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IPmux-1/1E Installation and Operation Manual Chapter 1 Introduction
Functional Description 1-19
PDV
t
t
Packets Leaving IPmux-1
Packets Arriving
Figure 1-17. Packet Delay Variation
PDVT (Jitter) Buffer
IPmux-1 is equipped with a Packet DVT (Delay Variation Tolerance) buffer. The
PDVT buffer or jitter buffer is filled by the incoming IP packets and emptied out to
fill the TDM stream. The buffer begins to empty out only after it is half full in order
to compensate for packet starvation from the Ethernet side. The time it takes for
half of the buffer to empty out is the maximum DVT time. Delay Variation
Tolerance is configurable. The PDVT (jitter) buffer is designed to compensate for
packet delay variation caused by the network + intrinsic PDV.
It supports a delay variation of up to 300 ms for E1 or T1 in static or dynamic CAS
modes, and up to 127 ms in CESoIP mode.
PDVT Buffer Effect on Delay
The PDVT buffer is on the TDM path; it adds to the total end-to-end delay (see
delay calculation, below).
Intrinsic PDV in Static Mode
If TDM bytes/frame is greater than 48, there is an intrinsic delay variation (intrinsic
PDV). The intrinsic PDV introduced by the module is a function of n>1 in
TDM bytes/frame configuration as follows:
I.PDV (ms) = [(n-1) x 1000) / (frames per second × n]
where n =
48
ebytes/fram TDM Confi
g
ured
(n = 1 to 8).
To configure jitter buffer depth:
The estimated or measured PDV introduced by the network + intrinsic PDV
(if it exists) introduced by the module as a result of configuring the
TDM bytes / frame > 48.
For a bundle that contains a few timeslots (i.e. 1 to 3) the minimal jitter buffer
should be 6 ms.
Note