Nat (Network Address Translation) Support - AudioCodes Mediant 600 User Manual

When Ethernet redundancy is implemented, the two Ethernet ports can be connected to the
same switch (segment / hub). In this setup, one Ethernet port is active and the other is
redundant. If an Ethernet connection failure is detected, the CPU module switches over to
the redundant Ethernet port. The CPU issues a Major alarm notifying of the failed physical
port. If the first Ethernet port connection is restored, the Major alarm is cleared. The first
physical port now becomes the redundant Ethernet port in case of failure with the active
physical port (which is currently the second physical port).
When the CPU module loses all Ethernet connectivity, a Critical alarm is generated:
When MIIRedundancyEnable is disabled: the alarm is generated when the single
physical connection is lost. The alarm is cleared when the single physical connection is
restored.
When MIIRedundancyEnable is enabled: the alarm is generated when both physical
connections are lost. The alarm is cleared when one or both of the physical
connections are restored.
10.3

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
traverse through NAT: signaling and media. A device (located behind a NAT) that initiates a
signaling path has problems in receiving incoming signaling responses (they are blocked by
the NAT server). Furthermore, the initiating device must notify the receiving device where to
send the media.
To resolve these issues, the following mechanisms are available:
STUN (refer to "STUN" on page 539)
First Incoming Packet Mechanism (refer to ''First Incoming Packet Mechanism'' on
page 540)
RTP No-Op packets according to the avt-rtp-noop draft (refer to ''No-Op Packets'' on
page 540)
For information on SNMP NAT traversal, refer to the Product Reference Manual.
SIP User's Manual
Figure 10-1: NAT Functioning
538
Mediant 600 & Mediant 1000
Document #: LTRT-83305