Synopsis of a Communication Session with a Packet-Switched Network

The events in a typical X.25 communication session are described in the following paragraphs.

Establish a Network Connection...
X.25 connections begin the same as point-to-point connections p; with a modem call to a remote system. Once connected to the network, however, you use the PAD to make one or more virtual connections to other nodes on the network.

Make a Virtual Connection...
The following procedure explains the steps for the major activities in X.25 communications.

Step 1:
Configure the modem for X.25.Before placing a call to the network, you must configure the
modem to make an X.25 connection. First, enter the modem command state:
Issue AT&Q5S44=3S46=6S48=0. This command string verifies that the modem is in the error-control mode (&Q5) and sets the values of three Sregisters that control feature negotiation of the modem. S48=0 controls the negotiation process; S46=6 stipulates an X.25 connection. Now, instead of negotiating a V.42 connection, the modem attempts connections using the X.25 protocol.

Step 2:
Call the network. Dial the number of the network to which you subscribe. This is a standard modem call made with the D - Dial Command command: ATDT9,555-1234 (for example). If the call is successful, the modem connects and issues a result code sequence. The carrier and connect messages you receive depend on the connection. To see the extended messages, issue the Wn
command. With this feature enabled, for a 2400 bits/s connection, the messages is CARRIER
2400 PROTOCOL: X.25/LAPB CONNECT 4800. The PAD automatically enters the command state for channel 1.

Step 3:
Make a virtual connection to the remote system. To establish a virtual call to a user on the network, you must have the network address of the other node to which you wish to connect and any other information required by the network. For example, to connect to a service on the network, you would issue: Set 1:1, 2:1 <CR>CALL R-311020200202 <CR>p; CALL to start a connection with a remote system. Th R command permits reverse charging if the user at the other end of the virtual connection requests it. 3110 is a network ID code and 20200202 is the destination address. If the call is accepted by the remote system, the network returns the result code sequence: CON COM: W2:2,P7:7,X0277 COM. The PAD then enters the data transfer state. If the call is not accepted, the network returns a response such as CLR DTE 157 FAC: (followed by network information as alphanumeric characters X000...). The PAD remains in the PAD command state.

Step 4: Perform online activities. Once connected, you can perform desired communications p; file transfers, interactive typing, etc.

Step 5: Clear the call. When ready to end the session, issue CTRL-P to return to the channel command state. Then issue CLR <CR>. This clears the current virtual connection. The network responds with CLR CONF FAC: (followed by network information as alpha-numeric characters X000...).

Note: All virtual calls should be cleared before returning to the AT command state.

Step 6: Exit the PAD.
EXIT <CR> p; Leaves PAD command state and enters the AT command state.

Step 7:
Terminate the network connection. ATH0 <CR> p; Breaks the physical connection to the network
node. This hangs up the telephone in the same way other communication sessions are terminated.
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