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NE20E-S2 V800R010C10SPC500 Feature Description - System Monitor 01

This is NE20E-S2 V800R010C10SPC500 Feature Description - System Monitor
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TWAMP Fundamentals

TWAMP Fundamentals


The Two-Way Active Measurement Protocol (TWAMP) defines a method for measuring round-trip IP network performance between two TWAMP-capable devices. Figure 7-1 shows how TWAMP is implemented.
  • The performance management system instructs the control-client to establish a test session with a specific TWAMP server.
  • The control-client establishes and completes the test session.
  • The performance management system collects statistics during the test are saved.
Figure 7-1 TWAMP implementation

TWAMP collects statistics about the delay, jitter, and packet loss rate.
  • The delay and jitter are calculated based on timestamps. The session-sender sends a probe carrying a sending timestamp T0, and the reflector replies with a response probe carrying a receiving timestamp T1 and a responding timestamp T2. After receiving the response probe, the session-sender records the receiving timestamp T3. The delay and jitter during a single period are calculated based on the four timestamps.
  • The packet loss rate is calculated based on the serial numbers (starting from 0) carried in probes. The session-sender sends a probe with a serial number, and the reflector replies with a response probe with the same serial number. Each time the session-sender sends a probe or the reflector replies with a response probe, the serial number increases by 1. The packet loss rate is calculated based on the two rows of serial numbers.

Intercommunication Model

TWAMP uses the client/server mode and defines four logical entities, as shown in Figure 7-2.
  • Control-client: establishes, starts, and stops a test session and collects statistics.
  • Session-sender: proactively sends probes for performance statistics after being notified by the control-client.
  • Server: responds to the control-client's request for establishing, starting, or stopping a test session.
  • Session-reflector: replies to the probes sent by the session-sender with response probes after being notified by the server.
Figure 7-2 Typical TWAMP logical architecture

To facilitate implementation, TWAMP unifies the four logical entities, as shown in Figure 7-3. Control signals are exchanged between the control-client and server through a TCP connection; probes are exchanged between the session-sender and session-reflector through a UDP connection. The control-client and server establish and start a test session. Once a test session starts, the control-client and server notify the session-sender and session-reflector respectively of the session information and allow the session-sender to send probes and the session-reflector to respond to the probes.

Figure 7-3 Typical TWAMP implementation architecture


On a live network, if a network element (NE) functions as a server and session-reflector alone, the NE participates in TWAMP session establishment and probe exchanges but does not compile statistics. If a device or tester functions as the control-client and session-sender, the device or tester proactively establishes a TWAMP session for statistics collection. Users manage the control-client alone to rapidly obtain statistics about the performance of the entire IP network.

Updated: 2019-01-02

Document ID: EDOC1100055478

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