Contents
SDLC Link Service (DCA)

Configuring an SDLC Link Service


Configuring an SDLC Link Service

An SDLC link service enables IRMA WorkStation to communicate with host or peer computers through full-duplex or half-duplex synchronous modems, over switched or leased telecommunications lines.  SDLC is IBM's implementation of a bit-oriented serial protocol with a standardized frame reader and block check sequence.  SDLC applies to synchronous transmissions; it organizes information in rigidly structured units called frames.

A default title is provided for the service; however, you can change this default.  To configure an SDLC link service, you need to select the line types for your service, and then determine whether the line is a constant RTS.  For higher throughput, choose constant RTS whenever you can.  It is generally used on leased lines and is often available on modems for switched connections as well.

Important:  Do not select the constant RTS option when configuring this link service for use by a multidrop connection.  Multidrop connections allow multiple SDLC connections to connect to the same physical wire.  Usually SDLC is a point-to-point connection protocol.

You can dial the line in one of three ways:  (1) manually, (2) with a modem that stores the phone number, or (3) with a modem that accepts a phone number from the software.  Note the following:

When dialing a line manually, dial the number when prompted to do so by IRMA WorkStation.

When dialing a line with a modem that stores the phone number, make sure the modem is configured to dial the number when the Data Terminal Ready (DTR) is raised, in conformance with the IEEE RS 232 Modem Specification for line 108.1.

The third method, sending a phone number from the softwares is described in the next section.

Sending a Phone Number String from the Software

To dial a line by a modem that accepts a phone number string from the IRMA WorkStation software, the modem must be set up to the following:

Supply clock signals during the command loading phase.

Accept dial commands in ASCII (8 data bits, no parity bit, 1 stop bit).

Set Clear to Send (CTS) and Data Set Ready (DSR) to on when ready to accept dial commands.

Set DSR to off again after accepting a dial command.

Set DSR to on again when (and only when) the dialed connection is made.

Change to synchronous mode after the dial-up has completed.

Change back to dial-command mode if DTR is dropped and raised again.

When IRMA WorkStation is sending a phone number to a modem, it ignores modem responses and holds the modem interface signals Select Standby and DTRP to off.

The dialing attempt initiated by IRMA WorkStation is assumed to have failed if one of the following occurs:

DSR stays on after the dial string has been sent.

The connection time-out expires before DSR comes on, which indicates the call is connected.

Note:  This protocol is supported by synchronous modems that use the Hayes "AT" command set, but is not supported by many others.

To configure an SDLC link service:

1	Select SNA SDLC Link Service (DCA) in the Available Link Services in the Link Service Installation dialog box and choose Install.  The DCA SDLC Link Service Setup dialog box is displayed.

2	To change the title for this service, in the Title box, delete the default, and type the new title.  You can use as many as 40 characters for the title.

3	Under Line Type, choose the option button for this service.

Note:  If you choose one of the switched options, you must use the SNA Admin to type the Dial Data.  For more information, see the Administrator's Guide.

4	If you would like the line to be a constant RTS, select the Constant RTS checkbox.

5	Make sure that the Interrupt, I/O Address, and DMA Channel settings match those for your communications adapter.  See your communications adapter documentation for more information.

6	Choose Continue.  Setup copies the required files, and the Link Service Configuration dialog box is displayed listing the entry for this link service.


constant RTS

A constant RTS is a devoted line for the modem.  This option is required for full-duplex modems.  It is optional for half-duplex modems.

Important:  Do not select this option when configuring this link service for use by a multidrop connection.


switched SDLC line

A switched SDLC line is a standard dial-up telephone line used for synchronous data link control (SDLC) connections.


leased SDLC line

A leased SDLC line is a telecommunications line committed solely to use by synchronous data link control (SDLC) connections.