Version 6.4 127 March 2012
SIP User's Manual 10. Network
10.7.2 First Incoming Packet Mechanism
If the remote device resides behind a NAT device, it’s possible that the device can activate
the RTP/RTCP/T.38 streams to an invalid IP address / UDP port. To avoid such cases, the
device automatically compares the source address of the incoming RTP/RTCP/T.38
stream with the IP address and UDP port of the remote device. If the two are not identical,
the transmitter modifies the sending address to correspond with the address of the
incoming stream. The RTP, RTCP and T.38 can thus have independent destination IP
addresses and UDP ports.
You can disable the NAT mechanism by setting the ini file parameter DisableNAT to 1. The
two parameters EnableIpAddrTranslation and EnableUdpPortTranslation allow you to
specify the type of compare operation that occurs on the first incoming packet. To compare
only the IP address, set EnableIpAddrTranslation to 1, and EnableUdpPortTranslation to 0.
In this case, if the first incoming packet arrives with only a difference in the UDP port, the
sending addresses won’t change. If both the IP address and UDP port need to be
compared, then both parameters need to be set to 1.
10.7.3 No-Op Packets
The device's No-Op packet support can be used to verify Real-Time Transport Protocol
(RTP) and T.38 connectivity, and to keep NAT bindings and Firewall pinholes open. The
No-Op packets are available for sending in RTP and T.38 formats.
You can control the activation of No-Op packets by using the ini file parameter
NoOpEnable. If No-Op packet transmission is activated, you can control the time interval in
which No-Op packets are sent in the case of silence (i.e., no RTP or T.38 traffic). This is
performed using the ini file parameter NoOpInterval. For a description of the RTP No-Op ini
file parameters, see 'Networking Parameters' on page 543.
RTP No-Op: The RTP No-Op support complies with IETF Internet-Draft draft-wing-
avt-rtp-noop-03 ("A No-Op Payload Format for RTP"). This IETF document defines a
No-Op payload format for RTP. The draft defines the RTP payload type as dynamic.
You can control the payload type with which the No-Op packets are sent. This is
performed using the RTPNoOpPayloadType ini parameter (see 'Networking
Parameters' on page 543). AudioCodes’ default payload type is 120.
T.38 No-Op: T.38 No-Op packets are sent only while a T.38 session is activated. Sent
packets are a duplication of the previously sent frame (including duplication of the
sequence number).
Note: Receipt of No-Op packets is always supported.
10.8 Configuring NFS Settings
Network File System (NFS) enables the device to access a remote server's shared files
and directories, and to handle them as if they're located locally. You can configure up to 16
different NFS file systems. As a file system, the NFS is independent of machine types,
operating systems, and network architectures. NFS is used by the device to load the cmp,
ini, and auxiliary files, using the Automatic Update mechanism (refer to the Product
Reference Manual). Note that an NFS file server can share multiple file systems. There
must be a separate row for each remote file system shared by the NFS file server that
needs to be accessed by the device.
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