Thursday, 6 October 2011


LAN Architecture and Topologies: Bus, Star, Ring and Tree

The components in a Local Area Network can be connected in a few ways, which is call LAN topologies. There exit 4 basic LAN topologies:
Star: All stations are connected by cable (or wireless) to a central point, such as hub or a switch. If the central node is operating in a broadcast fashion such as a Hub, transmission of a frame from one station to the node is retransmitted on all of the outgoing links. In this case, although the arrangement is physically a star, it is logically a bus. In the case of the central node acting as switch, an incoming frame is processed in the node and then retransmitted on an outgoing link to the destination station. Ethernet protocols (IEEE 802.3) are often used in the Star topology LAN.
Ring: All nodes on the LAN are connected in a loop and their Network Interface Cards (NIC) are working as repeaters. There is no starting or ending point. Each node will repeat any signal that is on the network regardless its destination. The destination station recognizes its address and copies the frame into a local buffer as it goes by. The frame continues to circulate until it returns to the source station, where it is removed. Token Ring (IEEE 802.5) is the most popular Ring topology protocol. FDDI (IEEE 802.6) is another protocol used in the Ring topology, which is based on the Token Ring.
Bus: All nodes on the LAN are connected by one linear cable, which is called the shared medium. Every node on this cable segment sees transmissions from every other station on the same segment. At each end of the bus is a terminator, which absorbs any signal, removing it from the bus. This medium cable apparently is the single point of failure. Ethernet (IEEE 802.3) is the protocols used for this type of LAN.
Tree: The tree topology is a logical extension of the bus topology. The transmission medium is a branching cable with no closed loops. The tree layout begins at a point called the head-end, where one or more cables start, and each of these may have branches. The branches in turn may have additional branches to allow quite complex layouts.
 Bus, Star, Ring and Tree
LAN Architecture and Topologies: Bus, Star, Ring and Tree
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/introlan.htm: Introduction to LAN protocols
http://www.javvin.com/protocolLAN.html: Local Area Network and LAN protocols


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