Question

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Computer Networks
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A transport-layer protocol provides two types of services: connectionless and connection-oriented. Define both of these services in your own words.

Answer 1

OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer.

The transport layer is a 4^th layer from the top.The main role of this layer is to provide the communication services directly to the application processes running on different hosts.A computer network provides more than one protocol to the network applications. For example, TCP and UDP are two transport layer protocols that provide a different set of services to the network layer.

Now coming to the connection ,here in this layer it is both that is connectionless and connection-oriented,

Bascically A transport-layer protocol provides two types of services : TCP where it is a Connection-Oriented protocol and UDP where it is a Connection-less protocol.

All transport layer protocols provide multiplexing/demultiplexing service. It also provides other services such as reliable data transfer, bandwidth guarantees, and delay guarantees.

Each of the applications in the application layer has the ability to send a message by using TCP or UDP. The application communicates by using either of these two protocols. Both TCP and UDP will then communicate with the internet protocol in the internet layer. The applications can read and write to the transport layer. Therefore, we can say that communication is a two-way process.

Nowadays, the operating system supports multiuser and multiprocessing environments, an executing program is called a process. When a host sends a message to other host means that source process is sending a process to a destination process. The transport layer protocols define some connections to individual ports known as protocol ports.

An IP protocol is a host-to-host protocol used to deliver a packet from source host to the destination host while transport layer protocols are port-to-port protocols that work on the top of the IP protocols to deliver the packet from the originating port to the IP services, and from IP services to the destination port.

Lets talk about each of them :

UDP:

1. UDP stands for User Datagram Protocol.
2. UDP is a simple protocol and it provides nonsequenced transport functionality.
3. UDP is a connectionless protocol.
4. UDP is an end-to-end transport level protocol that adds transport-level addresses, checksum error control, and length information to the data from the upper layer.
5. The packet produced by the UDP protocol is known as a user datagram.

User Datagram Format:

Source port address 16 bits	Destination port address 16 bits
Total length 16 bits	Checksum 16 bits

Data

Source port address: It defines the address of the application process that has delivered a message. The source port address is of 16 bits address.

Destination port address: It defines the address of the application process that will receive the message. The destination port address is of a 16-bit address.

Total length: It defines the total length of the user datagram in bytes. It is a 16-bit field.

Checksum: The checksum is a 16-bit field which is used in error detection.

Some of the limitations in UDP are:

UDP provides basic functions needed for the end-to-end delivery of a transmission.

It does not provide any sequencing or reordering functions and does not specify the damaged packet when reporting an error.

UDP can discover that an error has occurred, but it does not specify which packet has been lost as it does not contain an ID or sequencing number of a particular data segment.

TCP:

1. TCP stands for Transmission Control Protocol.
2. It provides full transport layer services to applications.
3. It is a connection-oriented protocol means the connection established between both the ends of the transmission.
4. For creating the connection, TCP generates a virtual circuit between sender and receiver for the duration of a transmission.

Features Of TCP protocol

Stream data transfer: TCP protocol transfers the data in the form of contiguous stream of bytes. TCP group the bytes in the form of TCP segments and then passed it to the IP layer for transmission to the destination. TCP itself segments the data and forward to the IP.

Reliability: TCP assigns a sequence number to each byte transmitted and expects a positive acknowledgement from the receiving TCP. If ACK is not received within a timeout interval, then the data is retransmitted to the destination.
The receiving TCP uses the sequence number to reassemble the segments if they arrive out of order or to eliminate the duplicate segments.

Flow Control: When receiving TCP sends an acknowledgement back to the sender indicating the number the bytes it can receive without overflowing its internal buffer. The number of bytes is sent in ACK in the form of the highest sequence number that it can receive without any problem. This mechanism is also referred to as a window mechanism.

Multiplexing: Multiplexing is a process of accepting the data from different applications and forwarding to the different applications on different computers. At the receiving end, the data is forwarded to the correct application. This process is known as demultiplexing. TCP transmits the packet to the correct application by using the logical channels known as ports.

Logical Connections: The combination of sockets, sequence numbers, and window sizes, is called a logical connection. Each connection is identified by the pair of sockets used by sending and receiving processes.