Telecom/1996-04-telecom-walnutcreek.iso/technical/ixo.tap.protocol

Internet Message Format | 1993-02-14 | 41.2 KB

From: mc/G=Brad/S=Hicks/OU=[e-mail]
Date: 11 Feb 93 22:58:48 GMT
Subject: IXO.TAP.protocol part 1


TRANSCRIBER'S FOREWORD: Items like [1] are their footnotes, and usually
follow the table they're in.  Items like {1} are my notes, based on my
experience implementing from this crummy document, and follow at the end.
If you have questions about this, consult your paging vendor's linesmen or
engineers, not me. If you just want to say thanks, grumble, or complain,
you can reach me at mc![e-mail], or at
[e-mail], or (X400) c=US, admd=ATTMail, prmd=MasterCard,
sn=Hicks, gn=Brad.
   I work for MasterCard as a senior PC specialist, and that's why their
name appears in my X.400 address. This document is 100% my responsibility;
if you have a beef, it's with me, not with them.


Glenayre Electronics
GLP-3000-180
Issue 5: 91/01/30

Print Date: 2/13/91
Copyright (c) 1991 Glenayre Electronics. All Rights Reserved.
Pages 7-1 through 7-12


7. TELOCATOR ALPHANUMERIC PROTOCOL (TAP)

7.1 Introduction

In order to decrease holding times on input lines to alphanumeric systems,
it was desirable to promote input devices which will allow off-line entry
of paging information and dump this data quickly after connection to the
central paging terminal. This protocol was known as the IXO alphanumeric
protocol until it was adopted for the input of paging requests. It is now
referred to as the Telocator Alphanumeric Protocol (TAP).

Table 7-1 Call Delivery Sequence

    +----------------------+----------------------+----------------------+
    | REM. ENTRY DEV. DOES | PAGING CENTRAL DOES  | COMMENTS             |
+---+----------------------+----------------------+----------------------+
| 1 | Off hook-access DDD  |                      |                      |
|   | line.                |                      |                      |
|   | Await dial tone.     |                      |                      |
|   | Dial stored access   |                      |                      |
|   | number               | Ring Answer          |                      |
+---+----------------------+----------------------+----------------------+
| 2 | Carrier up           | Carrier up           |                      |
+---+----------------------+----------------------+----------------------+
| 3 | "<CR>" [1]           |                      | <CR> is repeated at  |
|   |                      |                      | two second intervals |
|   |                      |                      | until paging central |
|   |                      |                      | responds with ID= at |
|   |                      |                      | correct baud rate or |
|   |                      |                      | until three trans-   |
|   |                      |                      | missions have been   |
|   |                      |                      | completed. (This     |
|   |                      |                      | step exists to allow |
|   |                      |                      | for possible future  |
|   |                      |                      | baud rate recogni-   |
|   |                      |                      | tion).               |
|   |                      |                      |                      |
|   |                      |                      | Some systems have    |
|   |                      |                      | chosen to send ID=   |
|   |                      |                      | from the central if  |
|   |                      |                      | they do not receive  |
|   |                      |                      | <CR> in about two    |
|   |                      |                      | seconds. This vari-  |
|   |                      |                      | ation appears to be  |
|   |                      |                      | acceptable as the    |
|   |                      |                      | central continues to |
|   |                      |                      | respond to <CR>s     |
|   |                      |                      | with ID= s.          |
+---+----------------------+----------------------+----------------------+
| 4 |                      | "ID= " {1}           | Request for ID re-   |
|   |                      |                      | turned within one    |
|   |                      |                      | second of receipt of |
|   |                      |                      | <CR>. Paging central |
|   |                      |                      | may, at its option,  |
|   |                      |                      | send <CR> or <CR><LF>|
|   |                      |                      | after ID=.           |
|   |                      |                      |                      |
|   |                      |                      | Paging central may   |
|   |                      |                      | optionally choose to |
|   |                      |                      | send ID= if it does  |
|   |                      |                      | not receive <CR>     |
|   |                      |                      | after an appropriate |
|   |                      |                      | waiting time.        |
+---+----------------------+----------------------+----------------------+

[1] All quotation marks or the symbols <> shown are used for notation
    and are not transmitted.

