We have been investigating what seems to be an obscure issue with
regards to Comcast speeds wired vs. wireless "G" speeds on a 30/5
circuit.
Here are the symptoms:
Wired (directly to modem): Speeds are what one would expect - 25-30
Mbps down and 4-5 Mbps up.
Wireless: Speeds are in the 6-9 Mbps. We have tried a variety of
consumer and higher end APs/Wireless routers. All with the same basic
results - the speeds are significantly slower.
- The wireless NIC was connected with a "good" signal at 54 Mbps.
- I verified that wireless interference was not an issue.
- I tried several different laptops to make sure that the
particular wireless NIC was an issue.
- The AP/Router were the only items on the circuit. Time of day
did not matter as I tried going back and forth between wired and
wireless - both produced consistent speeds each time.
What we did discover is that when testing the same equipment on a
cablevision/optimum online 30/5 circuit, the problems virtually
disappear. Wired speeds are equivalent to Comcast but wireless speeds
were in the 15-19 Mbps range.
In order to dig deeper, I captured wireshark traces for both
wired/wireless on Comcast and Optimum Online circuits. The biggest
difference I could find is that on the Comcast circuit both wired and
wireless, there were many: TCP Dup ACK packets (see below for an
example)
TCP [TCP Dup ACK 17802#55] http > apc-3052 [ACK]
Seq=8154484 Ack=307815 Win=206848 Len=0 SLE=370595 SRE=447975
SLE=331175 SRE=335555
I have seen the "tcp optimizers" and they have produced good results
and have improved the Comcast speeds to 12-16 Mbps but it seems very
odd that only Comcast seems to suffer from packets arriving out of
order (or whatever is causing this) but Cablevision does not. I don't
like the idea of having to change a client device when it seems like
this problem lies within the Comcast network.
Has anyone seen this before? Is there a solution without changing the
client laptop? We would like to have a solution that is hardware based
(router or firmware) rather than telling users they must all make
registry changes which makes us nervous (liability) and end-users
irritated that "it works on other networks without a problem"
Any insight on this would be greatly appreciated.
Will Howard
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