CANOGA PERKINS 9145ELB NID Software Version 4.01 - Manual (Page 58)

9145ELB NID Software User’s Manual Diagnostics
Latency/Jitter Test
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4.2 Latency/Jitter Test
The Latency/Jitter Test screen is used to initiate tests that measure frame delay, inter-frame
delay variation, and frame loss from the local 9145ELB to a remote 9145ELB or other IP agent.
At the Diagnostics menu, type 2 and press Enter. The Latency/Jitter Test screen (Figure 4-4)
opens.
The 9145ELB can be used to generate synthetic test traffic in order to measure frame delay,
inter-frame delay variation and frame loss. A test packet is a standard ICMP Echo Request
packet (RFC 792), with the data area containing fields for proprietary information. If the network
element responding to the Echo Request with an Echo Reply packet is a Canoga Perkins NID, it
can insert some information in the proprietary fields in the data area of the packet. If it is not a
Canoga Perkins NID, the packet will not get discarded, as it is standard ICMP. It will still get
responded to by the non-Canoga network element; however, it will contain less information
important for the Latency/Jitter test results.
Beneath the Maximum Latency and Maximum Jitter test results are the Far End P-Bit Sent/Rcvd,
Local P-Bit Sent/Rcvd, Far End DSCP Sent/Rcvd, and Local DSCP Sent/Rcvd values. This data
is used to determine if the programmed Packet Priority or DSCP was changed during the Round
Trip between the local 9145ELB and the destination 9145ELB (far end). Only a 9145, 9145E,
9145EMP, 9145ELB or 9145ELB device at the destination can provide the Far End PBit/DSCP
function.
The unidirectional path (Local to Far End or Far End to Local) on which the P-Bit remarking or
DSCP change is occurring will be identified. It is assumed that each Latency/Jitter test that is
initiated will take a particular path, so each round trip overwrites the previous round trip values.
The following values appear at the top of the screen (Figure 4-4):
Test IP Addr/VLAN The destination IP address and VLAN for the currently test or the last test
completed.
Round Trip Packets Number of completed round trips.
Test Duration The length of time the test has been running, or the length of the last test run.
Dropped Packets Number of packets sent which received no response.
Minimum Latency (ms) Time in ms for the shortest round trip.
Minimum Jitter (ms) Smallest absolute time difference between two consecutive round trips.
Average Latency (ms) Computed by adding all the round trip latencies and dividing by the
number of completed round trips.
Average Jitter (ms) Computed by adding all the absolute time differences between successive
round trips and dividing by the number of completed round trips minus 1.
Maximum Latency (ms) The highest time interval for a successful round trip.
Maximum Jitter (ms) The highest absolute time difference between two consecutive successful
round trips.
Far End PBit Sent The programmed priority value entered.
Far End PBit Rcvd The priority as it was received at the destination 9145ELB.
Local PBit Sent The programmed priority value is put back into the packet at the far end for the
return trip.