You cannot make networks larger just by adding new computers and more cable. Each network topology or architecture has limits. You can, however install components to increase the size of the network within its existing environment. Components that enable you to expand the network include:

     The basic connectivity components of a network include network adapters, cables, and wireless devices that connect the computers in the network. These components enable data to be sent to each computer on the network.

Network Adapters

     Network adapters, also known as network interface cards (NICs) are the physical interface between the computer and the network cable. As the data passes through the cable to the network adapter, it is formatted into packets. A packet is a logical grouping of information that includes a header, which contains location information and user data. The header contains address fields that include information about the data's origin and destination.

     Each network adapter has a unique address that is incorporated into chips on the card. This address is called the physical, or media access control (MAC), address.

The network adapter performs the following functions:

• Receives data from the computer's operating system and converts it into electrical signals that are transmitted onto the cable.
  
  
• Receives electrical signals from the cable and translates them into data that the computer's operating system can understand.
  
  
• Determines whether data received from the cable is intended for the computer.
  
  
• Controls the flow of data between the computer and the cabling.
  
  

Network Cables

     A cable that connects two computers or network components is called a segment. Cables differ in their capability to tranmit data at varying speeds, with different error rates. The three major categories of cables that connect most networks are:

• Twisted-Pair Cable: Twiseted-pair cable (10baseT) consists of two insulated strands of copper wire twisted around each other. There are two types of twisted-pair cable: unshielded twisted pair (UTP) and shielded twisted pair (STP). These are the most common cables used in networks and can carry signals for 100 meters. Twisted-pair cabling uses Registered Jack 45 or RJ-45 connectors to connect to an NIC.
  


• Coaxial Cable: Coaxial cable consists of a copper wire core surrounded by insulation, a braided metal shielding, and an outer cover. There are two types of coaxial cable: ThinNet coaxial cable (10base2) and ThickNet coaxial cable (10base5). Coaxial cable is a good choice when transmitting data over long distances and for reliability supporting higher data rates when using less sophisticated equipment. Coaxial cable must be terminated at each end. ThinNet can carry a signal for about 185 meters, ThickNet about 500 meters. The connection used with coaxial cable is called a BNC connector.
  


• Fiber-Optic Cable: Fiber-optic cable uses optical fibers to carry digital data signals in the form of modulated pulses of light. Because fiber-optic cable carries no electrical impulses, the signal cannot be tapped and its data cannot be stolen. A disadvantage of fiber-optic cable is that it breaks easily if you are not careful during installation. It requires special equipment to cut.
  

Selecting Cables
Cable Categories	Use If	Do Not Use If
Twisted-Pair	You want a relatively easy installation.	Your LAN requires a high level of signal shielding to protect from electromagnetic waves. You must transmit data over long distances at high speeds.
Coaxial	You need to transmit data for greater distances than is possible with less expensive cabling.	You need to change the network cables frequently due to relocation.
Fiber-Optic	You need to transmit secure data at very high speeds over long distances.	You have a small budget. You do not have the expertise to properly install it and connect devices to it.

Repeaters

     Repeaters receive signals and retransmit them at their original strength and definition. This increases the practical length of a cable. Repeaters do not translate or filter signals. For a repeater to work, both segments connected to the repeater must use the same access method.

Use a repeater to:

• Connect two segments of similar or dissimilar cabling.
  
• Regenerate the signal to increase the distance transmitted.
  
• Transmit all traffic in both directions.
  
• Connect two segments in the most cost-effective manner.
  

Hubs

     Hubs are connectivity devices that connect computers in a star topology. A single data packet sent through a hub goes to all connected computers.
There are two types of hubs:

• Passive Hubs: send the incoming signal directly through their ports without any signal processing. These hubs are usually wiring panels.
  


• Active Hubs: Sometimes called multiport repeaters, receive incoming signals, process the signals, and retransmit them at their orignal stregths and definitions to the connected computers or components.
  

Use a hub to:

• Easily change and expand a wiring system.
  
• Use different ports to accomodate a variety of cable types.
  
• Enable central monitoring of network activity and traffic.
  

Bridges

     A bridge is a device that passes data packets between multiple network segments that use the same communications protocol. If a packet is destined for a computer within the sender's own network segment, the bridge retains the packet within that segment. If the packet is destined for another segment, it passes the packet to that segment.

     As traffic passes through the bridge, information about the sending computer's MAC address is stored in the bridge's memory. The bridge builds a table based on MAC addresses, when the bridge receives a packet, the source address is compared to the source address listed in the table. If the source address is not present in the table, it is added to the table. The bridge then compares the destination address listed in the table. If a bridge recognizes the location of the destination address, it forwards the packet to this address. If it does not recognize the destination address, it forwards the packet to all segments.

Use a bridge to:

• Expand the length of a segment.
  
• Provide for an increased number of computers on the network.
  
• Split an overloaded network into two seperate networks.
  
• Link dissimilar physical cables, such as twisted pair and coaxial Ethernet cables.
  

Switches

     Switches are similar to bridges but offer a more direct network connection between the source and destination computers. When a switch receives a data packet, it creates a separate internal connection, or segment. This insulates the connection from the other ports and gives the source and destination computers access to the full bandwidth of a network.

Use a switch to:

• Send a packet directly from the source computer to the destination computer.
  
• Provide for a greater rate of data transmission.
  

Routers

     A router is a device that acts like a bridge or switch but provides more functionality. In moving data between different network segments, routers examine a packet header to determine the best path for the packet to travel. Routers enable all users in a network to share a single connection to the Internet or a WAN.

Use a router to:

• Send packets directly to a destination computer on another network or segment.
  
• Reduce stress on the network.
  

Gateways

     Gateways enable communications between different network architectures. A gateway takes the data from one network and repackages it, so that each network can understand the other network's data.

Use a gateway to link two systems that do not use the same:

• Architecture.
  
• Set of communcation rules and regulations.
  
• Data-formatting structures.