I am an Electrical Engineer and Cisco Certified Network Professional (CCNP), and I recently upgraded my router to a Cisco Linksys e1200 Wireless-N (not draft N) router, which I later found out is not supported by Comcast, and my WiFi Internet download speeds dropped to below 0.5 Mbps until I disabled Wireless Multimedia (WMM) Support in the router's Quality-of-Service (QoS) settings which was on by default because it is required for 802.11n Wireless-N. Upload speeds were unaffected at about 3 Mbps before and after I disabled WMM Support. I also ran a Wireshark sniffer capture with WMM enabled and saw a TON of TCP retransmits and duplicate acknowledgements.
Xfinity incompatibility with WMM is a huge problem because WMM (WiFi Qos) and WPA2 security are defined in the 802.11n standard as requirements for Wireless-N (not draft N) and disabling WMM or using WPA or WEP security causes Wireless-N devices to connect at the much slower Wireless-G speed of 54 Mbps. With WMM enabled, I connect at 300 Mbps and get about 250 Mbps between devices on my local LAN, but Internet access is broken.
Xfinity incompatibility with WMM is a huge problem for people who have the 50 or 100 Mbps Xfinity plans and actually *require* Wireless-N to get the full benefit from their WiFi connected devices of the download speed for which they are paying. It is a problem for me because Wireless-G limits the speed between devices on my local LAN and does not impact my 12 Mbps Xfinity plan. But I won't upgrade my plan because 54 Mbps is Wireless G in a clean room with no interference, i.e. no walls, phones, microwaves, neighbor WiFi, solar or background radiation, etc. In reality, I get about 25 Mbps on average but sometimes as low as 10 Mbps even on a channel that none of my neighbors use and with 1.9 GHz DECT 6.0 phones that do not interfere with the 2.4 GHz WiFi band.
If you Google "Comcast slow download fast upload," you find this article and see what I mean, and that it is not just limited to Cisco Linksys routers.
I just ask that you test what I have said and connect a Linksys E900, E1200, or E1500 with a Comcast "supported" Cisco DPC3008 DOCIS 3 modem and leave WMM enabled as it comes and see what kind of Internet download speeds you get from a wireless N connected device. I gaurantee you it will be 1 Mbps or less. I suggest you install Wireshark (www.wireshark.org) on the wireless-N connected device, and run a capture while trying to access websites and another capture while downloading a large file from a wireless N or wire connected PC on the local LAN with Filezilla FTP server installed.
My sniffer capture shows end-to-end traffic between my computer and the websites I access. It is not just limited to my local network. DUP ACKs and TCP retransmits occur because TCP is an end-to-end, i.e. host-to-host, layer 4 "connection oriented" protocol that does its best to gaurantee data delivery using a 3-way handshake. Retransmits occur because of failed 3 way handshakes. DUP ACKs are sent because the receiver did not acknowledge receiving the first one. This only occurs when I access the Internet with WMM enabled. This does not occur on my local LAN with WMM enabled. I get a Wireless-N 300 Mbps connection and acheive about 250 Mbps between wireless N connected devices or 75 Mbps to a 100 Mbps wired device with no DUP AKCs or TCP retransmits.
I would suspect the router if I did not personally experience the same exact thing with three Cisco models, E900, E1200, and E1500, or did not read about similar problems with Netgear, Belkin, DLink, and others. I suggest you Google "Comcast slow download fast upload" and see the plethora of articles and forum posts that reference this same exact problem wtih other models where the only fix is to disable WMM thereby disabling wireless-N. Also see the user comments at the end of this article:
Comcast does indeed support certain wireless routers, and it is posted plainly on the main Internet support page under "Beyond the Basics" but only lists outdated equipment and does not include any of the recent Cisco Linksys "E" models including the dual band N600 models.
I do understand that but there are a not more technicallty inclined folks on these forums than on the support line. I have tried calling to explain this to them, and then I hear crickets chirping. If you have a suggestion for a better avenue, I am glad to try it.
I am just tryhing to help Comcast before you see this on an AT&T commercial. There are just so many posts on the Internet about this problem and how it is specific to Comcast, and I can't believe they don't know about it.
All new certified wireless-N routers come with WMM enabled. So every customer out there who takes Comcasts own advice to use a wirless-N router is going to see less than 1 Mbps download from a wireless-N connected device until they realize they have to disable WMM and then they lose wireless-N.
Personally, I can live with wireless-G speed because its still faster than the 15 Mbps Xfinity service to which I subscribe. Sure it would be nice to actually use my router and laptops wireless N capabilities, but its not a requirement for me. But what about those customers who subscribe to 50 Mbps or 100 Mbps service? It is impossible to get what they pay for with a wireless connection.
At what speed does your Wireless Network Connection Status say that you are connected? For Windows 7 click the WiFi bars in lower right corner hover mouse over your network and a box pops up. Is the radio type G or N? Then right click your network and left click status and it will tell you the speed at which you are connected.
Please tell me where I made a blanket statement in any of my posts. I have taken care not to do just that. I said it happens on my Internet connection with the Cisco Linksys E900, E1200, and E1500 routers that I have personally tried. And these are widley popular routers at a low cost although only operate in the crowded 2.4 GHz range.
I never said this impacts ALL Comcast customers or EVERY router in any of my posts, although I have read in many forums other than this that many people have the same issue as I have, and they all have Comcast Internet, different router makes and models in different parts of the country. One was in Washington state. I live in Georgia.
