Appendix H - V.25bis Operation. Multitech MT1432BA, MT2834BAI, MT2834BA

Appendix H - V.25bis Operation

Appendix H - V.25bis Operation

Chapter 5 described a set of commands which let the modem dial, hang-up, and be configured for various applications. However, these commands, the AT command set, are only functional when the

DTE transmits data asynchronously. That is, they cannot be used with synchronous equipment such as that found in IBM's Binary Synchronous Communications (BSC) and Synchronous Data Link

Control (SDLC)* environments.

The ITU V.25bis commands provide you with an alternate set of commands and responses to those described in Chapter 5 for applications in which the DTE is synchronous. V.25bis commands support dialing functions in asynchronous or synchronous mode according to the recommendations of the

ITU; however, the AT commands are understood to reign in the asynchronous world, while the

V.25bis commands are relegated to the synchronous world of datacomm. If you need to establish a datacomm link over Public Switched Telephone Network (PSTN) dial-up services, and your equipment outputs a synchronous data stream, V.25bis commands are essential. V.25bis mode AT commands do not include any modem configuration commands. You can execute normal AT commands in V.25bis mode for modem configuration.

Delayed and Forbidden Numbers

V.25bis provides the facility to delay failed call retry attempts by putting numbers that failed to connect on a special Delayed Number list. Subsequent dialing of these numbers will be delayed (time specified by a country regulation) and an appropriate message displayed. If the number is retried more than the maximum allowed number of times (number is also specified by country regulation), it is placed on the Forbidden Numbers list, and no further retries will be allowed. When the Forbidden

Numbers list is full, no dialing is allowed and a CFIFF indication is given. The modem in AT command mode will respond with NO CARRIER. If country regulations require that the Forbidden Numbers list be checked in AT mode, then NO CARRIER will be the response to a dial attempt in AT mode.

Numbers will also be put on the Forbidden Numbers list if the Delayed Numbers list is full and a new number fails for the first time. In that case, the new number will be added to the Delayed Number list and the oldest existing number added to the Forbidden Numbers list. Numbers are removed from the

Forbidden Numbers list by after a certain time has past (also by country regulation).

Some country regulations have numbers remain on the Forbidden Numbers list permanently. The

Delayed Number and Forbidden Numbers lists are eight numbers long (20 characters each).

V.25bis Operation

Operation in V.25bis mode is similar to AT command mode in that certain DIP-Switch functions are important to its operation. V.25bis does not include any speed detection for asynchronous mode, so when you are giving commands, you must stay in your initial speed (i.e., if you change your terminal speed while entering an AT command, you will get no responses). In synchronous mode, the modem supplies the clock, so the synchronous terminal “knows” the speed.

You must be in V.25bis mode for the commands described here to function. Most AT commands will also function, except those associated with dialing such as ATD, ATN, ATO, and ATU. To get into

V.25bis mode, you type AT$V1. At this point your modem does no more speed or parity detection

(things associated with asynchronous operation). To get out of V.25bis mode and back into AT command mode, enter AT$VO. The AT$V2 command allows you to run one V.25bis command from

AT command mode without leaving AT command mode.

There is no command to select between asynchronous and synchronous V.25bis operation. The position of DIP-Switch #12 selects between modes. For synchronous mode, DIP-Switch #12 must be

UP, and the AT command mode enabled.

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Another asynchronous mode concern is the problem of connecting at a different speed than the speed at which the serial port is set. If your modem port speed is different from the serial port speed, you must either:

1)

2)

Enable speed conversion and have flow control on, or

Enable connect responses (with the ATX1 command) and change the serial baud rate after receiving a connect message.

If the $VD1 command is entered when in Auto-Answer mode, the modem answers immediately upon receiving the first ring.

There is no disconnect message (NO CARRIER) if a normal connection is made.

V.25bis Set-Up and Initialization

Before you operate your modem in the V.25bis mode, you need to make sure it is set up properly

(various RS-232 lines such as DSR and CTS act as specified in the V.25bis standard). Setup involves proper DIP-Switch settings and soft-switches (software controlled conditions).

V.25bis DIP-Switches

#1

#2

#3

#4

Unforced DTR

NA

NA

NA

#5

#6

Auto-Answer enabled

Async - Max throughput set

Sync - Slave Clocking unforced

Command Mode forced #8

#9 Digital Loopback Off

#10 Dial-Up

#11 Async - AT/Multi-Tech Resp.

#12 Async/Sync mode set per requirements

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Appendix H - V.25bis Operation

V.25bis Mode AT Commands

The following commands will either alter standard V.25bis behavior (so you must be careful in their use) or they are not allowed, as indicated. All other commands can be used in V.25bis operation.

;

,

U

W

X

P

T

N

N...N

O

!

