Cable Modem Error Rate
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codeword errors are available as a metric in most cable operator monitoring tools and Operations Support Systems (OSS). The monitoring tools and OSS generally provide data and dashboards for users to monitor overall network health and then identify a problem when it occurs. Metrics like codeword errors are uncorrectable codewords cable modem extracted directly from DOCSIS CMTSs using Simple Network Management Protocol (SNMP) or Internet Protocol Detail Records (IPDR), the later being preferred due to its reduced CMTS CPU utilization. What many people struggle with are what are those codeword errors, what do they mean, and how bad is bad? This artical will answer those questions and discuss Reed Solomon forward error correction including how it corrects bit errors in the DOCSIS network. Where Codeword Errors Come From When someone is using a device, such a PC or iPad, and transmits data over a DOCSIS cable modem that larger than 16 bytes of data, an error protection algorithm kicks in called Reed-Solomon (RS) forward error correction (FEC). There are two parts to RS FEC, one is the encoder, which is in the cable modem and the second is the decoder, which is
versus Bit Error Rate Testing Posted by Steve Day Steve Day Steve Day has over 20 years of experience in CATV and telecommunications operations and engineering leadership... User is currently offline codeword error rate definition on Tuesday, 22 January 2013 in Uncategorized Hits: 42991 0 Comments
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Subscribe to updates Print PDF Bookmark | Tweet Bit Error Rate (BER) is a metric that represents the
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number of bit errors relating to receive bits of data stream over a communications channel that has been impacted by noise, interference or synchronization errors (Wiki). It can http://volpefirm.com/docsis-codeword-errors/ always be impacted by a series of trade offs. Lower bit rate improves BER, but reduces capacity. Increased signal strength of the bit stream improves BER, but may not be practical. Slower and robust modulation also improves BER. BER = (number of bits) \ (total number of bits) While the basics are simplistic, it is not a trivial http://www.cheetahtech.com/component/easyblog/entry/code-error-rate-versus-bit-error-rate-testing measurement. It requires a referenced measurement setup, where a known data stream is sent through a system (transmitter and receiver). This is accomplished over a long period of time. See an example below from Agilent Technologies that reflects BER testing times at a 95% confidence level. A table of test times at 95% confidence level is given for standard data rates and bit error ratios: (click graphic to enlarge) A typical CATV DOCSIS data stream test can take from 3 to 9 seconds. In the test world, this is significantly long. JDSU states that "BER is an age old technique of characterizing the digital transmission system." For QAM 64 Annex B the symbol rate is 5.0569 Msps and each symbol has 6 bits. A technician who wants to complete a BER 1E-8 (1 error per 100,000,000 bits) would have to wait for the receiver (STB, test set, modem) to receive 100 million bits. At a transmission rate of 30 Mb/s it is a 3.3 second wait. Additionally, testing 256
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