Latency between LAP and clients

terry-norris · ‎08-03-2011

I am having an issue where I am seeing high ping times to wireless clients. Pings are normal to all intermediate (router, switch, AP) devices. The latency appears to be between the AP and the wireless client. Here are some ping results from one client across the network to a wireless client:

Reply from 10.x.x.x: bytes=32 time=839ms TTL=125

Reply from 10.x.x.x: bytes=32 time=862ms TTL=125

Reply from 10.x.x.x: bytes=32 time=886ms TTL=125

Reply from 10.x.x.x: bytes=32 time=34ms TTL=125

Reply from 10.x.x.x: bytes=32 time=1032ms TTL=125

Reply from 10.x.x.x: bytes=32 time=34ms TTL=125

Reply from 10.x.x.x: bytes=32 time=1045ms TTL=125

Reply from 10.x.x.x: bytes=32 time=1032ms TTL=125

Reply from 10.x.x.x: bytes=32 time=34ms TTL=125

Reply from 10.x.x.x: bytes=32 time=1045ms TTL=125

Reply from 10.x.x.x: bytes=32 time=36ms TTL=125

Reply from 10.x.x.x: bytes=32 time=1046ms TTL=125

Anyone experience this before? Thoughts?

The environment consists of WLCs running software version 7.0.98.0 and AIR-LAP1252AG-A-K9 APs running 12.4(23c)JA (802.11a/n and b/g/n).

Leo Laohoo · ‎08-03-2011

Things to consider:

1. Try pinging from client to the AP.

2. Link from AP to switch? Gig, FastEthernet? Duplex setting? Auto of Half-Duplex?

3. Radio interferrence - too much 2.4Ghz in the area? Try 5.0Ghz.

4. How many clients are currently connected to each AP? >25 clients per AP? This is too much.

Nicolas Darchis · ‎08-04-2011

ping is NOT a reliable latency measuremetn for wireless.

This brings the question "do you have a real issue ?" "do you notice latency other than in a ping ?". If not, then nevermind. If yes, then forget about ping and wonder where the latency comes from.

terry-norris · ‎08-04-2011

Nicolas,

Thanks for the reply, but could you elaborate on why ping is not a reliable latency test for wireless?

Nicolas Darchis · ‎08-04-2011

Wireless clients very often go to sleep after transmitting a frame.

A ping request it not considered important by most clients, so they won't wake up to reply to it.

Typtically if you start a very heavy FTP transfer on the client, the ping will show much better latency : because the client is sleeping much less.

But as Leo mentioned before, if your client is already awake, another explanation would be high amount of traffic or interference which means lots of retransmissions.