Robust Receipt Of Media Streams By Media Latching - AudioCodes Mediant 4000 SBC User Manual

11.11 Robust Receipt of Media Streams by Media Latching

The Robust Media mechanism (or media latching) is an AudioCodes proprietary
mechanism to filter out unwanted media (RTP, RTCP, SRTP, SRTCP, and T.38) streams
that are sent to the same port number of the device. Media ports may receive additional
multiple unwanted media streams (from multiple sources of traffic) as result of traces of
previous calls, call control errors, or deliberate malicious attacks (e.g., Denial of Service).
When the device receives more than one media stream on the same port, the Robust
Media mechanism detects the valid media stream and ignores the rest. Thus, this can
prevent an established call been stolen by a malicious attacker on the media stream.
For the involved voice channel, the device latches onto the first stream of the first received
packet. All packets (of any media type) received from the same IP address and SSRC are
accepted (for T.38 packets, the device considers only the IP address). If the channel
receives subsequent packets from a non-latched source, the device can either ignore this
new stream and remain latched to the first original stream (IP address:port), or it can latch
onto this
InboundMediaLatchMode parameter. If this mode is configured to latch onto new streams,
you also need to configure the following:

Minimum number of continuous media packets that need to be received from a
different source(s) before the channel can latch onto this new incoming stream.

Period (msec) during which if no packets are received from the current stream, the
channel latches onto the next packet received from any other stream.
Depending on media latch mode, if the device has latched onto a new stream and a packet
from the original (first latched onto) IP address:port is received at any time, the device
latches onto this original stream.
Latching onto a new T.38 stream is reported in CDR using the CDR fields, LatchedT38Ip
(new IP address) and LatchedT38Port (new port). In addition, the SIP PUBLISH message
updates the latched RTP SSRC, for example:
RemoteAddr: IP=10.33.2.55 Port=4000 SSRC=0x66d510ec

To configure media latching:
1. Open the Media Settings page (Setup menu > Signaling & Media tab > Media folder
> Media Settings), and then from the 'Inbound Media Latch Mode' drop-down list
(InboundMediaLatchMode), configure the media latch mode:
2. If you configure the parameter to Dynamic or Dynamic-Strict:
•
Define the minimum number of continuous media (RTP, RTCP, SRTP, and
SRTCP) packets that need to be received by the channel before it can latch onto
this new incoming stream:
♦
♦
♦
♦
•
Define a period (msec) during which if no packets are received from the current
media session, the channel can re-latch onto another stream:
♦
♦
♦
♦
♦
User's Manual
new stream. The
'New RTP Stream Packets'
'New RTCP Stream Packets'
'New SRTP Stream Packets'
'New SRTCP Stream Packets'
'Timeout To Relatch RTP'
'Timeout To Relatch SRTP'
'Timeout To Relatch Silence'
'Timeout To Relatch RTCP'
'Fax Relay Rx/Tx Timeout'
media latch mode
156
Mediant 4000 SBC
is configured using
Document #: LTRT-40203
the