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VoIP gateway IP400 version 5.01
Packet size
You can set the size of the packets used for exchanging encoded voice data
between telephony gateways under
Packet size
(
ms
). The value entered here
defines the period of time for collecting voice data prior to transmitting it as a
voice data packet. Voice transmission is delayed correspondingly. A value of
30 ms is perceived by the human ear as virtually without delay, a value of 100 ms
similarly, does not irritate most users.
Larger packets cause greater
Delays
in voice data transmission, but cause less
stress to the network since the
Overhead
involved in transporting packets in the
network is lower.
Note that the overhead is increased considerably if the
Packet size
is reduced,
since the overhead data required for transmission with the IP-protocol (on a LAN)
and also in the PPP protocol (in the WAN) remains the same per packet, whilst the
voice data quantity, and with it the data actually used, is reduced. The bandwidth
actually required is therefore considerably higher (depending on the packet size)
than the pure voice data bandwidth as specified in Table 11.
By background noise (crackling) or greatly increased delays, you can tell if voice
data can no longer be transmitted quickly enough, due to insufficient bandwidth
or excessive network transit times. In such a case, increase the packet size for the
telephony interface concerned to reduce the effect, or select a more efficient
encoding scheme (for example G.723-53 instead of G.729). Table 12 shows the
required bandwidths, depending on the encoding and packet size.