Specifications

Chapter 1 Introduction Installation and Operation Manual
1-18 Functional Description IPmux-8/16 Ver. 6.00
PDVT (Jitter) Buffer
IPmux-8/16 is equipped with a Packet DVT (Delay Variation Tolerance) buffer.
The PDVT buffer or jitter buffer is filled by the incoming packets and emptied out
to fill the TDM stream.
• A jitter buffer overrun occurs when it receives a burst of packets that exceeds
the configured jitter buffer size + packetization delay. When an overrun is
detected, IPmux-8/16 clears the jitter buffer, causing an underrun.
• A jitter buffer underrun occurs when no packets are received for more than
the configured jitter buffer size, or immediately after an overrun.
When the first packet is received, or immediately after an underrun, the buffer is
automatically filled with conditioning pattern up to the PDVT level in order to
compensate for the underrun. Then, IPmux-8/16 processes the packet
(packetization delay) and starts to empty out the jitter buffer to the TDM side. See
Figure 1-17 for the illustration of the PDVT buffer operation.
The PDVT (jitter) buffer is designed to compensate for the following network delay
variation:
• E1: 32 msec
• T1: 24 msec
• E3/T3: 29 msec (IPmux-16 only)
• CT3: 42 msec (IPmux-16 only).
PDVT Buffer Effect on Delay
Packets arriving from the PSN side are stored in the jitter buffer before being
transmitted to the TDM side, adding a delay to the TDM traffic. The delay time
equals to the jitter buffer size configured by the user.
PDVT (Jitter) Buffer Depth
Normal Operation
(No PDV)
Maximum Jitter Buffer Size
(2 PDVT + Packetization Delay)
PVDT Buffer + Packetization Delay
Figure 1-17. Jitter Buffer Operation
Packetization Delay
When IPmux-8/16 builds a frame, a packetization delay is introduced. The
packetization delay is calculated according to the following formula:
Packetization delay (ms) =
TS
0.125N 47
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