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IP network troubleshooting 51

TLAN packet loss errors

The VGMC/Signaling Server software contains detection mechanisms

for RTP packet loss. The impact of packet loss varies, but even single

lost packets can cause audible clicks, while high packet loss sounds like

choppy speech or periods of silence. Packet loss is usually due to a router

discarding the RTP packets when the network is busy.

Two types of messages are printed. The first type prints whenever the

software detects missing packets in the incoming RTP packet stream. The

following example warns that two incoming packets were lost at one time

for the call on channel 0. This type of detection is not available with the

SMC microengine architecture.

SEP 22 11:05:49 tRTP: Info SML GAP in RTP seqNo chan 0 (recd: 22802,

expect: 22800, sending 1001, gap 2, tick 98400)

The second message type prints a summary at the end of a call showing

the percentage of packets lost for that call in each direction (indicated in

the message as Receive [RX] or Transmit [TX] from the card perspective).

This message also generates an SNMP alarm.

In the following examples, the VGMC determined that 6.4 percent of the

incoming (received) packets on channel 0 were lost, while the IP Phone

reported 6.6 percent of the outgoing packets from the VGMC were lost.

The percentage is of the total RTP packets transferred for the call, so

depending on the call duration, the percentage of packet loss can have

varying degrees of impact. One to two percent is likely to be noticed and

usually 5 percent or more indicates choppy speech at some point in the

call.

Example: TLAN packet loss is reported for both IP to IP and IP to TDM

calls.

SEP 22 11:17:48 tRTP: Warning ITG4028 Voice packet loss: 0

6.4% rx 47.147.75.80 (26)

SEP 22 11:17:50 tVTM: Warning ITG4028 Voice packet loss: 0

6.6% tx 47.147.75.81 (26)

In this example, the first parameter (0) is the channel number, if the

reported packet loss is in Receive (RX) direction. This parameter is always

0, if the reported packet loss is in the Transmit (TX) direction. The second

parameter (6.4 percent) indicates the percentage of total RTP packets

transferred that were lost. The third parameter (Receive [RX] or Transmit

[TX]) is Receive (RX), if VGMC reports packet loss, or tx, if the IP Phone

reports packet loss. If reported packet loss is in the Receive (RX) direction,

the fourth parameter (47.147.75.80) is the IP address of the VGMC whose

Nortel Communication Server 1000

Troubleshooting Guide for Distributors

NN43001-730 02.02 31 December 2009

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