1. 7 Application
6 Presentation COMPUTER NETWORKS
5 Session OSI MODEL
4 Transport
3 Network
2 Data Link
1 Physical

2. 7 Application
6 Presentation Source
1. Computer Networks, Andrew S.
5 Session Tanenbaum
2. www.cisco.com
3. www.novell.com
4 Transport 4. www.rad.com
5. www.3com.com
3 Network
2 Data Link
1 Physical

3. 7 Application
6 Presentation
5 Session
4 Transport INTRODUCTION
3 Network
2 Data Link
1 Physical

4. 7 Application NETWORK GOALS
6 Presentation The two main benefits of networking computers are…
Communications
5 Session Information can be distributed very quickly, such
as email and video conferencing.
4 Transport
Saving Money
Resources such as information, software, and
3 Network hardware can be shared.
2 Data Link CPUs and hard disks can be pooled together to
create a more powerful machine.
1 Physical

5. 7 Application APPLICATIONS
6 Presentation A lot of things we take for granted are the result of
computer networks.
5 Session • Email
• Chat
• Web sites
4 Transport
• Sharing of documents and pictures
• Accessing a centralized database of information
3 Network • Mobile workers
2 Data Link
1 Physical

6. 7 Application NETWORK STRUCTURE
6 Presentation The subnet interconnects hosts.
Subnet
5 Session Carries messages from host to host. It is made up
of telecommunication lines (i.e. circuits, channels,
4 Transport trunks) and switching elements (i.e. IMPs, routers).
Hosts
3 Network End user machines or computers.
2 Data Link Q: Is the host part of the subnet?
1 Physical

7. 7 Application NETWORK ARCHITECTURES
6 Presentation A set of layers and protocols is called the network
architecture.
5 Session 1. Protocol Hierarchies
Networks are organized as layers to reduce design
4 Transport complexity. Each layer offers services to the higher
layers. Between adjacent layers is an interface.
3 Network Services – connection oriented and
connectionless.
2 Data Link Interface – defines which primitives and services
the lower layer will offer to the upper layer.
1 Physical Primitives – operations such as request, indicate,
response, confirm.

8. 7 Application NETWORK ARCHITECTURES
6 Presentation 2. Design Issues for the Layers
• Mechanism for connection establishment
• Rules for data transfer
5 Session
• Error control
• Fast sender swamping a slow receiver
4 Transport • Inability of processes to accept long messages
• Routing in the case of multiple paths
3 Network
2 Data Link
1 Physical

9. 7 Application OSI REFERENCE MODEL
6 Presentation The Open Systems Interconnection is the model
developed by the International Standards
Organization.
5 Session
Benefits
4 Transport • Interconnection of different systems (open)
• Not limited to a single vendor solution
3 Network
Negative Aspect
• Systems might be less secure
2 Data Link • Systems might be less stable
1 Physical

10. 7 Application OSI REFERENCE MODEL
6 Presentation 1. Physical Layer
a) Convert the logical 1’s and 0’s coming from
layer 2 into electrical signals.
5 Session
b) Transmission of the electrical signals over a
communication channel.
4 Transport
Main topics:
3 Network • Transmission mediums
• Encoding
2 Data Link • Modulation
• RS232 and RS422 standards
• Repeaters
1 Physical • Hubs (multi-port repeater)

11. 7 Application OSI REFERENCE MODEL
6 Presentation 2. Data Link Layer
a) Error control to compensate for the
imperfections of the physical layer.
5 Session
b) Flow control to keep a fast sender from
swamping a slow receiver.
4 Transport
Main topics:
3 Network • Framing methods
• Error detection and correction methods
2 Data Link • Flow control
• Frame format
• IEEE LAN standards
1 Physical • Bridges
• Switches (multi-port bridges)

12. 7 Application OSI REFERENCE MODEL
6 Presentation 3. Network Layer
a) Controls the operation of the subnet.
5 Session b) Routing packets from source to destination.
c) Logical addressing.
4 Transport
Main topics:
3 Network • Internetworking
• Routing algorithms
• Internet Protocol (IP) addressing
2 Data Link • Routers
1 Physical

13. 7 Application OSI REFERENCE MODEL
6 Presentation 4. Transport Layer
a) Provides additional Quality of Service.
5 Session b) Heart of the OSI model.
Main topics:
4 Transport
• Connection-oriented and connectionless services
• Transmission Control Protocol (TCP)
3 Network • User Datagram Protocol (UDP)
2 Data Link
1 Physical

