LAPB Configuration Parameters

The following parameters are sorted alphabetically by parameter name. Upper and lower case characters do not affect the sort sequence. Numbers occur before letters. Each parameter is followed by its default value, followed by an explanation of its effect.

Parameter

Default

Description

frm_extseq

0

Flag. If specified as 0, the frame level uses standard (modulo 8) sequence numbering. If 1, the frame level uses extended (modulo 128) frame sequence numbers, and values for the parameter k may be between 1 and 127.

k

7

Numeric field contains the Frame Level (LAPB) window size. The maximum number of frames that the LAPB protocol allows to be outstanding at any time.

linkenable

YES

Flag. Controls whether or not the local node will attempt to bring an LAPB link up with this port. When YES (true), the LAPB software sets up the hardware to send flags, and the frame level continually tries to start the link, unless your system is DTE and the passive_frm parameter is set to YES. When NO (false), the hardware deactivates the DTR signal and no flags are sent. Nothing is ever done on a disabled link.

N1

519

Maximum frame size in bytes, not including the CRC bytes or flags.

N2

10

Numeric field contains the Frame Level (LAPB) retry count. This is the number of times that the LAPB protocol will retry an operation before indicating failure.

netid

3

Network identifier that identifies the public network to which your system is connecting. The netid affects national facilities parsing, and the mechanism that is used to set up a LAPB link. DM are sent to start up an enabled link, unless indicated otherwise below:

0

Datapac '76
Parses Datapac '76 facilities for collect calling and priority service.

1

Datapac '80
Parses Datapac '80 national facilities for NUI and priority service.

2

Telenet
No Telenet national facilities parsing. Starts up LAPB links by sending DISC, rather than DM. If passive_frm is also YES for DTEs, nothing is sent to start up the link. It is up to the remote system to start the link (usually, by sending SABM).

3

Vanilla 1980 network
As for Datapac '80, except no national facility parsing.

4

DATEX-P
No Datex-P national facility parsing. Starts up LAPB links by sending SABM, unless passive_frm is also YES and your system is DTE, in which case DM are sent at startup. The use of 1984 X.25 facilities is enabled.

5

KDD
Same as for Vanilla 1980.

6

Vanilla 1984 network
No national facility parsing. Allows CCITT 1984 facilities.

7

PSS
No PSS national facility parsing. Starts up LAPB links by sending DISC, rather than DM. If passive_frm is also YES for DTEs, nothing is sent to start up the link; the link must be initiated at the remote system.

8

Tymnet
Same as for Vanilla 1980.

9

N/A

10

Infoswitch
Same as for Vanilla 1980, except for link startup. The link is started up by sending SABM, unless passive_frm is also YES and your system is DTE, in which case DM are sent.

11

Infonet

12

N/A

passive_frm

NO

Flag that determines whether or not the local node will attempt to bring up the LAPB link. If YES, don't send SABM as DTE; the remote system must send it.

speed

0

Baud rate in bits per second. For an externally clocked link, enter 0. Enter 1200 for 1200 bps, 9600 for 9600 bps, and so on.
speed controls the frequency of the clock signal that is presented on the transmit clock output pin as defined by the electrical interface specification (RS-232, V.35, X.21, etc.). speed also controls whether or not it presents any signal on that pin (speed=0).

T1

3

Numeric field contains the frame level (LAPB) retry timer (in seconds). DO NOT set this value to less than the time required to transmit the longest frame (see N1),
based on the speed of this link.

T2

0

Withhold acknowledgements timer. This allows N2 to suppress explicit RR packets in favor of "piggybacking" acknowledgements in outgoing data packets.

T3

0

If defined as 0, the link remains quiet when there is nothing to send. A non-zero value is the number of seconds of no link activity that will be allowed before RR is sent with the P bit. The remote system must respond to this poll within the T1 value.

Revision 6.3.0 (April 2004)