Developers guide

Chapter 22: Wireless Wide-Area Networking
Multiplexing
194 Psion Teklogix Mobile Devices SDK Developers Guide
22.3.1 Multiplexing
Most WWAN modems have only one serial port. Some modems can operate in
multiplexing mode.
While a modem without a multiplexing mode has a packet connection, it cannot provide status in-
formation to the user interface or to an application. Information such as signal strength cannot
be monitored.
The WWAN driver tells a suitable modem to switch to multiplexing mode. This creates several
virtual serial ports on the single physical serial port. The PPP connection is on one of the virtual
ports. AT modem commands and status data can be sent through another virtual port.
22.3.2 Virtual Serial Port
The Mobile Devices SDK makes a virtual serial port available. The virtual serial port is hard-
coded to COM8: on all Psion Teklogix computers. It behaves like any other COM port. As soon as
the WWAN modem is initialized, the WWAN driver publishes a COM port interface.
22.3.2.1 Using The Virtual Serial Port
The WWAN driver provides a virtual serial port so that other applications such as Windows CE
dial-up networking can access the WWAN modem concurrently with the WWAN user interface.
The main purpose is to support dial-up data connections in a more convenient manner. Compared
to previous software releases the addition of the virtual serial port offers a number of advantages:
• The WWAN driver does not need to be shut down in order to establish a dial-up data
connection
• For some modems where dial-up data connections were not possible before because of peculi-
arities of the modem they are now possible through the virtual port (Asus AGC-100; Novatel
U530, U630).
• For a number of modems the network status display and SMS functions remain available
during a dial-up data connection (Siemens MC75, Option Globetrotter, Option Globetrotter
Combo, Sierra AC775, Audiovox RTM-8000, CMCS NTN-000, Enfora ADT0110, Enfora
GSM0110).
• The WWAN driver and user interface provide the PIN handling.
• For all GSM/GPRS modems the APN for the virtual port can be automatically configured
through the WWAN user interface.
• The WWANDbg utility can be used to analyze the AT commands sent by legacy third-party
applications.
22.3.2.2 Configuration
The virtual serial port is available as COM8: with the name Virtual WWAN port. The port is
created dynamically if a WWAN modem is present and the modem initialization was successful
(including successful PIN authentication, if required). The virtual port should be configured as
follows:
• Any baud rate (this setting is ignored, the correct baud rate for the modem is chosen by the
WWAN driver).
• 8 data bits, no parity, 1 stop bit.
• No flow control (flow control for communication with the modem is handled by the
WWAN driver).