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Configure X.25 203
end-to-end is affected, that is, the efficiency between two sets of communicating
DTE increases.
5 Configure X.25 flow control parameter
It is essential to set correct default flow control parameters (window size and
packet size) for the operation of the link because X.25 protocol is good at traffic
control. However, most public X.25 packet networks use the default window size
and maximum packet size specified in ITU-T X.25 Recommendation, which is also
true for 3Com Router series. Therefore, this task may be optional without special
requirements of service provider.
After setting window size and maximum packet size, the SVCs that can be
established only with call process will use these values if related parameters are
not negotiated in the call process. The PVCs that can be established without call
process will also use these values if no window size or packet size option is
assigned when specifying PVC.
X.25 transmitting end will fragment the too long data packet of upper layer
according to the maximum packet size and mark in the last fragment packet (M
bit is not set). When the packet reaches the receiving end, X.25 reassembles all
these fragment packets, and judges whether a complete packet is received
according to M bit marker. Therefore, too small value of the maximum packet size
will consume too much router resources on packet fragmenting and assembling,
thus lowering efficiency.
Finally, the following two points should be noted:
■ Maximum packet size < MTU*8 < LAPB N1.
■ New configuration will take effect only after executing shutdown and undo
shutdown
commands
To set/cancel the default flow control parameter, perform the following tasks.
Table 239 Set the default flow control parameter
Configure X.25 Interface
Supplementary
Parameter
■ The Configuration of X.25 interface supplementary parameter includes:
■ Configure the time delay of X.25 layer 3 timer
■ Configure the attributes related to X.25 address, including the following
configuration items:
■ Configure the alias of interface address
■ Configure to skip the calling or called address
■ Configure whether to check the address code block in call accepting packet.
■ Configure whether to carry the address code block in call accept packet
■ Configure default upper layer protocol
Operation Command
Set the receiving window and sending window size
of virtual circuit
x25 window-size in-packets
out-packets
Cancel the set receiving and sending window size
of virtual circuit
undo x25 window-size
Set the receiving and sending maximum packet
length
x25 packet-size in-packets
out-packets
Cancel the set receiving and sending maximum
packet length
undo x25 packet-size