7.2 Configuring X.25
7.2.7 Configuring window parameters
X.25 uses a sliding window for flow control. Larger windows allow more packets to be in transit. A larger VC window size allows more packets in the network between the two VC endpoints. Windows and modulo values should match at both ends of the X.25 link. A larger LAPB window size allows more frames to be in transit between the immediate DTE/DCE connection.

Use the x25 win and x25 wout commands to set the default window size. The window size specifies the number of packets that can be received or sent without receiving or sending an acknowledgment. Both ends of an X.25 link must use the same default window size.

Therefore, to specify default unacknowledged packet limits, use the following commands:

Router(config-if)#x25 win packets

Router(config-if)#x25 wout packets

Table describes the x25 win and x25 wout commands.

The x25 modulo command specifies the packet-numbering modulus. It affects the maximum number of window sizes. Modulo 8 is widely used and allows VC sizes up to 7 packets. Modulo 128 is rare, but it allows VC window sizes up to 127 packets.

The command to define packet-level window counter limits follows:

Router(config-if)#x25 modulo modulus

Table describes the x25 modulo command. Both ends of an X.25 link must use the same modulo.