BT Monarch Services Cards

BT Monarch ASU 1A7/SA20077 Services Card

The Services Card, which interfaces with the speech switch and signalling units in a similar way to the Concentrating Shelf Interface, provides the following functional items:-

The Conference Unit
The Tone Generator
The Dial Tone Receiver -
The MF Signalling Receivers
The Test Unit
The Pattern Generator
The SSMF No. 4 Sender (not used with the present processor program)

NOTES:

1. In this figure the term "speech" includes digitally encoded tones/A.C. signals in the speech frequency band. and speech-like test patterns.

2. The signalling outputs from the Keyphone Receiver and the Pattern Generator utilise circuit elements in the Test Unit IC to achieve maximum design economy.

Extract from Monarch CD range Manual (375817)

All incoming information to the card arrives over a 2048 kbit/s highway from the Speech Switch or a 256 kbit/s highway from the Signalling Circuit. Similarly, all information leaving the card is sent over a 2048 kbit/s highway to the Speech Switch or a 256 kbit/s highway to the Signalling Circuit.

These highways provide 32 time slots (ports) which are allocated to the various items on the card, as shown above.

It will be noticed that most items do not require ports in all 4 highways, indeed, only the Test Unit makes use of all the different highways. Thus it is possible to use the same port on different highways for different items.

For example, the MF Signalling Receivers use ports 0 to 7 only on the incoming speech and outgoing signalling highways, and these ports on the outgoing speech highway are used for outputs from the Tone Generator

Each functional item on the card which requires to receive information from an incoming highway incorporates timing features at its own input which enable it to capture the required bit (or bits) in the time slot allocated to that item. Each item is responsible for collecting its own input data.

Depending on the function performed by an item, its output may be in the form of A-Law encoded speech (or equivalent, eg audible tones) at 2048 kbit/s, or in the form of signalling bytes (bits A to H) at 256 kbit/s, or both, as in the case of the Test Unit.

The outputs, which are in serially encoded form in all cases, are fed into a "Binder" circuit, the function of which is to ensure that output information is connected to the outgoing highways at exactly the correct port slot time. Depending on the design of the item concerned, its output may appear at the input to the Binder continuously at every port slot time, or only at a time corresponding to the port slot time allocated for use by the item. The Binder is not involved in the receipt of information by the Services Card (see Paragraph 3.9.3) and it does not insert any information of its own into the outgoing bit streams; it performs only the output data selecting function.

It will be seen that the signalling outputs from the MF Signalling Receivers and the Pattern Generator pass to the Binder via the Test Unit. This is not due to any functional relationship between the three items, but arises from the fact that economies have been achieved by making use of spare circuit elements in the Test Unit IC to perform the Pattern Generator function and to provide certain circuit elements required in the MF Receiver outputs.

1.The Conference Unit

The 16 ports allocated to the unit are divided into 4 groups, each comprising a conference "bridge" capable of interconnecting 4 ports.

Thus the unit can handle 4 conference calls simultaneously, each involving up to 4 ports. The conference unit performs its internal functions continuously regardless of whether the CPU is making use of them, and it is unaware of the occasions on which it is taken into use. The service that each bridge provides is to deliver an output to each of its 4 ports which is the sum of the inputs received from the other 3 ports. The summing operation is linear and introduces no gain or loss.

When the CPU receives a request for a conference call it connects the parties concerned to the time slots corresponding to one conference bridge on the 2048 kbit/s incoming and outgoing highways between the Speech Switch and the Services Card. The incoming highway from the Speech Switch appears at the input to the Serial-In-Parallel-Out Conversion Circuit which extracts each of the 8 bit speech bytes corresponding to the ports to be interconnected, and sends them in sequence to the Input RAM, where each of the 16 conference ports has its own store. The Accumulator receives the bytes from the Input RAM via an A-Law to Linear Convertor, which transforms the 8 A-Law encoded speech bits into 13 bits linear encoded PCM. The thirteenth bit is required to identify the centre point of a quantum level and thus ensure that the quantising distortion during this process does not exceed half a quantum level.

