Introduction To TCP/IP Reference Model

The OSI model was a conceptual representation, but the TCP/IP model is now a more common and widely used model. The TCP/IP Model enables you to choose the best method for connecting a particular computer to the internet and for transferring data between those computers. When multiple computer networks are linked together, you can more easily create a virtual network. The TCP/IP model’s goal is to enable communication over very long distances.

TCP/IP stands for Transmission Control Protocol/Internet Protocol. To provide a highly reliable end-to-end byte stream over an unreliable internetwork, TCP/IP Stack is specifically created as a model.

Each interactive module that makes up the hierarchical protocol TCP/IP offers a particular function. Hierarchical refers to the fact that at least two lower-level protocols support each upper-layer protocol.

The functionality of the TCP IP model is divided into four layers and each includes specific protocols.

Each layer of the TCP/IP server architecture is defined in accordance with a particular function that it is intended to carry out. The data is transmitted cooperatively between these four TCP/IP layers as it moves from one layer to another.

1. Process/Application Layer
2. Host-to-Host/Transport Layer
3. Internet Layer
4. Network Access/Link Layer

1. Process/Application Layer

The top three OSI layers—Application, Presentation and Session Layer—are fulfilled by this layer. It manages user-interface requirements and is in charge of node-to-node communication. This layer includes protocols like HTTP, HTTPS, FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP, DNS, DHCP, NFS, X Window and LPD, among others.

Main protocols used in the application layer

• HTTP: HTTP stands for Hypertext transfer protocol. This protocol allows us to access the data over the world wide web. It transmits data in the form of audio, video, and plain text. It is referred to as a hypertext transfer protocol because it is effective for use in a hypertext environment where there are quick transitions between different documents.
• SNMP: SNMP stands for Simple Network Management Protocol. It is a framework for controlling internet-connected devices using the TCP/IP protocol set.
• SMTP: SMTP stands for Simple mail transfer protocol. A Simple mail transfer protocol (SMTP) is the name of the TCP/IP protocol that underpins email. The data is sent to another email address using this protocol.
• DNS: DNS stands for Domain Name System. To uniquely identify a host’s connection to the internet, an IP address is used. However, names are more commonly used than addresses. Thus, a domain name system refers to the system that associates a name with an address.
• TELNET: It is an abbreviation for Terminal Network. In order for the local terminal to appear to be a terminal at the remote system, a connection must be made between the local computer and the remote computer.
• FTP: FTP stands for File Transfer Protocol. A common internet protocol called FTP is used to transfer files from one computer to another.

Functions of the Application Layer

• Application-layer aids in resource availability analysis, communication synchronisation and partner identification.
• It permits users to access a remote host.
• This layer offers a range of email services.
• This application provides access to global information about various objects and services from distributed database sources.

2. Host-to-Host/Transport Layer

This layer is comparable to the OSI model’s transport layer. It is in charge of ensuring seamless end-to-end communication and error-free data delivery. It protects the higher-layer applications from data complexity. The two main protocols present in this layer are:

Transmission Control Protocol (TCP)

• It provides full transport layer services to applications.
• It establishes a virtual circuit that is active throughout the transmission between the sender and receiver.
• TCP is a dependable protocol because it recognises the error and sends the faulty frames again. In order to ensure that the transmission is complete and a virtual circuit is discarded, it requires that all segments be received and acknowledged.
• TCP divides the entire message into segments at the sending end. Each segment has a sequence number that is needed to reorder the frames to create the original message.
• TCP gathers every segment at the other end and rearranges them according to their sequence numbers.

User Datagram Protocol (UDP)

• UDP does not specify which packet is lost. UDP contains only checksum; it does not contain any ID of a data segment.
• It offers connectionless service and end-to-end transmission delivery.
• The protocol is unreliable because it finds errors but does not identify them.
• The error is found by User Datagram Protocol, and the ICMP protocol notifies the sender that a user datagram has been damaged.
• The UDP includes the following fields:

1. Source port address: The address of the application programme that created the message is the source port address.
2. Destination port address: The address of the application programme that receives the message is the destination port address.
3. Total length: This specifies the user datagram’s overall byte count in bytes.
4. Checksum: A 16-bit field used for error detection is the checksum.

• UDP does not identify the lost packet. Only the checksum is contained in UDP; no data segment ID is present.

Functions of the Transport Layer

• It creates a sequence by segmenting and numbering the message received from the session layer.
• The transport layer makes sure that the message is delivered to the correct process on the destination machine.
• It creates a sequence by segmenting and numbering the message received from the session layer.

3. Internet Layer

The second TCP/IP layer of the TCP/IP model is known as the internet layer. Network layer is another name for it. This layer’s primary task is to send packets from any network and any computer so that, regardless of the path they take, they always reach their destination.

With the aid of various networks, the Internet layer provides a practical and procedural method for moving variable-length data sequences from one node to another.

There is no network layer protocol that guarantees to be reliable when messages are delivered at the network layer.

Layer-management protocols that belong to the network layer are:

1. Routing protocols
2. Multicast group management
3. Network-layer address assignment.

Main protocols residing at the Internet Layer

1. IP – By examining the IP addresses in the packet headers, IP is in charge of transmitting packets from the source host to the destination host. IP has 2 versions: IPv4 and IPv6. Currently, the majority of websites are using IPv4. However, IPv6 is expanding because there are fewer IPv4 addresses available compared to users.
2. ICMP – Stands for Internet Control Message Protocol. It is in charge of informing hosts about network issues and is encapsulated within IP datagrams.
3. ARP – Stands for Address Resolution Protocol. Its task is to use a known IP address to determine a host’s hardware address. Reverse ARP, Proxy ARP, Gratuitous ARP, and Inverse ARP are some of the different types of ARP.

Logical data packet transmission over the internet is handled by the Internet layer. It is comparable to the OSI model’s network layer.

Functions of the Internet Layer

• It sends packets of data to the link layer.
• It chooses the best route to take when routing each data packet separately from the source to the destination.
• When the out-of-order packets arrive at their destination, it reassembles them.
• It deals with data packet fragmentation and errors during transmission.

4. Network Access/Link Layer

The TCP/IP model’s network layer is its base layer. The OSI reference model defines a network layer as the union of the physical layer and data link layer. It specifies the physical method for transferring data across the network. Data transmission between two devices on the same network is primarily handled by this layer.

This layer’s duties include translating IP addresses into physical addresses and encapsulating the IP datagram into network frames. The protocols used by this layer are ethernet, token ring, FDDI, X.25 and frame relay.

ARP was just mentioned as an Internet layer protocol, but whether it should be classified as an Internet layer protocol or a network access layer protocol is a conflict. It is said to be contained by layer 2 protocols and resides in layer 3.

Functions of the Network Access Layer

• It is responsible for routing packets from the source host to the destination host. The routes may be built on rarely updated static tables or they may be automatically updated in response to changes in the network.
• The physical address is locally assigned by the data link layer. A logical addressing scheme is needed to distinguish between the source system and the destination system when data packets are routed to distant locations. This is provided by the network layer.
• This layer also provides mechanisms for congestion control.
• The network layer deals with things like avoiding jitters, minimising transmission delays, etc.