3.2b: Protocols & Layers

Exam Board:
OCR

Specification:
2020

Protocols

A protocol is a set of rules that allow devices on a network to communicate with each other.

TCP / IP

(Transmission Control Protocol / Internet Protocol)

TCP / IP is actually two separate protocols that combine together.

​TCP is a protocol that allows packets to be sent and received between computer systems.

 

It breaks the data into packets and reassembles them back into the original data at the destination.

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IP is a protocol in charge of routing and addressing data packets. This ensures data packets are sent across networks to the correct destination.

 

It is also an addressing system - every device on a network is given a unique IP address so data packets can be sent to the correct computer system.

HTTP is used to transfer web pages over the Internet so that users can view them in a web browser.

 

All URLs start with either HTTP or HTTPS
(e.g. https://www.csnewbs.com).

HTTPS is a more secure version of HTTP that works with another protocol called SSL (Secure Sockets Layer) to transfer encrypted data.

 

You should see a padlock symbol in the URL bar if your connection to that website is secure.

HTTP/HTTPS

(Hypertext Transfer Protocol)

Transfer Protocols

FTP (File Transfer Protocol) is used to transfer files across a network. It is commonly used to upload or download files to/from a web server.

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SMTP (Simple Mail Transfer Protocol) is a protocol used to send emails to a mail server and between mail servers.

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POP (Post Office Protocol) and IMAP (Internet Message Access Protocol) are both protocols for receiving and storing emails from a mail server.

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POP will delete an email once it has been downloaded to a device.

Pop!

IMAP syncs the message with an email server so it can be accessed by different devices.

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IP vs MAC Address

There are two versions of IP addressing currently used - IPv4 and IPv6.

 

IPv4 uses a 32-bit address that allows for over 4 billion unique addresses

 

IPv4 uses a numeric dot-decimal notation like this: 212.58.244.66

 

4 billion unique addresses may sound like a lot but there are nearly 8 billion people in the world. Therefore a newer version - IPv6 - was developed with a 128-bit address, represented in hexadecimal that allows for a mind-boggling number of unique addresses. 

A MAC address is a unique hexadecimal number assigned to each network interface card inside a networked device e.g. a router or a laptop


While an IP address may change, the MAC address can’t be changed.

Network Interface Card.png

Networking Standards

Networking standards are rules that allow computer systems to communicate across networks. Standards have been created to ensure devices can exchange data and work together.

4-Layer TCP/IP Model

The TCP/IP model is split into 4 layers. The model is used to visualise the different parts of a network as each of the four layers has a specific role.

Splitting a network design into layers is beneficial to programmers as it simplifies design, making it easier to modify and use.

Each layer has a certain purpose and is associated with different protocols.

The four layers are explained below:

4

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Allows humans and software applications to use the network e.g. browsers (HTTP/HTTPS) and email (SMTP) and file transfer (FTP).

3

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TCP breaks the data down into data packets. This layer makes sure the data is sent and received in the correct order and reassembled at the destination without errors.

2

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IP is responsible for addressing and routing data packets. The optimal route for the data to take is calculated in this layer.

Also known as the 'Internet Layer'.

1

data link.png

Ethernet sets out the format of data packets. This layer handles transmission errors and passes data to the physical layer.

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Questo's Questions

3.2b - Protocols & Layers:

 

1. Describe each of the following protocolsIt might be helpful to also draw an icon or small diagram for each one:

  • a. TCP [ 2 ]

  • b. IP [ 2 ]

  • c. HTTP & HTTPS [ 3 ]

  • d. FTP [ 2 ]

  • e. SMTP [ 2 ]

  • f. POP3 & IMAP [ 2 ]

2. State which protocol would be used in the following scenarios:

  • a. Transferring a music file to a friend over the internet. [1]

  • b. Sending an email to a family member in America. [1]

  • c. Using a webpage to enter a password securely. [1]

  • d. Receiving an email from a bank. [1]

3a. What are networking standards? [2]

3b. Describe why network designs are split into layers. [2]

4. Create a diagram similar to the one above and describe each layer of the TCP/IP Model. [8]

5. Look at the statements below and name the layer that is being described:

  • a. This layer ensures data packets are sent and received correctly.

  • b. This layer checks for errors in transmission and sets out the data packet format.

  • c. This layer allows software like web browsers to interact with the network.

  • d. This layer uses addresses to ensure data packets take the correct route.  [7]