What is ethernet?

• Ethernet is a baseband networking technology that has been defined by various standards. A baseband technology devotes the entire bandwidth of the media to one channel. Simplistically, bandwidth can be defined as a measure of network capacity - the greater the available bandwidth, the greater the network's resilience to loading. The inclusion of the word "base" in 10BaseT, 10Base5 etc., simply refers to ethernet's baseband nature.
  
  
• There are no levels of priority for transmission. All computers on an ethernet network are considered equal in terms of their access to the media. In contrast to token ring, there is no monitoring station that controls the network.
  
  
• Unless it is switched :
• ethernet uses carrier sensed multiple access with collision detection (CSMA/CD) as its method of medium access control.
• data in the ether is accessable to all connected devices.
• high loading on a LAN segment can lead to packet collisions and a marked drop in network efficiency.
• ethernet has a broadcast logical topology - data is sent to all nodes on the network simultaneously:



• As shown in the diagram, ethernet is the most dominant LAN technology:

The figures represented in the pie chart are relatively out of date, although ethernet still remains the most common LAN architecture. ATM has become important as a LAN technology in areas of the computing industry where high data tranfer rates are required. Multimedia, computer graphics and video conferencing all need fast networks, therefore ATM is a good choice, but the emergent gigabit ethernet may challenge ATM.
 

• Ethernet conforms to the OSI model and covers layer 1 - physical, and layer 2 - datalink (medium access control).
  
  
• Interfaces have been developed to connect all types of computer, across many types of media, to ethernet. PCs use a network interface card to manage medium access control and communicate with the layer 2 process.

Give me some examples!

• 10Base5. Commonly known as thick ethernet, it is characterised by its thick coaxial cable (RG-8). A viper-tap is required to pierce the tough outer armour, allowing a computer to connect via an interface card. It operates at 10Mbps, with a maximum segment (between repeaters) length of 500 metres. Thick ethernet is largely a legacy installation, but it was once used as a LAN backbone - a backbone is usually an installation in a bulding from which segments radiate. 10Base5 uses a bus physical topology.

• 10Base2. Commonly known as thin ethernet, thinnet or cheapernet, it is characterised by its thin coaxial cable (RG-58). Thin ethernet uses BNC T-piece connectors to link the interface card to the coaxial. It operates at 10Mbs, with a maximum segment length of 185 metres. Thin ethernet is also a legacy installation, having been superceded by 10BaseT and 100BaseT. 10Base2 uses a bus physical topology. BNC terminators are placed at the end of each segment. They prevent signal reflections which could cause interference in the ether.

• 10BaseT. Simply referred to as 10BaseT. It uses unshielded twisted pair cabling (commonly category 5 grade) and RJ45 connectors. UTP cable resembles domestic telephone wire. The RJ45 connectors are American telephone connectors. They look similar to the British connectors, although RJ45 is a little bigger. 10BaseT operates at 10Mbps, with a maximum 100 metres segment length. 10BaseT uses a star physical topology.

• 100BaseT. This is a logical progression from 10BaseT, it is fully compatible with 10BaseT and often referred to as fast ethernet. It uses category 5 UTP cable, RJ45 connectors and operates at 100Mbps across a star physical topology.

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