CLI-based Configuration Guide - Network Management and Monitoring

Related Concepts

TWAMP Light includes two modes: on-demand and continual.

• On-demand measurement: indicates that performance measurement is started manually within the specified time range aiming at network fault diagnosis. It is a one-off measurement in the diagnosis period.
• Continual measurement: indicates the measurement is performed continuously.

TWAMP Light Working Mechanism

To perform TWAMP Light performance measurement, you need to create a measurement service first.

1. Measurement service creation

   Figure 14-1  TWAMP Light measurement service creation
   

   In Figure 14-1, the controller is the sender and responder is the reflector.

   1. The controller creates a measurement session based on the local IP address, responder's IP address, local UDP port number, responder's UDP port number, and VPN instance name.
   2. The responder creates a measurement session based on the controller's IP address, local IP address, controller's UDP port number, local UDP port number, and VPN instance name.
   3. The controller starts performance measurement in on-demand mode or continual mode. After the measurement starts, the controller sends a TWAMP-Test packet of the UDP type to the responder. The TWAMP-Test packet carries the packet sending time and sequence number.

      The start mode decides the measurement mode. If on-demand measurement is used, performance measurement is started manually within the specified time range aiming at network fault diagnosis. It is a one-off measurement in the diagnosis period. If continual measurement is used, performance measurement is non-stop.

   4. The responder replies to the TWAMP-Test packet sent by the controller. The returned TWAMP-Test packet carries the packet receiving time stamp, response time stamp, and sequence number. The responder does not generate a sequence number. Instead, it copies the sequence number in the TWAMP-Test packet sent by the controller.

      The responder calculates the performance indexes such as bidirectional packet loss rate, delay, and jitter based on the sequence numbers and time stamps in the TWAMP-Test packets.

2. Performance measurement

   TWAMP Light defines TWAMP-Test packets in two directions:

   • Test-request: packet sent from controller to responder.
   • Test-response: packet sent from responder to controller.
   Figure 14-2  TWAMP Light performance measurement
   

   In Figure 14-2, after a measurement service is created, the TWAMP-Test packets are used as the probes for performance measurement and the packets use the pre-defined measurement session IP address and UDP port number. The controller sends a TWAMP-Test packet. After receiving the packet, the responder returns the Test-response packet to the controller. The controller collects statistics on TWAMP measurement. The performance measurement process is as follows:

   1. After receiving the Test-response packet from the responder, the controller calculates the bidirectional packet loss rate, delay, and jitter based on the sequence number and time stamp in the packet.

      Delay

      The delay is calculated based on time stamps. The TWAMP-Test packet sent by the controller carries the sending time t1, the TWAMP-Test packet sent by the responder carries the receiving time t1' and reply time t2', and the TWAMP-Test packet received by the controller carries the receiving time t2. The delay is calculated based on the four time stamps.

      Delay1 = t2 - t1- ( t2' - t1')

      Jitter

      The jitter is calculated based on the absolute delays in neighboring measurement intervals.

      Based on the preceding delay formula, the delay in the neighboring interval is Delay2 = t4 - t3 - (t4' - t3').

      Jitter = | Delay2 - Delay1 |

      Packet loss rate

      The TWAMP-Test sent by the controller carries a sending sequence number, but the responder does not generate a sequence number. Instead, the responder copies the sequence number in the TWAMP-Test sent by the controller as the response sequence number. The packet loss rate is calculated based on the numbers of sent and received packets.

      Packet loss rate = Number of lost packets/Total number of sent packets

   2. The controller reports the performance statistics to the NMS, and you can view the statistics on the web system.

      In different modes, the controller reports statistics to the NMS as follows:

      • Continual measurement: The controller reports statistics to the NMS through the Performance Monitoring (PM) module.
      • On-demand measurement: The controller reports statistics to the NMS through MIB.