problem with udbp and netgraph in the usb LAN

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Hi, all
I have usb2usb link cable (no name)and try make usb network on two hosts  
(FreeBSD 5.3).
I do everything as written in man 4 udbp:
kldload netgraph
kldload udbp
Result :
udbp0: Prolific Technology Inc. PL2302 Host-Host interface, rev 1.00/0.01,  
addr2, iclass 255/0.
Then make:
ngctl mkpeer udbp0: iface data inet, ifconfig ng0 10.0.0.1 10.0.0.2 on  
both hosts.
Ping from 10.0.0.1 to 10.0.0.2  disappear through 1 minutes.
How to make steady connection?
Thanks in advance, Yuri.