Aastra Telecom 57I CT, 55I, 53I manual Nortel Networks NAT, Configuring Nortel NAT optional

IP Phone Administrator Guide Network Settings

Configuring the IP Phones

Nortel Networks NAT

Nortel Networks provides a proprietary solution to support connectivity to their proxies from phones placed behind devices (such as routers or firewalls) that use NAT. Nortel uses the SIP ping request/reply between the Nortel proxy and the phone in order to keep the connection through the router or firewall active. A SIP Nortel NAT timer is the interval, in seconds (default is 60), that the phone sends SIP ping requests to the Nortel proxy.

When you use NAT in your network, a network device (usually a router) provides a “firewall” division between the public network (usually the Internet) and the private network, to which the IP Phones are connected. The firewall protects the network by translating port numbers within packets between the public and private networks. When using NAT, and an RTP packet arrives at the public side of the firewall, it is expected to have the NAT RTP port within the packet. If the packet contains the proper port number, the firewall changes the NAT RTP port number in the packet to the RTP port number that the phone recognizes, and then forwards it onto the private network. Often the router/firewall automatically discovers these various port numbers and other information concerning public and private sides of the network with the use of the Universal Plug and Play (UPnP) Protocol between the phone and the router/firewall.

Configuring Nortel NAT (optional)

You can configure Nortel NAT using the configuration files, the IP phone UI, or the Aastra Web UI.

Configuration Files

For specific parameters you can set in the configuration files, see Appendix A, the section, “Network Address Translation (NAT) Settings” on page A-20.

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