Contents
SDLC Link Service

  Configuring an SDLC Link Service


Configuring an SDLC Link Service

An SDLC link service enables SNA Server to communicate with host, peer, or downstream computers through full-duplex or half-duplex synchronous modems, over switched or leased telecommunications lines.

To configure an SDLC link service

1	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.

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

Note  The standard Attachmate SDLC card can only handle half duplex in DMA mode. If you want to use a transmission speed greater than 9600 baud, select half-duplex and not full-duplex in SNA Server Admin.

3	Under Line Type, select the appropriate option:

Leased

Switched: SNA Server-Stored Number

Select this option only if the modem can send clock signals when ready to accept a dial string. For more information, see:

Requirements for Using Server-Stored Numbers

Routines Used with Server-Stored Numbers

Switched: Modem-Stored Number

Switched: Manual Dial

4	If you would like the line to use constant RTS, select the Constant RTS check box. See Note About Constant RTS.

5	Choose Continue.

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


 SDLC

Synchronous Data Link Control. 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.


Leased

Choose this option for a dedicated telecommunications line.


Switched: SNA Server-Stored Number

Choose this option if the modem can accept a phone number from SNA Server, that is, if the modem can send clock signals when ready to accept a dial string. Modems with this capability include synchronous modems that use the Hayes "AT" command set, but not many other modems.


Requirements for Using Server-Stored Numbers

In order for a modem to accept a phone number string from SNA Server, the modem must be set up to:

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.

Note  The preceding requirements are supported by synchronous modems that use the Hayes "AT" command set, but are not supported by many others.


Routines Used with Server-Stored Numbers

When SNA Server is sending a phone number to a modem, it ignores modem responses and holds the modem interface signals Select Standby and DTR 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 time-out expires before DSR comes on to indicate the call is connected.


Switched: Modem-Stored Number

Choose this option for a modem that stores a phone number. Make sure that 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.


Switched: Manual Dial

Choose this option if you will dial the phone number. SNA Server will prompt you when it is time to dial the number.


constant RTS

Constant Request To Send. An option that causes the SDLC adapter to be in constant readiness to send data. This option is required if a line is to be used for full duplex. It cannot be used with multidrop.

If an SDLC adapter does not use Constant RTS, before the adapter can send data, it must raise RTS and then wait for the remote end to raise CTS (Clear To Send). In contrast, an adapter that uses Constant RTS holds RTS high so CTS is always high, and the wait is eliminated.


Note About 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.

However, do not select this 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.


switched SDLC line

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


leased SDLC line

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


Configuring Dialer Setup

In the Microgate Dialer Setup dialog box, specify options as follows:

COM Port

Select the number of the COM port; for example, for COM1, select 1.

If you are adding a COM port by adding the Microgate SDLC card, and you select a new number for that COM port, Setup responds by allowing you to access the appropriate dialog box for configuring the COM port within Windows NT.

The range is from None through 254. The default is None.

Baud Rate

Select the rate of transmission. The range includes relevant values from 75 through 115200. The default is 9600.

Incoming String

Type the string to be sent to the modem when an incoming call is detected. The default is AT&F&C1&S1&D3&Q1Q1S0=1. This string will be appropriate in most situations.

Outgoing String

Type the string to be sent to the modem when an outgoing call is detected. The default is AT&F&C1&S1&D3&Q1Q1S0=0DT. This string will be appropriate in most situations.