[Prev][Next][Index][Thread]

Re: baud compared to bps, ignore if you really don't care, WAS: Re:, 1.99p6 for everybody!



On Mon, 13 Nov 1995, Jered J Floyd wrote:

> So, at 14.4kps/2400 baud I'm encoding 6 bits of data in each state change.
> And, at 28.8kps/2400 baud I'm encoding 12 bits in each. Each of these
> standards used to have names like v.<foo> or CCITT <foo>.
> 
> To confuse matters more, compression is also added.  (That's why you set your
> DTE-DCE link speed to higher than your DCE-DCE speed.)  That's also why
> modem manfacturers advertise '4 to 1 compression!', though through some
> miracle they don't advertise the speed with compression. So, a 28.8 link
> with v.42 compression (I think that's the right name) could give you up to
> 115200 bps throughtput. But it's not very likely.
> 
> As for the names of the standards, I keep scrambling them.  I'm reasonably
> certain that v.42 is the common compression standard, and v.terbo was a 
> (interim ?) 28.8 kps encoding standard, but I'm shaky on v.32 vs v.32bis.
> Many modem manuals will explain these, though.

You're correct about the concept, but wrong on the v.foo standards:

v.32  - standard for 9600 bps transmission
v.32bis - standard for 14400 bps
v.FAST  - interim (proprietary Rockwell) standard for 28.8 (similar to v.34)
v.terbo - 19200 bps standard that didn't really catch on
v.34    - the final 28800 bps standard

v.42    - compression 2:1 (or is it error correction?)
v.42bis - 4:1 compression + error correction

And there are a few MNP standards for error correction and/or compression 
too, but most newer modems use v.42bis by preference.  Hope this clears a 
few things up.

---Jake


References: