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Discussion Starter · #1 ·
For the past several weeks I have been experiencing very erratic DSL download and upload speed. Doesn't matter which computer or OS. I typically use Firefox. Speed will vary from 0.8 to 5.78 on download. I'm paying for 6. I use http://speedtest.net/ and other sites to check speed.

One minute speed is fine, next it's in the pits. Rebooting the DSL modem helps only for a short time and then back to the pits. Emptying out the Firefox off line storage cache has NO effect.

Had many calls to AT&T but no solution. They even sent me a new DSL modem but little to no help.

Anybody experience this? Any suggestions on why? Or how to fix?


Thanks,


RC
 

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Solar Flares - Last 2 weeks have been pretty eratic... currently we have an M3 X-Ray for 24 hours...

Check it out:
SpaceWeather.com

Patrick
 

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What version of firefox? I've had some pretty nasty freezes and slowdowns since I upgraded to the latest version.
 

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Erratic problems are the hardest to figure out. Since it happens on more than one PC we can probably rule out any PC hardware or browser problems. And you've replaced the modem so we'll assume that's not the problem. What I would do is first check to see if your packets are being fragmented somewhere along the line, and then I would use traceroute to find where any slowdown is occurring as it hops from router to router.

I would do this while the speed is good, for a baseline, and again when experiencing the slowdown to see where the problem lies.

First we'll use 'ping' to make sure the packets aren't being fragmented. I have seen on two occasions with Verizon DSL where the standard MTU of 1500 was too large and all the packets were being fragmented, really slowing things down at times.

Open a command prompt in Windows. We're going to ping with different packet sizes to find the largest value to use. We'll set the 'do not fragment' flag so it won't automatically split packets that are too large and you'll know if it makes it through in one piece or not.

There are 28 bytes of overhead included in the MTU value, so we need to deduct those when pinging for maximum size. To utilize a MTU of 1500 we need to be able to get a 1472 byte packet through without fragmenting.

At the command prompt:

ping google.com -f -l 1472
Note that is a lowercase "L", which stands for "length" (size) of packet.
If you get the message back that 4 packets were sent and 4 received then all is well and an MTU of 1500 is the best. If you get the message "Package needs to be fragmented but DF set" it didn't make it so you need to decrease the packet size. Drop down 8 bytes and use a value of 1464. Increase/decrease 2 bytes at a time until you find the largest size you can use without fragmentation. Add 28 bytes to that and you'll have the optimized MTU value for your connection. You will want to do this when speed is good, and again when speed is poor to see if there is any difference.

Next we'll use traceroute to see where any slowdowns are occurring. Again you'll want to do this when the speed is good, and again when speed is poor to find out what is changing and where the slowdown is occurring.

At the command prompt:
tracert google.com
This will give you a list of the hops it made, and the time for each. Each hop will be tried three times giving you three values for every segment.

Each line will have a hop number on the left, followed by three time values and the destination. The values will tend to be higher as you go down the list as the destination is getting farther away. A hop with one high value and two lower values is not unusual, such as 194ms - 14ms - 19ms. That's usually a traffic issue and one packet of the three took a different route to the destination. Look for entries with three high numbers, that is a slowdown. You'll get different values each time you run tracert, you want to look for trends, high or low, rather than actual values.

Armed with traceroute info on where the problem is you'll get better tech support from AT&T, as they'll assume you know what you are doing and you'll move up a level from the support guy/gal just reading off a flow chart to diagnose the problem.
 

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Discussion Starter · #6 · (Edited)
JimmyN

Thanks.

Attached is a screen print of the results.

Speedtest.net yielded 244ms ping, 3.26 Mbps download, and 0.28Mbps upload. That's the fasted I can get now.

As a one man consulting engineer I am janitor, cook, RR cleaner up, computer "expert", etc. - besides trying to do "real" work. I am now "out of my element."

Running FireFox 7.0.1

Thanks,


RC
 

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Do you have a router, or are you using the router + modem from AT&T?

Do you have DSL filters installed on ALL phone jacks? Perhaps replace those? Have AT&T send you more.
 

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Discussion Starter · #9 ·
Do you have a router, or are you using the router + modem from AT&T?

Do you have DSL filters installed on ALL phone jacks? Perhaps replace those? Have AT&T send you more.

Yes, I even disconnect the other phones. Results running directly from the DSL modem are the same as through my router.
 

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On the outside of your house in the phone connection box there is a phone plug that the phone company uses to test your line. This is a direct connection to the street line so you will not get any interference from your house wiring. Plug your modem into this connection and then test your speed again. If you see a big improvement run a new dedicated phone line for your modem. Also DSL speed is highly affected by distance the signal travels through wiring and by users online taxing the system. For instance if you live in an apartment building you will see a huge slowdown in speed when everyone gets home from work.
 

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Discussion Starter · #12 ·
On the outside of your house in the phone connection box there is a phone plug that the phone company uses to test your line. This is a direct connection to the street line so you will not get any interference from your house wiring. Plug your modem into this connection and then test your speed again. If you see a big improvement run a new dedicated phone line for your modem. Also DSL speed is highly affected by distance the signal travels through wiring and by users online taxing the system. For instance if you live in an apartment building you will see a huge slowdown in speed when everyone gets home from work.
Testing at the the phone co's box will be in the next day or two as I have meetings.

For some reason I thought DSL was less sensitive to the number of users. Anyway, we live where houses rather far apart - no apartments. I need to see where the DSL box is for our area and how far away it is from our house.

This is taking WAY too much time!

Thanks,

RC
 

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Sorry I didn't get back to you sooner, things have been really busy.

Looks like your MTU setting is good, no fragmentation of packets, so that's not an issue.

Looking at the two images you can see the difference in latency, and where it's occurring when your speed drops off. From your modem to adsl-74-177-126-1.gsp.bellsouth.net you have 8~9ms when speed is good. But that jumped up to 164~272ms when you experienced the slowdown. All values are high in the traceroute after that due to the latency between you and the office switch.

I also noticed that in one instance with 4 packets sent/received you had a minimum of 32ms and a max of 804ms over a period of only 4 seconds, it's all over the place. I would guess it's a traffic issue, could be an AT&T equipment problem, but most likely traffic. DSL degrades rapidly with both distance and additional users on the line, it just doesn't have the bandwidth of coax cable so packets have to wait rather than being sent simultaneously when traffic levels are high.

Just a little trivia on latency and bandwidth, what they actually mean, and how they interact. This is a simplistic and general explanation, but you'll get the basic idea.

Latency is the round trip time, from point A to point B and back to A. It's going to take a given amount of time for a packet to travel from the east coast to the west coast and back to the east coast, as electricity has a finite speed, and it will pass through several routers en route as well. Bandwidth is the size of the "pipe" the packets are traveling through. Low bandwidth = small pipe, and it can only handle a given number of packets at the same time.

Suppose you want to view a web page on a server a thousand miles away, and that web page will require 5,000 packets of information be requested/sent. If you only sent one request and waited for it to come back before you sent the next you would be dealing with latency only, and the web page would load very very slowly. But bandwidth can offset the latency delay. Instead of sending one packet and waiting for a reply suppose you could send all 5,000 packets at once. The latency will be the same of course, but your "speed" would increase 5,000 fold, because of the available bandwidth. You could move 5,000 packets in the same time it would take for one, so latency is not as much of an issue.

With DSL the bandwidth is limited because it's using telephone cable. If other users on the same line are also moving a lot of data there will be more packets than the bandwidth can accommodate at one time, so they are held and spooled out. The lack of bandwidth increases latency because some of your packets are spooled part of the time and going nowhere. Latency doesn't effect bandwidth, but bandwidth (a lack of it) can increase latency.

They have probably been adding customers and now the line is frequently saturated because the bandwidth is maxed out, increasing your latency dramatically. What I'd do is call AT&T. Point out that the modem has already been replaced, but you are still not getting the service you're paying for. You used traceroute to locate the slowdown and it's occurring between your modem and adsl-74-177-126-1.gsp.bellsouth.net. Latency is only 8~9ms when speed is good, but usually speed is poor and latency runs as high as 800ms. Request they put a technician on it to figure out why the latency is so high on your line as it renders the service almost unusable at times. Also request that the technician contact you to let you know what he has found, and how long it will take to correct. That will put in contact with the guy in the field actually working on it, rather than the tech support desk which is not going to solve your problem. It also lets them know that you are knowledgeable and know exactly where the problem lies, so you're beyond any BS they would normally try to feed you.

