1. Please describe what is SMTP and what is basic electronic mail operation(send

Question

1. Please describe what is SMTP and what is basic electronic mail operation(sending email and receiving email). What is the difference between POP and IMAP?

2. Please describe what is DNS and and how it works.

3. Please describe what is HTTP and how it works. What are intermediate systems setup for HTTP operation?

4. Please describe main characteristics of real-time traffic.

5. Please describe main principles behind VoIP (including signaling (SIP) and processing).

6. Please describe main principles behind RTP and RTCP protocols.

Explanation / Answer

Answer1)

SMTP: The main function of SMTP is to transfer email between mail servers. To send email, the client sends the message to an outgoing mail server, which in turn contacts the destination mail server for delivery. For this reason, it is necessary to specify an SMTP server when configuring an email client.

Operation: An email message is created using a mail client program. This program then sends the message to a server. The server then forwards the message to the recipient's email server, where the message is then supplied to the recipient's email client. SMTP is used to transfer the data from originating server to destination server. POP and IMAP used to access the mail on client machine from server.

Difference between IMAP and POP:

IMAP allows the user to keep all messages on the server. It constantly synchronizes the e-mail program with the server and displays what messages are currently present. All the actions performed on the messages (reading, moving, deleting...) will be done directly on the server.

POP:

POP is set to download all the messages from the e-mail server onto your computer. This means that all the actions performed on the messages (reading, moving, deleting) will be performed on one's computer.
Because everything is kept on the user’s computer, the user will not be able to reopen messages from any location other than the computer where the messages have been downloaded.Once e-mail is downloaded it can be accessed only using the same computer.

2) DNS: It stnads for Domain Name Server where the URL gets resolved to IP address. since all the communication happens in the layer uses IP address so the URL has to be resolved against its IP address .

The moment we enter the URL in browser and press enter key , browser check with machine for the DNS server there it forwards the URL to get the IP address against that URL. once it is resolved we have the destination IP address where we can request and get the reply data tha we are looking from that URL.

Answer 3)

HTTP: Hypertext Transfer Protocol, is the application-level protocol that is used to transfer data on the Web. HTTP comprises the rules by which Web browsers and servers exchange information.It uses port number 80 on trnsport layer.

Process: HTTP is a request-response protocol. For example, a Web browser initiates a request to a server, typically by opening a TCP/IP connection. The request itself comprises

The server sends a response that comprises

Answer 4:

Characteristics of real time traffic:

For answer of 4,5 ,6 please post questions separately .

Thanks

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