two workstations in one cat5e?

meligio · 01-19-2007, 02:07 AM

hi,

is it possible to have two PC's in one cat5e cable? i had the 1-2 and 3-6 pair for one pc, 4-5 and 7-8 for the other. the pc's are to be used for highspeed internet connection..won't this affect the speed of data transmition or is it ok?

**johnwill** · 01-19-2007, 09:29 AM

No problem for 10/100 connections. Note that gigabit over copper uses all four pairs, so you'll obviously preclude gigabit connections.

I do this myself for a long run through my attic to the basement, I bring my FiOS connection up on two pairs, and then connect the stuff downstairs through the other one.

**Cellus** · 01-19-2007, 11:54 AM

There will be an increase of crosstalk, however it shouldn't affect it significantly. You may get a slight increase in collisions (dropped packets), but nothing really noticeable.

**cjessee** · 01-19-2007, 11:59 AM

I would hope that you are not trying to get around the purchase of a router. You can't really "split" the connection.

But you can connect two computers for base100 networks you will only use 2 pairs... so you can use the other two pairs for another computer... or a telephone for example....

**johnwill** · 01-19-2007, 07:07 PM

Actually, there should be no issue with crosstalk. The whole point of the twisted pairs is to deal with that issue. Note that gigabit connections use all the pairs in bi-directional mode, and that's not an issue.

**Cellus** · 01-20-2007, 04:38 PM

Twisted pairs do help a lot in reducing crosstalk, however the null wires in Fast Ethernet had the advantage of providing a buffer. In practice the wires not in use usually double for voice communication, however voice only goes at 64kbps so the affects of corruption, doubled with the fact it isn't data (so integrity isn't paramount, plus CSMA/CD isn't running on it), doesn't make much of a difference. However if you start mixing two Fast Ethernet connections on a single cable, the increased sensitivity to corruption and the detection of collisions (with CSMA/CD) can cause an increased drop in packets.

Gigabit Ethernet, while using all four pairs, uses things such as echo cancellation, 8B/10B binary encoding, and a 5-level signal to effectively use all four pairs. Fast Ethernet however does not use echo cancellation, runs on a 4B/5B binary encoding, and a 3-level signal.

There will be an (edit) increased sensitivity to corruption and possible near-end crosstalk when both connections are in use on the one cable, but not significant. Also if the cable is poorly split into two connections at both ends, you will have problems with interference and crosstalk. While it's doable, it is recommended to use two cables.

EDIT: I do this long speel and I suddenly realize I wasn't being elaborate enough where it counted. Yay me.

**johnwill** · 01-20-2007, 07:50 PM

I've run throughput tests on my 100' cable, and I have never been able to detect any dropped packets on either of the two interfaces, so I'm pretty confident that any crosstalk is minimal.

Also, in point of fact, the 5 level signal used by gigabit Ethernet makes it more sensitive to crosstalk, not less.

**Cellus** · 01-21-2007, 11:29 AM

The 5-level signal does in some regards, you are right. However on the other hand it gains protection from noise (some say immunity, but I'm not on that bandwagon) when it is used in conjunction with 4D modulation on all four pairs.

I'm thinking some have had mixed results on this, because I had this very same discussion back in December with a veteran in networking and when he and a few others were trying to run two Fast Ethernet connections on the same cable, they were finding problems. There were issues with near-end crosstalk, mainly with the Rx on wires 3/6, as they were sandwiched from the Tx on 1/2 and 4/5.

**Cellus** · 01-21-2007, 12:16 PM

I contacted him for good measure, where I ended up getting promptly scolded - the experiment was having both connections go through a single connector, not two. I knew something was wrong with my defense on this debate the moment started, but I couldn't quite put my finger on it.

You can throw your pie now John.

**johnwill** · 01-21-2007, 02:46 PM

That might explain it.

I ran mine to a two connector plate at each end. I do agree that you need to keep the twisted pairs twisted right up to the connector, even an inch or two of untwisted wire will degrade the signal.

It's actually quite amazing how good twisted pair is at rejecting common mode interference.

Quote:

Originally Posted by Cellus

You can throw your pie now John.

If you insist.

meligio · 01-22-2007, 08:29 AM

thanks for the info guys.

ill keep it in mind.

01-19-2007, 02:07 AM	#1 (permalink)
meligio Registered User Join Date: Jan 2007 Posts: 6 OS: Fedora 6	two workstations in one cat5e? hi, is it possible to have two PC's in one cat5e cable? i had the 1-2 and 3-6 pair for one pc, 4-5 and 7-8 for the other. the pc's are to be used for highspeed internet connection..won't this affect the speed of data transmition or is it ok?

01-19-2007, 09:29 AM	#2 (permalink)
johnwill Manager, Networking Forums Join Date: Sep 2002 Location: S.E. Pennsylvania, US Posts: 41,832 OS: Windows 7, XP-Pro, Vista, Linux Blog Entries: 1	No problem for 10/100 connections. Note that gigabit over copper uses all four pairs, so you'll obviously preclude gigabit connections. I do this myself for a long run through my attic to the basement, I bring my FiOS connection up on two pairs, and then connect the stuff downstairs through the other one. __________________ If TSF has helped you, Tell us about it! or Donate to help keep the site up! Microsoft MVP - Windows Desktop Experience

01-19-2007, 11:54 AM	#3 (permalink)
Cellus Moderator Networking Team Join Date: Aug 2006 Location: Canada Posts: 2,664 OS: Windows Vista Business SP1, Windows XP Professional SP3 My System	There will be an increase of crosstalk, however it shouldn't affect it significantly. You may get a slight increase in collisions (dropped packets), but nothing really noticeable. __________________ TSF Networking Team Virus/Trojan/Spyware Removal Help Donate!

