Chapter 3

BASIC PAGING SYSTEM

BASIC SYSTEM

The key components include an input source, the existing wireline telephone network, the paging encoding and transmitter control equipment and, of course, the receiver or pager itself.

Starting with the input source, a page can be entered from a phone, computer with modem, a desktop page-entry device or through an operator who takes the phone-in message and enters it on your behalf. Once it is entered, the page is sent through the Public Switched Telephone Network (PSTN) to the paging terminal for encoding and transmission through the paging system. Typically, the encoder accepts the incoming page, checks the validity of the pager number and looks up the directory or database for the subscriber's pager address, known as the cap code, and converts the address and message into the appropriate paging signalling protocol. The cap code is a unique address which enables you to "locate" the specific pager you want to reach instead of all other active pagers in the paging system. The encoded paging signal is then sent to the transmitters (base stations), through the paging transmitting control systems, and broadcast across the coverage area on the specified frequency.

Encoder

Encoding devices convert pager numbers into pager codes that can be transmitted. There are two ways in which encoding devices accept pager numbers: manually or automatically.

In manual encoding, a paging system operator enters pager numbers and messages via a keypad connected to the encoder while in automatic encoding, a caller dials up an automatic paging terminal and uses the phone keypads to enter pager numbers.

The encoding device then generates the paging code for the numbers entered and sends the code to the paging base station for radio transmission.

Base Station Transmitters

These transmit page codes on an assigned radio frequency. Most base stations used are specifically designed for paging but some of those designed for two-way voice can also be used.

Page Receivers (Pagers)

These are essentially FM receivers tuned to the same RF frequency as the paging base station in the system. A decoder unit incorpo-rated into each pager will be able to recognize the unique code assigned to the pager and reject all other codes for selective alerting. Pagers can be intentionally assigned the same code for group paging. There are also pagers that can be assigned multiple page codes, typically up to a maximum of four, for individual and group paging and other paging functions.

The most basic function of the pager is alerting. On receiving its own paging code, the receiver sets off an alert which can be audible (tone), visual (flashing indicator) or silent (vibrating). Messaging functions can also be performed and these include voice and/or display (numeric/alphanumeric) messaging. Some pagers are able to perform all three message functions.

Paging systems can be classified into two types – manual and automatic paging systems.

MANUAL PAGING SYSTEM

Operational Description

The page sender uses a standard telephone to call a paging operator and tells the operator who or what number to page. The operator then enters the pager number on the keypad of the paging encoder, which is typically a telephone-style 12-key numeric keypad. The encoder converts keypad entries to the actual pager code and outputs code in a format to be sent via RF. For example, in 2-tone paging format the coded information is two sequential tones having certain frequencies and duration.

The operator monitors the paging frequency for traffic. If the channel is free, the operator presses the transmit button to send the pager code and then goes on to the next page.

The transmitter control unit powers up the base station transmitter and sends the pager code to the base station where it is transmitted. All pagers that are tuned to the frequency and within range of the base receive the RF signal sent by the paging base station. The one pager that correctly decodes its own code activates its alert signal which notifies the subscriber to take action.

AUTOMATIC PAGING SYSTEMS

Paging Terminals

A paging terminal is an automatic page encoding device that answers a telephone line and allows users to enter pager numbers and numeric or voice messages from standard telephones. Some terminals also accept text messages via telephone line connections to text-entry devices like personal computers. Also, paging terminals normally include a control unit for the paging base station so that the terminal can automatically transmit pages.

The features and associated functions of an automatic paging terminal are summarized below.

Telephone interconnect ----- Automatic answer and hang up
Prompts (voice or tones) ----- Tells caller when to provide pager number and message information
Database ----- Has pager numbers, pager code data, type of message expected, etc. in computer lookup table
Encoding component ----- Generates transmittable analog or binary coded signals from pager number
Transmitter control unit ----- Monitors channel, keys transmitter and sends signals to transmitter

Operational Description

The flow of a page in an automatic paging system is presented below for Tone, Voice and Numeric Paging and for Alphanumeric Paging.

Tone, Voice and Numeric Paging

Dials subscriber pager number
Caller enters numeric message via DTMF keypad or speaks voice message; then signals end of input
Validates pager number dialled; call acceptance is signalled to the exchange
For tone-only calls, a specific beep signal is sent to indicate to caller that page has been accepted
For voice/numeric display paging, a specific beep pattern or a voice prompt is sent to signal caller to enter his voice message or telephone number
A specific page acceptance beep or voice prompt is sent to caller; call termination signal is then sent to the exchange
Routes call to paging terminal
Sets up direct voice path between caller and paging terminal
Disconnects voice path

Alphanumeric Paging

Caller enters phone number, pager number and alphanumeric (A/N) message into A/N device
Device dials phone number
Device signs on
Device sends pager number and A/N message
Message is divided into segments if it is too long
Device sends disconnect sequence
Device disconnects telephone line
Paging terminal responds
Terminal prompts device to sign on (with password)
Responds with sign-on acceptance signal. Sends go-ahead sequence when ready
Each segment is checked to ensure correct reception. According to result of check, the appropriate response is given, e.g. a resend will be requested in the event of transmission error. When last segment is received, page accepted signal is sent
Paging terminal responds and disconnects telephone line
Routes call to paging terminal
Sets up direct voice path between caller and paging terminal
Disconnects path

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