Handout 5 - Network Connectivity Devices

Network Connectivity Devices

Network  connectivity devices are devices that are used to connect computing devices to  a network, or connect them so that they form a network. Computing devices range  from Servers, to PCs to printers and scanners, and the network connectivity  devices range from NICs to hubs, switches and routers.

NICs (Network Interconnectivity Cards)

These are cards that fit into expansion slots  in PCs and servers (and are integrated into printers and laptops), that allow  them to connect to a network. It is responsible for packaging the data, that it  received from the computing device, and transmitting it out over the network, and  for receiving data from the network and transferring it back to the computing  device.

Because the NIC is the computing device's  interface to the network, it must provide a physical means of connecting the  device to the network - an RJ45 interface, or coaxial interface.

Each NIC has its own unique address called its MAC address (Media Access Control), and  this address uniquely identifies each NIC on a network. Although logical  addresses are used in the network, the logical addresses have to be mapped back  to these MAC addresses.

Wireless NICs allow computing devices (mostly  laptops) to be connected to a network in pretty much the same way as an  ordinary NIC except there is no physical connection, the connection is  wireless.

Switches and Hubs

Computing devices (servers, PCs and printers)  are connected, via their NICs, to hubs and switches in order that they  communicate with each other. Switches and  hubs are competing technologies to which computers, printers and other  networking devices are connected. (3Com, pg. 1.3)

Hubs  broadcast data across a network, whereas a switch will route the data to the  specific device. With switching, each  connection gets "dedicated bandwidth" and can operate at full speed. In  contrast, a hub shares bandwidth across multiple connections such that activity  from one PC or server can slow down the effective speed of other connections on  the hub. (3Com, pg. 1.3)

Although  more expensive, most new networks now use switches instead of hubs mainly  because they give an improved performance over a hub.

Bridges and Routers

Bridges and routers are used to segment LANs so as to conserve bandwidth. They do so by keeping data traffic that is local to a particular segment from spreading to the other network segments that are serviced by the router or bridge. (Habraken, page 51)

Bridges and routers learn which MAC Addresses belong to which segment and does not unnecessarily route data packets to a particular segment that do not have to go to that segment. They use routing tables and a routing protocol to learn which address is on which segment, and to decide how to route data packets.