RAD Data comm IPmux-11 Pdvt Jitter Buffer, Ethernet Throughput, Pdvt Buffer Effect on Delay

Chapter 1 Introduction Installation and Operation Manual

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) = 47 ⋅ N ⋅ 0.125
			TS
	Where:
	N =	TDM bytes/frame
	48
	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.
Note
	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.

1-12 Functional Description IPmux-11 Ver. 2.00