D1

TCP/IP protocols map to a four layer conceptual model.The four layers of the model are: Application, Transport, Internet and Network Interface.Each layer in the model corresponds to one or more layers of the seven layer Open Systems Interconnection (OSI) model; (application layer, presentation layer, session layer, transport layer, network layer, data-link layer and physical layer). 

Internet Layer- The Internet layers are responsible for addressing, packaging and routing functions. The core protocols of the Internet layer are IP, ARP, ICMP and IGMP. 

The Internet Protocol (IP)- this is a routable protocol responsible for IP addressing, routing and the fragmentation and reassembly of packets.

The Address Resolution Protocol (ARP)- this is responsible for the resolution of the Internet layer address to the Network Interface layer address such as a hardware address.

The Internet Control Message Protocol (ICMP) - this is responsible for providing diagnostic functions and reporting errors due to the unsuccessful delivery of IP packets. 

The Internet Group Management Protocol (IGMP) - this is responsible for the management of IP multicast groups. 





Transport Layer - The Transport layer is responsible for providing the Application layer with session and datagram communication services. The core protocols of the Transport layer are Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).

TCP provides a one-to-one, connection-oriented, reliable communcations service. TCP is responsible for the establishment of a TCP connection, the sequencing and acknowledgment of packets sent, and the recovery of packets lost during transmission. 

UDP provides a one-to-one or one-to-many, connectionless, unreliable communications service. UDP is used when the amount of data to be transferred is small (such as the data that would fit into a single packet), when the overhead of establishing a TCP connection is not desired or when the applications or upper layer protocols provide reliable delivery.

Application Layer- The Application layer provides applications the ability to access the services of the other layers and defines the protocols that applications use to exchange data. There are many Application layer protocols and new protocols are always being developed. The most widely-known Application layer protocols are those used for the exchange of user information: 

The Hypertext Transfer Protocol (HTTP)
this is used to transfer files that make up the Web pages of the World Wide Web. 

The File Transfer Protocol (FTP)
this is used to the interactive file transfer. 

The Simple Mail Transfer Protocol (SMPT)
this is used for the transfer of mail messages and attachments.