Friday, July 23, 2010

Jitter Buffer - PDV in TDM

Introduction -- TDM-over-Packet -- Jitter Buffer - PDV

The DS34T10x and DS34S10x families of TDM-over-Packet (TDMoP) devices use jitter buffers to compensate for the packet-delay variation (PDV) that is present in packet networks. These buffers are independently configurable on a per-bundle or per-connection basis. Additionally, they are dynamically adjustable, allowing them to be adapted in real-time to changes in the performance characteristics of the packet network. This application note discusses the jitter buffer controller and how to set its parameters to minimize the effects of PDV during TDM clock recovery.DS34T10x comprises the DS34T101, DS34T102, DS34T104, and DS34T108; DS34S10x comprises the DS34S101, DS34S102, DS34S104, and DS34S108.

Timing in a TDM Network

Variations in packet arrival time, called jitter, occur because of network congestion, timing drift, or route changes. Thus, when replacing the physical TDM connection with an IP/MPLS network and two TDMoP devices ,the receiving TDMoP device (slave) receives TDMoP packets with variable delays in arrival time.After processing the packets, the device should send TDM data to the TDM side at the constant rate of the TDM network to minimize the effects of this jitter. To achieve this constant data rate, the device works in clock-recovery mode to reconstruct the source TDM clock so that the destination TDM device can still work in loopback timing mode

There are two kinds of jitter buffers: static and dynamic. The static jitter buffer is hardware-based and is configured by the manufacturer. The dynamic jitter buffer is software-based and can be configured by a network administrator to adapt to changes in the network's delay and PDV.

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