The Role of Internet Character-

Oriented

Application Protocols in an

Elementary Communication

Protocols Course

Drago HercogUniversity of LjubljanaFaculty of Electrical EngineeringLjubljana, SloveniaDrago.Hercog@fe.uni-lj.si

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Drago Hercog 2

Different viewpoints of a communication system

use r

eng ineer

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Drago Hercog 3

Communication protocols

Implement communication system operation

Protocol messages bit-oriented character-oriented

Rules for message exchangeNot easy to be understoodNeed for understanding and

experience

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Drago Hercog 4

Internet

world-wide communication networkeasily availableno need for expensive equipmentwell-known from user’s point of

viewcan serve as a laboratory for

telecommunications students

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Drago Hercog 5

Protocols in Internet

application layer

transport layer

internet layer

access to network

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Application layer protocols

application layer

transport layer

internet layer

access to network

client-server oriented requests & replies

character-orientedaddressed by

port numbersExamples:

telnet SMTP, POP3, IMAP FTP HTTP

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Drago Hercog 7

Transport layer protocol: TCP

application layer

transport layer

internet layer

access to network

most frequently usedprovides for

connection betwen two endpoints

connection identified by two IP addresses two port numbers

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How to manually open a TCP connection

use of telnet program set local echo

port numbercomputer address

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Student-to-server communication

e t h e r n e t n e t w o r k

IP1 9 3 .2 .6 6 .1 3 7

te ln e t p ro g ramep h e m era l p o rt

T C P c o n n e c tio n

S M T P s e ss io n

T C PIP

1 9 3 .2 .6 6 .4 7IP lay e r

n e tw o rka c c e ss

c lie n t s id e s e rv e r s id e

sy stem S Wp o rt 2 5

T C Ptr a n sp o rt

la y e r

S M T Pse rv er

(m a ch in e)(s tu d en t)a p p l ic a tio n

la y e r

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Drago Hercog 10

A simple Internet mail system

m ail server

SM T P

sendm ail

PO P3

retrievem ail

SMT

P server POP3

ser

ver

POP3 clientS

MT

P cl

ient m a il

boxes

receiving usersend

ing

user

Experiments can easily be done with protocols SMTP and POP3 !

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Drago Hercog 11

Sending an e-mail usingSMTP protocol directly

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Retreiving an e-mail usingPOP3

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Conclusion

Experiments are simple pedagogically powerful provide experience with both protocol

messages and protocol rules require only few inexpensive resources can be carried out with different

application-layer protocols

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Drago Hercog 14

Thank you

for your

attention!