States and state transitions

The following tables describe:

• transport interface states

• transport interface and t_look() events

• outgoing events

• incoming events

• state transitions caused by transport system user actions

• transport interface state transitions

• TLOOK error events

Transport interface states

The following table describes the states used to describe the state transitions of the transport interface.

State	Meaning	Service type
T_UNINIT	Not initialized. Start and end state of the interface	T_COTS T_COTS_ORD T_CLTS
T_UNBND	Initialized but not bound	T_COTS T_COTS_ORD T_CLTS
T_IDLE	No connection established	T_COTS T_COTS_ORD T_CLTS
T_OUTCON	Outgoing connection waiting for the server	T_COTS T_COTS_ORD
T_INCON	Incoming connection waiting for the server	T_COTS T_COTS_ORD
T_DATAXFER	Data transfer	T_COTS T_COTS_ORD
T_OUTREL	Orderly connection shutdown (waiting for confirmation for orderly connection shutdown)	T_COTS_ORD
T_INREL	Incoming orderly connection shutdown (waiting for request for orderly connection shutdown)	T_COTS_ORD

Transport interface and t_look() events

The user can call the t_look() function to determine which event has occurred if a TLOOK error is reported. The TLOOK error has a special significance for the transport interface. TLOOK informs the user when a function of the interface was interrupted by an unexpected asynchronous event on the specified transport endpoint. An error indicated by TLOOK must therefore not be interpreted as an interface error. The called function is not executed because of the pending event.

Transport interface events:

Event	Meaning
T_LISTEN	A connection request arrived at the transport endpoint. T_LISTEN can only occur with a transport endpoint which is assigned an address with qlen > 0.
T_CONNECT	Confirmation of a previously sent connection request has arrived. The confirmation is sent when the server accepts a connection request.
T_DATA	User data has arrived.
T_DISCONNECT	A message reporting that a connection has been aborted or refused has arrived
T_ORDREL	The request for an orderly connection shutdown has arrived.
T_UDERR	The report about an error with a previously sent datagram has arrived.

TLOOK error events:

XTI function	Event
t_accept()	T_DISCONNECT, T_LISTEN
t_connect()	T_DISCONNECT, T_LISTEN
t_listen()	T_DISCONNECT
t_rcv()	T_DISCONNECT, T_ORDREL
t_rcvconnect()	T_DISCONNECT
t_rcvrel()	T_DISCONNECT
t_rcvudata()	T_UDERR
t_snd()	T_DISCONNECT, T_ORDREL
t_sndudata()	T_UDERR
t_unbind()	T_LISTEN, T_DATA
t_sndrel()	T_DISCONNECT
t_snddis()	T_DISCONNECT

If execution of an XTI function leads to a TLOOK error on a transport endpoint, subsequent calls to the same or other XTI functions affected by the same TLOOK return the TLOOK error until the causing event has been handled. You can identify the event causing the TLOOK error with the XTI t_look() function and then handle it with a suitable other XTI function.

Outgoing events

The outgoing events are described in following table. They correspond to the values returned by the specified transport functions, where the functions send a request or reply to the transport provider.

Some of the events (e.g. accept) in the table are discriminated according to the context in which they occur. The context depends on the values of the following variables:

• ocnt: Number of pending connection requests

• fd: File descriptor of the current transport endpoint

• refsd: File descriptor of the transport endpoint on which a connection is accepted

Event	Meaning	Service type
opened	Successful termination of t_open()	T_COTS T_COTS_ORD T_CLTS
bind	Successful termination of t_bind()	T_COTS T_COTS_ORD T_CLTS
optmgmt	Successful termination of t_optmgmt()	T_COTS_ORD T_CLTS
unbind	Successful termination of t_unbind()	T_COTS T_COTS_ORD T_CLTS
closed	Successful termination of t_close()	T_COTS T_COTS_ORD T_CLTS
connect1	Successful termination of t_connect() in synchronous mode	T_COTS T_COTS_ORD
connect2	TNODATA error with t_connect() in asynchronous mode or TLOOK error caused by a connection shutdown request arriving at the communications endpoint	T_COTS T_COTS_ORD
accept1	Successful termination of t_accept() with ocnt == 1, fd == resfd	T_COTS T_COTS_ORD
accept2	Successful termination of t_accept() with ocnt == 1, fd != resfd	T_COTS T_COTS_ORD
accept3	Successful termination of t_accept() with ocnt >1	T_COTS T_COTS_ORD
snd	Successful termination of t_snd()	T_COTS T_COTS_ORD
snddis1	Successful termination of t_snddis() with ocnt <=1	T_COTS T_COTS_ORD
snddis2	Successful termination of t_snddis() with ocnt >1	T_COTS T_COTS_ORD
sndrel	Successful termination of t_sndrel()	T_COTS_ORD
sndudata	Successful termination of t_sndudata()	T_CLTS

Incoming events

The incoming events correspond to the successful return values of the specified function, where these functions receive data or information about events from the transport provider. The only incoming event that is not connected directly to the return value of a function is pass_conn. The pass_conn event occurs when a user transfers a connection to another transport endpoint. This event occurs on a transport endpoint to which the connection was transferred, although no transport interface function was called for it. The pass_conn event describes the behavior when a user accepts a connection on another transport endpoint.

