3.9 Fundamentals of Communication and Networking Flashcards
1
Q
Internet address
A
Each device on a network needs to be uniquely identified so that the data can be sent to the correct destination
2
Q
what are URLs used for
A
URLs are used to specify the means of accessing a resource across a network and its location
3
Q
how is a URL formed
A
the protocol and the domain name of the resoruce
4
Q
URL
A
Uniform Resource Locator
5
Q
DNS
A
Domain Name System
6
Q
define the Internet
A
a network of interconnected computer networks which uses an end-to-end communication protocol
7
Q
ISP
A
Internet Service Provider
8
Q
what is an ISP?
A
a company that provides its customers with access to the internet
9
Q
TTL
A
Time To Live
10
Q
what name is given to the process of a packet moving from one router to another
A
hop
11
Q
primary components of a packet
A
sender’s address, receiver’s address, packet contents, TTL, sequence number
12
Q
gateways
A
a device that is used between networks that uses different protocols
13
Q
purpose of a sender’s address
A
identifies where the packet was sent from
14
Q
purpose of a receiver’s address
A
identifies the packet’s intended recipient
15
Q
purpose of packet contents
A
where the packet holds the data that is being transferred
16
Q
purpose of TTL
A
holds the number of hops a packet can go through before being dropped
17
Q
purpose of sequence number
A
contains the number of packets in a message and identifies a packet’s position in relation to others
18
Q
what is a domain name
A
it identifies an organisation or individual on the internet using alphanumerical characters
19
Q
FQDN
A
Fully Qualified Domain Name
20
Q
what is a FQDN
A
a domain that specifies an exact resource and can be interpreted in only one way, will always include the server’s host name
21
Q
three types of malware
A
worms, trojans, viruses
22
Q
worms
A
pieces of malware that can self-replicate between computers, either within a network or by users downloading and running a malicious file
23
Q
trojans
A
a type of malware that is disguised as a benign file, users can be tricked into opening this as an email attachment
24
Q
viruses
A
requires a host file to reside in, the files are typically executable, can lie dormant until the host file is opened, can spread between computers over a private network
25
precautions taken to prevent malware
antivirus software, employees can be trained about opening email attachments, good code quality to prevent malware exploiting bugs in code
26
firewalls
sit in between a device and the internet, regulates the packets that pass through them, either software or hardware, work as a proxy server to perform packet filtering and stateful inspection
27
stateful inspection
examines the contents of a packet before deciding whether to allow it through a firewall, can be filtered as firewalls can keep records of current connections in a network
28
packet
containers in which data is transmitted over networks, labelled with addresses for their sender and recipient, contains information intended for recipient
29
what is a packet switched network
network in which data is sent in packets
30
packet switched networks process
one message is split into multiple packets, each of which is sent to recipient via the best possible route, packets are reassembled with other packets, packets pass through routers before reaching destination, each packet has a finite number of hops, with each hop TTL is reduced, when TTL expires the packet is dropped, recipient will notice a missing packet and request that the sender transmit the missing packet again
31
how does a router know the fastest route
holds table with information relating to the fastest routes to certain devices
32
when must a packet be modified
where two networks use different protocols, packets must be modified by a gateway so as to conform to both protocols
33
packet filtering
firewalls use this to accept and block packets based on their IP address or the protocol that they are using (determined by their port number)
34
baud rate definition
number of signal changes per second
35
bit rate definition
number of bits that are transmitted per second, bits per second
36
bit rate formula
bit rate = baud rate x number of bits per signal
37
bandwidth definition
the range of frequencies that can be transmitted across a network connection
38
bandwidth and bit rate relationship
direct relationship, higher bandwidth = higher bit rate
39
latency definition
the delay between a signal being transmitted and it arriving, increases with distance
40
protocol definition
a set of rules (relating to communications between devices)
41
serial data transmission
data is sent one bit at a time
42
parallel data transmission
uses numerous parallel communication lines in order to send multiple bits simultaneously, more lines = more data sent at one time
43
disadvantages of parallel
skew may occur as bits may not arrive at exactly the same time (worse over long distances), more expensive because of multiple lines, crosstalk can occur leading to data corruption
44
advantages of serial over parallel transmission
doesn't suffer from skew or crosstalk so more reliable over long distances, cheaper
45
synchronous transmission
when data is transmitted, a clock signal is used to time when signals are sent, signals are sent at regular intervals and received in same order
46
asynchronous transmission
uses start and stop bits to indicate duration of transmission, sender and receiver use same baud rate
47
physical topology defintion
the physical layout/architecture of the cabling
48
logical topology definition
how data/packets flow around a network
49
physical star network topology
every device is connected to central hub, every device sends data via central hub, hub sends packets of data to intended recipient only, server can be added to network
50
physical star advantages
failure of one cable does not affect performance of rest of network, no collisions as each cable has just one device, packets sent directly to recipients
51
physical star disadvantages
if central hub fails all communication is stopped, expensive to install
52
physical bus topology
devices all connected to backbone (a single cable) with terminators at each end
