Cable Modem- Macs Slow, PC Fast

Z

zaxcom

Registered
I have three Macs (G5,G4,G3) and one PC on my network. Until last week everything ran fine, then monday all three Macs started to crawl on downloads, but the PC is fine. Thinking my cable modem was bad I got a new one, no change, went back and picked up another cable modem, still no change. I took my router out of the system and hooked up my G5 straight to the modem and still my download speeds are in the crapper.

Every speed test I run the Macs top out at 1.2 Mb, while the PC gets 5Mb. My downloads are creeping. Time Warner came out checked all my lines and everything is perfect. My up and down SNR and levels are fantastic. I have very low ping and latency. As I said the Macs have worked fast and perfect for 6 years until this past monday, and then all 3 at the same time hit the wall.

Time Warner brought a PC laptop over, hooked it to my network and it too got 5Mb down. They are washing their hands of the matter saying if the PC's work then its something wrong with the Macs.

I have turned off IPv6, tried forcing duplex and speeds, Cleared pref files, reloaded the entire OS. Even tried going all the way back to Panther, and still saw no improvement.

Equipment:
Surfboard 5101 Cable Modem
Dlink-604 Router (I can remove it, same problem)
G5 1.8Mhz single CPU
G4 800Mhz
iMac G3 500Mhz

All Run Tiger 10.4.6


Any help Ideas would really be appreciated.


Thanks


Zax
 
Do you notice the slowdowns only when you're browsing the web, or is it also when you're downloading files? Have you tried using other apps for web browsing and downloading in order to make sure it's not the applications that make it feel like it's downloading slowly?

Let us know what you find.
 
Downloads have come to a crawl and so has web browsing. This is occuring in Camino, Safari, Transmit and my email program.
 
Thanks, but I already went thru all possible combinations of duplex and speed. It had no effect on the problem.
 
Problem solved. Went back to an old AMBIT modem and my speeds were back to normal. The new chip set for DOCSIS 2.0 in the Motorola 5101 and the new AMBIT modem is not compatible with Mac computers.
 
I wouldn't really say that the problem is solved. I have no option to change modems.

This seems real strange to me... I think something that Apple should fix. It is definitely not a hardware issue - I heard that this slowdown problem also occurs on x86 hardware, but WinXP/Linux on exact same hardware performs fine.
 
Doughboy said:
.... I think something that Apple should fix. It is definitely not a hardware issue ....
Click to expand...
Something that Apple should fix? Unless the OP is doing something really stupid like using a USB connection between his cable modem and computer, then there is nothing that Apple can fix. A standard cable modem communicates via TCP/IP over Ethernet with the computer. I have never seen a Mac that demonstrated any trouble at all communicating via Ethernet.
 
MisterMe... maybe it is not something Apple will fix, but it is definitely isolated to OS X. This problem we are all having occurs when upgraded to faster DOCSIS modems. I have Shaw Extreme which is 7Mbps down and 1Mbps up

We are all connecting via ethernet as far as I know. (At least I am).

I have 4 macs here that have slow downstream bandwidth (appears to be capped at around 2Mbps) with my new DOCSIS modem. On the same network I have a Linux and 2 Windows machines that do not have this problem and I get 5-7Mbps consistently on speed tests. At a completely different location (at work), I have same brand of modem and exact same problem when comparing Macs to other OS.

Now if zaxcom claims that by changing to an older modem causes speeds in OS X to go back to normal, then the evidence is pointing to an issue with OS X. It is not an issue which makes ethernet stop working, or causes any other ethernet issue on the LAN. It is isolated to internet traffic through the DOCSIS modem. Maybe something to do with how the packets are handled at a lower layer than TCP/IP. This is not a far-fetched possibility - For example, I have heard many problems with some brands of routers causing speed bottlenecks, or even instability and lost data with certain network and/or hardware configurations while other users have no problems at all. This issue we are having could be similar and is worth investigating by someone.
 
Doughboy, I have no idea what problem you are having but I do have a DOCSIS cable modem. My Macs have no problems at all using the modem to access the Internet. I go through a Linksys wired router so that the modem doesn't actually see the computer. It sees only the router. Before I bought the router, I had to do power off the modem when switching between MacOS 9 and MacOS X 10, a known issue. This was a convenience issue, not a performance issue.

Your problem as described makes no sense. You ought to investigate your TCP/IP settings in the Network preferences pane in System Preferences.
 
