|Fixed Line SMS Modem|
Depending on your service provider, it is possible to send multiple messages in a single dial up session.
There is a 2 second delay after a message has been sent from the PC before starting to send it, allowing the PC a chance to submit further messages that will be sent in the same call to the server. This is limited by the number of message slots in the modem (20), and what the server will accept in a single call.
As an example, BT the UK service provider will accept 6 messages per session. It takes approximately 20 seconds to send the 6 messages, so under ideal conditions around a thousand messages can be sent an hour.
With the supplied debug software, it is possible to check the throughput of your local service provider. The debug software and instructions can be found here.
First enable the debug mode on the PC software by merging DEBUG.REG into the registry. This will cause a debug window to appear in the Z-text application, which shows everything sent to and received from the modem. Next, change the initialisation string to AT+NDB4=1 to tell the modem to output the required information.
The test can also be carried with a terminal program such as HyperTerminal, in this case it is not necessary to add DEBUG.REG to the windows registry, just enter the AT Command AT+NDB4=1
Next, unplug the telephone line from the modem to prevent message sending and send as many messages as you think the server can handle. When the telephone line is reconnected, the modem will dial the server and attempt to send all the messages. This is a typical result:
The '> DATA' is where the modem is attempting to send a message, if it is successful then it will be followed by '< ACK' from the server. In this case, the server will not accept more than 6 messages, and so the seventh was ignored, followed by the modem sending '> REL' to clear down the link after a timeout. An alternative possible behaviour would be for the server to respond with '< NAK', but this is unlikely as there isn't an appropriate error code to be included in it to cover this scenario.