Two options exist at this point:

* Automatic Mode (see section 5A)
* Manual Mode (see section 5M)

    +----------------------+----------------------+----------------------+
    | REM. ENTRY DEV. DOES | PAGING CENTRAL DOES  | COMMENTS             |
+---+----------------------+----------------------+----------------------+
| 5 | For automatic remote |                      | <ESC> signifies      |
| A | entry devices.       |                      | entry device intends |
|   |                      |                      | to talk in automatic |
|   | "<ESC>SST" {2}       |                      | dump mode. SS is a   |
|   |                      |                      | set of two alpha-    |
|   | Typical Example:     |                      | numeric characters   |
|   | "<ESC>PG1"           |                      | signifying a type of |
|   |                      |                      | service to be ac-    |
|   |                      |                      | cessed.              |
|   |                      |                      |                      |
|   |                      |                      | For a paging service |
|   |                      |                      | where:               |
|   |                      |                      | Field 1 = 'Pager ID' |
|   |                      |                      | and                  |
|   |                      |                      | Field 2 = 'Message'. |
|   |                      |                      |                      |
|   |                      |                      | SS will be sent as   |
|   |                      |                      | 'PG'.                |
|   |                      |                      |                      |
|   |                      |                      | Where T is a single  |
|   |                      |                      | alphanumeric char-   |
|   |                      |                      | acter relate to the  |
|   |                      |                      | type of terminal or  |
|   |                      |                      | device attempting to |
|   |                      |                      | send the message.    |
|   |                      |                      |                      |
|   |                      |                      | T = '1' is a cate-   |
|   |                      |                      | gory using the same  |
|   |                      |                      | protocol. The PETs   |
|   |                      |                      | and IXO devices are  |
|   |                      |                      | members of this      |
|   |                      |                      | category.            |
|   |                      |                      | T = '7,8,9' are re-  |
|   |                      |                      | served for wild card |
|   |                      |                      | terminals or devices |
|   |                      |                      | which may relate to  |
|   |                      |                      | a specific users'    |
|   |                      |                      | system.              |
+---+----------------------+----------------------+----------------------+
| 6 | "PPPPPP<CR>" {3}     |                      | This 6-character     |
|   |                      |                      | alphanumeric pass-   |
|   | GL-3000 will ignore  |                      | word comes from      |
|   | password             |                      | automatic terminals. |
|   |                      |                      | (Password is optional|
|   | Typical password for |                      | and is, in general,  |
|   | IXO is "000000"      |                      | reserved for future  |
|   |                      |                      | services. Password   |
|   |                      |                      | may be interpreted   |
|   |                      |                      | as either a caller   |
|   |                      |                      | ID or a system entry |
|   |                      |                      | key. Length of pass- |
|   |                      |                      | word, when used, may |
|   |                      |                      | be different in some |
|   |                      |                      | systems.)            |
|   |                      |                      |                      |
|   |                      |                      | When an incorrect    |
|   |                      |                      | logon sequence       |
|   |                      |                      | beginning with <ESC> |
|   |                      |                      | is received, the     |
|   |                      |                      | paging central may   |
|   |                      |                      | respond with an ID=  |
|   |                      |                      | if it requires a     |
|   |                      |                      | retransmission.      |
+---+----------------------+----------------------+----------------------+
|   |                      | "Message sequence    | Logon accepted       |
|   |                      | <CR><ACK><CR>"       |                      |
|   |                      |                      |                      |
|   |                      | or                   | or                   |
|   |                      |                      |                      |
|   |                      | "Message sequence    | Requested again      |
|   |                      | <CR><NAK><CR>"       |                      |
|   |                      |                      |                      |
|   |                      | or                   | or                   |
|   |                      |                      |                      |
|   |                      | "Message sequence    | Forced disconnect    |
|   |                      | <CR><ESC><EOT><CR>"  |                      |
+---+----------------------+----------------------+----------------------+
  * Gl3000 Typical Message Sequence: "Processing - Please Wait" or
                                     "4 pages sent"             or
                                     "Bad Phone Line Call Again".
    +----------------------+----------------------+----------------------+
    | REMOTE ENTRY         | PAGING CENTRAL DOES  | COMMENTS             |
+---+----------------------+----------------------+----------------------+
|   |                      |                      | A message sequence   |
|   |                      |                      | is defined as a      |
|   |                      |                      | series of short      |
|   |                      |                      | messages separated   |
|   |                      |                      | by <CR>s. A <CR>     |
|   |                      |                      | always follows a     |
|   |                      |                      | message sequence.    |
