network services

2. Learning Outcomes
1. Explain the Domain Name Service
(DNS)
2. Describe the relationship between
Web clients and servers.
3. Describe the relationship between
FTP clients and servers.
4. Explain e-mail protocols in clients and
servers: SMTP, POP3, IMAP4

3. Recap!!
Explain Domain Name
Service (DNS)???
DNS Server
Host
Yahoo
Server
Yahoo is
74.125.135.105
Request
&
Response
I need
Yahoo.com

4. Web Client & Server
• When a web client receives the IP address
of a web server, the client browser uses that
IP address and sends a request to
destination port.
• Hypertext Transfer Protocol (HTTP) - Port 80

5. Web Client & Server (cont…)
• Port 80 request, it responds to the client
request and sends the HTML (Hypertext
Mark-up Language) web page to the client.
• HTTP protocol is not a secure protocol.
• Secure transport protocols (HTTPS) – Port
443
• To provide security for the data, HTTP can be
used with secure transport protocols.

6. FTP Client & Server
• File Transfer Protocol (FTP) – Port 20 and 21. FTP
allows users to transfer files.
• Requests to begin a FTP session are sent to the
server using destination port 21. Once the session is
opened, the server will change to port 20 to transfer
the data files.
• FTP Control – Port 21, FTP Data – Port 20.
• Example: FileZilla, SmartFTP, CuteFTP

7. Email Client & Server
• Email is one of the most popular client/server
applications on the Internet. Email servers - interact
with clients and with other email servers over the
network.
• Mailboxes are identified by the format:
user@company.domain
hafizah@jtmk.ict.edu.my
• Various application protocols used in processing
email include SMTP, POP3, IMAP4

8. Simple Mail Transfer Protocol (SMTP)
• SMTP is a required configuration that
allow email to be transmitted over the
Internet.
• It is used by an email client to send
messages to email server.
• SMTP requests are sent to port 25.
Send Mail

9. Post Office Protocol (POP3)
• POP3 is an application layer Internet
standard protocol used to retrieve email
from a remote server to a local client over
a TCP/IP connection.
• By default, messages are not kept on the
server after they have been accessed by
the client.
• Clients contact POP3 servers on port 110.
Download Mail

10. Internet Message Access Protocol (IMAP4)
• IMAP is an application layer Internet
protocol that allows a local client to access
email on a remote server.
• A server that supports IMAP clients also
receives and stores messages addressed
to its users.
• Client requests on port 143.
Read Mail

11. E-mail Protocol in Client &
Server

12. Port Number Table
The table shows some of the more common well-known ports.

13. I don’t stop when I’m tired.
I only stop when I’m done…