Duplex?

[samuelnw53]

Swapping my Samsung stb for SACM tomorrow what duplex setting works best ie auto detect ,full 10 or 1/2,or full 100 or 1/2. thanks, Sam

[Web-Junkie]

WinXP has defaulted to 'TP Half Duplex' with my Realtek NIC card and Motorola SB4200 and that works no problem! I can't set any duplex options in the CM anyway!

[TheBlueRaja]

You should always leave it set to auto unless otherwise specified as this is what the other end will be set to provide. If you change this then the auto detection will probably default to either 10 or 100 HALF Duplex on the other side and you will experience packet loss.

[samuelnw53]

Thanks for your quick response ,will leave it as it is at auto detect.

[altis]

Sir Robin doesn't agree with you there...
It has been verified by experiment that certain auto-negotiating ethernet cards (both in PCs and in Macs), when connected to certain models of cable modem, sense the ethernet duplex setting incorrectly. Such a cable modem has ethernet hardware which is capable of operating only in half-duplex mode, at 10 Mbps, yet some auto-negotiating ethernet cards incorrectly sense the cable modem as full-duplex. If an auto-negotiation card incorrectly starts operating in full-duplex mode, there can be collisions between ethernet packets being transmitted in both directions at the same time, leading to packet loss, and repeated re-transmissions. There is no visible evidence of this apart from poor performance. This problem can be avoided by manually configuring your ethernet card to be 10 Mbps half-duplex.
taken from:
http://homepage.ntlworld.com/robin.d.h.walker/cmtips/ethernet.html

[Nemesis]

and from experience I'd agree with him

[DeadKenny]

Only applies to very old CMs though? Most these days have proper 10/100 support and will detect 100Mbps anyway. Though that's not what duplex is about, so why Robin mentions 10Mbps I'm not sure (does that somehow imply it's an old modem only capable of 10Mbps half-duplex?). Duplex is about being able to send whilst receiving.

[TheBlueRaja]

Sir Robin doesn't agree with you there...

taken from:
http://homepage.ntlworld.com/robin.d.h.walker/cmtips/ethernet.html

Sir Robin does, as Sir Raja wrote - "unless otherwise specified". Always helps to cover ones shiny metal ass. :D

And ok, assuming that he has a very old cable modem - what should he set it to? How would he determine how it should be set and what the cable modem defaults too? Anyone know? RTFM perhaps? (Seriously)

If it is a new one it should be set to auto IMO, as Robin mentiones that the cable modem is limited to 10mbps half-duplex on these old modems, so one way to tell might be the following, that if you plug in your cable modem and you get a 100Meg connection on auto detect then it is a newer modem and not an old one?

And therefore if you do the same thing with an old modem - would you auto detect 10Mbps and then force it to 10 Meg half-duplex on the PC?

[Nemesis]

From my experience, NIC cards set as Auto don't just have a problem negotiating with Cable Modems, I have seen this happen with Cisco Switches too.

I try Auto, and if it doesn't work, generally go for 10 Mbps Half Duplex or 100 Mbps Half Duplex. Try them all and see what works best.

It seems to be a problem with the Nic cards, and not the Modems/switches.

[TheBlueRaja]

I have seen problems with auto only when the other side is not Auto as well. In that case you MUST set your connection speed manually to equal what you are connecting too, otherwise it will probably default to X Speed Half Duplex.

I myself have done a lot of testing with this, not on Cable modems mind you but with VoIP Network testers.

[Chrysalis]

I have ambit 120 and I had to force to 10 half duplex, it slows down in 10 full duplex mode.

[BBKing]

Worth remembering that 10Mb/half duplex is capable of speeds way faster than any ntl cable modem or STB is able to deliver at present. The half duplex bit means that you can't send electrical signals in opposite directions at the same time, but this has no effect on being able to send actual data in opposite directions at the same time, the length of time each direction is blocked for is too tiny to notice.

[TheBlueRaja]

Worth remembering that 10Mb/half duplex is capable of speeds way faster than any ntl cable modem or STB is able to deliver at present. The half duplex bit means that you can't send electrical signals in opposite directions at the same time, but this has no effect on being able to send actual data in opposite directions at the same time, the length of time each direction is blocked for is too tiny to notice.

Are you sure BBKing,
Half - duplex IIRC means that you can transmit or receive information (aka packets) but not at the same time, full duplex on the other hand means you can transmit and receive information at the same time.

You are right though that 10Mb is way faster than necessary.

[BBKing]

can transmit or receive information (aka packets)

Not aka packets at all, we're talking waaay below the IP layer, this is purely the physical 1s and 0s as electrical impulses on the cable. That you choose to transmit IP packets over the top of these electrical impulses is completely irrelevant.

10Mb/half also puts less strain on the quality of your cabling.

[TheBlueRaja]

LOL,
Reading a bit too much into what i wrote BBKing, i was technically wrong in specifing packets - your right - i was trying to keep it simple.

I think your going too deep here and possibly confusing people with your statements, i doubt his cable will be any worse at half or full duplex - in fact i wouldnt even concider the cable at all unless it was falling apart at the seams.

