METRODATA NetTESTER FAMILY USER MANUAL
76-02-107 Rev.A
Page 124 of 133
APPENDIX A
TWAMP TECHNOLOGY PRIMER
TWAMP, Two Way Active Measurement Protocol is mechanism for measuring the
performance of a network. TWAMP uses peer to peer I
P/UDP PDU’s along with
hardware-based timestamping allowing accurate measurement of network latency
and jitter. TWAMP utilizes a Master (Generator) and Slave (Reflector) configuration
whereby
PDU’s are sent from the Generator, and are reflected back by the Reflector,
thereby allowing for the measurement of two-way (round trip) latency, and one-way
jitter.
LATENCY and JITTER MEASUREMENT
The TWAMP PDU is timestamped with the transmit time (T_tx1) as it leaves the
Generator, and is timestamped with the receive time (T_rx1) when it is received by
the Reflector. The PDU is then returned by the Reflector and is timestamped with
the new transmit time (T_tx2), and the receive time (T_rx2) by the generator. Having
the full set of timestamps enables the network round trip latency to be calculated.
Unless both Generator and Slave units have synchronized clocks, utilizing
1588/GPS etc. it is not possible to measure the one-way latency as the offset
between the two clocks is not known.
So, in this case, the total measured round-trip latency is calculated as
T_rtt = T_rx2
– T_tx1.
However, given the PDU was not instantly turned around by the reflector, it incurred
some software processing delays. This processing time is calculated as:
T_soft = T_tx2
– T_rx1
