Max speed of cable modems?

[Ron Jeremy]

Max speed of cable modems?



What is the maximum speed of current cable modems deployed on the ntl network (if they were uncapped what is the max download and upload speed)?

In the USA most cable modems run at 3meg down 256k up and telewest offer that too but is that maximum speed?

Thanks.

[Chris W]

the different cable modems have different specifications, eg the 3com cmx has a maximum 40 down 20 up i think, but the newer modems, eg ambit 200 these figures are higher.

I could get you all the specs for the modems ntl use but i am tired and i can't find them at the moment... i will find them for you tomorrow if i remember.

MB

[Andy C]

I think the maximum downstream is about 30mbps. At least it was on the 3com models, no idea about the ntl: branded modems.

Ahh, found the info... 3com CMX is "38 Mbps downstream, 10 Mbps upstream".

[Chris W]

3com
CMX: White box, which lies flat on desk, only has coax, ethernet
Sample MAC: 00 10 4B ## ## ##
Speeds: Down stream max 3Mbps, burst 38Mbps
Upstream max 1Mbps, burst 10Mbps
DOCSIS: DOCSIS v.1 compatible
Web Interface: No
Tailfin(home connect) 3CR9220
Sample Mac:
00 01 03 ## ## ##
00 03 03 ## ## ##
00 50 DA ## ## ##
00 40 DA ## ## ##
Speeds: Down stream max 38Mbps
Upstream max 10Mbps
DOCSIS: DOCSIS v.1 and v1.1 compatible
Web Interface: Yes
Diagnostics: Internal diagnostics available via web browser
<http://192.168.100.1/>
Connection: Ethernet

Motorola
SURFboard SB3100
Sample Mac: 00 20 40 ## ## ##
Speeds: Down stream max 38Mbps
Upstream max 10Mbps
DOCSIS: DOCSIS v.1.0 and v1.1
Web Interface: Yes
Diagnostics: Internal diagnostics available via web browser
<http://192.168.100.1/mainhelp.html>
Connection: Ethernet (RJ45)
Other: Can handle up to 32 PC's via hubs with internal DHCP.
SURFboard SB4100
Sample Mac: 00 20 40 ## ## ##
Speeds: Down stream max 38Mbps
Upstream max 10Mbps
DOCSIS: DOCSIS v.1.0 and v1.1
Web Interface: Yes
Diagnostics: Internal diagnostics available via web browser
<http://192.168.100.1/mainhelp.html>
Connection: Ethernet (RJ45), Universal Serial Bus(USB)
Other: Can handle up to 32 PC's via hubs with internal DHCP.

Terayon
Terajet TJ210
Sample Mac: 00 E0 6F ## ## ##
Speeds: Down stream max 30Mbps
Upstream max 5.12Mbps
Web Interface: No
DOCSIS: DOCSIS v.1.0 and v1.1

can't find the specs for the ambit modems atm...

[Jerrek]

I had an old Samsung/Cisco InfoRanger from 1999 that capped out at 7 Mb down. It was quite annoying because we paid for 10 Mb down. They sent us a newer modem and I think most newer models utilize the entire channel or more. 40 or so Mb at least.

[Paul]

Suffice to say the maximum is far higher than they are ever likely to be actually run at. :)

[ian@huth]

The bandwidth available on the UBR cards for both upstream and downstream is far less than the modems are capable of at this moment in time. Depends on whether they are running DOCSIS or EuroDOCSIS as to the actual bandwidths available.

[Defiant]

In the USA most cable modems run at 3meg down 256k up and telewest offer that too but is that maximum speed?

Thanks.


Allot of european countrys are the same

[Ignition]

The bandwidth available on the UBR cards for both upstream and downstream is far less than the modems are capable of at this moment in time. Depends on whether they are running DOCSIS or EuroDOCSIS as to the actual bandwidths available.

No, the modems are produced with the capacities of the equipment that they are connecting to in mind, the actual bandwidths available on a single downstream depends on the channel width, modulation type and modulation level in question.

Most cable modems can't sustain anywhere near the transfer rates the uBRs can simply because there was no need for them to, so cheaper less powerful DSPs have been used in their construction.

I'm not aware of any cable modem that can sustain a full 38Mbps down and 10Mbps up (the max capacity on DOCSIS1/1.1 that could be theoretically given to a single modem).

[danielf]

Suffice to say the maximum is far higher than they are ever likely to be actually run at. :)

I'm reminded of a Bill Gates quote regarding memory here. :)

"640K ought to be enough for anybody." -- Bill Gates, 1981.

[Ignition]

I had an old Samsung/Cisco InfoRanger from 1999 that capped out at 7 Mb down. It was quite annoying because we paid for 10 Mb down. They sent us a newer modem and I think most newer models utilize the entire channel or more. 40 or so Mb at least.

All cable modems utilise the entire channel as they have to decode all the information coming down to a point to decide which bits are intended for them. It's how quickly they finish the rest of the process that is the limiting factor really.

You can't use greater than the entire channel on any current cable modem or network right now, you're limited in the case of Cogeco to a 6MHz wide 27 or 38Mbit channel depending if you're in a QAM64 or QAM256 area - you are in a QAM64 area :)

[SMHarman]

I'm reminded of a Bill Gates quote regarding memory here. :)

Though I think the current SACMs will be obsolete before we are all considering subscribing to a high multi Mb service. Thats likely to need FTTH.

[ian@huth]

No, the modems are produced with the capacities of the equipment that they are connecting to in mind, the actual bandwidths available on a single downstream depends on the channel width, modulation type and modulation level in question.

Most cable modems can't sustain anywhere near the transfer rates the uBRs can simply because there was no need for them to, so cheaper less powerful DSPs have been used in their construction.

I'm not aware of any cable modem that can sustain a full 38Mbps down and 10Mbps up (the max capacity on DOCSIS1/1.1 that could be theoretically given to a single modem).

When I said "The bandwidth available on the UBR cards for both upstream and downstream is far less than the modems are capable of at this moment in time." I was using the fact that many UBRs (using DOCSIS and QAM64) have a downstream limit of around 27 Mbps which becomes nearer 20 Mbps after overheads and an upstream limit of around 2 Mbps.

[Ignition]

I was using the fact that many UBRs (using DOCSIS and QAM64) have a downstream limit of around 27 Mbps which becomes nearer 20 Mbps after overheads and an upstream limit of around 2 Mbps.

There are v few cable modems that can go anywhere near 20Mbps downstream, and most won't go near 2Mbps upstream either, certainly not for any length of time, simply because there is no need for them to.

You appear unaware that the upstream limit can be much higher while using the same modulation - doubling upstream channel width to 3.2MHz results in a doubling of usable bandwidth and is deployed in the field at the moment.

[BBKing]

Anyone missing the point that most CMs and STBs ntl use only have 10Mb ethernet ports? There's your downstream limit a lot of the time.

I've run an STB at 10Mb down/2Mb up and a Terayon (which I think has a 100Mb ethernet port) at 20Mb down. Wouldn't recommend it though.

Upstream the theoretical maximum is probably the upstream channel capacity (2.56 or 5.12Mbps depending on area).