@

+++AT<CR>

A

A/

A:

D

D...N

$D

E

&F

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Alters Operation ($D1 in V25bis is direct call mode)

Alters Operation

Alters Operation (removes modem from asynchronous V.42bis mode)

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Alters Operation (X0 no connect message, X1 connect message)

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Not Allowed

V.25bis Responses (Result Codes)

When in V.25bis mode (the AT$V1 command executed), your modem provides you with several responses which can help you follow the progress of V.25bis operations. These are similar to the

Result Codes associated with AT Command mode operation. The V.25bis responses are in the form of three-character mnemonics as listed below:

INC

VAL

DLCt

CFlrr

Incoming Call (same as RING indicator)

A valid V.25bis command has been attempted

Call delayed for t minutes (number on Delayed list)

Call failure indicator where rr equals:

LSNmm;dd...dd

LSDmm;dd...dd

LSFmm;dd...dd

CON ssss

et - Engaged tone (same as BUSY)

nt - Call Answered but No Answer Tone

ab - Call Not Answered

fc - Number on Forbidden List

ns - Number not stored in memory

ua - User Abort

nd - No Dialtone

ff - Forbidden List full

Phone number in V.25bis memory

Phone number on the Delay list

Phone number on the forbidden list

Connection at ssss speed (if X1 in effect)

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V.25bis AT Commands

The AT commands associated with V.25bis mode are described as follows. Note that one command enables and disables V.25bis mode and the rest are only operable in the V.25bis mode.

Enable/Disable V.25bis Mode ($V) Command

The function of the $V command is to select the V.25bis mode in asynchronous mode. (Synchronous mode is set up with switches. For example, the modem could be in AT command mode, (AT$V1), and if synchronous mode is enabled with AT Command mode enabled, then V.25bis mode is selected). Prior to executing this command, make sure that your modem is properly set up to perform the type of operation you will be performing. Refer to the initialization section of this appendix for information about modem set-up. When in V.25bis mode, most normal AT commands will also function (except D,N,O and U). V.25bis operates in asynchronous or synchronous modes (depending on the position of DIP-Switch #12), and does not check for terminal speed (so do not change speeds while in this mode) or parity. In synchronous mode, speed is not important since the internal clocks provide synchronization.

To place your modem in V.25bis mode from asynchronous mode, enter the AT$V1 command. To return to AT command mode, enter the AT$V0 command. AT$V2 allows you to run one V.25bis command from AT command mode without leaving AT command mode (the V.25bis command follows $V2 on the command line).

Change Serial Baud Rate (CSP) Command

The CSP command will change the serial baud rate of your modem by entering CSPsssss where

sssss can equal:

0300 =

1200 =

2400 =

4800 =

9600 =

19200 =

38400 =

57600 =

115200 =

300 bps

1200 bps

2400 bps

4800 bps

9600 bps

19200 bps

38400 bps

57600 bps

115200 bps (1932 and 2834 Series only)

Dial Phone Number Provided (CRN) Command

The CRN command permits the dialing of the phone number immediately following it (from the command line). It is similar to the D command of the AT command set, except that the number is first checked against the Delayed Number and Forbidden Number list. If permitted, depending on the country regulations in effect, the number will then be dialed. For example, if you enter CRN7859875 and hit RETURN, your modem will check the two lists. If the number is on the Delayed Numbers list, you can dial that number again after t minutes have passed. If the number is on the Forbidden list, a

CFIFC message will be displayed.

You can use various commands from the AT command set within the CRN command line to facilitate the dialing process, such as P, T, or : for pulse dialing, tone dialing and wait for dial tone. V.25bis supports “smart” dialing.

To dial a phone number, enter CRNdd...dd where dd...dd is the phone number, which can be up to

20 characters long using any character on the telephone pad (0 through 9, *, #, P, T, and :).

Some additional dialing characters may be available, based on country regulations.

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Appendix H - V.25bis Operation

Listing Delayed Phone Numbers (RLD) Command

When a phone number is dialed by a CRN command and a connection is not made, the number is entered in the modem's V.25bis Delayed Number list along with the number of retry attempts. Any further dialing attempts will be delayed some amount of time (determined by the regulations of each country). While the delay is in progress, the modem will give a DLC indication. The list contains eight numbers. When filled, the next number failing “bumps” off the oldest number on the list onto the

Forbidden Number list. Numbers on the Delayed Number list that succeed in a connect attempt are removed. If a certain number of failed attempts occur (the number of failed attempts is specified by each country), the number is entered into the V.25bis Forbidden Phone Number List. Forbidden phone numbers cannot be dialed at all. To list the phone numbers on the V.25bis Delayed Phone

Number List, enter RLD and hit RETURN.

Listing Forbidden Phone Number (RLF) Command

Those phone numbers that have failed to connect the required number of times as specified by country regulations are removed from the Delayed Number list and entered onto the V.25bis

Forbidden Number list. Numbers on the Forbidden Number list cannot be dialed at all for some maximum amount of time, which is also specified by country regulations. In some countries, the time might be one hour, and in others the number may never be dialed again. The forbidden list is eight numbers long, with the newest number replacing the oldest if the memory is full. To list the numbers in the Forbidden list enter RLF and hit RETURN.

Disregard or Connect to Incoming Calls (DIC or CIC) Command

The Disregard or Connect to Incoming Calls commands are used for Auto-Answer operations.

