Lesson 6. Protocols, Standards and Layers

Lesson Objective

Identify some core protocols used to communicate data.
Explain how the TCP/IP stack is used to send data over the Internet.

Lesson Notes

What is a Standard?

A network standard is set of agreed requirements for hardware and software. Standards are important as they allow manufacturers to create products and programs that will be compatible with products and programs from other manufacturers.

What is a Protocol?

A protocol is a set of rules that allow computers to communicate over a network.

HTTP and HTTPS

HTTP (hypertext transfer protocol) is used for accessing and receiving web pages in the form of HTML files on the Internet.

HTTPS (Hypertext Transfer Protocol Secure) is an extension of HTTP that works to protect communication between web servers and browsers when transporting data.

The key difference between these protocols lie in security. HTTP sends data in plain text, making it vulnerable to interception and tampering. HTTPS, on the other hand, secures connections using a digital security protocol that encrypts and validates data.

FTP (File Transfer Protocol)

(File Transfer Protocol) is a standard network protocol used for transferring files between computers over a TCP-based network, such as the Internet. FTP operates on a client-server architecture. FTP users can authenticate themselves using a plain-text sign-in protocol (usually a username and password).

Email Protocols

SMTP (Simple Mail Transfer Protocol): SMTP is responsible for sending emails from a client (like your email app) to a mail server. When you compose an email and click "send", SMTP handles the delivery process. It communicates with the recipient's mail server to relay the message.

IMAP (Internet Message Access Protocol): IMAP is an incoming mail protocol that allows you to access your email stored on a mail server. It keeps your email synchronized across multiple devices (phone, computer, tablet). IMAP downloads only email headers initially, improving efficiency. When you open an email, IMAP fetches the full content from the server.

POP (Post Office Protocol): It downloads entire emails from the server to your local device. Once downloaded, emails are removed from the server. POP is useful if you want to keep a local backup of your inbox. However, it's less suitable for managing emails across multiple devices.

TCP/IP

TCP/IP (Transmission Control Protocol/Internet Protocol) is a fundamental framework for organizing communication protocols used on the Internet and similar computer networks.

TCP is one of the main protocols in the Internet protocol suite. It originated alongside the Internet Protocol (IP) during the early days of network implementation. Together, TCP and IP form the foundation of the suite, commonly referred to as TCP/IP. TCP ensures reliable, ordered, and error-checked delivery of a stream of data (octets or bytes) between applications running on hosts connected via an IP network.

IP handles addressing and routing of data packets across networks. It ensures that data reaches the correct destination based on IP addresses. IP is connectionless and operates independently of TCP.

The TCP/IP Stack

The TCP/IP Stack, also known as the Internet Protocol Suite, is a fundamental framework for organizing communication protocols used on the Internet and similar computer networks.

The protocol stack defines four layers in which different protocols operate to pass data packets across a network. The four layers are divisions of network functionality, each carrying out different roles:

Application Layer:

The Application layer is where network applications operate.
When you use email, web browsers, or other software, they function at this layer.
The application selects the appropriate protocol based on the specific task (e.g., HTTP for web browsing, SMTP for email).

Transport Layer:

The Transport layer establishes communication between two computers (hosts).
Key tasks include:

Connection Setup: The two hosts agree on communication settings (like TCP or UDP).
Packet Size Negotiation: They decide how large the data packets will be.
Packet Numbering: Data is divided into numbered packets (e.g., 1 of 6).
Packet Reassembly: The recipient's Transport layer puts the packets back together.
Error Handling: Lost packets are retransmitted.

Network Layer:

Routers operate at the Network layer.
Their job is to forward data packets from one network to another.
Destination addresses are added to the packets, ensuring they reach the right place.
Think of this layer as the postal service sorting and routing mail.

Link Layer:

The Link layer deals with the physical hardware that connects hosts. Components include:

Network Interface Cards (NICs): These connect the computer to the network.
Cabling: Physical wires or wireless connections.
OS Device Drivers: They manage communication at this level.

In summary, the TCP/IP model provides a structured way to understand how data flows across networks, from applications down to the physical hardware.

Sending Data

The application you are using to send data will determine the correct protocol to use to communicate.

Recieving Data

Data packets move back up the layers to their destination application:

The link layer removes the MAC address and passes packets up to the Network layer.
The Network layer removes the IP addresses and passes them on to the Transport layer.
The Transport layer reassembles the packets and passes the data to the Application layer.
The Application layer finally uses the correct protocol to correctly display the data, web page or email for the user.

Layered Network Models

A layer is defined as a division of network functionality.

Modularity and Abstraction: Layered models break down complex networking tasks into smaller, manageable components (layers). Each layer focuses on specific functions, making it easier to understand and troubleshoot.
Promotes Interoperability: By defining standard interfaces between layers, different vendors and systems can communicate seamlessly. Interoperability ensures that devices from various manufacturers can work together effectively.
Ease of Development and Maintenance: Developers can work on individual layers without affecting others. Changes or updates to one layer don't necessarily impact the entire system. Maintenance becomes more straightforward because each layer has a well-defined purpose.

Extra: UDP (User Datagram Protocol)

UDP (User Datagram Protocol) maintains an open data connection to send a continuous stream of packets without verifying if they are received correctly. It's most useful in scenarios where waiting to fill in gaps caused by lost packets doesn't make sense.

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