MisterMe, It is not an issue of accessing the Internet. I can access the internet fine. The issue is a performance one - that with OS X the downstream speed is significantly slower than Windows XP or Linux. This is not noticeable in day to day browsing etc., nor are there any disconnection/connection issues. One has to do speed tests to see the problem. I have tried changing TCP/IP settings, swapped modems, adjusted parameters in the shell via sysctl with no luck.

Please try www.speakeasy.net/speedtest and tell me what your downstream is. I just tested and I got 1566 kbps down and 941 kbps up on my PowerMac and then tested right after with an XP Pro system and got 6804 kbps down and 917 kbps up.

Rather than rely solely on an Internet speedtest, I did a real world test also... downloaded same file off atitech.ca and watched the download speed in firefox - stabilized around 210KB/sec download with OS X and approx 2 minutes to download a 34.3 MB file. The same file downloaded with XP and firefox took only around 30 seconds and stabilized around 850KB/sec. To rule out possibility of OS X build of firefox having poor performance, I tried the same download in Safari and got the same slower speed of around 220KB/sec.

And I am not the only one with the problem... xaxcom posted that he was able to try an older modem and the performance went back up. In my previous post I was pointing out that it is possible for hardware to cause performance issues even though it appears to work fine. There appears to be something in the way OS X's ethernet communicates with the DOCSIS modem which causes it to operate slower than expected.
 
Doughboy, I did the test as you suggested. You may find the results difficult to accept, but they may explain the performance disparity between your Mac and Windows computer.

Using Safari 2.0.3 (417.9.3), my results are 5045 kbps download and 590 kbps upload. My connection is rated at 5 Mbps. This is inline with the other connection speeds I measure on the DSLReports.com website. Within expected variation, I am getting the performance I pay for.

In a moment of inspiration, I conducted the speed test again on the same hardware. This time I used Netscape 8.1 running on a fully updated Windows XP SP2 on Virtual PC 7.0.2. The results are 7049 kbps download and 1017 upload. This result is clearly not possible. The Windows browser claims that my connection is 40% faster than the line I pay for. Windows running under emulation on MacOS X cannot be faster the host MacOS X alone. It certainly can't overclock my ISP connection.

What is clearly going on here is a bug (or feature?) in the Windows port of Java. Accept your lower MacOS X numbers in the knowledge that they are accurate.
 
Your test seems fine under OS X. The VirtualPC test does not explain my problem because I am using a real PC to compare. (FYI, I also ran the speedtests in VirtualPC on my Mac and got slower than expected results - less than 2mbps).

I initially thought it was due to Flash being slow on OSX (speakeasy uses Flash program), causing the results to be lower than expected. That does not explain the slow download test - over 2 minutes on my OS X compared to 30 seconds on XP. I am going to see if I can test an older Teryon modem (which is not DOCSIS) and see if the downstream is approaching the 5Mbps that is advertised.

MisterMe, can you tell me what make/model your modem is?

Mine is a Motorola SB5101 Surfboard Modem.
 
Doughboy said:
Your test seems fine under OS X. The VirtualPC test does not explain my problem because I am using a real PC to compare. ...
Click to expand...
You don't understand. Virtual PC emulates a slow PC. The results of Windows running on the emulated slow PC are higher than those on native MacOS X. Since the two tests were run on the same hardware, the only difference between the two test was software. I could have run the Windows test using FireFox or Internet Explorer, but that would have been expected to "speed up" Windows even more. The point is that the numbers generated by the Windows test are unbelievably high. The numbers generated by the MacOS X test are as advertised.

Doughboy said:
.... I am going to see if I can test an older Teryon modem (which is not DOCSIS) and see if the downstream is approaching the 5Mbps that is advertised.
Click to expand...
Is your ISP still compatible with your old briefcase-sized Teryon cable modem?

Doughboy said:
MisterMe, can you tell me what make/model your modem is?

Mine is a Motorola SB5101 Surfboard Modem.
Click to expand...
I have a Toshiba PCX1100U.
 
MisterMe, I tried VirtualPC again and I am getting those real goofy high transfer speeds. I then tried to download a large file using Internet Explorer within an XP session in VirtualPC and I timed it with an external clock - a 40.9 MB file took 2 minutes and 15 seconds even though the transfer rate said 780K/sec. I downloaded the same file on a real PC running XP using Internet Explorer and the transfer rate said about 820K/sec. but it downloaded the file in 55 seconds. VirtualPC is not to be trusted with doing any sort of Internet speed tests.

