TCP/IP model
The TCP/IP model was developed prior to the OSI model.
The TCP/IP model is not exactly similar to the OSI model.
The TCP/IP model consists of five layers: the application layer, transport layer, network layer, data link layer and physical layer.
The first four layers provide physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model and these four layers are represented in TCP/IP model by a single layer called the application layer.
TCP/IP is a hierarchical protocol made up of interactive modules, and each of them provides specific functionality.
Here, hierarchical means that each upper-layer protocol is supported by two or more lower-level protocols.
Network Access Layer
A network layer is the lowest layer of the TCP/IP model.
A network layer is the combination of the Physical layer and Data Link layer defined in the OSI reference model.
It defines how the data should be sent physically through the network.
This layer is mainly responsible for the transmission of the data between two devices on the same network.
The functions carried out by this layer are encapsulating the IP datagram into frames transmitted by the network and mapping of IP addresses into physical addresses.
The protocols used by this layer are ethernet, token ring, FDDI, X.25, frame relay.
Internet Layer
An internet layer is the second layer of the TCP/IP model.
An internet layer is also known as the network layer.
The main responsibility of the internet layer is to send the packets from any network, and they arrive at the destination irrespective of the route they take.
Following are the protocols used in this layer are:
IP Protocol: IP protocol is used in this layer, and it is the most significant part of the entire TCP/IP suite.
Following are the responsibilities of this protocol:
IP Addressing: This protocol implements logical host addresses known as IP addresses. The IP addresses are used by the internet and higher layers to identify the device and to provide internetwork routing.
Host-to-host communication: It determines the path through which the data is to be transmitted.
Data Encapsulation and Formatting: An IP protocol accepts the data from the transport layer protocol. An IP protocol ensures that the data is sent and received securely, it encapsulates the data into message known as IP datagram.
Fragmentation and Reassembly: The limit imposed on the size of the IP datagram by data link layer protocol is known as Maximum Transmission unit (MTU). If the size of IP datagram is greater than the MTU unit, then the IP protocol splits the datagram into smaller units so that they can travel over the local network. Fragmentation can be done by the sender or intermediate router. At the receiver side, all the fragments are reassembled to form an original message.
Routing: When IP datagram is sent over the same local network such as LAN, MAN, WAN, it is known as direct delivery. When source and destination are on the distant network, then the IP datagram is sent indirectly. This can be accomplished by routing the IP datagram through various devices such as routers.
ARP Protocol
ARP stands for Address Resolution Protocol.
ARP is a network layer protocol which is used to find the physical address from the IP address.
The two terms are mainly associated with the ARP Protocol:
ARP request: When a sender wants to know the physical address of the device, it broadcasts the ARP request to the network.
ARP reply: Every device attached to the network will accept the ARP request and process the request, but only recipient recognize the IP address and sends back its physical address in the form of ARP reply. The recipient adds the physical address both to its cache memory and to the datagram header
ICMP Protocol
ICMP stands for Internet Control Message Protocol.
It is a mechanism used by the hosts or routers to send notifications regarding datagram problems back to the sender.
A datagram travels from router-to-router until it reaches its destination. If a router is unable to route the data because of some unusual conditions such as disabled links, a device is on fire or network congestion, then the ICMP protocol is used to inform the sender that the datagram is undeliverable.
An ICMP protocol mainly uses two terms:
ICMP Test: ICMP Test is used to test whether the destination is reachable or not.
ICMP Reply: ICMP Reply is used to check whether the destination device is responding or not.
The core responsibility of the ICMP protocol is to report the problems, not correct them. The responsibility of the correction lies with the sender.
ICMP can send the messages only to the source, but not to the intermediate routers because the IP datagram carries the addresses of the source and destination but not of the router that it is passed to.
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