WG102 - Ping Times

[GyrosGeier]

Another thing that bothers me a bit with my shiny new WG102 is that ping times over the wireless link are
suboptimal at best. The graph below shows average (blue) and maximum (red) times taken over the last day, one pixel width are approximately five minutes.



I'm not sure how these numbers can be explained, but it seems wrong to me. If anyone can provide a bit of insight, this would be greatly appreciated.

[fordem]

What are you pinging and what are you pinging it from? What type of network connects the two devices and what are the traffic levels that are flowing on that network at the time of the ping?

Ping theoretically reveals the time taken for a packet to go from host A to host B and return to host A - without knowing what type of network connects the two devices the ping times themselves are almost meaningless.

You may note that I used the word theoretically in the above explanation - the ping time also includes the time that host B takes to respond to the ping request - a fact which is frequently overlooked, but can be significant. Some network devices are programmed to place a higher priority on their function that they do responding to a ping.

As an example I have a network switch on which the ping time from a device directly attached to the switch averages 10mS - whilst a ping between devices both directly attached to the switch averages <1 mS. As traffic levels increase both response times increase, however the response time for a ping to the switch deteriorates noticeably faster - the switch processor is dedicating more and more resources to it's main function - switching.

[GyrosGeier]

Originally Posted by fordem

What are you pinging and what are you pinging it from? What type of network connects the two devices and what are the traffic levels that are flowing on that network at the time of the ping?

I'm pinging my laptop from my router, the network is otherwise idle.

The router is connected to a switch, which the AP is plugged into. If I cut out the AP and directly connect the laptop to the switch, ping times are below 1ms, as expected, however going through the WG102 they are as bad as shown in the original post.

Originally Posted by fordem

Ping theoretically reveals the time taken for a packet to go from host A to host B and return to host A - without knowing what type of network connects the two devices the ping times themselves are almost meaningless.

Just layer 2 components there -- a switch that is pretty fast (< 1ms) and the WG102.

Originally Posted by fordem

You may note that I used the word theoretically in the above explanation - the ping time also includes the time that host B takes to respond to the ping request - a fact which is frequently overlooked, but can be significant. Some network devices are programmed to place a higher priority on their function that they do responding to a ping.

Indeed, but both the router and the laptop are mostly idle at this point; also if that were relevant in that case (both are GHz-class machines :-) it'd show up when I replace the wireless link by a cable.

The only other place there could be a problem is the wireless card in the laptop, however that works fine everywhere, except for my home network, hence my belief that this is a problem that is related to the AP.

[fordem]

Can't fault your logic - what's the throughput like on wireless?

[GyrosGeier]

Originally Posted by fordem

Can't fault your logic - what's the throughput like on wireless?

Depends. A TCP stream that wants to use the full network capacity starts out at 600kB/s and then drops to 400kB/s after a few seconds. After about 10 to 15 seconds, it stalls completely, sometimes the client tries to reassociate (too many missed beacons). After about 30 seconds, it picks up for another ten seconds. In total, I get about 20kB/s.

VoIP and Internet radios work fine though, although there is a certain delay that is slightly unnerving in phone conversations (phone service at my place is through SIP only -- ping time over DSL to the SIP proxy is 8-15ms, depending on load, so the delay on the wireless is indeed noticeable).