Cisco Systems IPMUX-1, IPMUX-1E - page 121

Chapter 4 Troubleshooting and Diagnostics IPmux-1/1E Installation and Operation Manual 4-24 Performance Monitoring and Troubleshooting Statistics
Table 4-6. Bundle Connection Status Parameters (Cont.)
Parameter Description Jitter Buffer Underflow (cont.)
Recommendations:
Try increasing the Jitter Buffer size. Check reasons for sequence errors or lost/dropped packets (if present), system clocking configuration, Ethernet environment (full duplex) and connection, packets drop/loss/ignore by Routers/Switches or non-uniform packets output by Routers/Switches due to queuing mechanisms.
Make sure the same amount of TS for bundle is configured on each side of the IPmux application, and that the “TDM bytes in frame” parameter is identical in both IPmux units. Make sure Ethernet/IP network provides priority (Quality Of Service) to the IPmux traffic. Priority may be achieved by three means: VLAN tagging, IP TOS marking or by using the constant 2142 decimal value at each IPmux “UDP destination Port” field.
Jitter Buffer Overflows
The number of times an Overflow situation took place. Explanation: In steady state, the Jitter Buffer is filled up to its middle point, which means it has the space to hold an additional similar quantity of packets. Overflow is
opposite phenomenon of the Underflow, i.e., when a big burst of packets reaches the IPmux (a burst with more packets than the Jitter Buffer can store), the buffer will be filled up to its top. In this case, an unknown number of excessive packets are dropped and hence IPmux initiates a forced underflow by flashing (emptying) the buffer in order to start fresh from the beginning. An overflow situation always results in an immediate Underflow, forced by the IPmux. After the buffer is flashed, the process of filling up the buffer is started again, as explained above (“Underflow” section). An Overflow situation can be a cause of: A big burst of packets, filling up the buffer completely. The Burst itself can often be a cause of some element along the IP network queuing the packets and then transmitting them all at once. Too small Jitter Buffer configuration. When system isn’t locked on the same clock, it will lead to a situation in which data is clocked out of the Jitter Buffer at a rate different from the one it is clocked into. This will gradually result in either an Overflow or Underflow event, depending on which rate is higher. The event will repeat itself periodically as long as the system clock is not locked.
Recommendations:
Check network devices and try increasing Jitter Buffer configuration. Check system’s clocking configuration Make sure the same amount of TS for bundle is configured on each side of the IPmux application, and that the “TDM bytes in frame” parameter is identical in both IPmux units.