340 Chapter 10: X.25/Frame Relay Topologies
PVCs are nailed up from one endpoint to another. SVCs are brought up only when needed,
similar to a person making a phone call.
The routers are the DTE end of the connection in X.25. The switch is DCE at the carrier
providing the clock signal. The X.121 specification is the name of the addressing used in X.25.
In the figure, a PVC is being created from Router A to Router B. If your carrier is connected to
another carrier, or from an X.25 switch to an X.25 switch, you are probably using the X.75
specification in the cloud.
Some parameters can be adjusted with X.25 to improve performance:
·
win (windows in)--This value represents the number of packets that can be received
without receiving an acknowledgment. The default is 2 bytes. Example:
Router (config-if)#X25 win packets
X25 win packets
·
wout (windows out)--This value represents the number of packets that can be sent
without sending an acknowledgment. The default is 2 bytes. Example:
Router (config-if)#x25 wout 5
X25 wout 5
·
ips--This is the maximum input packet size. The default is 128 bytes. Example:
Router (config-if)#X25 ips bytes
X25 ips bytes
·
ops (output packet size)--This represents the maximum output packet size. The default is
128 bytes. Example:
Router (config-if)#X25 ops bytes
X25 ops bytes
Let's take a look at another X.25 configuration example, shown in Example 10-2.
Example 10-2
x.25 Configuration, Round Two
Interface serial 0
Encapsulation x25
X25 address 123455555555555
-------------specifies address of interface
X25 ips 1024
----------------------sets input packet size to 1024
X25 ops 1024
---------------------sets output packet size to 1024
X25 win 5
------------------------sets input window size to 7
X25 wout 5
-----------------------sets output window size to 7
87200333.book Page 340 Wednesday, August 22, 2001 2:53 PM