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modemmore about modem

modem

 

  3  definitions  found 
 
  From  WordNet  r  1.6  [wn]: 
 
  modem 
  n  :  (from  MOdulate-DEModulate)  a  communications  device  used  to 
  connect  computers  by  a  telephone  line 
 
  From  The  Free  On-line  Dictionary  of  Computing  (13  Mar  01)  [foldoc]: 
 
  modem 
 
    (Modulator/demodulator)  An 
  electronic  device  for  converting  between  serial  data 
  (typically  {EIA-232})  from  a  computer  and  an  audio  signal 
  suitable  for  transmission  over  telephone  lines.  In  one  scheme 
  the  audio  signal  is  composed  of  silence  (no  data)  or  one  of 
  two  frequencies  representing  0  and  1. 
 
  Modems  are  distinguished  primarily  by  the  maximum  {baud}  rate 
  they  support.  {Baud}  rates  can  range  from  75  baud  up  to  56000 
  and  beyond.  Data  to  the  computer  is  sometimes  at  a  lower  rate 
  than  data  from  the  computer  on  the  assumption  that  the  user 
  cannot  type  more  than  a  few  characters  per  second 
 
  Various  data  {compression}  and  error  correction  {algorithms} 
  are  required  to  support  the  highest  speeds.  Other  optional 
  features  are  {auto-dial}  (auto-call)  and  {auto-answer}  which 
  allow  the  computer  to  initiate  and  accept  calls  without  human 
  intervention.  Most  modern  modems  support  a  number  of 
  different  protocols,  and  two  modems,  when  first  connected, 
  will  automatically  negotiate  to  find  a  common  protocol  (this 
  process  may  be  audible  through  the  modem  or  computer's 
  loudspeakers).  Some  modem  protocols  allow  the  two  modems  to 
  renegotiate  ("retrain")  if  the  initial  choice  of  data  rate  is 
  too  high  and  gives  too  many  transmission  errors. 
 
  A  modem  may  either  be  internal  (connected  to  the  computer's 
  {bus})  or  external  ("stand-alone",  connected  to  one  of  the 
  computer's  {serial  ports}).  The  actual  speed  of  transmission 
  in  characters  per  second  depends  not  just  the  modem-to-modem 
  data  rate,  but  also  on  the  speed  with  which  the  processor  can 
  transfer  data  to  and  from  the  modem,  the  kind  of  compression 
  used  and  whether  the  data  is  compressed  by  the  processor  or 
  the  modem,  the  amount  of  noise  on  the  telephone  line  (which 
  causes  retransmissions),  the  serial  character  format 
  (typically  {8N1}:  one  {start  bit},  eight  data  bits,  no 
  {parity},  one  {stop  bit}). 
 
  See  also  {acoustic  coupler},  {adaptive  answering},  {baud 
  barf},  {Bulletin  Board  System},  {Caller  ID},  {SoftModem}, 
  {U.S.  Robotics},  {UUCP},  {whalesong}. 
 
  {Usenet}  newsgroup:  {news:comp.dcom.modems}. 
 
  (2000-12-10) 
 
 
 
  From  V.E.R.A.  --  Virtual  Entity  of  Relevant  Acronyms  13  March  2001  [vera]: 
 
  MODEM 
  MOdulator  DEModulator




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