3Com 10014299 manual Configure X.25 flow control parameter, Set the default flow control parameter

Configure X.25 203

end-to-end is affected, that is, the efficiency between two sets of communicating DTE increases.

5Configure X.25 flow control parameter

Configure X.25 Interface

Supplementary

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

Operation	Command
Set the receiving window and sending window size	x25 window-size in-packets
of virtual circuit	out-packets
Cancel the set receiving and sending window size	undo x25 window-size
of virtual circuit
Set the receiving and sending maximum packet	x25 packet-size in-packets
length	out-packets
Cancel the set receiving and sending maximum	undo x25 packet-size
packet length

■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