Newell Ryan D SrA 18 CS/SCBT wrote: > > If two 10 Base T Ethernet stations transmit at the same they > receive data on > their receive pins. Will both stations send out a 32 bit jam > sequence?
Yes. > If both stations do send a jam signal, why is the slot time > closely related > to round trip propagation delay? I would think it would be one > way. A collision could happen at the other end of the network segment. News of the collision has to travel back to the senders. The signal travels outwards; the collision news travels back. The goal is to make sure that the sender is still sending when the news travels back, even if the news had to come from the far end of the network segment. If the sender weren't still sending, it wouldn't know that its transmission got damaged and wouldn't back off and retransmit. You would lose the feature of the NIC ensuring succussful transmission, which happens in a microsecond time span, and have to depend on an upper layer figuring out that there's a missing ACK, which happens in a millisecond or worse time span. So, slot time is dependent on round trip time because it considers the time for news of the collision to travel back. Both senders transmit a jam signal to busy out the network for another 32 bit times. At least one of them has to do it, but they can't know that the other one did, so they both do it. Your question doesn't make sense, but hopefully there's some info in that which will help you. > > Ethernet, The Definitive Guide page 182 they have some values > to use to > figure out propagation delay on 10 MB networks. There is a base > value to > start with and from there you add delay per meter. Why is the > base value not > zero? Even light in a vacuum takes some time to travel any distance. It travels 299,792,458 meters per second to be exact, but still, it's not zero. A signal on a network cable travels about 2/3 the speed of light. I don't know what base value you are referring to, but zero times anything is zero, so I doubt they could use a base value of zero regardless. > Also between segments the numbers do not make any sense. > Going from > Base to Max I understand but between segments. A collision domain stops at the boundary between network segments. A network segment is devices connected via hubs or coax cable. In fact, it might help you to remember that Ethernet was originally a long bus, like a link of Christmas tree lights. The signal propagated outwards from the sender in both directions and travelled to the end of the segment, and hopefully not back if the segment was terminated correctly. But if there was a collision, the signal did bounce back. All hubs are is a way to gather this Christmas tree string of lights into a manageable structure. But when first learning CSMA/CD details, it helps to think of the segment like that string of lights. There's a ton of information about CSMA/CD in my book "Troubleshooting Camus Networks." Also, "Ethernet: The Definitive Guide" really is definitive. It's the bible. Don't doubt it. Try to understand it. _______________________________ Priscilla Oppenheimer www.troubleshootingnetworks.com www.priscilla.com > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63589&t=63581 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
