Successful Communications—5 components Sending device — initiates instruction to transmit data, instructions, or information Communications device — connects the communications channel to the receiving device Receiving device — accepts transmission of data, instructions, or information Communications device — connects the sending device to the communications channel Communications channel — media on which data, instructions, or information travel
Types of Networks
Collection of computers and devices connected via communications devices and transmission media
Local Area Network (LAN)
Network in limited geographical area—office building
Metropolitan area network (MAN)—covers city
Wide area network (WAN)
Potentially world-wide coverage
Internet is the largest WAN
Types of Networks
Peer to Peer
Simple network that connects fewer than 10 computers
Each computer has equal capabilities
One or more computers act as server and other computers, or clients , access server
Types of Networks
What is Internet peer-to-peer ( P2P )?
Restricted network usually within an organization
Allows sharing of organizational-related info without putting it out for public reading
p. 292 Fig. 8-11
Enables users to connect to each other’s hard disks and exchange files directly
Layout of devices in a network
All computers and devices connect to a central cable, or bus
Cable forms closed ring, or loop, with all computers and devices arranged along ring
p. 293 Fig. 8-14
All devices connect to a central device, called hub
All data transferred from one computer to another passes through hub
Ethernet and Token Ring Technology
Ethernet technology allows computers to contend for access to network
If two computers send data at same time, a collision occurs and computers must send again
Token ring technology controls access to network by requiring devices to pass a special signal, called token
TCP/IP and 802.11
Short-range radio waves transmit data between Bluetooth devices
TCP/IP ( T ransmission C ontrol P rotocol/ I nternet P rotocol) technology transmits data by breaking it up into small pieces, or packets
Commonly used for Internet transmissions
802.11 is family of standards for wireless LANs
What are IrDA , RFID , and Wireless Applications Protocol (WAP) ?
p. 294 IrDA specification allows data to be transferred wirelessly via infrared light waves Wireless Applications Protocol (WAP) allow wireless mobile devices to access Internet Radio Frequency Identification (RFID) uses radio signals to communicate with a tag placed in an object
What are examples of communications devices ?
p. 298 Next Common types are dial-up modems, ISDN and DSL modems, cable modems, network cards, wireless access points, and routers ISDN and DSL modems send and receive data from ISDN and DSL lines
Using the Telephone System to Communicate
Public switched telephone network (PSTN)?
Temporary connection using telephone line for communications
Costs no more than making regular call
Computers at any two locations can establish a connection using modems and telephone network
What is a cable modem ?
p. 300 Fig. 8-19
Sends and receives data over cable television network
Much faster than dial-up modem or ISDN
Sometimes called a broadband modem
What is a network card ?
p. 300 Fig. 8-20
Adapter card, PC Card, or compact flash card that enables computer or device to access network
What are ISDN and DSL modems ?
p. 300 Communications devices that send and receive digital ISDN and DSL signals Usually external devices in which one end connects to a telephone line and the other end connects to a port on the system unit Next
What is a wireless access point ?
p. 301 Fig. 8-21
Central communications device that allows computers and devices to transfer data wirelessly among themselves or to wired network
What is a router ?
Connects computers and transmits data to correct destination on network
Routers forward data on Internet using fastest available path
Allow messages to flow between networks
Program or hardware device that filters information coming from Internet connection
If packet of info is flagged, not allowed through
What is a channel ?
Transmission media on which data travels in communications system
Wire, cable, and other tangible materials used to send communications signals
Bandwidth is amount of data that can travel over channel
Transmission media are materials capable of carrying one or more signals
How is a request sent over the Internet using a communications channel?
p. 304 Fig. 8-24 Step 1. The sending device requests information using either a physical transmission media or a wireless transmission media. Step 2. When the request leaves the ISP, it travels over T1 lines, microwave stations, earth-based stations, and communications satellites until it reaches the Internet backbone. Step 3. The request travels over T3 lines along the Internet backbone. Step 4. The Request travels over T1 lines until it reaches the destination network server. Next
Physical Transmission Media
What are twisted-pair cable and coaxial cable ?
p. 305 Fig. 8-25—8-26
Twisted-pair cable is used for telephone systems and network cabling
Coaxial cable is often used for cable television wiring
Physical Transmission Media
What is fiber-optic cable ?
p. 306 Fig. 8-27
Capable of carrying significantly more data at faster speeds than wire cables
Less susceptible to interference (noise) and, therefore, more secure
Smaller size (thinner and lighter)
Wireless Transmission Media
What is wireless transmission media ?
Used when inconvenient, impractical, or impossible to install cables
Includes infrared, broadcast radio, cellular radio, microwaves, and communications satellites
Internet Telephony p. 285 Next Internet telephony transmission of phone calls over data network Sometimes called Voice over IP
Uses of Computer Communications
What are voice mail and wireless messaging services ?
p. 289 Fig. 8-7
Voice mail is voice message converted to digital form
Wireless messaging services include:
Collaboration and Groupware
What are collaboration and groupware ?
Microsoft Office 2003 allows collaboration
Groupware is software that allows people to share information
Collaboration is working with other users connected to a server
Public Access Points
Public Internet access point allows wireless connection to Internet in public location
Global Positioning System Next
Verichip (December, 2001)
Implantable Personal Verification System
Size of a TicTac
Implanted under the skin
Immediate ID and retrieval of subscriber supplied registry info