4.9 fundamentals of communication and networking - cs

need to double check if this is complete

what are parallel cables?

ribbons of several smaller cables used primarily for connecting internal components

how does serial transmission work?

data bits are sent in a sequence

what are the advantages of serial transmission?

reliable over long distances at high frequencies

not affected by skew

less wires

so minimises crosstalk

serial interfaces have fewer pins

so cheaper and easier to produce

how does parallel transmission work?

several bits are sent simultaneously along separate lines or channels

what are the disadvantages of parallel transmission?

only reliable over short distances (roughly 2m) and with lower bit rates than serial transmission

what is parallel transmission usually used for?

mainly used inside a computer and in some early peripherals - known as buses

do USBs use serial or parallel transmission?

serial

what is crosstalk?

electromagnetic interference between two adjacent channels or parallel wires

how does crosstalk worsen?

it gets more pronounced as the frequency of transmission increases

what is the consequence of crosstalk?

corrupted data may be transmitted

what is skew?

when bits transmitted across parallel links travel at different speeds

what is the consequence of skew?

data can fall out of sync with the clock signal and therefore be read incorrectly

what is synchronous transmission?

when all data transfers are timed to coincide with an internal clock pulse

the data is sent as one long stream or block of data with no gaps in the transmission

receiver counts the bits and reconstructs bytes

what kind of transmission is synchronous transmission used with?

parallel transmission

what is asynchronous transmission?

sends bytes separately as soon as they are available instead of waiting for a clock signal

each byte is preceded by a start bit and ends with a stop bit (short time between each set of bits)

what is asynchronous transmission best used for?

cheap and effective form of serial transmission but slow - suited to low-speed connections like keyboard + mouse

what is a parity bit/check bit?

the 8th bit

what is latency?

the time delay between the moment the first byte or packet of a communication starts and when it is received at its destination

what is protocol?

the set of rules relating to communication between devices

what are the things the protocol defines? (5)

standards for physical connections and cabling

the rate of transmission

data format

whether transmission is synchronous or asynchronous

error checking procedures

define bit rate

the number of bits transmitted per second

define baud rate

the rate at which signals on a wire may change

what is baud rate usually measured in?

Mbit/s (megabits per second)

what does the start bit in asynchronous transmission do?

it's used to signal the arrival of data and to synchronise the transmitter and receiver temporarily

what is bit rate measured in?

bps (bits per second)

what is a baseband system?

a system that uses a single data channel system in which the whole bandwith of the transmission medium is dedicated to one data channel at a time

what is the relation between bit rate and baud rate in baseband?

bit rate is the same as baud rate in baseband

what is broadband?

a multiple data channel system in which the bandwidth of the transmission medium carries several data streams at the same time

what is the equation linking bit rate and baud rate?

bit rate = baud rate x number of bits per signal

what is bandwith?

a measure of the maximum capacity of a communication channel

what is bandwidth usually measured in?

bps

what is the relationship between bit rate and bandwith?

bit rate is directly proportional to bandwith

how does the bus topology work?

all nodes are connected to a single backbone cable

the end of the backbone is connected to either a terminator or computer which stop signals bouncing back

each node is passive

data is sent in one direction at a time only

only one computer can transmit successfully at any one time

what are the advantages of the bus topology?

inexpensive

devices can easily be added

good for small networks

what are the disadvantages of the bus topology?

main cable is a point of failure

limited cable length

performance degrades with heavy use

owing to data 'collisions'

poor security

in terms of a bus topology

what is a data collision?

how does a star topology work?

each device on the network is connected to a central communication device

what is the difference between a hub and a switch?

a hub broadcasts a communication to every computer on the LAN

what are the advantages of a star topology?

easy to isolate problems

good performance

if a switch is used

more secure because data is only sent to the recipient

what are the disadvantages of a star topology?

can be expensive to set up due to length of cable required

central device is a point of failure

what is a MAC address?

a unique address hardcoded into each networked device's NIC (Network Interface Card) in manufacture

how does a switch use MAC addresses?

it holds all the MAC addresses of the devices connected to it and uses these to direct packets of data to the correct device

what is physical topology?

how devices in a network are physically connected

what is logical topology?

how devices in a network communicate across physical topologies

how can a network wired in star topology behave logically as a bus network?

by using a bus protocol and appropriate physical switching

what is a server?

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

what is a client?

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

what examples of the kinds of servers are there? (5)

file servers

how does a client-server network work?

most computers are nominated as clients and one or more as servers. the clients request services from the servers

how does a peer-to-peer network work?

there are no central servers

every computer can be configured to share its resources/hardware

peers communicate directly with each other and all have equal status

how do client-server and peer-to-peer networks compare in terms of SETUP COST?

c-s: servers (high performance computers) need to be set up and configured

p2p: no additional devices are needed

how do client-server and peer-to-peer networks compare in terms of PHYSICAL SECURITY?

c-s: servers can be located in secure rooms

p2p: workstations may be at multiple different locations so hard to oversee

how do client-server and peer-to-peer networks compare in terms of BACKUPS?

c-s: backups can be done centrally on the server

p2p: individual users responsible for backing up their own data

how do client-server and peer-to-peer networks compare in terms of POINTS OF FAILURE?

c-s: if server fails

p2p: if one device fails

most other users will be able to carry on w/ their work

what are the advantages of cloud storage?

can be accessed anywhere with internet connection

software and data does not occupy space on user's hard drive

multiple people can access the same data

central backup

what are the disadvantages of cloud storage?

need internet access

if there's an organisational security breach

a user's data is at risk

what is Wi-Fi?

wireless networking technology providing high-speed internet and network connections

what are the components needed to connect to a wireless network?

ISP (Internet Service Provider)

what is a NIC?

Network Interface Controller/Card - used to connect a device to a network

what is a WAP?

Wireless Access Point - a switch that allows devices to connect wirelessly

what is a modem used for?

it modulates the electrical signal

what is an SSID?

Service Set Identifier

string of alphanumeric characters specified during the setup of wireless devices

what can a SSID do?

can be set manually or automatically

can be hidden to make it harder to connect

can be set to broadcast to wireless devices in range of an access point

what is CSMA/CA?

Carrier Sense Multiple Access with Collision Avoidance - a protocol used in wireless networking that makes sure network collisions are avoided

what are network collisions?

when two devices attempt to communicate at the same time