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A level Comp Sci > Communication and Networking > Flashcards

Communication and Networking Flashcards

1
Q

what is a Symbol (signal)?

A
  • A symbol is a particular pattern of bits represented by a signal.
    • For example, a symbol of four bits might be 1101​
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2
Q

Baud Rate

A
  • A communication system’s Baud rate is the number of signal changes in the medium per second. - 1 Baud (or 1Bd) is equal to 1 symbol change per second.
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3
Q

Bit rate

A
  • A communication medium’s bit rate refers to the number of bits that are transmitted over the medium per second.
  • This is often measured in bits per second (bps).
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4
Q

How do you calculate a communication systems bit rate?

A

Bit rate = Baud rate x No of bits per signal

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5
Q

How is it possible for bit rate to be higher than Baud rate?

A
  • each signal change represents more than one bit of data
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6
Q

What is the exact relationship between the bit rate and the baud rate?

A

Directly proportional, the greater the bandwidth the higher the bit rate

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7
Q

Bandwidth

A
  • Expressed in Hertz(Hz)
  • Relates to the range of frequencies that a medium is capable of transmitting
  • Direct relationship between this and the bit rate
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8
Q

Latency

A
  • Often measured in Milliseconds(ms)
  • Difference between an action being initiated and its effect being noticed
  • Latency usually increases with distance
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9
Q

Protocol

A
  • Set of rules relating to communication between devices
  • Allow international organisations that have different devices to communicate seamlessly
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10
Q

What is Serial Data Transmission?

A
  • Where data is sent one bit at a time over one communication line (this is usually a metal wire, but could also be an optical fibre or a wireless channel).
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11
Q

What is Serial Data Transmission used for?

A
  • Transmitting data over medium to long distances (computationally speaking), such as from wired peripherals like mice and keyboards to your computer.
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12
Q

What is Parallel Data Transmission?

A
  • It uses numerous parallel communication lines in order to send multiple bits between components simultaneously.
  • The more lines, the more data can be transferred simultaneously.
  • Each line has slightly different electrical properties, meaning time taken for one bit to be transferred will be differed from line to line
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13
Q

What are the issues of PDT (e.g. skewing)?

A
  • Bits sent together may not be received together due to the differing electrical properties of each line. Over long distances this can cause overlapping of pulses, causing corruption of data.
  • It can also be more expensive due to use of multiple lines.
  • Crosstalk can also occur, where these tightly packed lines signals leak into each other, causing data corruption
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14
Q

What are the advantages of Serial DT over Parallel DT

A
  • Serial data transmission doesn’t suffer from skew or crosstalk, so it is more reliable over long distances, less likely to have errors
  • Serial communication mediums are cheaper due to using just one line/less wire
  • PDT is more likely to error due to needing the data to be kept synchronised over long distances
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15
Q

What is synchronous transmission?

A
  • A clock signal shared by transmission sender and receiver (synched) is used to time when signals are sent. - It is used in the FDE cycle.
  • Suitable for real time transmissions.
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16
Q

What is Asynchronous transmission?

A
  • Uses start and stop bits to indicate the duration of a transmission
  • Receiver and transmitter clocks do not need to be synchronized, transmission of data without use of external clock signal
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17
Q

How does an Asynchronous Transmission Start Bit operate?

A
  1. Start receiver clock ticking
  2. Synchronise the clock in the receiver to the transmitter clock
  3. Bring the clock in the receiver into phase with the transmitter
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18
Q

How does an Asynchronous Transmission Stop Bit operate?

A
  1. Provides time for the receiver to process/transfer the received data
  2. Allows the (next) start bit to be recognised
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19
Q

What is Physical Network Topology?

A

Refers to the actual physical architecture of a network.

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20
Q

What are two types of Physical Network Topology?

A
  • Star Topology
  • Bus Topology
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21
Q

What is a Physical Star Topology?

A
  • Each client has its own direct connection to the central hub (like a star)
  • The hub recieves packets for all of the clients connected to it and is responsible for delivering them to the correct recipient
  • A server can be added to the network in the same way that clients are connected to the central hub
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22
Q

What are the advantages of a Physical Star Topology?