In the following table, the rcvdis events are discriminated according to the context in which they occur. The context depends on the value of ocnt. The value of ocnt specifies the number of pending connection requests on the transport endpoint.

Event	Meaning	Service type
listen	Successful termination of t_listen()	T_COTS T_COTS_ORD
rcvconnect	Successful termination of t_rcvconnect()	T_COTS T_COTS_ORD
rcv	Successful termination of t_rcv()	T_COTS T_COTS_ORD
rcvdis1	Successful termination of t_rcvdis() with ocnt <= 0	T_COTS T_COTS_ORD
rcvdis2	Successful termination of t_rcvdis() with ocnt = = 1	T_COTS T_COTS_ORD
rcvdis3	Successful termination of t_rcvdis() with ocnt > 1	T_COTS T_COTS_ORD
rcvrel	Successful termination of t_rcvrel()	T_COTS_ORD
rcvudata	Successful termination of t_rcvudata()	T_CLTS
rcvuderr	Successful termination of t_rcvuderr()	T_CLTS
pass_conn	Receive a transferred connection	T_COTS T_COTS_ORD

State transitions caused by transport system user actions

In the state tables listed below, some state transitions are accompanied by a series of actions that have to be carried out by the transport service user. These actions are identified with the notation "[n]", where n is the number of the action to be executed.

The actions concerned are as follows:

1. Set the number of pending connection requests to 0.

2. Increment the number of pending connection requests.

3. Decrement the number of pending connection requests.

4. Transfer a connection to another transport endpoint, as specified in t_accept().

State tables

The state transitions of the transport interface are described in the following tables. The transition to the next state is shown for a current state and an event. All actions are also defined which are to be executed by the transport system user. Such actions are identified with "[n]".

The contents of each box indicate the follow-up state. This is dependent on the current state (at the head of the column) and the current incoming or outgoing event (at the left in the line concerned). An empty box means that the state/event combination concerned is invalid. Each box can contain an action list (as described in the previous section) in addition to the follow-up state. The transport service user must execute the actions in the listed order.

You should note the following points when reading the state tables:

• The t_close() function is also handled in the state tables (see the closed event in tho following table). However, t_close() can be called from any state to close a transport endpoint. If the address is bound to a transport endpoint, calling t_close() automatically releases the address.

• The transport provider detects when a transport service user calls a function outside the defined order. In this case, the transport provider refuses the function and sets t_errno to TOUTSTATE. The state does not change.

• If a different transport error occurs, the state does not normally change. An exception to this is a TLOOK or TNODATA error with t_connect(). Other exceptions are noted explicitly in the description of the functions in section "XTI(POSIX) user functions". In the state tables, it is assumed that the transport interface is used correctly.

• The t_getinfo(), t_getstate(), t_alloc(), t_free(), t_sync(), t_look() and t_error() functions are not included in the state tables as they do not affect the state.

The state transitions in the following phases are each handled in a separate table:

• local management (connection-oriented and connectionless service)

• data transfer in the connectionless service

• connection setup, data transfer and connection shutdown in the connection-oriented service

Local management state transitions:

Event	State
	T_UNINIT	T_UNBND	T_IDLE
opened	T_UNBND
bind		T_IDLE [1]
optmgmt			T_IDLE
unbind			T_UNBND
closed		T_UNINIT

Connectionless service state transitions:

Event	State
	T_IDLE
sndudata	T_IDLE
rcvudata	T_IDLE
rcvuderr	T_IDLE

Connection-oriented service state transitions:

Event	State
	T_IDLE	T_OUTCON	T_INCON	T_DATAXFER	T_OUTREL	T_INREL
connect1	T_DATAXFER
connect2	T_OUTCON
rcvconnect		T_DATAXFER
listen	T_INCONN [2]		T_INCONN [2]
accept1			T_DATAXFER [3]
accept2			T_IDLE [3][4]
accept3			T_INCON [3][4]
snd				T_DATAXFER		T_INREL
rcv				T_DATAXFER	T_OUTREL
snddis1		T_IDLE	T_IDLE [3]	T_IDLE	T_IDLE	T_IDLE
snddis2			T_IDLE [3]
rcvdis1		T_IDLE		T_IDLE	T_IDLE	T_IDLE
rcvdis2			T_IDLE [3]
rcvdis3			T_INCON [3]
sndrel				T_OUTREL		T_IDLE
rcvrel				T_INREL	T_IDLE
pass_conn	T_DATAXFER