These state machines MUST be observed by implementations which make use of authentication and/or authorization portion of application. They describe session lifecycle. In the state table, the event 'Failure to send X' means that the Diameter agent is unable to send command X to the desired destination. This could be due to the peer being down, or due to the peer sending back a transient failure or temporary protocol error notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the Result-Code AVP of the corresponding Answer command. The event 'X successfully sent' is the complement of 'Failure to send X'.

Stateful Client

The following state machine is observed by a client when state is maintained on the server:

State Machine Transitions for Stateful Client
State	Transition	Cause	Response/Action
Idle	1	Client requests access	Send to server service specific auth request
Idle	10	ASR Received for unknown session	Send ASA to server with Result-Code= UNKNOWN_SESSION_ID
Pending	3	Successful Service-specific authorization answer received with default Auth-Session-State value	Grant Access
Pending	4	Successful Service-specific authorization answer received but service not provided	Sent STR to server
Pending	4	Error processing successful Service-specific authorization answer	Sent STR to server
Pending	2	Failed Service-specific authorization answer received	Cleanup - free resources allocated for session
Open	6	User or client device requests access to service	Send service specific auth req
Open	6	Successful Service-specific authorization answer received	Provide Service
Open	7	Failed Service-specific authorization answer received.	Discon. user/device
Open	5	Session-Timeout Expires on Access Device	Send STR
Open	5	ASR Received, client will comply with request to end the session	Send ASA with Result-Code = SUCCESS,Send STR.
Open	6	ASR Received, client will not comply with request to end the session	Send ASA with Result-Code = SUCCESS
Open	5	Authorization-Lifetime + Auth-Grace-Period expires on access device	Send STR
Discon	8	ASR Received	Send ASA
Discon	9	STA Received	Discon. user/device

Stateful Server

The following state machine is observed by a server when it is maintaining state for the session:

State Machine Transitions for Stateful Server
State	Transition	Cause	Response
Idle	1	Service-specific authorization request received, and user is authorized	Send successful serv. specific answer
Idle	7	Service-specific authorization request received, and user is not authorized	Send failed serv. specific answer
Open	3	Service-specific authorization request received, and user is authorized	Send successful serv. specific answer
Open	2	Service-specific authorization request received, and user is not authorized	Send failed serv. specific answer, Cleanup
Open	4	Home server wants to terminate the service	Send ASR
Open	2	Authorization-Lifetime (and Auth-Grace-Period) expires on home server.	Cleanup
Open	2	Session-Timeout expires on home server	Cleanup
Discon	5	Failure to send ASR	Wait,resend ASR
Discon	6	ASR successfully sent and ASA Received with Result-Code	Cleanup
Not Discon	None	ASA Received	None
Any	2,6,7	STR Received	Send STA

Stateless Client

The following state machine is observed by a client when state is not maintained on the server:

State Machine Transitions for Stateless Client
State	Transition	Cause	Response
Idle	1	Client or Device Requests access	Send service specific auth req
Pending	2	Successful Service-specific authorization answer received with Auth-Session-State set to NO_STATE_MAINTAINED	Grant Access
Pending	4	Failed Service-specific authorization answer received	Cleanup
Open	3	Session-Timeout Expires on Access Device	Discon. user/device
Open	3	Service to user is terminated	Discon. user/device

Stateless Server

The following state machine is observed by a server when it is not maintaining state for the session:

State Machine Transitions for Stateless Server
State	Transition	Cause	Response
Idle	1	Service-specific authorization request received, and successfully processed	Send serv. specific answer

Accounting State Machines

Following state machines MUST be observed by implementations which use accounting portion of application or just need accounting services. Server side accounting state machine depends sometimes on application type, thus there are two types of state machines. Default state machine must be followed by all implemenations.

Client Machine - always stateless ?

This state machine is observer by client.

