3Com MSR 50 Series Configuration Manual page 288

288 C 14: X.25
HAPTER AND
LAPB C
ONFIGURATION
For the meanings of these six parameters, refer to
Table 4 Description of X.25 channel range delimitation parameters
Parameter
LIC
HIC
LTC
HTC
LOC
HOC
Each range (except PVC range) is defined by two parameters respectively working
as the upper limit and lower limit. The parameters are in the range of 1 to 4095
(including 1 and 4095), but they are regarded correct only if they satisfy the
following conditions:
In strict ascending order, i.e. 1 ≤ lic ≤ hic< ltc ≤ htc < loc ≤ hoc ≤ 4095.
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If the upper limit (or lower limit) of a range is 0, then the lower limit (or upper
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limit) shall also be 0, (which indicates this range is disabled from use).
Finally, following should be noted:
At the two sides (i.e. DTE and DCE) of a physical connection, these six
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parameters of X.25 must be equal in a symmetric way, as different settings at
the two sides are very likely to result in an improper procedure and hence result
in transmission failures.
In configuration process, implement the correct settings of parameters with
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consideration on the default of each parameter and the ascending order.
The new configuration cannot take effect immediately on a connection in use
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unless you reset the interface using the commands shutdown and undo
shutdown.
X.25 packet numbering modulo
The implementation of X.25 supports both modulo 8 and modulo 128 in packet
numbering, with Modulo 8 being the default.
The X.25 protocol requires DTE and DCE have the same packet sequence
numbering mode. The new configuration is not effective unless you reset the
interface using the shutdown command and undo shutdown command.
Besides, the packet sequence numbering mode of X.25 layer 3 is different from
the frame sequence numbering mode of LAPB (X.25 layer 2). When modulo 128
numbering mode is employed in the DTE/DCE interface with high throughput rate,
for LAPB, only the efficiency of local DTE/DCE interface is affected, that is,
point-to-point efficiency increases. While for X.25 layer 3, the efficiency of
end-to-end is affected, that is, the efficiency between the two DTE increases.
Traffic control parameters
X.25 protocol is a reliable transport protocol with powerful traffic control
capability due to the "window size" and "maximum packet size". However, it
Table 4.
Description
Lowest Incoming-only Channel
Highest Incoming-only Channel
Lowest Two-way Channel
Highest Two-way Channel
Lowest Outgoing-only Channel
Highest Outgoing-only Channel