A+: Network Topologies and Ethernet
The physical arrangement of computer, cables, and network devices is referred to as a network topology. There are four different types of network topologies:
• Bus— Computers in a bus topology share a common cable. Connections in this topology are made largely with coaxial 10BASE2 and 10BASE5 cables. The network goes down if a single computer on a bus-topology network fails, but the other network types stay up if one or more computers fail.
• Star— Computers in a star topology connect to a central hub or switch (wired) or access point (wireless). This topology is used by 10BASE-T (10 Mbps Ethernet), 100BASE-T (Fast Ethernet), and 1000BASE-T (Gigabit Ethernet) Ethernet networks and by Wireless Ethernet (Wi-Fi) when configured for the default infrastructure mode.
• Ring— Computers in a ring topology either connect as a physical ring, for example FDDI networks; or a logical ring, as is the case with Token Ring networks.
• Peer-to-peer (Mesh)—Computers in a peer-to-peer or mesh topology can connect directly to every other computer. This topology is used by computers with multiple network adapters, Wireless Ethernet (Wi-Fi) when configured for peer-to-peer mode, and Bluetooth.
Ring and Bus topologies are obsolescent; Star and Peer-to-peer rule.
Ethernet uses the Carrier Sense Multiple Access/Collision Detect (CSMA/CD) method of transmission access. Here’s how it works: A station on an Ethernet network can transmit data at any time; if two stations try to transmit at the same time, a collision takes place. Each station waits a random amount of time and then retries the transmission.
Wired Ethernet: The oldest network in common use today is Ethernet, also known as IEEE-802.3. Most recent wired Ethernet networks use unshielded twisted pair (UTP) cable, but older versions of Ethernet use various types of coaxial cable.
Wireless Ethernet is also known as IEEE 802.11, is the collective name for a group of wireless technologies that are compatible with wired Ethernet; these are referred to as wireless LAN (WLAN) standards. Wireless Ethernet is also known as Wi-Fi, after the Wireless Fidelity (Wi-Fi) Alliance (www.wi-fi.org), a trade group that promotes interoperability between different brands of Wireless Ethernet hardware. Wi-Fi certified hardware is 802.11-family Wireless Ethernet hardware that has passed tests established by the Wi-Fi Alliance. Most, but not all, 802.11-family Wireless Ethernet hardware is Wi-Fi certified.
Wireless Ethernet hardware supports both the star (infrastructure) network topology, which uses a wireless access point to transfer data between nodes, and the peer-to-peer topology, in which each node can communicate directly with another node.