|   |                      |                      | Message sequences    |
|   |                      |                      | are totally optional.|
+---+----------------------+----------------------+----------------------+
| 6 |                      | Optional message     | Central may insert   |
| a |                      | sequence <CR>        | short message        |
|   |                      |                      | sequence between     |
|   |                      |                      | steps 6 and 7.       |
+---+----------------------+----------------------+----------------------+
| 7 |                      | "<ESC> [p <CR>"      | Message go ahead is  |
|   |                      |                      | sent when paging     |
|   |                      |                      | central is ready for |
|   |                      |                      | new information.     |
|   |                      |                      | The 'p' is in lower  |
|   |                      |                      | case.                |
+---+----------------------+----------------------+----------------------+
| 8 | TRANSACTION #1       |                      | A block is up to 256 |
|   |      : "<STX>        |                      | characters in length,|
|   |      : FIELD #1 <CR> | {4}                  | with up to 250 char- |
|   | BLOCK: FIELD #2 <CR> | {5}                  | acters of info, plus |
|   | #1   :               |                      | 3 control characters |
|   |      : FIELD #N <CR> |                      | and a 3 character    |
|   |      : <ETX>         |                      | checksum. The block  |
|   |      : <CHECKSUM>    |                      | carries one trans-   |
|   |      : <CR>"         |                      | action (one set of   |
|   |                      |                      | fields 1 through N)  |
|   |                      |                      | or a portion of one  |
|   |                      |                      | transaction. A block |
|   |                      |                      | may be less than 256 |
|   |                      |                      | characters to        |
|   |                      |                      | accommodate short    |
|   |                      |                      | transactions.        |
+---+----------------------+----------------------+----------------------+
|   |                      |                      | A field may be any   |
|   |                      |                      | length and where     |
|   |                      |                      | necessary may be     |
|   |                      |                      | continued in         |
|   |                      |                      | following blocks.    |
|   |                      |                      | A field always ends  |
|   |                      |                      | with a <CR>. The     |
|   |                      |                      | <CR> field delimiter |
|   |                      |                      | suggests <CR> may    |
|   |                      |                      | not be used within a |
|   |                      |                      | field.               |
|   |                      |                      |                      |
|   |                      |                      | A block always       |
|   |                      |                      | begins with an <STX> |
|   |                      |                      | and ends with a      |
|   |                      |                      | checksum followed by |
|   |                      |                      | a <CR>. The char-    |
|   |                      |                      | acters preceding the |
|   |                      |                      | checksum depends on  |
|   |                      |                      | what, if anything,   |
|   |                      |                      | is continued beyond  |
|   |                      |                      | the block boundary.  |
|   |                      |                      |                      |
|   |                      |                      | The <ETX> is used as |
|   |                      |                      | a block termination  |
|   |                      |                      | indicator if a given |
|   |                      |                      | transaction (fields  |
|   |                      |                      | 1 through N) ends    |
|   |                      |                      | within the block     |
|   |                      |                      | currently being      |
|   |                      |                      | transmitted.         |
+---+----------------------+----------------------+----------------------+
|   | TRANSACTION #2 {6}   |                      | The <ETB> is used as |
|   |      : "<STX>        |                      | a block terminator   |
|   |      : FIELD #1 <CR> |                      | if the transaction   |
|   | BLOCK:               |                      | is continued into    |
|   | #2   : FIELD #J <CR> |                      | the next block, but  |
|   |      : <ETB>         |                      | the last field in    |
|   |      : <CHECKSUM>    |                      | the current block is |
|   |      : <CR>"         |                      | complete.            |
|   |                      |                      |                      |
|   |      : "<STX>        |                      | If the last field    |
|   |      : FIELD #J+1<CR>|                      | within the current   |
|   | BLOCK:               |                      | block is to be       |
|   | #3   : FIELD #L <US> |                      | continued in the     |
|   |      : <CHECKSUM>    |                      | next block, no <CR>  |
|   |      : <CR>          |                      | is inserted at the   |
|   |                      |                      | end of the first     |
|   |      : "<STX>        |                      | portion of the field |
|   |      : FIELD #L      |                      | and the <US> char-   |
|   |      : (CONTINUED)   |                      | acter is used as a   |
|   |      : <CR>          |                      | block termination    |
|   | BLOCK:               |                      | character. The <CR>  |
|   | #4   : FIELD <CR>    |                      | terminating the      |
|   |      : <ETX>         |                      | broken field is sent |
|   |      : <CHECKSUM>    |                      | at the end of the    |
|   |      : <CR>          |                      | field in whatever    |
|   |                      |                      | block the field      |
|   |                      |                      | actually terminates. |
|   |                      |                      |                      |
|   |                      |                      | No limit is estab-   |
