Unit 5 Networks Flashcards
What is the Internet?
- A group of inter-connected networks
- Many services use the Internet such as the web and email
- No one person or organization owns the Internet, this is known as collective or distributed ownership
How is the Internet different from World Wide Web?
- The World Wide Web is one service that makes use of the Internet
- The World Wide Web is the information system of interlinked web pages and other resources
- It is accessed from a web browser
What is the World Wide Web?
- The World Wide Web is the information system of interlinked web pages and other resources
- It is accessed from a web browser such as Chrome, Safari, Edge or Firefox
- It makes use of HTTP to send and receive data
Wide Area Networks
- Any network in which computers communicate using resources supplied by a ‘third party carrier’ such as BT, is a Wide Area Network (WAN)
- A WAN uses cables, telephone lines, satellites or radio waves to connect two or more remote locations
- The Internet is the largest WAN in the world
Name three organisations that may be using a WAN to connect locations
- Organisations such as universities and schools may have a number of geographical locations
- Each one will have its own network. When these networks are joined together they will create a WAN
Other organisations may use WANs including:
- Large companies with many offices such as banks
- Governments which have employees in many locations
- Research organisations which are located in more than one place
IP addresses
- Every computer in the world has an IP (Internet Protocol) address
- IP addresses are four 8-bit numbers (0-255) separated by dots
- Where packets of data are sent to or received from
A circuit switching network
- When you make a telephone call, a dedicated connection is set up between you and the person you are calling for the duration of the call
- This is called ‘circuit switching’
- It works fine for phone calls, but there could never be enough lines for all the billions of people sending data across the Internet
What works in place of a circuit switching network for the Internet?
Packet switching
What is contained in the header given to each packet?
- The IP address it is going to
- The IP address it has come from
- The sequence number of the packet
- The number of packets in the whole communication
- Error checking data
Data packets
- Each data packet will contain the same number of bytes, usually a data packet is 512 bytes
- The packets may flow through the Internet via different routes
- Each packet is marked with the packet number so that the packets can be put back together by the receiver
Reassembling the data packets
- The recipient computer re-orders the packets into the correct order
- Each packet is checked for errors
- Corrupt packets are requested to be resent
Moving packets on the net
- Points on a network diagram are called nodes
- Routers are any node that can route packets from one place to another
- Your home router, routes packets to the different devices on you home-network
- Internet routers route packets around the world like a mail sorting office
Network Interface Cards (NIC)
- A Network Interface Card (NIC) is built into every networked device
- It may be wireless with an antenna or wired with a network cable socket
- Most modern computers and phones incorporate the NIC into the motherboard
MAC addressing
- A Media Access Control (MAC) Address is assigned to each NIC by the manufacturer
- A smartphone will have two different MAC addresses: one will be for Wi-Fi and one for Bluetooth
- A computer may have more than one MAC address if it has both and Ethernet and Wi-Fi connection
- Every networked device in the world has a unique MAC address
Why doesn’t the Internet use a MAC address instead of an IP address to locate a web address?
MAC addresses do not change with location, but IP addresses do. The actual geographical location of a networked device can be determined by its IP address
The role of the MAC address
When you request a web page, each router along the way uses the MAC address of the next router to send the data packet on the next leg of its journey
Routers
- Looks at the destination of packets of data and sends them to the network that is closer towards their destination
- A home router will route packets between the home local area network (LAN) and the Internet
Switches
- Switches connect each node (computer) in a network
- They know the MAC address of all connected computers and devices
- When a packet of data arrives, they can send it to the correct computer
- Hubs, by comparison will send the data to all connected networks
Wireless networks
- Connect using Wi-Fi
- Broadcast using radio waves, these are part of the microwave spectrum
- Wi-Fi networking protocols, Wi-Fi is a family of related protocols, it is a trademark used to describe a Wireless LAN or WLAN
Wireless transmission
- Commonly uses radio waves for communication
- Susceptible to interference from objects and other nearby electronics or other wireless devices
Wireless access point
- A wireless Access Point (AP) is a device that allows wireless devices to connect to a wired network using Wi-Fi
- The AP usually connects to a router via a wired network
- Home Wi-Fi routers often combine the functions of a switch, router and wireless access point in one box
Wireless NICs
A wireless NIC is built into every networked device capable of connecting to a wireless network
Examples of wireless devices
- PCs
- Smartphones
- Wireless speakers
Packet
One unit of data sent through an IP network
Wireless and wired network
Wireless network - a network using radio waves
Wired network - a network using cables
What is a LAN?
