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Input Protocols

Input protocols can be broken down into two sub-groups: telephone trunk protocols and data input protocols. Telephone trunk protocols are those that are normally used by human callers accessing a paging terminal to enter tone only, numeric display, alphanumeric display and voice pages. Data input protocols are most often utilized to enter alphanumeric paging data into a paging terminal. This information can come from a handheld data entry device, such as the RTS palmtop Pagentry™ product; desktop data-entry devices like the Motorola AlphaMate™, Canamex QUIKPAGER or IXO TC-200 input devices; from laptop, personal or mainframe computers; and from computer terminals connected to computer networks. Telephone trunk protocols are generally manufacturer-specific. The alphanumeric input protocol, on the other hand, has become an industry standard and is known as the Telocator Alphanumeric Protocol, a.k.a. TAP. An industry standard alphanumeric and binary input protocol, known as the Telocator Data Protocol (TDP), was developed in conjunction with the introduction of paging receivers capable of receiving digital data within portable computer devices.

Radio page requests that are entered via an input protocol can be paged directly from the paging terminal that the caller has accessed. In addition, these page requests can be moved to other paging systems within a network of paging terminals in order to provide a coverage region that far exceeds the geographical area controlled from a single system. This "network paging" can allow subscribers to be alerted across multiple cities, multiple states, within entire time zones or across the nation. Several manufacturers have developed their own specific protocols for moving paging information within networks of their own paging terminals. BBL Industries, now part of Glenayre Electronics, developed the patented Data Link Module (DLM) protocol. Spectrum Communications, now part of Ericsson, developed the Data Link Handler (DLH) protocol. Motorola utilizes a proprietary inter-paging terminal protocol. However, the paging industry has standardized on manufacturer independent protocol for use both within paging terminal networks as well as between networks operated by different carriers. The Telocator Network Paging Protocol, TNPP, is currently used throughout the world to provide for "wide-area" paging. Another networking protocol has been adopted by the paging industry as a superset of TNPP. The TIPP protocol, based upon the same communication standards utilized within the Internet, is designed to provide all of the features of TNPP as well as enhanced networking capabilities.

Transmitter control protocols operate between the paging terminal equipment and the radio transmitter equipment that is connected to the antenna network. These protocols select a specific set of antenna sites that simultaneously transmit radio paging information.

Different paging device manufacturers have developed specific protocols to communicate "over-the-air" between the antenna sites connected to the paging terminals and the radio pagers themselves. The protocols are often referred to as "encoding formats" because paging information is "encoded" in various ways. These encoding formats provide techniques to uniquely identify individual pagers and may forward additional information, such as a voice message, a display message, or digital computer data which is specific to a single receiver. Most paging networks support many different paging formats over a single frequency. The proper technique to utilize in encoding paging information is defined through information which is stored in the database of the paging terminal processing the paging request.

The earliest pagers used analog techniques to alert pagers. The two-tone format initially was introduced and was followed later by the five-tone and six-tone formats. Digital paging formats, providing features and functions that exceed the capabilities of analog formats, are the preferred method of paging today. Among the many digital encoding formats in existence are: Golay, NEC-D3, Mark IV, Mark V, POCSAG, MBS, RDS, ERMES, APOC, and FLEX™. A proprietary digital technique based upon FM radio subcarrier is in use in the AT&E, now known as S&E Message Watch, wristwatch pager. A hybrid technique which provides many of the feature advantages of the digital formats but in an analog implementation, is known as hexadecimal sequential code (HSC). A commonly used format in the United States, which can be heard over radio paging frequencies (referred to as paging channels), is Morse code. The FCC requires that every radio station in the United States transmit its call signal at least once every hour, and this is most often sent as a Morse code signal.

Two-way paging has introduced the ability for a paging device to send responses and unsolicited messages in a wireless fashion directly from the paging receiver. With the introduction of two-way paging are a new set of page encoding formats capable of carrying the additional information required in a two-way messaging environment. Among these encoding techniques are the Motorola ReFLEX™ and InFLEXion™ protocols, the Nexus Telecommunications Ltd. NexNet™ protocol, and the Philips Telecom Radio Mail Protocol (RAMP) two way pager formats.

Each manufacturer has developed a system-specific digital communications protocol that allows an external computer system to perform customer database maintenance functions, billing functions and/or paging functions. Protocols known by such names as the Computer Port Interface (CPI) protocol, Host PX Interface (HPI) protocol and the Host Computer Port (HCP) protocol, commonly are used between "billing and customer database maintenance" business computers and the online paging terminals.

As new paging features and services are developed, some existing protocols are enhanced and new protocols are developed. Because of the requirement that protocols support both old and new equipment within a paging network, it is not unusual to find a large number of the protocols mentioned coexisting in a single network. For example, when paging receivers having a PCMCIA form factor for insertion into laptop and palmtop computers were introduced, a new protocol needed to be developed to support the transmission of data (spreadsheets, database information, computer programs and other binary data) to these devices. The TDP protocol, introduced for data entry on behalf of these devices, was designed to coexist with protocols already in place. Two-way paging capabilities will introduce further protocol enhancements and upgrades to support the capabilities introduced with this technology.

Please note that the material in the following sections will describe many different protocols used throughout current paging networks. The information discussed is meant to give the reader a general idea of how each protocol operates. For complete information on any protocol, more detailed reference manuals should be consulted.

Input Protocols
Paging request are forwarded to a paging network via a paging terminal. This is the central computer system that controls the receipt and forwarding radio page requests to the transmitter network or to remote paging terminals for transmission over one or more remote transmitter networks. Subscribers primarily access the paging terminal through the Public Switched Telephone Network (PSTN). Local telephone numbers may be used, foreign exchange (FX) lines may be accessed by callers in order to dial local numbers in remote locations or toll-free WATS (800) numbers may be accessed to provide wide-area service. The paging terminal is connected to these lines from a telephone company central office. The interconnection could be via individual lines, each carrying one telephone call, or via a digital link, such as T1 in the United States and CEPT/E1 overseas. A T1 link allows up to 24 simultaneous calls to be received over a single cable, while CEPT/E1 supports up to 30 simultaneous calls.

Over these incoming telephone lines, there are two major classes of protocols which operate. One class is often referred to as analog telephone trunk protocols, and the other class is the digital communication protocols. The analog trunk protocols allow callers to enter tone only, numeric display, alphanumeric and voice pages, while the digital protocols allows remote computer-driven devices to enter tone only, numeric or alphanumeric display pages as well as digital (binary) data for receipt and processing by computer programs in portable computing devices.

About Analog Trunk Protocols . . .

Selector Level and End-to-End Lines
Direct human access via telephone handsets in order to initiate a radio page request generally is performed through the analog trunk interface to the paging terminal. Part of the trunk protocol that is utilized for input is dependent upon the type of service that is arranged with the central office equipment. In general, there are two types of interconnection mechanisms that may be employed. One type is Direct Inward Dialing (DID) or Selector Level service, while the other is known as End-to-End service (see Chapter Six for additional information).

End-to-End service is the same type of service that normally terminates in a home. When someone calls into an End-to-End type line, the telephone will ring, and when the call is answered you must ask who is calling. The trunk protocols of the paging terminal must perform this same function in order to determine who is being called for the purposes of requesting service from the paging system.

Selector Level service is the same type that normally terminates in a Private Branch Exchange (PBX) used in many office situations. When someone calls into a Selector Level line, the telephone line indicates that a call is coming, and the last few digits of the called telephone number are forwarded by the central office to the paging terminal. Because the paging system is aware of the range of telephone numbers that are serviced by the incoming line, by receiving these digits, the called telephone number may be determined easily. Therefore, on DID lines, the paging terminal immediately knows that subscriber is being called.

The number of digits forwarded by the central office is determined when the service is ordered. Any number of digits from zero to seven may be forwarded. The more digits that are forwarded, the more telephone numbers that may share the single line. For example, a three-digit "feed" allows the thousand numbers of the form NXX-X000 to NXX-X999 to all reach the same selector level line.

Generic Telephone Input Protocol
There are many variations of analog trunk protocols used among the different manufacturers' paging terminal equipment. All of the existing trunk protocols allow the caller to access a particular subscriber and to optionally enter a message to send to the pager. Some trunk protocols go a step further in allowing the caller or the subscriber to access "value added services" over the same incoming telephone lines. Although they look very similar, there is no standardization among paging terminal equipment for these input mechanisms. But, many manufacturers emulate the trunk protocols of other manufacturers so that their equipment may replace existing equipment without retraining callers on the procedure for accessing the paging service.