A
  • Packets are sent directly to their recipient, over a cable that is only connected to the recipient, it is secure as other clients on the network cannot see packets that aren’t intended for them
  • It is easy to add and remove clients from the network
  • Each cable has just one device communicating over it, eliminating the possibility of collisions
  • Failure of one cable does not affect the performance of the rest
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23
Q

What are the disadvantages of a Physical Star Topology?

A
  • If the hub fails, communication over the whole network is stopped
  • Expensive to install due to the large amount of cable required
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24
Q

What is a Physical Bus Topology?

A
  • A physical bus connects clients to a single cable called a backbone. A device called a terminator is placed at either end of the backbone
  • No need for a central hub like in a physical star network and a server can be connected to the backbone just like a client
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25
Q

What are the advantages of a Physical Bus Topology?

A
  • There is no central hub, reducing chances of network failure and decreasing the cost of installation
  • Inexpensive to install as a smaller length of cabling is required
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26
Q

What are the disadvantages of a Physical Bus Topology?

A
  • Packets are sent through the shared backbone, allowing every client on the network to see packets that aren’t intended for them
  • The backbone promotes the risk of collisions as it is used for multiple clients communications
  • If the backbone fails, the entire network becomes unstable
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27
Q

What is a Logical Network Topology?

A
  • Refers to the flow of data packets within a network
  • A logical bus network delivers packets to all of the networks’ clients
  • Whereas a logical star network delivers packets to only their recipient
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28
Q

For what reasons would you segment a LAN?

A
  • To reduce network congestion/cut the number of collisions
  • To improve security by localising packet transmissions to one segment
  • To improve reliability by limiting effect of cable failure to one segment
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29
Q

What is the idea of mixing topologies?

A
  • A networks physical setup can be different to its logical set up.
  • For example, it could be set up as a physical star and behave as a logical bus.
  • A physical star topology could run a bus protocol on the hub so it distributes packets to all connected clients, so to act like a bus network.
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30
Q

What is a host?

A
  • A host is a device on a network that provides services.
  • e.g. a server that can provide file storage, printer sharing and internet access.
  • It can also be the clients on the networks themselves.
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31
Q

What are some advantages of Client-Server networking?

A
  • Ensures data is always available, server is unlikely to be turned off
  • Centralised backup
  • More system security/centralised confidentiality ect.
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32
Q

What is Client-Server networking?

A
  • resources stored on the server
  • One or more central servers provide services to clients on a network
  • Servers are connected to the network the same way as clients, but are often more powerful machines than the clients
  • The clients on the network request services, which the servers then respond to e.g. file storage, email management ect
  • centralised security/administration
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33
Q

What is Peer-to-Peer networking?

A
  • resources are stored on each individual device
  • every client has equal status e.g. one may manage print queues, emails
  • computers can communicate directly with eachother
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34
Q

What are the advantages of Peer to Peer Networking?

A
  1. More cost effective than client-server networking as there is no need for a powerful server to provide services
  2. They are easier to set up and maintain than their client-server counterparts
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35
Q

What are the disadvantages of Peer-To-Peer Networking?

A
  1. All clients providing services must be running in order for the network to be fully operational e.g. if the client responsible for managing storage is turned off/faulty, none of the networks clients can access their files
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36
Q

What is Wireless Networking?

A
  • Allow users to communicate within a network without being physically connected
  • Require a wireless access point which connects to a wired network, and a wireless network adapter in the device that connects to the wireless network
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37
Q

What is WPA/WPA2

A
  • WPA stands for Wi-Fi protected access and secures a wireless network by encrypting transmitted data.
  • The WPA also has protected access and requires that a new wireless client enters a password in order to connect to the network.
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38
Q

What is SSID?

A
  • SSID is service set identifier and is the locally unique name that identifies a wireless network.
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39
Q

What is SSID Broadcasting?

A
  • Being able to view it as a network to connect to
  • Disabling its broadcast stops wireless devices within range displaying that the network is available, only allowing those who know the SSID to connect.
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40
Q

What is a MAC address filter?