14. 7 Application OSI REFERENCE MODEL
6 Presentation 5. Session Layer
a) Allows users on different machines to establish
sessions between them.
5 Session
b) One of the services is managing dialogue
control.
4 Transport
c) Token management.
3 Network d) Synchronization.
2 Data Link
1 Physical

15. 7 Application OSI REFERENCE MODEL
6 Presentation 6. Presentation Layer
a) Concerned with the syntax and semantics of the
information.
5 Session
b) Preserves the meaning of the information.
4 Transport c) Data compression.
d) Data encryption.
3 Network
2 Data Link
1 Physical

16. 7 Application OSI REFERENCE MODEL
6 Presentation 7. Application Layer
a) Provides protocols that are commonly needed.
5 Session
Main topics:
• File Transfer Protocol (FTP)
4 Transport • HyperText Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
3 Network • Simple Network Management Protocol (SNMP)
• Network File System (NFS)
• Telnet
2 Data Link
1 Physical

17. 7 Application SERVICES
6 Presentation Each layer provides services to the layer above it.
1. Terminologies
5 Session
Entities – active elements in each layer (e.g.
process, intelligent I/O chip).
4 Transport Peer Entities – entities in the same layer on
different machines.
3 Network Service Provider – Layer N.
Service User – Layer N + 1.
2 Data Link
Service Access Points – places where layer N + 1
can access services offered by layer N.
1 Physical

18. 7 Application SERVICES
6 Presentation 2. Connection-Oriented and Connectionless
Connection-Oriented – before data is sent, the
service from the sending computer must establish
5 Session
a connection with the receiving computer.
4 Transport Connectionless – data can be sent at any time by
the service from the sending computer.
3 Network
Q: Is downloading a music file from the Internet
connection-oriented or connectionless?
2 Data Link
Q: Is email connection-oriented or connectionless?
1 Physical

19. 7 Application SERVICES
6 Presentation 3. Service Primitives
Request – entity wants the service to do some
work
5 Session
Indicate – entity is to be informed about an event
4 Transport Response – entity responds to an event
Confirm – entity is to be informed about its request
3 Network
Sending Computer Receiving Computer
2 Data Link 4 Transport 4 Transport
1. request 4. confirm 2. indicate 3. response
1 Physical
3 Network 3 Network

20. 7 Application BANDWIDTH
6 Presentation The capacity of the medium to transmit data.
Analog Bandwidth
5 Session
• Measurement is in Hertz (Hz) or cycles/sec.
4 Transport Digital Bandwidth
• Measurement is in bits per second (bps).
3 Network
Q: Is 100MHz = 100Mbps?
2 Data Link Q: Is 100Mbps = 100MBps?
1 Physical

21. Hello
7 Application AH Hello
6 Presentation PH AH Hello
5 Session SH PH AH Hello
4 Transport TH SH PH AH Hello
3 Network NH TH SH PH AH Hello
2 Data Link DH NH TH SH PH AH Hello DT
1 Physical Bits

22. 7 Application
6 Presentation
5 Session
4 Transport PHYSICAL LAYER
3 Network
2 Data Link
1 Physical

23. 7 Application OVERVIEW
6 Presentation 1. Signals
• Fourier analysis
• Maximum data rate of a channel
5 Session 2. Transmission Media
• Guided and Unguided
4 Transport 3. Analog Transmission
• Modulation
• Modems
3 Network • RS-232, RS-422
4. Digital Transmission
• Encoding schemes
2 Data Link
• Repeaters and hubs
5. Transmission and Switching
1 Physical • Multiplexing (FDM and TDM)
• Circuit vs. packet switching

24. 7 Application SIGNALS
6 Presentation 1. Fourier Analysis
a) All signals can be represented mathematically.
5 Session b) A periodic function can be constructed by
adding a number of sine and cosine functions.
4 Transport Fundamental frequency – where f = 1/T
Harmonics – integer multiples of the fundamental
3 Network frequency
Baud – number of signal level changes per second
2 Data Link
Q: Is baud and data rate different terms?
1 Physical Q: Is 1 baud equal to 1bps?

