A flat fee, also referred to as a flat rate or a linear rate, refers to a pricing structure that charges a single fixed fee for a service, regardless of usage.[1] Less commonly, the term may refer to a rate that does not vary with usage or time of use.
Synchronous: interrupt occurs as a result of current process, otherwise asynchronous. User requested: interrupt occurs because of direct result by user task, otherwise coerced. Maskable: if desired the interrupt can be disabled by a user task, otherwise unmasked.
DPD is disabled by default on Cisco routers. The default mode is on-demand if not specified. If the peer doesn't respond with the R-U-THERE-ACK the router starts retransmitting R-U-THERE messages every <retry-interval> seconds with a maximum of five retransmissions. After that the peer is declared dead.