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Loopback Tests for V.54 Data Communication Equipment

IP.com Disclosure Number: IPCOM000035797D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 5 page(s) / 47K

Publishing Venue

IBM

Related People

Bell, RA: AUTHOR [+2]

Abstract

Disclosed is a process for controlling loopback or wrap tests on a communication link. The process concentrates on V.54 data communication equipment (DCE) loops, but also includes communication controller adapter wrap and link level 2 test. The process provides a technique for determining where line failures exist. It is controlled by the host operator. The process covers point-to-point configurations, multi-point configurations (with and without fan-out capability) and tailed or tandem configurations.

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Loopback Tests for V.54 Data Communication Equipment

Disclosed is a process for controlling loopback or wrap tests on a communication link. The process concentrates on V.54 data communication equipment (DCE) loops, but also includes communication controller adapter wrap and link level 2 test. The process provides a technique for determining where line failures exist. It is controlled by the host operator. The process covers point- to-point configurations, multi-point configurations (with and without fan-out capability) and tailed or tandem configurations.

A loop is a way of looping back a circuit so that data can be transmitted, looped back, and checked at the originating end for proper transmission. The figure shows the loops that are currently defined. These include communication controller adapter wrap (loop 1), link level 2 test (loop 6; link level 2 test is supported by all IBM SDLC stations) and transmit/receive test (loops 3 and 5), which loops data between a modem pair.

V.54 is a standards recommendation for looping at locations 2 through 5. The numbering of the loops in the figure is different from the actual V.54 recommendation. The numbering scheme in the figure provides consistency for the host operator when loop locations must be selected.

The loop selection and execution process is controlled by a host application program. The process can be summarized by the following steps:
1. the host application program determines where loops can

be run;
2. a graphic menu of the loop locations is displayed. The

host operator chooses a loop location, a

repetition count

(optional) and a data field (also optional);
3. a request to execute the desired loop is sent to the

communication controller;
4. the communication controller, with its associated

hardware,

executes the address and test phases of the loop

operation

(these phases are described below);
5. the communication controller checks the returned

(looped)

data and keeps a count of the frames transmitted,

the frames received, the frames received in error, and

the frames received without error;
6. the communication controller sends the results of the

loop test back to the host application program;
7. the results are displayed for the operator.

The suggested process places under one command and one command menu all of the loops and provides the host operator with a simple procedure for stepping through line components to isolate a failure.

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Loop backs are a "GO, NO GO" kind of test. There is no information gained from the test concerning the real condition of the line. Loop 3, for example, if successful, indicates that traffic can flow to and from the data terminal equipment (DTE) side of the remote DCE. The loop does not occur externally to the remote DCE, but just inside the driver/receivers. Therefore, there is not a total guarantee that the remote DCE is operational. In the same fashion, loop 2 does not include the analog line driver/receivers and cannot give a gu...