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Simple Network Download Question

Posted: Sun Jun 05, 2011 3:40 pm
by JerryFreilich
I have a very simple question for all you networking geeks. Should be simple anyway. Tell me this.... Sometimes I begin to download a file which Safari's "Download Progress" window shows as coming down at me at 600-700/Kbs. I think that's pretty fast. But over the next 2-3 minutes while the file is coming down, that progress can slow down to 140 Kbs or even 90 Kbs. Not good. If I click the "stop download" button and then click the "resume download" button, the download starts again and may jump back up to 400 or even back to 600 again and all seems well. But then it slows down again.

Through experiment, I've found that if you don't touch the thing that it can, sometimes, slow down and speed up again without any intervention. Most of the time, however, the slowdown remains slow and the file gradually and painfully completes downloading at some very low speed. Sometimes I can go into the DHCP control panel and "renew the lease" and that will speed things up. But it is most often that files will slow when downloading.

I have internet service through Wave Broadband and The fact that files CAN come down very fast suggests to me that my computer is capable of handling that speed and that the lines between the ISP and my house are capable of providing the material that fast.

So my question is -- how do you troubleshoot the situation? How do I discover whether the slowdown is at the content's origin? At the ISP? Or someplace in between? There must be some combination of network tracing software (probably already on the Mac) that can reveal the number of packets and speed of the packets at each link in the process. Do any of you have experience with troubleshooting this stuff?

And the bottom line.... Is there anything I can do about this?

Re: Simple Network Download Question

Posted: Sun Jun 05, 2011 5:43 pm
by Jay Cline
It's likely a router or server along the way hits a bottleneck. When downloading or uploading files your computer says "send the data." A router somewhere along the line is busy and can't respond fast enough so packets being passed back and forth are slowed down. You can think of like this: the routers are negotiating the speed which they can send and receive. Sometimes the issue resolves by itself and sometimes sending and receiving packets stop altogether. I've seen this happen when sending large files to one of our ftp sites.

In your Utilities folder use Network Utility and "Ping" and "Traceroute" to find errors. Use "Ping" to see if the host computer is on the internet. The IP address for is

Ping has started…
--- ping statistics ---
20 packets transmitted, 20 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 15.880/20.143/31.190/5.129 ms

This stuff can be very boring, sounds like a SMUG meetingImage

"When you enter the traceroute command, the utility initiates the sending of a packet (using the Internet Control Message Protocol or ICMP), including in the packet a time limit value (known as the "time to live" (TTL) that is designed to be exceeded by the first router that receives it, which will return a Time Exceeded message. This enables traceroute to determine the time required for the hop to the first router. Increasing the time limit value, it resends the packet so that it will reach the second router in the path to the destination, which returns another Time Exceeded message, and so forth. Traceroute determines when the packet has reached the destination by including a port number that is outside the normal range. When it's received, a Port Unreachable message is returned, enabling traceroute to measure the time length of the final hop. As the tracerouting progresses, the records are displayed for you hop by hop. Actually, each hop is measured three times. (If you see an asterisk (*), this indicates a hop that exceeded some limit.)"

Re: Simple Network Download Question

Posted: Sun Jun 05, 2011 8:26 pm
by Stephen Hart
I would add two things:
1. Many times, slowdowns arise at the server. Apple often gets hit with huge numbers of requests, and can be slow. A day or so later, it can be fine.
2. Don't trust the time-to-completion displays. Today, I started an Adobe download of a plugin. I came back hours later and found the display showing 36 hours to completion, or something like that. Turns out I needed to quit Photoshop. Then the download started again and the display quickly changed from 36 hours to 24, then 12, 5, 1, 10 minutes, 5 seconds, etc.

Re: Simple Network Download Question

Posted: Sun Jun 05, 2011 9:41 pm
by JerryFreilich
So you're suggesting that TraceRoute is the tool of choice? And will I be able to understand which of the various "nodes" of the complete circuit (from the sender thru the ISP to me) is which? A tiny more of an example would help me because I've tried this before and not understood the results.

Also, I VERY MUCH appreciated the entomological attempt at humor!

Re: Simple Network Download Question

Posted: Mon Jun 06, 2011 6:09 am
by Jay Cline
My simple mind doesn't understand the intricacies of Traceroute, perhaps this site will help. Please give us a brief when you finish.

Re: Simple Network Download Question

Posted: Mon Jun 06, 2011 3:55 pm
by Bob Wiswell
I use Qwest and Olypen and I experience the same type of slowdown on downloads. I'm glad Jerry asked the question because I have been afraid to ask thinking it was a dumb question and somehow I just didn't understand the process. I have never seen it speed back up, but the rate of decay certainly varies. I have also experienced the time to download message as changing from hours to minutes and then being completed almost instantly.

Thank you Jerry for asking this question. The bottom line seems to be that this is the way it will be. Sit back and relax and be happy when the decay rate is slow.

Re: Simple Network Download Question

Posted: Mon Jun 06, 2011 4:07 pm
by Stephen Hart
Just as an addendum to my post above.
Something on your own computer can slow a download. Note in my post that what slowed that particular download was that I didn't quit Photoshop. Other culprits can be anything that sucks bandwidth. One common example: you start up iTunes, and it suddenly starts downloading the ten podcasts that are pending.

Re: Simple Network Download Question

Posted: Wed Jun 08, 2011 3:04 pm
by JerryFreilich
The question is how to know where the slowdowns occur. I will try TraceRoute but the bottom line is that it is a complicated beast showing a lot of details about all the various nodes in a message's journey from Point A to Point B. Stephen's comments about things going on in your own computer further complicate the question. Yes, the slowdown could be at any point along the chain. The question is how do you figure out which it is? I will spend some time with the Trace Route article. Thanks Jay.