We can find all kinds of topics regarding WiFi dropout issue on OS X and someone may suggest standard procedure to get around this. For WiFi settings, Apple would like to stick to standard MTU size at 1500 bytes for Ethernet network. But, why?
With WiFi connection, we can do a ping test like this:
$ $ $ ping -D -s 1500 google.com PING google.com (203.5.76.246): 1500 data bytes ping: sendto: Message too long ping: sendto: Message too long
Note:
Option -D suppresses fragmentation for the packet (force to transmit whole packet at a time)
Option -s 1500 specify the packet size, i.e., 1500 bytes
Problem is there is an overhead added on top of packet size for every transmission. That is why we get 'Message too long' responses from there.
To rectify this problem, let's do the math:
Optimum MTU size = Packet size + Overhead
What about the overhead? The overhead would be 28 bytes because 20 bytes are reserved for the IP header and 8 bytes must be allocated for the ICMP Echo Request header.
So, maximum packet size permitted in each network packet is actually:
Optimum MTU size = Non-fragmented Packet size + 28 bytes
Here we say MTU size will theoretically be 1500. Packet size allowed would be
(1500 -28)=1472 bytes
But, is it practical? Let's test this.
To test this magic number, issue the following command in Terminal:
$ $ $ ping -D -s 1472 google.com PING google.com (203.5.76.246): 1472 data bytes 1480 bytes from 203.5.76.246: icmp_seq=0 ttl=56 time=7.787 ms 1480 bytes from 203.5.76.246: icmp_seq=1 ttl=56 time=4.838 ms 1480 bytes from 203.5.76.246: icmp_seq=2 ttl=56 time=4.360 ms 1480 bytes from 203.5.76.246: icmp_seq=3 ttl=56 time=6.184 ms
Packets are now transmitted successfully with this payload (1472). Therefore, we can be sure the optimum MTU payload size would be 1500 (luckily a theoretical value this time) just for this particular WiFi network.
With no fragmentation happening, each packet should be theoretically transmitted as a whole and not broken in parts. This can improve the network speed effectively in an ideal signal condition.
Just remind that the size of payload can be different across various locations and wireless routers. You might need to find the smallest optimum payload which sits within the size range of successful transmission for most networks you'll be connecting, either at home or office. Try stepping down the value until you find transmission works for all the networks you have tried.
Apply this payload value in Network settings panel and hopefully it'll help reduce the number of WiFi dropout and improve the WiFi network speed.