25. 7 Application SIGNALS
6 Presentation 2. Maximum Data Rate of a Channel
Nyquist
Maximum data rate = 2H log2V (bits/sec)
5 Session
H = line bandwidth
V = a signal with V discrete levels
4 Transport
Example:
3 Network A noiseless 3kHz channel cannot transmit binary
(2 level) signals at a rate faster than 6000bps
2(3k) log22 = 6000bps
2 Data Link
logAV = (1 / ln A) ln V
1 Physical

26. 7 Application SIGNALS
6 Presentation Shannon
Maximum data rate (bits/sec) = H log2(1+ PS/PN)
H = line bandwidth
5 Session PS = signal strength in watts
PN = noise strength in watts
4 Transport
Example:
A 3kHz channel with a noise ratio of 30dB
3 Network
(PS/PN = 1000) cannot transmit at a rate faster
than 30,000bps
2 Data Link
(3k) log2(1001) = 30,000bps
1 Physical Note: SNR = 10log10(PS/PN)

27. 7 Application SIGNALS
6 Presentation 3. Attenuation vs. Amplification
Attenuation
The signal received is weaker than the signal sent.
5 Session
Attenuation (dB) = 10log10(P1/P2)
4 Transport
Amplification
The signal received is stronger than the signal
3 Network sent.
Amplification (dB) = 10log10(P2/P1)
2 Data Link
Note:
P1 = transmitted signal power in watts
1 Physical P2 = received signal power in watts
Q: If the result of the attenuation formula is negative, what
happened to the signal?

28. 7 Application TRANSMISSION MEDIA
6 Presentation 1. Guided
Data is sent via a wire or optical cable.
5 Session Twisted Pair
Two copper wires are twisted together to reduce
the effect of crosstalk noise. (e.g. Cat5, UTP, STP)
4 Transport
Baseband Coaxial Cable
3 Network A 50-ohm cable used for digital transmission. Used
in 10Base2 and 10Base5.
2 Data Link Broadband Coaxial Cable
A 75-ohm cable used for analog transmission such
1 Physical as Cable TV.

29. 7 Application TRANSMISSION MEDIA
6 Presentation Fiber Optic Cables
Two general types are multimode and single
mode.
5 Session
In multimode, light is reflected internally. Light
source is an LED.
4 Transport
3 Network
In single mode, the light propagates in a straight
line. Light source come from expensive laser
2 Data Link diodes. Faster and longer distances as compared
to multimode.
1 Physical
* Fiber optic cables are difficult to tap (higher security)
and are normally used for backbone cabling.

30. 7 Application TRANSMISSION MEDIA
6 Presentation 2. Unguided
Data is sent through the air.
5 Session
Line-of-sight
Transmitter and receiver must “see” each other,
4 Transport such as a terrestrial microwave system.
Communication Satellites
3 Network
A big microwave repeater in the sky. Data is
broadcasted, and can be “pirated.”
2 Data Link
Radio
Term used to include all frequency bands, such as
1 Physical
FM, UHF, and VHF television.

31. 7 Application ANALOG TRANSMISSION
6 Presentation 1. Modulation
Modulating a sine wave carrier to convey data.
5 Session
Amplitude Modulation (AM)
Amplitude is increased/decreased while frequency
4 Transport remains constant.
Frequency Modulation (FM)
3 Network
Frequency is increased/decreased while amplitude
remains constant.
2 Data Link
Phase Modulation
Wave is shifted, while amplitude and frequency
1 Physical
remains constant.

32. 7 Application ANALOG TRANSMISSION
6 Presentation 2. Modems
A device that accepts digital signals and outputs a
modulated carrier wave, and vice versa.
5 Session
It is used to interconnect the digital computer to the
4 Transport analog telephone network.
* Modems for PC’s can be external or internal.
3 Network * Nokia makes modems for leased line connections.
2 Data Link
1 Physical

33. 7 Application ANALOG TRANSMISSION
6 Presentation 3. RS-232 and RS-449
Two well known physical layer standards.
5 Session
RS-232
• 20 kbps
4 Transport • Cables up to 15 meters
• Unbalanced transmission (common ground)
3 Network
RS-422
2 Data Link • 2 Mbps at 60 meters
• 1 Mbps at 100 meters
• Balanced transmission (a pair of wires for Tx, Rx)
1 Physical

34. 7 Application DIGITAL TRANSMISSION
6 Presentation 1. Encoding Schemes
Converting logical data into electrical signals
suitable for transmission.
5 Session
Manchester
4 Transport • Mid bit transition for clock synchronization and
data
• Logic 0 = high to low transition
3 Network • Logic 1 = low to high transition
2 Data Link Differential Manchester
• Mid bit transition for clock synchronization only
1 Physical • Logic 0 = transition at the beginning of each bit
period
• Logic 1 = no transition at the beginning of each
bit period

