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Double outlet Ethernet Cable?


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#1 OFFLINE   JerryM

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Posted 15 January 2006 - 07:14 PM

Is there such a thing as an ethernet cable with two outlets that you could connect two computers to?I do have WIFI but I am curious as to whether one could hardwire, through the ethernet, two computers on one line.Thanks.Jerry

#2 OFFLINE   Pete!

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Posted 15 January 2006 - 07:22 PM

It's called a crossover cable.It lets you network two computers (or hubs).I used one for several years, to back-up data and documents to the HD on an old machine. Much faster than floppies or CD burning.See: http://www.windowsne...htm#cross-cable

Edited by Pete!, 15 January 2006 - 07:26 PM.


#3 OFFLINE   Marsden11

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Posted 15 January 2006 - 07:50 PM

I think he means 2 computers using (sharing) a single CAT5 cable. Yes it is possible to split the 4 pairs of wires. 4 wires (2 pairs) for connection 1 and the other 2 pairs for connection 2.

#4 OFFLINE   lewmur

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Posted 15 January 2006 - 08:19 PM

View PostMarsden11, on Jan 15 2006, 08:50 PM, said:

I think he means 2 computers using (sharing) a single CAT5 cable. Yes it is possible to split the 4 pairs of wires. 4 wires (2 pairs) for connection 1 and the other 2 pairs for connection 2.
Not and maintain Cat5e capabilities.  It might work with 10/100 but not gigabit.  Even with 10/100 there is no telling how much the crosstalk would degrade performance.

Edited by lewmur, 15 January 2006 - 08:24 PM.


#5 OFFLINE   FuzzButt

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Posted 16 January 2006 - 12:42 AM

It is very possible to custom make a 2 ended ethernet cable. Since maybe 1% of people have Giga-Ethernet and it really only has a slight preformance boost anyway.Both 10 and 100 use 4 wires. Wire #'s 1,2,3,6 that leaves you with 4,5,7,8 free for other things. Phone or POE (Power over Ethernet) are some that some to mind. if anything the 42V POE has to have issues with signal degradation but it does not seem to be an issue. Anyway you could cut the ends off a cat5 4 pair twisted pair cable and remove both the orange conductors, and the green pairs and terminate them on one RJ45 plug then use the remaining 4 wires substituting the brown pair and the blue pair. Just as long as both ends are identical and you remove no more then 1/2 a twist in the cable in order to terminate them in the RJ45 plug. Even more helpful would be 2 patch cables like this but only having one end of each patch cable divided like this so you can use a cat5 jack in the wall/patch panel. We do something like this at work for use with a 25 pin serial cable that uses 12 wires. 8 of them go on a 4 pair RJ45 and 2 pair go on an RJ11.Now what I think you are asking. Can you share 1 Ethernet connection with 2 PC's using 1 wire feed from the outside. No. Not without using another piece of equipment.

Edited by FuzzButt, 16 January 2006 - 12:20 PM.


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#6 OFFLINE   lewmur

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Posted 16 January 2006 - 01:15 AM

View PostFuzzButt, on Jan 16 2006, 01:42 AM, said:

It is very possible to custom make a 2 ended ethernet cable. Since maybe 1% of people have Giga-Ethernet and it really only has a slight preformance boost anyway.
You've got to be kidding.  File transfers are five to ten times faster with gigabit.  If all you are doing is connecting to the Internet, then it won't make ANY difference.  But if you are transferring files from one computer to another, gigabit makes a dramatic difference.If I had existing wiring in the wall and really needed to avoid running a second cable, then certainly I'd double up.  But, on the other hand, if I were running new wiring there is no way I wouldn't stick to Cat5e specs.

Edited by lewmur, 16 January 2006 - 01:17 AM.


