A site-to-site VPN tunnel is where two firewalls are used to create a VPN tunnel. At Wireless Logic, we use IPSEC VPN tunnels. We configure a firewall on our side and then send the config parameters to the customer. The customer would then needs to enter the config parameters onto their firewall/router.
This would then enable any machine(s) on a company's LAN to connect to its devices with our m2m SIMs and vice versa. This is an always-on VPN connection. To create a site-to-site tunnel, customers would need to have a hardware firewall/router capable of setting up an IPSEC VPN tunnel.