Defining LAPB Parameters

Your network may require some adjustment to the values set by default for LAPB operation. You can adjust the LAPB parameter values using the Configurator, as follows:

1. Select Configure, WAN/Data Services, and X.25 from the navigation menu:



2. Click on the X.25 LAPB link at the top of the screen. You will see the X.25 LAPB Mapping screen.
3. Click on Modify next to the LAPB index whose parameters you want to adjust. You will see the Modify an X.25 LAPB Entry screen, with the operational parameter values displayed, like this example:



Parameter	Range of Values	Default Value	Description
X.25 Station Type	DTE | DCE	DCE	Select whether the LAPB layer is to operate in DTE or DCE mode. Make sure that one end of the X.25 connection is set to DCE and the other end is set to DTE.
Sequencing	Modulo8 | Modulo128	Modulo8	Select the modulus used for the LAPB sequence numbers.
Tx Window Size	1..127	7	Enter the default transmit window size for this interface. The transmit window size specifies the maximum number of unacknowledged PDUs that may be outstanding from this end of the connection at any one time.
Rx Window Size	1..127	7	Enter the receive PDU window size for this interface. This is the maximum number of unacknowledged sequenced PDUs that may be outstanding from the remote end at any one time.
N2 Rxmit Count	0..65535	20	This is the N2 retry counter. This counter specifies the number of times a PDU will be resent after the T1 timer expires without an acknowledgement for the PDU.
T1 ACK Timer	1..65535	3000	The T1 timer specifies the maximum time in milliseconds to wait for an acknowledgement of a PDU.
T2 ACK Delay Timer	100..65535	100	The T2 timer specifies the maximum time in milliseconds to wait before sending an acknowledgement for a sequenced PDU. 0 means there is to be no delay generating the acknowledgement.
T3 Disconnect Timer	1..65535	60000	The T3 timer specifies the time in milliseconds to wait before considering the link to be disconnected. 0 means the link will be disconnected upon completion of the frame exchange to disconnect the link.
T4 Idle Timer	0..2147483647	60000	The T4 timer specifies the maximum time in milliseconds that may elapse with no frames being exchanged on the data link. 0 disables the T4 timer function.
Busy Timer	0..65535	10000	Enter the value to be used for the busy timer (the time to wait before transmitting an RR frame after receiving an RNR from the remote end).



4. Make the necessary changes to the parameter values and click on the Save button.
5. Reset the unit. Select Administration and System Reset from the navigation menu. Select Configuration as the Reset Type. Then, click on the Reset button.

End of procedure.