Are we using TCP/IP or OSI in internet?

The internet is based on TCP/IP which is a "simplified" implementation of the theoretical OSI model. Maybe it's even better to say TCP/IP was inspired by the OSI model, since it does not really match up on closer review.

More info here:

http://en.wikipedia.org/wiki/OSI_model#Comparison_with_TCP.2FIP_model

and here:

http://en.wikipedia.org/wiki/TCP/IP_model#OSI_and_TCP.2FIP_layering_differences

When i was searching the answer, even i found it dificult to understand as the answers(even if correct) are not exactly matching the doubts in the question.

The question is actually regarding the differnce between OSI model and TCP/IP model and not TCP/IP protocol which the answers are based on. A person who doesn't know the difference will get confused or not get satisfied with the answer at all. I thought i will try to answer this question with little more explanation.

Sorry for all the above blah blahs .. Here is the answer :

TCP/IP model was formed by DoD( Department of Defence ) which came almost 10 years earlier than OSI model and is defined with 4 layers as TCP and IP are the two protocols just like FTP, UDP, SNMP, SMTP, Telnet, etc. It was also called Internet Model. But i know the name itself is confusing. The layers were not defined properly as they were just based on protocols.

But after some research the layers were again got redfeined and OSI model shows us 7 layers which should be the way of implementation of any communication.

TCP/IP model had lots of issues like Transport Layer doesn't guarantees the delivery of packets, doesn't have a seperate Presentation layer, replacing protocol is not easy as they are not hidden unlike OSI model and you bet thats how OSI model came into existence

Now as both are just models, in real world we just worry about protocols as thats how the things are implemented. So OSI model is a reference on how we use internet today and not the TCP/IP model.

TCP/IP or UDP/IP are just protocols of Internet. They are in the 4th Layer of OSI. TCP or UDP are used to determine what kind of connection is to be established whether Connection-Oriented or Connection-Less.

Connection Oriented which uses TCP/IP protocol is used when there is a need to establish a session and where lost packets have to be retransmitted if lost like when you use email, you dont want to send a mail with uncertainty of whether the mail will reach its destination or not and moreover with uncertainty of sending incomplete mail with lost packets.

Connectio-Less which uses the UDP/IP protocol is used when you dont want waste time on establishing a connection and you dont want to retransmit the lost packets as the latest packet is more necessary to reach the destination like when using chat, you dont want to resend the old packets or data later or else it will be like you are talking on some other topic and the earlier packet reaches later out of nowhere. Same can be said for buffering of a video.

Hope it clears your doubt. For further queries google the uses of TCP/IP and UDP/IP and do go through the OSI model once and try to understand what each layer does and there contribution in transmission of data packets.

The ISO/OSI model is, essentially, a theoretical construct.

TCP/IP is roughly an implementation of it.