/////////////////////////////////////////////////////////////////////////// // // // 4TEL in TXK1 Local Exchanges // // Expunged Into Digital Form by Keltic Phr0st // // // /////////////////////////////////////////////////////////////////////////// This article decsribes experience in Severnside District of using the 4Tel Automated Subscriber Loop Test System, supplied by Teradyne Ltd., to replace the Automatic Line Insulation Tester (ALIT) in TXK1 crossbar Local Exchanges. The article decsribes some of the problesm encountered, and how the redundant ALIT was modified to make the 4TEL equipment more efficient and cheaper to purchase. INTRODUCTION ============ Early in 1983, the then Bristol Telephone Area began trials of a new American-designed system for testing customers lines, supplied by Teradyne Ltd. The system, known as the 4TEL Automated Subscriber Loop Test System, comprised a central main computer installed at the Bristol Repair Service Centre, and remote dial-and-test units fitted at distant satellite telephone exchanges. The remote units, known as Central Office Line Testers (COLTs), seize and test customers lines via the normal test access circuits. Tests can be carried out overnight by using a routine mode in which lines are automatically tested in the sequence 0000-9999. The results are stored in the central computer and can be printed out when required. Alternatively, individual lines can be tested on demand, and the results displayed on a Visual Display Unit. One of the exchanges chosen for the trail was the TXK1 crossbar exchange at Henbury, which had a multiple of 10,500 lines. Investigations showed that a COLT with one dial circuit could test only about 4000 circuits each night. Another Dial Circuit was added at extra cost, but still only about 8000 lines per night could be tested. The problem was caused by the method used to access line circuits in a TXK1 exchange. Each COLT dial circuit was connected to a test transmission relay group (TTRG), and dialled a four-digit code to seize each line circuit, including all spare lines. The two dial circuits tended to operate simultaneously and dial consecutive numbers. At the Linemarker stage of a call set-up, only one terminating call at a time can be processed. The co-incident calls sometimes led to an apparent system failure and, consequently, a fault print-out on the exchange tele-printer. Fig. 1 shows original equipment configuration. Fig. 1 - Original Method of interfacing the COLT to a TXK1 Exchange ------------------------------------------------------------------- ROUTER SWITCHES DISTRIBUTOR SWITCHES ÚÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄ¿ ³ COLT ÃÄÄÄ´ TTRG ÃÄÄ-´ RSA Ã-´ RSB Ã-´ DSA Ã-´ DSB ÃÄ-Ä´ LINE ÃÄÄÄÄÄÄ- ÀÄÄÄÄÄÄÙ ÀÄÄÂÄÄÄÙ ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÙ ³ CIRCUIT ³ ÀÄÄÄÄÄÂÄÄÄÙ ÚÄÄÄÄÁÄÄÄÄÄ¿ ³ ³ INCOMING ³ ³ ³ REGISTER ³ ³ ³ DETECTOR ³ ³ ÀÄÄÄÄÂÄÄÄÄÄÙ ³ ³ ÚÄÄÄÄÁÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÁÄÄÄ¿ ³ INCOMING ÃÄ-Ä-Ä´ ROUTER ÃÄÄÄÄÄÄ-ÄÄÄÄÄÄ-ÄÄÄÄÄÄ´ LINE ³ ³ REGISTER ³ ³ CONTROL ³ ³ MARKER ³ ÀÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÙ Incoming Register Connector Operations Doubled Router Controls Operations Doubled 'Preference Choice' Incoming Registers Operations Ten Times Doubled The massive increase in the use of registers caused concern because the wear, and subsequent failure, of pulsing relays is major service hazard in TXK1 exchanges. It was therefore suggested that the automatic line Insulation Tester (ALIT), made redundant by the 4TEL system, could be used to set up the 4TEL calls. The ALIT is, in essence, a register that has the ability to test lines, and the great advantage of being able to increment calls sequentially without re-dialling. Using the ALIT as an interface between the the 4TEL and the router control (see Fig.2) would eliminate the extra wear on the registers. Fig. 2 - New method of Interfacing ---------------------------------- ROUTER SWITCHES DISTRIBUTOR SWITCHES ÚÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄ¿ ³ COLT ÃÄÄÄ´ ALIT ÃÄ-Ä´ RSA Ã-´ RSB Ã-´ DSA