Bluetooth Serial Port Sync on Windows Mobile 6.5

Windows Mobile 6.5 relied on the Bluetooth Serial Port Profile (SPP) to create wireless synchronization partnerships with host computers. By emulating physical RS-232 serial cabling over a Bluetooth radio link via the RFCOMM protocol, SPP allowed Microsoft ActiveSync and Windows Mobile Device Center to recognize mobile devices as if they were connected through traditional serial cables. This article explains the role of SPP, how virtual COM ports enabled wireless syncing, and the technical mechanics behind establishing these partnerships.

The Role of the Serial Port Profile (SPP)

The Bluetooth Serial Port Profile (SPP) defines the requirements for Bluetooth devices necessary to set up emulated serial cable connections. Built on the RFCOMM protocol—which provides emulation of RS-232 control and data signals—SPP translates wireless data streams into standard serial data.

For Windows Mobile 6.5, SPP served as the bridge between legacy synchronization architecture and wireless convenience. Because original synchronization software was designed around physical USB and RS-232 serial connections, SPP allowed the operating system to maintain backward compatibility without rewriting the core transport protocols of ActiveSync.

Virtual COM Port Emulation

To facilitate wireless synchronization, Windows Mobile 6.5 and the host PC assigned virtual communication (COM) ports to the Bluetooth connection:

  1. Inbound and Outbound Ports: The host PC configured an "Inbound" COM port within its Bluetooth software stack (such as the Microsoft, Broadcom/Widcomm, or Toshiba stack). Windows Mobile configured an "Outbound" COM port directed toward the host PC’s Bluetooth address.
  2. Software Binding: Microsoft ActiveSync (on Windows XP) or Windows Mobile Device Center (on Windows Vista and Windows 7) was configured to monitor the specific inbound COM port assigned to the Bluetooth connection.
  3. Handshake and Emulation: When a sync was initiated, the mobile device opened a connection over SPP to the PC's virtual port. The PC treated this incoming connection identically to a hardware serial cable attachment.

Establishing the Wireless Partnership

To create an active sync partnership without wires on Windows Mobile 6.5, users executed a specific setup sequence:

  • Device Pairing: The host PC and Windows Mobile device discovered each other, paired via a secure PIN, and established a trusted bond.
  • Service Selection: During device discovery, Windows Mobile detected the available Bluetooth services on the PC and selected the "ActiveSync" or "Serial Port" service.
  • Port Assignment: Under the Bluetooth settings on Windows Mobile 6.5, the user created a new Outgoing Port linked to the paired PC.
  • Sync Initiation: In the mobile ActiveSync application, the user selected "Sync via Bluetooth." The operating system engaged the SPP virtual COM port, established the RFCOMM link, and initiated data synchronization for contacts, calendars, emails, and tasks.