improving transport over lossy links ?

[Bill Vermillion]

Throwing caution to the wind and speaking without thinking about
what was being said on Sun, May 21, 2006 at 11:09 ,
Mike Tancsa blurted this:

> At 05:26 AM 21/05/2006, Brian Candler wrote:
> >On Fri, May 19, 2006 at 12:38:31PM -0400, Mike Tancsa wrote:
> >>         Thanks for the reply.  Even at 28.8 I am seeing loss with
> >> the connection dropping and seeing dropped packets (e.g.
> >> May 19 12:04:43 soekris4801 ppp[3404]: tun0: Phase: 1: HDLC errors ->
> >> FCS: 1, ADDR: 0, COMD: 0, PROTO: 0)

> >If you have an error-correcting modem, but you are seeing data corruption,
> >then I'd expect the data corruption is occuring on the RS232 link between
> >the PC and the modem at one end or the other. You may have a handshaking
> >problem (i.e. ensure the modem is configured for CTS/RTS handshaking, and
> >the port is configured for this too; with pppd it's "crtscts", I don't know
> >about userland ppp; and ensure the cables are wired properly)

> >If your app could cope with the lack of bandwidth, forcing the modems to
> >2400bps operation can make links over dodgy lines a lot more reliable.
> 
> Hi,
>         Its not so much data corruption of packets on the wire, but 
> the modem dropping the connection, retraining and 
> renegotiating.  When the retrains and re negotiations happen, this 
> can cause problems for the VPN as keep alives are missed, tx buffers 
> can fill up etc.  I have tried a number of modems, the current one 
> being U.S. Robotics 56K FAX INT V5.22.70.  and I am also trying an 
> external Intel at the office

The best modems I've found are the ones from Multi-tech. Even their
super-small ones.   Before we added a PRI and a Livingston we were
thinking about using the MT's in the 19" rack mount box they have.

And when performing fax from email - using sendmail incoming and
routing to fax [in the early days of the current 'net before many
people had 'net connections] the MT's were the only ones that
worked with virtually ever target fax machine.

The MTs are external.

Bill

-- 
Bill Vermillion - bv @ wjv . com