RFC 904 (rfc904) - Page 2 of 29
Exterior Gateway Protocol formal specification
Alternative Format: Original Text Document
D.L. Mills
finite-state automaton with defined events, state transitions and
actions. The following diagram shows a simplified graphical
representation of this machine (see Section 3.4 for a detailed state
transition table).
+-------+
| |---------------+---------------+
+---->| Idle | A A
| | |-----------+ | |
| +-------+ | | |
| | A Request | | Cease | Cease
| Start | | Cease | | |
| V | Refuse V | |
| +-------+ Confirm +-------+ Up +-------+
| | |-------->| |-------->| |
| | Aqsn | | Down | Down | Up |
| | |----+ | |<--------| |
| +-------+ | +-------+ +-------+
| | | |
| Stop | | |
| Cease-ack | Stop | Stop | Stop
| +-------+ | | |
| | | V V V
+-----| Cease |<---+--------+-----------------+
| |
+-------+
Following is a brief summary and overview of gateway operations by
state as determined by this model.
Idle State (0)
In the Idle state the gateway has no resources (table space)
assigned to the neighbor and no protocol activity of any kind is in
progress. It responds only to a Request command or a Start event
(system or operator initiated) and ignores all other commands and
responses. The gateway may optionally return a Cease-ack response
to a Cease command in this state.
Upon receipt of a Request command the gateway initializes the state
variables as described in Section 3.1, sends a Confirm response and
transitions to the Down state, if resource committments permit, or
sends a Refuse response and returns to the Idle state if not. Upon
receipt of a Start event it sends a Request command and transitions
to the Acquistion state.
Acquisition State (1)
In the Acquisition state the gateway periodically retransmits
Request commands. Upon receiving a Confirm response it initializes
Exterior Gateway Protocol Formal Specification
