Fundamentals of Communication and Networking and the internet

What is Serial and Parallel transmission

Serial data transmission  

• Bits are sent one after another, one bit at a time  

Parallel data transmission – several bits are sent simultaneously along multiple separate lines 

Advantages/disadvantages of serial and parallel transmission

Serial

• Reliable but slow 

• Good for transmitting data over medium to long distances, such as from wired peripherals like mice and keyboard to the computer. 

• doesn't suffer from skew or crosstalk making it a more reliable communication method especially over long distances 

• Serial connection is cheaper as it is only one line 

Parallel

• Faster 

• More expensive due to use of multiple lines 

• Mainly good for high intensity short distance connections like between parts of the processor and within RAM 

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What is the problem with skew and crosstalk

skew

• bits travel at different speeds along each of the wires.

• Skew is worse over long distances and in extreme cases can lead to bits from different pulses overlapping causing corruption of data 

crosstalk

• This refers to the electromagnetic interference between two adjacent channels or parallel wires 

• It gets more pronounced as the frequency increases 

• To prevent crosstalk, either use fiber optic or use twisted cables 

 

What is synchronous and asynchronous transmission?

Synchronous data transmission

• all data transferred are timed to coincide with an internal clock pulse 

Asynchronous transmission 

• Each byte is sent separately the moment it is available instead of waiting for a clock symbol 

  Each byte is preceded by a start bit and ends with a stop bit  

  • a short time between each set of bits allows sets of bits to prepare arrival of the next 

  • The start bit can either be a 0 or a 1 and the stop bit must always be the opposite of the start bit 

  • Start/stop bit lets the receiving computer know when new data has arrived 

What is latency?

Latency

• The time delay between the moment the first packet is sent and when it is received as its last destination 

Bit and Baud rate

• Bit rate is the number of bits that can be sent in one second 

• baud rate is the number of times a signal in a communications channel changes state 

• Bit rate is baud rate x no of bits per signal 

What is broadband and bandwidth

Broadband is  the transmission of high-quality data of wide bandwidth. 

Bandwidth is the maximum capacity of a communications channel

Features of a logical bus network

• all devices on the network share the same communication channel.  

• Devices send data across the network, and every other device can see the data, but only the intended recipient actually accepts and processes it. 

Advantages of a logical bus network

Advantages- 

• Cost-Effective: Requires less cabling and hardware since all devices share the same communication medium. 

• Ease of Installation: It is simple to set up compared to more complex topologies

• Scalability in a Small Network: Adding new devices is easy without disrupting the entire network. 

             Disadvantages- 

• Network Collisions: Since all devices share the same communication channel, collisions can occur when multiple devices attempt to send data simultaneously

• Decreased Performance with Size: As more devices are added, performance can degrade significantly because of increased collisions.

• Single Point of Failure: If the main communication channel (logical bus) fails, the entire network can go down.

physical star network features, advantages and disadvantages.

• Each client has its own direct connection to the central hub 

• The hub receives packets for all of the clients connected to it and is responsible for delivering them to the correct recipient 

Advantages – 

• Packets are sent directly to their recipient over a cable 

• failure of one cable doesn't affect the rest of the network 

• each cable is only connected to one device eliminating collisions 

Disadvantages -  

• Expensive to install due to the large amount of cable needed 

• if the central hub fails, all communication along the network fails 

 

peer to peer and client server advantages/disadvantages

Peer-to-Peer networking

• Cost affective compared to client-server as no server is needed 

• Easier to setup and maintain 

• The clients that are providing the services such as storage must leave their computer running in order for the network to be fully operational 

Client-Server networking

• They allow for central management 

• They improve security 

• Expensive to set up 

 

what does connecting to a wireless network require?

Connecting to a wireless network 

• ISP (internet service provider) 

• Modem and wireless router (often combined) 

• Device with a network interface controller  

• wireless access point (WAP)

• wireless network adapter

What methods can be used to secure WI-FI

encrypting transmitted data using WPA or WPA2 (Wi-Fi protected access)  

• WPA requires that a new wireless client enters a password in order to connect to the network 

disabling SSID broadcast (service set identifier) 

• It identifies each network with a unique name 

• Disabling SSID broadcast stops wireless devices within range of the network from displaying the network is available, only allowing those who know the SSID to connect. 

