10

To add to Ron's point - a hub (...or a number of hubs) basically models the behavior of the original Ethernet, which is to say basically a big piece of coaxial cable. If one station transmits, all the others receive. When a station wants to transmit, it waits for an opening. If multiple stations try to transmit at the same time then a collision occurs and ...


10

Are uplink ports simplex ? Hub interfaces are simply hub interfaces, there really are no uplink interfaces. Why is it not possible for the hubs to read from the uplink port and broadcast the frame to the remaining ports ? Hubs are stupid. They simply copy the signals received on any interface to all other interfaces. They do not read anything, and they ...


6

It's not that you cannot physically create a hierarchy of hubs. You can. And it will work to some extent (limited by timeouts once your network is too big). The thing to know is that such a configuration from a networking point of view is flat - it is not a hierarchy. Why is a hierarchy not a hierarchy? Because as mentioned before, hubs are stupid. The ...


4

An Ethernet network (without fancy extensions) MUST be a tree. You can put a sticker on one of those hubs saying "main hub" and call it the top of your hierachy if you want the protcol doesn't care. What you can't do is have a hub at a lower level of the hierachy connected to more than one hub at the next level up of the heiracy. Furthermore the ...


4

Switches and NICs don't actually detect the FCS and compare it with their own calculation. They receive a frame until the carrier stops or an idle symbol is detected, depending on the physical-layer variant. On reception, the FCS is calculated in real time across the whole frame, including the FCS field itself. Some clever math is used, so when the carrier ...


4

The end of a frame is signaled by loss of carrier or by a special symbol or sequence in the line coding scheme for a particular Ethernet physical layer, so the length of the frame does not always need to be encoded as a value in the Ethernet frame. However, as the minimum payload of an Ethernet frame is 46 bytes, a protocol which uses EtherType must include ...


2

"We also know that the minimum MTU is 576 Bytes." No, we do not know that because it is not true. I am not sure where you got such an idea. The MTU is the maximum payload of the data-link protocol. In the case of ethernet, the IEEE standard says that is 1500 bytes. The minimum payload size is 46 bytes (42 bytes for tagged frames), but that is not a ...


2

I think your terminology of "uplink port" might be a source of confusion. Connecting a pair of hubs together by a patch cable will fail, unless one or both of the hubs does auto MDI detection, also known as MDI-X for Crossover. Some hubs have a doubled-up port where two RJ45 jacks are present, with one wired "straight" and the next one ...


2

I came to know that we cannot create a hierarchy of hubs. My question is why so? That depends on the book's definition of "hierarchy". In CSMA/CD, no repeater has more "weight" than any other, so there's no hierarchy in terms of priority. However, you can (and should) arrange repeater hubs in a tree (multi-star) topology, so there's a ...


1

Yes, a switch is exactly what you need. Using a switch, each device can communicate with any other in the same network. The switch uses the interfaces' MAC addresses to direct the traffic where it should go - no further configuration required (only for TCP/IP, see below). It's like connecting them directly, the only difference is that without a dedicated ...


1

sender should be transmitting for at least the 2*PT,where PT is end to end propagation delay. Worst case is between senders that are located at opposite ends of a collision domain. Imagine sender 1 transmitting at one end. Its signal propagates to the far end where sender 2 has just started transmitting as well. Sender 2 detects the collisions, abort the ...


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