4200 User Manual Edgewater Networks, Inc.
Version 3.0 21
be 20% lower than this number (eg.: if Maximum Bandwidth is set to
1000k, then only 800k of actual voice/video will be allowed through).
o Alias Restrictions --
Alias Restrictions sets a limit to the number
of aliases that are allowed to register with the system. If this number
is exceeded when a client tries to register, the registration will be
rejected. If the value is set to 0, the maximum is not enforced.
⇒
Select Submit
NAT
⇒
Select NAT
Network Address Translation (NAT) is a method of allowing two connected
networks to use different and incompatible IP addressing schemes. Address
translation allows hosts on a private internal network to transparently
communicate with devices on an external network and vice versa.
After traffic shaping, the packets undergo the NAT process, which maps the
single public IP address of the system and the IP port number associated with
a particular session to the private address and port number of the appropriate
IP phone device.
For VoIP, the system restricts the UDP port range on the public side to the
minimum required for the number of simultaneous calls desired. This is
typically 4 times the number of sessions: an RTP port and RTCP port in both
directions. This is done to minimize the UDP port range that must be opened
when using an external firewall.
Additional security is provided by dynamically creating port mappings when a
communication session is initiated and destroyed when a session is
terminated. In addition to VoIP devices, the NAT function can be used for
standard data applications and devices.
Network Address Translation Configuration
Network Address Translation allows many private IP addresses to be mapped
to a single public address. However, another feature of NAT typically used for
security, is that devices behind NAT are hidden and not directly addressable
from a public network. This is a problem for IP phone devices that need to
accept calls from the public network. To handle this issue, the system
implements a call-agent proxy to map the common public address to unique
private addresses.
Note: NAT can be used to translate the LAN IP addresses to the public
routable IP address that is assigned to the WAN port.
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