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Slow speeds for non-comcast network traffic

Slow speeds for non-comcast network traffic

My customer recently had the Business class 75/15 service installed. It took 3 weeks to get a reliable connection to the comcast network. Now, when testing speeds using the comcast speedtest tools, everything looks great (95% of rated speeds).


However, using off-network tools, such as or megapath, the speeds are awful. Awful, as in < 5% of the rated download speeds. This suggests that there are issues with the comcast equipment/connectivity at the NAP, and NOT with my customers CPE.


General 'internet' performance, and inbound data speeds are unacceptable.


Rather than just rant about the problem, I would like to ask the community of they have had similar probems, and what effective methods they used with comcast to achieve resolution.

My customer is located in a brand new service area in Chicago, which might contribute to the issues. I would be inclined to think that Comcast would appreciate the detailed feedback and troubleshooting and network improvement consulting that I have, in effect, been providing to them for free. It will result in a better product and a higher level of satisfaction for new customers, which can only be good for their buinsess.


Any comcast folks are free to chime in, but I am really interested in simply getting my customer problem solved.

Thanks !

Forum Contributor

Re: Slow speeds for non-comcast network traffic

Are we talking upstream or downstream speeds?


IMHO the downstream speeds are pure unadulterated electronic BS.  Think for a minute if everyone on the Internet had 75MB down.  Think of how many people there are on the Internet.


Here is a table of speeds of circuits:


Comcast's backbone is 40G.  There is a picture of it here:


There are 8 backbone links coming into it.  40G / 75Mbt = 533 users per link X 8 links that's a grand total of 4,264 subscribers.  Chicago's population is 2.7 million people.  Somehow I think that Comcast has more than a tenth of a percent of the Chicago's populaiton as subscribers.


But you can have some hope because Comcast is working on upping their backbone to 400G.  So then instead of a tenth of Chicago's pupulation maxing them out, only 1% of Chicago's population would be able to max them out if everyone was all hammering on their links at the same time.  (like for if example everyone decided to stream the SuperBowl over their Comcast links)


And this is just assuming downstream speeds.  The downstream speeds have to come from somewhere.  Well they come from other people's servers that have - you gessed it - limited UPSTREAM speeds.


In summary, downstream speeds are lies designed to sell service to people who are looking at other carrier's lies.


Basically what you want to so is since it's not doing it for you, call customer support and knock the speed down to the next tier.  And see if that makes any difference.  Most likely it won't.  Then keep doing that until it does make a difference and that's the point that your gonna get the best bang for the buck

Re: Slow speeds for non-comcast network traffic

Thank you for taking the time to reply, however none of this information is helpful to me in solving my problem. I am more than aware of the techical aspects of network delivery and I did not request an irrelivant lecture.

Forum Contributor

Re: Slow speeds for non-comcast network traffic

Your not getting any help from anyone because you are insisting that you have a problem - then ignoring the proof that you DON'T have a problem.


As I said, the concept of everyone getting 75Mb downstream all the time on Comcast's network is rediculous even considering it with just Comcast's own network - which should be the highest speed.


The idea that you would get 75Mb downstream on a regular basis from networks external to Comcast is even more rediculous.


The majority of web servers on the Internet are not paying for the connectivity that would allow them to transmit 75MB to a user, even if that user was the only user on the site.  You aren't even paying for that yourself.  (or your customer is not)


Yet you appear to be expecting it.  That is the problem.


If you want to go searching for a technical problem - which would be a wild goose chase most likely - then I will say this:


Sites on the comcast network are "close"  Meaning that your RTT times to them would be low - maybe under 30ms


Sites on "the internet" external to Comcast are going to be many more hops away - 50-100ms or greater.


As a general rule, the higher the RTT a TCPIP link has, the more sensitive it is to packet loss.  Such as, packet loss from ethernet duplex mismatches, etc.


What this means is that you could have an ethernet duplex mismatch in your gear that would be dropping 50% of your packets yet still get good throughput on sites with low RTT times - but the higher RTT destinations would take a terrible throughput beating.


Other forms of packet loss exist - a slow CPU in your router, etc.


Anyway, please be realistic in your expectations.  75MB on a regular basis from sites external to Comcast's network is absolutely unrealistic.  Maybe at night, 2am, when activity is low, you will get this from the major sites like CNN.COM, Ebay, Amazon, etc.  But not from smaller sites.


Re: Slow speeds for non-comcast network traffic

Again, none of this information is relevant to the problem, of which you are not aware of any of the technical details or history. I appreciate what you are saying, but you are simply barking up the wrong tree here. Your shotgun approach of spewing details about service delivery and network operations without understanding the problem immediately disqualifies you from being a productive member of this discussion. The entire point of my original post, since you obviously missed it, was asking for community advise on ways to effectively engage comcast to work with me on the problem. And, despite everything you have written, my request has simply gone unaddressed.


As for having a reasonable service expectation, I expect better than sub 5Mb service with an average 30% packet loss and approximately 3400 frame errors per 24 hour period (at the comcast router). On top of that, there are latency issues (>2000ms) which result in packets timing out, which is having a disasterous impact on basic service use.


Using your approach to logic, I should be happy that the electric car I drive gets 50 miles per charge, even though it is rated for 300 miles, because road conditions change, and there are pedestrians everywhere, and  occasionally a guy with a blue shirt walks by, and sometimes it gets cloudy, and ...


Also, I have been working directly with the network support group and we are working on the issue.