Transmission Control Protocol (tcp)

The Transmission Control Protocol (TCP) is a transport protocol that is used on top of IP to ensure reliable transmission of packets. TCP includes mechanisms to solve many of the problems that arise from packet-based messaging, such as lost packets, out of order packets, duplicate packets, and corrupted packets. Since TCP is the protocol used most commonly on top of IP, the Internet protocol stack is sometimes referred to as TCP/IP

The Internet Protocol (IP) is a communications protocol for routing and addressing packets of data across a computer network. Its task is to deliver the packet from the source host to the destination host using only an IP address in the packet header.

TCP/IP Model

Packet format

When sending packets using TCP/IP, the data portion of each IP packet is formatted as a TCP segment.

From Start To Finish

• Step 1: Establish connection
• Step 2: Send packets of data
• Step 3: Close the connection
• Determining lost packets

Step 1: Establish connection

When two computers want to send data to each other over TCP, they first need to establish a connection using a three-way handshake.

Step 2: Send packets of data

When a packet of data is sent over TCP, the recipient must always acknowledge what they received.

Step 3: Close the connection

Either computer can close the connection when they no longer want to send or receive data.

Detecting lost packets

TCP connections can detect lost packets using a timeout.

More

DNS

While IP can be used to access information on the Internet, people most frequently use those domain names that could be easily memorized, like google.com. The Domain Name System (DNS) is basically the phonebook of the Internet. The purpose of DNS is to translate domain names to IP addresses. DNS resolution is a process of converting a hostname into an IP address.

A Uniform Resource Locator (URL), often called a web address, is a reference to a web resource that specifies its location on a computer network and a protocol for retrieving it.

Network Commands

ping - sends echo request messages to another machine

traceroute / tracert - shows the path taken by packets to a destination computer

netstat - displays active TCP connections

The Hypertext Transfer Protocol (HTTP) is the foundation of the World Wide Web. It is the essential protocol to view web pages and surf the Internet. HTTP is an application layer protocol. The most used version of HTTP is HTTP/2. A typical process of communications over HTTP presupposes a client making a request to a server, which then sends a response message.

The Hypertext Transfer Protocol (HTTP) is the foundation of the World Wide Web. It is the essential protocol to view web pages and surf the Internet. HTTP is an application layer protocol. The most used version of HTTP is HTTP/2. A typical process of communications over HTTP presupposes a client making a request to a server, which then sends a response message.

Terms

User agent - The user-agent is any tool that acts on behalf of the user. This role is primarily performed by the Web browser, but it may also be performed by programs used by engineers and Web developers to debug their applications.

Web server- On the opposite side of the communication channel is the server, which serves the document as requested by the client.

Proxy - Proxies are intermediaries that act as intermediaries between clients (such as web browsers) and servers in the HTTP (Hypertext Transfer Protocol) communication.

Proxy

Http Methods

GET

The GET method requests a representation of the specified resource. Requests using GET should only retrieve data.

HEAD

The HEAD method asks for a response identical to a GET request, but without the response body.

POST

The POST method submits an entity to the specified resource, often causing a change in state or side effects on the server.

PUT

The PUT method replaces all current representations of the target resource with the request payload.

DELETE
The DELETE method deletes the specified resource.
CONNECT
The CONNECT method establishes a tunnel to the server identified by the target resource.
OPTIONS
The OPTIONS method describes the communication options for the target resource.
TRACE
The TRACE method performs a message loop-back test along the path to the target resource.
PATCH
The PATCH method applies partial modifications to a resource.