A
  • Media Access Control addresses are assigned to every wireless device by their manufacturer and are unique to that device.
  • MAC address whitelists can be created to only allow specific devices to connect to a network
  • Mac address blacklists can also be used to block specific devices from connecting to a network.
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41
Q

What is Carrier Sense Multiple Access with Collision Avoidance?

A
  • CSMA/CA is a protocol used in wireless networks to avoid data collisions caused by multiple devices communicating simultaneously
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42
Q

How does CSMA/CA work? How does it work with RTS?

A
  1. When ready to transmit, a device listens to a communication channel to check whether it is idle
  2. If idle, the data is then transmitted, if not idle, the device waits a random period of time before checking again
  3. ## An exponential back off algorithm can be used to increase the time the device waits with each check of the channel
  4. RTS is a protocol that the CSMA sender can send after checking a channel is idle
  5. If the receiver/server is idle, it will respond with a CTS message
  6. If a CTS message is not received, the server is busy communicating with a hidden node and the transmitting device will wait
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43
Q

What is the problem with hidden nodes on a larger network?

A

CSMA/CA cannot overcome hidden nodes, in which the device checking for an idle channel cannot ‘see’ some parts of the network on which communication may be occuring

44
Q

What is Request/Clear to send? (RTS/CTS)

A
  1. RTS is a protocol that the CSMA can send after checking a channel is idle
  2. If the server is idle, it will respond with a CTS message
  3. If a CTS message is not recieved, the server is busy communicating with a hidden node and the transmitting device will wait
45
Q

Define the Internet

A
  • The internet is defined as a network of interconnected computer networks which uses an end-to-end communication protocol
  • Mostly a wired network, with cables that pass under oceans
46
Q

What is an Internet Service Provider(ISP)

A
  • A company that provides its customers with access to the internet.
  • National ISP’s provide internet to smaller regional/local ISP’s from whom homes and businesses buy internet access
47
Q

What is a packet?

A
  • A packet is a container in which data is transmitted over networks
  • They are labelled with addresses for sender and recipient and contain informaiton intended for the recipient
48
Q

What is a packet switched network?

A
  • Data is sent in packets
  • One message is frequently sent in multiple packets (can be given a sequence number), reassembled after being sent
49
Q

How does Packet Switching work?

A
  1. When packets are sent through a network, they have to pass through a number of routers before reaching their destination (each pass is known as a hop)
  2. A router uses the recipient address on a packet to determine where to send it
50
Q

What is a Packet Time To Live?

A
  1. Each packet can only pass through a finite number of hops. This is known as the TTL
  2. When the TTL expires the packet is dropped/deleted (prevents infinitely hopping packet if transmission error occurs)
  3. The recipient will notice a missing packet and may request a retransmission
51
Q

What is a Router and What is a Gateway?

A

Router
- Send packets via the fastest possible route e.g. least congested or lower number of hops
- Routers hold tables with information relating to fastest routes to certain device that they frequently update to enable maximum performance

Gateway
- Gateways strip away most of a packets details in order to give them new senders and reciever addresses to comply with the new protocol
- This allows two networks that use different protocols to be transferred between

52
Q

What are some purposes of routers?

A
  • To store/make use of a routing table
  • To manage congeestion
  • To forward packets between networks
  • To examine the destination of each packet.
53
Q

What is a URL?

A

A Uniform Resource Locatior is an address assigned to files on the internet. Different protocols can be used in URLS to access files in different types of ways.

54
Q

what does the ‘https://’ of the URL do?

A
  • The protocol being used to access a file. Http: Hypertext transfer protocol (s for secure)
55
Q

What does ‘www’ of a URL do?

A
  • Subdomain for the world wide web. Usually points to the web server hosted at the following domain
  • Other subdomains can be used to point to specific directories e.g. news.bbc.co.uk
56
Q

What is the difference between the WWW and the internet?

