ActiveSync 4.x requires the following Winsock Transmission Control Protocols (TCP) to be available:

•	990 (RAPI)
•	999 (Status)
•	5721 (DTPT)
•	5678 (Legacy Replication)
•	5679 (Handshake & Legacy Replication)
•	26675 (Airsync)

If socket port filtering occurs on any of these Winsock ports, ActiveSync does not synchronize with Microsoft Windows mobile devices.

Winsock ports can be filtered by firewalls and by some routers in a networked environment. They can also be installed locally on the desktop system running ActiveSync. Network administrators may filter Winsock ports as a security measure, to limit the types of connections that can be made to the server. If synchronization is being attempted on a network where the above ports are blocked, ActiveSync fails to synchronize with the connected Windows mobile devices.

In most situations, the Windows mobile device connects to the client. However, if ActiveSync synchronization does not begin, the connection eventually times out.

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base: