Protocols & Layers

Today's Mission

• Describe and understand the uses of communications protocols

• Explain the concept of layers in the TCP/IP protocol stack

Protocol

• "An agreed set of rules, for how devices should communicate on a network"

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There are 7 Protocols you need to know

• HTTP / HTTPS

• FTP

• SMTP

• IMAP

• POP

• TCP

• IP

HTTP & HTTPS

• Hyper Text Transfer Protocol (HTTP)

• This is used for accessing and receiving web pages in the form of HTMP files on the internet.

• The protocol requests the web server to upload the requested web page to the user's browser for viewing.

• Hyper Text Transfer Protocol Secure (HTTPS)

• Same as HTTP - but the connected is encrypted. That way any intercepted data cannot be understood by hackers.

FTP

File Transfer Protocol (FTP)

This is when a computer sends or retreives files from a remote server or computer.

E.g OneDrive, iCloud, etc..

Sends from client to server // sends from server to client

Email

Mail servers pass on or store emails until they are collected​

You must log in to a mail server to collect mail​

Examples of mail providers are Gmail or Yahoo

SENDING EMAIL

SMTP

• Simple Mail Transfer Protocol (SMTP)

• Used for SENDING emails only.

• This protocol is used to transfer email between mail servers.

• Another way to remember it is: Sending Messages To People

RECEIVING EMAIL

POP & IMAP

• These protocols fetch message data from a mail server

• Post Office Protocol (POP)

• Will download the entire message to your local device. The original is deleted from the server.

• Internet Message Access Protocol (IMAP)

• Downloads the message header, until the message is opened.

• The message remains on the server. The devices synchronise.

TCP

Transmission Control Protocol (TCP)

This protocol is responsible for:

• Breaking up messages sent over the Internet into small chunks called packets

• Reassembles the packets at the other end

• Detects errors

• Resends lost messages

IP

Internet Protocol (IP)

This is the set of rules that dictate how data should be delivered over the public (Internet)

This routes the individual network packets.

Devices connected to the internet are given an "IP Address"., a unique identifier on where they are on the internet.

TCP/IP Layer Model

This layer model has 4 layers where different protocols operate to pass data across a network.

The four layers are:

- Application

- Transport

- Network

- Link

SENDING DATA

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

This is then sent through the layers in turn.

The 4 layer Responsibilities:

• Application - The application selects the correct protocol to use depending on which application it is and what you are trying to do. - _{SMTP, HTTP, HTTPS, IMAP, POP, FTP work here}

• Transport - Creates the connection, Splits the packets for sending, numbers them, reassembles them (at receivers end) _{- TCP works here}

• Network - Assigns the IP Address of sender and the destination to the packet. _{- IP works here}

• Link - This is the physical hardware (cables, Network cards, etc)

Why layers are used

• A layer can be removed/changed etc. …without affecting any other layers

• Each layer has its own purpose so it does not need to consider what the other layers do …so it can be programming individually

• Individual protocols are each smaller/simpler to manage

• Different layers can interface with different hardware