How do I decrease excessive network buffering over Wireless-N I've got a mid-2009 Macbook Pro running Lion over 802.11n with an Airport Extreme and cable internet. I've been seeing drop-outs while using video chat (be it Facetime, Skype, Google Chat) and doing anything else (gaming, Hulu, Netflix, etc) on the network.

I ran ICSI's Netalyzr and found that the network buffering was 4000ms upstream and 3200ms downstream, which is abysmal. Running the same test on my Windows 7 machine (over 802.11b) results in 220ms upstream and 1800ms downstream.

Aggravatingly enough, when I switch my Macbook to 802.11b, Netalyzr fails to complete. I initially chalked this up to a bad test, however, video still drops out and a ping somedomain.com in the background will show progressively increasing RTT's and packetloss.

No such deficiencies exist on my Win7 desktop.

I was unable to find any option under network preferences, and searches only brought up complaints about buffer-bloat without specifics. How do I "improve" the buffering behavior under Lion?
I don't have any specific recommendations when tweaking network configurations. However, I did come across one blog post that discussed various network settings that could be adjusted in /etc/sysctl.conf:


kern.ipc.maxsockbuf=4194304
kern.ipc.somaxconn=512
kern.ipc.maxsockets=2048
kern.ipc.nmbclusters=2048
net.inet.tcp.rfc1323=1
net.inet.tcp.win_scale_factor=3
net.inet.tcp.sockthreshold=16
net.inet.tcp.sendspace=262144
net.inet.tcp.recvspace=262144
net.inet.tcp.mssdflt=1440
net.inet.tcp.msl=15000
net.inet.tcp.always_keepalive=0
net.inet.tcp.delayed_ack=0
net.inet.tcp.slowstart_flightsize=4
net.inet.tcp.blackhole=2
net.inet.udp.blackhole=1
net.inet.icmp.icmplim=50



You'll definitely want to back up the original file before fiddling with these system settings. Various readers also contributed to a lengthy discussion in the comments for the blog post.

Apple Support also has a KB for OS X 10.7 detailing changes that can be made to the MTU for Ethernet, which might also be adjusted for performance issues. However, there were no specific instructions for Wi-Fi.

There's an associated Support KB for older versions of OS X (10.4 and 10.5) that details changes for both Wi-Fi and Ethernet - you may be able to apply use the Wi-Fi instructions in Lion.

If you take the first path (adjusting the sysctl.conf settings), some trial and error may be necessary.