A
  • The WWW is a system of interlinked hypertext documents accessed via the internet using a HTTP protocol
  • The internet is a network of interconnected computer networks using a globally unique address space and end to end communication protocol
57
Q

Explain each part of this URL : https://www.bbc.co.uk/news/technology/index.html

A
  • https -> hypertext transfer protocol secure, protocol being used to access a file
  • www -> World wide web, usually point to the web server hosted at the following domain
  • bbc.co.uk -> Domain, BBC is the organisations name. ‘.uk’ is the top-level domain (TLD) and ‘.co’ is a second level domain (2LD)
  • /news -> Directory of file being requested
  • /technology -> Subdirectory of the file requested
  • /index -> Name of the file being requested
  • .html -> The file extension. Hypertext markup language (HTML) is frequently used for creating web pages
58
Q

What is a Domain Name?

A
  • A domain name identifies an organization or individual on the internet.
  • They use alphanumeric characters which make them easy for humans to remember
59
Q

What is the purpose of a Domain Name Server on the internet?

A
  • To translate domain names into IP addresses
60
Q

What is a Fully Qualified Domain Name (FQDN)?

A
  • A domain that specifies an exact resource and can be interpreted in only one way.
  • A FQDN will always include the servers host name

FQDN: https://www.bbc.co.uk/news…..
NOT A FQDN: https://bbc.co.uk/news….

61
Q

What is an IP address?

A
  • An Internet Protocol(IP) address os assigned to every computer on the internet and every device that communicates on a network
  • Domain names are used for humans as IP addresses are not easy to remember. Domain names map to IP addresses.
62
Q

What is a Domain Name Server System?

A
  • A domain name server is used to translate the domain name into its corresponding IP address, it does this through a table it stores of Fully Qualified Domain names and their corresponding IP address.
  • If a domain name server does not have a record of the domain you are trying to access, your request will be passed to another name server
  • Small and rarely visited websites will require numerous changes of servers meaning these websites are often slower to access
63
Q

What is an internet registry?

A
  • An organisation responsible for the allocation of IP addresses. Only 5 in operation, serving different geographical areas
  • An IR has to protect the worlds depleting pool of unallocated IP addresses.
  • When a new IP is requested, an IR will first look for a now unused IP address rather than allocating a brand new IP
64
Q

What is a Firewall?

A
  • A firewall sits between a device and the internet, regulating packets that pass through it
  • Can either be software or hardware, working as a proxy server which can perform both packet filtering and stateful inspection
65
Q

What is Packet filtering?

A
  • Accept and block packets based on their source IP address or the protocol being used(determined by port number)
  • A network admin can specify particular IPs/Protocols to block or use automatic filtering software that can blokc suspicious packets
66
Q

What is Stateful Inspection?

A
  • Examining the contents of a packet before deciding whether to allow it through the firewall
  • Can sometimes filter out packets that arent related to acitivity on the network
67
Q

What is a Proxy Server?

A
  • A server that sits between a public and private network
  • These devices manage every packet that passes between the two
  • Firewalls can be said to act as proxy servers when they control the movement of packets between public and private networks
68
Q

What happens to the IP of a packet from a private network when sent through a firewall?

A

Rather than being sent with their IP, they are sent with the sender address of the firewall, to keep their private IP protected

69
Q

Describe symmetric encryption for sending information over a Network? What is a problem with this and how can it be overcome?

A
  1. Both sender and receiver share the same private key, these must be exchanged before sending information
  2. A key being exchanged over a network, is vulnerable to interception, this is a major floor that asymmetric encryption overcomes.
70
Q

Describe the process of asymmetric encryption?

A
  1. Each device has a pair of mathematically related keys, public+ private
  2. Before a message is sent, it is encrypted by the sender using the recipients public key (which is shared)
  3. This means that the recipient is the only person who can decrypt the message, using their private key
71
Q

What is a Digital Signature?

A
  • A digital signature can be used to verify the sender of a message and to verify that a message has not been tampered with during transmission
72
Q

How is a Digital Signature used during asymmetric encryption?

A
  1. A digest of the message is created (via hashing/checksum ect), the value depending on the content of the message
  2. The digest is encrypted with senders private key, and appended to the message
  3. The digest can be decrypted using the senders public key
  4. The recipient then carries out the same hashing/checksum/algorithm on the message and checks whether their result matches the decrypted digest
  5. If yes, recipient can be sure the message was sent by sender, and hasn’t been tampered/corrupted with during transmission
73
Q

What is a Digital Certificate?

