2.7.1 Connection Disconnected
A common failure scenario is an unexpected connection breakdown between the system and external entities. A disconnection can be caused when the network is not available or when one of the communicating participants becomes unavailable. In the case where the network is not available, both participants remain active and expect the other party to continue the communication pattern specified by the protocol being executed at the time of the failure. Similarly, in the case where one of the participants is not available, the active participant expects the communication to proceed as specified by the protocol being executed.
Generally, a protocol detects a connection breakdown failure through either of the following methods:
By using a timer object that generates an event if the corresponding participant has not responded within a reasonable time span.
By being notified by the underlying protocol that the connection is disconnected.
When a connection disconnected event is detected, it causes the protocol to tear down all related communications and update any necessary data structures to maintain the system state.
Details about how each protocol detects a connection disconnected event, and how it behaves under this scenario, are provided in the specifications of the member protocols, as listed in section 2.2.
A content client that fails to find content on a hosted cache server is not considered a common failure, but rather a normal operation. The first time any content client attempts to retrieve data from a hosted cache server, it fails to find the content, and the client simply requests the full content from the content server.