[comp.dcom.modems] Binary file xfer and MNP

Owens-Christopher@cs.yale.edu (Christopher Owens) (07/27/89)

A more general question that someone may be able to explain to me.  Is
it true that doing binary file transfer using MNP error-correcting
connections implies the need for hardware (RTS/CTS) flow control? 

My reasoning: MNP link needs some kind of flow control, since the
modem-to-modem link can be arbitrarily slower than the
computer-to-modem link.  But, if doing binary file transfers, XON and
XOFF may appear in the data stream, so XON/XOFF flow control is no good.  
Therefore, one needs hardware flow control.  Is this right?  Is there any way 
around this?

thanks,

ARPA:    Owens-Christopher@cs.yale.edu  
UUCP:    {harvard,cmcl2,decvax}!yale!Owens-Christopher
BITNET:  Owens@yalecs

njs@scifi.UUCP (Nicholas J. Simicich) (07/27/89)

Yes, this is generally true.  The line can be extremely slow, so
sending data to the modem can overrun it.  I frequently do binary data
transfer over a modem that uses error correction, and which does not
have flow control (because my computer does not support it).   

To make this work, you need to use a protocol which requires
end-to-end acknowledgements, and your modem must be able to buffer.
The maximum amount of unacknowledged data under the protocol must be
less than the buffering capacity of the modem.

-- 
Nick Simicich --- uunet!bywater!scifi!njs --- njs@ibm.com (Internet)