4 - Data Transmission Protocol

Question 1

What is a protocol?

Answer 1

A protocol is a set of rules that defines how data is transmitted between devices over a network.

Question 2

Electronic mail uses several protocols including:

Answer 2

• SMTP
• POP3
• IMAP

Question 3

What is SMTP used for?

Answer 3

SMTP (Simple Mail Transfer Protocol) is used to:

• Send email from a client to an outgoing mail server
• Transfer email between mail servers

Question 4

Describe the SMTP process

Answer 4

1. SMTP connects to outgoing mail server#
2. Email + recipient address sent to server
3. Recipient’s domain identifies their SMTP server
4. Email forwarded to recipient’s server

Question 5

What is POP3 used for?

Answer 5

POP3 downloads emails from a mail server to an email client.

Question 6

How does POP3 work?

Answer 6

1. Client connects to mail server
2. Emails download to the device
3. Emails are removed from the server
   → Can only be accessed on one device

Question 7

What is IMAP used for?

Answer 7

IMAP is an alternative to POP3, allowing email to stay on the server and** sync across multiple devices.**

Question 8

How does IMAP work?

Answer 8

• Emails remain on the server
• Device syncs with server
• Changes (read, delete, folder move) sync across all devices

Question 9

What is the key difference between POP3 and IMAP?

Answer 9

**POP3: **Downloads email to 1 device
**IMAP: **Keeps email on server & syncs to many devices

Question 10

What protocols are used for VoIP (voice/video calls)?

Answer 10

• SIP
• RTP
• RTCP

Question 11

What is SIP used for?

Answer 11

SIP (Session Initiation Protocol) is used to:
* Establish a connection between caller & receiver
* Locate devices (using IP address)
* Agree on CODECs for audio/video

Question 12

Describe the SIP process.

Answer 12

1. Caller sends SIP packet to recipient
2. Recipient’s device rings
3. Additional packets negotiate CODECs
4. Final SIP packet ends the session

Question 13

What is RTP and its purpose?

Answer 13

RTP (Real-Time Transport Protocol):

• Sends voice/video data packets
• Works after SIP sets up connection
• Built on UDP (no retransmission)
• Must deliver packets in real time

Question 14

Why does RTP use UDP instead of TCP?

Answer 14

UDP doesn’t retransmit packets → avoids delay.
Real-time calls cannot wait for lost packets.

Question 15

What does RTCP do?

Answer 15

RTCP sends control packets with quality feedback:

• Bytes sent
• Packet count
• Jitter
• Round-trip time
• Used to adjust CODECs for better call performance.

Question 16

How do SIP and RTP work together?

Answer 16

**SIP: **Sets up and ends the call
RTP: Transmits the audio/video during the call