- LAN stands for Local Area Network
- Operates on a single site such as a school, hotel or business using their own cabling systems
What is the difference between LAN and WAN?
- LANs are local and located within one location such as a building
- WANs connect networks at remote locations via leased lines
Advantages of LANs
- Computers can share resources such as printers
- Files can be accessed through any computer in the network
- Data is easy to back up as it is stored centrally on the server
Disadvantages of LANs
- Purchasing the network hardware is expensive
- Managing a large network is complicated
- Viruses may be able to infiltrate the network and infect every computer
What is a topology?
The way in which parts of a system are connected
Network topologies
There are many topologies for setting up networks and LANs. Two of these topologies are:
- Star
- Bus
Example of network topologies
The London Underground network has a topology that shows where connections, and lines are
Star topology
In a star topology, computers and other devices (known as nodes) are all connected to a central switch
Advantages of star topology
- Fast data transfer to the hub as each wire isn’t shared with other computers
- If one cable fails the other computers are not affected
Disadvantages of star topology
- Requires additional hardware such as the central switch and network cables
- If the central switch fails the whole network goes down
Bus topology
- In a bus topology, computers and other devices are all connected to a central coaxial cable
- Terminators are placed at each end of the cable to absorb signals and prevent them reflecting down the cable
Advantages of bus topology
- Less cable so cheaper to install the network
- Easier to add more devices as they only need to connect to a central cable
Disadvantages of bus topology
- The single cable is shared by many devices so there will be many ‘collisions’ of data if data is sent at the same time, which slows down data transfer
- If the cable is damaged, the whole network fails
- Any device can view all data on the cable creating a security risk
Why does star topology not have a security risk?
- All connected devices pass through a switch/hub
- The switch/hub implements safety features
Network security methods
- Authentication
- Encryption
- Firewall
- MAC address filtering
Authentication
- Authentication is checking that the computer and the user are allowed to access content
- This is most commonly done using a username and password
Intercepting data
- Data that is transmitted over a network can be intercepted
- Any intercepted data can be read and understood unless measures are taken to prevent it from being interpreted
- These measures are known as encryption
Encryption
Encryption is the encoding of data so that it can no longer be easily understood
Plaintext
The original message to be encoded
Ciphertext
The encrypted message
Key
A sequence of numbers used to encrypt or decrypt, often data using a mathematical formula
Encryption algorithm
The formula for encrypting the plaintext
State the two encryption techniques
- Private key (symmetric encryption)
- Public key (asymmetric encryption)
Private key
- Symmetric encryption
- A single key is used to encrypt and decrypt a message and must be given to the recipient of your message to decrypt the data
Public key
- Asymmetric encryption
- Two keys are used, one (public key) to encrypt and the other (private key) to decrypt data
- This is more secure as it means that you never have to send or reveal your decryption key
Caesar shift cypher
- The earliest known substitution cipher was invented by Julius Caesar
- Each letter is replaced by a n positions further on in the alphabet
- n is the key and is used to encrypt and decrypt the message
- This is an example of symmetric encryption
State the two most common wireless security standards
- WEP (Wired Equivalent Privacy)
- WPA (Wi-Fi Protected Access)
WEP
- Older method of encryption
- Can be cracked in seconds
- This standard should no longer be used to protect a home
Strong and weak encryption
- Encryption can be considered to be ‘strong’ when the useful lifetime of the encrypted data is less than the time taken to break the code
- With weak encryption, the code may be broken in time to use the information, but it wouldn’t be worth the effort trying
What is a protocol?
A set of rules
HTTP and HTTPS protocol
- HTTP (hypertext transfer protocol) is used for accessing and receiving web pages via the Internet
- These are written in HTML (Hypertext mark-up language)
- The protocol requests a web page from the web server
- The server then sends its response which contains the web page
- HTTPS (secure HTTP) encrypts the information so that it cannot be understood by an eavesdropper
Specific types of sites that use HTTPS
- Banks, to prevent theft
- Online shops, for bank and log in details
- Social networks, for log in details and personal data
FTP
- File Transfer Protocol (FTP) is used for sending or retrieving files to or from a FTP server
- A graphical interface will allow files to be dragged from your computer to the server
How email works
- When an email is sent from a computer it will first be sent to a mail server using the SMTP protocol
- It is then forwarded on by other SMTP servers
- When it reaches the destination mail server it is stored
- The user’s computer uses POP or IMAP to access the email
What are POP and IMAP?
