Port Numbers


In this article we will discuss Port Numbers, will make brief discussion on Port Numbers, In last article we discuss about TCP Header – TCP segment.

Port Numbers

The source port number is associated with the originating application on the local host. The destination port number is associated with the destination application on the remote host.

Source Port

The source port number is dynamically generated by the sending device to identify a conversation between two devices. This process allows multiple conversations to occur simultaneously. It is common for a device to send multiple HTTP service requests to a web server at the same time. Each separate HTTP conversation is tracked based on the source ports.

Destination Port

The client places a destination port number in the segment to tell the destination server what service is being requested, as shown in the figure. For example, when a client specifies port 80 in the destination port, the server that receives the message knows that web services are being requested. A server can offer more than one service simultaneously such as web services on port 80 at the same time that it offers File Transfer Protocol (FTP) connection establishment on port 21.

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