The simple fact of the matter is this-

Always run AUTO unless it is specified otherwise or you KNOW that the connected equipment is forced at a specific speed or duplex. In this case your speed and duplex setting should be set to match that of the connected equipment.

[ian@huth]

LOL,

The simple fact of the matter is this-

Always run AUTO unless it is specified otherwise or you KNOW that the connected equipment is forced at a specific speed or duplex. In this case your speed and duplex setting should be set to match that of the connected equipment.

I would tend to disagree as using auto on both CM and NIC relies on both of them correctly determining the speed and duplex settings of the other which is not always the case.

New CMs such as the NTL:Home Ambits can be set to any combination of speed and duplex settings and may have been set to something other than auto by the user at some point in time. If the user then fits a NIC that doen't detect the CMs settings correctly on auto then there could be problems as Robin Walker pointed out. I would tend to accept his vast knowledge of the subject over any theory expressed by others.

[TheBlueRaja]

So what would you suggest you set it too then?

[Matth]

For the Pace STB (1000) 10 half is definitely the answer - if set to FULL, it works, but the netword card control panel counts rather too many errors.

In the old days, Ethernet ran on a dirty great hosepipe of coaxial cable, or on "thinwire" coax for smaller installations (10base5 and 10base2).

Since there was only one cable, it could not be duplex.

The way it worked , was under CSMA/CD (carrier sense multiple access / collision detect).
When an interface had a packet to send, it listened for carrier, and held off if busy.
Then it switched over to transmit, but kept listening - if another interface also switched at the same time, a collision resulted.
On a collision, both interfaces transmiot a collision signal for long enough that it will traverse the maximum permissible network delay due to line length and repeater delay, and then back off for a random interval.

The UTP cables were originally treated in exacly the same way, but then they started using the seperate transmit and receive paths to improve throughput.

But setting full duplex when it's not supported, will cause the full dduplex device to stomp on incoming packets with outgoing ones, since under full duplex, the two channels are assumed to be seperate - that's why mis-setting full duplex causes a loss in performance.

[Paul]

Set the CM and the PC to 10/Half and enjoy your error free web browsing. :D

[Chrysalis]

well you right auto works ok, but If I set 10/full then it is pretty bad throughput is all over the place, 10/half gives me the best result.

[kronas]

something wierd was happening to me when i tried to change settings on my machine due to issues with my connection.

i first tried 10mbit full duplex then 10mbit half duplex, my cm lost the pc light on both occasions, then i tried 100mbit full then half duplex it was still out, i set it to auto and everything started working....

[samuelnw53]

I am on 1.5 meg on an NTL 200 modem so would you still set computer at 10/half?

[Paul]

I am on 1.5 meg on an NTL 200 modem so would you still set computer at 10/half?Yes, set them both to 10/half.

Remember - 10mbps is already over 6 times faster than your internet connection, more than enough.

[samuelnw53]

When you say set them both to 1/2 what do you mean , i have gone into network conns and set that to 10 1/2 but what else do i need to do?

[Paul]

When you say set them both to 1/2 what do you mean , i have gone into network conns and set that to 10 1/2 but what else do i need to do?Set the CM to 10 half as well (it's probably on Auto atm).

[samuelnw53]

How do i set the CM to 1/2, im a silver surfer and have little up top?:dunce:

[altis]

Follow this: http://root:root@192.168.100.1/

Select 'set ethernet type'

Select 10M half

Click save and reset

[samuelnw53]

your follow this ....Page cannot be displayed.

[altis]

What model of SACM do you have?

[MovedGoalPosts]

What about the cable router between the PCs and Samsung STB?

If, as above, the PCs NIC autodetect may not work correctly, then surely the same issue can happen with the router, or are they more reliable? I cannot see any way of changing the router speed though, mines a D-Link 804V.

[samuelnw53]

Supplied by NTL last week it is a 200 thats as much as i know

[altis]

See if this helps:
http://www.cableforum.co.uk/board/showthread.php?t=18057

[samuelnw53]

go to that site but it asks for name and password when i imput them it access denied error 401

[daxx]

go to that site but it asks for name and password when i imput them it access denied error 401errr odd, it's this site, just tried it from here opens fine. Try right click over link, "copy shortcut" and paste into new browser (blank) window

or try this ht t p://w w w.cableforum.co.uk/board/showthread.php?t=18057

just remove the spaces

[samuelnw53]

Got onto site 192.168.100.1 some of the readings are downstream Snr 29.6.... power -7.1dbmv and upload 38.0dbmv hope that means something to coz i don't ave a clue

[samuelnw53]

Got onto site 192.168.100.1 some of the readings are downstream Snr 29.6.... power -7.1dbmv and upload 38.0dbmv hope that means something to coz i don't ave a clueNever put off till tomorrow,what you can do today ,coz if you enjoy doing it today ,you can do it again tomorrow

[daxx]

sorry m8, dont know the limits on the CM's BUT they look ok from here, no doubt ignition or BBK will pop along later int day and sort whatever I've said.

Edit: check Robins site for acceptable power levels http://homepage.ntlworld.com/robin.d.h.walker/ a good site full of very useful info and this http://homepage.ntlworld.com/robin.d.h.walker/cmtips/signal.html section on signal levels which is what those figures are part of