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IBM SDLC Link Service Help

Contents

Step-by-Step Instructions

  Configuring an IBM SDLC Link Service


Configuring an IBM SDLC Link Service

Use this dialog box to configure an IBM SDLC link service.  An SDLC link service enables SNA Server to communicate with host or peer computers through full-duplex or half-duplex synchronous modems, over switched or leased lines.  Leased is the default.  SDLC (Synchronous Data Link Control) is IBM's implementation of a bit-oriented serial protocol with a standardized frame reader and block check sequence.  As the name implies, 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 card and line types for your service, then determine whether the line is a constant carrier.  For higher throughput, choose Constant Carrier 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 carrier option when configuring this link service for use by a multipoint connection.

The line is dialed in one of three ways:  manually, by a modem that stores the phone number, or by a modem that accepts a phone number from the software.

To dial a line manually, dial the number when prompted by SNA Server.

To dial a line by a modem that stores the phone number, the modem must be configured to dial the number when the DTR is raised, in conformance with the IEEE RS232 Modem Specification for line 108.1.

Sending a Phone Number String

To dail a line by modem that accepts a phone number string from SNA Server, the modem must be set up to do the following:

Supply clock signals during the command loading phase.

Accept dial commands in ASCII (eight data bits, no parity bit, one 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 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 Data Terminal Ready (DTR) is dropped and raised again.

When SNA Server 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 SNA Server is assumed to have failed if one of the following occurs:

DSR stays on after the dial string has been sent.

The connection timeout expires before DSR comes on to indicate the call is connected.

Note  This protocol is supported by synchronous modems that use HAYES "AT" command sent, but is not supported by many others.

To configure an SDLC link service

1	To change the title for this service, delete the default in the Title box, and type the new title for this link service.

You can use as many as 40 characters for the title.

2	In the Card Type box, select the card you will be using.

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

Note  If you select the switched option, you must use the SNA Server Admin to type the Dial Data.  For more information, see the Microsoft SNA Server Administration Guide.

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

5	Choose Continue.

Setup copies the required files and the Link Service Configuration dialog box appears listing the entry for this link service.


Constant Carrier

A constant carrier 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 multi-point connection.


Switched SDLC Line

A switched SDLC line is a standard 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.