CHEATSHEET

Comm System Framework 1. Data source produces data to be sent 2. Transmitter - encodes data into signal suitable for transmission medium 3. Transmission medium - channel in which signal is transmitted to destination 4. Switching/Routing – data travels along different paths/mediums 5. Destination - receiver of the information

Network = a number of computers and their peripheral devices connected together

Communication Systems Coaxial: TV antenna, video link

Advantages: More durable than TP Less susceptible to RFI & EMI Supports faster data rates than TP Widely available Disadvantages: Can be effected by strong interference More expensive than TP Lower bandwidth than other mediums (fibre optices) Bulkier and heavier than TP Fibre Optics: submarine cables, LAN backbones, international telephone

Advantages: Fastest speed Resistent to RFI & EMI Highly secure Disadvantages: Expensive in cost & service Specialised installation Satellite: Satellite phones, Global Positioning, Television

Twisted Pair: telephone, LAN, crossover cable

Advantages: Inexpensive Readily available Well tested Used in existing phone lines Disadvantages: Susceptible to RFI & EMI Lower bandwidth than other mediums Not good over long distances (100’s of kms)

Advantages: Accuracy Fast Speed Well tested Disadvantages: Expensive Line of sight Safety Radio Wave: Radio Broadcast, Mobile Phones, Airport, Bluetooth Advantages: Inexpensive for receivers Readily available Adds portability to consumer devices Disadvantages: Security due to broadcast nature Costly for transmitters Interference

LAN = local area network; network of computers within a building or several buildings on one site

Wireless Mediums: Satellite Microwave Radio Wave Infra-red

BPS = bits per second; number of binary digits (bits) sent per second Bandwidth = the difference between the highest and lowest frequencies in a communication channel

Node = any device on a network

WAN = wide area network; network covering larger geographic areas, like 10’s, 100’s & 1000’s of kms Wire-based Mediums: Twisted Pair Coaxial Fibre Optics RCA

Microwave: Local TV links, Data transfer over medium distance

Advantages: Fast speeds 1000’s satellites Long distances Disadvantages: Very expensive Complex set-up Complex Maintenance NIC or Network Interface Card is a transmitter who encodes and decodes data

Infra-Red: TV Remote, Mobile phone data link Advantages: Cheap as chips Readily available Wireless features in consumer devices Disadvantages: Very short range Very limited bandwidth Line of sight limitation

Protocol = set of rules that governs the transfer of data between computers; defined how data is to be transmitted & how errors are to be detected TCP/IP = two part protocol used for the Internet; TCP stands for Transmission Control Protocol and refers to controlling transmission using data packets; IP stands for Internet Protocol and refers to the identification of nodes using an IP address (eg. 104.98.4.5) Ethernet – a standard (operating at the Transmission level) which controls the transmission and reception of data (NIC)

Baud rate = number of electronic signal changes per second; each baud can carry 1, 2, 3 etc bps; 14400 Baud could = 28800 BPS if each electronic signal sends 2 bits Servers: computers that provide services to other computers on a network; examples include file, print, mail, proxy, web and database servers Parity Checking = a method of checking for errors in transmission of data; a parity bit is added to the end of each byte to make the sum of the 1’s either odd or even; eg. for odd parity, sending a byte consisting of 10110001, the computer would add a 1 so that the sum of 1’s is 5 (odd). Cyclic Redundancy Check = a method of error checking where a division process is used; both sender & receiver divides data by a fixed divisor then the remainders are compared. Checksum = a method of error checking where packets of the data sent are added by both sender and receiver; if sums are the same it is assumed the data was sent successfully. Error Correction refers to fixing the problem of data not being sent successfully. The most common method is to resend data Network Topologies are the physical arrangements possible for devices on a network Bus Network: all devices are connected to a single line called a bus. Devices are identified by a unique address. Devices check the bus to see if the mmessage travelling down it is for them. Can still operate if one device goes down. MAC Address: a unique address assigned to the computer hardware. Switches use Mac addresses.

Star Network: all computers or devices are attached to a central point which acts as a switching station or exchange allowing access to any other device on the network. If this central device goes down the network becomes unavailable to all nodes. If a node goes down it does not affect other nodes or the central device. Ring Network: all nodes are connected to a closed loop. If a node fails data transfer stops until the node is restored. Teleconferencing refers to the use of technology to allow a meeting of people to take place while participants are in different locations. Advantages: save cost of airfares, save time in travelling Disadvantages: lose faceto-face interpersonal experience, ideas are more easily clarified via face-to-face meeting Messaging Systems are systems where people can send messages to others which can be received at different times in different locations eg. voicemail, email Voicemail: messages recorded via phone for an intended recipient; stored digitally on a computer; mssgs can only be retrieved by intended recipient using a PIN from any phone; recipent dials into the voicemail computer system. Email: a system that allows messages to be sent mainly using text; attachments can be added to an email allowing transfer of graphics & other files; first part of email contains the persons address, incl. their account name and the domain name separated by an @; the domain name refers to the specific computer or server where the email is stored. Mailing List: a list of people who want to receive the same messages, usually part of a club or special interest group (eg. IPT students).