10 Replies Latest reply: Mar 25, 2014 3:34 PM by BRenES RSS

    Certification Guide book question; PCM vs PAM

    charles

      There is a question from the CCNA Voice Official Certification guide that I have problems answering and would appreciate advise. This is the question;

       

      Which of the following processes samples an analog waveform at timed intervals to obtain a digital mesurement of the electrical signal?

       

      A. Quantization

      B. PAM

      C. PCM

      D. Codec

       

      The book says the correct answer is B. I checked with PeasonView and they contacted the author and the author says B. I think it is C.

      The following is from Wikepedia for PCM;

       

      In telephony, a standard audio signal for a single phone call is encoded as 8,000 analog samples per second, of 8 bits each, giving a 64 kbit/s digital signal known as DS0. The default signal compression encoding on a DS0 is either μ-law (mu-law) PCM (North America and Japan) or A-law PCM (Europe and most of the rest of the world). These are logarithmic compression systems where a 12 or 13-bit linear PCM sample number is mapped into an 8-bit value. This system is described by international standard G.711.

       

      Could someone explain why the answer is pulse amplitude modulation instead of pulse code modulation? Aren't voice systems using PCM?

       

      thanks