Transport Service Interface Sequence of Primitives

The allowable sequence of primitives are described in the state diagrams and tables in ``Allowable Sequence of TPI Primitives'' for both the connection-mode and connectionless-mode transport services. The following are rules regarding the maintenance of the state of the interface:

• It is the responsibility of the transport provider to keep record of the state of the interface as viewed by the transport user.

• The transport provider must never issue a primitive that places the interface out of state.

• The uninitialized state of a stream is the initial and final state, and it must be bound (see T_BIND_REQ primitive) before the transport provider may view it as an active stream.

• If the transport provider sends a M_ERROR upstream, it should also drop any further messages received on its write side of the stream.

• A transport connection release procedure can be initiated at any time during the transport connection establishment or data transfer phase.

• The state tables for the connection-mode transport service providers include the management of the sequence numbering when a transport provider sends multiple T_CONN_IND requests without waiting for the response of the previously sent indication. It is the responsibility of the transport providers not to change state until all the indications have been responded to, therefore the provider should remain in the T_WRES_CIND state while there are any outstanding connect indications pending response. The provider should change state appropriately when all the connect indications have been responded to.

• The state of a transport service interface of a stream may only be transferred to another stream when it is indicated in a T_CONN_RES primitive. The following rules then apply to the cooperating ``streams'':

  • The stream which is to accept the current state of the interface must be bound to an appropriate protocol address and must be in the idle state.

  • The user transferring the current state of a stream must have correct permissions for the use of the protocol address bound to the accepting stream.

  • The stream which transfers the state of the transport interface must be placed into an appropriate state after the completion of the transfer.