CHAPTER13 Network
Mediant 1000 Gateway & E-SBC | User's Manual
2. Configure the time interval during which the device sends No-Op packets when silence occurs
(i.e., no RTP or T.38 traffic), using the [NoOpInterval] parameter.
3. For RTP No-Op packets, configure the payload type of the No-Op packets, using the
[RTPNoOpPayloadType] parameter.
The receipt of No-Op packets is always supported.
Fax Transmission behind NAT
The device supports transmission from fax machines (connected to the device) located inside
(behind) NAT. Generally, the firewall blocks T.38 (and other) packets received from the WAN,
unless the device behind the NAT sends at least one IP packet from the LAN to the WAN through
the firewall. If the firewall blocks T.38 packets sent from the termination IP fax, the fax fails. To
overcome this problem, the device sends No-Op (“no-signal”) packets to open a pinhole in the NAT
for the answering fax machine. The originating fax does not wait for an answer, but immediately
starts sending T.38 packets to the terminating fax machine upon receipt of a re-INVITE with T.38
only in the SDP, or T.38 and audio media in the SDP. This feature is configured using the
[T38FaxSessionImmediateStart] parameter. The No- Op packet feature is enabled using the
[NoOpEnable] and [NoOpInterval] parameters.
Robust Receipt of Media Streams by Media Latching
The device's Robust Media feature (or media latching) filters 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.
Configuring Quality of Service
This section describes how to configure Layer-2 and Layer-3 Quality of Service (QoS).
Configuring Class-of-Service QoS
The QoS Settings page lets you configure Layer-3 Class-of-Service Quality of Service (QoS). This
configures Differentiated Services (DiffServ) values for each CoS. DiffServ is an architecture
providing different types or levels of service for IP traffic. DiffServ (according to RFC 2474),
prioritizes certain traffic types based on priority, accomplishing a higher-level QoS at the expense
of other traffic types. By prioritizing packets, DiffServ routers can minimize transmission delays for
time-sensitive packets such as VoIP packets.
You can assign DiffServ to the following class of services (CoS):
■ Media Premium: RTP packets sent to the LAN
■ Control Premium: Control protocol (SIP) packets sent to the LAN
■ Gold: HTTP streaming packets sent to the LAN
■ Bronze: OAMP packets sent to the LAN
The mapping of an application to its CoS and traffic type is shown in the table below:
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