NEC UNIVERGE SV9100 Manual page 162

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Each CODEC has different voice quality and compression properties. The correct choice of CODEC will be
based on the amount of bandwidth available, the amount of calls required and the voice quality required.
Available Codecs for SIP Trunks
· G.711 64Kbps codec MOS 4.4
· G.722 64Kbps codec MOS 4.4
· G.726 32Kbps codec MOS 4.2
· G.729 8Kbps codec MOS 4.0
The bandwidth values quoted for these codec's are for the digitized speech in one direction only. The
actual bandwidth required for a call will depend on many other factors and will be much higher than these
figures.
The above MOS values are quoted for ideal network conditions. The value could be lower depending upon
the network performance.
To change the codec in use for SIP Trunks network use the Audio Capability Priority setting in Easy Edit –
Advanced Items/VoIP/SIP Networking/Profile x/SIP Profile x - Trunk General Settings/SIP Profile x -
CODEC Settings (PRG84-13-28)
DTMF Relay (RFC2833)
By default any DTMF tones transmitted across SIP Trunks will be sent as audio tones in the speech path. It
is possible that these tones can be misinterpreted by the receiving device because of packet loss or errors
due to the codec compression.
DTMF relay is a way of converting the DTMF tone into a signal then sending the signal across the IP
network instead of the actual tone.
To enable this feature set the DTMF Relay Mode option to RFC2833 in Easy Edit –
SIP Networking/Profile x/SIP Profile x - Trunk General Settings/SIP Profile x - DTMF Settings (PRG84-34-
01)
T.38 Fax Relay
SIP Trunks have the ability to communicate using the T.38 Fax Relay protocol.
By default any Fax tones transmitted to or from a SIP Trunk will be sent as audio tones in the speech path.
It is possible that these tones can be misinterpreted by the receiving device because of packet loss or
errors due to the codec compression.
T.38 Fax Relay is a way of converting the Fax tones into a signal then sending the signal across the IP
network where the signals are converted back to Fax tones.
The SIP Carrier or Server must support T.38 for this to work.
Enable Fax Relay by using the 'Fax Relay Mode' option in Easy Edit –
Networking/Profile x/SIP Profile x - Trunk General Settings/SIP Profile x - FoIP Settings (PRG84-33-01).
There are several other options to do with T.38 Fax relay that can also be found on the same page. These
commands would usually be left at the default settings but may occasionally need altering depending on
the SIP Carrier/Server, fax machine and network connection.
Advanced Items/VoIP/
Advanced Items/VoIP/SIP