9: Fundamentals of Communication & Networking Flashcards
1
Q
Serial Transmission Method
A
Data bits are sent one at a time over a single wire
2
Q
Parallel Transmission Method
A
Several bits are sent simultaneously over multiple wires
3
Q
Serial over Parallel Transmission (4)
A
- Cheaper due to needing fewer wires
- Does not suffer from crosstalk as there is only one transmission line
- Does not suffer from data skewing as only one bit is transmitted at a time
- Can be used over longer distances due to needing fewer wires, there being only one transmission line and only one bit transmitted at a time
4
Q
Synchronous Transmission (3)
A
- Streams of bits are transferred over a communication channel at a constant rate
- The transmitter and receiver are synchronised to a common clock signal
- There is no need for start and stop bits so more information is sent per unit time
5
Q
Asynchronous Transmission (3)
A
- There’s no common clock signal so start and stop bits are used to control communication
- The start bit synchronises the clock in the receiver to the transmitter clock
- The stop bit provides time for the receiver to process the received data and allows the next start bit to be recognised
6
Q
Baud Rate
A
Number of signal changes per second
7
Q
Bit Rate
A
Number of bits transmitted over a channel per unit time
8
Q
Bandwidth
A
The range of frequencies that can be transmitted across a network connection
9
Q
Latency
A
Delay from the time the signal is sent to when it is received
10
Q
Protocol
A
A set of rules that allow two devices to communicate
11
Q
Differentiation between Baud Rate & Bit Rate (2)
A
- Bit rate can be higher than baud rate if more than one bit is encoded in each signal change
- Bit rate = Baud rate x Bits per signal change
12
Q
Bit Rate is ____ to Bandwidth
A
Directly proportional
13
Q
Physical Star Topology (4)
A
- Every device is directly connected to a central node
- Every device sends data via the central node
- The switch sends packets of data to the intended recipient only
- The hub sends every packet of data to every device
14
Q
Logical Bus Topology (4)
A
- A node broadcasts data to the entire network
- All nodes on the network receive the data
- A node examines the received data to check if it is the intended recipient
- Only one node can successfully transmit data at a time as nodes use a shared transmission medium
15
Q
Peer-to-Peer Networking (4)
A
- Each computer has equal status
- Resources stored on any computer
- No centralised management of security
- The same resource can be shared from multiple computers
16
Q
Client-Server Networking (5)
A
- One or more computer(s) nominated as server(s), other computers are clients
- Clients access resources from server(s)
- Centralised management of security
- Resources cannot be accessed if server(s) turned off
- Hardware and software on server(s) can be optimised for providing services
17
Q
WiFi (2)
A
- A wireless local area network that is based on international standards
- Used to enable devices to connect to a network wirelessly
18
Q
Components Required for Wireless Networking (2)
A
- Wireless network adapter
- Wireless access point
19
Q
Wireless Network Adapter
A
Adds wireless connectivity to a device, allowing it to connect to a wireless network
20
Q
Wireless Access Point
A
Creates the wireless network by sending and receiving data signals with devices over a radio wave communication channel
21
Q
How Wireless Networks are Secured (3)
A
- Strong encryption of transmitted data using WPA (WiFi Protected Access) / WPA2
- SSID (Service Set Identifier) broadcast disabled
- MAC (Media Access Control) address white list
22
Q
WPA / WPA2
A
WiFi Protected Access are protocols, that encrypt all data, which is transmitted on the network
23
Q
SSID Broadcast Disabled
A
Broadcasting of SSIDs can be disabled so only clients, who know the SSID, can find the network. However, it is still possible to discover an SSID maliciously
24
Q
MAC Address Whitelist (3)
A
- MAC addresses of authorised devices are added to a whitelist on the wireless access point
- When a device tries to connect to the network, the wireless access point checks the MAC address of the device
- If the MAC address is on the whitelist, the device is allowed to connect
25
CSMA / CA (3)
- Carrier Sense Multiple Access with Collision Avoidance is a protocol for preventing data collision on a wireless network
- A transmitting device listens to the communication channel. If it is idle, it sends the data. Otherwise, it waits a random amount of time and retries
- The hidden node problem is where multiple devices are out of each other's broadcast range but have the wireless access point in their broadcast ranges. If node A is transmitting, node B would not be able to detect it. Thus, they could be transmitting simultaneously but unable to see that the channel isn't idle so their data signals would collide at the wireless access point and be unable to be received
26
CSMA / CA with RTS / CTS (9)
- Carrier Sense Multiple Access over Collision Avoidance with Request To Send / Clear To Send is a protocol, which alleviates the hidden node problem
- Transmitting device checks for traffic
- If a signal is present, then the transmitter continues to wait
- If the channel is detected as idle, the transmitter would send an RTS
- WAP responds to one RTS signal with a CTS signal
- If CTS is not received, the transmitter would wait a random amount of time before resending the RTS
- When CTS is received, the transmitter begins transmitting data
- Receiver sends acknowledgement (ACK) if all data is received
- If no ACK is received then data is resent
27
SSID
Service Set Identifier is a locally unique ID for a network. A wireless client must use the same SSID as the one put in the access point to join
28
Structure of the Internet
A group of WANs across the globe connected by various mediums
29
URL
A uniform resource locator is a full address of a file on the Internet
30
Domain Name
Identifies the organisation on the Internet, where a resource resides
31
FQDN
A fully qualified domain name is the domain name preceded by its server
32
IP Address
Identifies every device that sends and receives data on a network and the internet
33
Domain Name Organisation
They contain the organisation name, type of organisation and then the country the organisation is registered to
34
Packet Switching
Where data packets with the same end points go through different routes based on what is fastest at the time
35
Router (4)
* A networking device that forwards data packets between computer networks
* Routers are used in homes, small and large businesses and ISP networks
* Core routers are part of the Internet backbone and can forward a packet to many interfaces so it arrives quickly at its destination
* Each router has a routing table, which is a set of rules used to to determine the best router-to-router hop a packet should take
36
Gateway (3)
* Used when packets are passed between networks with different protocols
* Convert a packet to a different protocol
* The header data is modified to the format of the new protocol
37
Firewall
Sits between a trusted and untrusted (such as the Internet) network and performs packet filtering or stateful inspection to block unwanted incoming or outgoing traffic
38
Packet Filtering
Inspects packet headers and uses a set of rules based on IP addresses, ports and protocols to block unwanted traffic
39
Stateful Inspection
Keeps track of open conversations in a connection table to ensure incoming and outgoing packets are expected and checks packet payloads for suspicious activity
40
Proxy Server (5)
* Sits between clients and the firewall
* Provides anonymity to clients by masking their IP addresses
* Adds web-filtering
* Caches websites to speed up performance
* Can monitor client's network history
41
Symmetric Encryption
Uses the same key for encryption and decryption meaning the key must be exchanged with the data
42
Asymmetric Encryption (2)
* Uses a public key to encrypt data and private key to decrypt data
* The public key is exchanged with the senders whereas the private key is kept hidden by the receiver
43
Digital Signature (3)
* A hash of the data transmitted with the packet
* Ensures that it was not altered by a third-party
* Authenticates the sender
44
Digital Certificate
An electronic document, issued by an official certificate authority, to authenticate a sender
45
Virus (2)
* A self-replicating malware, which infects other files
* Its initiation requires a host program to be run
46
Worm (2)
* A self-replicating malware, which is used to spread to other computers and waste their resources
* Operates independently of a host program
47
Trojan (2)
* A non-self-replicating malware, which appears to be a legitimate software to trick the user into running it
* They steal information or inflict damage to the computer
48
Vulnerabilities (3)
* Social engineering on humans to make them download malware
* Bugs in unpatched software can be exploited by malware
* If code quality is poor, malware could exploit the weaknesses
49
Defence against Malware (3)
* Improved code quality means that malware cannot exploit common weaknesses in programs and not infect a computer
* Monitoring by other programmers or ethical hackers reviewing code to make it more secure
* Protection by using anti-malware software to detect and destroy malware on a computer
50
Application Layer
Uses protocols designed to work with certain types of applications (such as web browsers and email clients)
51
Transport Layer (3)
* Breaks / rebuilds application data into / from segments
* Allocates sequence numbers and adds source and destination port numbers to segments
* Acknowledges delivery and retransmits lost segments
52
Network Layer
Adds source and destination IP addresses to packets
53
Link Layer
Transports data frames across each individual medium (such as 3G and fibre-optic cable), which makes up the path between the client and server
54
Socket (2)
* A combination of IP address and port number
* Identifies a certain session on a server
55
Role of MAC Addresses in TCP/IP Protocol
The link layer uses a source and destination MAC address to transmit a data frame, making a packet hop
56
Client Port
Each request from the application layer is allocated a client port number so that the data can be returned to the correct process
57
Well-Known Port
Servers use pre-set well-known port numbers to transmit data
58
Difference between Client & Well-Known Port
Client port numbers are randomly allocated from a bank of numbers on the client device whereas well-known port numbers do not change so do not need to be looked up by clients
59
FTP