MAC address filter (media access control)

• MAC address whitelists can be created to only allow specific devices to connect to a network.

• Likewise MAC address blacklists can be used to block specific devices from connecting to a network

How can interference affect WI-FI

• It is typically used indoors where there are lots of objects to block the signal or reflect and echo a transmitted signal into the path of the other 

• If two frames emitting frequencies collide with each other when they are within interference range, there is a good chance that neither of the frame will be properly decoded at the receiver. 

How does CSMA/MA protocol work to avoid collisions

The CSMA/CA protocol would first check if the channel is idle, if so then it will send an RTS (request to send) message to the receiver, if the receiver responds with a CTS (clear to send) message then the laptop will begin transmitting packets of data to the receiver, if the CTS message does not get sent to the laptop then there is another device transmitting.

What is the pre shared secret key?

• Pre-Shared secret key  (PSK) 

  • In WPA/WPA2, the access point and stations that are allowed to join the wireless network share a secret key called the PMK, this s 256bit key (32 bytes) 

• Generating the PMK 

  • IN WPA/WPA2, the PMK is generated from a passphrase/password known to the user and the SSID 

what is the advantage of IPv6 over IPv4

IPv4 is 32 bits in length whilst IPv6 is 128 bits in length. The IPv6 protocol can process packets more efficiently, improve performance, and increase security. 

What is packet switching

This is where messages to be sent are split into a number of segments called packets. The packets of a message are allowed to travel along independent paths through a network of routers.      

what does a packet consist of?

source IP address , destination IP address, sequence number, time to live, checksum, the actual data

what is a router and a gateway and what are their differences

Routers and gateways are special packet switches that receive incoming packets of data from one host  and send them as outgoing packets to another host. 

gateways allow networks using different protocols/ links to still communicate with each other through translation

what is the end-to-end principle

It states that two endpoint hosts should be in control of the communication.  

• Both endpoint hosts are able to survive a partial network failure as the failure Is detected and the packets are resent. 

• Packets can be rerouted along alternative paths 

• All control and security of the transmission is done by the endpoints 

• Each endpoint only needs to be aware of the router which it is directly connected to 

what is a FQDN (fully qualified domain name)

A fully qualified domain name (FQDN) is a domain that specifies an exact resource and can be interpreted in only one way. It will always include the servers host name. 

what is the domain name and IP address

A domain name is the human-readable address of a website, like example.com, used to access websites easily without needing to remember numbers.

An IP address is a numerical label assigned to each device on the internet, like 192.168.1.1, which identifies and locates it for communication purposes.

what is the domain service (DNS)

The function of DNS is to translate human-readable domain names (like example.com) into IP addresses (like 192.168.1.1) that computers use to identify and communicate with each other. This allows users to access websites using easy-to-remember names instead of numerical IP addresses.

how is routing achieved across the internet

Routing across the internet is achieved using routers that direct data packets between networks based on their destination IP addresses. Each packet includes the source and destination IP, and routers use routing tables and algorithms (like Dijkstra's or distance-vector algorithms) to determine the best path to send the data.

what is the 4 layers of the TCP/IP stack protocol and there function

• Application - this layer interacts with the users application software and selects and uses the correct protocol to transmit data. 

• Transport - Establishes an end-to-end connection between the sender and the receiver. The layer splits the transmission into packets. The packets contain a sequence number (identifies position) and a port number (identifies the type of protocol in use)

• Network - provides the correct IP addresses for each packet source and destination. The routers work within the network layer, using the IP addresses on a packet to send to their destination. 

• Link - controls physical connections between pieces of hardware in a network. It adds MAC addresses from packets which it receives from the network layer. The mac addresses change with every hop through a network. 

what is an IP address split into?

an IP address is split into a network identifier part and a host identifier part.

