My system is NetBSD-4.0_BETA2, AMD Athlon XP 2500+, 2 fxp NICs.
Network is:

Media server <----> NetBSD 4.0 <----> Media Client

I want to test Media-Client's PPPoE performance.
So I install rp-pppoe on it and run pppoe-server.
When PPPoE is connected, Media-Client watch TV from Media-Server.
With "netstat -w1 -b -Ifxp1", I know the baud-rate is about 2.5Mbps.
After about 15 seconds, the connection is terminated.
I test the same case with a Linux box:
(Pentium III 750Mhz, 2 RealTek8139; pppd-2.4.2, Fadera Core 4),
during the 4-hour-testing, the PPPoE connection is OK always.
So, I guess it seems pppd's problem. (NetBSD4 use pppd-2.4.4)

"top" says: CPU is almost 95% idle.

/var/log/messages:
Jan 31 20:17:16 pc006 pppd[17841]: local  IP address 192.168.30.1
Jan 31 20:17:16 pc006 pppd[17841]: remote IP address 192.168.30.111
Jan 31 20:17:32 pc006 pppd[17841]: write: No buffer space available
Jan 31 20:17:42 pc006 pppd[17841]: write: No buffer space available
Jan 31 20:17:52 pc006 pppd[17841]: Terminating on signal 15
Jan 31 20:17:52 pc006 pppd[17841]: Child process /usr/pkg/sbin/pppoe -n -I fxp1
-e 12:00:50:18:31:2c:bc -S '' (pid 4838) terminated with signal 15
Jan 31 20:17:52 pc006 pppd[17841]: Modem hangup
Jan 31 20:17:52 pc006 pppd[17841]: Connect time 0.6 minutes.
Jan 31 20:17:52 pc006 pppd[17841]: Sent 5227983 bytes, received 7859 bytes.
Jan 31 20:17:52 pc006 pppd[17841]: Connection terminated.