Email retrieval protocols that fetch message data and attachments from your remote mail server
POP
- POP (Post-Office Protocol) will download every new message to your local device and with them no longer being available on the server
- This is similar to the protocol of sending a letter through a post office
IMAP
- IMAP (Internet Message Access Protocol) will leave the messages on a server
- They can be accessed by multiple devices and they only are removed if the user deletes them
SMTP
- Simple Mail Transfer Protocol (SMTP) is an email protocol used for sending email
- Email software, such as Outlook, sends the email to the SMTP server used by the company or individual
- The mail server then relays the message through various other servers known as mail relays
- Finally, the email arrives at the destination mail server
TCP
Transmission Control Protocol (TCP)
- Breaks up messages sent over the Internet into data packets
- Reassembles the packets at the other end
- Detects errors
- Resends lost messages
IP
Internet Protocol (IP) routes the individual packets from one IP address to another
The TCP/IP protocol stack
- The protocol stack defines four layers that enable communication on the Internet
- This is a modular design with each layer being responsible for a small part of the communication process
- The four layers are divisions of network functionality, each carrying out different roles:
- application layer
- transport layer
- internet layer
- link layer
Application layer
- Applications such as email clients and web browsers create data to send in this layer
- SMTP, FTP and HTTP operate in this layer
Transport layer
- The Transport layer creates the connection between two computers, or ‘hosts’
- The two computers agree the communication settings and the size of the packets they will send and receive
- Data is then divided up into packets and given a packet number
- Packets are reassembled by the recipients Transport layer
- Lost packets are resent
- This layer uses the TCP (Transmission Control Protocol) or the UDP (User Datagram Protocol)
Receiving data
- Data packets move back up the layers on arrival
- The link layer removes the MAC address and passes packets up to the Internet layer
- The Internet layer removes the IP addresses and passes packets up the Transport layer
- The Transport layer reassembles the packets and passes the data to the Application layer
- The Application layer uses the correct protocol to correctly display the data, web page or email for the user
The advantages of layers
- Layers are self-contained, the functionality of one layer can be changed without affecting the functionality of other layers
- Different hardware or software operates on a particular layer providing interoperability between providers and systems
UDP
- The User Datagram Protocol (UDP) maintains an open data connection to send a stream of packets without checking they are received correctly
- UDP is unreliable as it isn’t known if a packet was received
- UDP makes most sense to use when it doesn’t make sense to wait and fill in gaps left by lost packets: online gaming, video streaming
What is a PAN?
- Personal Area Network
- A computer network used for data transmission among devices such as computers, laptops, phones
- A PAN can be used for communication between the devices themselves or for connecting to the Internet
What is a firewall?
A network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules
Advantages of using fibre optic cables
- Not affected by electromagnetic interference
- Greater bandwidth
- Do not break as easily as copper cables
- Faster transmission
Disadvantage of fibre optic cables
More expensive than using copper cables
What is a network?
A group of devices connected together, wirelessly or using cables, so that they can communicate with each other and share resources
What are the four layers of the TCP/IP stack (in order)?
- Application layer
- Transport layer
- Internet layer
- Link layer
Explain the function of the application layer
- Where data is sent from software applications into the protocol stack
- At the other end of the communications link, the application layer passes the data to the receiving application
- The data is encoded so that it will be understandable by the recipient
- The protocols used in the application layer are: HTTP, HTTPS, FTP, SMTP AND IMAP
Explain the function of the transport layer
- Breaks the application data into data packets
- Adds packet information to the header: sequence numbers, source and destination
- TCP and UDP operate in this layer
- Data sent using the TCP protocol will be resent if there are any missing data packets
- Data sent using the UDP protocol will not be resent if there are any missing data packets
- Passes the data down to the Internet layer
Explain the function of the internet layer
- Addresses and packages data for transmission and routes the packets across the network
- Attaches the IP address of the sender and destination
- IP operates on this layer
- The internet layer passes the data down to the link layer
Explain the function of the link layer
Attaches the MAC addresses of the sender and recipient, allowing the packet to be directed to a specific device
What are the advantages of using a wired network?
- Connection speeds are typically faster
- They typically have higher bandwidth
- They typically have better security
What are the advantages of using a wireless network?
- Typically have lower setup costs as there is no need to lay cables
- Easier to connect more devices
- Devices can be portable within the range of the access point
What are the disadvantages of using a wired network?
- Can be expensive to setup
- Not all devices can connect via cable
- Cables can be hazardous and unsightly
What are the disadvantages of using a wireless network?
- Can be less reliable than wired networks
- If many devices try to use the same access point at the same time, the connection can be very slow
- Connection speed reduces the further the device is from the access point
