Bus Topology

Topics: Network topology, Ethernet, Computer network Pages: 7 (2250 words) Published: March 11, 2011
Bus Topology
http://compnetworking.about.com/od/networkdesign/a/topologies.htm http://fallsconnect.com/topology.htm
Bus topology
Bus topology refers to a single cable that connects all the workstations, servers, printers and other devices on the network. The cable runs from device to device by using tee connectors that plug into the network adapter cards. Each end device has a terminator on one end of the tee and a cable going out to the next device on the other end, while all devices in the middle have one cable coming in and one going out. The terminators on each end device simply stop the network signal from reflecting back into the cable and colliding with other transmissions. The most common type of network cable used for a bus topology is RG-58 thin net. The network speed is limited to 10 megabits per second, making it a suitable media for only 10 BASE 2 Ethernet. There are also network size limitations. You may have a maximum of twenty network devices on a segment, and the segment cannot exceed 185 meters in total length. By using a device called a repeater that boosts the signal, you can have up to five segments on a network. However, only three of these segments can have devices attached to them. The other two segments are used to link the three populated segments, giving you a maximum number of sixty devices with a total network length of 925 meters. This topology works equally well for either peer to peer or client server.

Ring Topology
Ring topologies are used on token ring networks. Each device processes and retransmits the signal, so it is capable of supporting many devices in a somewhat slow but very orderly fashion. A token, or small data packet, is continuously passed around the network. When a device needs to transmit, it reserves the token for the next trip around, then attaches its data packet to it. The receiving device sends back the packet with an acknowledgment of receipt, then the sending device puts the token back out on the network. Most token ring networks have the physical cabling of a star topology and the logical function of a ring through use of multi access units (MAU). In a ring topology, the network signal is passed through each network card of each device and passed on to the next device. All devices have a cable home runned back to the MAU. The MAU makes a logical ring connection between the devices internally. When each device signs on or off, it sends an electrical signal which trips mechanical switches inside the MAU to either connect the device to the ring or drop it off the ring. The most common type of cabling used for token ring networks is twisted pair, although there are nine different types that can be used. With IBM Type 1 Shielded cable, you can have up to 33 network segments with 260 devices on each. Transmission rates are at either 4 or 16 megabits per second.  Advantages

* Very orderly network where every device has access to the token and the opportunity to transmit * Performs better than a star topology under heavy network load * Can create much larger network using Token Ring

* One malfunctioning workstation or bad port in the MAU can create problems for the entire network * Moves, adds and changes of devices can affect the network * Network adapter cards and MAU's are much more expensive than Ethernet cards and hubs * Much slower than an Ethernet network under normal load

Tree Topology
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone. Advantages of a Tree Topology

* Point-to-point wiring for individual segments.
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