AudioCodes Mediant 500 E-SBC, User Manual

Page: 133 / 920

User's Manual 12. Network
Version 6.8 133 Mediant 500 E-SBC
Parameter Description
Port (1-3)
CLI: port-1|2|3
[Srv2Ip_Port1/2/3]
Defines the TCP or UDP port on which the service is to be found.
12.9 Network Address Translation Support
Network Address Translation (NAT) is a mechanism that maps internal IP addresses (and
ports) used within a private network to global IP addresses and vice versa, providing
transparent routing to end hosts. The primary advantages of NAT include (1) reduction in
the number of global IP addresses required in a private network (global IP addresses are
only used to connect to the Internet) and (2) better network security by hiding the internal
architecture.
The design of SIP creates a problem for VoIP traffic to pass through NAT. SIP uses IP
addresses and port numbers in its message body. However, the NAT server is unable to
modify the SIP messages and thus, can’t change local addresses to global addresses.
This section discusses the device's solutions for overcoming NAT traversal issues.
12.9.1 Device Located behind NAT
Two different streams traverse through NAT - signaling and media. A device located
behind a NAT that initiates a signaling path has problems receiving incoming signaling
responses as they are blocked by the NAT server. Therefore, the initiating device must
inform the receiving device where to send the media. To resolve this NAT problem, the
following solutions are provided by the device, listed in priority of the selected method used
by the device:
a. If configured, uses the single Static NAT IP address for all interfaces - see
''Configuring a Static NAT IP Address for All Interfaces'' on page
134 .
b. If configured, uses the NAT Translation table which configures NAT per interface - see
Configuring NAT Translation per IP Interface on page
135 .
If NAT is not configured by any of the above-mentioned methods, the device sends the
packet according to its IP address configured in the Interface table.
Note: The priority list above is applicable only to the Gateway calls.