1. A method of prioritizing traffic in a packet communication system destined for a receiving sub-network hosting a virtual private network (VPN) gateway, the method comprising: forwarding packets from an end user device and destined for the receiving sub-network through a gateway in an access network; at the gateway, determining whether packets from the end user device are requesting a new session with the VPN gateway; at the gateway, non-invasively and independently of any shared secrets between the VPN gateway and the end user device inferring from packets requesting a new session whether the request was accepted by the VPN gateway; and if it is inferred that the request was accepted by the VPN gateway, maintaining traffic flows for a session between the VPN gateway and the end user device at a priority level higher than a default priority level.