To start off, let's learn a brief history of the Ethernet. In 1973 Xerox created the Ethernet cable to transport data without having to move data through data disks. The rate was a (now) measly 3 mbps. Later in 1979 they looked to promote Ethernet, and found partners such as Intel to sponsor it. By then they had improved it so it had a transfer rate of 10 mbps. The Ethernet standard was controlled by the IEEE which created a committee just for the cable called 802.3 Committee.
Now let's look at the Topology of it. Since the 90s all Ethernet cables have used what is known as a "hybrid star-bus topology". Instead of switches, people used hubs which was just a repeater and interpreter of the binary codes coming in from one port and sending a signal to other ports. But how does it interpret the data that is going in and out?
Well, each Ethernet frame is organised into seven pieces of information. As stated before, the sending computer will make it so other computers are not allowed to use the cable until it is done transferring the data. When a data frame is corrupted, the sending computer will retransmit it until the data makes it to its destination. Now let's look at the seven pieces of a frame: The Preamble, the MAC Addresses of the sending systems, as well as the receiving system, there's also the type of data, a pad, the data, and a CRC (Cyclic Redundancy Check.)
All the preamble is, is a set of 64-bit binary code which all end in 11. It is meant to give time for the receiving NIC to expect a data frame. That's all with that, now the MAC Addresses. So as we know the MAC Address is generally used as an identifier for an NIC, and it still is in this case. The Ethernet is meant to identify the MAC Address. So when the data frame arrives at the hub, the hub is able to create a copy of the frame for every port. With that said, there is also a security vulnerability that comes with this process. Network diagnostics programs or "sniffers" have the ability of making your NIC run in "promiscuous mode" which makes the NIC read all data, regardless of its recipients' MAC Address. Although it's a good tool for troubleshooting, it does not discriminate against people with malicious intent.
Continuing, I will talk more about the "Type, Data, Pad, and FCS (Frame Check Sequence)". The type of Ethernet frames vary on the data it's sending. This helps differentiate the data, like if it were carrying IPv4 or IPv6 data. However this field does not specify the level of data it's carrying (like if it were an e-mail or webpage.) Now the data is the cargo of the frame. If it's an IP packet it carries information about the recipient and sender IP. Now, since the minimum Ethernet frame is 64-bytes when a frame is smaller than that a pad is used. The pad is basically a way of compensating by adding more data to the frame so it fits the minimum requirement. Finally, there is the Frame Check Sequence which is a CRC (Cyclic Redundancy Check) that enables Ethernet to detect any bad corruption within data. For detecting errors, the computers add codes to each frame. The sending device adds a calculation formula so the receiving computer can determine whether the frame is good. If it's not, then the receiving computer asks for a re-transmission. That's where this entry ends. Yes, it was pretty long. But be expecting a short entry on how to make the most popular types of Ethernet cables. Thanks for reading, and tschuss!
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