RE : TCP/IP

Transmission Control Protocol / Internet Protocol (TCP/IP)

Basic communication language or protocol of the Internet.
It can also be used as a communications protocol in a private network (either an intranet or an extranet)

TCP/IP is a two-layer program :-

(i) The higher layer, Transmission Control Protokol manages the assembling of a
message or file into smaller packets that are transmitted over the Internet and
received by a TCP layer that reassembles the packets into the original message.
(ii) The lower layer, Internet Protocol, handles the address part of each packet so that
it gets to the right destination.

Layers in the TCP/IP

The layers near the top are logically closer to the user application, while those near the bottom are logically closer to the physical transmission of the data.

(A) Link Layer

(a) The Link Layer is the networking scope of the local network connection to which a
host is attached.
(b) This regime is called the link in Internet literature. This is the lowest component layer
of the Internet protocols, as TCP/IP is designed to be hardware independent.
(c) The Link Layer is used to move packets between the Internet Layer interfaces of
two different hosts on the same link. The processes of transmitting and receiving
packets on a given link can be controlled both in the software device driver for the
network card, as well as on firmware or specialized chipsets.

(B) Internet Layer

(a) The Internet Layer solves the problem of sending packets across one or more networks.
Internetworking requires sending data from the source network to the destination
network. This process is called routing.
(b) In the Internet Protocol Suite, the Internet Protocol performs two basic functions :-
(i) Host addressing and identification: This is accomplished with a hierarchical addressing
system (see IP address).
(ii) Packet routing: This is the basic task of getting packets of data (datagrams) from source
to destination by sending them to the next network node (router) closer to
the final destination.

(C) Transport Layer

(a) The Transport Layer's responsibilities include end-to-end message transfer capabilities
independent of the underlying network, along with error control, segmentation, flow control,
congestion control, and application addressing (port numbers).
(b) The Transport Layer provides this service of connecting applications through the use of
service ports.

(D) Application Layer

(a) The Application Layer refers to the higher-level protocols used by most applications for
network communication.
(b) Examples of application layer protocols include the File Transfer Protocol (FTP) and the
Simple Mail Transfer Protocol (SMTP).