53
physical bus advantages
inexpensive to install as less cables and no extra hardware
54
physical bus disadvantages
packets sent through shared backbone so all clients see packets even if not intended for them, backbone is used by multiple clients so higher risk of collisions, if backbone fails entire network becomes unusable
55
logical bus topology
packets distributed to all devices, data can not be simultaneously transmitted in both directions (no duplex transmission)
56
logical star topology
only delivers packets only to recipient
57
client-server networking
devices connected to central server, clients hold their own files whilst servers provide resources and services
58
client-server advantages
better security as files stored in central location, centralised backups, data and resources can be shared
59
client-server network disadvantages
expensive to install and manage, staff needed to maintain the servers
60
peer-to-peer networking
services provided by clients themselves and they all have equal status as no central server
61
peer-to-peer advantages
users can share resources, cost effective as no server and easier to maintain/set up
62
peer-to-peer disadvantages
all devices must be running so that all functions are available, management of security is more difficult
63
WiFi
local area wireless technology that enables you to connect a device to internet via a wireless network access point (WAP)
64
WPA/WPA2
WiFi protected access, encrypts transmitted data, requires client to enter password to connect to network, reduces chance of unauthorised devices reading transmitted data
65
disabling SSID broadcast
SSID will not be visible when trying to connect so only users who know it can connect
66
MAC address whitelist
MAC address is unique to every NIC, whitelist only allows approved MAC addresses (devices) to join network
67
CSMA/CA is used for
carrier sense multiple access with collision avoidance is a protocol used in wireless networks to avoid data collisions caused by multiple devices communicating simultaneously
68
CSMA/CA with RTS/CTS steps
transmitting device checks for traffic, if another transmission in progress transmitter waits, once channel is idle transmitter sends RTS, receiver responds with CTS, if CTS not received, transmitter waits random amount of time before resending RTS, when CTS received transmitter begins transmitting data, receiver sends ACK, if no ACK received then data is resent
69
CSMA/CA disadvantages
cannot overcome hidden nodes, which is why RTS/CTS is used
70
CSMA/CA steps
device that is ready to transmit listens to comms channel and waits until it is idle, then transmits the data
71
proxy server definition
server that sits between a public network and a private network
72
device in private network sending packet into public
the packet's sender address is that of the firewall rather than the device's private IP address for some anonymity
73
symmetric encryption
both sender and receiver share the same private key, the key is used to both encrypt and decrypt
74
key exchange problem
75
asymmetric encryption
four different keys are used between two devices, each device has a pair of related keys, one is private and the other is public, when a message is encrypted with a public key, only the corresponding private key can decrypt it and vice versa, recipient is only one who can decrypt
76
digital signature
used in asymmetric encryption to verify the sender of a message and that message has not been tampered with
77
digital signature steps
digest of message is created (using hashing or checksum), value depends on contents of message, digest is encrypted with sender's private key (which can be decrypted with sender's public key), encrypted digest is appended to message, encrypted with recipient's public key, recipient decrypts with public key to verify, recipient carries out hashing/checksum algorithm to check it matches and confirm that no tampering or corruption has occurred
78
digital certificates
verifies ownership of a key pair in asymmetric encryption and can check that a fake key pair isn't being used, serial number, owner's name, expiry date, owner's public key are included
79
TCP/IP
protocol used in all parts of the Internet to enable different devices to communicate
80
TCP/IP stack layers
application, transport, network, link
81
role of the application layer
selects and uses correct protocol to transmit data, interacts with user through application software
82
role of the transport layer
establishes a virtual path - an end to end connection between sender and receiver, layer splits transmission into packets, each packet labelled with packet and port numbers, requests retransmission of lost packets if needed
83
role of the network layer
provides the correct IP addresses for each packet's source and destination, routers work within the layer, using IP addresses to send to its location
84
role of the link layer
controls physical connections between pieces of hardware in a network, adds MAC addresses to packets which it receives from network layer to locate the correct piece of hardware, MAC address changes with each hop
85
once packet is received
TCP/IP stack is reversed, link removes MAC addresses, network removes IP addresses, transport uses port number to determine correct application to send packet to, application (layer) removes port number and reassembles packets in correct order
86
thin-client network
majority of network's processing power belongs to servers
87
thin-client exam q
88
thick-client network
clients are powerful enough to provide their own processing power and storage, removing need for server
89
thin-client advantages
easy to set up/maintain, software and updates can be installed on server and automatically distributed to each client terminal, more secure since data is kept in one place
90
thin-client disadvantages
reliant on server so if server goes down terminals lose functionality, requires very powerful and reliable server so expensive, server demand and bandwidth increased, maintaining network connections for portable devices consumes more battery power than local data processing
91
thick-client advantages
