User`s guide

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Configuration - Network > Legacy Protocols > X.25 > LAPB
LAPB (Link Access Procedure Balanced) is a standard subset of the High-Level
Data Link Control (HDLC) protocol. It is a bit-oriented, synchronous, link-layer
protocol that provides data framing, flow control and error detection and
correction. LAPB is the link layer used by X.25 applications.
On Digi TransPort routers LAPB can be used over ISDN or over a synchronous serial port.
Configuration - Network > Legacy Protocols > X.25 > LAPB n
Use: Serial port Port x (in Synchronous Mode)
To use the LAPB instance over a synchronous serial port enable this setting and select a
serial port number. To configure settings of the synchronous port such as speed and clock
source navigate to Configuration - Network > Interfaces > Serial > Serial Port n >
Sync Port n.
Use: ISDN
Enable this setting to use LAPB over ISDN.
Mode DTE or DCE
Determines whether LAPB will behave as DTE (Data Terminal Equipment) or DCE (Data
Circuit-terminating Equipment) in an X.25 protocol sense. (Physical DTE vs. DCE wiring
cannot be changed by configuration.)
N400 Counter x
This is the standard LAPB retry counter. The default value is 3 and it should not normally be
necessary to change this.
RR Timer x milliseconds
This is a standard LAPB “Receiver Ready” timer. The default value is 10,000ms (10 seconds)
and it should not normally be necessary to change this.
T1 Timer x milliseconds
This is a standard LAPB timer. The default value is 1000 milliseconds (1 second) and under
normal circumstances, it should not be necessary to change it.
T200 Timer x milliseconds
This is the standard LAPB re-transmit timer. The default value is 1000 milliseconds (1
second) and under normal circumstances, it should not be necessary to change it.
X.25 Window Size
This parameter is used to set the X.25 window size. The value range is from 1 to 7 with the
default being 7.
Disconnect link if there has been no X.25 activity for x seconds
This parameter may be used to specify the length of time (in seconds) before the link is
disconnected if there has been no X.25 activity. If this parameter is zero or not specified,
then the inactivity timer is disabled.
Disconnect link if there has been no activity for x seconds
This parameter may be used to specify the length of time (in seconds) before the link is
disconnected if there has been no activity. If this parameter is zero or not specified, then
the inactivity timer is disabled. It is useful to set this to a short period of time (say 120
seconds) when a LAPB instance is being used over ISDN for example with TPAD. Should the
POS device fail to instruct TPAD to hang up then this timer can be used as a backup hang-
up timer thus saving ISDN call charges. When LAPB is being used on a synchronous port,
this parameter should normally be set to 0.