In planning situations involving tight deadlines, a commonsense reasoner may spend a substantial amount of the available time in reasoning towards and about the formulation of the (partial) plan. This reasoning involves, but is not limited to (partial) plan formulation, asking decisions about available and conceivable alternatives, plan sequecing, and also plan failure and revision. However, the time taken in reasoning about a plan brings the deadline closer. The reasoner should therefore take account of the passage of time during that same reasoning, and this accounting must continously affect every decision under time-pressure. Step-logics were introduced as a mechanism for reasoning situated in time. We employ an extension of them here, called ‘active logics’, to create a logic-based planner that lets a time-situated reasoner keep track of a approaching deadline as he/she makes (and enacts) his/her plan, thereby treatilng all facets of planning (including plan-formation and its simultaneous of subsequent execution) as deadline-coupled. While an agent under severe time-pressure may spend a substantial amount of the available time in reasoning towards and about a plan of action, in a realistic setting the same agent must also measure up to two other crucial resource limitations as well, namely space and computation bounds. We address these concerns and offer some solution by introducing a limited short-term memory combined with a primitive relevance mechanism, and a limited-capacity inference engine. We propose heuristics to maximize an agent's chances of meeting a dedline within these additional realistic constraints. We give examples from commonsense planning, including ones we have solved and implemented in Prolog.

Reason-based actions plunge the reasoner into temporal considerations from all angles. We see this not only when time enters explicitly into the problem statement, but also in formal robot blocks-world scenarios, in the Yale Shooting Problem, and other associated versions of the frame problem (e.g., Hanks and McDermott1), in various specialized actions (e.g., hiding, as in Allen2), and so on. In short, where there is action, there is time, and where there is time, there is a potential need for reasoning about time. Where, then, is the action? It certainly includes the usual overt physical acts of motion, and also certain covert behaviors such as hiding or watching. In these, of course, time is important. But there is another angle that is not usually noted, one that we have been exploring for the past several years3–6. Namely, action also occurs in the form of mere thinking or reasoning. Moreover, the very same temporal considerations apply to this reasoning behavior. This leads us to view reasoning itself as a kind of action, with the obvious yet nontrivial consequence that our reasoning goes on “as the world turns.” the present article offers various arguments in support of this position.

The design of a multiservice packet network must ensure that delays to speech packets are minimized while data and other types of packets are delivered without error. The author suggests some ways in which error detection, forward error correction (FEC), and automatic repeat request (ARQ) schemes may be utilized in integrated services packet networks (ISPNs) to ensure that satisfactory error performance and reliability standards are achieved. The results show that ARQ schemes combined with reliable error detection are the most practical way of achieving reliable error control in integrated services networks. Also, such error control schemes can have performance advantages if applied on a region-by-region basis rather than simple end-to-end.>

In high bit rate data transmission systems with ARQ error control, the throughput efficiency is a function of bit error rate, block or packet size, and the effect of significant round trip delays such as may be experienced in satellite communication systems. The selective-repeat ARQ scheme is capable of providing superior throughput performance independent of round trip delay, but requires excessively large receiver buffers; as a result the inferior GoBackNprocedure is commonly adopted. This paper analyzes a class of mixed-mode ARQ protocol models which incorporate a selectiverepeat mode with finite receiver buffer. The protocol models are shown to be amenable to exact throughput analysis, but do assume that the round trip delay is constant and known, blocks are of constant length, and the ACK/NAK signals are returned error free. These assumptions might create difficulties for practical implementation. However, the analytical model results highlight those aspects of ARQ protocols which affect throughput performance as round trip delays increase. The results show that it is desirable for best throughput performance in practical systems that at least the first retransmission of a block following an error should be in the selective-repeat mode to obtain superior performance over GoBackNschemes. Furthermore, alternative secondary retransmission modes are considered which ensure that reliable transmission can be achieved without receiver buffer overflow, even if the selective-repeat mode retransmissions fail. It is shown that the choice of secondary mode does not have a significant effect on the throughput efficiency but has a bearing on complexity.