Ã-´ DSB ÃÄ-Ä´ LINE ÃÄÄÄÄÄÄ- ÀÄÄÄÄÄÄÙ ÀÄÄÂÄÄÄÙ ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÙ ³ CIRCUIT ³ ³ ÀÄÄÄÄÄÂÄÄÄÙ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÚÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÁÄÄÄ¿ ÀÄÄÄÄÄÄÄÄÄÄÄ´ ROUTER ÃÄÄÄÄÄÄ-ÄÄÄÄÄÄ-ÄÄÄÄÄÄ´ LINE ³ ³ CONTROL ³ ³ MARKER ³ ÀÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÙ Preliminary investigations also indicated that time could be saved by changing the COLT control program. In Strowger Exchanges, the 4TEL program includes some call incrementing. The COLT dials via the test selector access to the first outlet of the test final selector bank. After the test has been completed, the wipers are stepped on to the second outlet. This continues up to digit 9, when the COLT clears and redials the number ending in '0'. It was thought that this increment feature of 4TEL could be used in a TXK1 exchange. Calculations showed that, by using only one dial circuit, more than 10,000 tests per night should be possible. DEVELOPMENT =========== The ALIT is normally set up for a test programme by code digits dialled from a remote access point into relay stores, as follows : First Digit Type of start; for example, immediate or delayed Second Digit Insulation Test Limits Third Digit 10,000-line group to be tested Fourth Digit 1000-line start group to be tested (For example, 2000) Fifth Digit 100-line start group to be tested (For example, 2300) Sixth Digit 1000-line finish group (For example, 3000) Seventh Digit 100-line finish group (For example, 3599) The tens and units counting stores are automatically set to zero, ready to increment from there. In the example given, the ALIT would have tested from 2300-3599. The first stage of the development was to list the COLT requirements, check the COLT signalling arrangements, and then modify the ALIT accordingly. The COLT had to be able to A) Set up a call to any number, and increment if neccesary for the routine mode; B) Control the increment; C) Receive Information on Line status, that is, FREE, BUSY, Number UnObtainable, etc, etc... D) Test the Line if FREE; E) Monitor the Line if BUSY; and F) Clear on completion of the test programme. The first two digits of the original ALIT programming were not neccesary as the type of start was always going to be immediate and the COLT would do the testing. The first two ALIT information stores were therfore strapped out, so that the digits dialled by the COLT became: First Digit 10,000-line group to be tested Second Digit 1000-line group to be tested Third Digit 100-line group to be tested Fourth Digit 10-line group to be tested Fifth Digit Unit number to be tested The rewiring work that allowed the COLT to operate the tens and units stores for digits four and five was a major task. The OPERATE leads that originally went to the finish stores of the ALIT had to be diverted to the tens and units stores. This enabled the COLT to pre-set the tens and units stores to any required number. As spare relay contacts were used, only four extra diodes were required to carry out these changes. The increment feature of the ALIT stayed much the same as before, but, instead of it being automatic, the COLT controlled it. Thus the COLT initiates a one-step increment, checks that one step has occurred, and then proceeds with testing. Once the fifth set-up number has been received, the ALIT reverses the potential of the dialling wires. The COLT recognises this signal, and sends an earth to the ALIT on the START leads. The ALIT then acts as a register and seizes a free router control. When the router control has interrogated the line circuit required, the relevant information on line status is returned to the ALIT. If the line is FREE, then the call is completed and the ALIT signals to the COLT. If the Line is BUSY, then the call is completed and the ALIT signals the two facts to the COLT. Where there a is Number UnObtainable (NU), Change Number Interception (CNI), or Equipment engaged tone (EET), this information is passed from the ALIT to the COLT on seperate leads. When a call is completed