Motorola Cable Modem Incompatibility

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Motorola Cable Modem Incompatibility

Motorola Surfboard cable modems limit internet connection/download speeds to around 2.5 - 3.0 Mbits/sec.

I have just completed months of debugging of a "slow connection" problem with my PowerMac G4 (dual 1.42 GHz mirror door model running Tiger) which included replacing the Motorola Surfboard cable modem supplied by my carrier (Comcast) and replacing the logic board and processors as authorized by Apple Care. Connecting to the internet via a PCI ethernet card (D-Link DFE-530TX+) did not correct the problem either. Finally, replacing the Motorola modem with a Scientific Atlanta modem instantly solved the problem. Interestingly, when connected directly to a T1 line at an Apple Store, my G4 had the same fast connect speeds as store machines, both before and after the repair work.

Apple Care denies any knowledge of the problem. Motorola (thus far) denies any knowledge of the problem. Comcast says it has anecdotal evidence of the problem, which they say may also occur with G5 computers, and is now taking a serious look.

I am concerned that there is a very widespread problem here. albeit it underreported and under diagnosed. I imagine that most users do not notice a problem (or assume "that's just the way it is") with routine web surfing, the most common use of the internet. It would take large file downloads, navigation to the speed test websites and a concerted effort to really quantify and document the issue.

One has to wonder whether other model Motorola cable modems or DSL modems have the same incompatibility. And all of this is discussed without even broaching the question of "fault;" is the problem with the modem or with the Apple circuitry, with certain software or with a particular combination of these factors?

G4 Mac OS X (10.4.6)

Posted on Jul 11, 2006 12:20 PM

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Answer 1

Jul 12, 2006 2:48 AM in response to salientis

Which model of Surfboard?

We have taken a 5101 'to the wall'. That is, over 30Mbps, on a single TCP stream. The 5101 is the current model.

I just this instant pulled over 7Mbps to a G4 which is through an older model 4200 connected via a firewall PC.

Are you saying the Surfboard is slow, or that it is slow connected to a Mac?

I'm somewhat interested, as I work for a telco in New Zealand, and if there is a problem I'm keen to know about it.

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Answer 2

salientis Author

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Jul 12, 2006 3:51 PM in response to Michael Newbery

Which model of Surfboard?

We have taken a 5101 'to the wall'. That is, over
30Mbps, on a single TCP stream. The 5101 is the
current model.

I just this instant pulled over 7Mbps to a G4 which
is through an older model 4200 connected via a
firewall PC.

Are you saying the Surfboard is slow, or that it is
slow connected to a Mac?

I'm somewhat interested, as I work for a telco in New
Zealand, and if there is a problem I'm keen to know
about it.

Both the 4200 and the 5101 Surfboard modems have the same problem associated. My issue occurs with either a direct connect to the modem or with a router in line. Your hookup is different, perhaps in a critical way that may be of diagnostic value.

I do not know the ultimate cause of the problem, only that my Motorola based PowerMac G4 (and perhaps others as well) has connect (download) speeds limited to between 1.5 Mbits/sec and 3 Mbits/sec when connected to the 5101 modem, whereas it connects at the cable company's maximum rated speed (9 Mbits/sec) when connected via a Scientific Atlanta cable modem, with or without a router in place. Also, my G4 connects at high speed when hooked directly to a T1 line. I even tried the experiment of connecting the modem through a PCI ethernet card, but that didn't solve the problem. Motorola engineering is now involved and there seems to be a distinct possiblity that this is a widespread problem.

I do not know where the "fault" lies (software, hardware, softwarwe+hardware???), only that there is some sort of incompatibility.

Why don't you try connecting your G4 DIRECTLY to the 5101 and seeing what happens? How are you measuring speed?

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Answer 3

Jul 12, 2006 8:58 PM in response to salientis

Thanks, I'll investigate further.

I presume you checked the half/full duplex settings?

I checked speed using a couple of local speed test sites (which tend to under report, if anything), and also in the past with iperf, stop watch, and various other methods.

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Answer 4

salientis Author

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Jul 12, 2006 9:41 PM in response to Michael Newbery

Thanks, I'll investigate further.

I presume you checked the half/full duplex settings?

I checked speed using a couple of local speed test
sites (which tend to under report, if anything), and
also in the past with iperf, stop watch, and various
other methods.

Yes, I checked the settings and no change.

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Answer 5

Jul 13, 2006 5:42 AM in response to salientis

Just tried. G4/466 directly to Surfboard 4200. >8Mbps download, no problems.

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Answer 6

salientis Author

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Jul 13, 2006 8:33 AM in response to Michael Newbery

Just tried. G4/466 directly to Surfboard 4200. >8Mbps
download, no problems.