Generically, a telephone trunk protocol for paging input operates as follows:

Generic Trunk Protocol over Selector Level Lines

Caller Telephone Central Office Paging Terminal
Goes off hook and dials the subscriber's telephone number, such as 555-7892. Alerts the paging terminal that a call is coming and then forwards the digits 7892. Collects the incoming digits and determines that account 555-7892 has been accessed. If the number is found to be valid, the paging terminal accepts the call by signaling the central office.
  Accepted call signal causes a direct voice path to be connected from the caller to the paging terminal. Generates at least one ringing tone to the caller.

For tone-only calls, the paging terminal may generate a specific beep pattern to indicate that a valid subscriber has been accessed and a tone only page has been accepted. Some paging terminals may generate a voice prompt to indicate that the page was accepted.

For a display paging call the paging terminal may generate a specific beep pattern, play a generic voice prompt, or play a subscriber prerecorded voice message asking for the caller to enter his/her telephone number.

Caller enters digits to be displayed on the pager. After the last digit the user may hang up, just wait for a few seconds or, in some paging terminals, depress the "#" key to indicate immediately that this is the complete message.   A specific page acceptance beep tone or generic voice prompt is played. The central office is then signaled to terminate the call.
  The voice path from the caller to the paging terminal is broken down.   

The generic protocol followed over End-to-End lines is similar except that the first phase of the call, when the telephone company automatically forwards the last few digits of the telephone number, is replaced with a manual procedure that requests that the caller enter the last few digits of the number. Upon calling into the paging terminal, a specific beep pattern or generic voice prompt is heard, soliciting the caller to enter the subscriber's identification number. After this number is specified, the call proceeds in exactly the same way as if the digits arrived automatically from the central office.

The input protocols also use the "*" key for a special meaning. In many cases, this key indicates that an incorrect digit has been entered and that the input is being restarted. In some systems this key is used to enter punctuation (spaces and hyphens) into the display message that ultimately will be transmitted. There are other systems which utilize this key to indicate that specialized services are to be activated.

Voice paging can be initiated through these same trunk protocols. If a voice account is accessed, rather than entering dial digits, the caller may speak a message into the system. Following the speech input, the caller may wait for a page acceptance signal or, in some paging terminals, the caller may depress the "#" key to indicate that the message is complete.

Alphanumeric Input Via Analog Trunks
Different protocols to support alphanumeric input via analog trunks from normal telephones have been implemented in several makes of paging terminals. These input protocols are not in general use because the telephone keypad is not easily used for typing textual messages. In many of these implementations, the same key is depressed multiple times to enter a particular letter. The Touch Tone™ telephone keypad appears as follows:




The key sequence to enter the message "CALL HOME" could be:

   222*   2*   555*   555*   *   44*   666*   6*   33*   #
    C     A     L      L         H     O      M    E

Notice that each key is pressed the number of times to indicate its position. Once for left, twice for middle, three times for right. The missing letter "Q" can be the "7" key pressed four times, and the missing letter "Z" can be the "9" key pressed four times. Note that this simple message required the caller to press 28 keys.

Another input protocol requires that the caller enter the key number plus "1" for left, "2" for middle, "3" for right and "4" for one of the missing letters. With this protocol the same message would be:

   23   21   53   53   *   42   63   61   32   *   #
   C    A    L    L        H    O    M    E

This sequence requires 19 keystrokes for the same simple message. Although it is shorter than the other variation, both mechanisms require the user to enter an excessive number of keystrokes. In addition, it is easy to forget where you are in the input. If these mechanisms are used by callers, the amount of telephone trunk time required to enter these messages is excessive compared with the time to enter a numeric page. This increased call-holding time requires that the system administrator provide many more incoming telephone lines to avoid busy signals.

A proprietary protocol has been developed that allows an 80-character alphanumeric message to be input via Touch Tone™ signals in approximately the same amount of time as a normal numeric display page. This protocol uses data compression techniques to represent text messages in as few digits as possible. The protocol is too complex for a caller to directly enter alphanumeric messages using this technique. Instead, this protocol, known as AlphaTone™, is implemented in a handheld data entry device known as Pagentry™. Messages are prepared before calling into the paging terminal and are then transmitted via this Touch Tone™ signaling method. AlphaTone has the added advantage to the service provider that it allows callers to enter alphanumeric pages over the same telephone lines as those used by numeric display paging callers, and that these calls do not increase the average call holding time of the incoming telephone lines.

Enhanced Services via Analog Trunks
Some paging terminal manufacturers have provided "escape" mechanisms to leave the generic trunk protocol and allow the caller or subscriber to specify enhanced services. These mechanisms allow the same incoming telephone lines to be used to specify special features and services. For paging systems in which the subscriber numbers are not allowed to start with a leading "0," this key may be reserved to specify that enhanced services are required. Optionally, a combination of the "*" and "#" keys can be used to indicate that other services are being requested.

In many systems that have implemented these enhanced services, after the entry of the special key sequence, a voice prompt often is heard that indicates the sequence of digits that must be pressed to initiate different types of services. Depending on what service was selected, additional voice prompts may be heard giving further instructions. Among the types of special services that could be requested are:

The TAP Digital Input Protocol
The Telocator Alphanumeric input Protocol (TAP) has become the paging industry standard protocol for sending page requests from automated equipment, computers and other data-entry devices to radio paging systems. The TAP protocol primarily is used to forward one or more alphanumeric pages over a single telephone connection. TAP is a digital communications protocol, and devices that want to forward page requests use modem (modulator/demodulator) devices to convert computer digital information into a signaling format that can be decoded back into their original format via a modem at the paging terminal. This digital information is basically a sequence of ones and zeros that, grouped according to the TAP protocol, define a paging message.

In many paging systems, an End-to-End telephone number connected to the paging terminal is accessed by the remote data entry device. Because the paging terminal must use a modem to convert the incoming call back into its original digital format, separate sets of telephone lines normally are used to send pages digitally. Therefore, there normally is one set of telephone trunks for human callers and another set of trunks for computer-driven calls. Some manufacturers have developed telephone interfaces which allow touch-tone driven calls and modem signaled calls to utilize common incoming trunks.

The TAP protocol consists of three major phases:

These phases will be described in the following sections. The protocol does not specify the operational speed of the data transmission between the remote device and the paging terminal. Oftentimes, the paging terminal will adjust itself automatically to the speed of the input device. Speeds of 300, 1200, 2400, 4800, 9600 and 19,200 bits per second typically are used. The highest speeds sometimes are used on direct hardwired connections between computers and paging terminals, and the lower speeds are used on dial-up connections. Transmission normally takes place using seven-bit ASCII data with even parity. All of the alphanumeric data and control characters that are used follow the standard ASCII character set. In the subsequent sections the nomenclature of "<name>" refers to an ASCII control character of the given name. For example, <STX> refers to the character known as the Start of Text.

The TAP Sign-On Phase
Normally, the set of pages to be sent is prepared off-line in the remote entry device. When it is time to send the pages, this device will go off hook and dial into the special End-to-End telephone number. After the modems connect, the paging terminal will await the entry of a carriage return and respond with a prompt to solicit the "sign on" sequence. Several carriage returns may be required before the paging terminal responds. The complete sign-on sequence proceeds as follows:

Remote Entry Device Paging Terminal
Sends a Carriage Return <CR>  
  Responds with "ID=". This sequence may optionally be followed with a Carriage Return or a CR and a Line Feed <LF>.
Sends <ESC>PG1
<optional password>
Responds with the sign-on accepted sequence: <optional message><CR> <AK><CR>

When the paging terminal is ready to enter the transaction phase of the call, it responds with the Go Ahead sequence:


The incoming PG1 sequence indicates that this is an automatic paging input request. If an "M" is entered, this is a request to enter pages digitally, but in a manual entry mode. The paging terminal will provide prompts to solicit the pager number and message it is to send. Because the primary purpose of the TAP protocol is the automatic entry of messages, we will focus on this portion of the protocol.

There may be a small delay between the sign-on acceptance sequence and the "Go Ahead" sequence while the paging terminal prepares for message input.

If the paging terminal can not process paging calls at the present time, it may request that the caller disconnect. This is noted by sending this sequence -- <ESC><EOT><CR> -- instead of the "Go Ahead" sequence.

TAP Transaction Phase
During the Transaction Phase of the TAP protocol, the page requests are forwarded to the paging terminal. Each page request consists of the identification or access number of the pager to be alerted and the text of the message to be displayed to that account number. These two pieces of information are put together in a data block that must be fewer than 256 bytes (characters) in total. If the message being sent is so long that the total block size created exceeds the maximum size, the message text is broken up into segments of no more than 256 bytes.

For each transaction segment, TAP associates a "checksum" value with the block. This checksum, a value that will be sent with the data block to the paging terminal, is a mathematical value that is dependent on the data in the block. When the data block is received by the paging terminal, the same mathematical calculation is performed on the receive data, and the result is compared to the checksum value that was also received. If the values do not match, the paging terminal knows that the data or the checksum value was transmitted incorrectly and a retransmission is requested. With the checksum inclusion, the TAP protocol can ensure error detection and retransmission so that the message is received accurately.

The format of a complete TAP transaction is:

<STX> Pager_ID <CR> Message_Text <CR> <ETX>Checksum <CR>

If the transaction block can not fit the entire message text without the entire block exceeding 256 bytes, than the transaction is broken up as follows:

<STX> Pager_ID <CR> Partial_Message_Text <CR> <ETB> Checksum <CR>

as block one and

<STX> Additional_Message_Text <CR> <ETB> Checksum <CR>

for additional segments of the message and

<STX> Last_Segment_of_Message_Text <CR> <ETX> Checksum <CR>

for the last segment.

Each transaction block is transmitted and acknowledged for proper acceptance separately. On forwarding a transaction block, the paging terminal will respond with one of the following sequences:

Response Sequence Definition
Optional_Message<CR><AK><CR> Block received correctly, send next block if the block ended in an ETB. Page Accepted, send next message, if this is the last block of this transaction (block ends in ETX).
Optional_Message<CR><NK><CR> A transmission error has occurred, resend the block. A checksum error has probably occurred.
Optional_Message<CR><RS><CR> This may only be sent when the entire transaction is received. It means that the data was received correctly but the account can not be paged for the reason given in the message.

After accepting or rejecting a received page request, the paging terminal is immediately ready to move on to the next transaction. The calling device may immediately begin sending another page request as a sequence of one or more blocks. Some paging terminals may place a limit on the number of page requests on a single connection so that the incoming telephone lines are not tied up too long for one caller.

When the calling device has no more pages to send, it should move on to the disconnect phase of the call.

TAP Disconnect Phase
When the calling device wishes to disconnect from the paging terminal, it should perform the disconnect sequence before hanging up the telephone line. This is a "clean" method of disconnecting rather than abruptly hanging up on the call as if there were a problem in the telephone connection. The disconnection sequence proceeds as follows:

Remote Entry Device Paging Terminal
Sends: <EOT><CR> Responds with:
<Optional_Message><C R><ESC><EOT><CR>
  Hangs up the telephone line.
Hangs up the telephone line.  

Telocator Data Protocol (TDP)
The Personal Communications Industry Association (PCIA), formerly known as Telocator, is the governing body which administers paging protocols which are developed within its technical committees. The organization released a paging protocol which is known as the Telocator Data Protocol (TDP). TDP was developed as a next generation of the TAP protocol. Although TAP is being used successfully to input alphanumeric pages into paging systems around the world, the protocol does not provide mechanisms for a caller to activate any of the special features which are often available in paging systems. Some of these features, such as priority paging, time-of-day paging and periodic paging can often be activated through telephone trunks by the use of mechanisms that allow the caller to exit from the normal telephone protocols and begin a specialized protocol.

In addition to traditional paging, the TDP protocol supports the input of "data" pages into paging systems. A data page is any binary information that is to be broadcast to remote receiving devices. TDP is designed to allow database information, spreadsheet data, computer programs and other types of binary data to be sent into a paging system for eventual broadcast to laptop computers and palmtop (calculator sized) data organizers.

TDP is actually a family of individual protocols which work together in the receipt of messages and the delivery of this data in a well defined form to the receiving device. It is designed to support the input and delivery of wireless messages which are significantly larger in size than previously supported in paging networks.

The set of protocols and specialized message formats which comprise TDP are as follows:


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