🚀 go-pugleaf

in comp.sys.ibm.pc.misc, smahn@vx.cis.umn.edu (Seokmin Ahn) said:


>Hi! netters,
>
>The advertisement about modems confused me about Baud rate and BPS.
>
>Would someone please clear up this for me ?

Probably not.  But I'll give it a try:


Short answer:  When people say "baud" they usually mean "bits/sec",
               but not always.  When they don't mean "bits/sec" they'll
               usually take pains to make that clear, but not always.
 
Slightly longer answer:  (from TNHD)

  baud [simplified from its technical meaning] n.  Bits per second [...];
  this coincides with bps only for two-level modulation with no framing
  or stop bits.  Most hackers are aware of these nuances but blithely
  ignore them. 
 
Even longer answer: (from DEC Technical Aspects of Data Communications) 
 
  Baud:  A unit of signalling speed equal to the number of discrete
  conditions or signal events per second.  In asychronous transmission, 
  the unit of signalling speed corresponding to one unit interval per 
  second; that is, if the duration of the interval is 20 ms, the 
  signalling speed is 50 baud.  Baud is the same as "bits per second" 
  only if each signal event represents exactly one bit. 
 

Another perspective (from Andy Tanenbaum's Computer Networks book)

  The time T required to transmit the character depends on both the
  encoding method and the signalling speed (the number of times per
  per second that the signal changes its value).  The number of changes
  per second is measured in baud.  a B baud line does not necessarily
  transmit B bits/sec, since each signal might convey several bits.
  If the voltages 0,1,2,3,4,5,6,7 were used, each signal value could
  be used to convey three bits, so the bit rate would be three times
  the baud rate.

And another one (from UDS Applied Data Communications Handbook)

  Baud - The unit of signalling.  It is the number of signal elements
  per second.  Since a signal element can represent more than one bit,
  baud rate is not the same as bits per second.  Baud rate is the bit
  rate divided by bits per symbol.

-- 
mitchell@mdd.comm.mot.com (Bill Mitchell)