R2511-HP MSR Router Series Layer 2 - WAN Command Reference(V5)

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[Sysname] interface serial 2/0
[Sysname-Serial2/0] lapb retry 20
lapb timer
Use lapb timer to configure the LAPB timers T1, T2, T3, and T4.
Use undo lapb timer to restore their default values.
Syntax
lapb timer { t1 t1-value | t2 t1-value | t3 t3-value | t4 t4-value }
undo lapb timer { t1 | t2 | t3 | t4 }
Default
The T4 timer is 0 seconds, and the T4 timer is disabled.
Views
Interface view
Default command level
2: System level
Parameters
t1 t1-value: Sets the T1 timer in milliseconds. The value range for the t1-value argument is 2 to 64000,
and the default is 3000.
t2 t2-value: Set the T2 timer in milliseconds. The value range for the t2-value argument is 1 to 32000, and
the default is 1500.
t3 t3-value: Sets the T3 timer in seconds. The value range for the t3-value argument is 0 to 255, and the
default is 0.
t4 t4-value: Sets the T4 timer in the range of 0 to 255 seconds.
Usage guidelines
LAPB defines the following timers:
• T1—Retransmission timer. It determines how long a transmitted frame can remain unacknowledged
before LAPB polls for an acknowledgement. When the T1 timer expires, the DTE or DCE retransmits
the frame.
• T2—Explicit acknowledge deferral timer. It determines the time that the DTE or DCE waits before
sending an explicit acknowledgement. The acknowledgement is piggybacked with data, unless no
data exists and then an explicit acknowledgement is sent when the timer expires. T1 must be no
smaller than 2 × T2.
• T3—Idle channel state timer. It is set on the DCE. When the T3 timer expires, the DCE reports an
excessively long idle channel state condition to the packet layer. T3 must be greater than the DCE
T1 timer. To disable the T3 timer, set it to zero.
• T4—Timer to detect unsignaled link failures. The T4 timer is reset every time a frame is received from
the partner on the link. If the T4 timer expires, a Receiver Ready frame with the Poll bit set is sent to
the partner, which is required to respond. If the partner does not respond, the standard polling
mechanism determines whether the link is down. You must set T4 to be greater than T1, the LAPB
retransmission timer. When the number of transmission attempts exceeds the LAPB N2 parameter,
the link is re-negotiated. To disable the T4 timer, set it to zero.