A
  • Verifies ownership of a key pair used in asymmetric encryption
    Digital Ceritifcate Contains:
  • A serial number
  • The owners name
  • an expiry date
  • The owners public key
  • the certificate authority’s digital signature
74
Q

Explain 3 types of malware (worms, trojans, viruses)

A

Worms:
- Pieces of malicious software that can self replicate between computers, within a network or by users downloading/running malicious file
Trojans:
- File disguised as a benign file that user is tricked into opening e.g. fake email scams
Viruses:
- Require a ‘host’ file in which to reside, usually executable, can spread when open or run

75
Q

How can you prevent malware?

A
  • Good quality code
  • Up to date software, antivirus scanning ect.
  • employee/citizen awareness of suspicious files ect
76
Q

What are the four layers of the TCP/IP stack?

A
  • Application Layer
  • Transport Layer
  • Internet Layer
  • Link layer
77
Q

What does the Application Layer of the TCP/IP stack do in sending?

A
  1. Selects and uses correct protocol to transmit data
  2. Interacts with the application software like a web browser
78
Q

What does the Transport Layer of the TCP/IP stack do in sending?

A
  1. Establishes a virtual path, an end to end connection between the sender and receiver
  2. Breaks the application data into segments (TCP) or datagrams (UDP)
  3. Sequence numbers are allocated, and source/destination and port numbers (which identify the protocol in use) are added to the header. (FOR TCP delivery is acknowledged and lost segments are retransmit)
79
Q

What does the Internet/Network Layer of the TCP/IP stack do in sending?

A
  1. Prepares packets for the internet, source/destination IP addresses are added
  2. Routers work within the network layer, using the IP addresses to send to its destination
80
Q

What does the Link Layer of the TCP/IP stack do in sending?

A
  1. Controls physical connections between pieces of hardware in a network, responsible for transporting IP packets across each individual link between client and server
  2. Networking protocols, such as ethernet, are used at this level
  3. MAC addresses are added which are received from the network layer, they are unique to a device
  4. MAC addresses identify the hardware to which a packet should be sent. They change with every hop through a network.
81
Q

How does the TCP/IP stack work at the receiving end?

A
  • When the packet has been received, it is stripped of its extra information via reversing the TCP/IP stack
  1. Firstly, the Link Layer removes MAC addresses
  2. Then, the Network Layer removes IP addresses
  3. Then, Transport Layer determines which application to send the packet to via port number, and ensures it is in the correct position via sequence number
  4. Finally, the Application Layer receives the packets and displays the information to the user accordingly.
82
Q

What is a Socket Address?

A
  • A socket address is formed from an IP address, followed by a colon, and then the port number which is in use.
  • A socket address identifies which applications on the recipient device a packet should be sent to,
83
Q

Identify the IP address, Port Number and Socket Number
114.26.20.199:443

A

IP ADDRESS : 114.26.20.199
PORT NUMBER: 443
SOCKET ADDRESS: 114.26.20.199:443

84
Q

What are FTP(File Transfer Protocol) Protocols’ ports and what is it used for?

A
  • 20 & 21
  • Used for sending files between devices
  • clients can access FTP servers anonymously or non-anonymously using username/password
85
Q

What are HTTP + HTTPS Protocols’ ports and what are they used for?

A
  • 80 for HTTP and 443 for HTTPS
    1. Web servers hold web pages in text form, which they can deliver to clients using HTTP
    2. Application software on the client recieves these text files and renders them as text pages
    3. HTTPS ‘S’ just means secure, encrypting the information during transmission.
86
Q

What are SMTP(Simple Mail Transfer) Protocols’ ports and what is it used for?

A
  • 25, 587 & 465
  • For sending emails, used between a client and email server
87
Q

What are POP3(Post Office) Protocols’ ports and what is it used for?

A
  • 110 & 995
  • Used for retrieving emails from an email server, can check and download any new messages
88
Q

What are the network and host identifiers of an IP address?

A
  • A network identifier is shared by each computer in a network
  • A host identifier is independent to a device
89
Q

How does more bits on a network identifier and more bits on a host identifier effect a network?

A
  • More bits on a network identifier of an IP address, allows for more subnets on a network
  • More bits on a host identifier allow for more devices to be connected to a subnet simultaneously
90
Q

What is the difference between IPV4 and IPV6 addresses?

A

IPV4
- Uses 32 bits
- Each of the 4 parts are assigned one byte, allowing 0 to 255 to be represented

IPV6
- Uses 128 bits
- Eight blocks, each part contains four hexadecimal characters

91
Q

Why might IPV6 be better than IPV4?

A
  • Can represent a much greater number of ip addresses/ identifiers
92
Q

What is the difference between a public and private IP address?

A
  • If every device had its own public IP (routable) address, there would not be enough to go around, as they are globally unique
  • Most homes have multiple private IPs (non-routable), as they are only unique to a network.
93
Q

What is the Dynamic Host Configuration Protocol?

A
  1. Used to assign IP addresses to devices as they join a network
  2. Uses a pool of available address to allocate them
  3. Once a device leaves the network, its IP returns back to the pool for reallocation
94
Q

What is the process of Network Address Translation and why is it needed?

A
  1. Each computer is allocated a private IP address
  2. The network’s router has two IP addresses, one private address on the private networks side, and a public address on the Internet’s side.
  3. There is a server connected to the internet with a routable IP address
  4. If a device on the network sent a packet to this server, the server couldnt respond becausue the computers IP is non-routable
  5. NAT overcomes this by sending packets through the router, which makes record of the packet, before replacing the private IP of the computer with its own routable IP
  6. When a response is received, it is sent to the routers public IP, which then forwards the response to the correct private IP using the record it made when sending the packet
95
Q

What is Port Forwarding?

A
  • Used when a client needs to communicate with a server that is connected to a private network
    1. Client sends packets to the public IP of the router attached to the network
    2. Packets sent by client contain port number of the application running on the server that the client wishes to access
    3. The private network’s router then forwards the packets to the server using NAT.
96
Q

What is the Client Server Model?

A
  • In a network that uses the client server model, clients send request messages to servers, which reply to the clients with response messages, these may contain:
  • Requested information
  • Confirmation of a completed action
  • Message explaining incompleted action
97
Q

What are API protocols?

A
  • Define how interactions between the applications should be carried out.
98
Q

What is the Websocket protocol?

A
  • API which operates in the application layer
  • Uses a full-duplex connection to provide constant dream of information
  • Allows for fast transmission of data by using reduced packet headers
99
Q

What are the CRUD operations?

A
  • Create, Retrieve, Update, Delete

each of these commands has an SQL equivalent

  • INSERT, SELECT, UPDATE, DELETE
100
Q

What is the REST methodology?

A

A design methodology for online database applications that are queried with a web browser

It uses 4 HTTP request methods:
- POST, GET, PUT, DELETE

it also has 4 SQL equivalents:
- INSERT, SELECT, UPDATE, DELETE

101
Q

How does a client connect to a database?

A
  1. Client-server request made to the web browser
  2. Web browser reponds with web page delivered as a text file which contains javascript which can load an API
  3. The API then uses REST to enable the database server to be queried by the client via HTTP reuqest methods
  4. The database responds to requests using either JSON or XML
  5. The clients browser processes the JSON or XML and displays the response to the user
102
Q

XML or JSON when delivering database responses to queries?

A
  • JSON is more compact, easier to read, easier to create and faster for computers to process
  • XML is sometimes seen as more flexible than JSON
103
Q

Thin Vs Thick Client Networks requirements?

A

Thin Client System:
- Higher bandwidth network connection required for the network
- Slower processor/clockspeed needed on the clients, can also have reduced RAM
- Server needs multiple processors/processors with many cores, server needs a lot of RAM

Thick Client System:
[opposite]

104
Q

Peer-to-peer networking versus Client-Server networking

A

Peer to peer

  • Each computer has equal status (often more powerful than client-server clients)
  • Resources stored/shared from any computer
  • No centralised security management
  • No reliance on central server

Client server

  • Opposite info
105
Q

What is Thin/Thick Client computing?

A
  • Thin client computing is where processing is carried out on a singular/series of powerful application server,
  • thick is where processing is carried out across a series of more powerful clients

A level Comp Sci (13 decks)

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