Communications devices

Term 2, 2011Week 2

CONTENTS

• Communications devices– Modems– Network interface cards (NIC)– Wireless access point– Switches and routers

• Communications software• Questions

Communications devices

• Enable computer users to communicate and exchange items such as data, instructions and information with another computer.

• Analog signals may need to be converted to digital (or vice versa) depending on the communications device.

Modems

• A computer’s digital signal must be converted into analog signals before they are transmitted over standard telephone lines. A dial-up modem performs the conversion.

• Both the sending and receiving ends of a communications channel must have a modem for data transmission to occur.

• Where a digital signal is available, a special modem is required (e.g. ADSL, ADSL & cable broadband modems). No conversion takes place.

Network interface cards

• Network interface card (NIC) – a card you insert into an expansion slot of a computer. Can also be built into motherboard. Peripherals can have a NIC built in.

• Computers on a LAN typically contain an NIC.• NIC coordinates the transmission and receipt of data,

instructions and information to and from the computer or device containing the NIC.

• NIC performs three functions: increases the strength of the signal from the computer, packages the data for transmission, and controls access to and from the network cable.

• Works with a particular network technology, such as Ethernet.

• An Ethernet card is the most common type of NIC for hard-wired networks.

• Depending on the time of wiring used, transfer rate on an Ethernet network is 10 Mbps, 100 Mbps or 1000 Mbps. Ethernet cards typically support one or more of these speeds.

• Available in a variety of styles.• Many NICs have more than one type of port, enabling

cables to be connected to the NIC (some cable and DSL modems require cable to be plugged into modem and NIC).

• An NIC for notebook or other mobile computers provides wireless connection to a network.

• Can be embedded in device or attached to an external slot.

• Internal connection used a mini PCI wireless network card with an antenna built in to the surrounding cover of the notebook’s screen.

• External adaptors are in the form of a USB network adaptor, ExpressCard Network card or a memory card.

Wireless access point

• Central communications device that allows computers and devices to transmit data wirelessly among themselves.

• Normally placed near the ceiling, though often it is connected to a wired network backbone for faster transmission of data back to the network server.

• To guard against hackers on a wireless network, consider using a protocol other than TCP/IP, such as Ethernet, for file sharing.

• If it a large area, multiple access points can be used. If using multiple access points, each access point must overlap its neighbours.

• Provides a seamless area for users to move around in.

Switches and routers

• A switch is a device that provides a common connection point for cables from devices on a network.

• A router is a communications device that connects multiple area networks.

• Network traffic in a LAN typically follows specific paths that connect members of a work group, such as the accounts department of an organisation.

• A switch stores the address of every device down each cable connected to it.

• When a packet enters the switch, it uses simple logic to detect the destination of the packet and sends the packet down the cable that contains the addressed device.

• The packet reaches the destination quickly and doesn’t collide with packets being sent to other devices.

• However, some traffic may need to be sent from one work group to another. Due to the need for many people to communicate, the network can become slow and frustrating if only connected via a single LAN. To overcome this, each work group can be established with a LAN and a switch with a router used to link the work group LANs. The router can also be used to connect both networks to the internet.

• The only device that sees every message sent by very computer on the network is the router. The router sees the recipient address for packets and forwards it.

• A router will connect LANs and WANs regardless of the hardware and network communications protocol used in each area.

• Routers for home networks can also join multiple networks. These are designed to join the home to the Internet.

• Switches are not capable of joining large multiple networks or sharing an Internet connection.

Small router

Large routers

Communications software

• Some communications devices are pre-programmed to accomplish communications tasks; others require separate communications software to ensure proper data transmission.

• Communications software help you establish a connection to another computer or network and manage the transmission of data, instructions and information.

• Must have compatible communications software on both computers communicating.

• Usually, separate communcations programs each serve a different purpose. For example, one type helps you establish a connection to another computer on the Internet using Wizards, onscreen messages etc. Once the Internet connection is established, software provides a means to access the Internet using an Internet service provider.

• Some communications software support file transfer protocol (FTP). This is an Internet standard that allows you to upload and download files to and from a web server, called the FTP server.

• To view or use a file on an FTP server, you can either download the file from the server to your computer or use an FTP program to access the file directly on the FTP server.

• Some FTP sites are public, others require a username and password.

Questions• Explain what FTP is, and what purpose it serves.• What is the purpose of a network interface card?• What is the point of a wireless access point? When is it

necessary?• Routers and switches are used to connect separate networks.

Explain the circumstances in which each of these would be used. • Using the internet to research prices, approximate the cost of

setting up a network for a business which contains four large teams (taking into consideration five workstations per team, three printers, and the necessary amount of routers and switches.) Draw a diagram showing the hardware and how the devices would connect. HINT: use Figure 2-23 on page 72 of your text book to assist you.