The speech bits from each combination 3 ports in a bridge are successively summed in the Accumulator, and the results are sent in 12 bit parallel form to a linear to A Law converter: the thirteenth bit is discarded (rounded up). The sum values, now in 8 bit parallel A-Law coded form, are converted to serial form and each sent via the Binder, to the remaining port of the bridge on the outgoing highway to the Speech Switch. Thus, the bits from Ports 1,2 and 3 in the bridge are added together and sent to Port 0, the bits from Ports 0, 2 and 3 in the bridge are added together and sent to Port 1 and so on. The intermediate conversion to linear encoding is necessary to permit simple addition of the sample values in the Accumulator.

If only three parties are connected together on a conference call, the unused port in the bridge must be connected to silence, and the CPU effects this automatically by connecting the port via the Speech Switch to Port 10 on the Services Card. Similarly, if any party clears down from a four party conference call, the CPU must connect the port which it was using to silence. However, if a party clears down from a 3 party conference then the two remaining parties are connected directly to each other, and the conference bridge is returned to the idle pool.

BT Monarch conference unit - Accumulator Diagram

The early Monarchs had a separate card for the conference unit .. ASU 1A1/SA20031 GEC 81/1 x42463

3.Dial Tone Receiver

In some of the older designs of public exchange, a significant delay may occur between seizure of an exchange line and the establishment of dialling conditions at the exchange. To cater for these cases, pulsing out from the PABX must be inhibited until dial tone has been received, and accordingly, a Dial Tone Detector is required at the PABX. The characteristics of dial tone in respect of amplitude, fundamental frequency and harmonic content vary so widely throughout the network as a whole that the following criteria have been found the most satisfactory for recognising the tone:- a. it must reach a level of -21 dBm within every 8 ms sampling period over a nominal period of 600 ms. b. the sign of the AC signal comprising the tone must have alternated at least 8 times. When the CPU recognises that a call requires to be routed via the public exchange, it selects an outgoing exchange line and sets up a connection between the "receive" path of the line and Port 13 on the Speech Highway to the Services Card. As soon as conditions (a) and (b), above, are satisfied in the Dial Tone Receiver, it sends a signal to the CPU indicating that it may be released and pulsing out may start.

A block schematic diagram of the Dial Tone Receiver is shown above. The amplitude detector examines the PCM encoded bits in the time slot corresponding to Port 13 in the incoming speech highway, to determine whether the signal level is above or below -21 dBm, and the alternator detector similarly examines the bits to determine the sign changes in the received AC signal. As long as the requirements of the amplitude detector continue to be satisfied, the persistence timer continues to count for approximately 600 ms, after which a signal is extended to the check circuit. Meanwhile, providing the required number of alternations has been detected by the alternation detector, this also sends a signal to the check circuit, and provided both signals are being received, the check circuit extends a signal to Port 13 of the Signalling-In highway, via the Binder, and thence to the Signalling Circuit and CPU. If, at any time during the 600 ms recognition period, the received tone fails to satisfy the requirements of the amplitude detector, this detector connects a signal to the drop-out lead, which causes both the persistence timer and the alternation detector to be reset; it is then necessary for acceptable conditions to be received for a further 600ms before an output signal can be extended to the Binder.

END OF DIAL TONE DETECTOR

4.The MF Signalling Receivers

The MF Signalling Receivers are designed to accept signals conforming to the internationally agreed system (referred to in British Telecom as Signalling System Multi-Frequency No. 4 - SSMF4) in which each signal is represented by a combination of 2 frequencies - one in the Band 697 Hz to 941 Hz, and the other in the Band 1209 Hz to 1633 Hz. On receipt of an "off hook" signal from an extension provided with an MF keyphone Class of Service, the CPU immediately sets up a connection in the "send" direction to an MF Receiver port on the Services Card, and in the "receive" direction to dial tone (Port 8 on the Services Card), thus connecting dial tone to the extension user. The MF digits are accepted by the receiver and forwarded to the CPU, via the Binder and Signalling-In highway, in appropriately coded form using the 8 signalling bits A to H, as described in Part 2. When the CPU concludes that all the digits have been received, it releases the connection to the MF Receiver and sets up a call from the originating extension to the required extensions, or other destination, in the usual way.

The Services Card can accommodate up to 6 MF Receivers and 2 spare ports are left to accommodate a further 2 receivers for possible later applications. A block schematic diagram of a Services Card MF Receiver is given in Figure 36 from which it will be seen that the outputs of the receivers are connected in series and are passed in succession over a single path to the Binder and thence to the Signalling-In highway. The output from the receiver shown in full lines is sent to Port 0, the output from the receiver shown in dotted lines is sent to Port 1, and so on. The required time delays are inserted automatically as the receiver outputs pass down the chain.

Teltone M-927

The Teltone M-927 is a high-quality Dual-Tone Multifrequency (DTMF) digital receiver and/or rotary dial pulse counter. The M-927 is contained in a 40-pin package and requires no external components except a single 3.579 MHz television color burst crystal.

As shown in Figure 2, the M-927 is typically connected in parallel with the voice pair (Tip and Ring) of a telephone line.

It receives signals from a DTMF generator or pulsing mechanism and translates them into logic level outputs for use by other devices, permitting applications such as data entry via telephone or instrument and control system access and activation. For applications such as DTMF-to-rotary conversion, additional outputs provide early indications of signal presence. Logic inputs to the M-927 enable or disable the receiver, inhibit or enable the reception of DTMF or rotary signals, and select from the output formats listed in Table 1.

Considering now the operation of one receiver, the incoming MF signals, in binary encoded form are captured from the incoming speech highway at the appropriate port time, and after conversion to analogue are applied to the input of a standard MF signal receiver. Provided that one signal, and only one signal is present in each of the signalling bands, and provided the levels of the 2 signals are both within the prescribed limits, and their presence exceeds a predetermined duration (the "Recognition Time"), DC signals are passed to the Signal Encoding Circuit, where they are converted to binary and sent in serial form via the Binder to the appropriate port on the 256 kbit/s Signalling-In highway.

2. The Tone Generator

EET, Plessey - Beeston, Notts 1981

GEC 1981/1

GEC

EET

All the supervisory tones used by the system originate from the Tone Generator, where they are stored as digital patterns on an Erasable Programmable Read Only Memory (EPROM). The cadences for the different tones are hard wired. The outputs are fed via the Binder onto the 2048 kbit/s highway to the Speech Switch.

The Tone Generator has 12 ports, each of which can supply a different type of tone. The bit patterns corresponding to the tone supplied by each port are continuously sent over the speech highway to that port in the Speech Switch. To connect a tone to a line it is only necessary for the CPU to cause the speech switch to make a connection between the port supplying the required tone and the time slot serving the line concerned. If more than one line requires the same tone, one Speech Switch connection is made to each time slot from the tone port. No problems of tone supply loading arise because of the nature of the Speech Switch. A block schematic diagram of the Tone Generator is given in Figure 34 .

The digitally encoded tones are read out from the EPROM on which they are stored, under the control of clock pulses, and passed in 8 bit parallel form to a Parallel-In-Serial-Out conversion circuit which extends the bits in serial form via the Binder to the highway to the Speech Switch. The EPROM contains a table of silence samples, so that in effect silence becomes another tone. The cadences for the different supervisory tones are provided by the cadence logic which causes silence samples to be read out during the "off' periods of the tones.

The Table shows the various tones currently assigned to the different ports allocated to the Tone Generator, and the levels of tones as measured at the Main Distribution Frame (MDF). Lower levels have been adopted for the 1000 Hz and 1400 Hz tones to take account of psophometric weighting considerations. The 1000 Hz tone is not used at present. The interrupted dial tone reminds the user that calls to his extension are being diverted. Different tones required in other networks, can be provided as an alternative by suitably programming the EPROMs and, where cadence changes are required, by replacing one of the ICs.