robust and reliable, can operate without connection to server, generally better for running more powerful software applications, reduced likelihood of collisions
92
thick-client disadvantages
more expensive computers required, installation of software required on each terminal separately, harder to maintain
93
XML
written in <>, database servers deliver responses to this query (or JSON), more flexible than JSON in terms of structure and data types
94
JSON
written using {}, ; and "", database servers deliver responses to this query (or XML)
95
advantages of JSON over XML
easier for human to read due to its data oriented format, more compact, easier to create due to simple syntax, easier for computers to parse using standard JavaScript function
96
CRUD in SQL
Create - INSERT,
Retrieve - SELECT,
Update - UPDATE,
Delete - DELETE
97
steps for client connecting to database (REST)
client-server request made by client to web browser, web browser responds with requested web page, text file contains JavaScript which loads an API which uses REST to enable database server to be queried by client, client sends HTTP requests to database server, server responds using either JSON or XML, client's browser processes this and displays it to user
98
HTTP requests from CRUD and SQL
Create - INSERT - POST
Retrieve - SELECT - GET
Update - UPDATE - PUT
Delete - DELETE - DELETE
99
client-server model
clients send request messages to servers, which reply to clients with response messages which may contain the requested info, confirmation of completed action, or why the action hasnt been completed
100
API (application programming interface)
set of protocols relating to how different applications communicate with each other, sets out format of requests and responses between client and server
101
Websocket protocol
an example of an API operating in application layer (of TCP/IP stack), provides constant stream of information between two devices, full-duplex so data transmission bi-directional at the same time, allows for fast transmission due to reduction of packet header size so used for gaming and messaging
102
port forwarding
when a client needs to communicate with a server that is connected to a private network, client sends packets to public IP address of router belonging to server's private network, packets contain port number of application, private network's router forwards packets to server using NAT
103
DHCP (Dynamic host configuration protocol)
DHCP is used to assign IP addresses to devices as they join a network, so that an IP address is not wasted by assigning it to a device that might not join again, uses a pool of available IP addresses to allocate IP addresses for the duration of the session, then returned to pool
104
NAT (network address translation)
gets around problem of trying to communicate with non-routable (private) IP address, device on private network sends packets through router, makes record of packet before replacing the private IP address with its own routable IP address, when a response is received, sent to router's public IP which forwards response to private IP by using record
105
routable IP
public, globally unique
106
non-routable IP
private, devices can have same one
107
IPv4
four parts separated by dots, each part is assigned one byte
108
IPv6
formed of eight blocks separated by colons, each block contains 4 hexadecimal characters, allows for more unique permutations
109
IP address structure
split into two: network identifier and host identifier
110
working out which subnet a device belongs to (e.g IP = 192.168.3.24, subnet = 255.255.255.0)
translate IP into binary, translate subnet mask, AND the two operations, translate back into denary
111
FTP port
20/21 - sending files between devices, anonymously or non-anonymously
112
SSH port
22 - remote management of computers, requires username/password and encrypts during transmissions
113
HTTP port
80 - web server in text form
114
HTTPS port
443 - same as HTTP but encrypts information, keeping it secure and free from tampering
115
POP3 port
110 & 995 - retrieving emails from email server, checks and downloads new messages
116
SMTP port (simple mail transfer protocol)
25, 587, 465 - used for sending emails
117
socket address
when an IP address is combined with a port number, IP address, followed by colon and port number
118
how is it possible for bit rate to be higher than baud rate
if each signal level represents more than one bit
119
why might browsing the Internet be slower at a public hotspot than at home on a wireless network
at a public hot spot speed could be limited for each device, more clients connecting to one access point, might have less bandwidth, may be more collisions
120
why do peripherals usually use a serial communication method instead of parallel
to avoid problems of cross-talk, cheaper to manufacture, might need greater distance
121
explain why the LAN has been segmented
to reduce congestion by cutting number of collisions, improvs security by localising packet transmission to one segment
122
what hardware component is needed for each device that is going to be connected to a wireless network
network interface card (NIC)
123
explain role of SSID in wireless networking
identifier for wireless network, clients must use same SSID as one put in access point to join so clients are prevented from accessing network until they are using same SSID as access point
124
why would preventing students from using wireless network improve the performance of school network
network has limited bandwidth so fewer devices means reduced likelihood of colliding or transmissions interference
125
why is FQDN preferred to IP address
easier to remember as a human
126
explain what NAT is and why it is used
modifying IP addresses as they pass through a router, used as private IP addresses used on LAN are not routable so cannot be used for routing on Internet, to improve security of LAN
127
explain why programs written in JavaScript language are interpreted rather than compiled
Internet users have range of devices with different processors, compiled program will only execute on processor of specific type
128
two differences between routable and non-routable IP addresses
