Dt004a

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JULY 1994 DT004A V.35 BERT CUSTOMER SUPPORT INFORMATION Order toll-free in the U.S.: Call 877-877-BBOX (outside U.S. call 724-746-5500) FREE technical support 24 hours a day, 7 days a week: Call 724-746-5500 or fax 724-746-0746 Mailing address: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018 Web site: www.blackbox.com • E-mail: [email protected] V.35 BERT TRADEMARKS USED IN THIS MANUAL Any trademarks mentioned in this manual are acknowledged to be the property of the trademark owners. 2 CONTENTS Contents 1.0 SPECIFICATIONS ................................................4 2.0 INTRODUCTION.................................................6 3.0 USING THE V.35 BERT .......................................7 3.1 How the BERT works .....................................7 3.2 Controls and Displays ..................................10 3.3 Error-Rate Test Configurations...................13 3.4 V.35 Error-Rate Testing ...............................15 3 V.35 BERT 1. Specifications Test Capability — Bit-error-rate testing, blockerror-rate testing, errored-seconds testing Test-Length Selection — Preset test lengths allow true error rate when test is completed—no need for external rate calculations Test Lengths — Bit-Error-Rate Testing: 104, 105, 106, 107, 108 bits, or continuous; Block-Error-Rate Testing: 10, 102, 103, 104, 105 blocks, or continuous; Errored-Seconds Testing: 10, 102, 103, 104, 105 seconds, or continuous Test Data Patterns — Pseudorandom bit patterns of length 511, 2047, or 215-1 seconds or continuous Speed — Up to 2.048 Mbps, set by external clock source Operation — Synchronous Testing — End-to-end or loopback; automatic compensation for transmission delay; single-bit error injection for test verification 4 CHAPTER 1: Specifications Display — 4-digit LCD displays error rate, with overflow and test-state indications Interface — V.35 male connector on attached ribbon cable, configured as DTE Power — From plug-in wallmount transformer or two 9-volt alkaline batteries (batteries provide 3 hours of continuous use) Physical Characteristics — Durable vinyl softpack case; zipper access to front panel, cable, and battery compartments; acrylic front panel with back-screened legends; high-impact inner plastic case Size — 7"H × 4.5"W × 2"D (17.8 × 11.4 × 5 cm) Weight — 2.1 lb. (1 kg), including power transformer 5 V.35 BERT 2. Introduction The V.35 BERT is used to isolate faulty components and measure transmission quality in a communications network. It performs this function by comparing what it receives from the communication link with what it (or another unit) sent to the communication link. The resulting measurement of line quality is expressed in one of three industry-standard formats: • Bit Error Rate • Block Error Rate • Errored Seconds Rate You can choose any one of those three tests. You can also choose from a selection of test lengths, so you can test to the accuracy you desire. You’ll find the BERT easy to use. The faceplate is clearly labeled, so you can find all the functions quickly. Test selections and their associated lengths have been color-keyed for accuracy. The BERT indicates when a test is in progress and when it is completed. 6 CHAPTER 3: Using the V.35 BERT 3. Using the V.35 BERT 3.1 How the BERT works The V.35 BERT consists of a digital transmitter, a receiver, and an error counter. The transmitter circuit generates one of six selected serial bit patterns and drives the V.35 P and S pins (SD). The receiver circuit generates an identical bit pattern and compares it with the incoming data stream on R and T (RD). Whenever an incoming bit does not match the expected bit pattern, one bit error is counted. The bit error rate is a measure of the total number of bits in error related to the the total number of bits transmitted, usually expressed as errors in 106 bits, errors in 105 bits, etc. Block-error-rate testing is used to emulate blockmessage data transmission. For test measurements, a block is defined as 1000 bits, and a block error is a group of 1000 bits that has one or more errors in it. Since errors usually come in bursts rather than by single bits, the block error rate gives a better indication of the percentage of message blocks that would have to be retransmitted because of errors than calculations based on the bit error rate. The block error rate is similarly expressed as errors in 103 blocks, errors in 104 blocks, and so on. 7 V.35 BERT Errored-seconds (or error-free-seconds) testing indicates valid data transmission per unit time, rather than by number of bits or blocks transmitted, and is thus independent of the transmission. An errored second is a second of transmission time in which one or more errors have been received. Conversely, error-free