Depending on the country regulations, your modem will wait some amount of time or number of rings before answering the call. During that time, you can stop the modem from answering the call by entering the DIC (Disregard Incoming Calls) command. The CIC (Connect to Incoming Calls) command will cause your modem to answer the call (either reversing the effect of a DIC command or simply have your modem answer the call immediately without waiting the regulation time before answering).

DTR Dialing ($D) Command

DTR Dialing is an alternate method of causing the modem to automatically dial a number. Data

Terminal Ready (DTR) is a signal that comes into the modem from the terminal or computer to which it is connected via pin 20 of the RS-232 interface. In DTR Dialing, the modem will automatically dial a stored number as soon as it receives a high DTR signal. The DTR Dialing method is popular when using the modem in synchronous applications.

To enable DTR Dialing, enter the command AT$D1 and hit Return. The modem will now dial the phone number you have stored as N0 when it receives a high DTR signal (see the D...N command in

Chapter 5).

DTR must remain high for the duration of the call, until disconnect. To disable DTR Dialing, enter the command AT$D0 (or AT$D) and hit RETURN.

When you use DTR Dialing, be sure that DIP-Switch #1 is in the UP position, so that DTR is not forced on.

In addition, when using DTR Dialing in a synchronous application, be sure that DIP-Switch #8 is in the UP position to disable V.25bis Command mode.

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ITU V.25bis Country Specific Information

Due to the flexibility of the V.25bis standard, each country may establish specific regulations governing the way operations are handled. The purpose of this document is to detail each country's specific regulations that affect operation of V.25bis in Multi-Tech modems.

1. Italy a) b) c)

Command/Indication modifications

1.

Phone number indications include status ;ZPSTTT a) b)

Z - U, D, or F, for Unrestricted, Delayed or Forbidden

P - Delay time if delayed c) d)

S - Number of retries so far

TTT - Interdiction time to further attempts

Delayed and Forbidden list behavior

1.

5 retries without delay

2.

3.

4.

5.

2 minute delay between next 4 retries

After 9 retries the number is put on the forbidden list

120 minute timer is started on entry to delay list

When it runs out, the number is removed from which ever list it is on

Auto-Answer mode behavior

1.

Auto-Answer in 5 seconds if no DIC

2.

3.

Get 10 seconds after DIC to enter CIC

If 10 seconds times out then no connection is possible

2. Switzerland a) b) c)

Command/Indication modification

1.

Modem must remain on-hook for 5 seconds after disconnect

2.

3.

4.

Modem must remain on-hook for 5 minutes after 4 consecutive failed calls

If modem must remain on-hook, then it is “paused”

If the modem is paused and a call is attempted a PAU indication is given.

a) PAUt Modem is paused for t minutes

Delayed and Forbidden list behavior

1.

2 minute delay between 4 retries

2.

3.

After 4 retries the number is put on the forbidden list

The number remains on the forbidden list forever

Auto-Answer behavior

1.

Auto-Answer mode after 2 rings if no DIC

3.

Austria a) b) c)

Command/Indication modification (none)

Delayed and Forbidden list behavior

1.

2.

No delay between retries

After 2 retries to numbers that answer, but give no answer tone (CFINT), the

3.

number is put on the forbidden list

After 10 retries with busy or no dialtone, the number is put on the forbidden list

The number remains on the forbidden list forever 4.

5.

Delayed and Forbidden Numbers lists are checked when dialing in AT mode.

If dialing is not possible then NO CARRIER is the response.

Auto-Answer behavior

1.

Auto-Answer in 5 seconds if no DIC

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Appendix H - V.25bis Operation

4. France a) b) c)

Command/Indication modification (none)

Delay and Forbidden list behavior

1.

2.

2 min. delay after 1st call, 4 after 2nd, 6 after 3rd, etc.

After 5 retries, the number is put on the forbidden list

3.

4.

The number remains on the forbidden list forever

Delayed and Forbidden Numbers lists are checked when dialing in AT command mode. If dialing is not possible then No Carrier is the response.

Auto-Answer mode behavior

1.

Auto-Answer in 5 seconds if no DIC

5. Belgium a) b) c)

Command/Indication modification (none)

Delay and Forbidden list behavior

1.

2.

3.

1 min. delay between calls

After 4 retries, the number is put on the forbidden list

The number remains on the forbidden list for 1 hour after entry to forbidden list

4.

Delayed and Forbidden Numbers lists are checked when dialing in AT command mode. If dialing is not possible then No Carrier is the response.

Auto-Answer behavior

1.

Auto-Answer in 5 seconds if no DIC.

6. Singapore a) b)

2.

3.

4.

5.

Command/indication modifications

1.

Dialing digit ‘=’ means wait for dialtone (acts the same as ‘:’ in dialing string).

Delay and Forbidden list behavior

1.

5 retries without delay

2 minute delay between next 4 retries

After 9 retries the number is put on the forbidden list

120 minute timer is started on entry to delay list

When it runs out, the number is removed from whichever list it is on.

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