What is a firewall

A firewall sits between the device and the internet and regulates the packets that pass through it. 

They can either be hardware or software and work as a proxy server which can perform both packet filtering and stateful inspection. 

What is stateful inspection

Stateful inspection actually examines the contents of a packet before deciding whether to allow it through a firewall. 

Some firewalls keep a record of current connections in a network, allowing them to filter out packets that aren’t related to activity on the network. 

Proxy server

It is a server that sits in between a public network and a private network. 

These devices manage every packet that passes between the two networks. 

what is a worm, trojan and virus

Worms - pieces of malicious software that can self-replicate between computers, either within a network or by users downloading and running a malicious file.  

Trojans - a type of malware that is disguised as a benign file that users can be tricked into opening. These are often spread as email attachments or downloaded from malicious websites.  

Viruses -  require a host file in which to reside. These files are typically executable files, meaning that viruses can lie dormant in a computer until their host file is opened or run.

How do you prevent malware.

Good code quality is an important factor in preventing malware and small oversights by developers can have devastating consequences.  

Other vulnerabilities that malware exploit include a lack of antivirus software, out-of-date software and poor security. One general rule for preventing malware is to install antivirus software. 

 Antivirus programs are specialist pieces of software that scan the files on a computer and remove any suspicious files. Many modern operating systems come with some level of antivirus installed as a default.  

In organizations, employees can be trained about the risks of opening suspicious email attachments in order to reduce the risk posed by malware.  

What is symmetric encryption and asymmetric encryption?

symmetric:

Both the sender and the receiver share the same private key used to encrypt and decrypt data. 

asymmetric:

Before a message is sent, it is encrypted by the sender using the recipient’s public key. 

This means that the message can only be decrypted by the recipient’s private key, which only the recipient has access to 

advantages of asymmetric encryption and disadvantage of symmetric encryption

advantage:

the recipient is the only person who can decrypt the message. 

disadvantage:

If the key is exchanged over a network, it is vulnerable to interception. This is a major floor in symmetric encryption that asymmetric encryption overcomes.  

What is a digital signature?

When using asymmetric encryption, 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.  

what is the process for achieving a digital signature?

1. A digest of the message is created, perhaps by a hashing or checksum algorithm.

2. This digest is encrypted with the senders private key. (which can be decrypted with the senders public key) 

3. The encrypted digest is appended to the actual message being sent

4. The message and appended digest are encrypted with the recipients public key, meaning that only the recipient can decrypt the information 

5. When the recipient receives the message, they first decrypt it using their private key, leaving them with the decrypted message and an encrypted digest 

6. As the digest was encrypted using the sender’s private key in stage 2, it can be decrypted using the sender’s public key.

7. The recipient then carries out the same hashing or checksum algorithm on the message and checks whether their result matches the now decrypted digest.  

what are FTP, SSH and HTTP/HTTPS protocols and their respective port numbers

• File transfer protocol (FTP) 

  • PORT 20, 21 

  • Used for sending files between devices. FTP software allows clients to connect to FTP servers which send files requested by the client. They can be accessed by logging in with a username and password. 

• Secure shell (SSH) 

  • PORT 22 

  • Used for remote management of computers allowing computers to be accessed and controlled remotely. 

  • To access a remote computer, SSH requires a  username / password combination and encrypts information during transmission.  

• HTTP/HTTPS  

  • HTTP – PORT 80, HTTPS = PORT 443 

  • Holds web pages in a text form which can be delivered to clients using HTTP. 

  • HTTPS encrypts the information during transmission 

what are POP3, SMTP and IMAP protocols and there respective port numbers

• POP3 

  • PORT: 110  

  • Used for retrieving emails from an email server. POP3 communicates with email servers to check and download new messages. (it then deletes the email from the server) 

• SMTP 

  • PORT: 25 

  • Used to send emails and forward them between mail servers till they reach their destination 

•  IMAP 

  • Port : 143 

  • Manages emails on a server so multiple clients can access the same email account at the same time  

what does an IP address consist of?