|   |                      |                      | lished within the    |
|   |                      |                      | protocol itself      |
|   |                      |                      | regarding the number |
|   |                      |                      | of transactions, the |
|   |                      |                      | number of fields or  |
|   |                      |                      | the number of blocks |
|   |                      |                      | per field; however,  |
|   |                      |                      | a particular user    |
|   |                      |                      | system may have      |
|   |                      |                      | limits on any of     |
|   |                      |                      | these items.         |
|   |                      |                      |                      |
|   | LAST TRANSACTION     |                      | Some systems may be  |
|   |                      |                      | limited to one block |
|   |                      |                      | per transaction and  |
|   |                      |                      | one transaction per  |
|   |                      |                      | telephone connection.|
|   |                      |                      |                      |
|   |                      |                      | Each checksum is     |
|   |                      |                      | computed by perfor-  |
|   |                      |                      | ming the simple      |
|   |                      |                      | arithmetic sum of    |
|   |                      |                      | the 7-bit values of  |
|   |                      |                      | all values of all    |
|   |                      |                      | characters preceding |
|   |                      |                      | it in that block.    |
|   |                      |                      | (This means that the |
|   |                      |                      | STX and ETB/ETX are  |
|   |                      |                      | included in the sum).|
|   |                      |                      | The checksum is then |
|   |                      |                      | the least signifi-   |
|   |                      |                      | cant 12 bits of this |
|   |                      |                      | resulting sum.       |
+---+----------------------+----------------------+----------------------+
|   |                      |                      | The checksum is      |
|   |                      |                      | transmitted as three |
|   |                      |                      | printable ASCII      |
|   |                      |                      | characters having    |
|   |                      |                      | values between HEX   |
|   |                      |                      | 30 and HEX 3F (the   |
|   |                      |                      | characters 012345678 |
|   |                      |                      | 9:;<=>?). The most   |
|   |                      |                      | significant four     |
|   |                      |                      | bits of the sum are  |
|   |                      |                      | encoded as the 4 LSB |
|   |                      |                      | of the third char-   |
|   |                      |                      | cter. See example.   |
|   |                      |                      |                      |
|   |                      |                      | A normal paging sys- |
|   |      : "<STX>        |                      | tem will have two    |
|   |      : FIELD #1 <CR> |                      | fields only:         |
|   | LAST :               |                      |                      |
|   | BLOCK: FIELD #N <CR> |                      | Field 1 = Pager ID   |
|   |      : <ETX>         |                      | (normally up to      |
|   |      : <CHECKSUM>    |                      | eight digits. May    |
|   |      : <CR>"         |                      | include function and |
|   |                      |                      | check digit).        |
|   |                      |                      |                      |
|   |                      |                      | Field 2 = Message    |
|   |                      |                      |                      |
|   |                      |                      | Field 1 or field 2   |
|   |                      |                      | may be empty. For    |
|   |                      |                      | example, when a page |
|   |                      |                      | is tone only, field  |
|   |                      |                      | 2 will be empty.     |
|   |                      |                      | Even when empty, a   |
|   |                      |                      | field is followed by |
|   |                      |                      | a <CR>. Some systems |
|   |                      |                      | will reject trans-   |
|   |                      |                      | actions which have   |
|   |                      |                      | an empty field 2 for |
|   |                      |                      | a display page or    |
|   |                      |                      | transactions which   |
|   |                      |                      | have an empty field  |
|   |                      |                      | 1. Other systems are |
|   |                      |                      | less restrictive.    |
+---+----------------------+----------------------+----------------------+
|   |                      |                      | The response to each |
|   |                      |                      | block is one of four:|
|   |                      |                      |                      |
                     |                      | "Message sequence    |
<ACK><CR> = OK, send |
|   |                      | <CR> <ACK> <CR>"     | next block.          |
|   |                      |                      |                      |
|   |                      | or                   |                      |
|   |                      |                      |                      |
|   |                      | "Message sequence    | <NAK><CR> = checksum |
|   |                      | <CR> <NAK> <CR>"     | or transmission      |
|   |                      |                      | error, send last     |
|   |                      |                      | block again.         |
|   |                      | or                   |                      |
|   |                      | "Message sequence    | <RS><CR> = abandon   |
|   |                      | <CR> <RS> <CR>"      | current transaction  |
|   |                      |                      | and go to next. RS   |
|   |                      |                      | may occur when the   |
