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[WLC/WLA] Calculating rfping output on WLC controllers

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Summary:

This article explains how to calculate round trip time (RTT) by using the rfping output in WLC, which can be used to diagnose any network connection issues.

 

Symptoms:

RTT and rfping can be used to troubleshoot the following symptoms:

  • Intermittent wireless connection
  • Latency in the wireless network

  • Slow wireless connection

 

Solution:

Packet round trip time (RTT) is calculated in the following way:

  • For the first packet, the round trip time is the time of ACK reception minus the time that the packet was enqueued.
  • For the second and subsequent packets, RTT is the time of ACK reception of the current frame minus the time of ACK reception for the previous frame.
  • Because all the packets are enqueued at the same time, it is not possible to compute RTT from the packet-enqueue time for any packets other than the first packet.

For example:

WLC2800# rfping mac 64:27:37:aa:94:21

RF-Link Test to 64:27:37:aa:94:21
Session-Id: 119
Packets Sent  Packets Rcvd    RSSI     SNR    RTT (micro-secs)
------------  ------------   -------  -----  ----------------
          20            20      -42     52        241         

 

From the above “rfping” output:

  • Note that 20 ping packets were sent.
  • Now check whether 20 acknowledgement (ACK) receptions were received for these packets.
RTT is calculated based on the reception time of ACK of the ping packets. The overall average RTT of these 20 ping packets is shown in the rfping command output in WLC.

 

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