Network Types

The A+ Certification Exam expects you to be familiar with the key features of major network types such as Ethernet and others. See the following sections for details.

Ethernet uses theCarrier 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 Types

The oldest network (30 years old in 2003!) 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.

Table 21.2 lists the different types of Ethernet networks and their major features.

For more information about cables and connectors, see "Cable and Connector Types," p. 782 . For more information about network topologies, see "Network Topologies," p. 778 .

Table 21.2. Wired Ethernet Networks

Network Type	Cable and Connector Type	Also Known As	Maximum Speed	Network Topology Supported	Maximum Distance Per Segment
10Base2	RG-58 coaxial with BNC connector	Thinnet	10Mbps	Bus	185 meters
10Base5	Thick coaxial cable with external transceiver	Thicknet	10Mbps	Bus	500 meters
10BaseT	UTP Category 3 cable with RJ-45 connector	Ethernet	10Mbps	Star	100 meters
100BaseTX	UTP Category 5 cable with RJ-45 connector	Fast Ethernet	100Mbps	Star	100 meters
1000BaseTX	UTP Category 5 cable with RJ-45 connector	Gigabit Ethernet	1000Mbps	Star	100 meters

Wireless Ethernet

Wireless Ethernet , also known as IEEE-802.11, is the collective name for a group of wireless technologies that are compatible with wired Ethernet. 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.

Fiber- optic cables can also be used for Ethernet signaling. They are particularly common for long cable runs with Fast and Gigabit Ethernet.

Table 21.3 compares different types of Wireless Ethernet to each other.

Table 21.3. Wireless Ethernet Standards

Wireless Ethernet Type	Frequency	Speed	Interoperable With
802.11a	5GHz	54Mbps	Requires dual-mode (802.11a/b or 802.11a/g) hardware
802.11b	2.4GHz	11Mbps	802.11g
802.11g	2.4GHz	54Mbps	802.11b

Wireless Ethernet hardware supports both star (infrastructure) network topologies, which uses a wireless access point to transfer data between nodes (required for Internet sharing), and peer-to-peer topologies, in which each node can communicate directly with another node.

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.

Token Ring

A token-ring network (also known as IEEE-802.5) includes two or more computers with token-ring adapters, a device known as a MAU (media access unit ) and an RJ-45 UTP Category 3 or Category 5 or 9-pin STP Type 1 cable between each computer's token-ring adapter and a port on the MAU.

Externally, the combination of computers, cables, and MAU resemble a star topology. However, inside the MAU, the actual network topology is a ring topology: When a workstation needs to send information, it inserts the information and destination address along with a signal known as a token into the empty frames of information passed continuously within the MAU. The workstation receiving the message changes the token to indicate the message has been received and reinserts the token back into the flow of frames being passed from port to port. This method of information transfer is designed to avoid the collisions inherent in Ethernet.

Token-ring networks originally ran at 4Mbps, but most recent token-ring network hardware runs at both 4 and 16Mbps. Token-ring networks have become far less common in recent years with the rise of high-speed, low-cost Ethernet variants.

Bluetooth

Bluetooth is a short-range, low-speed, wireless network designed to operate in a peer-to-peer mode between PCs and other devices such as printers, projectors, smart phones, and others. Bluetooth runs in the same 2.4GHz frequency used by IEEE-802.11b and g, but uses a spread-spectrum frequency- hopping signaling method to help minimize interference. Bluetooth devices use the peer-to-peer network topology.