Slow WiFi on Comcast? DSCP issue?

[Keenan]

The below is a re-post from a thread at DSLReports.com,

There is a critical bug in Comcast's network configuration that is likely crippling thousands of routers and pretty much only Comcast has this issue. It is an edge case interaction caused by bad DSCP information coming from Comcast and poor condition handling by the WMM driver on certain linksys/cisco eseries routers and possibly others as well. This issue can appear on both stock and modded routers. Comcast's network is misconfigured and has been for years and has likely caused many people to needlessly replace fully functional routers, IPv6 speeds always worked for me because DSCP was configured correctly for that but it is incorrect for IPv4. Since the only packets with this bad information are the ones that are being downloaded upload is not affected nearly as badly. This can affect any router that uses QoS or WMM(every wireless N router has WMM)

This is the fix I made and used on an e2000 and e3000 running shibby 112:

put this in init scripts section:
insmod xt_DSCP.ko

and this in wan up scripts:
iptables -t mangle -A PREROUTING -i vlan2 -j DSCP —set-dscp 0

these may need to be modified slightly depending on configuration.

This corrects the bad DSCP header information as soon as a packet hits the WAN interface on a router.
DSCP as received from Comcast's network is 0x08 this is the lowest priority possible which WMM interpertes as being unimportant to transmit quickly.
The scripts listed changes the DSCP on all packets to 0x00 which essentially means unclassified which WMM handles properly. This is how virtually every other ISP uses DSCP and is why the issues is specific to Comcast.
I have confirmed this issue on connections in both Chicago and Boulder, CO and it is likely to be present on Comcast's entire network.
Cisco appears to have at some point released new WMM drivers for stock firmware that largely resolve the issue on current stock firmware, otherwise implementing my temp fix as a GUI option would probably be a good idea for the affected routers. The ability to assign DSCP to all traffic on chosen interfaces also might be a good thing to add anyways.

Link to full thread -> [Speed] PSA: Slow WiFi on Comcast? May be Comcasts Fault

My reason for posting is that I appear to suffer from this problem but I'm not sure how to implement the "fix" the DSLReport poster has indicated in his post. I'm figuring that a script needs to used/created in the "Run Cmd" page in the RT-N66U webgui but I want to be sure I'm using a correctly corrected script and how to implement it. I'm not a complete novice to this sort of thing but as it's been at least a decade or more I prefer to ask those that do such things every day for some guidance.

Thanks much.

Router - RT-N66W
FW - 3.0.0.4.374.38_1-em

Below is a few more links apparently related to this issue,

http://brikis98.blogspot.com/2012/02/got-slow-download-but-fast-upload.html

http://ber.gd/post/22374588073/video-streaming-net-neutrality

 

[jim769]

I'm using comcast and the n66 and have no speed issues get the same speed wired as I do wireless. And disabling WMM is not a solution I will cripple your router back to G status. Also had no issues with WMM on my linksys ea4500 and the netgear wndr4500.

 

[Keenan]

I'm not well versed in much of this at all, and apparently it doesn't happen with all Comcast subs but there seemed to be enough anecdotal evidence posted in that thread to give it a try. My wireless download speed is maybe a third of my 50 Mb/s wired speed while the wireless upload speed matches my wired upload speed.

My connection is Comcast 50/10, typically 54-55/10-12 while my iPhone 4 and Nook(Nova Launcher) Android tablet never get above maybe 16 Mb/s DL speed.

 

[L&LD]

Keenan,

Don't depend on wireless speed tests done with phones or tablets.

You need to use a laptop/desktop with better hardware and antenna inside.

Smaller, portable devices sacrifice performance too much for battery life, imo. To me; they use more battery overall this way (cpu, radio, screen, etc. is all on for longer than they need to be for a given task).

 

[Keenan]

Yes, I realize my test devices are not the best, it's just that I've always wondered why the DL speeds were always much lower on those devices than the wired computers. My laptop died back in November and I haven't replaced it yet, should have a new one in a few weeks.

As for the information posted in that thread, is there anything to it, or is it completely off the mark?

 

[L&LD]

It may just be coincidence with your downgraded wireless devices (which are simply a hardware issue and/or power management or device driver from the manufacturer issue).

I would guess that with a new laptop, this 'issue' will be limited to the much lower demands and capabilities of your portable gadgets.

Of course, you can test it and see on the small portables you use now. Any differences though does not imply only Comcast as the sole issue (otherwise, it would be visible on every device connected to Comcast).

 

[Keenan]

I just remembered I had a wireless adapter lying around so I hooked it up to the desktop, disabled/disconnected the hard line, and sure enough, the speeds are the same as the wired connection. It's only about 5' from the router but the results would seem to indicate that I'm chasing ghosts and there's nothing wrong with how the wireless is working.

Sorry for the bother, and thanks for the responses!

Jim

 

[jim769]

I just remembered I had a wireless adapter lying around so I hooked it up to the desktop, disabled/disconnected the hard line, and sure enough, the speeds are the same as the wired connection. It's only about 5' from the router but the results would seem to indicate that I'm chasing ghosts and there's nothing wrong with how the wireless is working.

Sorry for the bother, and thanks for the responses!

Jim

FWIW i dont get full speed on my tablets iPad and Galaxy only show between 30 and 36 mbps download were my desktops and laptops both show full speed . 57/11.5 comcast blast. I think your working ok and would not worrie to much about it.

 

[Keenan]

FWIW i dont get full speed on my tablets iPad and Galaxy only show between 30 and 36 mbps download were my desktops and laptops both show full speed . 57/11.5 comcast blast. I think your working ok and would not worrie to much about it.

Yes, it does seem as if everything is okay, and thanks for the input!

 

[L&LD]

I just remembered I had a wireless adapter lying around so I hooked it up to the desktop, disabled/disconnected the hard line, and sure enough, the speeds are the same as the wired connection. It's only about 5' from the router but the results would seem to indicate that I'm chasing ghosts and there's nothing wrong with how the wireless is working.

Sorry for the bother, and thanks for the responses!

Jim

No bother! I am learning just as much as you, even if I'm not on Comcast or using/depending on small portable devices for my internet fix.