One Way Packet Loss

This section contains the definition of the One Way Packet Loss (OWPL), it's accuracy, some recommnedation about the sampling and the statistics which should be retrieved from the samples.

A Singleton Definition for One-way Packet Loss

The definition below is the one from the IETF IPPM RFC 2680 with some slight changes to highligths our needs (introduction of ToS and version field) .

Metric Parameters

Src, the IP address of a host
Dst, the IP address of a host
T, a time
S, a ToS value
V, the IP version field
L, the packet lenght in bits

Metric Units

The value of a One-way-Packet-Loss is either a zero (signifying successful transmission of the packet) or a one (signifying loss).

Definition

>>The *One-way-Packet-Loss* from Src to Dst at T for a given S, V and L, is 0<< means that Src sent the first bit of a packet to Dst at wire-time* T and that Dst received that packet.
>>The *One-way-Packet-Loss* from Src to Dst at T for a given S, V and L, is 1<< means that Src sent the first bit of a packet to Dst at wire-time T and that Dst did not receive that packet.

Accuracy

There is no accuracy related to it. The packet is received (valid packet) or not. From there, a distinction can be made between the various type of losses/packet invalidity.

Methodologies

Generally, the methodology would proceed as follows:

Arrange that Src and Dst have clocks that are synchronized with each other. The degree of synchronization is a parameter of the methodology, and depends on the threshold used to determine loss.
At the Src host, select Src and Dst IP addresses, Type of Service and IP version and form a test packet of with these parameters.
At the Dst host, arrange to receive the packet.
At the Src host, place a timestamp in the prepared packet, and send it towards Dst.
If the packet arrives within a reasonable period of time, the one-way packet-loss is taken to be zero.
If the packet fails to arrive within a reasonable period of time, the one-way packet-loss is taken to be one. Note that the threshold of "reasonable" here is a parameter of the methodology.

Sample

This section will present the recommendation on how to sample the packets to measure the OWPL.

The challenge here is to find out how the measurements could be significant. How many packets have to be sent to give meaningfull information without impacting the line? How log should be these test? Which "traffic pattern" should be used? (poisson distribution, predefined pattern, else)

Statistics

This section will present the statistics which have to be retrieve from the samples.

The amount of packet lost and packet loss rate during a given period of time.

What else do we want to measure here? The loss ratio for a given path. We could be interrested by measuring a loss ratio of 10^-4 over a long period. If the measurement target is O(10^-4), the amount of packet send should be 10^-5, so 10 packets loss would means a granularity of 10^-4.
Why could we target 10^-4? Because it is what some applications request this type of packet loss. Drawback, applications request on a very short period and we would only be able to monitor it on a long period without being disruptive.
Which statistics are should be presented to which user? (average, SDR, median, percentiles?) How can the statistics be added according to the distribution used? Can the evenements between domains be considered as independant? (statistics related question)

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Contact: Performance monitoring mailing list or Nicolas Simar