3Com 10014299 manual Finally, the following should be noted, Set/cancel X.25 virtual circuit range

202CHAPTER 16: CONFIGURING LAPB AND X.25

Table 237 Set/cancel X.25 virtual circuit range

Operation	Command
Set X.25 virtual circuit range	x25 vc-range { in-channel hic lic
	bi-channel htc ltc out-channel
	hoc loc }
Cancel the set vc-range { in-channel hic lic	undo x25 vc-range
bi-channel htc ltc out-channel hoc loc }

The above shows that each section (except the permanent virtual circuit section) is defined by two parameters: upper limit and lower limit, the value of which ranges between 1 and 4095 (including 1 and 4095). Correct configuration must satisfy the following conditions:

■In strict numerically increasing order, i.e. 1lichic<ltchtc<lochoc4095.

■If the upper limit (or lower limit) of a section is 0, then the lower limit (or upper limit) shall also be 0, (which indicates this section is prohibited to use).

Finally, the following should be noted:

■At the two sides (i.e. DTE and DCE) of a physical connection, the six parameters of X.25 must be equal correspondingly, otherwise, the procedure will possibly operate abnormally, resulting in data transmission failure.

■During the configuration, after ensuring the numerically increasing order, pay attention to the default values of various parameters, and set the parameters according to actual condition.

■Because X.25 protocol requires DTE and DCE to have the same virtual circuit range parameters, the new configuration can not take effect immediately after successful X.25 protocol negotiation. It is necessary to first execute shutdown and undo shutdown commands.

4 Configure X.25 modulo

The implementation of X.25 in 3Com Router series supports both modulo 8 and modulo 128 packet sequence numbering. Module 8 is the default.

To set/cancel the packet sequence numbering, perform the following task in the interface view:

Table 238 Set/Cancel X.25 packet numbering modulo

Operation	Command
Set the packet sequence numbering mode	x25	modulo { 8		128 }
Cancel the set packet sequence numbering mode	undo	x25	modulo

By default, X.25 interface use modulo 8 mode.

Please note that X.25 procedure requires DTE and DCE to have the same packet numbering mode, therefore the configuration will take effect by executing the shutdown and undo shutdown commands.

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