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Teddy Boom
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reply to Dmole

Re: [Cable] Cable modem - what to buy

said by Dmole:

Any one know the specifications of the missing information on this chart?:
»internet.wikia.com/wiki/Comparis···e_Modems

That chart needs a lot of help..

The WAN bandwidth of Docsis 2 is variously 42.88mbit/s, 38mbit/s, or about 35mbit/s depending on how you want to count (that is: absolute maximum including overhead, maximum after overhead, and practical approximation respectively).

For Docsis 3, the WAN bandwidth of the SMCD3GN and the SB612x are the same (all 4 channel modems). Similarly, the WAN bandwidth of the DCM47x, DCW775 and Huawei are the same (all 8 channel modems). The discrepancy in the chart is because different spec sheets are calculating differently.

Anyway, the maximum bandwidth isn't particularly relevant. What we care more about is what speed the cable operator will allow on a given modem. I've heard it said that Rogers cut off speed for Docsis 2 is 15mbit/s. Of course there are no packages at that speed, and Rogers will be allowing TPIA to use D2 modems on all packages upto 32mbit/s until April, so it is pretty confusing.

For the record, some knowledgeable posters here say that modems running up to, or at least near, their full capacity shouldn't really be causing the operators any issues, and imposing a bandwidth limit at below half the theoretical number is misguided.

I seriously doubt the MSRP on the DCM476 is $70. There may be an online dealer selling at that price, but that will be below MSRP for sure. There is no way the MSRP on the DCM425 is as low as $30--Canada Computers sells them at $48.99, and Canada Computers is almost always below MSRP.
(I sell DCM425 for $25 nowadays, but then they aren't new--better than new, but definitely used )

Finally, I'm pretty sure that Teksavvy could start accepting the DCW775 any time they want to. Would be nice if we could have an update on that though (hello TSI-people ).
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electronicsguru.ca

Dmole

join:2008-07-11
Reviews:
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Thanks for the post Teddy, do you know where to find a spec sheet on the Huawei?

Won't the CPU/firmware choice effect the transfer speed?
I'm assuming not all 4 channel modems are the same because my experience with other hardware (routers) tells me stability and actual throughput varies by model.
the alternative is that modems are built with more quality then routers, but I have also added heat syncs to a DSL modem to stabilize it so I'm kinda doubtful about that.

Anyway you sell the things (right?) so you probably know more about it than I do.

I'll try and update that wiki page to reflect your input but feel free to add to it yourself.



Teddy Boom
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said by Dmole:

Thanks for the post Teddy, do you know where to find a spec sheet on the Huawei?

No idea, I've looked in the past.. Very little information on that modem anywhere. Strange

said by Dmole:

Won't the CPU/firmware choice effect the transfer speed?

Sort of. All modems available are either based on Puma5 CPU (4 channel modems plus the SB6141 at 8 channels) or Broadcom CPU (all other 8 channel modems). So ya, there will be little firmware differences I suppose, but the fundamental abilities are pretty much the same across all models.

Certainly Docsis 2 modems are all about the same, I've used many (TJ715x, DCM425, SB510x, DPC2100).

Anyway, the throughput maximums you are thinking of would be very hard to test, and it wouldn't be that useful anyway. Network conditions dominate any throughput limitation in the modem.
(would be nice to hear about practical experience from people on 150mbit at Rogers, that's the only way we'll confirm my theories or learn anything useful)

I have seen a comment here at DSLr about throughput testing on the LAN side of the SMCD3GN. The results were kind of mediocre to poor

said by Dmole:

the alternative is that modems are built with more quality then routers, but I have also added heat syncs to a DSL modem to stabilize it so I'm kinda doubtful about that.

Well, adding heatsink is more about stability I would think. Clock rate and amount of RAM dictate speed, until it crashes, and then the speed is zero
(of course there is some middle ground--performance degrades before the crash happens, or whatever--but I don't think it is so significant)
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electronicsguru.ca