A system comprising: a trusted network; an untrusted network; on-board equipment on-board a movable vehicle; wayside equipment, central equipment, and station equipment (136, 132, 134) communicatively coupled with the trusted network; one or more first security devices (126a, 126b) on-board the movable vehicle and communicatively connecting the on-board equipment and the untrusted network; and a security device bank (124a, 124b, 124c) communicatively connecting the trusted network and the untrusted network, the security device bank comprising: a common bus or a local network; and one or more second security devices connected to the common bus or the local network, wherein each second security device of the one or more second security devices is configured to establish one or more communication tunnels through the untrusted network between the security device bank and the one or more first security devices, wherein each second security device is configured to handle a predetermined number of communication tunnels, the communication tunnels are in compliance with an Internet Engineering Task Force Internet Protocol Security, IPSEC, standard, the security device bank is scalable to increase a communication capacity of the security device bank by adding second security devices to the security device bank, and connecting the added second security devices to the common bus or the local network, the wayside equipment, central equipment, and station equipment are communicatively coupled with the untrusted network through only the security device bank, and the wayside equipment, central equipment, and station equipment are communicatively coupled with one another through the trusted network independent of the security device bank. a trusted network; an untrusted network; on-board equipment on-board a movable vehicle; wayside equipment, central equipment, and station equipment (136, 132, 134) communicatively coupled with the trusted network; one or more first security devices (126a, 126b) on-board the movable vehicle and communicatively connecting the on-board equipment and the untrusted network; and a security device bank (124a, 124b, 124c) communicatively connecting the trusted network and the untrusted network, the security device bank comprising: a common bus or a local network; and one or more second security devices connected to the common bus or the local network, a common bus or a local network; and one or more second security devices connected to the common bus or the local network, wherein each second security device of the one or more second security devices is configured to establish one or more communication tunnels through the untrusted network between the security device bank and the one or more first security devices, wherein each second security device is configured to handle a predetermined number of communication tunnels, the communication tunnels are in compliance with an Internet Engineering Task Force Internet Protocol Security, IPSEC, standard, the security device bank is scalable to increase a communication capacity of the security device bank by adding second security devices to the security device bank, and connecting the added second security devices to the common bus or the local network, the wayside equipment, central equipment, and station equipment are communicatively coupled with the untrusted network through only the security device bank, and the wayside equipment, central equipment, and station equipment are communicatively coupled with one another through the trusted network independent of the security device bank.