The Customer Edge Router (CE-R) must filter inbound AS-SIP-TLS traffic addressed to the local Session Border Controller (SBC) based on the source address of the signaling messages.

The CE-R (premise or perimeter) router is the first line of defense at the gateway to the enclave or LAN. The data firewall and SBC functions are the second line of defense. The SBC processes VVoIP traffic in the form of AS-SIP-TLS and SRTP/SRTCP packets, and the CE-R must forward these packets to the SBC. A filter performed by the CE-R to prevent a denial-of-service is to filter the AS-SIP-TLS packets based on their source address. Within the DISN IPVS network, Local Session Controllers (LSC) only signal to their assigned Multi-Function Soft Switch (MFSS) and its backup. MFSSs are only to signal with their assigned LSCs, for which they are primary or backup, and other MFSSs. To support this, the SBC is required to authenticate the source of, and validate the integrity of, the signaling packets it receives and only process authenticated and valid packets, thereby only signaling with the appropriate devices. Still, the SBC could be flooded and overloaded with too many unauthenticated or invalid signaling packets. The CE-R can help prevent this by preventing signaling packets that are not sourced from authorized devices from ever reaching the SBC.