seconds are units of time that have no transmission errors. The V.35 BERT records errored seconds, since this number is normally much smaller than error-free seconds, and so less likely to overflow the error counter. To convert to error-free seconds, just subtract the number of errored seconds from the total test length. The test-pattern selections for error-rate testing are industry-standard pseudorandom bit patterns of length 511, 2047, or 215-1 bits, alternating mark/space, all space, or all mark. The pseudorandom patterns have statistical properties that approximate real-world random data streams. These patterns repeat after the specified length, so the longer the sequence, the better it approximates random data. The faster the data rate, the longer the pseudorandom sequence should be. Since these pseudorandom sequences are standard with other bit-error-rate testers, you can use the V.35 BERT in end-to-end testing with testers from other manufacturers. 8 CHAPTER 3: Using the V.35 BERT You can select the test length so that the error count stops after a preselected number of bits or blocks have been received, or after a preselected number of test seconds have passed. The count displayed at the end of the test is the number of errors counted over the selected test length. You can read this number directly as the error rate. For example, if you selected a bit-error test of 105 bits, and the display reads “5” at the end of the test, then the bit error rate is 5 in 105 bits or 0.00005. Pushing the RESET/RESYNC button at the start of the test resets both the test-length counter and the reset counter. During the test, the arrow indicator in the upper left-hand corner of the error display flashes to indicate that a test is in progress. When the test is finished, the arrow stays on steady, and the counter displays the error rate. If there are no errors, the display goes blank. When you press the RESET/RESYNC button, the receiver section synchronizes with the incoming data stream. Since the transmitter and receiver circuits are functionally independent within the BERT, transmission delays between the transmitted data and the received data are automatically compensated for. 9 V.35 BERT 3.2 Controls and Displays See Figure 1 on the next page. The numbers here refer to the numbered arrows in the figure. ① ON/OFF—The power switch. ② Power jack—For external power supply. Always turn the BERT off and plug the power supply into the BERT before you plug the power supply into the wall outlet. The batteries are automatically disconnected when the power supply is connected. ③ Error display—Indicates the number of bit errors, block errors, or errored seconds, depending on the test you’ve selected (see ④ below). A “+” indicates counter overflow (usually due to loss of sync). The arrow flashes while the test is in progress, then lights steady when ready for a test or when the test is finished. Leading zeros are blanked when the test is complete. If there are no errors, the display is blank. ④ TEST—selects the type of test to perform: • BIT: Bit-error-rate test • BLOCK: Block-error-rate test • SEC: Errored-second test • STOP: Stop transmission; SD=mark, 10 CHAPTER 3: Using the V.35 BERT Figure 1. Controls and displays. 11 V.35 BERT RTS=off; clear display ⑤ PATTERN—Selects the data pattern to be transmitted: • 511: 511-bit-long pseudorandom bit pattern • 2047: 2047-bit-long pseudorandom bit pattern • 215-1: 32767-bit-long pseudorandom bit pattern • ALT: Alternating 1/0 pattern • MARK: All-mark (logical 1) transmission • SPACE: All-space (logical 0) transmission ⑥ LENGTH—Selects the length of the test. Color-coded columns indicate the test-length selection (in number of bits, blocks, or seconds) for the type of test selected. The error count is stopped and displayed when the selected test length has been counted by the receiver. If you select “CONTINUOUS,” the test keeps going until you stop it. ⑦ RESET/RESYNC—Resets the error count, initializes the test-length count, and synchronizes the receiver with the incoming data stream. Used to begin a test. 12 CHAPTER 3: Using the V.35 BERT ⑧ INJECT ERROR—Injects a single bit error into the transmitted data stream. Used to verify test setup. ⑨ V.35 Connector—Male, configured as DTE. 3.3 Error-Rate Test Configurations Figure 2 shows a typical terminal−modem−computer link. To test the transmission-error rate of the link and isolate the faulty component, substitute the tester for the local terminal (DTE) device. Beginning with digital loopback at the local modem, each portion of the transmission channel is successively looped back and tested. The four standard loopback configurations are shown in Figure 3. You can identify a faulty channel by noticing that the error rate increases significantly at that stage of loopback. Figure 2. A typical terminal-modem-computer link. 13 V.35 BERT Figure 3. Loopback testing. 