NEC SL1100, Сетевое руководство

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NEC SL1100 Issue 6.0
Networking Manual 9 - 71
S
ECTION
14
NAPT
14.1 Introduction
NAPT, or Network Address Port Translation, is a method by which a private
address (or addresses) and their TCP/UDP ports are translated into a single
public address and its TCP/UDP ports. In the case of IP phones with the
SL1100 it allows their connection to a public (Internet) IP address which is
then converted back to the private (non-Internet) IP address on the customer’s
network. The translation is available at the SL1100 end as well as at the
remote IP Phone end of the connection if required.
Enhancements
With SL1100 V3.5 or higher the NAPT feature is enhanced. Previously
when the DR700 connects to the system via NAPT, the intermediate
router/firewall could possibly close the port due to inactivity for a period
of time. The solution for this was to lower the Registration and
Subscribe expiry timers. However these timers were system wide and
would affect all terminals (not just NAPT terminals), causing an
increased network and CPU load.
To correct for this issue V3.5 or higher added these timers on a per
station basis. This way the NAPT terminals can lower the timers and not
affect all of the NON NAPT terminals. No new license is required for this
feature; all existing licenses are still required.