4.9 Fundamentals of communication and networking Flashcards
(107 cards)
1
Q
define serial data transmission
A
sends one bit at a time, serial uses a single wire, typically used for transmitting data over medium to long distances
2
Q
define parallel data transmission
A
sends multiple bits simultaneously, parallel uses several wires, the more lines that the medium uses the more data can be transferred simultaneously, used for short distances
3
Q
advantages of serial over parallel transmission (three reasons)
A
1) parallel communication requires more wires so higher cost and more difficult to manage when setting up the system
2) parallel needs the data to be synchronised across the wires so more chance of errors and limiting factor on transmission speed
3) parallel carries risk of crosstalk between wires so also more chance of errors
4
Q
what is skew and how does it occur
A
skew is a problem where the bits sent will not be received together - each of the communication lines in parallel transmission will have slightly different electrical properties meaning time takes for bit to transfer will differ slightly - skew is worse over long distances and an lead to buts from different pulses overlapping causing corruption
5
Q
what is crosstalk
A
occurs in parallel transmission when the communication lines are tightly packed signals from one line can leak into another also causing data corruption
6
Q
define synchronous data transmission
A
a clock signal shared between sender and receiver is used to time when signals are sent - used within buses in the FDE cycle - signals sent in regular intervals will be received in the same order so suitable for transmitting information in real time systems
7
Q
define asynchronous data transmission
A
start and stop bits are used to indicate the duration of a transmission - start bits are either 0 or 1 and stop bits are the opposite of the start bit - sender and receiver must use the same baud rate so they only need to synchronise clock for duration of data transmission
8
Q
define baud rate
A
number of signal changes per second - measured in bauds
9
Q
define bit rate
A
the number of bits that can be sent in one second - measured in bits per second (bps)
10
Q
relationship between bit rate and baud rate
A
bit rate = baud rate x no of bits per signal
11
Q
define bandwidth
A
bandwidth relates to the range of frequencies that a communication medium is capable of transmitting - measured in hertz
12
Q
what is the relationship between bit rate and bandwidth
A
bit rate is directly proportionate to bandwidth
13
Q
how can bit rate be higher than baud rate
A
each signal change represents more than one bit of data
14
Q
define latency
A
time delay between a signal being transmitted and it being received - measured in milliseconds - usually increases with distance
15
Q
define protocol
A
a set of rules relating to communication between devices
16
Q
what is a physical network topology
A
the physical architecture of the cabling between devices on the network
17
Q
what is a logical network topology
A
the flow of data packets around a network
18
Q
what is a physical star topology
A
each client has a direct connection to a central node, the central node receives all packets and delivers them to the recipient
19
Q
advantages of a physical star topology - 4 reasons
A
1) packets are sent directly to recipient so other clients on the network can’t see packets not intended for them - improved security
2) easy to add and remove clients to and from network
3) speed of links are constant as no collisions
4) improved reliability as if one link fails the other links are not affected
20
Q
disadvantages of physical star topology - 2 reasons
A
1) if the central hub fails, all communication is stopped
2) its expensive to install as lots of cables required
21
Q
what is a physical bus topology
A
connects clients to a single cable called the backbone - a device called a terminator is placed on either end of the backbone with the server connected via the backbone too
22
Q
advantages of a physical bus topology
A
1) no central hub so reduces chance of network failure and cost of installation
2) inexpensive to install as a minimum length of cable required
23
Q
disadvantages of a physical bus topology
A
1) low security as packets are sent through shared backbone so all clients can see them
2) the backbone may be used by multiple clients - increasing risk of collisions
3) if the backbone fails the entire network becomes unusable
24
Q
difference between logical bus and star topology
A
logical bus network delivers packets to all clients on the network whereas logical star network only delivers the packet to the recipient
25
how can a physical star topology behave logically as a bus network
by using a bus protocol and appropriate packet switching to distribute packets to all connected clients
26
what is a host on a network
a device on a network that provides services - often a server - includes file storage, printer sharing and internet access
27
what is peer-to-peer networking
each computer has equal status, services are provided by the clients themselves - any device can access and share resources from any other client
28
what is client-server networking
one or more central servers provide services to the clients on the network, servers are often more powerful machines than the clients - clients request services from the servers
29
advantages of client-server networking
allows for central management of clients on a network - improves security
30
disadvantages of client-server networking
requires expertise to set up and manage
31
advantage of peer-to-peer networking
more cost effective as there is no need for a powerful server - easier to set up and maintain
32
disadvantage of peer-to-peer networking
all clients which provide services must be running in order for the network to be fully operational
33
when is client-server networking used
most schools and business organisations use it to allow central management of clients on network
34
when is peer-to-peer networking used
large file-sharing networking and multimedia providers use is to provide high performances services without needing a server
35
explain the purpose of wifi
wifi is used to enable devices to connect to wireless networks, refers to a wireless local area network that is based on international standards, this allows a device made in one part of the world to seamless connect to wireless networks all over the world
36
what components are required for wireless networking
requires a wireless access point which connects to a wired network and a wireless network adapter in the device that connects to the wireless network
37
How are wireless networks secure
by encrypting transmitted data using a WPA or WPA2, disabling SSID broadcoast and set up a MAC address allow list
38
what is a WPA
stands for wifi protected access anf requires that a new wireless client entrers a password in order to connect to the network
39
what is SSID and how does disabling it enhance security
stands for service set identifier it is the name that identifies wireless networks - disabling it stops wireless devices within range of the network from displaying it is available so only those who know the SSID can connect
40
what is a MAC address and how does setting up an allow list enhance security
stands for media access control - addresses are assigned to every wireless device and is unique - mac address allow lists are used to only allow specific devices to connect to a network
41
Describe how the CSMA/CA method is used to transmit data and avoid collisions
computer monitors for data signal
if another transmission in progress then continue to wait
when no data signal present start to transmit
wait to receive acknowledgement packet to confirm data received and not corrupted
if no acknowledgement received within a reasonable time period then wait a random time period then retransmit
CTS/RTS - before starting to transmit a computer sends a Request to Send (RTS) to access point
access point will respond with a Clear to Send (CTS) to only one computer at a time
only the computer that receives the CTS signal will transmit
waiting period is random to reduce likelihood of two computers transmitting a the same time again
if a collision occurs again then wait a longer random time before attempting to transmit again
use of exponential back-off algorithm to determine wait time
42
What is the structure of the internet
a network of interconnected computer networks which uses an end-to-end communication protocol
43
What is an internet service provider
a company that provides its customers with access to the Internet - the largest internet service providers are national companies and are referred to as national internet service providers
44
What is a packet
a container in which data is transmitted over networks
45
What is a packet switched network
a network in which data is sent in packets - one message is split into multiple packets each of which is sent to the recipient via the best possible route before being reassembled by the recipient
46
What is a router's role in a packet switched network
the packet is sent through a number of routers before reaching the destination, the routine uses the recipient address to determine where to send the packet - when a packet passes through a router a 'hop' is said to occur
47
What is a packet's TTL
a packets time to live as each packet can only pass through a finite number of hops - reduced by one each hop - when the packet's TTL expires the packet is deleted so the recipient had to request the packet again
48
What are the main components of a packet
sender's address - identifies where the packet was sent from so indicates where to send a response to
receiver's address - identifies where the packet needs to sent to
packet contents - the data held in the packet needed to be transferred
TTL - number of hops a packet can go through before being dropped
sequence number - contains number of packets in the message and identifies the packet's position in relation to others allowing the packets to be reassembled
49
What is a router
A router connects different networks to allow a packet to reach its destination by sending the packet via the fastest possible route so lowest number of hops at least congested at that time
50
What is a gateway
When two networks use different protocols the packets must be modified to conform to both protocols - so gateways strip most of the packets details leaving just the content and then will give the packets new sender and receiver addresses which comply to the new protocol
51
What does each section of this URL mean
https://www.bbs.co.uk/news/technology/index.html
https:// - protocol
www - subdomain for the web server (in this case world wide web)
bbc.co.uk - domain with bbc being name of organisation .uk being the top level domain and .co being a second level domain www.bbs.co.uk - (address of bbc's world wide web server)
/news - directory of file
/technology - subdirectory of file
/index - file name
.html - file's extension
52
What is a URL
a uniform resource locator is an address assigned to files on the internet
53
What is a domain name
a domain name identifies an organisation on the internet using alphanumeric characters for humans to remember
54
What is a fully qualified domain name
a FQDN is a domain that specifics an exact resource and can only be interpreted in one way - always includes server's host name
55
What is an IP address
an internet protocol address is assigned to every computer on the internet and every device communicating over a network
56
When to use a gateway over a router
when you need to convert the protocols between the networks
57
What is a domain name server and what is it used for
it stores a table of domain names and their corresponding IP address - used to translate the domain name into its corresponding IP address as each domain name has direct relationship with an IP address
58
What will happen if a domain name server does not have a record of the domain
the request will be passed to another domain name server
59
What is an internet registry
an internet registry's is responsible for the allocation of IP addresses and to protect the world's depleting pool of unallocated IP addresses so it allocates unused ones rather than new ones when a new IP address is requested
60
What is a firewall
a firewall is between a device and the internet that regulates the packets that pass through it
61
How do firewalls use packet filtering
they use it to accept and block packets based on source IP address or protocol used - networks administrator can specify IP addresses or protocols to block
62
How do firewalls use stateful inspection
examines the contents of a packet before deciding to allow it through the firewall
63
How do firewalls use a proxy server
a server that sits between a public network and a private network and they manage every packet that passes between the two networks - when sending a packet through a firewall, the packet's sender address is that of the firewall rather than the private IP address to provide some anonymity
64
What three features do firewalls have
packet filtering, stateful inspection and proxy server
65
What is a protocol
a set of agreed rules for data exchange between systems
66
Why use a FQDN rather than an IP address
easier to remember a FQDN than an IP address
67
Explain the differences between the World Wide Web and the Internet
WWW is a system of interlinked hypertext documents accessed via the internet using http protocol whereas the internet is a network of interconnected computer networks using a globally unique address space using end to end communication protocol
68
if the packet's socket address is 12.23.45.89:80
what does 12.23.45.89 and 80 mean
12.23.45.89 - is the IP address
80 - the port number
69
explain why browsing the internet might be slower at a public hotspot than at home on a wireless network
at the public hotspot speed could be limited, more clients connecting to one access point, connection might have less bandwidth and more collisions
70
How does symmetric encryption work
both the sender and receiver share the same private key which is used to both encrypt and decrypt data sent between them - before sending data the sender and receiver participate in a key exchange to ensure that they both have a copy of the shared key
71
in symmetric encryption what happens if the key is exchanged over a network
it is vulnerable to interception
72
How does asymmetric encryption work
each device has a pair of mathematically related keys - one is kept secret (private key) and the other is shared on the internet (public key) - when a message is encrypted with a public key it can only be decrypted with the corresponding private key and vice versa - when sending a message the sender uses the recipients public key to encrypt the message so it can only be decrypted with the recipients private key
73
why are digital signatures used in asymmetric encryption
used to verify the sender of a message and to verify that a message has not been tampered with during transmission
74
how are digital signatures used in asymmetric encryption
1) a digest of the message is created using a hashing or checksum algorithm - value depends on content of message
2) the digest is encrypted with the sender's private key - anyone can decrypt with senders public key
3) the encrypted digest is appended to the message
4) the message and appended digest are encrypted with the recipients public key so only their private key can decrypt it
5) when the recipient receives the message they first decrypt it with their private key and they decrypt the digest with the senders public key - verifying it was sent by the sender as they only have access to their private key
6) the recipient then carries out the same hashing or checksum algorithm and check whether it matches the digest - if everything matches then its certain the message was sent my the sender and hasn't been corrupted
75
What are digital certificates in asymmetric encryption
verifies ownership of a key pair so used to check that a fake key isn't being used by an imposter - they are issued by certificate authorities containing serial number, owners name, expiry date, owners public key and the certificate authority digital signature
76
What are worms in malware
pieces of malicious software that can self replicate between computers, either within a network or by users downloading and running a malicious file
77
what are trojans in malware
malware disguised as a benign file that users can be tricked into opening usually from email attachments or downloaded from malicious websites
78
what are viruses in malware
viruses require a host file to reside, these files are typically executable files meaning viruses can lie dormant in a computer until their host file is opened or run - viruses can spread between computers over a private network, internet or even use of physical medial such as hard drives
79
How to prevent malware
1) use good code quality as bugs or vulnerabilities such as lack of antivirus software, out of date software and poor security can be exploited to take hold of a computer system
2) install antivirus software which are specialist pieces of software that scan files to remove suspicious files
3) in organisations employees can be trained about the risks of opening suspicious email attachments in order to reduce the rick posed by malware
80
What does TCP / IP stand for and what is it used for
transmission control protocol / internet protocol - used in all parts of the internet to enable different devices to communicate - data is passed down between layers
81
What are the layers in a TCP / IP stack
application, transport, network and link
82
What is the role of the application layers in the TCP / IP stack
selects and uses the correct protocol to transmit data - the layer's role is to interact with the user using an application software like a web browser or the users system
83
What is the role of the transport layers in the TCP / IP stack
establishes an end to end connection between the sender and the receiver (virtual path)
it then splits the data into packets - each packet has a sequence number which identifies packets position in relation to the other packets - also the packets contain the port number to be used to identify the protocol being used
84
What is the role of the network layers in the TCP / IP stack
provides the packets with the correct IP addresses for the source and destination - routers work within the network layer using IP addresses on the packet to send them to its destination so involved with packet routing
