Matrix SPARSH VP710 User Manual page 535

Network Address Translation (NAT)
Network Address Translation (NAT) is essentially a translation table that maps public IP address and port
combinations to private ones. This reduces the need for a large number of public IP addresses. NAT ensures
security as each outgoing or incoming request must first go through a translation process. In the VoIP environment,
NAT breaks end-to-end connectivity. Image
NAT Types
In Symmetrical NAT, the NAT router stores the address and port to which it sent the packet. Only packets coming
from this address and port are forwarded back to the private address.
In Full Cone NAT, all the packets from a private address (e.g., iAddr: port1) to public network is send through a
public address (e.g., eAddr: port2). Packets coming from the address of any server to eAddr: port2 will be
forwarded back to the private address (e.g., iAddr: port1).
Address Restricted Cone NAT works similar like full cone NAT. A public host (hAddr: any) sends packets to iAddr:
port1 through eAddr: port2 only if iAddr: port1 has previously sent a packet to hAddr: any. "Any" means the port
number doesn't matter.
Port Restricted Cone NAT works similar like full cone NAT. A public host (hAddr: hPort) sends packets to iAddr:
port1 through eAddr: port2 only if iAddr: port1 has previously sent a packet to hAddr: hPort.
NAT Traversal
NAT traversal is a general term for techniques that establish and maintain IP connections traversing NAT gateways,
typically required for client-to-client networking applications, especially for VoIP deployments.
STUN is one of the NAT traversal techniques supported by the IP phone.
STUN (Simple Traversal of UDP over NATs)
STUN is a network protocol, used in NAT traversal for applications of real-time voice, video, messaging, and other
interactive IP communications. The STUN protocol allows entities behind a NAT to first discover the presence and
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