3.9 Fundamentals of communication and networking

Question 1

synchronous transmission

Answer 1

streams of bits are transferred over a communication channel at a constant rate, transmitter and receiver are synchronised using a clock signal

Question 2

asynchronous transmission

Answer 2

no clock signal so start and stop bits are used to control communication, data is transmitted when available, channel can be idle

Question 3

serial transmission

Answer 3

data bits are sent one after the other over a single wire

Question 4

parallel transmission

Answer 4

several bits are sent at the same time over their own wires

Question 5

parallel transmission disadvantages

Answer 5

only works over short distances and with lower bit rates due to skew and crosstalk

Question 6

crosstalk

Answer 6

transmitting corrupted data due to electromagnetic interference

Question 7

skew

Answer 7

when bits are transmitted across parallel links at different speeds so fall out of sync

Question 8

why serial transmission is preferred over parallel transmission

Answer 8

serial transmission can operate at higher bit rates and transmitting over longer distances and uses fewer wires

Question 9

bit rate

Answer 9

the number of bits that are transmitted over a channel each second

Question 10

the higher the bit rate

Answer 10

the faster the data arrives

Question 11

baud rate

Answer 11

number of times that the signal changes per second

Question 12

why are bit rate and baud rate sometimes different?

Answer 12

a symbol doesn’t always encode one bit

Question 13

bit rate (when different to baud rate)

Answer 13

baud rate x symbol

Question 14

baud rate (when different to bit rate)

Answer 14

bit rate/ symbol

Question 15

bandwidth

Answer 15

maximum rate of data transfer of a communication channel, directly proportional to bit rate

Question 16

how are bandwidth and bit rate directly proportional?

Answer 16

the greater the amount of data that can be transmitted over a channel, the more bits can be transmitted per second

Question 17

latency

Answer 17

the delay from the time that a signal is sent to the time that it is received

Question 18

protocol

Answer 18

a set of rules that determine the communication between devices to set the standards of the communication

Question 19

physical network topology

Answer 19

refers to the actual architecture of a network

Question 20

physical star network topology characteristics

Answer 20

each client has its own direct connection to a central hub, hub receives packets for all clients and delivers them to its recipient, server can be added

Question 21

physical star network topology advantages

Answer 21

packets sent directly to recipient so no one else can access, easy to add and remove clients, each cable has one device so eliminates collisions, failure of one cable does not affect the rest of the network

Question 22

physical star network topology disadvantages

Answer 22

if central hub fails all communication is stopped, expensive

Question 23

physical bus topology

Answer 23

connects clients to a single cable called backbone, a server can be connected to backbone

Question 24

physical bus topology advantages

Answer 24

no central hub so less chance of network failure, cheap to install

Question 25

physical bus topology disadvantages

Answer 25

packets are sent through backbone so all clients can see, collisions are likely to happen, if backbone fails entire network is unusable

Question 26

logical network topology

Answer 26

refers to the flow of data packets within a network

Question 27

logical bus network

Answer 27

delivers packets to all clients on the network

Question 28

logical star network

Answer 28

delivers packets only to their recipient

Question 29

what can be used to make a physical star network behave as a logical bus?

Answer 29

a bus protocol

Question 30

server

Answer 30

a program on a computer that shares resources with or provides services to any authorised client

Question 31

client

Answer 31

a program that runs on a device used by an end-user

Question 32

client-server networks process

Answer 32

a client sends a request to the server, the server processes the request and sends a response back to the client

Question 33

peer-to-peer networks

Answer 33

no central servers, peers can share resources and hardware, peers gives permission to access resources, equal status, computers must be switched on to share

Question 34

client-server vs peer-to-peer: setup cost

Answer 34

client-server: servers will need to be set up and configured, peer-to-peer: no additional devices

Question 35

client-server vs peer-to-peer: physical security

Answer 35

client-server: servers can be located in rooms which can be monitored, peer-to-peer: workstations may be at multiple locations so it is hard to oversee

Question 36

client-server vs peer-to-peer: backups

Answer 36

client-server: easy to make sure files are backed up, peer-to-peer: individual users are responsible for backing up their own data

Question 37

client-server vs peer-to-peer: points of failure

Answer 37

client-server: if a server fails, many users will be affected, peer-to-peer: if one device fails, it will not impact many

Question 38

personal area network (PAN)

Answer 38

connected devices that are located within a few metres of each other

Question 39

local area network (LAN)

Answer 39

single network that is located in a small geographical area

Question 40

wide area network (WAN)

Answer 40

network that connects two or more networks over a wider geographical area

Question 41

three types of wireless security protocols

Answer 41

WEP, WPA WPA2

Question 42

Wired Equivalent Privacy (WEP)

Answer 42

symmetric encryption algorithm, same key to encrypt and decrypt data

Question 43

WEP disadvantages

Answer 43

keys are too short and can be easy to decipher

Question 44

WiFi Protected Access (WPA)

Answer 44

generates a new encryption key for each data packet, requires a password to connect

Question 45

WPA2

Answer 45

each message is encrypted several times depending on key size

Question 46

SSID letters stand for

Answer 46

service set identifier

Question 47

service set identifier (SSID)

Answer 47

string of alphanumeric characters specific to a wireless network to identify it

Question 48

disabling SSID broadcast

Answer 48

stops wireless devices within range from displaying that the network is available so only those who know the SSID can connect

Question 49

disabling SSID broadcast disadvantage

Answer 49

even hidden SSIDs can be found

Question 50

media access control (MAC) address filter

Answer 50

whitelists can be created to allow specific devices to connect, blacklists can be used to block specific devices from connecting

Question 51

wireless access point (WAP)

Answer 51

WLAN is based around this central communications device

Question 52

WiFi

Answer 52

wireless local area network that is based on international standards

Question 53

CSMA/CA letters stand for

Answer 53

carrier sense multiple access with collision avoidance

Question 54

purpose of CSMA/CA

Answer 54

it is a protocol used in wireless networks to avoid data collisions caused by multiple devices communicating simultaneously

Question 55

CSMA/CA process

Answer 55

when a device is ready to transmit, it listens to communication channel to check whether it is idle, if so, data is transmitted, if channel is busy the node waits for a random period of time before checking channel again

Question 56

CSMA/CA disadvantage

Answer 56

hidden nodes may interfere with data transmission as they are undetected

Question 57

RTS/CTS stands for

Answer 57

request to send/clear to send

Question 58

purpose of RTS/CTS

Answer 58

to overcome the hidden node problem