Specifications

Installation and Operation Manual Chapter 4 Troubleshooting and Diagnostics
MPW-1 MP-4100 Ver. 2.0 Monitoring Performance 4-9
Parameter Description
Jitter Buffer
Underflows Seconds
Displays the number of seconds during which at least one jitter buffer underflow
event has been detected.
MPW-1 is equipped with a Packet Delay Variation Tolerance buffer, also called a
“jitter buffer”, which is used to automatically compensate for packet network delay
variation (jitter). Each pseudowire has its own jitter buffer. Although packets leave
the transmitting MPW-1 at a constant rate, they will usually reach the far end at a
rate which is not constant, because in practice the network transmission delay varies
(due to factors such as congestion, rerouting, queuing mechanisms, transport over
wireless or half-duplex media, etc.).
TDM equipment at both ends of a pseudowire require a constant flow of data, and
cannot tolerate delay variation. Therefore, the receive side jitter buffer is required to
provide the TDM equipment with a synchronous and constant flow.
For this purpose, when a pseudowire is set up (and at any time after communication
is restored), the jitter buffer is loaded with packets up to its middle point: only after
this point it starts outputting TDM data towards the connected TDM equipment. The
stored packets assure that the TDM equipment will continue receiving data even if
the network delay momentarily increases. Obviously, if packets are delayed too long,
the buffer is gradually emptied out until it underflows (this situation is called buffer
starvation, and it affects the end-to-end voice/data integrity).
Each underflow event increases the jitter buffer underflow counter by 1.
Jitter Buffer
Overflows Seconds
Displays the number of seconds during which at least one jitter buffer overflow
event has been detected.
As explained above, during steady state, the jitter buffer is filled up to its middle
point, which means that it has space to hold additional packets. An overflow will
occur when the network delay suddently decreases, for example, when a large burst
of packets reaches the MPW-1. If the burst includes more packets than the jitter
buffer can store at that instant, the buffer will be filled up to its top. In this case, an
unknown number of excess packets are dropped. To correct the situation, MPW-1
initiates a forced underflow by flushing (emptying) the buffer. Therefore, an
overflow always results in an immediate underflow. After the buffer is flushed, the
process of filling up the buffer is started again
Min Jitter Buffer
Level (usec)
Actual minimum size of the jitter buffer recorded for this pseudowire in the selected
interval, in μsec
Max Jitter Buffer
Level (usec)
Actual maximum size of the jitter buffer recorded for this pseudowire in the selected
interval, in μsec
Max Jitter Buffer
Deviation (usec)
The maximum jitter buffer deviation (variation of delay, in μsec) reported during the
selected interval. This is the maximum jitter level that had to be compensated for in
the selected interval
Time Elapsed The elapsed time since the beginning of the current interval (for a selected interval,
the displayed time is always 15 minutes), or the elapsed time since the beginning of
the curent 24 hour interval
Valid Intervals The total number of 15-minute intervals for which valid data is available