The OSI Model analogy
SOURCE (A)
7. Application Layer - Source Host (A)
Analogy: After riding your new bicycle around
London, you decide that you want to give it as a
present to friend who lives in California.
Function of application layer:
User Application Services
Protocols and Technologies:
DNS; DHCP; SNMP; FTP; TFTP;SMTP; POP3;
IMAP; HTTP; Telnet
6. Presentation Layer - Source Host (A)
Analogy: Make sure you have the proper
directions to disassemble and reassemble the
bicycle.
Function of Presentation layer:
Data Translation; Compression and Encryption
Protocols and Technologies:
SSL; EBCDIC and ASCII
GIF & JPEG
5. Session Layer - Source Host (A)
Analogy: Call your friend to make sure you have his
correct address.
Function of the Session layer:
Session Establishment, Management and
Termination
Protocols and Technologies:
NetBIOS, Sockets, Named
Pipes, RPC, PPTP, RTCP, H.245, ASP, PAP
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4. Transport Layer - Source Host (A)
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3. Network Layer - Source Host (A)
Analogy: Disassemble the bicycle and put different pieces in
different boxes. The boxes are labeled “1 of 4”, “2 of 4”, and
“3 of 4” and “4 of 4”, (Sequence numbers)
Function of the Transport layer:
Ensures the reliable arrival of messages and provides error
checking mechanisms and data flow controls
Protocols and Technologies:
TCP and UDP; SPX; NetBEUI/NBF
Analogy: Put your friend's complete mailing address and
yours on each box. Since the boxes are too big for your
mailbox, you decide to go to the post office
(In London)
Function of the Network layer:
Logical Addressing; Routing; Datagram, Encapsulation;
Fragmentation and Reassembly; Error Handling and Diagnostics
Protocols and Technologies:
IP; IPv6; IP NAT; IPsec; Mobile IP; ICMP; IPX; RIP,
BGP, OSPF, EIGRP
DEVICES: Routers and Multi-Layer Switches
2. Data Link Layer – Source Host (A)
Analogy: London post office takes possession of the boxes.
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Function of Data-Link layer:
Logical Link Control; Media Access Control;
Data Framing; Addressing; Error Detection and Handling;
Defining Requirements of Physical Layer
Protocols and Technologies:
IEEE 802.2 LLC, Ethernet, FDDI, IEEE 802.11(WLAN,
Wi-Fi); ATM; PPP, MPLS, CDP, PPP
DEVICES: Switches and Bridges
1. Physical Layer - Media
Analogy: The boxes are flown from London to USA.
(Bits = 1s and 0s)
Function of Physical layer:
Encoding and Signaling; Physical Data
Transmission; Hardware Specifications;
Topology and Design
Protocols and Technologies:
USB, ISDN, 100Base-TX, Bluetooth
DEVICES: Hubs, and cables
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DESTINATION (B)
2. Data Link Layer – Destination (B)
Analogy: California post office receives your
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3. Network Layer – Destination (B)
boxes.
(DigitalAnalogueDigital conversion)
(Framing = Separating new from old frames
on the wire)
Analogy: After checking the destination
address, California post office determines
that your boxes should be delivered to your
written home address.
(Route selection and Packet delivery)
4. Transport Layer – Destination (B)
Analogy: Your friend calls you and tells you
he got all 4 boxes and he is having another
friend named Alice reassemble the bicycle.
(Checking the sequence numbers and
acknowledgement)
5. Session Layer – Destination (B)
Analogy: Your friend hangs up because he is
done talking to you.
(Session management: initiation, monitoring
and teardown)
6. Presentation Layer – Destination (B)
Analogy: Alice is finished and “presents” the
bicycle to your friend. Another way to say
it is that your friend is finally getting him
“present”.
(Translation and compression of data)
7. Application Layer – Destination (B)
Analogy: Your friend enjoys riding his new
bicycle in California
(End User application)
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