TCP IP Reference model

The Transmission  Control Protocol/Internet Protocol suite was created by the Department of Defense (DoD) to ensure and preserve data integrity, as well as maintain communications in the event of catastrophic war.
The DoD OR TCP/IP model is basically a condensed version of the OSI model , it composed of four, instead of seven, layer: 1. Process/Application Layer, 2. Host-to-Host/Transport Layer, 3. Internet layer, 4. Network Access Layer

The TCP/IP Protocol Architecture

TCP/IP defines a large collection of protocols that allow computers to communicate. TCP/IP defines the details of each of these protocols inside documents called Requests for Comments (RFC). By implementing the required protocols defined in TCP/IP RFCs, a computer can be relatively confident that it can communicate with other computers that also implement TCP/IP. An easy comparison can be made between telephones and computers that use TCP/IP. 

Layer 4: The TCP/IP Process/Application Layer

TCP/IP application layer protocols provide services to the application software running on a computer. The application layer does not define the application itself, but rather it defines services that applications need—such as the capability to transfer a file in the case of HTTP.

The following protocol and application are used in Application / process layer

* FTP

* HTTP

* DNS

* DHCP

* Telnet

* SMTP

* NFS

* LPD

* SNMP .etc....

     In short, the application layer provides an interface between software running on a computer and the network itself. Arguably, the most popular TCP/IP application today is the web browser. Many major software vendors either have already changed or are changing their software to support access from a web browser. And thankfully, using a web browser is easy—you start a web browser on your computer and select a website by typing in the name of the website, and the web page appears.

Layer 3: The TCP/IP Transport OR Host-to-Host Layer

The main purpose of the Transport/Host-to-Host layer is to shield the upper layer application from the complexities of the network. This layer says to the upper layer, " Just give me your data stream, with any instructions, and I will begin the process of getting your information ready to send".

The TCP/IP application layer includes a relatively large number of protocols, with HTTP being only one of those. The TCP/IP transport layer consists of two main protocol options:

* Transmission Control Protocol (TCP)

* User Datagram Protocol (UDP).

Key features of TCP and UDP

Layer 2: The TCP/IP Transport OR Host-to-Host Layer

In the DOD OR TCP/IP model, there are two main reasons for the internet layer`s existence: routing and providing a single network interface to the upper layer.

The internet layer of the TCP/IP networking model, primarily defined by the Internet Protocol (IP), works much like the postal service. IP defines addresses so that each host computer can have a different IP address, just as the postal service defines addressing that allows unique addresses for each house, apartment, and business. Similarly, IP defines the process of routing so that devices called routers can choose where to send packets of data so that they are delivered to the correct destination.

The following protocol are used in this layer:

* IP (Internet Protocol)

* ICMP (Internet Control Message Protocol)

* ARP (Address Resolution Protocol)

* RARP ( Reverse Address Resolution Protocol)

* Proxy ARP

Layer 1: The TCP/IP Network Access Layer

The network access layer defines the protocols and hardware required to deliver data across some physical network. The term network access refers to the fact that this layer defines how to physically connect a host computer to the physical media over which data can be transmitted.

The network access layer includes a large number of protocols. For instance, the network access layer includes all the variations of Ethernet protocols and other LAN standards. This layer also includes the popular WAN standards, such as the Point-to-Point Protocol (PPP) and Frame Relay.

TCP/IP Protocol Suite