#7 OFFLINE   Marsden11

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Posted 16 January 2006 - 04:27 AM

Please explain PoE or Power over Ethernet. Works fine on CAT5.Crosstalk has nothing to do with unused pairs. It has everything to do with the number of twists per inch in a single pair. The more twists per inch the higher the CAT rating.CAT6 cable is being made with 23 guage conductor wire as opposed to the slightly smaller 24 guage for CAT5e and also has a separator to handle crosstalk better. Crosstalk is the "bleeding" of signals carried by one pair, onto another pair through the electrical process of induction (wires need not make contact, signals transferred magnetically). This is an unwanted effect, that can cause slow transfer, or completely inhibit the transfer of data signals over the cable segment. The purpose of the wire twists, in CAT 5E cable is to significantly reduce the crosstalk, and it's effects. Two types are: NEXT (Near End Crosstalk), and FEXT (Far End Crosstalk). Fiber Optic cable is the only medium that is 100% immune to the effects of crosstalk.

#8 OFFLINE   JerryM

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Posted 16 January 2006 - 10:15 AM

WOW!What I was wanting to do is have another outlet on my ethernet cable so that I could connect a laptop temporarily and shut the other computer down. It would  be more convenient than disconnecting one computer and connecting to the laptop. But maybe it is not a good idea. Thanks for the replies.Jerry

#9 OFFLINE   Pete!

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Posted 16 January 2006 - 11:02 AM

Not sure about that one...if only one computer was connected at a time ??I don't think you're going to be able to buy a cable like that. I guess you could try to make one and see if it works...The easiest way out may be to get an inexpensive hub.

#10 OFFLINE   lewmur

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Posted 16 January 2006 - 11:32 AM

View PostMarsden11, on Jan 16 2006, 05:27 AM, said:

Crosstalk has nothing to do with unused pairs. It has everything to do with the number of twists per inch in a single pair. The more twists per inch the higher the CAT rating.
Again, you are making false statements.  When those "unused" pairs are being used to carry signals, those signals CAN create crosstalk on the other pairs.  In Cat5e cable, those "unused" pairs are grounded to help isolate the two pairs that are carrying signals and reduce crosstalk on them.  Just as the extra 40 wires do in an 80 wire IDE cable.

View PostPete!, on Jan 16 2006, 12:02 PM, said:

Not sure about that one...if only one computer was connected at a time ??I don't think you're going to be able to buy a cable like that. I guess you could try to make one and see if it works...The easiest way out may be to get an inexpensive hub.
Yes, the hub is your answer.  What you are talking about would be called a "spitter," and you can't do that with an ethernet cable.  That is the purpose of a bub.  But you might find it easier to find a cheap router than a cheap hub.  That would give you the additional benifit of a hardware firewall.

Edited by lewmur, 16 January 2006 - 11:34 AM.


#11 OFFLINE   FuzzButt

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Posted 16 January 2006 - 12:17 PM

View Postlewmur, on Jan 16 2006, 12:15 AM, said:

File transfers are five to ten times faster with gigabit.  If all you are doing is connecting to the Internet, then it won't make ANY difference.  But if you are transferring files from one computer to another, gigabit makes a dramatic difference.If I had existing wiring in the wall and really needed to avoid running a second cable, then certainly I'd double up.  But, on the other hand, if I were running new wiring there is no way I wouldn't stick to Cat5e specs.
All I am saying is that Giga while being faster is not so fast as to warrant any difference in a discussion like this. From what I gather Giga uses all 8 wires so there are none free anyway. The biggest issue with Giga from what I have here is the fact that the rest of the PC cannot keep up with the speeds since the PCI bus is only so fast. I move files between 2 PC's all the time. Sometimes 2 GB at a time. Even with using Remote Desktop sharing on the same connection I see up to 10MB/s using 100BaseT and a switch. The good thing about Giga is when there are more than 2 users there is still room in the pipe.

View PostMarsden11, on Jan 16 2006, 03:27 AM, said:

Please explain PoE or Power over Ethernet. Works fine on CAT5.
POE. Quite simply a way to power a remote network device. We use it to power an Access Point about 75 feet from the Switch that it is plugged into. It seems to work well but then again there is no way to speed test it since it is wireless limited to "B" speeds. See http://www.powerover...?article_id=271 for more info. It is real cool stuff. This is not ethernet over power, where you use the power lines in your house as a network.

