The standard HDLC family of protocols has been designed for low to moderate BERs. But as BER increases frequent losses or corruptions of certain frames will cause extensive timeout recovery. Too many timeouts means low throughput. A new retransmission scheme is presented which depends on the transmitter to automatically initiate retransmission instead of the conventional way where the receiver automatically requests retransmission. The retransmission strategy is based on two ideas: the receiver can report without any restriction its buffer status by using a multiple acknowledgement frame and the transmitter keeps a record of the transmission order in which frames were sent. This new approach significantly reduces the use of timeout recoveries, and hence it gives a higher throughput efficiency than the standard and extended HDLC protocols.>

This paper generalizes time-discrete autoregressive source coding results of rate-distortion theory to two dimensions. A 2-D discrete autoregressive source is defined and shown to produce a 2-D widesense Markovian field. The rate distortion function of the source is then obtained under assumption of Gaussian field statistics and a squared error fidelity criterion. A procedure for generating an ensemble of 2-D codewords whose statistics satisfy the variational equations forR(D)is given. These 2-D codewords are, by space-time mappings, 1-D tree codes, and it is noted that a tree coding theorem of Jelinek, Berger, Davis and Hellman applies. The problem of instrumenting nearly optimum 2-D sequential encoding is discussed briefly. The paper stresses potential application to image coder design.

This paper shows that, under certain weak restrictions, a two-dimensional discrete Markov process can be represented either "causally" by a one-sided difference equation, or "noncausally" by a multiple-sided difference equation. The former representation is pertinent to the analysis of image coders and processors that operate sequentially on scanned image data. The latter representation is applicable to the analysis of block coders and processors. The general relation between the two representations is given and the specialized forms resulting under separable scene covariance studied.