01-19-2007, 07:07 PM	#5 (permalink)
johnwill Manager, Networking Forums Join Date: Sep 2002 Location: S.E. Pennsylvania, US Posts: 41,832 OS: Windows 7, XP-Pro, Vista, Linux Blog Entries: 1	Actually, there should be no issue with crosstalk. The whole point of the twisted pairs is to deal with that issue. Note that gigabit connections use all the pairs in bi-directional mode, and that's not an issue. __________________ If TSF has helped you, Tell us about it! or Donate to help keep the site up! Microsoft MVP - Windows Desktop Experience

01-20-2007, 04:38 PM	#6 (permalink)
Cellus Moderator Networking Team Join Date: Aug 2006 Location: Canada Posts: 2,664 OS: Windows Vista Business SP1, Windows XP Professional SP3 My System	Twisted pairs do help a lot in reducing crosstalk, however the null wires in Fast Ethernet had the advantage of providing a buffer. In practice the wires not in use usually double for voice communication, however voice only goes at 64kbps so the affects of corruption, doubled with the fact it isn't data (so integrity isn't paramount, plus CSMA/CD isn't running on it), doesn't make much of a difference. However if you start mixing two Fast Ethernet connections on a single cable, the increased sensitivity to corruption and the detection of collisions (with CSMA/CD) can cause an increased drop in packets. Gigabit Ethernet, while using all four pairs, uses things such as echo cancellation, 8B/10B binary encoding, and a 5-level signal to effectively use all four pairs. Fast Ethernet however does not use echo cancellation, runs on a 4B/5B binary encoding, and a 3-level signal. There will be an (edit) increased sensitivity to corruption and possible near-end crosstalk when both connections are in use on the one cable, but not significant. Also if the cable is poorly split into two connections at both ends, you will have problems with interference and crosstalk. While it's doable, it is recommended to use two cables. EDIT: I do this long speel and I suddenly realize I wasn't being elaborate enough where it counted. Yay me. __________________ TSF Networking Team Virus/Trojan/Spyware Removal Help Donate! Last edited by Cellus; 01-20-2007 at 05:01 PM.

01-19-2007, 11:59 AM	#4 (permalink)
cjessee Uh oh. Join Date: Aug 2005 Location: Ohio Posts: 794 OS: Windows NT/2000/XP, Dictaphone, Windows 2003 Server	I would hope that you are not trying to get around the purchase of a router. You can't really "split" the connection. But you can connect two computers for base100 networks you will only use 2 pairs... so you can use the other two pairs for another computer... or a telephone for example....

01-20-2007, 07:50 PM	#7 (permalink)
johnwill Manager, Networking Forums Join Date: Sep 2002 Location: S.E. Pennsylvania, US Posts: 41,832 OS: Windows 7, XP-Pro, Vista, Linux Blog Entries: 1	I've run throughput tests on my 100' cable, and I have never been able to detect any dropped packets on either of the two interfaces, so I'm pretty confident that any crosstalk is minimal. Also, in point of fact, the 5 level signal used by gigabit Ethernet makes it more sensitive to crosstalk, not less. __________________ If TSF has helped you, Tell us about it! or Donate to help keep the site up! Microsoft MVP - Windows Desktop Experience

01-21-2007, 11:29 AM	#8 (permalink)
Cellus Moderator Networking Team Join Date: Aug 2006 Location: Canada Posts: 2,664 OS: Windows Vista Business SP1, Windows XP Professional SP3 My System	The 5-level signal does in some regards, you are right. However on the other hand it gains protection from noise (some say immunity, but I'm not on that bandwagon) when it is used in conjunction with 4D modulation on all four pairs. I'm thinking some have had mixed results on this, because I had this very same discussion back in December with a veteran in networking and when he and a few others were trying to run two Fast Ethernet connections on the same cable, they were finding problems. There were issues with near-end crosstalk, mainly with the Rx on wires 3/6, as they were sandwiched from the Tx on 1/2 and 4/5. __________________ TSF Networking Team Virus/Trojan/Spyware Removal Help Donate! Last edited by Cellus; 01-21-2007 at 11:31 AM.

01-21-2007, 12:16 PM	#9 (permalink)
Cellus Moderator Networking Team Join Date: Aug 2006 Location: Canada Posts: 2,664 OS: Windows Vista Business SP1, Windows XP Professional SP3 My System	I contacted him for good measure, where I ended up getting promptly scolded - the experiment was having both connections go through a single connector, not two. I knew something was wrong with my defense on this debate the moment started, but I couldn't quite put my finger on it. You can throw your pie now John. __________________ TSF Networking Team Virus/Trojan/Spyware Removal Help Donate!

01-22-2007, 08:29 AM	#11 (permalink)
meligio Registered User Join Date: Jan 2007 Posts: 6 OS: Fedora 6	thanks for the info guys. ill keep it in mind.