Inalp Networks SmartWare Release 2.10, Software Configuration Manual

Page: 318 / 357

318 VoIP Profile Configuration
Example: Configure Voice Volume
The following example shows how to set the voice volume for the VoIP profile to 10 dB and specify
an other value 20 dB for a specific H.323 interface
SN> enable
SN# configure
SN(cfg)# profile voip ISoIPProfile
SN(pf-voip)[ISoIPPr~]# voice-volume 10
SN(pf-voip)[ISoIPPr~]# exit
SN(cfg)# context cs
SN(ctx-cs)[switch]# interface h323 IpBackbone
SN(if-h323)[IpBackb~]# voice-volume 20
32.8 Configure Dejitter Buffer (Advanced)
Packet networks always introduce a certain amount of jitter in the arrival of voice packets. To
compensate for the fluctuating network conditions, SmartWare has implemented a dejitter buffer in
its voice gateway. Typical voice sources generate voice packets at a constant rate. The matching voice
decompression algorithm also expects incoming voice packets to arrive at a constant rate. However,
the packet-by-packet delay inflicted by the network may be different for each packet. The result:
packets that are sent in equal spacing from the left gateway arrive with irregular spacing at the right
hand gateway, as shown in Figure 32-5.
Figure 32-5: Jitter and Dejitter Buffer
Since the receiving decompression algorithm (voice decoder) requires fixed spacing between the
packets, the typical solution is to implement a dejitter buffer within the gateway. The dejitter buffer
deliberately delays incoming packets in order to present them to the decompression algorithm at
fixed spacing. It will also fix any out-of-order errors by looking at the sequence number in the RTP
frames.
Such a buffer has the effect of smoothing the packet flow, increasing the resiliency of the codec to
packet loss, delayed packets and other transmission effects. However, the downside of the dejitter
buffer is that it can add significant delay. The dejitter buffer size is configurable and can be
optimized for given network conditions. The dejitter buffer size is usually set to be an integral
multiple of the expected packet inter-arrival time in order to buffer an integral number of packets. It
is not uncommon to see dejitter buffer settings approaching 80 ms for each direction.
Software Configuration Guide Release 2.10, Revision 1.00