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Chapter 16: Paging Components

The ability to locate and send some kind of message to someone carrying a small electronic device (a pager) has become a mainstay of modern existence. Once the province of the wealthy and of high level business figures; one now sees pagers hanging from the belts and purses of dock workers, secretaries, and even teenagers.

The ability to send and receive alphanumeric messages (i.e., those containing textual information beyond the simple digits easily entered from a telephone keypad), is increasingly common among modern paging equipment.

The desire to be able to send and receive such information has also increased, perhaps somewhat in advance of the technology for doing so, as until recently the primary method for entering and sending such data has been restricted to proprietary (and often expensive and difficult to use) hardware devices or computer software provided by paging services.

The fairly recent development of new standards for preparing and sending alphanumeric messages has made it possible to create generalized software solutions for performing these tasks. However, these “protocols” remain somewhat obscure and awkward to implement at the basic software level.

Given Async Professional’s mission of providing well structured and encapsulated solutions to serial, telephony, and basic TCP/IP communications needs; and with the new availability of standardized means of performing the required transmissions, Async Professional now includes paging components.

Sending Alphanumeric Pages

Async Professional provides components that support sending messages to alphanumeric paging devices using either TAP (Telelocator Alphanumeric Protocol) with a modem over a phone line, or SNPP (Simple Network Paging Protocol) over Internet using a TCP/IP socket connection.

While these two protocols are fairly different in their implementations, the Async Professional paging components provide a consistent interface to sending messages regardless of which transmission medium is in use.

TApdGSMPhone Component

The TApdGSMPhone component provides access to cellular phones and other GSM compliant devices. One of the more popular uses of GSM is the sending and receiving of SMS messages. The TApdGSMPhone component can send SMS messages through the GSM device, provide notification when SMS messages are received, and provide access to the GSM device’s internal message store.

Async Professional and SMS messaging

The TApdGSMPhone component encroaches upon a technology that is often misunderstood. GSM is the Global System for Mobile communications, a consortium of several leading cellular companies. GSM defines the communication protocol between the cell phone and the cellular service provider. GSM also defines a communications protocol between a terminal device (PC) and the cell phone. The TApdGSMPhone uses the text-mode AT command set defined by GSM Technical Specification 07.05 version 5.1.0, dated December 1996.

One of the features that make GSM popular is the text messaging that it provides. When people think of GSM text messaging they think of SMS. SMS stands for “Short Message Service”, and defines a message format that can be transmitted and received by GSM compliant cell phones. In Europe and Asia, SMS is very popular. The idea behind SMS is gaining popularity in the US, but most US cellular service providers take some liberties with their definition of SMS. Most US cellular service providers advertise SMS, but they do not use the SMS defined by GSM.

There are several cellular protocols being used around the world. GSM is used primarily in Europe and Asia; TDMA and CDMA are used in the US. TDMA and CDMA do not define the protocol between the PC and the cell phone, and cell phones using these protocols use different AT command sets.

The TApdGSMPhone component requires a GSM capable device that support text-mode AT commands. This usually means a GSM cell phone. At the time of this writing, very few US cellular service providers offered GSM cell phones. The TApdGSMPhone was tested in-house with a Nokia 5190. The TApdGSMPhone component uses only the commands specified as mandatory in the GSM Technical Specification for text-mode operation. If your cell phone is not GSM capable, most cellular service providers will offer a TAP or SNPP gateway. See the TApdTAPPager and TApdSNPPPager components for details on sending messages using those paging protocols.

GSM—more than paging

The TApdGSMPhone component supports sending and receiving SMS messages through the GSM device. It also supports managing the message store maintained by the device. The TApdGSMPhone component can retrieve all of the messages in the GSM device’s memory, delete messages, add messages, and otherwise manage the message store.

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