You may be right. It very well could be a bug in the routers that I have tried, but the routers mentioned in this thread including yours that are not affected are more expensive higher end dual band routers that operate in the 2.4 and 5 GHz bands that frankly the average consumer doesn't need. Not sure why dual band versus single band would matter, but the issues that I have and have read about are with single band 2.4 GHz N routers. I have yet to hear from anyone with a single band 2.4 GHz N router being able to leave WMM enabled with no download issues but would love to.
I would also love to hear from anyone specifically with a Linksys E900, E1200, or E1500 router that they have WMM enabled, connect at wireless-N speed, and have no download issues. I would also like to know what version of firmware they have. I am running the very latest. I wish Linksys would post older versions, and I would downgrade and try those, but they don't.
I am totally open to the possibility of the issue being my router, but so far the evidence doesn't suggest that. Again, only Comcast subscribers are affected. Not DSL or other cable providers customers.
i had same problem. I just bought a laptop with 802.11n adapter finally. Brutally slow download speeds on 802.11n or mixed mode wit linksys/cisco e1500. As soon as I disabled wmm QOS, download speed improved drastically. Otherwise, I had to run in 802/11b or g only to get reasonable speeds. For some reason, cisco e1500 qos wmm firmware algorithm is messed up
psmith2100 wrote: Please tell me where I made a blanket statement in any of my posts. ...
This part of your post on 8-08-2012 at 12:41 PM might be taken that way:
... every customer out there who takes Comcasts own advice to use a wirless-N router is going to see less than 1 Mbps download from a wireless-N connected device until they realize they have to disable WMM ...
But moving on, you wrote:
... I am running the very latest [firmware]. I wish Linksys would post older versions, and I would downgrade and try those, but they don't. ...
Have you tried asking Linksys?
... only Comcast subscribers are affected. Not DSL or other cable providers customers.
Have you tried hooking up your equipment to a non-Comcast internet connection? If so, what were the results? If not, why not?
I am having the exact same problem. My laptop is getting extremely low dl speeds using a linksys e1200, just switched to wireless-g to increase it. Hopefully Comcast will recognize this fault and fix it asap.
@psmith .. You're exactly right. I'm running a D-link 655, single band wireless N... a very common router (rated #7 in all of electronics at amazon).. meaning, I'm not using some offbeat, fluke device. Anyhow, same exact issues as you described. I'm a business subscriber, so this is major issue for me. The reason I do not switch to dual band, is because I would have to give up range for speed, and in my particular work environment (building) it's not feasible to trade possible speed for distance. Especially given that single band on business should be blazing fast. Thank you for your post. It did help me troubleshoot until Comcast comes around. Please update if you have any other work-arounds. By the way, I'm not certain why it's thought Comcast doesn't specify certain routers. They do. When I joined business class, they sent me the following link. Further, they said D-link was on their list (via phone) before we purchased our router. http://customer.comcast.com/help-and-support/internet/comcast-supported-routers-gateways-adapters
I think you should contact the manufacturer of the device since the issue is happening when you activate a particular piece of software. That is just the logical part of me. Although Comcast will tell you what devices it finds are compatible with it services, it can not be sure that every configuration will work. Any tech that comes to your house will demark at the back of their modem if your router is showing issues.
I've heard of several people having this issue with Cisco equipment and personally I think it is a firmware issue on their end. I've been running a D-link DIR-865L without any issues. I hear of a lot of problems with Ciscos entry level equipment anymore and if this was going into a business I don't see the reasoning for skimping out on a $45 residential router.
I had the very same problem with a CISCO E1200. I had terrible performance on my ipad and my computer which is setup with a wireless N connection. I ran wireshark on my computer and saw a huge number of retransmitted packets which was abnormal. My ipad also performed terrible and I could not watch videos without the video stopping because data was not coming in fast enough. I followed your instructions and disabled WMM and presto, no more performance problems. Wireshark on the desktop now shows very few retransmitted packets (which indicates little data lost) and performance improved considerably.I have dealt with it for over 6 months until I finally got around to doing a little research. And I found this post after a friend at work clued me in on the issue.
One would think as many problems as people have had that Comcast would work with CISCO to get this issue identified and resolved. One way to know for sure if it is the Cisco Router or Comcast is to do a wireshark capture of the traffic on the LAN side and the WAN side of the CISCO and see if packets are getting dropped by the CISCO router
I am also having the same issue with an e1200 router. I had DSL until a couple of weeks ago. When I got my new connection i did a speedtest from a wired connection and got 25Mb down and 5Mb up. From my laptop running OSX Mountain Lion and 2 iPads running IOS 5.x I tested at speeds below 1Mb up and down and was not even able to watch youtube, netflix or even get email. Once I shut off the N broadcast and selected B and G only, the devices neared the 20Mb range. Also as of note, whenI was on DSL up to a couple of weeks ago, my wireless devices matched my wired speeds when testing out to the internet.
I've seen a lot of back and forth posts that try to shift the blame around, but it's pretty clear that my router is not the issue when it works on N internally and on DSL without issues but not on Comcast.
This is very interesting, I am not as technically savy as many on this forum, but I can confirm some of the findings, when I tried to set up a Belkin router on comcast speeds were less than 1Mbps until we turned off WMM , then they went to 28 Mbps. I also have another setup with a Cisco E3200 also with Comcast as the ISP, this router is dual band and was running at around 15/4. Just for fun I turned off WMM and download speeds jumped to 20. It would seem that Comcast has a problem with WMM, does it make any sense it is far worse on single band or cheaper routers?