Metrics

Time Metrics

Time metrics are related to latency, that is, the passing of time between the sending of a packet and its reception.

Packet Delay

Depending on which type of session is producing the result record (RR), a delay metric can hold one-way or round-trip data. E.g. if the session type is 1xOneWay, the metric holds one-way delay data and if the session type is eth-lb, the metric holds round-trip delay data. The max value is 16.77 seconds expressed as microseconds.

Inter Packet Delay Variation (IPDV)

The IPDV metrics are of type Inter Packet Delay Variation (IPDV). IPDV is defined as the absolute value of the difference in delay between two consecutive received packets.

Depending on which type of session is producing the result record (RR), a delay variation metric can hold one-way or round-trip data. E.g. if the session type is 1xOneWay, the metric holds one-way delay variation data and if the session type is eth-lb, the metric holds roundtrip delay variation data. The max value is 16.77 seconds expressed as microseconds.

Packet Delay Variation (PDV)

The Packet Delay Variation (PDV) metrics compare a delay percentile with the minimum delay value. Thus, it gives a view of the span between minimum delay value and the percentile. This is sometimes referred to as Real Jitter.

Depending of which type of session is producing the result record (RR), a delay variation metric can hold one-way or round-trip data. E.g. if the session type is 1xOneWay, the metric holds one-way delay variation data and if the session type is eth-lb, the metric holds round-trip delay variation data. The max value is 16.77 seconds expressed as microseconds.

Count Metrics

Count metrics hold information about number packets received and metrics derived from packet sequence numbering such as lost, reorder and duplicate.

Number of Packets and Bytes

Packet Loss

The packet loss metrics counts the number of lost packets, number of periods of lost packets and the minimum and maximum length (lost burst) of the lost periods during a result record (RR) interval.

Lost packets are counted for the following reasons:

• A packet does not arrive in RR interval N.
• A packet arrives with a larger sequence number than expected and the sequence discontinuity is not caused by reordering.
• A packet, expected to arrive in RR interval N, arrives late and reordered in RR interval N+1. Such packet is counted as lost in RR N and as tooLate and reordered in RR N+1.
• A packet expected to arrive in RR interval N, arrives late in order in RR interval N+1. Such packet is counted as lost in RR N and as tooLate in RR N+1.
• A packet arrives but is corrupted.

Examples, consider a stream of 10 packets sent as (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) during an RR interval and arriving as:

• (1, 2, 3, 4, 5, 6, 7, 8, 9, 10): No packets are lost. All packet loss metrics are 0.
• (1, 3, 4, 5, 6, 10): Packet 2,7,8,9 are lost. Number of lost packets is 4. Number of lost periods is 2. The minimum and maximum lengths of the periods are 1 and 3 respectively.

Packet Reorder

The packet reorder metric counts the number of packets received with a sequence number not earlier received and smaller than expected during a result record (RR) interval.

If a packet arrives with a larger sequence number than expected, this indicates sequence discontinuity caused by either packet loss or reordering.

Examples, consider a stream of 4 packets, sent as (1, 2, 3, 4) and arriving as:

• (1, 2, 3, 4): No packets are reordered in the stream.
• (1, 2, 4, 3): The packet with sequence number 3 is reordered.
• (1, 2, 4, 3, 3): The first packet with sequence number 3 is reordered and the second one is duplicated.

Packet Duplication

The packet duplication metric counts the number of additional identical and uncorrupted copies received. Packets are considered identical if they belong to the same session (contain identical information fields) and have the same sequence number. For IP packets, e.g. L field may vary if a duplicated packet has been routed differently. A duplicated packet is both counted as received and duplicated.

Examples, consider a stream of 4 packets, sent as (1, 2, 3, 4) and arriving as:
(1, 2, 3, 4): No packets are duplicated.
(1, 1, 2, 2, 3, 3, 4, 4): Every packet is duplicated once.
(1, 2, 3, 4, 3): The packet with sequence number 3 is duplicated.

Packet tooLate

A packet tooLate is a packet received in result record (RR) interval N+1 but is already incorrectly counted as lost in previous RR interval N.

As examples, consider a stream of 10 packets sent as (1,2,3,4,5,6,7,8,9,10) and arriving in RR interval N as (1,2,3,4,6) and in interval N+1 as (7,5,8,9,10). The packet with sequence number 5 is received reordered in interval N+1. Since the packet is already counted as lost in interval N, the tooLate (and the reorder) counter is increased in interval N+1. Here, the tooLate counter indicates the false count of lost packet in previous interval N.

Packet Field Metrics

Packet field metrics are derived from IP or Ethernet packet header fields.

Quality Metrics

A quality metric is a higher-level metric derived from one or many metrics to form a customer experience
measure.

Meta Metrics

The meta metrics holds information about the result record (RR) such as identification, status, timing, error codes and numbering information.