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Command
x25 mod modulus
x25 k window-size
x25 n1 bytes
x25 n2 tries
x25 t1 seconds
x25 t2 seconds
Key Word:
U(undo)
D(default)
......
(12)mod
(13)n1
Set LAPB max frame length
(14)n2
Set LAPB retransmitting time
......
(20)t1
Set LAPB transmitting timeout timer
(21)t2
Set LAPB receiver timeout timer
......
Please Input the code of command to be excute(0-26): 12 （you can input12,14,20 or 21 to meet your requirement）
Key Word:
Q(quit)
(00)8/128
Module 8 or 128
Please Input the code of command to be excute(0-0): 0
Please input a string:8 （input the module number）
Will you excute it? (Y/N):y
LAPB Modulo and LAPB K--The LAPB modulo determines the operating mode. Modulo 8 (basic mode)
is widely available, because it is required for all standard LAPB implementations and is sufficient for
most links. Modulo 128 (extended mode) can achieve greater throughput on high-speed links that have
a low error rate (some satellite links, for example) by increasing the number of frames that can be
transmitted before waiting for acknowledgment (as configured by the LAPB window parameter, k). By
its design, LAPB's k parameter can be at most one less than the operating modulo. Modulo 8 links can
typically send seven frames before an acknowledgment must be received; modulo 128 links can set k
to a value as large as 127. By default, LAPB links use the basic mode with a window whose size is 7.
♦ LAPB N1--When connecting to an X.25 network, use the N1 parameter value set by the network
administrator. This value is the maximum number of bits in a LAPB frame, which determines the
maximum size of an X.25 packet. When you are using LAPB over leased lines, the N1 parameter
should be eight times the hardware maximum transmission unit (MTU) size plus any protocol
overhead. Default value is highly recommended.
♦ LAPB N2--The transmit counter (N2) is the number of unsuccessful transmit attempts that are
made before the link is declared down.
♦ LABP T1--The retransmission timer (T1) determines how long a transmitted frame can remain
unacknowledged before the D-LINK IOS software polls for an acknowledgment. For X.25 networks,
the retransmission timer setting should match that of the network.
♦ LAPB T2—The value of T2 of DTE can be different from that of DCE, however, they should inform
each other. If the T2 timer is expired, the DTE(or DCE) must send a confirmation frame to the
DTE(or DCE) of the partner before the partner's T1 timer expired.
For leased-line circuits, the T1 timer setting is critical because the design of LAPB assumes that a
frame has been lost if it is not acknowledged within period T1. The timer setting must be large enough
to permit a maximum-sized frame to complete one round trip on the link. If the timer setting is too small,
the software will poll before the acknowledgment frame can return, which may result in duplicated
frames and severe protocol problems. If the timer setting is too large, the software waits longer than
necessary before requesting an acknowledgment, which reduces bandwidth.
Model Name
Purpose
Set the modulo,
Set the window size（K）
Set
the
maximum
bits
frame(N1)
Set the counter for sending
frame(N2)
Set the retransmittion timer(T1)
Set the hardware outage period
（T2）
Q(quit)
Set LAPB and X.25 module(8/128)
- 73 -
Values or Ranges
8 or 128
2～(modulo minus-1)frames
per
137-1512
1-255 times
1-64 sec
1-32 sec
Default
8
7
1500
16
3
0
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