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Modem Timeline and Breakdown

Released Vendors Generic BPS Protocol Notes
July 2000 Internationaly accepted.

56K downstream
48K upstream

 V.92 V.90 compatible. Modem on Hold (Where available). Quick Connect. upstream rate increase by 42%.
Internationaly accepted.
56K downstream
33.6K upstream
 V.90

X2 and K56Flex compatible. Only one A/D conversion point can be used.

Only one conversion point where an A/D conversion point appears. If more then one A/D conversion point is present, rates cannot achieve 56k.

Images courtesy of 3com. See the May 11th 2000 snapshot of their V.90 FAQ. (snapshot courtesy of Web Archive)
  Lucent, Rockwell K56Flex Lucent Win modems and Windows ME. Use S38=0, then S38=0-V90=0 to disable. See References below for 56.COM for additional information.
  3Com, U.S. Robotics X2
  
      V.42 bis
      V.42 No speed improvment over V.32 bis. Offers better error correction.
1996   33600 V.34-1996

 

Every A/D conversion adds noise. More noise means less data and speed. Prior to ISPs using digital lines and the V.90 advancement, 33.6K was the ceiling. Some phone networks still have legacy systems, and are still limited to these connection speeds at best.

 
Sep 1994 ITU 28800 V.34 28.8K with auto fallback to 24K or 19.2K. Backwards compatible with V.32 and V.32 bis
      V.FC Interm modem standard. V. Fast Class. Rarley used or seen since V.34. Not compatible with rates in excess of 28.8 KBPS.
Feb 1991 ITU (CCITT) Study Group 17 14440 V.32 bis V.32 compatible. Rapid Rate Renegotiation (allows fast resych on the fly). 12000 and 7200 BPS fall back.
1989 ITU 9600 V.32 4800 and 2400 BPS fall back. Data compression and Error correction can push connection speeds to 19.2 KBPS
1989 Microcom   MNP Use of MNP becomes a de facto standard.
    2400 V.22 bis  
    1200 V.22  
      V.21 Full duplex.
1984       Bell System split up. Increased competition begins.
1984   9600   Uses echo cancelation
      Bell 202(x)  
    1200 Bell 212 Uses PKS (Phase Key Shifting)
1962 AT&T 300 Bell 103

First publicly available modem.

Uses FKS (Frequency Key Shifting)

Error Correction vs Speed

Error correction requires retransmission when an error is spotted. This allows it to replace the parts that were not received correctly. Retransmission slows data throughput, and can even choke out a connection. This is why faster isn't always better. Sure you can fix it fast, but if you have to fix it constantly, that's all you are doing. If you slow the rate, it's possible to have fewer errors. The less errors, the higher the throughput

Another note about speed from Lucent, a common modem manufacturer is here (a text highlighted copy in Google's cache). Additional references below discuss the Lucent win-modem and common troubleshooting.

References

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