|   |                      |                      | checksum is OK, but  |
|   |                      |                      | the current trans-   |
|   |                      |                      | action violates a    |
|   |                      |                      | system rule. At the  |
|   |                      |                      | option of the system,|
|   |                      |                      | it may occur in      |
|   |                      |                      | other cases.         |
|   |                      | or                   |                      |
|   |                      |                      |                      |
|   |                      | "Message sequence    | <ESC><EOT><CR> =     |
|   |                      | <CR> <ESC> <EOT>     | begin disconnect.    |
|   |                      | <CR>"                |                      |
|   |                      |                      | Any of the responses |
|   |                      |                      | may have an optional |
|   |                      |                      | message sequence     |
|   |                      |                      | before them,         |
|   |                      |                      | although the system  |
|   |                      |                      | designer should      |
|   |                      |                      | understand the con-  |
|   |                      |                      | sequences to the     |
|   |                      |                      | user with all        |
|   |                      |                      | planned entry        |
|   |                      |                      | devices.             |
+---+----------------------+----------------------+----------------------+
|   |                      |                      | It is expected that  |
|   |                      |                      | many systems will    |
|   |                      |                      | save their message   |
|   |                      |                      | sequence responses   |
|   |                      |                      | until immediately    |
|   |                      |                      | before disconnect.   |
|   |                      |                      | For some entry       |
|   |                      |                      | devices, it may also |
|   |                      |                      | be desirable that    |
|   |                      |                      | messages describing  |
|   |                      |                      | non-checksum errors  |
|   |                      |                      | associated with a    |
|   |                      |                      | particular trans-    |
|   |                      |                      | action in a PG       |
|   |                      |                      | service will begin   |
|   |                      |                      | with the letter ID   |
|   |                      |                      | followed by the      |
|   |                      |                      | contents of field 1  |
|   |                      |                      | for that transaction.|
+---+----------------------+----------------------+----------------------+
| 9 | "<EOT> <CR>"         |                      | After reception of   |
|   |                      |                      | an <ACK> or <RS> for |
|   |                      |                      | the last transaction |
|   |                      |                      | in a given service,  |
|   |                      |                      | the entry device     |
|   |                      |                      | sends <EOT> <CR>     |
|   |                      |                      | meaning there are no |
|   |                      |                      | more transactions    |
|   |                      |                      | remaining in this    |
|   |                      |                      | service.             |
+---+----------------------+----------------------+----------------------+
|10 |                      | "<Message sequence>  | An optional message  |
|a  |                      | <CR>"                | may be sent at this  |
|   |                      |                      | point to indicate    |
|   |                      |                      | the degree of accep- |
|   |                      |                      | tability of infor-   |
|   |                      |                      | mation in all trans- |
|   |                      |                      | actions received     |
|   |                      |                      | during the current   |
|   |                      |                      | interchange.         |
|   |                      |                      | Although optional,   |
|   |                      |                      | this message is      |
|   |                      |                      | highly desirable.    |
+---+----------------------+----------------------+----------------------+
|10 |                      | "<RS> <CR>"          | An <RS> <CR> should  |
|b  |                      |                      | be sent at this      |
|   |                      |                      | point if the paging  |
|   |                      |                      | central finds any    |
|   |                      |                      | data <ACK> in step 8 |
|   |                      |                      | to be unacceptable   |
|   |                      |                      | because of content   |
|   |                      |                      | (e.g. an invalid     |
|   |                      |                      | pager number or a    |
|   |                      |                      | message field inap-  |
|   |                      |                      | propriate for the    |
|   |                      |                      | type of pages, etc.) |
|   |                      |                      | [2]                  |
+---+----------------------+----------------------+----------------------+
|10 |                      | "<ESC> <EOT> <CR>"   | <ESC> <EOT> = begin  |
|c  |                      |                      | disconnect.          |
|   |                      | followed by dropping |                      |
|   |                      | of carrier and       |                      |
|   |                      | hanging up.          |                      |
+---+----------------------+----------------------+----------------------+
|11 | Drops carrier and    |                      |                      |
|   | hangs up.            |                      |                      |
+---+----------------------+----------------------+----------------------+
 [2] It is desirable to catch all types of errors in step 8, but
     practically, some systems will be too slow to catch content
     errors as they happen.

