Role of OSI Layer when we open a webpage

Our sessions are role of OSI layer when we open a webpage in a real world 

When you are trying to open a web page on your PC this is what typically happens (I am just putting the basic concepts together for understanding, most of the steps below are much more elaborate, complicated and involves more devices, protocols  & lot of other details than shown below)

Role of OSI Layer when we open a website

Keep in mind that although the OSI model is what we study, we don't use OSI in real work networks. We use the TCP/IP Network Model.  The OSI model is still taught due to it's usefulness in separating concepts into modules (layers).  The OSI model is translated to the TCP/IP model.

Understanding of OSI Layer Model

User Launches a site in the browser, You typically  type an web address (Uniform resource locator)  in a Web browser. Web browser uses something called Hypertext Transfer Protocol  which is an Application layer protocol. 

OSI Layer Datas, Protocols and Activities 

Behind the scene the web browser get the IP address of the URL you typed (say http://www.spansid.blogspot.com) using a process can Domain Name System which is also an Application layer protocol.

Role of OSI layer when open a webpage in Seven Layer

• User tells their browser to fetch a page from url
• Browser makes an HTTPS request to url
• To fetch the required web page it passes the request to its HTTP protocol handler, that is Layer 7 of the OSI model, the Application layer

Role of OSI layer when open a webpage in Application Layer

• HTTP protocol handler at Layer 7 recognizes that the request is for a secure document, it passes the request to the TLS library at Layer 5 and 6 of the OSI model. These layers are called the Session and Presentation layers.
• In order to open a secure channel, the TLS library needs to establish a connection to the destination
• It passes a connection request to TCP which lives at Layer 4 of the OSI model, the Transport layer

 SSL and TLS together secure communications between billions of computers, servers, Internet of Things (IoT) devices, and embedded systems. The security provided by an SSL/TLS Library depends on the underlying strength of its cryptography which is used to encrypt communications.

Role of OSI layer when open a webpage in Session Layer

• The TCP handler receives the connection request. Then, it creates a packet with the “SYN” flag set — the first part of the three-way handshake with the remote server to establish a connection
• After the TCP handler has created a packet to initiate a connection, it passes the packet down to IP which lives at OSI Layer 3, also called the Network Layer

Role of OSI layer when open a webpage in Transport Layer

• The network layer receives the packet and adds the correct IP information to its header. That informs the internet routers how to route the packet to its destination IP address.
• Now that the network layer has a routable packet, it passes it down to Layer 2, the Data-Link layer.

Role of OSI layer when open a webpage in Network Layer

• The data-link layer adds the router’s MAC address as the local destination address, allowing the router to send the packet out to the Internet.
• In order for the packet to get onto the basic networking transmission technologies of the network, it is then passed to OSI Layer 1 or the Physical Layer to complete the task.

Role of OSI layer when open a webpage in DataLink Layer

The physical layer takes the binary packet and physically encodes it onto network cabling — or places it onto the airwaves in the case of a WiFi network — and the packet begins its journey across the local network and out to the wider Internet.

Role of OSI layer when open a webpage in Physical Layer

Once the packet reaches the destination server, the whole process reverses and the packet travels back up the layers of the OSI model.

Role of OSI layer when open a webpage in seven Layers

OSI Model Mnemonics

OSI Model Mnemonics

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