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238 Chapter 8: Establishing an X.25 Connection
In Table 8-3, the command structure looks a bit strange until it is pointed out the l's and h's
mean "low" and "high," respectively. The i's, o's and t's are "incoming," "outgoing," and "two-
way," respectively. So, ltc means "low two-way circuit." The rest is easy to figure out. The rule
of circuit numbering specify that PVCs must have a circuit number that has a value that is lower
than any SVC range. When entering a range of circuit numbers, the low circuit must be lower
than the high circuit. If both low and high are 0, the range is unused.
To function properly, both sides of the X.25 connection must be configured identically.
Otherwise, when X.25 sees an event from a VC in a nonspecified range, it considers it an error
and therefore ignores it.
Configuring Packet Size
The maximum inbound and outbound packet sizes can be specified. The default value is 128
bytes; however, based on customer requests or carrier mandates, the size can be altered. Valid
values are 16, 32, 64, 128, 256, 512, 1024, 2048, and 4096 bytes. The commands to specify
packet size are as follows:
To set the inbound packet size, use the x25 ips command:
Router(config-if)#x25 ips size
To set the outbound packet size, use the x25 ops command:
Router(config-if)#x25 ops size
CAUTION
The inbound and outbound packet size values should match unless otherwise specified by the
carrier.
If different, the network must be able to support asymmetric transmission; otherwise, a
conflict occurs.
Configuring Window Size
The default window size in the X.25 network can be modified as needed. The default window
size is two packets. It is easy to see where the need might arise to modify this number. As with
ips and ops, this parameter must be supported by the carrier and must match at both ends to
avoid conflict. The range of valid sizes is equal to or 1 less than the modulus size. Modulus size
is discussed in the next section. The commands to specify window size are as follows:
To set the inbound window size, use the x25 win command:
Router(config-if)#x25 win no. of packets
To set the outbound window size, use the x25 wout command:
Router(config-if)#x25 wout no. of packets