
Chapter 12: RAS (Remote Access Service)
RAS Architecture
Psion Mobile Devices Developers Guide
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12.3 RAS Architecture
In the Windows networking architecture, the Windows-based device functioning as a RAS server communi-
cates directly with PPP. This corresponds with the underlying WAN miniport — either PPTP or AsyncMAC —
through Transmission Control Protocol/Internet Protocol (TCP/IP). When PPP receives requests to send IP
packets from TCP/IP, it passes the packet on to the AsyncMAC miniport. After receiving a packet from PPP,
the AsyncMAC miniport performs the asynchronous framing, and then forwards the packet to the TAPI
device by calling Microsoft Win32 serial APIs. When receiving a packet through the network, the AsyncMAC
miniport strips the asynchronous framing off the packet, verifies the Cyclic Redundancy Check (CRC), and
passes the packet to PPP through the NDIS layer.
In a VPN, the PPTP WAN miniport communicates directly with TCP/IP. After receiving a packet that is
addressed to the private network from TCP/IP, PPP performs the framing, and then forwards the packet to
the PPTP WAN miniport. The PPTP WAN miniport encapsulates the information contained in the packet
header, and then reroutes the packet back to TCP/IP. IP then attaches another header that contains the
address of the PPTP server to the packet, and passes the packet on to PPP. PPP forwards the packet to
either the AsyncMAC WAN miniport or a local area network (LAN) adaptor, such as an NE2000 adaptor.
After receiving the packet over the network, the PPTP server strips the PPTP header off the packet, and
then passes the packet to PPP.
12.4 RAS on Windows Mobile (Connection Manager)
In addition to RAS, Windows Mobile devices come with a Connection Manager which some applications,
such as Internet Explorer, use to determine if there is an Internet connection. If an Internet connection is
made using the Mobile Devices SDK RAS API, the Connection Manager will not be aware of it, thus any
applications that rely on the Connection Manager will not be able to connect to the Internet through it.
Microsoft provides an API for creating connections through the Connection Manager. For more information,
visit the following URLs:
http://msdn2.microsoft.com/en-us/library/bb416435.aspx
http://msdn2.microsoft.com/en-us/library/bb840031.aspx
Applications using direct socket connections will still be able to connect using a RAS connection on both
Windows CE and Windows Mobile devices.
12.5 Getting Started with RAS
For articles on Ingenuity Working that will guide you in getting started with working with RAS:
community.psion.com/tags/ras/noteDG
12.6 Code Samples for RAS
For postings on Ingenuity Working that contain code samples that use RAS see:
community.psion.com/tags/ras/codeDG
Omnii XT10 (7545XV) Windows Embedded CE 6.0 Yes
Omnii XT15 (7545XA) Windows Embedded CE 6.0 Yes
Omnii XT15 (7545XA) Windows Embedded Hand-Held 6.5 Yes
Omnii RT15 (7545XC) Windows Embedded CE 6.0 Yes
Omnii RT15 (7545XC) Windows Embedded Hand-Held 6.5 Yes
EP10 (7515) Windows Embedded Hand-Held 6.5 Yes
Computer Operating System Supports RAS
Supports Windows
Connection Manager
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