-=> Quoting Rodrigo Cesar Banhara to Leonard Erickson <=-

 LE> You do pay for this. Anytime a new byte isn't ready to be sent in
 LE> time, you have to add a "dummy" byte to maintain synch. And usually,
 LE> you dedicate one byte value to this, and have to use some sort of
 LE> escape char to actually send that value. Even so, synch is still faster
 LE> than async.

 LE> synch links tend to be *inherently* bi-directional also.
 
 LE> The main reason I'm interested in synch links is because I've got a
 LE> pair of CSU/DSU units that can do 56k if connected to a sync
 LE> interface, and only 19.2k if hooked to an async one.

 RCB> Interesting!! Neat, truely... 8)
 RCB> Part2: Driver for OS/2?!

That's another problem. :-)

First you need to find a synch card, then you need to find/write a
driver. 

 RCB> Where may be found this type of modem?

A CSU/DSU isn't a modem. It's *digital* interface, not an analog one.
These are old and fairly obsolete. They're intended for leased lines or
possibly the old "switched 56k" service.

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