Do you know any of your neighbors to see if they are having the same problem? I'll bet they are, and it would be beneficial to have them call and complain about the high latency and slow connection as well. The squeaky wheel gets the grease.
 

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Discussion Starter · #14 ·
TommyN

Thanks so much!

Now I have something concrete to nail AT&T and get by the "gatekeepers".
 

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I am not expert in broadband but have years in LAN/WAN (T1/Frame Relay). It is my understanding of DSL that what you are experiencing is the nature of the beast and you are at the mercy of your service provider. As they add more subscribers, the net of your performance will go down, on average. Sometimes, the performance changes will be dramatic. JimmyN states this as well.

Your purchased subscription rate of 6 (Mbps?) is most likely a theoretical number based on solar flares, phase of the moon, dew point, atmospheric pressure (ok, I am joking) but the number of concurrent users will definitely have an impact on your performance at any given time. I think if you read the fine print on your contract, you will find that AT&T states this, in so many words, and it precludes them from having to actually deliver the stated bandwidth you bought. I could be wrong as I have not seen your contract, but would be shocked if they are legally bound to provide you 6 Mbps. They provision you for that rate (meaning they allow up to 6Mbps to your home), but there is no guarantee that is what you will get. By all means - call them, get them on-site, show them the latency, you may get some mileage out of them. But don't be shocked if the net result isn't what you were hoping for.

I was told to avoid this, I should use my CATV service to minimize this issue - if offered. I do have Charter in my area and have been fairly happy with them.
 

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One thing I noticed is that you are double NAT'ing. If you are going to use a third party router, like linksys o dlink or any other, you need to make sure that your AT&T DSL modem is in bridge mode, otherwise both devices, router and modem, are doing network address translation. That can cause issues.

The give away is that your first hop is 192.168.0.1 and the second one is 192.168.1.254

Google your modem model number and how to put it into bridge mode. Dslreports.com should have something on it.
 

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Discussion Starter · #17 ·
BKG-22

Thanks. One of the "gate keepers" tried to tell me 3.6 was an "acceptable" speed. I replied that it may be acceptable to her, but totally unacceptable to me when I am paying for 6. She dropped that line of bs.

We don't have cable here. Going with anything else will mean a new E-mail address which would be a REAL pia!. We have had the same address for at least 10 years. Business cards, etc. would be a pain.

Thanks for your comments.

RC
 

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BigDog[RE];18141821 said:
The give away is that your first hop is 192.168.0.1 and the second one is 192.168.1.254
You're right, I don't know how I missed that, it's right there...duh. The tracert results show less than a millisecond for that hop so it's not creating the slowdown which is occurring between your modem and AT&T, but it's certainly not the optimum setup for a home or SOHO LAN. My preference would be to use a switch rather than a second router, then you'd have your single gateway to simplify things and actually better performance on your LAN for devices connected to the switch, rather than running everything through the router.

That's the only way I can get 970+mbps transfer speeds on a 1gig LAN is by using a switch, since they work at the hardware level and just port forward via MAC address. I can't get that kind of speed running it through a router, as they operate at the network level and use IP addresses. So in my LAN setups the router only serves wireless, internet access, printers, etc, where max speed is not an issue, as the speed is limited already. All the PC's and NAS boxes are hard cabled to a 1gig switch for max file transfer rates.
 

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Discussion Starter · #19 · (Edited)
In my testing, I connected my lap top directly to the AT&T DSL Modem and the speeds were still over the place.

I do have a switch but don't I need the router for protection against attacks? Note, my router is wireless and I do use the wireless for the laptop, a Kindel, and one other computer on occasion.

I have been compiling time vs speeds before I call AT&T back. The traces always have 1 ms for the first two hops.

What do you suggest at this point?

THANKS!

RC
 

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Do you have a router/modem combo, plus another router of your own plugged into that? You need the wireless router, but it appears there are two routers in the trace between your NIC and the modem.
 
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