POCSAG Coding Rules

Group Calls - General

Pager group call

Terminal group call

Information Services

Invalid POCSAG codes

Code Assignment Strategy

Source Identification

Function Codes for Information Services

Message Indication Types

Mail Drop

Paging Terminal and Mail Drops

Message Storage

Group Calls

Group Call Capcode Assignment

Capcode Assignment Illustration

POCSAG frames

ADVISOR™ Message Receiver - POCSAG Coding Rules

The Motorola ADVISOR™ is capable of supporting 1, 2, 3, or 4 POCSAG codes.

Here are the rules when requiring two POCSAG codes:

• Every pager must have a Code A.
• Code A and Code B must be in the same frame.
  (formula provided below)

Here are the rules when requiring three POCSAG codes:

• Every pager must have a Code A.
• Code A and Code B must be in the same frame.
  (formula provided below)
• The frame of Code C cannot be equal to the frame of Code A and Code B.
• The frame of Code A and Code B must be less than the frame of Code C.

Here are the rules when requiring four POCSAG codes:

• Every pager must have a Code A.
• Code A and Code B must be in the same frame. (Formula provided below)
• There must be a Code C to have a Code D.
• Code C and Code D must be in the same frame
• The frame of Code A and Code Be cannot be equal to the frame of Code C and Code D.
• The frame of Code A and Code B must be less than the frame of Code C and Code D.

Formula to find the frame number:

• Divide each Capcode by 8.
• Take the decimal remainder and multiply by 8.
• The result is the value of the frame (or frame number).

More Examples

Group Calls - General
There are two general methods of performing "group call." When several users are assigned to a common group so that they can all be paged in one transmission, this is called Pager group call. All the pagers in the group must have a common capcode. This type of group call is only possible with pagers that can have more than one capcode because of the requirement for both individual and group message reception. Since most modern pagers can be programmed with several different capcodes, this is now the most widely used type of group call.

Another type of group call that is not used very much anymore, is the Terminal group call. In this type of group call, the individual capcodes within the group are unrelated to each other. This group call is initiated by sending one message to a subscriber record, or a "pilot number" in the paging terminal. The paging terminal contains all the members of that group stored in its memory. The terminal then sends the message to each subscriber in the group, one after another. This results in separate transmissions to each subscriber and is very expensive in terms of air time. Not all paging terminals can do a group call of this type, and some paging companies do not offer this type of group call to their customers although their terminal has the capability. There are two reasons for this: 1) This type of group call is wasteful of air time since the group call message must be sent separately to each member of the group, and 2) some older paging terminals slow down considerably while they search the whole data base to locate all the members of the group. This can also create a delay between the time the first pager in the group and the last pager, receive their copy of the message.

Information Services
Subscription to information services is a very promising application of radio paging. Information services may include news headlines, weather forecasts, sports scores, and financial information. It is important to understand how to properly assign group call or Mail Drop codes for this type of service for the following reasons:

• The overall throughput of the paging system is dependent on the POCSAG batching efficiency of the system. The POCSAG code contains eight "frames" in each "batch" and all frames must contain some kind of information when a batch is transmitted to the pagers. Each pager capcode always gets sent in its assigned frame. So, if it is time to send out a POCSAG transmission, and there are no pages waiting in queue for any of the eight frames, the paging terminal must substitute an "idle codeword" (which is an unused capcode) to fill the space in the frame. The point is that if too many idle codewords are transmitted this is a waste of valuable airtime, a decrease in the grade of service, and a reduction of the number of subscribers that can be supported on the radio channel.

• Properly assigned group call codes in the same frames as the individual codes, will not cause a decrease in the useful life of the pager's battery. Assignment of a second code, outside the frame of the individual code, will result in an approximate 30% decrease in the pager's battery life.

• A logical plan is required to allow for an orderly and well planned use of the two million POCSAG codes available per radio channel. The actual number is 2²¹ or 2,097,152 (* less some invalid codes as shown below). Or, if you count the total number of addresses, the number is 2²³ (over 8 million) per channel. There are about 250,000 available capcodes per frame.

The POCSAG code makes it easy to order pagers evenly distributed across the eight frames of a batch. The eight frames are numbered zero through seven (0-1-2 3-4-5-6-7). If pagers for individual messaging use are programmed sequentially, they will be equally distributed, because each time the capcode is incremented by one, the next code is assigned to the next higher frame until frame seven is reached. After frame seven, the assignment jumps back to frame zero. This can be easily seen in the POCSAG frame tables that begin on page below.

Code Assignment Strategy
Since this is a paper about the ADVISOR pager, it will continue to be used as an example while different ideas are presented about pager code assignments. These same ideas should be applicable to other model pagers by taking into consideration their different specifications especially those relating to code and memory capacity.

Source Identification
It was pointed-out previously that an ADVISOR pager can be programmed with up to four cap codes. Page one of this paper explained how these codes must be related to each other. Each POCSAG code has four "sub-codes" which are called, Function Codes, Addresses, or Source Identifiers. All three of these names are commonly used to describe the same thing. These codes were first used to show the source of a tone-only page. By assigning different numbers to the paging terminal and then giving out these access numbers to certain people, it was possible know the source when receiving a page. For example you could give one number to your boss, another to your wife, and another to your secretary. When your (tone-only) pager beeps, a distinct sound would show which number at the paging terminal was called and therefore the source (or origin) of the call.

It would work something like this: Your boss wants to get in contact with you, s/he would dial 364-3779. The public telephone network would switch the call to the carrier's paging terminal and relay the last four digits "3779" to the paging terminal. The paging terminal would use the incoming "3779" digits to look up your subscriber record. This record would show that your tone-only pager has capcode "1234567" with function code number one activated. The paging terminal would send your code over the correct radio channel. IF you are within the radio coverage area, IF your pager is turned on, IF your battery is good, and IF there are no strong electrical noises in the vicinity, then your pager will beep. Key to identifying the source is that there are four different sounding beeps. The best way to show this is with another example:

So, if you hear the sound associated with source-code (or address) number one, you know it is your boss calling, the sound for source-code two means it is your wife, and the sound for source code three could mean for you to call your secretary.

That is how the source code got started - to show the source of the call to a tone only pager. With a numeric or an alphanumeric display pager the source-code is not so useful since the telephone number of the calling party is displayed on the pager, or better-yet, a complete alphanumeric message tells you everything you need to know.

Function Codes for Information Services
For Information Services we can make very valuable use of this extra part of the capcode as an "address code." Since the ADVISOR has a capacity of four capcodes and each capcode has four Addresses, (also called source-codes or function codes) then we can have up to sixteen different Addresses in the pager. This is great for Information Services and is exactly what we do when we set up the "Mail Drop" feature in the ADVISOR.

Message Indication Types
Messages sent to the ADVISOR can be selected as individual, group, or Mail Drop. Individual messages, also called personal messages, are shown on the first line of the message-status screen. Group messages are indicated by a special group prompt at the end of the message. Individual messages can be shown with the address number if the Show-Source option is selected. Mail Drop messages are displayed on the second line of the message-status screen.

Mail Drop
Any of the four address codes can be selected as Mail Drop. Mail-Drop messages differ from private messages as follows:

• Mail-drop messages always go into a designated slot corresponding to the "address" number, i.e. an address-two message goes into the second slot of line two of the display
  
• Mail Drop messages cannot be locked, they are automatically replaced by a new message
  
• No duplication of Mail Drop messages
  
• Mail Drop messages cannot be transferred to the History Dump File
  
• If the "Save Mail Drops" option is selected, all Mail Drop messages will be saved in non-volatile memory.

Paging Terminal and Mail Drops
Each of the 16 possible addresses in the ADVISOR must be treated as a separate capcode in the paging terminal. This can easily be accomplished in most paging terminals. It is simply a matter of setting up four subscriber records for each capcode and programming each record for a different address (function code or source code). Please refer to the Capcode Assignment Illustration below. If the carrier is offering four information services on one capcode and a subscriber only wants to pay for three of them, then the ADVISOR can be programmed with an "X" in that slot, making that address inactive.

Message Storage
The ADVISOR can store up to 20 personal messages (individual or group) that are located on the first line of the message-status screen. Newer (or unread) messages are located on the right side of the first line; older messages are located on the left side of the first line. The pager can store up to 16 Mail Drop messages that are located on the second line of the message-status. (If all 16 are used there would be no address available for personal messages.) Also, up to ten messages can be stored in the history dump file and up to ten messages in the personal message file. A single alphanumeric message can be up to 2000 characters in length, depending on system capability.

Group Calls
Group calls are very effective for firemen, security personnel, and medical response teams. A cardiac-arrest-response team might be made up of several doctors and nurses each having an individual code for private messages and a group-call code for alerting them all at the same time that someone has had a heart attack.

For a large-scale Information Service operation, Group Calls probably do not offer enough flexibility for long-term growth. It would be better to allocate code "C" and/or code "D" for Information Services. This will cause a minor reduction in the pager's battery life (approximately 30%), due to its operation in two different frames, but will make the assignment of the different Information Services easier.

Another example: the table on the following page shows how to select a group call code and then assign ten pagers with individual codes to the group. Each pager will have an individual code for private messaging, and a group call code for messages of common interest to the whole group. This table illustrates the rule that each individual code in the group must skip eight codes in the sequence so that all the codes will be in the same frame. Another table follows on the next page, showing the same codes which were selected, but illustrating them grouped together.

This is an illustration of the ten codes selected from above. There are ten individual codes and one common group-call code. The assignment of capcodes to Code "A" and Code "B" in the pager is also shown. All the codes are in the same POCSAG frame ( i.e. frame 7 ).

Please note that according to the Coding Rules on page one, a pager programmed according to this example cannot have Codes "C" and "D" added later. Let's review the rules for four POCSAG codes in the ADVISOR:

• There must be a code A
  
• Codes A and B must be in the same frame
  
• If there is a code D there must be a code C
  
• Codes C and D must be in the same frame
  
• Codes C and D cannot be in the same frame as code A
  
• Codes C and D must be in a higher frame than codes A and B

So if there is any possibility that these users would want to subscribe to Information Services in the future, it would be better if their codes were in a frame less than frame seven. This, however, would not be a major problem since a pager can be easily reprogrammed at any time. If a carrier should want to offer eight different Information Services, on the following page there is an example of one way to program ADVISOR pagers for Individual, Group, and Information Services. An ADVISOR can only operate in two frames.

Capcode Assignment Illustration

To determine which frame a capcode is in, locate the last 3 digits of the 7 digit capcode in this table. The column will indicate the correct frame for all capcodes.