That seems to be not ssh protocol issue. I know for sure that ssh
session can be held even after a couple of minutes without network
connection. And when connection comes back, ssh session successfully
continues. Perhaps a putty has to be configured somehow.

Hari Sekhon wrote:
> Hi,
> I have a remote worker who uses SSH tunneling to connect into the
> office while on the road. He is running Windows with PuTTY connecting
> to a Linux OpenSSH server. He has been reporting that it is extremely
> unstable and that the connection drops. However, I and a colleague of
> mine use this method regularly and have had no problems.
> I suspect that this is simply due to his use of a 3G card which has a
> very slow dial-up speed connection, whereas myself and my colleague
> have broadband (actually it does drop more when my internet pipe is
> flooded).
> Is there anything I can do to make the connection more tolerant and
> not drop?
> Or perhaps any advice for further isolating this (bearing in mind the
> remote worker is not technical and I don't have access to the laptop
> at the times he's on the road...)
> This same remote worker was previously using an ipsec vpn with 3des
> and had no problems so I suspect that 3des is more forgiving that the
> ssh protocol(s) being used for cryptography, although I am aware that
> ssh can use several different crypto algorithms, and reading the man
> page again it seems that 3des is the default on linux but PuTTY seems
> to default to AES first so perhaps it is AES being less forgiving that
> 3des?
> Does anyone know more about the actual AES and 3DES protocol
> internals, is AES less tolerant to timing issues because of it's
> stronger cryptography (sort of like Kerberos system times being used
> in the crypto algorithm)?
> Any ideas or feedback on this issue?
> Thanks
> -h