3Com V6100, User Manual Manual, Page: 246 / 496

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V6100 and V7122 User Guide
In this configuration, T.30 faxes use Relay mode (T.38) while V.34 fax uses Bypass mode.
In order to use V.34 fax in Relay mode (T.38), you must configure:
FaxTransportMode = 1 (Relay)
V34ModemTransportType = 0 (Transparent)
V32ModemTransportType = 0
V23ModemTransportType = 0
V22ModemTransportType = 0
This configuration forces the V.34 fax machine to work in T.30 mode.
ThroughPacket™
The gateway supports a proprietary method to aggregate RTP streams from several
channels to reduce the bandwidth overhead caused by the attached Ethernet, IP, UDP and
RTP headers, and to reduce the packet / data transmission rate. This option reduces the
load on network routers and can typically save 50% (e.g., for G.723) on IP bandwidth.
ThroughPacket™ is accomplished by aggregating payloads from several channels that are
sent to the same destination IP address into a single IP packet.
ThroughPacket™ can be applied to the entire gateway or, using IP Profile, to specific IP
destinations (see
IP Profile Settings ). Note that ThroughPacket™ must be enabled on both
gateways.
To enable ThroughPacket™ set the parameter ‘RemoteBaseUDPPort’ to a nonzero value.
Note that the value of ‘RemoteBaseUDPPort’ on the local gateway must equal the value of
‘BaseUDPPort’ of the remote gateway. The gateway uses these parameters to identify and
distribute the payloads from the received multiplexed IP packet to the relevant channels.
In ThroughPacket™ mode, the gateway uses a single UDP port for all incoming multiplexed
packets and a different port for outgoing packets. These ports are configured using the
parameters ‘L1L1ComplexTxUDPPort’ and ‘L1L1ComplexRxUDPPort’.
When ThroughPacket™ is used, Call statistics aren’t available (since there is no RTCP flow).
Dynamic Jitter Buffer Operation
Voice frames are transmitted at a fixed rate. If the frames arrive at the other end at the same
rate, voice quality is perceived as good. In many cases, however, some frames can arrive
slightly faster or slower than the other frames. This is called jitter (delay variation), and
degrades the perceived voice quality. To minimize this problem, the gateway uses a jitter
buffer. The jitter buffer collects voice packets, stores them and sends them to the voice
processor in evenly spaced intervals.