Specifications

Chapter 1 Introduction Installation and Operation Manual
1-16 Functional Description IPmux-24 Ver. 1.5
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Frame
1
Frame
2
Frame
N
Frame 1
425 425 425
Frame 2 Frame N
L2/L3
Header
Control
Word
CRC Ethernet Packet
TDM Payload
FRG bits = 00
(no fragmentation)
Figure 1-12. CESoPSN Encapsulation (E1, Bundle with Timeslots 4 and 25)
Packet Delay Variation
TDMoIP packets are transmitted by IPmux-24 at a constant rate towards the PSN
(Packet-Switched Network). Packet Delay Variation is the deviation from the
nominal time the packets are expected to arrive at the far end device. IPmux-24
has a jitter buffer that compensates for the deviation from the expected packet
arrival time to ensure that the TDM traffic is sent to the TDM device at a constant
rate.
The jitter buffer needs to be configured to compensate for the jitter level
introduced by the PSN. If the PSN jitter level exceeds the configured jitter buffer
size, underflow/overflow conditions occur, resulting in errors at the TDM side.
PDV
t
t
Packets Leaving IPmux-216
Packets Arriving
Figure 1-13. Packet Delay Variation
PDVT (Jitter) Buffer
IPmux-24 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 usually occurs when IPmux-24 loses its clock
synchronization
• A jitter buffer underrun occurs when no packets are received for more than
the configured jitter buffer size, or immediately after an overrun.