14 CHAPTER 3: Using the V.35 BERT It is not possible, however, to tell with loopback testing whether the transmit channel or the receive channel is causing the transmission errors, since the data system is looped through both channels. If it is necessary to perform this level of fault isolation, use end-to-end testing with a second tester (see Figure 4). Now errors registered at each tester indicate errors on the receive channel to that end of the transmit channel. You can measure separate error rates for the transmit and receive channels with this arrangement. Figure 4. End-to-end testing. 3.4 V.35 Error-Rate Testing 1. Turn the power switch off. If you want to use the external power supply, plug it into the BERT before you plug it into the wall outlet. 15 V.35 BERT The batteries are automatically disconnected when the power supply is connected. 2. Set the TEST switch to BIT, BLOCK, or SEC, depending on which test you want to run. 3. Set the PATTERN switch for the appropriate test (usually 511, 2047, or 215-1 pseudorandom pattern). 4. Set the LENGTH switch for the test length you want. Refer to Table 1 for test durations. 5. Disconnect the terminal from the modems. Connect the BERT to the modem cable. 6. The modem should provide the transmitter clock on Pins Y and AA and the receiver clock on Pins V and X. The data rate is controlled by the modem. The BERT returns the transmitter clock signal on Pins V and W to the modem. For use with a Bell 306-type interface. 7. Turn the power switch on. The arrow will light steadily in the upper left corner of the error display. The BERT will transmit data until the test timer expires, or until you turn it off or set the TEST switch to the STOP position. 8. Set the transmission channel for loopback testing, or establish a connection with a remote tester for end-to-end testing. 16 CHAPTER 3: Using the V.35 BERT 9. Push the RESET/RESYNC button to begin the test. The error display will show “0000” with a flashing arrow. The error count will increment as each error is detected. If the counter is incrementing rapidly (with each received data unit), the receiver is not synchronized with the transmitted data. Verify data connections to the modem, and push the RESET/RESYNC button again to resynchronize the receiver. 10. You can inject single bit errors into the data stream to verify the connection. In loopback testing, the error count should increment each time you press the INJECT ERROR button. With end-to-end testing, errors injected at one end will be counted at the opposite end. 11. When the test is complete, the arrow will light steady, and the error will be displayed with leading zeros blanked. If no errors were detected, the error count will be blank. A “+” to the left of the error count indicates counter overflow (usually due to loss of sync). 17 V.35 BERT Table 1. Test Durations LENGTH TYPICAL BAUD RATES Bit Blk 408 Kbps 104 10 <1 sec 105 102 106 103 107 104 108 105 2.5 sec 25 sec 4.1 min 41 min 48 Kbps 56 Kbps 64 Kbps 256 Kbps 1.544 Mbps <1 sec <1 sec <1 sec 2.1 sec 21 sec 3.5 min 35 min 1.8 sec 18 sec 3 min 30 min 1.6 sec 16 sec 2.6 min 26 min <1 sec <1 sec <1 sec <1 sec 4 sec <1 sec 39 sec 6.5 min 6.5 sec 65 sec For other speeds, use this equation to calculate the test duration: Test Length (bits) Test Duration (seconds) = —————— Baud Rate (bps) LENGTH (seconds) DURATION 10 1 min, 40 sec 103 16 min, 40 sec 104 2 hours, 47 min 10 27 hours, 47 min 5 18 10 sec 102 ⎞ May exceed battery ⎟ life. Use external ⎠ power supply. CHAPTER 3: Using the V.35 BERT Table 2. V.35 Modem-Terminal Interface V.35 PIN NAME FUNCTION SOURCE SPEC. A B C D E F H J K FG SG RTS CTS DSR RLSD DTR RI LT Frame Ground Signal Ground Request To Send Clear To Send Data Set Ready Received Line Signal Detector Data Terminal Ready Ring Indicator Local Test DTE DCE DCE DCE DTE DCE DCE RS-232 RS-232 RS-232 RS-232 RS-232 RS-232 RS-232 MON. PIN P S SD SD Send Data (A) Send Data (B) DTE DTE V.35 V.35 2 2 R T RD RD Receive Data (A) Receive Data (B) DCE DCE V.35 V.35 3 3 U W SCTE SCTE Serial Clock Transmit External (A) Serial Clock Transmit External (B) DTE DTE V.35 V.35 24 24 V X SCR SCR Serial Clock Receive (A) Serial Clock Receive (B) DCE DCE V.35 V.35 17 17 Y AA SCT SCT Serial Clock Transmit (A) Serial Clock Transmit (B) DCE DCE V.35 V.35 15 15 1 7 4 5 6 8 20 22 18 L, M, N, Z, BB, CC, DD, FF, HH, JJ, KK, LL, MM, and NN are reserved for future use. NOTE: Lower-case letters may be used on connector to indicate corresponding double-letter pins—for example, “a” for AA. 19 © Copyright 1994. Black Box Corporation. All rights reserved. 1000 Park Drive • Lawrence, PA 15055-1018 • 724-746-5500 • Fax 724-746-0746