Version 6.4 125 March 2012
SIP User's Manual 10. Network
To configure the Internal SRV table:
1. Open the Internal SRV Table page (Configuration tab > VoIP menu > Network
submenu > DNS submenu > Internal SRV Table).
Figure 10-7: Internal SRV Table Page
2. In the 'Domain Name' field, enter the host name to be translated. You can enter a
string of up to 31 characters.
3. From the 'Transport Type' drop-down list, select a transport type.
4. In the 'DNS Name 1' field, enter the first DNS A-Record to which the host name is
translated.
5. In the 'Priority', 'Weight' and 'Port' fields, enter the relevant values
6. Repeat steps 4 through 5, for the second and third DNS names, if required.
7. Repeat steps 2 through 6, for each entry.
8. Click Submit to apply your changes.
9. To save the changes so they are available after a hardware reset or power fail, see
'Saving Configuration' on page 482.
10.7 NAT (Network Address Translation) Support
Network Address Translation (NAT) is a mechanism that maps a set of internal IP
addresses used within a private network to global IP addresses, 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); (2) Better network security by hiding its internal architecture.
The following figure illustrates the device's supported NAT 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 and the NAT server can’t modify SIP
messages and therefore, can’t change local to global addresses. Two different streams
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