An IP address consists of two parts: 

• Network ID – left hand bits of 32-bit number used to define the network where nodes are communicating 

• Host ID – right hand bits of 32-bit number, used to identify separate nodes on the network. 

why do we use a subnet mask?

we use a subnet mask to identify two separate parts of the address. All the bits that are 1s in the sequence indicate how many bits are used for the network ID.

How does a Ip address get calculated

1. the subnet mask is ANDed with the original Ip address

2. the network ID part of the ANDed address should match with the network ID part of the original Ip address, that’s how we know it matched correctly.

3. the remaining bits are the used for the subnet ID (optional) or host ID.

what is NAT

• Contains a public address ( which is routable and connected to the internet) and an private address (which is unrouteable and only used throughout the local network 

• The translation device records the source and destination socket address for each request 

  • It then communicates on the hosts behalf with the destination IP address  

  • When a response returns, it is passed back to the host that made the original request 

What is port forwarding

• Servers accessible to the public can be given a non-routable IP address within a private network. 

  1. The client sends packets to the public IP address of the router belonging to the server’s private network.  

  2. The packets sent by the client contain the 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.  

what is the client server model?

• A server presents it services to requesting clients 

• If the request cannot be fulfilled a suitable notification will be sent 

Application Programming Interface (API) 

• An API is a set of functions and protocols that clients can use  

• A server side web API is a set of web services or web resources to enable programmers to build web applications 

what HTTP requests are there?

GET - request data from a source
POST - submit data to be processed
PUT - uploads a new resource to a server
DELETE - removes a resource from a server

These map CRUD commands (Create, Update, Retrieve, Delete) 

Limitations of HTTP communications: 

• Client has to request ("PULL") data from the server 

• If too much time passes between establishing a socket connection between client and web server, the server drops the connection to conserve its resources and returns an error message 

what is WebSocket protocol 

• • • Includes an API for establishing a TCP socket connection 

      • It is designed for a web browser and server, but any type of client and server can use it. 

      • Server can offer push data to the client 

      • WebSocket secure is encrypted 

Web CRUD applications

•  A principle for how a database should be functioned. 

• Create - write a record to a database

• Retrieve - retrieve a record from a database

• Update - amend a record

• Delete - remove a record from a database

what is Representational State Transfer (REST)

Rest is an architectural style which determines how systems communicate with each other 

• Typically REST uses HTTP request methods to interact with online databases 

• RESTful systems and APIs separate the client from the server database allowing either to be uploaded independently without impacting on the other. 

advantages of JSON and disadvantages of XML

• Advantage of JSON files 

  • Easier for a human to read, write and maintain 

  • More compact so requires less storage 

  • Can be directly manipulated by java script 

• Disadvantage of XML files 

  • Expansive use of tags make it difficult to follow 

  • Only works with specific data types 

what is a thick client and state its advantages and disadvantages

• A thick client (also known as a fat client) does most of the processing on the client side. 

• The server provides some resources, but the client runs the applications and handles most of the data processing. 

• Examples: A personal computer running software like Microsoft Word or Photoshop, where most of the work happens locally. 

  • Advantages: 

    • Can function with less reliance on the server. 

    • Better performance as most processing is done locally. 

  • Disadvantages: 

    • Higher hardware requirements (needs powerful local machines). 

    • More complex to update and maintain across multiple clients. 

what is a thick client and state its advantages and disadvantages

Thin Client: 

• A thin client does minimal processing on the client side. Instead, most of the work (processing, storage, etc.) is done on the server. 

• The client primarily acts as an interface to send inputs to the server and display the results. 

• Examples: Web-based apps like Google Docs or Virtual Desktop setups, where the server does most of the computing. 

  • Advantages: 

    • Easier to maintain and update (most changes are made on the server). 

    • Cheaper hardware requirements (clients don’t need powerful processors or storage). 

  • Disadvantages: 

    • Relies heavily on the server and network connection. 

    • If the server or network fails, the client becomes unusable.