WTP provides three transaction classes that can be invoked by WSP or another higher layer protocol they are:

• Class 0: Unreliable invoke message with no result message
• Class 1: Reliable invoke message with no result message.
• Class 2: Unreliable invoke message with one reliable result message.

Class 0: Class 0 provides an unreliable datagram service, which can be used for an unreliable push operation. Data from a WTP user are encapsulated by WTP (the initiator, or client) in an Invoke PDU and transmitted to the target WTP (the responder, or server), with no acknowledgment. The responder WTP delivers the data to the target WTP user.

Class 1: Class 1 provides a reliable datagram service, which can be used for a reliable push operation. Data from an initiator are encapsulated in an Invoke PDU and transmitted to the responder. The responder delivers the data to the target WTP user and acknowledges receipt of the data by sending back an ACK PDU to the WTP entity on the initiator side, which confirms the transaction to the source WTP user. The responder WTP maintains state information for some time after the ACK has been sent to handle possible retransmission of the ACK if it gets lost and/or the initiator retransmits the Invoke PDU.

Class 2: Class 2 provides a request/response transaction service and supports the execution of multiple transactions during one WSP session. Data from an initiator are encapsulated in an Invoke PDU and transmitted to the responder, which delivers the data to the target WTP user. The target WTP user prepares response data, which are handed down to the local WTP entity. The responder WTP entity sends these data back in a result PDU If there is a delay in generating the response data beyond a timer threshold, the responder may send an ACK PDU before sending the result PDU This prevents the initiator from unnecessarily retransmitting the Invoke message.

WTP provides three transaction classes that can be invoked by WSP or another higher layer protocol they are:

• Class 0: Unreliable invoke message with no result message
• Class 1: Reliable invoke message with no result message.
• Class 2: Unreliable invoke message with one reliable result message.

Class 0: Class 0 provides an unreliable datagram service, which can be used for an unreliable push operation. Data from a WTP user are encapsulated by WTP (the initiator, or client) in an Invoke PDU and transmitted to the target WTP (the responder, or server), with no acknowledgment. The responder WTP delivers the data to the target WTP user.

Class 1: Class 1 provides a reliable datagram service, which can be used for a reliable push operation. Data from an initiator are encapsulated in an Invoke PDU and transmitted to the responder. The responder delivers the data to the target WTP user and acknowledges receipt of the data by sending back an ACK PDU to the WTP entity on the initiator side, which confirms the transaction to the source WTP user. The responder WTP maintains state information for some time after the ACK has been sent to handle possible retransmission of the ACK if it gets lost and/or the initiator retransmits the Invoke PDU.

Class 2: Class 2 provides a request/response transaction service and supports the execution of multiple transactions during one WSP session. Data from an initiator are encapsulated in an Invoke PDU and transmitted to the responder, which delivers the data to the target WTP user. The target WTP user prepares response data, which are handed down to the local WTP entity. The responder WTP entity sends these data back in a result PDU If there is a delay in generating the response data beyond a timer threshold, the responder may send an ACK PDU before sending the result PDU This prevents the initiator from unnecessarily retransmitting the Invoke message.