Paging infrastructure: differentiating services
Primary considerations of paging providers are protecting capital investment, allowing for incorporation of new technologies and ensuring system redundancy,
Radio paging’s odyssey has taken it from 1950s simplicity through the development of wide-area networks in the 1960s to the establishment of satellite systems and the current mix of protocols and diverse applications. The current availability of, and demand for, multiple services places the paging providers in a position of requiring infrastructure that will help reduce churn, manage subscribers, increase revenue and differentiate that provider from competitors.
Infrastructure for providers has graduated from the original model (call input to system control to transmitter to pager), to broadly based services accommodating monitoring and remote control, in-building coverage and multiple base sites, as shown in Figure 1 below.
New coding systems added tones to increase address capacity. Simple alert paging was succeeded by tone-plus voice and both numeric and alphanumeric display.
Although alphanumeric is the most rapidly growing segment of radio paging, many providers need to accommodate all these formats.
The availability of new frequencies is changing the type of equipment used as well, with narrowband PCS spectrum being targeted for two-way paging, and speech recognition software entering the market.
The ability to handle multiple protocols is requisite. The many analog and digital protocols include two-tone, Reach, DTMF, HSC, 5/6-tone, POCSAG, NEC and Golay. Golay is still expected to have several years of life, and POCSAG will probably be around for at least another decade. New digital protocols, like Motorola’s Flex, designed to provide greater error immunity and higher data rates, are being rapidly adopted.
Some manufacturers are promoting open architecture platforms. Wayne Morris, general manager of TGA Systems, Norcross, GA, said recently that primary considerations of paging providers are protecting capital equipment investment, allowing for incorporation of new technologies and ensuring system redundancy.
The following is a synopsis of infrastructure advances currently available in the market.
Terminals and transmitters Paging terminals are available for both analog trunk and digital (T1 or E1) trunk groups. Incorporated databases list details of pager type, current status and capcode and channel information. Voice processors are now available to store voice messages for user retrieval. Digital paging network analyzers monitor paging channels and can display the paging format, the frequency under observation, the total pages by format and elapsed time between batches.
Some VHF paging transmitters feature adjustable power, intelligent communications controllers to detect analog/digital mode, signal processor modules and VHF modulators and exciters to provide stability and frequency agility.
High-speed UHF paging transmitters, with power options as high as 500W, are available to support all existing protocols, including Flex. When coupled with a controller, the transmitters can be upgraded remotely using a network manager, reducing the time and cost of site visits.
Modular and small systems Modular paging systems allow flexibility in configuration. Transmitter, receiver and monitor modules can be set up in rack-mount or panel-mount configurations. Manufacturers can also supply completely assembled paging stations with power supply and other options combined in a single cabinet. Transmitters can be programmed by a PC for as many as 128 frequencies.
Terminals specifically designed for small and medium size in-house paging systems (about 1,000 subscribers) can be used as plug-in modules to an existing PC. This allows both tone-only and numeric pages to be sent with a telephone interface or alphanumeric pages to be sent directly from the keyboard, or from remote terminals using an IXO input protocol.
Amplifiers A unidirectional amplifier allows extension of coverage into areas where RF penetration is difficult. Channelization of the amplifier allows for high selectivity, which enables it to ignore other paging services in the same area. Units can also selectively amplify multiple 900MHz frequencies. Some models offer individual gain adjustment for each channel for continuous control.
Directors To increase centralization of network architecture, high-capacity directors can be added to RF control systems. Capable of supporting from 350,000 to millions of subscribers on a single system, directors have high-capacity CPUs in a multiprocessor design that simplifies and upgrades as an operator’s subscriber base grows. Migration to higher-capacity CPUs allows the Ethernet speed to be increased to 100Mb per second. By enhancing existing directors, paging operators can consolidate equipment resources and minimize costs.
Expanders Alphanumeric paging port expanders offer higher baud rates and enhancements to equipment. TDD access features are now available, which make a system ADA-compliant without additional lines or modems. Modem cards can be obtained in 2,400bps and 14,400bps versions.
Controllers TNPP network controllers allow extension of coverage on a regional or nationwide basis. Statistics computers can be added to the controllers to allow customer use information to be collected for subscriber management purposes such as reseller billing.
Multipurpose communications controllers use computer and digital signal processing technology. Windows-based GUIs, a larger system disk and memory storage for user databases and voice files can be included. Users can access voice mail and paging subsystems with a single phone call. Users can also define their own access preference, message notification schedule, greeting messages and mailbox tree. Controller systems can be expanded from four trunks to 128 trunks to accommodate operator expansion.
Encoders Pager testers, or universal paging encoders, allow accurate measurement of pager receiver sensitivity. Line filters on inputs and outputs serve to prevent EMI in both directions.
When incorporated into a computer-based system, paging encoders can accommodate capcode increment/decrement, one-key configuration change and preprogrammed canned messages. Repeat modes, test mode and over-the-air programming are available on some computer-based encoders.
Gateways Applications gateways allow the connection of wireless networks to the Internet. This allows new two-way paging applications such as multistage email transmission with multiple response capabilities. Services such as World Wide Web messaging allow paging operators another way to differentiate themselves in their market.
Load management modules The increase in paging subscribers and differentiation of services, such as Internet gateways and automatic alarming, has created a market for products aimed at load management. Sentries, which can be added to messaging gateways, monitor incoming traffic to prevent overloading and system abuse. The sentries can identify and control traffic trends, abrupt changes in calling patterns, excessive message length and unusual leaps in volume from a single source or to a specific subscriber. Bottlenecks in traffic can be prevented by flagging messages for administrator intervention, trickling out messages, segmenting transmissions or deferring traffic to off-peak periods.
For a discussion of testing and monitoring paging infrastructure, see the feature on remote control on page 30.