What is SMTP? SMTP stands for Simple Mail Transfer Protocol and is used by email carriers to send and receive emails. SMTP uses the store and forward technique to send emails between two connections. [Actually, there are two different servers running on a server machine : the SMTP server and the POP3 or IMAP server. We will focus only on the SMTP and the functionality of the SMTP server in this blogpost]. How does SMTP work [or how emails use SMTP?] ? Consider the following expected communication between John and Brendon: Fig 1 : Expected communication between John and Brendon Suppose John is going to send his email using Outlook express. First, Outlook express should connect to John's network and then to the SMTP server using Port 25 (SMTP usually uses TCP port 25 for connections). Then Outlook express should notify the server the message to be sent, the address of the sender and that of the recipient. Suppose Brendon's address is Brendon@pqr.com. Fig 2
We discussed about switches in a previous post and this post will explain you about routers. In this article : 1. Routers vs Switches 2. Use of routing tables 3. How data packets are transferred by a router Routers vs Switches Consider the following two networks. Fig 1 : Network at the start Suppose you want to connect the computers in the first network together, you could use a switch for that purpose. Same thing could be done with the second network. However, if you want to communicate from one of the computers in the first network with that of a second network, can you just use switches? The answer is no. This is where routers come in to play. Use of routers for such connections serves many purposes. But most importantly, routers enable you to connect to all sorts of networks like local area networks (LANs), metropolitan area networks (MANs) or even wide area networks (WANs, such as the Internet). For example, assume the first network in some part of Asi