Introduction to TWAMP testing

Netrounds supports the use of TWAMP Light for measuring two-way (and in part also one-way) loss and delay.

TWAMP is short for "Two-way Active Measurement Protocol" and is defined in IETF RFC 5357. TWAMP is based on OWAMP (One-way Measurement Protocol, IETF RFC 4656), to which it adds two-way measurement capabilities.

The difference between TWAMP Light (defined in Appendix I of RFC 5357) and "normal" TWAMP is that the Light version does not require support for the TWAMP control protocol, which performs a handshake between initiator and reflector.

When used for TWAMP testing the Netrounds Test Agent is typically placed in the core part of the network, or in the data center, and initiates UDP streams towards TWAMP-capable routers or other devices. These reflect the streams back to the Netrounds Test Agent, which collects measurements and calculates various network KPIs.

The main benefit of the above setup is that you can activation test, monitor, and troubleshoot your network end-to-end without the need for a dedicated test device at the customer site. This saves time and money. The downside compared to using a Netrounds Test Agent at both ends is that the testing capabilities are more restricted.

Although TWAMP is a two-way measurement protocol, it is still possible to measure one-way packet loss, that is, separate loss values for the forward and backward directions. This is possible since the reflector places its own sequence number in the packet. In fact, the loss values are always one-way, and the loss threshold always refers to one-way loss.

The formula used to calculate forward and backward packet loss is aligned with the ITU-T Y.1731 standard. This has the consequence that duplicates and misorders can give rise to negative loss values.

The reflector also places its own timestamps in packets, so it is possible to measure one-way delay and delay variation. This is enabled by setting the Time sync input parameter to Yes. However, for this measurement the sender Test Agent and the reflector must have their clocks synchronized. Round-trip delay is measured in this case, too; however, when time sync is enabled, the delay thresholds are applied to one-way delay values rather than to round-trip delay.

Test Agent capabilities

Preinstalled Test Agents (installed on hardware by Netrounds) support from 100 to 10,000 concurrent streams in TWAMP testing, depending on the hardware used.

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