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+22 votes

The transport layer protocols used for real time multimedia, file transfer, DNS and email, respectively are

  1. TCP, UDP, UDP and TCP
  2. UDP, TCP, TCP and UDP
  3. UDP, TCP, UDP and TCP
  4. TCP, UDP, TCP and UDP
in Computer Networks by
edited by | 3.6k views

In real time multimedia we generally use UDP.

For sending file TCP is more powerful than any other protocol.

And we know that DNS uses the UDP at transport layer.

Last is SMTP is used for mail sending.
for simple one request one reply kind of messages we use UDP..because in TCP we have to estabilish the connection, then data transfer and then close the connection..

4 Answers

+40 votes
Best answer

Real Time Multimedia: Data packets should be delivered faster. Also it can be unreliable. Therefore UDP.
File Transfer: For example downloading a file. It should be secure and reliable. Therefore TCP.
DNS: uses both UDP and TCP for its transport. But to acheive efficiency DNS uses UDP. To start a TCP connection a minimum of three packets are required (SYN out, SYN+ACK back, ACK out). UDP uses a simple transmission model with a minimum of protocol mechanism. UDP has no handshaking dialogues.
Email: uses SMTP protocol which uses TCP protocol.

Therefore, C is the answer.

edited by

Therefore, C is the answer.

the best example to understand UDP is SKYPE video calling
DNS support UDP when data size <512B ,if data size>=512B TCP will be used as transport layer protocol...just extra information
+8 votes

DNS :-> uses both UDP and TCP  But to achieve efficiency DNS uses UDP why?

reason :-> A client-server application such as DNS uses the services of UDP because a client needs to send a short request to a server and to receive a quick response from it. The request and response can each fit in one user datagram. Since only one message is exchanged in each direction, the connectionless feature is not an issue; the client or server does not worry that messages are delivered out of order.

Real Time Multimedia :-> use UDP Why?

reason :-> Assume we are watching a real-time stream video on our computer. Such a program is considered a long file; it is divided into many small parts and broadcast in real time. The parts of the message are sent one after another. If the transport layer is supposed to resend a corrupted or lost frame, the synchronizing of the whole transmission may be lost. The viewer suddenly sees a blank screen and needs to wait until the second transmission arrives. This is not tolerable. However, if each small part of the screen is sent using one single user datagram, the receiving UDP can easily ignore the corrupted or lost packet and deliver the rest to the application program. That part of the screen is blank for a very short period of the time, which most viewers do not even notice. However, video cannot be viewed out of order, so streaming audio, video, and voice applications that run over UDP must reorder or drop frames that are out of sequence.

+3 votes

Suppose u are looking at the video on you tube and quality of video is not HD then u are just using UDP.When u want to see video in 720HD,1080HD or 2160HD in that case TCP is used.

For file transfer we use TCP but for file downloading we use FTP or for small file we use TFTP.

DNS,RIP,OSPF,BOOTP,DHCP,NNP,NAT,TimeStamp and quote of day all uses UDP.

SMTP is application layer protocol but it uses TCP for sending mail.

Suppose u are looking at the video on you tube and quality of video is not HD then u are just using UDP.When u want to see video in 720HD,1080HD or 2160HD in that case TCP is used.

Why so? UDP has streaming limit?

Is that true sir? The points I know are:

Tcp does not guarentee constant data rate but guarentee reliable transmission.

Tcp uses buffer to collect the data and then transmit it for smooth play, and therefore it is not suitable for live streaming.

Is there something related to these points? Correct me if I am wrong
Your first point is correct but


Tcp uses buffer to collect the data and then transmit it because if it does not do this

Let for every byte it add the header into it and send it to reciver so by doing this efficiency will reduce(because every byte contain at least 20 byte header) .So it collect some data and then add the header and send that packet

@Arjun sir you raised a question please answer

Why so? UDP has streaming limit?


+1 vote
option c

file transfer and email uses tcp protocol to send and receive.
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