TCP-IP Stack Implementation

# TCP/IP Stack Implementation

The TCP/IP stack, also known as the Internet Protocol Suite, is the conceptual model and set of communications protocols used in the Internet and similar computer networks. It is commonly known as TCP/IP because the foundational protocols in the suite are the Transmission Control Protocol (TCP) and the Internet Protocol (IP).

## 1. Layers of TCP/IP Stack

The TCP/IP stack consists of four layers:

1. **Network Interface Layer**: Handles all hardware details of physically interfacing with the network, such as Ethernet.
2. **Internet Layer**: This layer is responsible for sending packets across potentially multiple networks. IP protocol exists in this layer.
3. **Transport Layer**: Establishes basic data channels that applications use for task-specific data exchange. TCP and UDP protocols exist in this layer.
4. **Application Layer**: Contains all protocols for specific data communication tasks on process level. Protocols like HTTP, FTP, SSH, DNS exist in this layer.

## 2. Working of TCP/IP Stack

TCP/IP uses the client/server model of communication. A computer running a program that is requesting services is called a client and the computer running the program that gets the request and provides the services is the server.

Here's a very basic example of how a message might get sent from a user's computer to a website server using the TCP/IP stack:

```python
from socket import socket, AF_INET, SOCK_STREAM
s = socket(AF_INET, SOCK_STREAM) # Create a socket object
s.connect(("www.example.com", 80)) # Connect to server
s.sendall(b"GET / HTTP/1.1\r\nHost: www.example.com\r\n\r\n") # Send request
data = s.recv(1024) # Receive response
s.close() # Close connection
```

In this Python code snippet, we first create a socket object. We then connect to the server at "www.example.com" on port 80, which is the standard port for HTTP. We then send an HTTP GET request to the server. After that, we receive the response from the server and finally close the connection.

During this process, the TCP/IP stack in both the client and server are at work. The Application Layer handles the HTTP protocol, the Transport Layer deals with the TCP protocol, the Internet Layer handles the IP protocol, and the Network Interface Layer takes care of the physical sending and receiving of data.

In essence, the TCP/IP stack abstracts the complexity of network communication into different layers, allowing us to focus on the specific layer we're dealing with while ignoring the details of all the other layers. This modular design makes the TCP/IP stack very flexible and powerful.