35. 7 Application DIGITAL TRANSMISSION
6 Presentation 2. Repeaters and Hubs
These are physical layer devices.
5 Session Repeaters
• Restores the strength of an attenuated signal.
4 Transport • Used to increase the transmission distance.
• Does not filter data traffic.
3 Network Hubs
• Multi-port repeater.
2 Data Link • Interconnects several computers.
• Does not filter data traffic.
1 Physical
* Picture from 3com.com

36. 7 Application
6 Presentation
5 Session
4 Transport NETWORK LAYER
3 Network
2 Data Link
1 Physical

37. 7 Application OVERVIEW
6 Presentation 1. Routing Algorithms
• Shortest Path
• Flooding
5 Session • Flow-based
• Distance Vector
• Link State
4 Transport
• Hierarchical
• Broadcast
3 Network • Multicast
• Routing for Mobile Hosts
2 Data Link 2. Congestion control
3. IP Addressing
4. Routers
1 Physical

38. 7 Application ROUTING ALGORITHMS
6 Presentation 1. Shortest Path
B(A,2) C(B,3)
5 Session B 1 C
2
4 Transport A(-,-) 3 2 3
D(E,3)
2
A F(E,4)
3 Network D
1
1 F
E(A,2) 2
2 Data Link 2
E
1 Physical
A–E–D–F
A – E – F is the answer.

39. 7 Application ROUTING ALGORITHMS
6 Presentation 2. Flooding
Packet to IMP C
5 Session Packet IMP Packet to IMP D
4 Transport B Packet to IMP E
To prevent packets from circulating indefinitely, a
3 Network packet has a hop counter. Every time a packet arrives
at an IMP, the hop counter is decrease by 1. Once the
2 Data Link hop counter of a packet reaches 0, the packet is
discarded.
1 Physical

40. 7 Application IP ADDRESSING
6 Presentation Format
xxxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx
where x is either 0 or 1
5 Session
Example 1:
4 Transport 11111111. 11111111.00000000.00000000
255.255.0.0
3 Network
Example 2:
2 Data Link 11111111. 11111111.10000000.00000000
1 Physical 255.255.192.0

41. 7 Application IP ADDRESSING
6 Presentation Network Address
Example 1:
5 Session IP address of computer 180.100.7.1
Mask 255.255.0.0
Network address 180.100.0.0
4 Transport
Example 2:
3 Network IP address of computer 180.100.7.1
Mask 255.255.255.0
2 Data Link Network address 180.100.7.0
Example 3:
1 Physical
IP address of computer 180.100.7.2
Mask 255.255.192.0
Network address 180.100.0.0

42. 7 Application IP ADDRESSING
6 Presentation Mask
Valid mask are contiguous 1’s from left to right.
5 Session
Examples:
4 Transport Valid
255.0.0.0
255.255.0.0
3 Network
255.255.255.0
2 Data Link Invalid
255.1.0.0
255.0.255.0
1 Physical
255.255.64.0
200.255.0.0

43. 7 Application IP ADDRESSING
6 Presentation Subnets
The Internet is running out of IP address. One solution
is to subnet a network address.
5 Session
This is done by borrowing host bits to be used as
4 Transport network bits.
Example:
3 Network
Class B mask 255.255.0.0
Borrowing 1 bit gives a subnet mask of 255.255.128.0
2 Data Link Borrowing 2 bits gives a subnet mask of 255.255.192.0
Borrowing 3 bits gives a subnet mask of 255.255.224.0
Borrowing 4 bits gives a subnet mask of 255.255.240.0
1 Physical

44. 7 Application IP ADDRESSING
6 Presentation Example:
Given an IP address of 180.200.0.0, subnet by
borrowing 4 bits.
5 Session
Subnet mask = 255.255.240.0
4 Transport The 4 bits borrowed are value 128, 64, 32, 16. This will
create 16 sub networks, where the first and last will be
unusable.
3 Network
Sub network address:
2 Data Link 180.200.0.0
180.200.16.0
180.200.32.0
1 Physical
180.200.48.0
180.200.64.0
etc…

45. 7 Application IP ADDRESSING
6 Presentation The first 3 usable sub networks are:
180.200.16.0
180.200.32.0
5 Session 180.200.48.0
4 Transport For sub network 180.200.16.0, the valid IP address
are:
3 Network 180.200.16.1 to 180.200.31.254
2 Data Link Directed broadcast address is:
180.200.31.255
1 Physical

46. 7 Application ROUTERS
6 Presentation A layer 3 device that is used to interconnect 2 or more
logical networks.
5 Session Can filter broadcast traffic, preventing broadcast traffic
from one network from reaching another network.
4 Transport
3 Network 180.200.0.0 202.5.3.0
2 Data Link
1 Physical