RAD Data comm IPmux-11 Specifications download pdf (Page 26)

Chapter 1 Introduction Installation and Operation Manual

1-12 Functional Description IPmux-11 Ver. 2.00

PDVT (Jitter) Buffer

IPmux-11 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. The PDVT (jitter) buffer

is designed to compensate for packet delay variation caused by the network +

packetization delay. It supports a delay variation of up to 300 ms for E1 or T1.

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).

Packetization Delay

When IPmux-11 builds a frame, a packetization delay is introduced. The

packetization delay is calculated according to the following formula:

Packetization delay (ms) =

0.125N 47

Where:

N =

ebytes/framTDM

TS = number of assigned timeslots (in unframed mode= 32 for E1, 24 for T1)

Jitter Buffer Depth

The jitter buffer depth is configured according to the following formula:

Jitter buffer = PDV introduced by the network (measured or estimated) +

packetization delay.

For a bundle that contains a few timeslots (i.e. 1 to 3,) the recommended number

of TDM bytes/frame is 48 in order to prevent excessive packetization delay.

Ethernet Throughput

Increasing payload size reduces the ratio of the TDMoIP header segment in the

packet, thus reducing the total Ethernet throughput.

Increased payload reduces the IP/Ethernet overhead segment of the total packet

and thus can reduce the total Ethernet throughput.

On the other hand, packetization delay is increased; this contributes to a higher

end-to-end delay. This effect can be small and negligible when a full E1 (or many

timeslots) are transferred, but can be very significant when few timeslots are

transferred. In this case, when configuring a large value of TDM bytes/frame, the

packetization delay can be very large and may exceed the maximum PDVT (jitter)

buffer on the receiving end.

Note

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RAD Data comm IPmux-11 Specifications Page 26