by - The TCP/IP model was created in the 1970s by the Defense Advanced Research Project Agency (DARPA)as an open, vendor-neutral, public networking model as a part of a research project of network interconnection to connect remote machines.
- It describes general guidelines for designing and implementing computer protocols.
- It is the network model used in the current Internet architecture as well.
- These protocols describe the movement of data between the source and destination or the internet. They also offer simple naming and addressing schemes.
TCP/IP reference model :
•Support for a flexible architecture. Adding more machines to a network was easy.
•The network was robust, and connections remained intact until the source and destination machines were functioning.
•The overall idea was to allow one application on one computer to talk to(send data packets) another application running on a different computer
Layer 1: Host-to-network Layer
•It is the lowest layer that is concerned with the physical transmission of data.TCP/IP does not specifically define any protocol here but supports all the standard protocols
•defines the protocols and hardware required to deliver data across a physical network. The lowest layer of all.
•Protocol is used to connect to the host so that the packets can be sent over it.
•Varies from host to host and network to network
Layer 2: Internet layer
•It defines the protocols for the logical transmission of data over the network. The main protocol in this layer is Internet Protocol (IP) and it is supported by the protocols ICMP, IGMP, RARP, and ARP.
•Selection of a packet switching network that is based on a connectionless internetwork layer is called an internet layer. (supports only connection-less services.)
•It helps the packet to travel independently to the destination and Order these in which packets are received is different from the way they are sent.
•IP (Internet Protocol) is used in this layer. The various functions performed by the Internet Layer are:
•Addressing.
•Routing
•Delivering IP packets
•Performing routing
•Avoiding congestion
•IP –stands for Internet Protocol and it is responsible for delivering packets from the source host to the destination host by looking at the IP addresses in the packet headers. IP has 2 versions: IPv4and IPv6. IPv4is the one that most of the websites are using currently. But IPv6is growing as the number of IPv4addresses is limited in number when compared to the number of users.
•ICMP–stands for Internet Control Message Protocol. It is encapsulated within IP datagrams and is responsible for providing hosts with information about network problems.
•ARP –stands for Address Resolution Protocol. Its job is to find the hardware address of a host from a known IP address. ARP has several types: Reverse ARP, Proxy ARP, Gratuitous ARP, and Inverse ARP.
Layer 3: Transport Layer
•It is responsible for error-free end-to-end delivery of data. It decides if data transmission should be on a parallel path or a single path. This layer is also known as the host-to-host layer. It provides a logical connection between two hosts
•The applications can read and write to the transport layer. The transport layer adds header information to the data.
•Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer. and also arrange the packets to be sent, in sequence.
•It defines two end-to-end protocols: TCP and UDP
•TCP(Transmission Control Protocol): It is a reliable connection-oriented protocol that handles byte-stream from source to destination without error and flows control.
•UDP(User-Datagram Protocol): It is an unreliable connectionless protocol that does not want TCPs, sequencing, and flow control. Eg: One-shot request-reply kind of service.
- Functions such as multiplexing, segmenting, or splitting into the data are done by the transport layer.
- Main functions of this layer are following: –
- Segmentation
- The process of breaking up large data files into smaller and identifiable pieces is known as Segmentation and each piece produced in the segmentation process is known as a segment.
- Reliability
- The process of breaking up large data files into smaller and identifiable pieces is known as Segmentation and each piece produced in the segmentation process is known as a segment.
- Flow control
- Flow control ensures that the remote host does not become overwhelmed by the source sending too many segments at once.
- Connection multiplexing
- Multiplexing allows a host to initiate multiple connections with one or many hosts simultaneously
- Layer 4: Application Layer
- This layer defines the protocols and standards that an application requires to connect with the network. For example, an application layer protocol HTTP defines how a web browser can fetch a web page from a web server.
- Application layer does not define the application itself. It only defines the standards, services, and protocols that an application needs to connect with a remote computer.
- The TCP/IP specifications described a lot of applications that were at the top of the protocol stack. Some of them were TELNET, FTP
- TELNETis a two-way communication protocol that allows connecting to a remote machine and running applications on it.
- FTP(File Transfer Protocol) is a protocol, that allows File transfer amongst computer users connected over a network. It is reliable, simple, and efficient.
- SMTP(Simple Mail Transport Protocol) is a protocol, which is used to transport electronic mail between a source and destination, directed via a route.
- DNS(Domain Name Server) resolves an IP address into a textual address for Hosts connected over a network.
- It allows peer entities to carry a conversation.
- Merits of TCP/IP model
- It operated independently.
- It is scalable.
- Focus on Client/server architecture.
- Supports a number of routing protocols.
- Can be used to establish a connection between two computers.
- Demerits of TCP/IP
- In this, the transport layer does not guarantee the delivery of packets.
- The model cannot be used in any other application.
- Replacing protocol is not easy.
- It has not clearly separated its services, interfaces, and protocols.
