BusinessPhone Communication Platform 4.0
System Description ASB 150 02

## Support Functions For Telephony

Only functions that assist in the establishment of telephony calls and that support interconnection with other units are dealt with here. Telephony functions (and facilities) that interface with telephony users are described in other documents.

### Switch

#### PCM-channels

The switch in the system consists of a central switch circuit that, via two PCM-busses, is connected to all regional device boards. See also Switches and transmission.

128 individual devices can be connected to the central switch. The device boards possess regional switches, whereby the individual devices on a board can be connected when required. The 128 possibilities to connect devices to the switch are administered by the system as a central resource, consisting of 64 PCM-channels.

"PCM-channel" denotes a bothway (voice) connection between two parties.

#### Capacity

When a telephone call is established between two parties, telephone to telephone (internal traffic), telephone to public line (external traffic) or similar, a PCM-channel is seized and the relevant regional devices are ordered to connect themselves to the bus. When the call is terminated the devices are ordered to disconnect, whereafter the channel is declared free.

The 64 PCM-channels are used in the following manner:

- 1 channel is permanently reserved for silence and for music-on-hold connected via CPU‑D_
- 2 channels are permanently reserved for certain supply of tones to extension lines (ELU‑A, ELU‑C, ELU‑D_)
- 61 channels are used for telephone traffic, voice messages and for background music.

If background music is connected in the system one PCM-channel (permanent) per music source is reserved. This channel is then used for all who listen to the music.

For conference calls and intrusion one PCM-channel is required per participant. For example in case of a 4‑party conference 4 PCM-channels are occupied.

For loudspeaker paging one PCM-channel (temporary) is used, irrespective of how many telephones are connected.

For each connected PBX-operator console, one PCM-channel will be reserved, even if the console is not used. For traffic another channel will be seized.

In cases where a "blocking-free" possibility is desired for connection to the public exchange, it is possible, via system programming, to reserve some of the PCM-channels for external traffic (corresponding to the number of connected public lines). This means that these PCM-channels will not be occupied by internal traffic.

### Tone generation

In this context, tone generation means traffic tones that are sent to extension lines and public lines (dial tone, busy tone, ring control tone, etc.) as well as digit transmission type DTMF to externally connected units (public lines and voice mailboxes).

All tones are generated by the tone sender unit (TSU) located on CPU-D_. TSU can generate all types of tones for all kinds of connected devices. Certain tone information is supplied to all extension boards ELU-A, ELU-C and ELU-D_ (two PCM-channels are reserved especially for this purpose). The extension boards can then generate certain cadences, but only to their own telephone lines.

TSU has the capacity to generate 32 simultaneous tone messages or DTMF-digits. 4 of these possibilities are permanently connected for tone generation on the extension boards. The remaining 28 possibilities of generating tone messages are utilised by the application programs in order to supply tone to an individual (telephone line) when required.

Theoretically some congestion can arise, but the possibility to supply tone messages to 28 individuals simultaneously is very adequate for a PBX of this size. Furthermore a tone queue is used, that is, if all of the 28 possibilities are busy when the tone is ordered, the order will be queued, and the tone message will be started as soon as some other tone message has been completed.

For extensions that have not been interconnected with any other device and which shall have a tone message, e.g. dial tone, busy tone, congestion tone etc. the tone message is generated by the extension board. There the tone generation is congestion free, i.e. a tone message can always be supplied.

The tones that are generated from TSU can be changed via system programming. Frequencies, levels and cadences can be chosen freely within certain limits (so that the same hardware can be used for all markets).

In the PBX a number (about 30) of different tone messages are defined for different traffic situations, e.g. dial tone, congestion tone, ring tone, warning tone, verification tone.

These 30 tone messages can, via programming by means of RASC, be given the character that applies for a certain market or an individual installation. This is executed by defining the cadence (times for tone/pause) for each tone message as well as of which tone elements (frequency/level) the tone message consists.

### Register signalling

#### General

Register signalling in this context means such signalling as can be exchanged between telephony units that are connected to the PBX (decadic pulsing, DTMF-digits, etc.).

Different types of signalling require different forms of hardware support. A certain type of unit is located on each device board and is used only for that board. Another type of unit is used as a central resource and is "lent" when needed.

