TCP/IP Model

The OSI Model we just looked at is just a reference/logical model. It was designed to describe the functions of the communication system by dividing the communication procedure into smaller and simpler components. But when we talk about the TCP/IP model, it was designed and developed by Department of Defense (DoD) in 1960s and is based on standard protocols. It stands for Transmission Control Protocol/Internet Protocol. The TCP/IP model is a concise version of the OSI model. It contains four layers, unlike seven layers in the OSI model. The layers are:

1) Process/Application Layer 

2) Host-to-Host/Transport Layer 

3) Internet Layer 

4) Network Access/Link Layer 

TCP/IP Model

• Application Layer
  
• Transport Layer
• Internet Layer
• Network Access Layer

OSI Model

• Application Layer
• Presentation Layer
• Session Layer
• Transport Layer
• Network Layer
• Data Link Layer
• Physical Layer

TCP/IP

1. TCP refers to Transmission Control Protocol.
2. TCP/IP has 4 layers.
3. TCP/IP is more reliable
4. TCP/IP does not have very strict boundaries.
5. TCP/IP follow a horizontal approach.

OSI

1. OSI refers to Open Systems Interconnection.
2. OSI has 7 layers.
3. OSI is less reliable
4. OSI has strict boundaries
5. OSI follows a vertical approach.
6. OSI uses different session and presentation layers. 
7. OSI developed model then protocol. 

1) Network Access Layer 

• This layer corresponds to the combination of Data Link Layer and Physical Layer of the OSI model. It looks out for hardware addressing and the protocols present in this layer allows for the physical transmission of data. We just talked about ARP being a protocol of Internet layer, but there is a conflict about declaring it as a protocol of Internet Layer or Network access layer. It is described as residing in layer 3, being encapsulated by layer 2 protocols.

2) Internet Layer 

• This layer parallels the functions of OSI’s Network layer. It defines the protocols which are responsible for logical transmission of data over the entire network. The main protocols residing at this layer are : 

• IP – stands for Internet Protocol and it is responsible for delivering packets from the source host to the destination host by looking at the IP addresses in the packet headers. IP has 2 versions: IPv4 and IPv6. IPv4 is the one that most of the websites are using currently. But IPv6 is growing as the number of IPv4 addresses are limited in number when compared to the number of users.

3) Transport Layer 

• Transport layer provides services to application layer and takes services from network layer. The data in the transport layer is referred to as Segments. It is responsible for the End to End delivery of the complete message. Transport layer also provides the acknowledgment of the successful data transmission and re-transmits the data if an error is found. 

4) Application Layer 

• At the very top of the OSI Reference Model stack of layers, we find Application layer which is implemented by the network applications. These applications produce the data, which has to be transferred over the network. This layer also serves as a window for the application services to access the network and for displaying the received information to the user.

Client and Server Model

• A client and server networking model is a model in which computers such as servers provide the network services to the other computers such as clients to perform a user based tasks. This model is known as client-server networking model. 
• The application programs using the client-server model should follow the given below strategies:  

Client

• A client is a program that runs on the local machine requesting service from the server. A client program is a finite program means that the service started by the user and terminates when the service is completed. 

Server

• A server is a program that runs on the remote machine providing services to the clients. When the client requests for a service, then the server opens the door for the incoming requests, but it never initiates the service.
• A server program is an infinite program means that when it starts, it runs infinitely unless the problem arises. The server waits for the incoming requests from the clients. When the request arrives at the server, then it responds to the request.

Domain Name System (DNS)

• DNS stands for Domain Name System.  
• DNS is a directory service that provides a mapping between the name of a host on the network and its numerical address. 
• DNS is required for the functioning of the internet. 
• Each node in a tree has a domain name, and a full domain name is a sequence of symbols specified by dots. 
• DNS is a service that translates the domain name into IP addresses. This allows the users of networks to utilize user-friendly names when looking for other hosts instead of remembering the IP addresses.
• DNS is a TCP/IP protocol used on different platforms. The domain name space is divided into three different sections: generic domains, country domains, and inverse domain.  

Label                               Description                            

aero               Airlines and aerospace companies 

biz                  Businesses or firms 

com                Commercial Organizations 

coop               Cooperative business Organizations 

edu                 Educational institutions 

gov                 Government institutions     

info                Information service providers 

int                  International Organizations 

mil                 Military groups 

museum       Museum & other nonprofit organizations 

name             Personal names 

net                 Network Support centers 

org                 Nonprofit Organizations 

pro                 Professional individual Organizations 

Working Of DNS

• DNS is a client/server network communication protocol. DNS clients send requests to the. server while DNS servers send responses to the client. 
• Client requests contain a name which is converted into an IP address known as a forward DNS lookups while requests containing an IP address which is converted into a name known as reverse DNS lookups. 
• DNS implements a distributed database to store the name of all the hosts available on the internet. 

Filer Protocol (FTP)

• FTP stands for File transfer protocol. 
• FTP is a standard internet protocol provided by TCP/IP used for transmitting the files from one host to another. 
• It is mainly used for transferring the web page files from their creator to the computer that acts as a server for other computers on the internet. 
• It is also used for downloading the files to computer from other servers. 

• FTP client is a program that implements a file transfer protocol which allows you to transfer files between two hosts on the internet. 
• It allows a user to connect to a remote host and upload or download the files. 
• It has a set of commands that we can use to connect to a host, transfer the files between you and your host and close the connection. 
• The FTP program is also available as a built-in component in a Web browser. This GUI based FTP client makes the file transfer very easy and also does not require to remember the FTP commands. 

Telnet

• The main task of the internet is to provide services to users. For example, users want to run different application programs at the remote site and transfers a result to the local site. This requires a client-server program such as FTP, SMTP. But this would not allow us to create a specific program for each demand. 
• The better solution is to provide a general client-server program that lets the user access any application program on a remote computer. Therefore, a program that allows a user to log on to a remote computer. A popular client-server program Telnet is used to meet such demands. Telnet is an abbreviation for Terminal Network. 
• Telnet provides a connection to the remote computer in such a way that a local terminal appears to be at the remote side.