Table 7-1 (continued) Call Delivery Sequence

Manual Entry procedure

    +----------------------+----------------------+----------------------+
    | REM. ENTRY DEV. DOES | PAGING CENTRAL DOES  | COMMENTS             |
+---+----------------------+----------------------+----------------------+
| 5 | (For manual remote   |                      | Lack of <ESC> at     |
| M | entry as opposed to  |                      | at beginning of      |
|   | Automatic Entry      |                      | response to ID=      |
|   | shown previously in  |                      | signifies manual     |
|   | this table under 5A) |                      | operation where      |
|   |                      |                      | applicable.          |
|   | "M <CR>"             |                      |                      |
+---+----------------------+----------------------+----------------------+
|   |                      | "Enter pager ID(s):  | Any manual operation |
|   |                      | (Tone only or        | is user defined      |
|   |                      | voice)"           or | after logon.         |
+---+----------------------+----------------------+----------------------+
|   | e.g.                 |                      | Echo transmission is |
|   | "1000 2000 1247 400  |                      | allowed after manual |
|   | <CR>"                |                      | conversation is      |
+---+----------------------+----------------------+ established. M <CR>  |
|   |                      | "Enter Alphanumeric  | can be replaced by   |
|   |                      | message (alpha):" or | any non-null         |
|   |                      | "Enter Numeric       | sequence ending in   |
|   |                      | message (numeric):"  | <CR> and not         |
+---+----------------------+----------------------+ beginning with       |
|   | "Message <CR>"       |                      | <ESC>.               |
+---+----------------------+----------------------+                      |
|   |                      | "Can't Deliver Page  |                      |
|   |                      | ID xxxxxx"        or |                      |
|   |                      | "Too Slow - Good     |                      |
|   |                      | Bye" (40 second      |                      |
|   |                      | timeout)          or |                      |
|   |                      | "Too Many Errors -   |                      |
|   |                      | Good Bye" (occurs if |                      |
|   |                      | 3 or more errors) or |                      |
|   |                      | "Page Blocked"       |                      |
+---+----------------------+----------------------+----------------------+


7.2 Modems

For initial implementation of the protocol, it is recommended that Bell
103 compatible modems be used to receive at 300 baud. Additional speeds or
modem types may be used if desired.

The standard practice will be ASCII with XON, XOFF either direction using
a 10-bit code (1 start, 7 data, 1 parity, 1 stop) with even parity. {7}

In the case of delays, the paging central shall wait at least four seconds
(eight seconds in steps 3 and 4) before disconnecting the remote entry
device; the remote entry device shall wait at least ten seconds for a
character from the central before hanging up.

The paging central may, at its option, send <CR><LF> in place of <CR> at
the end of any sequence.

For initial use of the protocol, the paging central shall be equipped to
receive full duplex using a Bell 103 compatible modem at 300 baud.
Optionally, certain inputs may be capable of receiving 110 baud Bell 103
full duplex, 300/1200 baud Bell 212 full duplex. No echo shall be employed
in full duplex mode. Any attempts at automatic baud rate determination
shall be within the restraints of the specified protocol.


Example:

Leaving a message TEST for customer #1
Data: 7 Bits/1 Stop Bit/No Even Parity {8}

USER                               GL-3000

<CR> every 1 second unit ...
                                   ID=
<ESC> PG1 <CR>
                                   <ESC> [p <CR>
<STX> 1 <CR> TEST <CR> <ETX>
190 <CR>
("TEST" is the message)            Processing - Please Wait<CR>
("190" is the Checksum)            <ACK><CR>

                                   +++,,,,,,,,,,ATH0<CR> {9}
                                   Carrier Drop

   Figure 7-2 Example of Typical Command - Acknowledge Sequence


7.3 Telocator Protocol (TAP) Checksum Example {9}

The following table shows an example of a complete block containing a
correct checksum which is: <STX>123<CR>ABC<CR><ETX>17;<CR>

+---------+---------+---------+
|  STX  *|    000        *|   0010        *|
|   1     |    011      *|   0001  |
|   2     |    011      *|   0010        *|
|   3   *|    011  |   0011      *|
|  CR   *|    000        *|   1101        *|
|   A   *|    100  |   0001      *|
|   B   *|    100        *|   0010        *|
|   C   *|    100        *|   0011        *|
|  CR     |    000      *|   1101        *|
|  ETX  *|    000        *|   0011        *|
|       *+---------+---------+
|       *| 1 0111  |   1011  |
|       *| 1   7   |     ;       *|
+---------+---------+---------+
                Checksum = 17;


TRANSCRIBER'S FOOTNOTES:

{1} It lies. All the way through this document, it lies. BEWARE OF EXTRA
    SPACES! The only time there should be a space in this protocol is
    in message sequences or in the user's field 2.

{2} Protocol didn't say, "Simon says." Notice that there IS NO <CR> here.
    The <CR> is way down at the end of the optional password field, in
    step 6.

{3} I have yet to run into a system that used anything OTHER than
    <ESC>PG1<CR> for the login sequence. But to follow up on what I said
    in note {2}, if you do find one, it's <ESC>PG1paswrd<CR>, not
    <ESC>PG1<CR>paswrd<CR>.

{4} They take forever to get around to telling you what you most want to
    know: field 1 is pager ID, field 2 is message. On both of the systems
    I've tried, pager ID does not work if there is ANY punctuation in it,
    so strip out those dashes and spaces. I'm told that some systems
    require eight digits, so it may be safe to zero pad to that length.

{5} Field 2 is the message. The rest of transaction 8 goes into gory
    detail on how to handle message blocks longer than 250 characters,
    but you probably shouldn't waste your time: most pagers can't handle
    more than 180. Numeric pagers can typically only handle 12 to 20.
    On the numeric pagers I tried, zero to nine, space, and dash are the
    only legal characters.  No, not asterisk, even though that's what key
    you hit to include an extra dash when you're touch-toning it.

{6} They go out of their way to confuse this, and as I said in note {5},
    even if you do get it to work it probably won't work.  But let me
    try to break this down into simple rules:

    Every packet starts with <STX> and ends with a three-byte checksum
    and <CR>.

    The last character before the checksum is:

        IF this the last packet in the transaction THEN
           it's <ETX>
        ELSE IF the packet ends on a boundary between fields,
                that is to say, with a <CR>, THEN
           it's <US>
        ELSE
           it's <ETB>
        END IF

    How do you know whether or not to break a field across more than one
    packet?  The easy way is to build the whole transaction, break it into
    250 byte chunks, look at the end of each chunk for a <CR>.  If you
    find the <CR>, send <ETB>, else <US>.  After the last packet, send
    <ETX> instead.

{7} Who ever heard of calling this a ten-bit code?  Here's what they mean:
    300 bps, 7 bits, even parity, 1 stop bit.  They mean it, too; neither
    of the ones I've tried would sync at above 1200 bps.

{8} Egregious typo. I fixed some others, but this is too weird. I THINK
    they mean even parity; maybe they mean it works with either even or
    no parity.

{9} Their example almost clears it up, but maybe a code example will help
    more.  The following HyperTalk code was what I wrote to calculate the
    checksum and put it onto the end of a packet:

    repeat with i = 1 to the length of TempPacket
       add charToNum(char i of TempPacket) to checkSum
    end repeat
    put numToChar((checkSum div 256) mod 16 + 48) into checkSumString
    put numToChar((checkSum div 16) mod 16 + 48) after checkSumString
    put numToChar(checkSum mod 16 + 48) after checkSumString
    put checkSumString & CR after TempPacket