Retransmission strategies for error control in packet transmission protocols

Packet transmission is based on a hierarchial model in which each of several levels uses the services of a lower level. This approach, which is essential for good visualization of the different functions necessary for transmission, also allows for the distinction of two levels in error control. A higher level is related to control on packet aerial (implemented by mechanisms of numbered packets, of responses to numbered packets, and to retransmission of nondischarged numbered packets). The lower level is related to the contents of numbered packets to responses (implemented by error detecting codes). These two levels clearly and precisely define different retransmission strategies. Two classes of strategies are defined: when the retransmission is due uniquely to a temporization which is implemented in the higher level, or when the retransmission is equally implemented following errors detected by the inferior level. In each class, different strategies are defined which result from different possible modalities.