Modems made with the Rockwell or Conexant HCF 56k chipset are fairly standard modems.  They do however  need constant firmware updates to work well.  Anything under the firmware revision  2.1.2.135 should definitely be upgraded ASAP.  There is no common modem with the Rockwell HCF chipset, these modems are all over the place and made by many different manufacturers.  Modems made with the Rockwell or Conextant ACF chipset are somewhat different, using a different AT Command set and different firmware, but as with any modem the firmware for these should also be upgraded.  The most common modems with the ACF chipset is the Diamond SupraExpress.  Modems made with the HSF(Soft56) chipset are the cheaper end winmodems.  The HSF(Soft56) chipset is Rockwell/Conexant's version of the HSP (Host Signal Processing) chipset, meaning that the modem has not DSP (Digital Signal Processor) and instead uses the computer's processor for most of it's needs.  For more info on what an HSP modem is, see the PC-Tel article.  I cannot stress enough the need to get the latest driver for your modem.

The following fixes will help either get a user online to get their drivers or if their drivers are updated and they are still having problems:

For all of the following modems you can always try lowering the Fifo buffers and the port speed to 57600 when still trying to attain 56k, and 38400 when trying v34.

(NOTE: Hewlett Packard Rockwell HCF (Riptide's) choke on the following inits.  Try using -v90=0 until I find a better init.  Their latest drivers SHOULD fix any problems)

HCF Inits:

AT&F&C1&D2+MS=v90,0  (Connection problems, but trying to retain v90)  

AT&F&C1&D2+MS=v34  (Force v34)

AT&F&C1&D2&K3+MS=v34  (Force v34)

AT&F1 (Basic factory reset)

ACF (driver version 3.xx) Inits (3.xx uses the HCF command set):

AT&F&C1&D2+MS=v90,0  (Connection problems, but trying to retain v90)  

AT&F&C1&D2+MS=v34  (Force v34)

AT&F&C1&D2&K3+MS=v34  (Force v34)

AT&F1 (Basic factory reset)

ACF (driver version 2.xx) Inits:

AT&F&C1&D2+MS=12  (Connection problems, but trying to retain v90)

AT&F&C1&D2+MS=11  (Force v34)

AT&F&C1&D2&K3+MS=11  (Force v34)

AT&F2  (Basic factory reset)

AT&FW2  (Basic factory reset #2 + W2)

HSF(Soft56) Inits:

AT&F&C1&D2+MS=v90,0  (Connection problems, but trying to retain v90)

AT&F&C1&D2+MS=v34  (Force v34)

AT&F&C1&D2&K3+MS=v34  (Force v34)

AT&F1  (Basic factory reset)

Here is a partial list of manufacturer websites who make modems with a Rockwell/Conexant chipset: