The transport layer can be considered as an extension to the host-to-host communication services offered by the network layer. This extension results in process-to-process communication and is facillitated via multiplexing and demultiplexing. In this context, briefly describe these two services and how they allow processes running on machines connected by a network to communicate.

Explanation:

The 2 services namely, host to host and process to process are completely different. The network layer is responsible for host-host-communication. This means that it is concerned with the packet transmission from a host to another host. It is not concerned about what communication is happening inside the host. When a message is transmitted from the sender to the receiver, it has to transmitted from process to process and not just host to host. A message to be transmitted is inside a process and not just inside the host. So, when the message is transmitted the port number of the process is also necessary in addition to the IP address.

Function of network layer Sender Host Receiver Host

The transport makes use of the term socket which is the combination of port number and IP address which brings the process to process communication.

Example : Suppose a user is typing something in a search engine. Let the search engine be G1. When the user types the data, the transport layer makes use of port number 80 as accessing website is done using HTTP protocol. At the send time, the user opens another tab and accesses the mail website. Suppose the mail website and the search engine belongs to the same host. Then, the transport layer performs multiplexing the 2 communication into 1 and when the comunication at the other end takes place by demultiplexing the single transmission into 2 transmissions inside the host. This is how the process to process communication takes place.

Function of Transport Layer Receiver Sender Search engine process server mail website process server Multiplexing Demultiplex

only #2 represents an object at rest on a table.

in #1, there is no normal force due to the table; the object is accelerating downward.

in #3, the vertical forces are not balanced; the object is accelerating downward.

in #4, neither the vertical nor the horizontal forces are balanced. the object is accelerating upwards and to the right.