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#12 OFFLINE   lewmur

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Posted 16 January 2006 - 12:55 PM

View PostFuzzButt, on Jan 16 2006, 01:17 PM, said:

All I am saying is that Giga while being faster is not so fast as to warrant any difference in a discussion like this. From what I gather Giga uses all 8 wires so there are none free anyway. The biggest issue with Giga from what I have here is the fact that the rest of the PC cannot keep up with the speeds since the PCI bus is only so fast. I move files between 2 PC's all the time.thernet over power, where you use the power lines in your house as a network.
Not so.  Most of *today's* PC's are MUCH faster than a gigabit in all but the IDE transfer.  And that is where the difference lies.  The gigabit card allows you to transfer files at about the same speed as the current IDE bus allows.  Which is 5 to 10 times what you could do with 10/100.  And I doubt you are getting 100mbits if you are using your powerlines.  Just for the fun of it, if you want, I'll time transferring a 700mb cd iso file over my gigabit system and you try it on your system and we can compare results.

#13 OFFLINE   FuzzButt

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Posted 16 January 2006 - 01:44 PM

Allright,Using 678MB sample (as close to 700MB as I have) 100mb Ethernet Transfer from this PC to my other PC from hard drive to hard drive. (had to use the stopwatch on my cell phone since I don't own a watch)694,620 KB MPG file transfered in 1:28.53 or 7.846 MB/s714,758 KB AVI file transfered in 1:29.98 or 7.942 MB/sSince 100BaseTx os only good for 12.5MB/s max and there is 2.6% overhead with TCP/IP for a loss of 3.25MB/s I should see 1.4MB/s more speed.Just for giggles transfering the same file via USB2 to an external drive took 33.29 seconds or 21.47 MB/s.I know transfering 12.5 GB across firewire takes about 45 minutes from my miniDV camera.I am thinking about setting up a gigabit subnet here between the 2 PC's or if I have to between all of them seperating the lan and wan. but it's a time/money thing. Os the money invested worth the time saved. Not really I don't mind waiting.

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#14 OFFLINE   JerryM

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Posted 16 January 2006 - 03:42 PM

Thanks. I think a hub is the way to go in this instance.Jerry

#15 OFFLINE   FuzzButt

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Posted 16 January 2006 - 03:49 PM

If you need to purchase a hub I would suggest spending a few more dollars and get a switch instead.

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#16 OFFLINE   lewmur

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Posted 16 January 2006 - 04:03 PM

View PostFuzzButt, on Jan 16 2006, 02:44 PM, said:

Allright,Using 678MB sample (as close to 700MB as I have) 100mb Ethernet Transfer from this PC to my other PC from hard drive to hard drive. (had to use the stopwatch on my cell phone since I don't own a watch)694,620 KB MPG file transfered in 1:28.53 or 7.846 MB/s714,758 KB AVI file transfered in 1:29.98 or 7.942 MB/sSince 100BaseTx os only good for 12.5MB/s max and there is 2.6% overhead with TCP/IP for a loss of 3.25MB/s I should see 1.4MB/s more speed.Just for giggles transfering the same file via USB2 to an external drive took 33.29 seconds or 21.47 MB/s.I know transfering 12.5 GB across firewire takes about 45 minutes from my miniDV camera.I am thinking about setting up a gigabit subnet here between the 2 PC's or if I have to between all of them seperating the lan and wan. but it's a time/money thing. Os the money invested worth the time saved. Not really I don't mind waiting.
I don't know what kind of equiptment you are running but I just ran a test on mine.  I have True Image backup file that is 1.126gb.  My desktop rig has a builtin 10/100 card and a gigabit PCI card.  When I copy the file from disk to disk on the desktop, it takes just over two minutes.  When I copy from my desktop to my labtop using the gigabit card, it also takes just over two minutes.  But when I switch to the 10/100 card in the desktop and copy to the laptop it takes 19 minutes.  And with what people are spending on computer stuff today, the extra expense is minimal.  Gigabit PCI nics can be had for under $15/ea and a 5 port switch for about $30.

