Please explain why an RJ45 splitter won't work
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
Posted by =?ISO-8859-1?Q?Tom=E1s_=D3_h=C on March 28, 2008, 2:03 pm
Please log in for more thread options I understand that you can't use an RJ45 splitter as an ethernet "double adapter". But could someone please explain to me why? I'm not thick, I'll understand. . . I was under the impression that a very basic hub was a "dumb device" that just connected certain wires together; I thought you'd be able to make one using a wire stripplers, an ethernet cable, and a few RJ45's. Or does a hub need some sort of processing? | ||||
|
Posted by P.Schuman on March 28, 2008, 2:41 pm
Please log in for more thread options The bits are formed into an Ethernet frame and transmitted on the media. The receiver gathers the bits, buffers them, and re-creates the full frame. The hub acts as a go-between to perform the same functions. If you connect 2 computers together on the same wire at the same time, as you are attempting - then what happens when both transmit at exactly the same time, or both receive at exactly the same time...... the bits would be all shuffled together creating garbage. That's why the Ethernet standard for twisted pair wires requires a hub in the middle. The original coax standard, using T-'s - did exactly that... share the media. However, the network card would first "listen" to see if anyone else was transmitting, and if not - then it would transmit. If collisions happened, then each station would back off, and after waiting a random amount of sub-second time - try to transmit again. With the Ethernet twisted pair standard, this has changed somewhat. Hubs are powered, electronic devices that perform all the magic - they are dumb in one sense - but they are intelligent... not just splicing the wires together - else they would not be powered. If you need more - do a search on Ethernet wiring - Tomás Ó hÉilidhe wrote: | ||||
|
Posted by =?ISO-8859-1?Q?Tom=E1s_=D3_h=C on March 28, 2008, 4:34 pm
Please log in for more thread options P.Schuman:
> If you connect 2 computers together on the same wire at the same time,
> as you are attempting - then what happens when both transmit at exactly the > same time, > or both receive at exactly the same time...... the bits would be all > shuffled together creating garbage. I was under the impression that all network hosts perform CSMA/CD. Are you saying that only hubs do? (I'd like to leave switches out of the conversation for now) When you connect two computers together with a cross-over cable, is the reason you don't get collisions = that you have separate pairs for sending and receiving? | ||||
|
Posted by Albert Manfredi on March 28, 2008, 5:12 pm
Please log in for more thread options > P.Schuman:
> > > If you connect 2 computers together on the same wire at the same time,
the
> > as you are attempting - then what happens when both transmit at exactly = > > same time,
> > or both receive at exactly the same time...... the bits would be all > > shuffled together creating garbage. >
> I was under the impression that all network hosts perform CSMA/CD. Are > you saying that only hubs do? (I'd like to leave switches out of the > conversation for now) > > When you connect two computers together with a cross-over cable, is > the reason you don't get collisions =3D that you have separate pairs for > sending and receiving? When two computers are connected with a cross-over cable, you can indeed get collisions. The point is, both computers can detect the collision, because the Tx pair of one goes to the Rx pair of the other. A computer would detect the collision when it sees energy in its Rx pair, while at the same time it is transmitting. So with two computers set up this way, no problem. Now parallel multiple computers on a single RJ-45 connection. How do you do that? All Tx spliced together, all Rx spliced together? Okay. let's try that. One of the computers starts transmitting. How do the others hear that transmission? Certainly not from the signal present on their Tx pairs, right? So how? Bert | ||||
|
Posted by Robert Redelmeier on March 28, 2008, 5:29 pm
Please log in for more thread options > When two computers are connected with a cross-over cable, you
> can indeed get collisions. The point is, both computers can > detect the collision, because the Tx pair of one goes to the Rx > pair of the other. A computer would detect the collision when > it sees energy in its Rx pair, while at the same time it is > transmitting. So with two computers set up this way, no problem. This is not a collision because no data gets mangled. This is just normal full duplex operation. -- Robert | ||||
| Similar Threads | Posted |
| Please explain why an RJ45 splitter won't work | March 28, 2008, 2:03 pm |
| RJ45 splitter for Ethernet - possible ? | March 28, 2008, 11:56 am |
| please explain udld in detail | May 14, 2007, 1:22 pm |
| Why doesn't a hub work for WAN sharing? | February 21, 2006, 10:27 pm |
| how does auto-mdix work | August 22, 2005, 7:56 pm |
| Router connected to a switch. How does it work? | December 3, 2004, 6:18 am |
| Best Percentage Split for MM Ethernet Splitter? | July 31, 2007, 1:31 pm |
| how switches work - collision-free / full-duplex | March 23, 2007, 9:33 am |
| WakeONLAN did not work for direct cable connection ? (Nics were shutdown after a night of sleep ?) | February 9, 2008, 4:56 am |
| RJ45 connectors with a larger "gate"? | September 22, 2004, 10:22 pm |
| RJ45 connectors with a larger "gate"? | September 23, 2004, 9:59 pm |
| Ambiguity for the names of hte RJ45 pins | November 2, 2004, 3:38 am |
| straight-through / cross-over RJ45: interchangeable: why? | July 1, 2007, 3:08 pm |
| Rj45 cable optimized for low space | May 8, 2008, 5:36 am |
| Supply RJ45 Crimping Tools(Punch Down Tool) | November 1, 2005, 5:10 pm |
> "double adapter".
>
> But could someone please explain to me why? I'm not thick, I'll
> understand. . .
>
> I was under the impression that a very basic hub was a "dumb device"
> that just connected certain wires together; I thought you'd be able to
> make one using a wire stripplers, an ethernet cable, and a few RJ45's.
>
> Or does a hub need some sort of processing?