File Transfer Protocol transfers files between a client and a server
60
HTTP
Hypertext Transfer Protocol transfers multimedia files (web pages and linked resources from a web server) between a client and a server
61
HTTPS
Hypertext Transfer Protocol Secure uses public encryption when transferring data and provides a digital certificate
62
POP3
Post Office Protocol v3 retrieves emails by downloading them onto a client device and deleting them from the server
63
SMTP
Simple Mail Transfer Protocol sends emails by transferring them from a client device to the linked mail server and, if the recipient is on a different domain, forwarding the email to the recipient's mail server
64
SSH
Secure Shell provides an encrypted connection for users to access a remote computer
65
FTP Client Software
Accesses directories on the server and requests files
66
FTP Server
Has access to the storage space to store files and sends them out
67
Anonymous Access
The server does not require client authentication to upload and download files
68
Non-Anonymous Access
The server requires client authentication to upload and download files
69
SSH Client
Makes a TCP connection to a remote port for the purpose of sending application-level commands
70
Email Server (2)
* When the user opens their email client, it connects to their email server and downloads any new emails
* When sending emails, the email is transferred to the linked email server and, if the recipient has a different domain, forwarded onto the correct email server
71
Web Server (3)
* Web servers store web pages in text form and listen for requests
* A client sends an HTTP request to the server
* The server sends the web page to the client
72
Web Browser
Requests web pages and linked resources from a server and renders these
73
Network Identifier Part
The first part of an IP address, which identifies the network a host is on
74
Host Identifier Part
The last part of an IP address, which identifies the particular host on a network
75
Subnet
A subdivision of a network treated as a separate network with a different network identifier
76
Subnet Mask
Contains 1s for the network id and 0s for the host id. A bitwise AND operation with the IP address identifies the network identifier part
77
IP Address Standards
v4 and v6
78
Introduction of IPv6
Has a longer address structure to allow more devices to simultaneously be connected to the Internet
79
Non-Routable IP Address
Used in a private network and is only unique in the local network
80
Routable IP Address
Used in the Internet and is globally unique
81
DHCP
Dynamic Host Configuration Protocol dynamically assigns private IP addresses to devices trying to join a network
82
NAT
Network Address Translation converts a private IP address on an outgoing packet to a public, routable IP address before sending it out to the Internet
83
Purpose of NAT
Private IP addresses are not globally unique so responses from the server could be returned to the wrong device (with the same public IP address)
84
Port Forwarding
A server is on a private network and the router is configured to forward all inbound traffic on a certain port to the server
85
Client Server Model
The client sends a message to a server and the server responds to the request by replying with a response message to the client
86
Websocket Protocol (4)
* The websocket specification defines an API establishing a full-duplex 'socket' connection between a web browser and a server over TCP
* This means that there is a persistent connection between a client and server, allowing both parties to send data at any time
* Data can be pushed from the server without having to be initiated by a client request, increasing performance
* It is used when response times are important such as a browser game
87
Principles of Web CRUD Applications & REST (5)
* Database connected to browser using REST (Representational State Transfer) which relies on HTTP
* REST allows JavaScript to talk to server through HTTP
* REST API created and run on server and browser JavaScript calls API
* JSON (JavaScript Object Notation) or XML can be used to transmit data between a server and web application
* JavaScript referenced by HTML file is run in browser
88
CRUD (4)
* C - Create
* R - Retrieve
* U - Update
* D - Delete
89
REST (1:4)
Enables CRUD to be mapped to database functions (SQL) as follows:
- GET → SELECT
- POST → INSERT
- DELETE → DELETE
- PUT → UPDATE
90
JSON Compared with XML (4)
* Easier from humans to read
* More compact
* Easier to create
* Easier for computers to parse and therefore quicker to parse
91
Thin-Client Computing
Processing is carried out on an application server
92
Thick-Client Computing
Most processing is done and resources are held on a high-performance client device and the server sends minimal data
93
DNS (7)
* Translates FQDNs into IP addresses
* DNS stores a database of FQDNs and corresponding IP addresses
* DNS is a distributed database of mappings
* Individual mappings are only known by some DNS servers
* DNS servers are organised into a hierarchy
* If one DNS server cannot resolve a lookup the query will be passed to another
* DNS servers support load distribution by returning one IP address from a list
94
Internet Registries
Ensure that a particular domain name is used by only one organisation so there is no ambiguity on which website a client want to access
