AASTRA 6700i series, 9143, 9480i, 9480i CT SIP Administrator Guide EN - Manual (Page 254)

41-001343-01 Rev 03, Release 3.2.2 4-91
RTP Port
RTP is described in RFC1889. The UDP port used for RTP streams is traditionally an
even-numbered port, and the RTCP control is on the next port up. A phone call therefore uses one
pair of ports for each media stream.
The RTP port is assigned to the first line on the phone, and is then incremented for each
subsequent line available within the phone to provided each line a unique RTP port for its own use.
On the IP phone, the initial port used as the starting point for RTP/RTCP port allocation can be
configured using "RTP Port Base". The default RTP base port on the IP phones is 3000.
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 Aastra Web UI.
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.
Aastra 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 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 Algorithm
Packetizatio
n Time
Silence
Suppression
G.711 a-law 64 Kb/s PCM 30 ms enabled
G.711 u-law 64 Kb/s PCM 30 ms enabled
G.729a 8
Kb/s
CS-ACELP 30 ms enabled