MisterMe, sounds like you disbelieve me (I am not the only one with this problem btw) and I don't really blame you because it is difficult to believe unless experienced for yourself. I was hoping that someone knew more info about this problem and have some magic internet setting/tweak that I could do to solve. I have tried them all... change MTU, turn off IPv6, manually configure ethernet adapter to full duplex etc. I have tried with a router, and also my Mac directly into the modem. I have tried several different Internet speedup/optimizers for OS X and even an official one from Apple designed for FOS. Nothing I have tried caused the speed to increase.

To summarize...

I have a DOCSIS Motorola modem. Shaw Extreme 7Mbps down 1Mbps up.

Typical tests at speakeasy.net/speedtest : XP Pro 6883 Kbps down, 903Kbps up. Mac OS X: 1563Kbps down, 940Kbps up. (note these tests vary slightly every time)

Downloading large 32MB driver file from know fast site (atitech.ca): XP Pro 30 sec. at around 850 KB/sec and Mac OS X over 2 minutes at around 200 KB/sec.

As a control, I put that same file on my local linux server and downloaded in firefox on OS X. It dowloaded so quick that it was difficult to time. I then used a much larger 1.4GB test file which took under 2 minutes at around 11000 KB/sec.

I can transfer on LAN at high speeds to/from XP/Linux and OS X. This speed issue only affects packets via the Motorola modem. Others have reported same problem only when they upgraded their cable service to a higher speed and changed the modem. The older modems seemed to work fine, and one person in this thread "solved" by replacing modem and speed went back up.

The problem could be Apple or Motorola. Since the Motorola modem works fine with XP and Linux, therefore it is leaning towards the problem being solvable on the OS X end. Maybe there is some sort of QOS thing going on that the Motorola is signaling OS X into doing.

My network still works with the Teryon modems.
 
Doughboy, if you are getting 11,000 kbps when when your Mac transfers files from your Linux server, then there is nothing wrong with your Mac's Ethernet performance. You seem to have an issue with DOCSIS modems with your ISP. The fact that you and other people experience the same problem is not evidence of a general problem with DOCSIS modems. Many other people, including I, have DOCSIS modems which work fine with our Macs.

The fact that your Teryon modem seems to work better than your Motorola modem with your Mac leads me to believe that any real problem must lie with the Motorola. I take it that you own your own modems. You should seriously consider replacing the Motorola with a new DOCSIS modem. As you know, you have to register the serial number and MAC address of the new modem with your cable ISP.
 
Well DoughBoy, I am having the very same problem you are and I have the very same setup you do. I was just setup with a new SB5101 to replace the old SB4220 and my performance fell through the floor. The PCs on my LAN are all fine with download speeds over 9000 kbps while the macs (one intel and the other G5) both are hovering around 793kbps down.

I tried going back to the SB4220 but it wouldn't sync up. The Cox Cable has been NO help at all. Any suggestions from anyone?
 
I have to agree with Dougboy. I started a thread regarding the same issue.
http://www.macosx.com/forums/showthread.php?t=272957
I "think" there is a valid issue out there and it should be acknowledged by apple even if thier answer is, we know there is a problem and don't have a solution. That would at least keep some of us from spinning our wheels all day long trying to solve it on our own. :)
 
I had Comcast come by to do a routine check of my Internet speed today. they sent him out for free, as I was threatening to change to DSL.

He brought his PC laptop and measured speeds around 4 MB/sec - which is the level of service I am paying for. He used speakeasy.com for his tests and also dslreports. All yielded the same results.

He measured at the modem and in two remote rooms. I have a CAT6 LAN system - not wireless. Results were the same everywhere.

However, both my G3 and my G4 clocked dowloads at about 380 kbs. I have tested Safari, Firebox, 10, 100, half duplex and full duplex. There are slight and inconsistent differences. I did not run enough tests to have a legimate sample to average. However the differences - if any - are not worth worrying about.

According to my database, I have a Motorola SB4100 Cable Surfboard modem. I have had it for several years.

I am running Mac OS 10.4.7

I was shocked to learn how fast I could be downloading if I had a PC. I doubt I have ever had download speeds approaching half a MB - much less 4 mb. I am sure I would have noticed.

We had a very strange observation. On the G3 only, uploading was in excess of 7 MB/ second. We ran this test several times. It actually appeared that the test had not run at all, since the speed was blazingly fast. But each time it posted a speed at the bottom of the page.
 
You must log in or register to reply here.
Back
Top