the corresponding
data is not displayed). Recognition should be based on the value used in the message type byte.
If a CPE recognises a particular message type byte given in a multiple data message, but does
not recognise one or more of the parameter type bytes within the multiple data message,
the CPE should process the message as follows:
· All recognised parameter types should continue to be processed (i.e
the corresponding data is displayed).
· All unrecognised parameter bytes should be ignored (i.e the corresponding data
should not be displayed).
The PSTN wilt be capable of delivering a sequence of data messages, and the CPE
should therefore include the ability to receive consecutive messages that may be sent
during the silent interval between initial and regular ring signals.
Details of the message content for service applications are described in feature specific
Telstra Analogue Supplementary Services documents.
4.3. Error Detection
The exchange will generate a check sum which is transmitted as the last byte of the
data message. The check sum consists of the two's complement of the modulo 236 sum
of the other bytes in the data message (i.e. from the message type to the last data byte
of the last parameter of the data message).
The receiving equipment obtains the modulo 256 sum of all bytes received in the
data message (including the check sum). Both recognised and unrecognised
parameter type bytes and associated parameter length and parameter data bytes
are included in the computation of the modulo 256 sum. Any result other than zero
for this addition shows that the data message was not received correctly. A result
of zero usually indicates that the message was correctly received however, this method
cannot detect all transmission errors. Specifically it cannot detect offsetting bit errors
occurring in the same bit positions in two, four or six (or any multiple of two) bytes of
the data message.
If the CPE detects an error, none of the parameters of the received data should be
displayed. No messages are sent to the exchange indicating that an error was detected,
and the exchange will not attempt to retransmit data.
5.REFERENCES
[1] Bellcore Generic Requirements GR-30-CORE "LSSGR: Voiceband Data Transmission
Interface, Section 6.6", A Module of LSSGR, FR-NWT-000064 issue-1, Dec 1994.
[2] DC.001 - Calling Line Identification Presentation - Analogue.
[3] DC.017 - VMWI - Visual Message Wait Indication.
[4] DC.O18 - CLNPA Calling Name Presentation for Analogue.
[5] TS O02 1997 Austel/ACA Technical Standard 002.
[6] TS 004 - 1996 Austel/ACA Technical Standard 004.
[7] TS 030 - 1997 Austel/ACA Technical Standard 030.
End Of Document.
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