You need to plan carefully for X.25 configuration. You need to consider the following:
Multiplying the group number by 256 and adding the logical channel number gives a number in the range from 0 through 4095, which uniquely identifies a logical channel. This combination is sometimes referred to as the logical channel number.
The CCITT X.25 recommendations define a number of optional facilities that your network might support.
Some facilities have parameters that can be specified or negotiated by an application program during call setup and clearing using the facilities fields in the call request, call accepted, and clear request packets.
The X.25 connection can be configured to support the following facilities during call setup:
Define the facilities during X.25 DLC configuration.
To avoid problems, your configuration parameters must match the details of your network subscription. For instance, if you configured 20 SVC logical channels but only subscribed to 10, the DCE would detect an error condition when you attempted to use the 11th logical channel.
Figure 36 shows how an X.25 network can provide a connection from an SNA gateway to a host.
Figure 36. X.25 and SNA Gateway Connectivity
Actual charges depend on the billing practices of the X.25 network provider, but charges usually consist of some or all of the following elements:
A one-time installation charge when you first subscribe to the X.25 network.
This charge depends on the facilities supplied by your network provider. For instance, you can expect to pay a charge for each optional network facility that you subscribe to. You can also expect to pay a charge for each available logical channel. PVCs generally cost more than SVCs because they require dedicated network resources.
This charge depends on the length of time for which you are logically connected to the network, possibly subject to a minimum charge.
This charge is related to the amount of data transmitted over the network during a billing period.