Back to the Ethernet question. Does the splitter simply take the four wires that 10BaseT uses and make 2 wires out of each, sending one of each to each port? What an awful thing to do to an Ethernet! You bad boys. ;-)
As Scott mentioned, some books make it sound like the sender loops back what it sends so that it can compare that with what it receives back from the hub, sort of implying that the hub sends back the transmitter's bits to the transmitter. A hub doesn't do that. And the loopback isn't used to do a bit-wise comparison with what the hub is sending, like some books imply. That would be computationally expensive and also isn't necessary. Simply receiving while you are sending means a collision occurred. What this means is that in this RJ45 splitter situation, the two senders don't know when the other one is sending. The hub isn't putting it back onto their receive wires. They can still do ordinary collision detection if some other station in the collision domain sends while they are sending, but they can't hear each other. The result must be severly errored frames that the hub merrily propagates to all ports! That's very bad. I think the only reason it works is because the recipient NICs drop the garbage and upper layers at the sender retransmit. Also, it works because the stations aren't actually sending at the same time a lot of the time. Now I wonder why the splitter didn't work on the switch? Did the switch diable the port due to the high number of CRC-errored frames or did it recognize some other problem?? Was there a link light? Priscilla s vermill wrote: > > Priscilla Oppenheimer wrote: > > > > Sim, CT (Chee Tong) wrote: > > > > > > Hi.. I have a friend staying in the hostel room which has a > > > wall port > > > (RJ45) link to the internet. As there are two persons (two > > PC) > > > staying in > > > that room. So they bought a cable splitter. (one side with > > > one female RJ45 > > > jack and another side with two female RJ45 jack). So that > two > > > PCs can > > > connect to internet at the same time, > > > > Are you sure it's Ethernet at your friend's hostel? Maybe it's > > ISDN or something?? Someone will correct me if that's a dumb > > statement. :-) > > > > If it was Ethernet, the only way it could have worked is if > the > > second pair happened to go to another switch port. You can't > > turn one switch port into two simply by splitting the cable. > > > > As Chuck said, buy a hub. A 4-port hub is really cheap (at > > least in the U.S!? ;-) > > > > Priscilla > > > > It's probably a hub in the hostel. I seem to recall > occasionally using an RJ-45 splitter on my wall jack when we > still used hubs. I had my PC in one port of the physical > splitter and my laptop in the other. It was, in essence, a > physical hub tied to an electrical one. I'm not saying this > was a good thing to do for any length of time. But it did, on > the surface, appear to work. > > What I never bothered to find out was whether or not the hub > actually returned what I was transmitting on the receive pair. > A lot of text books tell us that the NIC internally bridges its > transmit to its receive so that it can detect a collision. I > accept that. But I'm not sure if there is a reason why the hub > wouldn't have repeated back on the same port that was being > transmitted on? I wonder that, because if it had, it would > have prevented collisions between the two machines tied to the > physical splitter. Otherwise, I imagine I caused a lot of > collisions between the two, since neither would know when the > other was transmitting (I never realized how much background > traffic an idle Windows machine can generate until I started > doing some packet captures while reading your latest book). > > Now that I think about it, there is one good reason a hub > wouldn't repeat back on the transmitting port: the propagation > delay might make the comeback copy look like an entirely > different transmission (i.e. a collision). I'm sure there are > other good reasons too. > > Or maybe I dreamt the whole thing... > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=55764&t=55667 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
