Python Network Basics And Socket Programming

Socket programming in Python

TCP Layers

.

Layers Explained

Application Layer: Top most Layer and is is utilized to ensure communication

between applications on a network.example:DNS,HTTP,FTP,SSH,DHCP etc

Transport Layer: Transport layer ensures whole message arrives intact and in

order, ensuring both error control and flow control at the source to destination

level.example:

TCP,UDP,RDP

Internet Layer:IP works at this layer.this protocol has the responsibility of

identifying hosts based upon their logical addresses and to route data among

them over the underlying network.example- IPV4,IPV6

Layers...

Network Access Layer:The Network Access Layer is the layer in the TCP/IP model

at which data is transmitted and received across the physical

network.Example:Ethernet,ATM

How TCP Works:

1. SYN: open is performed by the client sending a SYN to the server. The client sets the segment's sequence number to a

random value A.

2. SYN-ACK: In response, the server replies with a SYN-ACK. The acknowledgment number is set to one more than the

received sequence number i.e. A+1, and the sequence number that the server chooses for the packet is another random

number, B.

3. ACK: Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgement

value i.e. A+1, and the acknowledgement number is set to one more than the received sequence number i.e. B+1.

Sockets

Sockets may communicate within a process, between processes on the same

machine, or between processes on different continents.

Socket Module:

s = socket.socket (socket_family, socket_type, protocol=0)

socket_family: This is either AF_UNIX or AF_INET(For IPV4),AF_INET6 (For IPV6)

Socket Type: This is either SOCK_STREAM(For TCP) or SOCK_DGRAM(UDP)

Sockets

Basic Example Code:

Create a Socket :

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

Get IP Address by hostname:

ip = socket.gethostbyname('www.google.com')

print ip

Sockets..

s.bind() This method binds address (hostname, port number pair) to

socket,,otherwise it doesn't know what address (ip-address/port pair) it should

listen to.

s.bind((HOST, PORT))

s.listen(arg) : This method sets up and start TCP listener.the argument to listen

tells the socket library that we want it to queue up as many as 5 connect requests

(the normal max) before refusing outside connections.

s.listen(5)

sockets...

s.accept() : accept TCP client connection, waiting until connection arrives.

accept() returns an open connection between the server and client, along with the

address of the client.

connection, client_address = sock.accept()

select.select(): It monitors sockets, open files, and pipes (anything with a fileno()

method that returns a valid file descriptor) until they become readable or writable.

makes it easier to monitor multiple connections at the same time.

readable, writable, exceptional = select.select(inputs, outputs, inputs) /*Wait for at least one of the sockets to be ready for

processing.

Code for sockets

BAsic Socket Code: https://repl.it/HKOF/0

The above Code create a socket,resolves the ip and then connect to the ip/host.

Chat Server And Client

Chat Server: