Losing throughput AT the modem?

DaveC426913

Gold Member
18,237
1,843
I've got Bell Sympatico (through a third party, Iristel).

I'm supposed to be getting 5Mb/s but have only gotten 3, so I started complaining until they sent a techie.

The techie showed me on his doohickey that I was was actually getting 6Mb/s to the pole, and 5 all the way to the modem.

However, when I run various speedtests, they come in at only 4.25Mb/s. Is there a reason why I would be losing .75Mb/s though the modem or router?



Wait. My upload throughput shows as .66Mb/s.
Are those additive? i.e. 4.25 + 0.66 = 4.91?
 

rcgldr

Homework Helper
8,599
485
If there is a router or router functionality within the modem, that would be changing some of the addressing data within each packet sent or received. This address changing within the packet can be an overhead depending on the design of the router / modem.

In an environment with only a single computer connected, a router or router functionality would not needed if the modem's DHCP feature assigns the external ip (the one used for internet) directly to the network connection on your computer's ethernet port. It's also possible to have a setup where the modem assigns separate external ip's addresses to multiple computers, but this is relatively expensive with DSL (the pricing with cable companies is much less).

On Windows XP, you can check this by opening a dos console window and running the command "ipconfig" to see what the ip value is.

I don't know about DSL, but in the case of my cable modem, the throttling algorithm is a bit wierd. I have "next to lowest" speed 15 mpbs download, 1 mbps upload, although there's a 20 second or so delay before any throttle kicks in. The download throttling operates as expected, but a sustained upload at 1 mbps will greatly reduce the download speed, probably from 15 mbps to 1 mbps, reducing total bandwidth to 2 mpbs. Tech support claims this is how cable modems work. So the upload case is worse than "additive".

Getting back to your question about "additive", that only happens if there's actual download and upload activity occurring at the same time. If you're just downloading a file or running a speed test (the download part), there isn't much upload activity, and you should be getting your full download speed.
 
Last edited:

DaveC426913

Gold Member
18,237
1,843
OK. So...

Should I expect 5Mb/s out if I'm getting 5Mb/s in?
 

rcgldr

Homework Helper
8,599
485
Should I expect 5Mb/s out if I'm getting 5Mb/s in?
A modem has a limited buffer size, so you can't have a sustained difference in throughput of data going through the modem (otherwise the amount of buffered data would exceed the buffer size of the modem). Something is throttling your downloads, could be the modem, or it could be your ISP (Bell).

The transfer rate between your computer and the modem will probably be 100 mpbs, but it could be 10 mbps, or 1000 mbps, depending on the ethernet speed of your computer and the modem. This shouldn't be a significant since all of these speeds are faster than the 5mbps you're supposed to be getting.

What I don't understand is what that device was that the Bell technician used to measure bandwidth. I don't understand how the transfer rate could be 6 mbps at the "pole", and 5 mpbs just before the modem, unless data packets were getting lost and had to be retransmitted. Then again, maybe there's some device at the pole that changes transfer rates, or there's overhead that accounts for the difference between 6 mpbs and 5 mbps.

This is probably a case of somewhat misleading advertising. Maybe the rate is stated at "up to 5 mbps" rather than just stating an average max download rate of 5 mbps.

You didn't mention which modem (which brand and model) you have.

I did a web search for "Bell Sympatico transfer rate" and got a lot of hits and some reviews, although most of the articles seemed old (2007 or so).

What is the fastest speed Bell Sympatico offers? This is probably the actual transfer rate between Bell Sympatico and your home. The reduced rate is a result of throttling by delaying response times.
 

DaveC426913

Gold Member
18,237
1,843
Something is throttling your downloads, could be the modem, or it could be your ISP (Bell).
It is the modem/router - not the ISP. Again, I am getting 5Mb/s to the box, so...

What I don't understand is what that device was that the Bell technician used to measure bandwidth. I don't understand how the transfer rate could be 6 mbps at the "pole", and 5 mpbs just before the modem, unless data packets were getting lost and had to be retransmitted.
That is my assumption.


This is probably a case of somewhat misleading advertising. Maybe the rate is stated at "up to 5 mbps" rather than just stating an average max download rate of 5 mbps.

What is the fastest speed Bell Sympatico offers? This is probably the actual transfer rate between Bell Sympatico and your home. The reduced rate is a result of throttling by delaying response times.
No! :grumpy:

The whole point here (and something I keep having to keep reminding Customer Support of) is:

If I were only getting 4.25Mb/s to my box, I would have no complaints. They do not guarantee 5Mb/s, so I cannot expect it.

But I am getting 5 to the box. So why would the box be the bottleneck? That's something that should be solvable.

They've sent me the latest modem, presumably with up-to-date firmware, so I'm out of ideas.
 

rcgldr

Homework Helper
8,599
485
Note that Bell Sympatico downloads some parameters to your modem that affects the throttling of transfer rate. (I don't know if there's any throttling upstream of your modem). Regardless of the actual transfer rates between your modem and the ISP hub, the modem throttles the effective download rate (by delaying responses) as programmed by Bell.

Some web sites claim that the throttling by Bell may change depending on what you download, such as torrents being throttled more than other stuff. I doubt they'd throttle any of the speed test sites though.

Sometimes you can get information from the modem by accessing some specific ip. For motorola cable modem it's
http://192.168.100.1. I don't know what it would be for you modem, but a web search for your particular modem may provide the ip you need to see configuration information, as well as more specific information about your modem.

What is the max rate possible with Bell Sympatico? This is probably the real effective transfer rate between Bell and your modem.

Some test sites:

http://speakeasy.net/speedtest

http://www.dslreports.com/speedtest

http://www.speedtest.net
 
Last edited by a moderator:

Related Threads for: Losing throughput AT the modem?

  • Posted
Replies
3
Views
3K
  • Posted
Replies
11
Views
3K
  • Posted
Replies
11
Views
4K
  • Posted
Replies
6
Views
3K
  • Posted
Replies
19
Views
1K
  • Posted
Replies
3
Views
3K
  • Posted
Replies
12
Views
7K
  • Posted
Replies
3
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top