Thanks for the notes.  Urban Boquist suggested that I set
asyncmap to 0, and that changed the success rate to 9/10 tries!
(the failure also was different from the previous failures, so
I've included the full logs below).  Without asyncmap 0, it was
negotiated to be 0xa0000 -- is part of the IPCP negotiations
not properly escaping/unescaping escaped characters (here, ^Q and ^S)?

> From: Frederick Bruckman <fb@enteract.com>
> Why do you have "novjccomp"? What happens when you omit that?
> Methinks you also need to have "noauth" in there somewhere,
> unless you have a wildcard in /etc/ppp/pap-secrets.

  Without novjccomp, my machine tries to send <compress 0f 01>,
and the remote end seems a bit unhappy with that, but
eventually agrees to it.  I figured I'd try to minimize
ConfNaks, and novjccomp helped a bit.  As for noauth, I don't
have it, nor do I have /etc/ppp/pap-secrets.  It's always
``worked'' as is, so I haven't messed with it.  Your
suggestions about mtu and ip-down were correct, and I've
modified my setup accordingly.  Thanks.

  The single failure caused the following.  It looks like
things are going great, with an IP assigned, and then something
backfires (the remote end keeps insisting on <compress 0f 00>?):
A failure like this months ago might be why I added novjccomp
in the first place.

Aug 30 12:39:37 k9 pppd[651]: pppd 2.3.4 started by bgrayson, uid 2000
Aug 30 12:40:05 k9 pppd[651]: Serial connection established.
Aug 30 12:40:06 k9 pppd[651]: Using interface ppp0
Aug 30 12:40:06 k9 pppd[651]: Connect: ppp0 <--> /dev/tty02
Aug 30 12:40:06 k9 pppd[651]: sent [LCP ConfReq id=0x1 <mru 576> <asyncmap 0x0> <magic 0xfb0cfdb9> <pcomp> <accomp>]
Aug 30 12:40:07 k9 pppd[651]: rcvd [LCP ConfReq id=0x1f <asyncmap 0xa0000> <magic 0x754a9aa7> <pcomp> <accomp>]
Aug 30 12:40:07 k9 pppd[651]: sent [LCP ConfAck id=0x1f <asyncmap 0xa0000> <magic 0x754a9aa7> <pcomp> <accomp>]
Aug 30 12:40:09 k9 pppd[651]: sent [LCP ConfReq id=0x1 <mru 576> <asyncmap 0x0> <magic 0xfb0cfdb9> <pcomp> <accomp>]
Aug 30 12:40:09 k9 pppd[651]: rcvd [LCP ConfNak id=0x1 <mru 1500>]
Aug 30 12:40:09 k9 pppd[651]: sent [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0xfb0cfdb9> <pcomp> <accomp>]
Aug 30 12:40:09 k9 pppd[651]: rcvd [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0xfb0cfdb9> <pcomp> <accomp>]
Aug 30 12:40:09 k9 pppd[651]: sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <compress VJ 0f 01>]
Aug 30 12:40:09 k9 pppd[651]: rcvd [IPCP ConfNak id=0x1 <addr 128.83.112.115>]
Aug 30 12:40:09 k9 pppd[651]: sent [IPCP ConfReq id=0x2 <addr 128.83.112.115> <compress VJ 0f 01>]
Aug 30 12:40:09 k9 pppd[651]: rcvd [IPCP ConfAck id=0x2 <addr 128.83.112.115> <compress VJ 0f 01>]
Aug 30 12:40:12 k9 pppd[651]: rcvd [IPCP ConfReq id=0x12 <compress VJ 0f 00> <addr 0.0.0.0>]
Aug 30 12:40:12 k9 pppd[651]: sent [IPCP ConfRej id=0x12 <addr 0.0.0.0>]
Aug 30 12:40:12 k9 pppd[651]: rcvd [IPCP ConfReq id=0x13 <compress VJ 0f 00>]
Aug 30 12:40:12 k9 pppd[651]: sent [IPCP ConfAck id=0x13 <compress VJ 0f 00>]
Aug 30 12:40:12 k9 pppd[651]: Could not determine remote IP address
Aug 30 12:40:12 k9 pppd[651]: sent [IPCP TermReq id=0x3 "Could not determine remote IP address"]
Aug 30 12:40:12 k9 pppd[651]: rcvd [IPCP TermAck id=0x3]
Aug 30 12:40:12 k9 pppd[651]: sent [LCP TermReq id=0x3 "No network protocols running"]
Aug 30 12:40:12 k9 pppd[651]: rcvd [LCP TermAck id=0x3]
Aug 30 12:40:12 k9 pppd[651]: Connection terminated.
Aug 30 12:40:14 k9 pppd[651]: Exit.

  Brian
-- 
"Al!" - The MOB