A special register signalling unit (RSU) can support several different forms of signalling. This unit is located on BTU-D, REG and VMU-HD boards. The MFU board offers 4 registers and 4 DTMF receivers.

The BTU-D additionally provides the connection equipment for the digital trunk. The BTU-D can be strapped so that only the RSU-part is active. As an alternative, the REG board with only the RSU-part mounted exists.

The board has 12 common register-signalling units and is administered as a central resource. These 12 units can individually be receivers for DTMF- digits, dial tone receivers or senders/receivers for MFC/MFE. All depending on the current requirements of the PBX. Several boards can be installed, if required.

The VMU-HD provides voice storing capability and if selected can provide 8 voice channels and 4 common register-signalling units.

The MFU provides voice storing capability and 4 register-signalling units if the flash card is mounted.

#### Digital digit transmission

Digital signalling from and to our own system telephones is dealt with entirely by the respective line boards ELU-C and ELU-D.

Digital signalling to and from ISDN-connections is administered by the digital trunk on BTU-D and BTU-B. Other types of digital interfaces (CAS) are administered entirely by the digital trunk on BTU-D.

#### Decadic pulsing

Reception of decadic pulses (rotary dial) is administered locally on the analogue extension board, ELU-A, and on the analogue trunk board BTU-C. This function is completely non blocking.

Transmission with decadic pulsing to the public exchanges takes place locally, non blocking, on analogue trunk boards BTU-A and BTU-C.

#### DTMF-digits

Reception of DTMF-digits on analogue extension lines takes place locally on the ELU-A board. The board possesses four receivers that are shared by the board's 16 extensions.

For reception of DTMF-digits on all other device boards (trunks) the common register signalling units (RSU) on the BTU-D, VMU-HD or REG boards are used. For voicemail on the MFU 4 DTMF receivers are available.

To forward DTMF-digits from extensions or other interfaces to the public exchange, the digits are regenerated by the tone sending unit (TSU) that is located on the CPU-D. The BTU-_s enable the conversion from pulse dialling to DTMF-digits.

#### MFC/MFE

MFC or MFE signalling for all types of trunks is administered solely by the common register signalling units (RSU) on the BTU-D or BTU-E boards.

Note that the MFC/MFE-signalling on a line demands two of the twelve RSU-individuals (one sender and one receiver). Four concurrent send and receive signalling processes can take place at the same time.

#### E&M

E&M signalling exists only locally on the BTU-E board.

#### Dial tone

Receivers for detection of dial tone exist for local use on the BTU-A, BTU-C and BTU-E boards. One or two receivers per board are common for all individuals on the board.

When dial tone detection is needed for digital lines connected with the BTU-D boards, one of the common register signalling units (RSU) on the BTU-D boards is utilised.

#### Transmission

The PBX works internally with the speech information converted digitally to CCITT G.711 8-bit PCM A-law.

Connection to a digital environment with standard 8-bit PCM is achieved with the ELU-D and BTU-D boards. All other line boards have some form of conversion to/from 8-bit standard PCM.

On the extension boards for analogue telephones (ELU-A) and on the line boards for analogue trunks (BTU-A, BTU-C and BTU-E) the conversion to/from the analogue signals takes place with circuits that furthermore can adjust the relative levels of the analogue interface with the help of programmable parameters that are stored in the database.

In addition to the basic settings the relative levels of each interface can be modified depending on its connection case. The respective data is stored in a programmable matrix where one can specify how different groups of lines shall be adjusted when they are connected to one another. Eight different transmission groups can be administered. Each individual line can then be assigned any transmission group number (0-7).

One example of use is that the transmission in analogue tie lines usually is more attenuated when they are connected to one another (internal calls) than when they are connected to a telephone.

### Music

Analogue sound sources, such as radio or cartridge tape recorder, can be used for background music or music-on-hold.

The basic version of the PBX offers an analogue input on the CPU-D_ board. If more inputs are required, analogue trunk line connections (BTU-A) can be used as music inputs.

Additionally music-on-hold is a function that can be utilized using the MFU or VMU-HD by storing this part of music and playing it repeatedly.

Revision: K © Ericsson Enterprise 2003