State Machine Transitions for Client
State	Transition	Next	Cause	Response/Action
Idle	1	PendingS	Client or device requests access	Send accounting start req.
Idle	2	PendingE	Client or device requests a one-time service	Send accounting event req
Idle	3	PendingB	Records in storage	Send record
PendingS	4	Open	Successful accounting start answer received
PendingS	4	Open	Failure to send and buffer space available and realtime not equal to DELIVER_AND_GRANT	Store Start Record
PendingS	4	Open	Failure to send and no buffer space available and realtime equal to GRANT_AND_LOSE
PendingS	5	Idle	Failure to send and no buffer space available and realtime not equal to GRANT_AND_LOSE	Disconnect user/dev
PendingS	4	Open	Failed accounting start answer received and realtime equal to GRANT_AND_LOSE
PendingS	5	Idle	Failed accounting start answer received and realtime not equal to GRANT_AND_LOSE	Disconnect user/dev
PendingS	6	PendingS	User service terminated	Store stop record
Open	7	PendingI	Interim interval elapses	Send accounting interim record
Open	8	PendingL	User service terminated	Send accounting stop req.
PendingI	9	Open	Successful accounting interim answer received
PendingI	9	Open	Failure to send and (buffer space available or old record can be overwritten) and realtime not equal to DELIVER_AND_GRANT	Store interim record
PendingI	9	Open	Failure to send and no buffer space available and realtime equal to GRANT_AND_LOSE
PendingI	10	Idle	Failure to send and no buffer space available and realtime not equal to GRANT_AND_LOSE	Disconnect user/dev
PendingI	9	Open	Failed accounting interim answer received and realtime equal to GRANT_AND_LOSE
PendingI	10	Idle	Failed accounting interim answer received and realtime not equal to GRANT_AND_LOSE	Disconnect user/dev
PendingI	11	PendingI	User service terminated	Store stop record
PendingE	12	Idle	Successful accounting event answer received
PendingE	12	Idle	Failure to send and buffer space available	Store event record
PendingE	12	Idle	Failure to send and no buffer space available
PendingE	12	Idle	Failed accounting event answer received
PendingB	13	Idle	Successful accounting answer received	Delete record
PendingB	13	Idle	Failure to send
PendingB	13	Idle	Failed accounting answer received	Delete record
PendingL	14	Idle	Successful accounting stop answer received
PendingL	14	Idle	Failure to send and buffer space available	Store stop record
PendingL	14	Idle	Failure to send and no buffer space available
PendingL	14	Idle	Failed accounting stop answer received

The states PendingS, PendingI, PendingL, PendingE and PendingB are "waiting" states coresponding to request related to Start, Interim, Stop, Event or buffered record, respectively.

Server Stateless

The default server side state machine requires the reception of accounting records in any order and at any time, and does not place any standards requirement on the processing of these records. Implementations of Diameter MAY perform checking, ordering, correlation, fraud detection, and other tasks based on these records. Both base Diameter AVPs as well as application specific AVPs MAY be inspected as a part of these tasks. The tasks can happen either immediately after record reception or in a post-processing phase. However, as these tasks are typically application or even policy dependent, they are not standardized by the Diameter specifications. Applications MAY define requirements on when to accept accounting records based on the used value of Accounting-Realtime-Required AVP, credit limits checks, and so on.

State Machine Transitions for Sateless Server
State	Transition	Next	Cause	Response/Action
Idle	1	Idle	Accounting start request received, and successfully processed.	Send accounting start answer
Idle	1	Idle	Accounting event request received, and successfully processed.	Send accounting event answer
Idle	1	Idle	Interim record received, and successfully processed.	Send accounting interim answer
Idle	1	Idle	Accounting stop request received, and successfully processed	Send accounting stop answer
Idle	1	Idle	Accounting request received, no space left to store records	Send accounting answer, Result-Code = OUT_OF_SPACE

Server Stateful

This state machine MAY be followed by applications that require keeping track of the session state at the accounting server. Due to incompatibility with the ability to sustain long duration connectivity problems use of this state machine is recommended only in applications where the value of the Accounting-Realtime-Required AVP is DELIVER_AND_GRANT, and hence accounting connectivity problems are required to cause the serviced user to be disconnected. Otherwise, records sent by client after connection is reestabilished, might got dropped by server. The state machine is supervised by a supervision session timer Ts, which the value should be reasonably higher than the Acct_Interim_Interval value. Ts MAY be set to two times the value of the Acct_Interim_Interval so as to avoid the accounting session in the Diameter server to change to Idle state in case of short transient network failure. Only event listed in table are valid, any other should be treated as error. In the state table, the event 'Failure to send' means that the Diameter client is unable to communicate with the desired destination. This could be due to the peer being down, or due to the peer sending back a transient failure or temporary protocol error notification DIAMETER_OUT_OF_SPACE, DIAMETER_TOO_BUSY, or DIAMETER_LOOP_DETECTED in the Result-Code AVP of the Accounting Answer command.

The event 'Failed answer' means that the Diameter client received a non-transient failure notification in the Accounting Answer command. Note that the action 'Disconnect user/dev' MUST have an effect also to the authorization session state table, e.g., cause the STR message to be sent, if the given application has both authentication/authorization and accounting portions.

State Machine Transitions for Sateful Server
State	Transition	Next	Cause	Response/Action
Idle	1	Open	Accounting start request received, and successfully processed.	Send accounting start answer,Start Ts
Idle	2	Idle	Accounting event request received, and successfully processed.	Send accounting event answer
Idle	2	Idle	Accounting request received,no space left to store records	Send accounting answer, Result-Code= OUT_OF_SPACE
Open	3	Open	Interim record received, and successfully processed.	Send accounting interimanswer, Restart Ts
Open	4	Idle	Accounting stop request received, and successfully processed	Send accounting stop answer,Stop Ts
Open	4	Idle	Accounting request received, no space left to store records	Send accounting answer, Result-Code= OUT_OF_SPACE, Stop Ts
Open	4	Idle	Session supervision timer Ts expired	Stop Ts

-- Main.baranowb - 08 Jun 2006

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