LAN Technologies

LAN technologies refer to the physical and datalink layer (Layer 1 and Layer 2) technologies used to create LANs. These can be categorized to wired and wireless technologies.

Wired LAN Technologies

Ethernet

Ethernet is the most widely used wired LAN technology today. Over time the physical layer evolved through coaxial, twisted pair and fibre optic cables and media interfaces to achieve bandwidths from 10Mbps to 100Gbps. Ethernet over twisted pair is the most common these days.

Historically the older standards used coaxial cables and were called 10BASE2 and 10BASE5 and these were called thinnet and thicknet respectively. Today these have become obsolete but they still exists in some old networks.

Common NameIEEE StandardAlternate NameCable TypeSpeed
ThicknetIEEE 802.310BASE5Thick Coax10 Mbps
ThinnetIEEE 802.3a10BASE2Thin Coax10 Mbps

Today's most common Ethernet standards all use either twisted pair or fibre optic cables.

Common NameIEEE StandardAlternate NameCable TypeSpeed
EthernetIEEE 802.3i10BASE-TTwisted Pair10 Mbps
Fast EthernetIEEE 802.3u100BASE-TXTwisted Pair100 Mbps
Gigabit EthernetIEEE 802.3ab1000BASE-TTwisted Pair1 Gbps
IEEE 802.3z1000BASE-XFibre Optic1 Gbps
10 Gigabit EthernetIEEE 802.3ae10GBASE-XFibre Optic10 Gbps

Older Ethernet variants that use shared media used CSMA/CD (Carrier Sense Multiple Access with Collision Detection) as the Media Access Control Method. This method basically involves each station waiting for the medium to be free, try to transmit a frame when the medium appears to be idle, if a collision is detected stop transmitting and transmit a jam signal to inform other stations, wait for a random interval and try again.

Typically many devices would be connected to a multiport device called hub, which only splits and forwards the signal to all of its ports. This allows for only half-duplex communication. Half duplex means one way communication i.e., data can flow only in one direction at a time. The same wire pair is used for transmission and reception. When A transmits to B, it cannot simultaneously receive data from B or vice versa.

Modern Ethernet networks are built with switches which avoids collision. Switches are intelligent multiport devices. They learn the MAC addresses of devices connected on each port by examining the source address of the frames sent by the device. They maintain the table of MAC addresses and corresponding port numbers and hence they can make forwarding decisions based on the destination address of frames. Also two wire pairs provide separate transmit path and receive path. All this allows for full duplex communication between devices. The devices connected to a switch can each transmit and receive at the same time. There are no collisions and higher data transfer rates can be achieved.

Last Updated: 07-May-2013


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