Panasonic KX-TDA3480 Programming Manual page 22

2.2 Programming
Required Bandwidth for Voice Communication via WAN (PPP: Point-to-Point Protocol)
CODEC
G.711
G.729A
G.723.1 5.3 kbps —
G.723.1 6.3 kbps —
When assessing your bandwidth requirements, keep in mind that the longer the packet sending
interval, the smaller the amount of required bandwidth, and vice versa.
However, also consider that the shorter the packet sending interval, the clearer the expected
speech quality, because delays in packet transmissions will be small. When the packet sending
interval is long, delays are more likely to occur, resulting in overall degradation in speech
quality with more pauses and loss in voice communications.
Therefore, it is recommended that you select the shortest packet sending interval that network
bandwidth can accommodate.
DTMF Detection
A VoIP network does not guarantee accurate end-to-end transmission of DTMF signals
because the DTMF signals are coded/decoded during VoIP communications, in the same way
as voice signals. In addition, packets can get lost during transmission.
To compensate for this problem, it is possible to enable DTMF detection for the VoIP Gateway
Card to carry out accurate end-to-end DTMF relay over the network. Upon detecting DTMF
signals from the PBX, the card encodes the signals and then sends them to the destination,
instead of as voice signals. Then at the destination, the card regenerates the DTMF signals
from the received encoded signals, and then sends them to the PBX.
Note that when this feature is enabled, the sending of packets is delayed by approximately 30
ms. Therefore, it is recommended that you disable this feature unless DTMF detection is
necessary.
FAX Signal Detection
When sending fax signals using a CODEC other than G.711, the signals cannot be received
accurately at the destination because they are coded/decoded over the VoIP network, in the
same way as voice signals.
To compensate for this problem, it is possible to enable fax detection for the card. Upon
detecting fax signals (CED tones) from the PBX, the card automatically switches the CODEC
to G.711 to communicate with the card at the destination. With the G.711 CODEC, it is possible
to assure error-free fax communications to a certain extent.
To further assure fax communications, it is strongly recommended that the communicating fax
machines be equipped with the ECM (Error Correction Model) feature, an automatic error
correction feature. When, for example, the receiving fax machine detects errors in
transmission, it can have the sending fax machine resend the relevant data.
When using the fax detection feature, the communicating cards must share the same value
(either "G.711Mu" or "G.711A") for the parameter Voice CODEC Priority (see "Voice CODEC
Settings" in "2.2.2 H.323 Parameters").
22 Programming Guide
20 ms 30 ms
84 kbps 77.3 kbps
28 kbps 21 kbps
18.7 kbps
19.7 kbps
Packet Sending Interval
40 ms
74 kbps —
18 kbps —
— 12 kbps
— 13.1 kbps
60 ms 90 ms
—
—
9.8 kbps
10.8 kbps