#17 OFFLINE   FuzzButt

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Posted 16 January 2006 - 06:35 PM

Ya but I need 8 giga ports on a quality switch. I suppose 5 will do but I have 7 active ports on my 10/100 router.My equipment is a 3com ec905btx nic in one PC going across a Linksys BEFSR81 Router then to a Intel 10/100/1000 NIC built-in to my Intel 865PE mobo. Your speed on 1,126,000KB is 9.33MB/s Not too bad for 100mb ethernet

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#18 OFFLINE   Marsden11

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Posted 16 January 2006 - 10:11 PM

Let's get technical shall we?Ethernets consist of two transmission lines.  Each transmission line is a pair of  twisted wires.  One pair receives data signals and the other pair transmits data signals.  A balanced line driver or transmitter is at one end of one of these lines and a line receiver is at the other end.The twisted-pair Ethernet employs two principle means for combating noise.  The first is the use of balanced transmitters and receivers.  A signal pulse actually consists of two simultaneous pulses relative to ground: a negative pulse on one line and a positive pulse on the other.  The receiver detects the total difference between these two pulses.  Since a pulse of noise usually produces pulses of the same polarity on both lines one pulse is essentially canceled by out the other at the receiver.  Also, the magnetic field surrounding one wire from a signal pulse is a mirror of the one on the other wire. At a very short distance from the two wires the magnetic fields are opposite and have a tendency to cancel the effect of each other out.  This reduces the line's impact on the other pair of wires and the rest of the world.Not technical enough?The balanced voltage receiver eliminates the effects of Electromagnetic Interference (EMI) that produces identical signals on both wires.  But suppose they aren't equal?  That's where the twist comes into play. Picture two untwisted parallel wires connecting an Ethernet’s transmitter to its receiver (or at the beginning and end of any chunk of wire in between).  Let's say at any instant there are voltages Vin, Vnoise, and Vout.  Vnoise is an induced voltage difference between the wires caused some sort of EMI, distortion in the cable geometry, differences in the conductors, etc.  Kirchoff's 2nd law states that the sum of voltages around a loop equals zero.  That is, - Vin + Vnoise + Vout = 0.  Or, Vout = Vin - Vnoise.  Let's divide-up Vnoise into a series of voltages for each inch (or other unit or length; e.g., twist interval) of the parallel wires; i.e, Vnoise = V1 + V2 + V3... = Vnoise.  Nothing has changed.  Now twist the wires one twist per inch, then represent the voltages on both wires in an untwisted circuit diagram, and watch the magic.  Assuming V1 = V2 = V3… Vnoise = +V1 - V2 + V3 - V4 + V5... = V1 (at maximum).  Or, Vout = Vin - Vnoise/n where n = the number of twists.  This of course is a simplification and an approximation; however, it certainly demonstrates the importance of the word "twist" in "twisted-pair."  CAT 5e actually has about one twist per half inch and CAT 6 is tighter.  Untwist CAT 5e one inch and you will double the noise (on a linear scale).4 (2 pairs) of the unused wires in any CAT5, CAT5e, or CAT6 cables are wasted wires.

#19 OFFLINE   FuzzButt

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Posted 17 January 2006 - 09:59 AM

Pretty cool info there Marsden. Thanks

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#20 OFFLINE   lewmur

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Posted 17 January 2006 - 10:48 AM

View PostMarsden11, on Jan 16 2006, 11:11 PM, said:

Let's get technical shall we?Ethernets consist of two transmission lines.  Each transmission line is a pair of  twisted wires.  One pair receives data signals and the other pair transmits data signals.  A balanced line driver or transmitter is at one end of one of these lines and a line receiver is at the other end.4 (2 pairs) of the unused wires in any CAT5, CAT5e, or CAT6 cables are wasted wires.
That whole disertation was about as technical as telling kids daddy left a baby in mommy's stomach.  But then you top it off with an out and out falsehood.  Try not connecting the second two pairs of "wasted wires" in a Cat5e cable and plugging them into a gigabit system and watch what happens to your transfer speeds.  Those second two pairs are used for the SAME PURPOSE AS THE TWIST.  They increase the bandwidth by reducing the EMI by acting as a "sheild."

