Computer Science - OCR GCSE - 1.3.2 Network Topologies, Protocols And Layers

What is Ethernet?

• Ethernet is a set of protocols and associated hardware  which are commonly used in wired local area networks.

• It provides a simple interface for connecting multiple devices, such computers, routers, and switches.

• With a single switch and a few Ethernet  cables , you can create a LAN, which allows all connected devices to communicate with each other

Describe the different types of Ethernet cables:

Category	Bandwidth/ How much data can be sent at a given period of time/ per second
3	Up to 10Mbps
4	Up to 16Mbps
5	Up to 100Mbps = CAT 5 Up to 1Gbps = C
6	Up to 10Gbps

Using Ethernet, data is sent around a network using the concept of “frames”.

What is an Ethernet frame?

Messages are broken down into conveniently sized packets which are called frames. They contain for example, the source and destination MAC address of the data.

 An Ethernet frame contains different pieces of data. Label the contents of the Ethernet frame below using the terms given:

Ethernet Frame
A	B	C	D	E	F
7 bytes	1 byte	6 bytes	6 bytes	2 bytes	42-1500 bytes

Frame Section	Contents
A	Preamble (identifies that this is an ethernet frame)
B	SFD - Start Frame Delimiter (beginning of the frame)
C	Destination MAC address
D	Sender MAC address
E	Payload (part of the actual message being sent)
F	Checksum CRC

Describe the features of Ethernet:

• Stable connection

• Reduced possibility to be hacked

• More secure

• Wider bandwidth

Describe the features of Wi-Fi

• Cheap set-up costs

• More vulnerable to hacking

• The signal quality will reduce through walls or obstructions

• Interference can occur

• Generally will have a good quality signal

• Less disruption to the building due to no wires being installed

• User not tied down to a specific location

• Can connect multiple devices without the need for extra hardware

• May not be able to receive a signal

• The connection can “drop off”

• Tend to have slower transfer speeds

Give a diagram for the old style “bus” ethernet network:

This:

Give a diagram for the star ethernet network:

This:

What does WiFi stand for and what does it mean?

Wireless Fidelity - Wireless connections on a LAN using radio waves

What equipment is needed to connect a device to a Wi-Fi network?

• Wireless Access Point - Receives data from a network via a physical connection

• Integrated Wireless Network Card/Wireless Adapter - Allows device to connect to network

What is the role of a Wireless Access Point (WAP)?

• Receives data from a network via a physical connection

• Creates an area of connectivity called a hotspot

• Allows wireless enabled devices to communicate with it at frequency of 2.4GHz or 5GHz

• Allows wireless access devices to connect to the wired network by connecting the WAP to a switch and access resources such as server, printers, file shares

• The WAP may be connected to a router thus providing an internet connection

• A WAP allows users to send and receive data on a LAN

Diagram for Wireless Network:

This:

Give three reasons why wireless networking is less beneficial than wired networking:

• Limited Range

• More vulnerable to hacking

• Bandwidth stealing

Give three reasons why wireless networking is more beneficial than wired networking:

• Cheap set-up costs

• Good quality signal

• No wires

• Easier to add new devices

• Easier to set up

• Portability and Convenience

Give three ways in which wireless networks can be made more secure:

• Encrypt data - Ensures that data transferred over a wireless connection is less likely to be intercepted and readable

• Password protection

• Restricting the number of devices that can connect to a WAP - by their MAC address

• Disable SSID (i.e. the name of their wireless network) to make it more difficult to locate

State three applications of Bluetooth:

• Connecting I/O devices to a computer e.g. Keyboard, Headphones

• Transferring files e.g. downloading photos, video and contacts from a phone or digital camera between devices

• Linking a hands-free headset to a smartphone e.g. making it possible to talk and drive at the same time

Complete the table below to compare WiFi with Bluetooth:

	WiFi	Bluetooth
Range	Both are affected by obstacles, up to around 100m	Usually about 10m to 20m
Typical Bandwidth	Around 1Gbps	About 2Mbps
Power Consumption	More than Bluetooth	Less than Bluetooth
Security	Encrypted	Encrypted

What is encryption?

• Before Transmission - Data is scrambled/encrypted using a key into ciphertext

• During Transmission - If intercepted, the ciphertext is meaningless/unreadable without the key

• After Transmission - Data is decrypted/unscrambled from ciphertext back into a readable form, using the key

This is Symmetric encryption:

This is Asymmetric encryption:

What is an IP address?

Internet Protocol - An IP address is a unique address allocated to nodes on the internet that identifies a device on the internet or a local network, it changes as it moves location. 

The address is allocated by an internet provider/ router/ server and can change

Used by routers on the internet to send data packets to the correct destination

Write down an example IP address

IPv4 → 65.123.217.14

IPv6 → BC43:71A9:0000:044c:3879:0000:55FD:286B

Explain the following terms relating to an IP address:

• octet

• 0 to 255

• ipv4

• ipv6

• Octet →A number that can represented by 8 bits

• 0-255 → The range of denary values that can be displayed in an octet in IPv4

• IPv4 → Written in denary, 32bit address, formed by 4 decimal numbers separated by full stops

• IPv6 → Written in hexadecimal, a 128 bit address, formed by 8 groups of 4 hexadecimal digits, separated by colons

What is a MAC address?

• A unique address allocator to nodes on a LAN

• Physically embedded on the Network Card by the manufacture, making it permanent

• Switches route data on a LAN using MAC addresses

How are MAC addresses composed and how do they relate to binary numbers?

Written in 12 Hexadecimal Characters which are represented by a 48 bit Binary Number

How could a MAC address be used in network security?

Only certain MAC addresses are allowed/ not allowed to connect to a switch or router

Why are MAC addresses not used for sending data packets over the internet?

MAC addresses are used on LANs. IP addresses are used to send packets over the internet

Complete the table below to compare/contrast IP and MAC addresses

	IP Address (IPv4)	MAC Address
How it is allocated to a node	By an ISP/ Router/ Server	By the manufacturer of the NIC
Permanency	Changes with the device’s network	Permanent
Number System	Decimal/ Denary	Hexadecimal
Number of bits	32 (IPv4) 128 (IPv6)	48
Main use	Routing data packets to the correct nde over the internet	Routing data frames to the correct route node over a LAN

What are network standards?

Standards are a set of specifications for hardware or software that make it possible for manufacturers and producers to create products and services which are compatible with each other. Without standards most devices wouldn't be able to communicate with each other.

Give examples of some standards related to Computing:

ASCII/UNICODE

IEEE

HTML

Document, image and sound standards

What is a network protocol?

Network protocols are a set of rules or conventions which control the communication between divides on a network.

What do protocols specify?

• Data Packets format

• Addressing system being used eg IPv4 or 6

• Transmission Speed

• Error checking procedures

For the next slides:

Full Name, What it does, When would it be used

TCP/

• Transmission Control Protocol/Internet Protocol

TCP:

• Breaks data down into packets at sender’s end 

• Gives each packet a sequence number

• Packets are reassembled and resequenced at the receiving node

• Lost/damaged packets are detected and resent

IP:

• A destination and source IP addresses are assigned to each data packet

• Routers send data to the correct destination by inspecting the packets destination address

• Anytime data is transferred across the internet

HTTP

• Hyper Text Transfer Protocol

• Use for accessing and receiving web pages in the form of HTML. The protocol requests a web server to provide a certain web page to the user’s web browser for viewing.

• When requesting a website to be viewed.

HTTPS

• HyperText Transfer Protocol Secure

•  An extension of HTTP where any information transferred between a web browser and a web server is encrypted.

• When accessing a webpage/website where you may want to encrypt data – e.g. a Bank website.

FTP

• File Transfer Protocol

• Allows the transfer of files between local client computers and remote servers on the internet.

• To publish website files from a local computer to a remote live web server. For example, updating the live website.

POP

• Post Office Protocol

• Email messages are downloaded from the mail server. POP creates local copies of emails and deletes the originals from the mail server

• Viewing Emails

IMAP

• Internet Messaging Access Protocol

• Email messages are stored on the mail server and viewed/deleted on the server itself. No local copies of emails are made.

• When email is being accessed by multiple clients simultaneously, or email  is being accessed on multiple

SMTP

• Simple Mail Transfer Protocol

• Used for sending email messages between clients and mail servers

• When sending an email

What is meant by the concept of “layering” in computer networks?

Layering in a computer network is defined as a model where a whole network process is divided into various smaller sub-tasks. These divided sub-tasks are then assigned to a specific layer to perform only the dedicated tasks.

Why do computer networks use layers?

• Reduces complexity of network into subprograms

• Products from different vendors work together

• Devices can be manufactured to work at a particular layer

Complete the table below which describes the layers used in the TCP/IP protocol:

Layer	Function
Application Layer	Encodes data so that it will be understandable by the recipient. Formats data as required using protocols such as HTTP
Transport Layer	Splits data into packets and adds information to these such as sequence numbers. Managed by the TCP protocol
Internet/Network Layer	Adds source and destination IP address to packets. Routers operate at this layer.
Link Layer	The MAC address of the recipient/sender is added so that the packet can be directed to the correct recipient on the LAN

Difference between POP3 vs IMAP:

POP3	IMAP4
Since emails are kept on one local device, the changes made to emails aren’t shown on other devices	Emails are kept on a server and they are synchronized across devices.
Since the emails are on one local device, they cannot be accessed from a different device.	Multiple devices can access emails simultaneously
If you want to read an email, downloaded emails don’t require an internet connection	Internet connection is necessary all the time
Emails are downloaded to a local device instead of the server.	Any change made to emails or general settings are synchronized across devices
In order to read the email, one should first download them.	Email headers can be read without downloading whole content