Billion BiGuard S20

[Christoph Langbein]

Hello,
I own an Billion BiGuard S20
(http://www.billion.com/product/ssl-ipsec-vpn/biguards20-ssl-vpn-security-gateway.html). The Router is using the applet from www.javassh.org and one applet I think from http://properjavardp.sourceforge.net/ . Old firmware versions have an OS Fingerprint shown as Linux OS, this has changed with the current firmware. But I'm not really sure.

The firmware is named BiGuardS20_v313.afw. I've tried to mount it
loopback, no success.a "file BiGuardS20_v313.afw" shows
BiGuardS20_v313.afw: data
The firmware begins with 3.13^@ÿÿÿX1234567890abcdei<84><98>.
Any hints how I could open such an image ?

Thanks in advance
Christoph