#21 OFFLINE   FuzzButt

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Posted 17 January 2006 - 02:11 PM

We seem to be veering away from the original wuestion that was answered as "Yes a hub is your way to go".But I thought I would add this

View Postlewmur, on Jan 17 2006, 09:48 AM, said:

Try not connecting the second two pairs of "wasted wires" in a Cat5e cable and plugging them into a gigabit system and watch what happens to your transfer speeds.  Those second two pairs are used for the SAME PURPOSE AS THE TWIST.  They increase the bandwidth by reducing the EMI by acting as a "sheild."
(1)  In the cabling there are 2 ways to reduce EMI. The twists (6 per foot) is one way. The signaling is the other. The way the signaling takes place on the balanced transmitters and recievers is key. You can download the pdf at http://www.iol.unh.edu/training/ge/ Charles has some good info and links.(2) If you don't connect the other 4 wires in the 4 pair cat5e or what ever varient you will not have a connection. 1000BaseT (802.3z) is set up like this.       MDI           MDI-X1    BI-DA+    BI-DB+2    BI-DA-     BI-DB-  3    BI-DB+    BI-DA+4    BI-DC+    BI-DD+5    BI-DC-     BI-DD-6    BI-DB-     BI-DA-7    BI-DD+    BI-DC+8    BI-DD-     BI-DC-See http://www.windowsne...sic/n1000bt.gif for a picture if you want for 1000BaseT, http://www.windowsne...ic/croscabl.gif for 100BaseTx and http://www.windowsne...ic/crostpt4.gif for 100Base4 (which does use all 8 wires)(a good reference is http://www.windowsne...t-Ethernet.html if your interested)The way you get the 1000Mb speed is using PAM-5 Implementation, a signal rate of 125MHz, 2 cycles per second and 4 pairs of cable. 125*2*4 = 1000Now in one of your previous responses you mention you can transfer 1.126GB in 2 minutes. About 9MB/s. Hard to say since 2 minutes is a bit vauge. My slightly slower 100BaseT network can transfer data at 7.8-8.0 MB/s all day long. I even tested it using an 8GB backup file. The only advantage gigabit or GbE offers is in a multiple PC or switch-switch environment where there is more traffic or if you can use jumbo frames.

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#22 OFFLINE   Marsden11

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Posted 18 January 2006 - 04:02 AM

Interesting but incorrect.I'm currently using 2 D-Link DWL1000 cards connected with CAT2 phone cable and running Gigabyte Ethernet over that connection.BTW, that CAT2 phone cable only has 2 pairs.What I'm doing tonight you claim can't be done. Total BS!All you posted are wiring diagrams which does not mean diddley when it comes to what is actually used or unnecessary.740MB/s sustained bandwidth. Now, I do loose some packets but not enough to really matter because packet loss in TCP is recoverable.I'm an iEEE lifelong member and I'll post the specs for CAT5e and CAT6 when I get a chance.

#23 OFFLINE   Marsden11

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Posted 18 January 2006 - 04:29 PM

Looking at the standards from iEEE we are both right and wrong.There are two standards for 1000Base Ethernet communications. 802.3z or 1000Base-X (1000BaseSX - short wave covers up to 500m, and 1000BaseLX - long wave covers up to 5km)802.3ab or 1000Base-T defines the Gigabit Ethernet over the unshielded twisted pair wire (1000Base-T covers up to 75m)Fast Ethernet 802.3uLike Ethernet, 100BASE-T is based on the CSMA/CD LAN access method. There are several different cabling schemes that can be used with 100BASE-T, including: 100BASE-TX: two pairs of high-quality twisted-pair wires 100BASE-T4: four pairs of normal-quality twisted-pair wires 100BASE-FX: fiber optic cables I'll post more details later. I would post a link but the standards are available only by fee unless your a member of the iEEE group.




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