Early Monarchs the 1 had a whole card set aside for tone generation. Below is a 1981 ASU 1A1/SA20032 supply tone generator

ASU 1A1 SA20032 SUPY TONE GENERATOR

7.The MF Sender

An SSMF4 Sender is provided on the Services Card to enable outgoing calls to be set up over exchange lines that terminate on public exchanges equipped with SSMF4 keyphone receivers but the main processor program does not enable this to be used at present. When the CPU recognises that an outgoing call requires to be routed over a circuit which employs MF signalling, it immediately sets up a connection between Port 13 on the outgoing Speech Highway from the Services Card and the "send" path of the circuit concerned. A connection is set up at the same time between the Dial Tone Receiver (Port 13 on the incoming Speech Highway of the Services Card) and the "receive" path of the circuit concerned. When enabled by the Dial Tone Receiver the CPU then forwards each digit as it is received over the Signalling-In highway to Port 13 on the Services Card, and the SSMF4 Sender converts the digit from the binary form in which it is received over the signalling highway to the appropriate MF tone combination for transmission over the outgoing circuit. As soon as the CPU concludes that dialling has been completed it releases the connection to the SSMF4 Generator and sets up a connection between the calling extension and the outgoing circuit.

The binary to keypad signal converter captures the required binary encoded signalling bits from the signalling-out highway during the appropriate port slot time, and converts them into a DC encoded form identical to that produced by the key pad in an MF keyphone. The signals then enter a standard tone generator, as used in MF keyphones, and the resultant MF signals are fed via a low pass filter, (to eliminate any unwanted frequency components) into a standard analogue to PCM coder, the output of which is connected via the Binder to the outgoing speech highway at the appropriate port time.

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The SSMF No 4 Sender 5.7.1 The SSMF4 Sender produces MF tone signals to represent digits 0 to 9 and the * and # symbols. Each digit, or symbol, is represented by a combination of two tones, one in the frequency band 697 to 941 Hz and the other in the band 1209 to 1633 Hz. Four of the 16 possible frequency combinations are unused at the present time. Each signal is sent in response to an instruction from the CPU and all timing is carried out by the CPU. For example, the insertion of inter-digital pauses is effected by the CPU releasing the connection through the Speech Switch between the sender and the outgoing exchange line. This allows the sender to be time shared, when necessary by a number of concurrent calls.

A schematic diagram of the SSMF4 Sender is shown above. Instructions from the CPU are received via Port 13 on the highway from the Signalling Circuit and the 4 bits of the signalling byte which represent the digit or symbol to be sent, are converted to parallel form by an SIPO converter. These bits are then set in a latch which maintains the conditions on 4 leads to a signal format converter. This converter changes the binary encoded signals into coded combinations on 8 parallel wires corresponding to the output from the standard keypad on an MF Keyphone. The information is then fed into a standard MF keypad tone generator (Mostek MK 5089, or equivalent),

which produces the required MF combination in analogue form. The analogue signals are passed via a band limiting filter, which removes any unwanted harmonics, to the input of an analogue to digital converter (the coding half of a codec of the type used on the non-concentrating line shelf, running at 2048 kbit/s) from which they emerge in PCM encoded form and are forwarded via the Binder to port 13 on the outgoing speech highway. The unused half of the codec is used to provide the digital to analogue conversion circuit in one of the MF Keyphone Receivers.

The Binder

A block schematic diagram of the Binder, the function of which is described in Part 1, is given in Figure 33. It consists of 2 separate parts -

a "speech binder" shown in the upper half of the figure, and a "signalling binder" shown in the lower half.

Considering the speech binder, the outputs of the various items on the Services Card which require access to the speech highway are' connected to the input terminals of a data selector. A speech time slot counter, which is re-synchronised at the start of every lms multi-frame, provides the drive for selection logic which causes the selector to connect each input to the outgoing speech highway at the correct

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