Mitel 6867i Administrator's Manual page 237

For example, if the RTP base port value is 5000, the first voice patch sends RTP on port 5000
and RTCP on port 5001. Additional calls would then use ports 5002, 5003, etc.
You can configure the RTP port on a global-basis only, using the configuration files, the IP
Phone UI, or the Mitel Web UI.
SYMMETRICAL/ASYMMETRICAL RTP PORT HANDLING
By default, the phone supports symmetrical RTP port handling (i.e. the phone will only play an
RTP stream if it comes from a "source" port that is the same as the "listening" port negotiated
by the call manager.
Administrators can configure the phones to support asymmetrical RTP port handling by defining
the "rtp symmetric port" parameter as "0". By defining the parameter as "0" (i.e. disabling
symmetrical RTP port handling), the phone will accept the RTP stream coming from the different
"source" port and send RTP traffic to the caller at the "listening" port.
You can configure symmetrical/asymmetrical RTP port handling behavior using the
configuration files only.
BASIC CODECS (G.711 U-LAW, G.711 A-LAW, G.729)
CODEC is an acronym for COmpress-DECompress. It consists of a set of instructions that
together implement one or more algorithms. In the case of IP telephony, these algorithms are
used to compress the sampled speech data, to decrease the content's file size and bit-rate (the
amount of network bandwidth in kilobits per second) required to transfer the audio. With smaller
file sizes and lower bit rates, the network equipment can store and stream digital media content
over a network more easily.
Mitel IP phones support the International Telecommunications Union (ITU) transmission
standards for the following CODECs:
• Waveform CODECs: G.711 pulse code modulation (PCM) with a-Law or u-Law
companding
• Parametric CODEC: G.729a conjugate structure - algebraic code excited linear prediction
(CS_ACELP)
All codecs have a sampling rate of 8,000 samples per second, and operate in the 300 Hz to
3,700 Hz audio range. The following table lists the default settings for bit rate, algorithm,
packetization time, and silence suppression for each codec, based on a minimum packet size.
Default Codec Settings
CODEC BIT RATE
G.711 a-law 64 Kb/s
G.711 u-law 64 Kb/s
G.729a 8 Kb/s
PACKETIZATION
ALGORITHM TIME
PCM 30 ms
PCM 30 ms
CS-ACELP 30 ms
Global SIP Settings
SILENCE
SUPPRESSION
enabled
enabled
enabled
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