Introduction to Ethernet


Ethernet Basics

In this section we will explore the basics of Ethernet. Ethernet was first created by Xerox in the year 1973 as a technology based on bus with a max speed of 3 Mbps. The next iteration could handle up to 10 Mbps and was called the DIX standard. DIX then came under the control of the IEEE and 10BaseT emerged as the first version of Ethernet to use UTP cabling. 10BaseT used  CSMA/CD and employed data frames.

The topology of Ethernet can involve a hybrid star-bus. This bus acts as a central hub for many connections via ports. Each port connection is called a node and nodes share information between one another. All network technologies, including Ethernet, are organized in frames. These frames contain seven key pieces of information. These pieces are the preamble, the data itself, the destination’s MAC address, the pad, the source’s MAC address, the frame check sequence, and finally the length.

In this topology, sniffers can run in what is called promiscuous mode and compromise the security of this type of network. These networks run on CSMA/CD. This stands for Carrier Sense Multiple Access Collision Detection. Carrier Sensing examines frames on the wire prior to sending, Multiple Access means all devices have equal access to the wire, and Collision Detection checks for two transmissions being sent at the same time.

10BaseT was created in 1990 and is used in over 99% of every network. The name comes from 10 Mbps, the Baseband signal type, and finally T for twisted pair cabling. 10BaseT typically used unshielded twisted cables, or UTP, with RJ-45 connectors. One pair of cable sends and the other receives information. Each pin in RJ-45 connectors has its own purpose. 1 and 2 send while 3 and 6 receive. These wires are connected with color code by what is called a crimp. You need to know the color codes for both TIA/EIA 568A and TIA/EIA 568B. Telephones use RJ-11 connectors, which is a similar technology that uses only two wires at the 2 and 3 positions with a second phone line at the 1 and 4 positions. 10BaseT connections cannot exceed 100 m or 1024 computers connected.

10BaseFL has a maximum distance of 2000 m and is totally immune to EMI. These connections use multimode fiber optic cables with ST and SC connectors. When connecting different types of Ethernet networks, you can use a media converter to connect. Uplink ports can be used to extend and enhance Ethernet networks into groups known as segments. These ports can daisy-chain four hubs and it is worth your time to figure out the proper connections. These connected be connected as hierarchical configurations. These segments can be connected by a crossover cable, which reverses sending and receiving pairs. You can also connect segments with a bridge, which acts as a sort of hub between segments. It can also filter and record information passing through it. These bridges operate on the data link layer and can only be connected using the same types of data frames.

Switched Ethernet is an alternative to hubs that are able to more efficiently handle increased bandwidth. Switches are similar in appearance to hubs, but they can learn and track the MAC addresses of all the devices connected to it. This eases traffic and creates point-to-point connections between computers. Switches are more efficient and allow for hierarchical architecture. These switches can be connected in any configuration, don’t allow for collisions, and prevent bridge loops via the spanning tree protocol.

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