I'm encountering latency trouble with my 15" 2011 Macbook Pro (running 10.6.7) when on an 802.11n (5GHz) wireless network hosted by a Time Capsule (version 7.5.2). When I ping the Time Capsule, the ping numbers are all over the place, like so:
64 bytes from 10.0.1.1: icmp_seq=216 ttl=255 time=3.461 ms
64 bytes from 10.0.1.1: icmp_seq=217 ttl=255 time=236.725 ms
64 bytes from 10.0.1.1: icmp_seq=218 ttl=255 time=157.924 ms
64 bytes from 10.0.1.1: icmp_seq=219 ttl=255 time=79.511 ms
64 bytes from 10.0.1.1: icmp_seq=220 ttl=255 time=1.295 ms
64 bytes from 10.0.1.1: icmp_seq=221 ttl=255 time=0.833 ms
64 bytes from 10.0.1.1: icmp_seq=222 ttl=255 time=150.669 ms
226 packets transmitted, 226 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.718/115.353/303.004/96.717 ms
The location of my computer doesn't seem to matter. My signal shows up consistently at four bars, and I get the same ping results whether I'm in a different room, different floor, or right in front of the Time Capsule.
A second 15" unibody Macbook Pro (Mid 2009, also running 10.6.7) doesn't have this problem on the same network. All pings to the Time Capsule from this second machine report <4 ms.
If I connect my computer via ethernet to the Capsule, I get a solid <1ms ping, as expected. Only the wireless appears to have wild jumps.
I have tried resetting my network settings (deleting all network configurations from the library), disabling IPv6, changing my "Network Location", resetting the PRAM, resetting SMC, recycling power on the Time Capsule, but none of it seems to have had any effect. I've tried to make sure I have no programs running in the background – Software Update has been turned off and running lsof -i on Terminal only reports SystemUIS as having two open IPv4 connections. There is also no significant network traffic taking place, so it's not a matter of congestion.
Any ideas on something else I can try? I'm sort of at a loss as to why one computer is fine and this one is not.
Best Answer
Edit: Apple released two updates for the MBP this week, including an EFI update. While neither update explicitly mentioned wireless connectivity, the update seems to have partially fixed the problem. After installing both updates, I get a pretty consistent 3-5 ms ping with a very very occasional spike to 100. At least it's much better than before.
In the meantime, the trick below still works if you want a 1 ms response instead.
There's an interesting tip from someone on Apple's discussion forums that can work as a workaround.
It appears that if the network card is inactive for more than 200 ms, it powers down and has to be powered up to send network traffic again, hence the random spikes. But, if you can keep the network card active (at the cost of a small amount of CPU power and some extra traffic), then the latency goes away.
The command recommended by seanfromcolumbus was:
sudo ping -i .2 192.168.1.1(The -i .2 specifies an interval of 200 ms)
Indeed, with this running, I get consistent results of <2 ms.
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