85
What is the role of the link layers in the TCP / IP stack
controls physical connections between pieces of hardware in a network - adds MAC addresses to packets when they are received from the network layer - the MAC addresses identify the hardware the packet should be sent - these MAC addresses change with every hop through a network
86
What happens when a user receives packets of data sent
it is stripped of the extra information by reversing the TCP / IP stack
first link layer removes MAC address, then network layer removes IP address, then the transport layer uses the port number to determine the correct application to send the packet to and uses the sequence number to rearrange packets into the correct order, then application layer displays the information to the user
87
What is a socket address and its purpose
when an IP address is combined with a port number separated by a colon - a socket address identifies which of the applications on the recipient device a packet should be sent to
88
what does FTP stand for, its port and purpose
file transfer protocol
port 20 and 21
used for sending files between devices - FTP client software can run on devices allowing them to connect to FTP servers which send files requested by clients, clients can access FTP servers anonymously or non-anomalously by logging in with username and password
89
what does SSH stand for, its port and purpose
secure shell
port 22
used for remote management of computers, in order to access remote computers it requires a username/password and encrypts info during transmission, SSH clients are pieces of software which can be used to make a TCP connection to a remote port - once a connection is established the commands for application level protocols can be sent to the remote computer
90
what does HTTP stand for, its port and purpose
hyptertext transfer protocol
port 80
web servers hold web pages in text form which they can deliver to clients using HTTP - application software on the client recieves these text files and renders them as web pages
91
what does HTTPS stand for, its port and purpose
hyptertext transfer protocol secure
port 443
same as http but encrypts information during transmission - helps keeps info secure and prevent info from being modified during transmission
92
what does POP3 stand for, its port and purpose
post office protocol 3
port 110 and 995
used for retrieving emails from an email server, checks for and downloads new messages
93
what does SMTP stand for, its port and purpose
simple mail transfer protocol
port 25, 587 and 465
used for sending emails
94
what happens if the SMTP data cant be sent
SMTP uses a queuing system to
hold on to the email and then attempts to send it at a later time. It will continue
to do this for a set number of times. If it still fails to send, it will send a message
back to the sender indicating that delivery has failed.
95
what is the role of an email server in retrieving and sending emails
it is a high specification machine with large
storage capacity that stores a database of all the network users and their email addresses as well as all outgoing and incoming mail
specific software on the server is used to handle the storage and transmission
of emails, allowing users to access their emails, when the user started to use the application, if POP3 was being used, port 110 would be used to retrieve incoming emails while port 25 would be used to send
emails by SMTP
96
what is the role of a web server in serving up web pages
a web server hosts a website and handles traffic from users to the site
data stored on a web server may be in various formats including text,
scripts, and multimedia content so web servers will use various
protocols including HTTP to ensure that all of these data are correctly
handled and formatted so that they appear correctly when viewed over the
Internet regardless of the hardware and software being used by the user.
97
what is the role of a web browser
A web browser is an application that allows users to view web pages and other resources, it is critical in ensuring that websites appear exactly how they were designed
a browser needs to retrieve resources via
the URL, format them so that they display correctly on the screen
When a web page is loaded, a request is made to the domain name server (DNS), which translates the URL into an IP address. This IP address is then used to access the web page host. The host then serves the web page to the browser on the client computer
98
what happens if the browser caches the web page
it is stored it temporarily so if the user wants to revisit the same page then it can be retrieved from the local cache rather than having to make the request to the DNS and host servers again
99
what does an ip address consist of
a network identifier and a host identifier
100
what is a subnet
when networks are divided into smaller networks - these networks are called subnets
101
how to identify the network identifier part of the ip address
using a subnet mask so convert the IP address and the subnet mask into binary and then use a bitwise AND operation between the bits aligned and translate back to decimal - this allows us to work out which subnet the device belongs to
102
what happens if more bits are assigned to the network identifier on an IP address
the more different subnets a network can have
103
what happens if more bits are assigned to the host identifier on an IP address
the more different devices can be connected to each subnet
104
what are the two standards of IP addresses
v4 - dotted quad numbers so four parts separated by a dot - each of the four parts are assigned one byte allowing numbers 0-255 to be represented e.g 192.168.34.7
v6 - eight blocks separated by colons - each block contains four hexadecimal characters - so more unique permutations than v4
105
why was ip address v6 introduced
because ipv4 addresses are in short supply as the number of devices on the internet is increasing rapidly so a new version was created
106
what is the difference between a routable or non-routable IP addresses
routable IP addresses are globally unique whereas millions of devices can have the same non-routable IP address as long as they are not on the same network
107
