Browse Prior Art Database

Software-Based Communication-Line Transition Interpreter

IP.com Disclosure Number: IPCOM000036682D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 7 page(s) / 177K

Publishing Venue

IBM

Related People

Billingsley, RE: AUTHOR [+3]

Abstract

This article describes the software concept used in a communications system to interpret physical communication-line transitions. These physical line transitions form the communication base between the data terminal equipment (DTE) and data circuit-termination equipment (DCE).

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Software-Based Communication-Line Transition Interpreter

This article describes the software concept used in a communications system to interpret physical communication-line transitions. These physical line transitions form the communication base between the data terminal equipment (DTE) and data circuit-termination equipment (DCE).

The communications software controlling the DTE and DCE must be able to understand the meaning of the physical line handshaking before data transmission or reception can occur. Three separate communication interface signal state tracking processes were developed in order for the software to correctly interpret the transitions of three different communication interface signals on both switched and leased networks. The three communication lines being tracked are Data Set Ready (DSR), Clear to Send (CTS) and Receive Line Signal Detect (RLSD). These are illustrated in Figs. 1, 2 and 3, respectively.

Fig. 1 shows the most basic scenario of the three-state tracking of DSR on a switched communications network. Once interrupts for this particular line have been enabled, the software examines the signal

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state and determines that it is either active or inactive. After this determination has been made, no further line tracking is required until a positive or negative transition occurs. The positive or negative edge of such a transition results in an interrupt for that particular signal. The signal is either debounced positive or negative depending upon the initial transition direction. This line debounce procedure continues until the transition stabilizes to either an active or inactive state. In the case of DSR on a switched network, an unsolicited negative DSR transition that results in a stabilized inactive state is interpreted by the DTE as an immediate error condition that requires disconnection of the communication connection. As can be seen, such a negative transition can be detected which, in turn, allows the software to perform the link disconnection.

The scenario illustrated in Fig. 2 is built from the state tracking base formed in Fig. 1. The line tracking process is identical to Fig. 1 with the exception of the action taken when an unsolicited negative transition results in a stable inactive signal state. In

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this situation, the negative transition is not considered to be an immediate error. Such a transition indicates that data transmission and/or reception must cease. This is shown by a drop warning condition being posted to the decision-making software. The signal may return to the active state after an undetermined amount of time, in which case data transmission and/or reception may resume. However, the line may remain inactive, forming the basis for a permanent error. A user-defined inactive line delay time period is used by the software to distinguish between the active and drop conditions. Fig. 8 provides a more detailed diagram of the inactive line delay logic.

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