I suppose we'll just have to await the results from Motorola's testing. Perhaps it's a problem limited to my particular model computer, a software/hardware conflict or any one of numerous other possibilities. Thanks.

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Answer 7

Jul 21, 2006 6:24 PM in response to salientis

AH! I believe this is a valid problem. I posted elsewhere that I've been having speed problems. I recently switch to cable from DSL and have a Motorola Surfboard 5100 modem.

I am getting no where near the 7Mbps rates that my PC on the same network is getting, it seems capped b/w 2.5-3Mbps. I've tried Safari and Firefox and both yield the same results.--speeds less than 3Mbps.

The strange thing is that if I run winxp via bootcamp or parallels, I get the 7Mbps speed. This is thru speedtests from dslreports and thru downloading large files off microsoft and apple servers.

Now the other interesting thing is, the speeds are fast on OSX if I use 'downloadthemall' the extension on firefox. It seems something is limiting the speed of each download thread. If I use the extension and create a multichunk (or threaded) download, I can achieve the prescribed speeds. if I only choose one chunk and not a multichunk download the speeds fall back down to 2-3Mbps...

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Answer 8

salientis Author

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Jul 21, 2006 6:35 PM in response to captaincanuck

AH! I believe this is a valid problem. I posted
elsewhere that I've been having speed problems. I
recently switch to cable from DSL and have a Motorola
Surfboard 5100 modem.

I am getting no where near the 7Mbps rates that my PC
on the same network is getting, it seems capped b/w
2.5-3Mbps. I've tried Safari and Firefox and both
yield the same results.--speeds less than 3Mbps.

The strange thing is that if I run winxp via bootcamp
or parallels, I get the 7Mbps speed. This is thru
speedtests from dslreports and thru downloading large
files off microsoft and apple servers.

Now the other interesting thing is, the speeds are
fast on OSX if I use 'downloadthemall' the extension
on firefox. It seems something is limiting the speed
of each download thread. If I use the extension and
create a multichunk (or threaded) download, I can
achieve the prescribed speeds. if I only choose one
chunk and not a multichunk download the speeds fall
back down to 2-3Mbps...

What replies have you had to your other posts and what computer and OS are you using? I hope your information proves valuable in getting to the root cause of this problem. Do you have suggetions on where else to post our discussion to better reach the masses and discover more about how widespread the problem is?

Thank you!

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Answer 9

Jul 22, 2006 4:49 PM in response to salientis

Ah, this might lead to something.

Can you run the tweak test on http://www.dslreports.com/tweaks

What does it report? Does it show a high level of retransmits? If so, this could suggest a reason for the observed behaviour. If it doesn't, then the following hypothesis can be ignored...

TCP reacts to packet loss by throttling back the speed. It does so very aggressively. The effect is magnified at higher speeds, where even small amounts of packet loss will severely limit you throughput.
See this page to calculate your theoretical maximum throughput. Note that it's pretty technical, but if you play around, you'll find that at high speeds, even small amounts of packet loss can be really bad.

One way to deal with this problem (well, it helps somewhat), is Selective ACK (SACK :RFC 2018). WIndows XP implements it. Mac OS X does not (which is bizarre, because the code is available in the Darwin kernal, just not turned on).

A better way is for your cable provider to improve its plant, so there are fewer errors 🙂

And, changing cable modems might also help, if either there is some sort of mismatch between the cable modem and the cable headend which results in higher than usual errors; or if one model of cable modem produces significantly more errors.

Note that we use Motorola Surfboards, and they perform well, so our experience has not been that the Surfboards cause problems. Be aware though that there are a whole lot of different settings down at the link level which could well affect performance. Do you know if you are running DOCSIS 1.0, DOCSIS 1.1, or DOCSIS 2.0? They have different transmission characteristics.

If it is SACK that is the significant factor, that would be something important to know. You could test this on a WIndows 2k/XP machine by setting the registry key (WARNING: Here Be Dragons!)
HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
SackOpts="0"
That is, change it from its current setting of "1" to '0" (turning it off) and seeing if that makes the WIndows machine perform the same as the Mac. If it does, then we can conclude that SACK is the magic bullet. If it doesn't, then we are back at square one, searching for a reason.

G4/466, eMac 800, iBook 1.33 Mac OS X (10.4.7)

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Answer 10

Aug 6, 2006 5:16 AM in response to salientis

Just tried. G4/466 directly to Surfboard 4200.
8Mbps
download, no problems.

I suppose we'll just have to await the results from
Motorola's testing. Perhaps it's a problem limited to
my particular model computer, a software/hardware
conflict or any one of numerous other possibilities.
Thanks.

I have the same problem with a G5 iMac and the Motorola Surfboard SB5101. Pc's on the same network are getting up to 11,300kpbs while my G5 is only managing a max of 3,800kpbs, and an older G3 iMac can only reach up to 3,000kpbs.

I've been testing this for over a week now with serveral speed and download tests, all result in the same; PC's are much faster. I have played around with Ethernet settings and have opted for manually setting the speed to 10baseT, full duplex at 1400 MTU, doing so gives me a bit more speed, sometimes up to 5100kpbs, which I never got before, but still slower than the PC's which fly.

The G5 is up to date with patch upgrades, although keeping the OS down to 4.3 due to an issue with Adobe apps in 4.7.

You say Motorola are testing this, what have they said, as nobody here in Australia seems to be aware that there is a problem? Is there a another link with the results, as this forum is a month old now.

cheers

iMac G5 Mac OS X (10.4.3)

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Answer 11

salientis Author

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Aug 6, 2006 7:02 AM in response to Tony Gilmore

Just tried. G4/466 directly to Surfboard 4200.
8Mbps
download, no problems.

I suppose we'll just have to await the results

from

Motorola's testing. Perhaps it's a problem limited

to

my particular model computer, a software/hardware
conflict or any one of numerous other

possibilities.

Thanks.

I have the same problem with a G5 iMac and the
Motorola Surfboard SB5101. Pc's on the same network
are getting up to 11,300kpbs while my G5 is only
managing a max of 3,800kpbs, and an older G3 iMac can
only reach up to 3,000kpbs.

I've been testing this for over a week now with
serveral speed and download tests, all result in the
same; PC's are much faster. I have played around with
Ethernet settings and have opted for manually setting
the speed to 10baseT, full duplex at 1400 MTU, doing
so gives me a bit more speed, sometimes up to
5100kpbs, which I never got before, but still slower
than the PC's which fly.

The G5 is up to date with patch upgrades, although
keeping the OS down to 4.3 due to an issue with Adobe
apps in 4.7.

You say Motorola are testing this, what have they
said, as nobody here in Australia seems to be aware
that there is a problem? Is there a another link with
the results, as this forum is a month old now.

cheers

iMac G5
Mac OS X (10.4.3)

I just emailed the Motorola tech to request an update. I'll post his reply. The otehr posts int his forum have valuable leads. As you suggest, a lot of people probably do not recognize that they have this problem. My own solution has been to simply switch to a Scientific American cable modem - it works fabulously.

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Answer 12

Aug 6, 2006 4:19 PM in response to salientis

I think I've been following your messages on a few forums over this weekend. Thank you for highlighting the problem, as it does seem to be an issue with the modem to Mac. I hope Motorola actually do test and do something about it. Getting another modem isn't an option at the moment.

I'll keep checking back.

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Answer 13

salientis Author

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Aug 7, 2006 8:06 AM in response to salientis

This from Motorola today:

"Engineering is still investigating, but has identified a possible issue between Apple computers and certain networking configurations. Due to the fact that multiple devices are involved, the root cause is not yet known. We are continuing to investigate and will take the appropriate action once the cause and correction are known."

They're moving at a snail's pace. I wonder why.

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Answer 14

Aug 7, 2006 7:54 PM in response to salientis

Oddly enough I emailed Motorola Support in the States and received this reply this morning:

“Response (Charles) - 08/07/2006 03:00 PM
Hello
Thank you for choosing Motorola. I apologize for any inconvenience you may have experienced and I will be happy to help you.
I did some more research on it, and the problem seems to be only with DOCSIS capable modems, if you were to use an older modem, it would perform faster, I know that sounds crazy but that's what some Mac users have found out. It's not going to be the hardware itself if it works fine on Windows and Linux operating systems.
If you have any further questions, please feel free to reply to this email or call us 24/7 at 1-877-466-8646. Thank you again for choosing Motorola and have a nice day.
Thank you again for choosing Motorola and I hope you have a pleasant day,
Motorola Email Support”

Not sure if the tech support guy “researched” these forums, but not much help there, except to use an older modem.
Salientis – stick with your other brand.

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Answer 15

Aug 8, 2006 11:10 AM in response to salientis

This thread made MacFixIt today. I've got an 8 Meg connection at Comcast, a Motorola SB5100 modem connected to an Airport with 4 Macs (1 wired, 3 wireless), and I see this same problem. Speedtests generally show results in the 3 Mbit range. However, if I reboot the modem and run it again, I see speeds in the 10 Mbit range or higher (Powerboost). I've just gotten in the habit of occasionally rebooting my modem. I've manually set the Airport to Full Duplex and 100Mbps, and the TCP Send and Receive to 128480 using Cocktail, but this doesn't seem to make much difference.

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