Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs:
| reply to billaustin
Re: [DSL] Embarq Modems
said by billaustin  :The sync rate is controlled by the DSLAM. The actual throughput, or 'speed' as many refer to is, is controlled by the modem. Just because different modems sync at the same rate, does not mean they will pass data at the same rate. The modem chipset, processor, RAM, ethernet chipset, and supported connections all factor in to this. That is incorrect. The DSL Sync Rate is the raw data rate before ATM and TCP/IP overhead which after that is subtracted, remains what is seen on a typical speed test. The DSL Modem does not control either of those at all as it is a passive device.
»DSL FAQ »What is the 80% bandwidth / speed
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billaustin
Bill
Premium,MVM
join:2001-10-13
North Las Vegas, NV | The DSL Modem is an active bridge. It transfers the packets between the DSLAM and the ethernet port. When operating as designed, it is transparent, but it can affect the throughput of the connection. |
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RadioDoc
58ef2c0
Premium,ExMod 2000-03
join:2000-05-11
 ·AT&T Midwest
1 edit | reply to Doctor Olds
said by Doctor Olds :The DSL Modem does not control either of those at all as it is a passive device. Control? No. Influence? Youbetcha. Many people ran into just that with older equipment when SBC introduced the 6016/608 sync profile. Some Efficient Networks units could not keep up until their firmware was upgraded and even then were not able to pass data at the full line rate. If I put my trusty 9 year old Efficient 5861 online I suffer about a 10% reduction in throughput compared with the 4200 or a three year old 2-Wire 1701HG.
Back to the subject: I have a two year old 660R which valiantly holds 5000+/640 on a disastrous 12,500 foot long line. Currently it is at 5632/640 with the following stats:
noise margin upstream: 6 db
output power downstream: 18 db
attenuation upstream: 31 db
noise margin downstream: 3 db
output power upstream: 12 db
attenuation downstream: 57 db
As you can see it is possible to get decent sync rates with far less than optimal conditions.
In the OP's case something is wrong with the line. The upstream noise margin is horrible. I'd play with things a bit and see if you can improve it as the modem is running flat-out (20 dB) and barely keeping it's head above water. Something might be loading the line on the low frequency end like an unfiltered POTS device. |
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Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs:
| reply to billaustin
said by billaustin :The DSL Modem is an active bridge. It transfers the packets between the DSLAM and the ethernet port. When operating as designed, it is transparent, but it can affect the throughput of the connection. It doesn't work that way as a DSL Modem is a passive Bridge (neither blocking or filtering anything as it blindly passes all traffic when Bridged or when a Bridge Modem alone), only when a DSL Modem has a built-in Router does it become "active" as is any Router. A stand alone Router behind a Bridge Modem works the same way a built-in Router works inside a DSL Modem, you just have one device instead of two and if the Routing is not handled in the Router/Modem such as when it is placed into Bridge Mode, the speed isn't affected by NAT/NAPT, SPI, IP Filtering or Firewall actions since they are dormant.
DSL Modem/Bridges and Ethernet Routers work at different OSI Layers. The same applies to a built-in Router that is in the same case as a DSL Modem operating at different layers, but when it is disabled being used as only a Bridge that Router layer isn't being looked at or touched by the Bridged DSL Modem.
Regards,
Doctor Olds
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What’s the point of owning a supercar if you can’t scare yourself stupid from time to time? |
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RadioDoc
58ef2c0
Premium,ExMod 2000-03
join:2000-05-11
·AT&T Midwest
| Nope. Not passive. It is very much an active participant. And the throughput is very much dependent on the processing horsepower of the DSP chips inside. And it is almost impossible to find a true bridge (modem) such as the old Westell units these days since they all are IP addressable for ease of administration. Your definition no longer reflects reality. Even a "bridged" modem/router is still a router passing all traffic across the network boundary. If not you'd never be able to turn it back into a router. |
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