from the ALIT to a line circuit, a test is made by the COLT. To facilitate this, the test wires of the ALIT were diverted from the original testing element to the COLT test Circuit. The Line test takes about two seconds, and then the COLT can either increment or Clear Down. If the line under test is BUSY, then the call is still completed. This is not a normal feature of the ALIT, but was achieved by giving the ALIT a Class-Of-Service (COS) isentical to the TTRG. Thus the router control overrides the BUSY signal, and the call is set up as if the line is FREE. If the COLT monitoring facility is in use, then the line being tested is checked. If voice frequency Modulation is present (KpT : ie, If yer gabbing to yer bird, or yer modem is whistling dixie) the COLT recognises this as a succesful call in progress. This information can then be shoen in the results. If monitoring is not required, the COLT can increment immediately. A call is not set up to a line circuit where there is NU tone, CNI, or EET. In these cases, the information on line conditions is stored, and the COLT increments or Clears Down. When the COLT has finished its tests, an earth signal is sent to operate the ALIT Clear-Down relay. OPERATIONAL EXPERIENCE ====================== The modified ALIT has been in use since mid-July 1984, and has proved to be very reliable. Fig. 3 shows a comparison between the old and the new system for testing ten lines, and shows an approximate saving of 22-24 seconds per ten tests. This saving means that, under the new arrangement, only one dial circuit in the COLT needs to be used to test 10,000 lines each night. Assuming that all lines are working, and no re-tests are required, then the time required to test 10,000 lines is approximately 10 Hours. Fig. 3 - Comparison of test timings between the Original and new methods ------------------------------------------------------------------------ OLD NEW COLT REGISTER ELAPSED TIME COLT ALIT COLT Seizes ÄÄÄÄÝÄÄ- 0 COLT Seizes ALIT ÄÝÄÄÄÄ- Register Ý 1 Ý Ý 2 Ý Dials Number Ý 3 Dials Number Ý xxx0 (Four -ÄÄÝÄÄÄ Call 4 xxxx0 (Five Ý Digits) Ý Set Up 5 Digits) Ý COLT Tests Ý 6 -ÄÄÝÄÄÄÄ Call COLT ClearsÄÄÄÝÄÄÄ- 7 COLT Tests Ý Set Up COLT Seizes ÄÄÄÄÝÄÄ- 8 COLT ClearsÄÝÄÄÄ- ALIT Releases Register Ý 9 COLT Seizes ALIT ÄÝÄÄÄ- Ý 10 Ý Dials Number Ý 11 Ý xxx1 (Four -ÄÄÝÄÄÄ Call 12 Dials Number Ý Digits) Ý Set Up 13 xxxx1 (Five Ý COLT Tests Ý 14 Digits) Ý COLT ClearsÄÄÄÝÄÄÄ- 15 -ÄÄÝÄÄÄÄ Call COLT Seizes ÄÄÄÄÝÄÄ- 16 COLT Tests Ý Set Up Register Ý 17 COLT Increment ÄÝÄÄÄÄÄ- Ý 18 -ÄÄÄÄÄÄÄÄ¿ÝALIT Increments - xxx2 Dials Number Ý 19 COLT Tests ÀÝÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Call xxx2 (Four -ÄÄÝÄÄÄ Call 20 COLT Increment ÄÝÄÄÄÄÄ- Set Up Digits) Ý Set Up 21 -ÄÄÄÄ¿ ÝALIT Increments - xxx3 COLT Tests Ý 22 COLT TestsÀÄÄÄÄÄÄÝÄÄÄ Call Set Up COLT ClearsÄÄÄÝÄÄÄ- 23 ÄÄÄÝÄÄÄ- COLT Seizes ÄÄÄÄÝÄÄ- 24 Ý Register Ý 25 Ý Ý 26 Ý Ý 27 Ý Ý 28 Ý Ý 29 Ý Ý 30 Ý Ý 31 Ý Ý 32 Ý Ý 33 Ý Ý 34 Ý Ý 35 End of Test on 10 Circuits Ý 36 -ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÝÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Ý 37 Ý Ý 38 Ý Ý 39 Ý Ý 40 Ý End of Tests On Ten Circuits Approx. 60 s. As previously explained, the COLT can increment 1-9, but then clears and re-dials to 0. Changes to the software could make the COLT increment from 0-9, and possibly 0-99. These modifications would enable the time required to test 10,000 lines to be reduced to approximately 8.8 and 8.0 hours respectively. CONCLUSION ========== The New ALIT-COLT interface has proved a sucess. The wear and tear on registers is back to normal, and the nightly 4TEL routine can now test 10,000 lines per night. Financial as well as time savings have been achived as only one dialler instead of two is required. The modifications take about three days to complete, and the extra equipment needed is one standard relay, six diodes, and the cabling. The new system is being adopted in other large TXK1 exchanges in Severnside District, and interest has been shown from other Areas/Districts suffering from the same problems with the 4TEL system.