The present invention provides a method by which the connectivity status
of network connections on a PC is determined in real-time by passively
reviewing packet information from the TCP/IP stack. To achieve high
accuracy of the connectivity status determination, the method involves
the determination of the edge of a local network. In cases where little
or no network traffic is observed on the network, scalable active probing
methods are designed to make accurate connectivity determination. Special
considerations for network setups like networks with web proxy servers,
NAT or edge firewalls are also included to improve the accuracy of the
determination in those environments.