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What are two roles of the transport layer in data communication on a network ?

What are two roles of the transport layer in data communication on a network ? Choose two.

  1. Identifying the proper application for each communication stream
  2. Supplying frame delimiting to distinguish the bits that make up a frame
  3. Cyclic redundancy checking the frame for mistakes
  4. Establishing a connection between applications and the network infrastructure that messages are sent over
  5. Tracking the individual communication between applications on the source and destination hosts

The Answer is 1 and 5.

Explanation: The transport layer is responsible for a few different things. The following items are included among the primary responsibilities:

  • Monitoring each individual communication stream that occurs between applications running on the source host and the destination host
  • The process of data segmentation at the source, followed by data reassembly at the destination
  • Utilizing port numbers in order to determine which application should be used for each individual communication stream

Transport Layer responsibilities

In both the TCP/IP model and the OSI model, the Transport Layer is the second layer. In the OSI model, it is the fourth layer. It is a layer that runs from end to end and is responsible for delivering messages to hosts. It is referred to as an end-to-end layer due to the fact that it establishes a point-to-point connection rather than a hop-to-hop connection between the source host and the destination host in order to reliably deliver the services. A segment is the basic building block for the encapsulation of data at the Transport Layer.

Working of Transport Layer:

The Network layer is responsible for providing services, and the Transport layer is responsible for providing those services to the Application layer.

At the sender’s side: The application layer sends data, which is known as a message, to the transport layer, which then processes the data and performs segmentation on it. Next, the transport layer divides the actual message into segments, adds the port numbers of the source and destination into the header of the segment, and then sends the message on to the network layer.

At the receiver’s side: The transport layer is responsible for receiving data from the network layer, reassembling the data after it has been segmented, reading the header, determining the port number, and then sending the message to the appropriate port in the application layer.

Responsibilities of a Transport Layer:

Process to process delivery:

While the Data Link Layer requires the MAC address of source-destination hosts to correctly deliver a frame and the Network Layer requires the IP address for appropriate routing of packets, the Transport Layer similarly requires a Port number to correctly deliver the segments of data to the correct process among the multiple processes running on a particular host. A MAC address is a 48-bit address that is contained inside the Network Interface Card of every host machine. The technique of distinguishing between client and server applications makes use of a 16-bit address called a port number.

End-to-end Connection between hosts:

The two protocols that the transport layer uses the most commonly to achieve its main objective of creating an end-to-end connection between hosts are TCP and UDP. The Transmission Control Protocol (TCP) is a connection-oriented protocol that prioritises security and makes use of a handshake protocol to establish a reliable connection between two end hosts. TCP is used in a wide variety of applications because it guarantees the reliable delivery of messages. The User Datagram Protocol (UDP), on the other hand, is a stateless and unreliable protocol that guarantees delivery using best efforts. Applications like video conferencing, which require sending a large amount of data, are a good fit for this protocol because they do not place a high priority on flow or error control. It is frequently used in the protocols for multicasting.

Multiplexing and Demultiplexing:

The process of multiplexing makes it possible for users of multiple applications to access the same host computer network simultaneously. This mechanism, which is provided by the transport layer, is what enables us to send packet streams originating from multiple applications concurrently over a network. These packets are accepted from the various processes, which can be distinguished from one another by the port numbers they use, and then the transport layer sends them on to the network layer after adding the appropriate headers. In a similar vein, in order to obtain the data coming from the various processes, demultiplexing must first be performed on the receiving end. The data segments are passed down from the network layer to the transport layer, where they are received by the transport layer, which then delivers them to the appropriate process running on the machine of the receiver.

Congestion Control:

When too many data sources on a network seek to send data at once, the router buffers start to fill up and packets start to get lost, which is the phenomenon known as network congestion. As a direct consequence of this, the retransmission of packets from the sources contributes to an even greater increase in congestion. In this scenario, Congestion Control is being provided in a variety of different ways by the transport layer. It uses open-loop congestion control to prevent congestion in a network and closed-loop congestion control to remove congestion once it has already occurred in a network. Congestion control is handled by TCP through the use of the AIMD (additive increase multiplicative decrease) and leaky bucket techniques.

Data integrity and Error correction:

It uses error detection codes, computes checksums, ensures that the data that has been received has not been corrupted, and uses the ACK and NACK services to inform the sender of whether or not the data has arrived and checks for the integrity of data. The application layer sends messages to the transport layer, which then checks those messages for errors using error detection codes and computing checksums.

Flow control:

Within the TCP/IP model, the transport layer serves as a mechanism for controlling the flow of data between the adjacent layers. By imposing certain flow control strategies, TCP is also able to prevent data loss that would otherwise be caused by a fast sender but a slow receiver. It makes use of the sliding window protocol, which involves the receiver returning a window to the sender along with information on how much data the receiver can hold in that window.