Describe Internet Layer or Network Layer

 Ans : The Internet layer is an important layer in the protocol suite. At this layer, TCP/IP

supports Internetworking Protocol (IP). IP is a host-to-host protocol. This layer is
responsible for the format of datagrams as defined by IP, and routing a datagram or
packet to the next hop, but is not responsible for the accurate and timely delivery of
datagrams to the destination in proper sequence. IP allows raw transmission functions
allowing user to add functionalities necessary for given application. Ensuring
maximum efficiency, TCP/IP supports four other protocols: ARP, RARP, ICMP and
IGMP in this layer.

• Address Resolution Protocol (ARP)
On a LAN, each machine is identified with a unique physical address imprinted
on the network interface card. ARP is used to find the physical address of a
machine when its IP address is known.

• Reverse Address Resolution Protocol (RARP)
It is used to find the IP address of a machine when its physical address is
known. It is used when a diskless computer is booted or a computer is
connected to the network for the first time.

• Internet Control Message Protocol (ICMP)
IP is unreliable are best effort delivery. In case of failures ICMP is used to send
notifications to the sender about packet problems. It sends error and query
messages.

• Internet Group Message Protocol (IGMP)
It is used for multicasting, which is transmission of a single message to a group
of recipients.

Transport Layer
At this layer, TCP/IP supports two protocols: TCP, UDP, IP is host-to-host protocol,
which can deliver the packet from one physical device to another physical device.
TCP, UDP, are transport level protocols, responsible for delivering a packet from one
process on a device to another process on the other device.

User Datagram Protocol (UDP)
It is simpler of the two protocols. It does not provide reliability. It is, therefore faster,
and using for applications in which delay is intolerable (in case of audio and video).

Transmission Control Protocol (TCP)
TCP is reliable, connection oriented protocol. By connection oriented, we mean that a
connection must be established between both ends before either can transmit data. It
ensures that communication is error-free and in sequence.

Application Layer
As said earlier, it is closer to combined session, presentation, and application layer of
OSI model. It allows the user to run various applications on Internet. These
applications are File Transfer Protocol (FTP), remote login (TELNET), email
(SMTP), WWW (HTTP). The session layer of OSI model is almost dropped in
TCP/IP