Fundamentals of Communication and Networking Flashcards
Baud rate
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.
Bit rate
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).
Bit rate = Baud rate × № of bits per signal
What is the Bit Rate Formula?
Bit rate = Baud rate × № of bits per signal
What is the relationship between bandwidth and baud rate?
Directly proportional
Bandwidth
Bandwidth (Hz) relates to the range of frequencies that a communication medium is capable of transmitting.
There is a direct relationship between bandwidth and bit rate. Higher bandwidth results in a higher bit rate.
Latency
Latency in a communication medium, is the difference in time between an action being initiated and its effect being noticed.
For example, if you press the “R” key on your keyboard and the letter R appears on screen 26ms later, the latency in the link between your keyboard and the application you are using is 26ms.
Latency usually increases with distance.
Protocol
A protocol is a set of rules relating to communication between devices. International organisations decide upon and publish protocols which allow devices made by different manufacturers in opposite ends of the world to communicate seamlessly.
Serial data transmission
In serial data transmission, 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).
Serial data transmission is frequently used for transmitting data over medium to long distances (computationally speaking), such as from wired peripherals like mice and keyboards to your computer.
Parallel data transmission
Parallel data transmission uses numerous parallel communication lines to send multiple bits between components in a computer simultaneously.
Serial vs Parallel Transmission:
Due to skew, parallel wires are very unreliable over longer distances (> 2M)
Parallel Transmission tends to be more expensive; this is because it uses more connection lines.
Parallel transmission suffers from “Crosstalk”, Serial does not.
What is Crosstalk?
Occurs in Parallel transmission
It’s where there’s interference between the different lines which can result in data corruption
The stronger the signal, the worse the problem. This is why Serial can transmit more data; it can handle higher signals.
In Parallel Transmission, what’s the relationship between number of lines and data transfer?
The more lines that a parallel communication medium uses, the more data can be transferred simultaneously.
What is Skew?
Each of the communication lines that forms part of a parallel communication medium will have different electrical properties, meaning that the time taken for one bit to be transferred will differ slightly from line to line.
This means that bits sent together may not be received together, a problem referred to as skew.
Skew is worst over long distances and, in extreme cases, can lead to bits from different pulses overlapping, causing corruption of data.
Synchronous transmission
Data is transferred at regular intervals
Synchronised by a clock pulse
Often used in parallel transmission
Useful for real-time data: VoIP and chat
Asynchronous transmission
Each byte is sent separately.
Sent as soon as the data is ready, doesn’t have to wait for a clock pulse.
Each item is set with a parity bit, start bit and stop bit.
Instead of using a shared clock; it uses start and stop bits to indicate the duration of a transmission.
The sender and receiver must use the same Baud rate and only need to synchronise their clocks for the duration of the transmission.
Start bit
Used in Asynchronous Transmission
Wakes up the receiver
Synchronises the receiver and the transmitter’s clocks
Stop bit
Allows the next start bit to be recognised
Provides time for receiver to process/transfer the received data
Network topology
Topology refers to the structure of a network.
There are two types of topologies to consider: physical and logical.
Physical network topology
Physical network topology refers to the actual architecture of a network.
Networks using one physical topology will interconnect components differently to those networks that use another physical topology
Physical star network topology
In a physical star network, each client has its own direct connection to the central hub/switch.
The hub/switch receives packets for all the clients connected to it and is responsible for delivering them to the correct recipient.
Physical bus topology
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.
There is no need for a central hub like in physical star networks and a server can be connected to the backbone just like a client.
Advantages of Bus Topology
Cheap to install
Does not require any hardware beyond the main cable
Disadvantages of Bus Topology
If main cable fails, no network data can be transmitted
Performance degrades heavily with increased traffic
Security is poor, as all computers on network can see all transmissions
Why is a Terminator placed at the ends of the backbone?
A terminator in bus topology absorbs signals to prevent them from bouncing back and forth, allowing other components to send signals.
Logical network topology
In contrast to a network’s physical topology, a network’s logical topology refers to the flow of data packets within a network.
A logical bus network delivers packets to all clients on the network whereas a logical star network delivers packets only to their recipient.
Mixing topologies
If a network is set up as a physical star, it can still behave as a logical bus.
Even if the physical connections between clients and the central hub follow that of the physical star topology, running a bus protocol on the hub allows it to distribute packets to all the connected clients to act like a bus network.
Client-server networking
In a client-server network, one or more central servers provide services to the clients on the network. Servers are connected to the network in the same way as clients but are often more powerful machines than the clients.
Peer-to-peer networking
Peer-to-peer networks don’t have a shared server.
Instead, services are provided by the clients themselves and every client has equal status.
For example, one computer on the network might manage print queues, another manage storage and a third manage emails.
Routers and gateways
A router is a device that directs data packets between networks. It uses routing tables and protocols to determine the most efficient path for forwarding the packets.
A gateway, on the other hand, is a network node that serves as an access point to another network. It is often used to connect networks that use different protocols. It can also translate between different protocols, allowing them to communicate.
Uniform resource locators
A uniform resource locator (or URL) is an address assigned to files on the Internet. Different protocols can be used in URLs to access different types of files in different ways.
Domain names
A domain name identifies an organisation or individual on the Internet. They use alphanumeric characters which make them easy for humans to remember. E.g. “google.com”
IP Addresses
An internet protocol address (IP address) is a “Unique address which is given to a single network device.”
What is a Fully Qualified Domain Name?
Host (www.) + domain name
Domain Name Server (DNS)
An internationally agreed structure which classifies the area an internet resource resides.
DNS stands for Domain Name System. It’s like an internet phone book that translates website names into their corresponding IP addresses.
What is Packet Filtering?
Packet filtering is a process where data packets are examined based on predefined rules as they pass through a network.
The rules can be based on criteria like IP addresses, port numbers, or protocol type.
If a packet matches a rule that allows it, it’s forwarded to its destination.
If it matches a rule that blocks it, it’s discarded.
This helps enforce network security by controlling data flow and protecting against unauthorized access.
What is Encryption?
The process of encoding a message so that it can be read only by the sender and the intended recipient.
Packet switching process
Network Interface Card (NIC) gets a message to send out data
NIC breaks message into equal packets and numbers them.
Each packet gets a checksum calculated and added to it for error checking.
Packets go to the local Internet Service Provider [ISP] and are checked for errors.
Packets are sent to the router. They may take different paths based on bandwidth and congestion.
Each packet is checked for errors again.
Packets reach the destination computer’s ISP.
Packets reach the destination computer. TCP puts the packets in the correct order.
Protocol bits are removed from the packets, and the data is sent to the application that needs it.
Symmetric Encryption
Symmetric encryption is a method of encryption where the same key is used for both the encryption and decryption of data.
Asymmetric Encryption
Asymmetric encryption uses two keys: a public key for encryption and a private key for decryption. The public key can be freely distributed, while the private key is kept secret.
Sender and receiver both share there public keys with each other. When sending data the data is encrypted with receivers public key and the receiver decrypt it with their own private key.
