1. CPEG 419 COMPUTER COMMUNICATION NETWORKS
Instructor: Stephan Bohacek
Course webpage:
Office: Evans 315
Phone:
TA: Ignjat Kilibarda
TA’s
U of D CPEG 419

2. University of Delaware CPEG 419
Textbooks:
Require textbook: W. Stallings, Data and Computer Communications, 6th edition, Prentice Hall.
Other books:
Peterson and Davie, Computer Networks.
Tanenbaum, Computer Networks.
Grading:
Homework and quizzes (20%)
Midterm (20%)
Project (20%)
Final exam (40%)
Homework consist of short problems, programming and ns simulations.
University of Delaware CPEG 419

3. University of Delaware CPEG 419
Who are you?
Write the following on a piece of paper
Name, , Majors, Year.
Why 419?
Do you know what the Fourier transform is?
Do you know how to program? (C, sockets?)
Have you taken any probability?
Circuits? What is an RC circuit?
Do you know what ARP is?
What is 10base-T?
What is the speed of 10base-T?
University of Delaware CPEG 419

4. University of Delaware CPEG 419
Course Objectives:
Basic understanding of computer networks and their protocols.
OSI’s 7 layer protocol stack and the TCP/IP protocol suite.
Internet.
LANs.
University of Delaware CPEG 419

5. University of Delaware CPEG 419
Course Outline
Introduction
Basic concepts
Layers
OSI
TCP/IP
Physical Layer
Data Link Layer
MAC Layer
Multiplexing
LANs
University of Delaware CPEG 419

6. University of Delaware CPEG 419
Outline (cont’d)
Network Layer
Routers versus bridges
Routing and forwarding
Addressing and subnetting
Internetworking
IP: IPv4 and IPv6
ICMP
Internet routing: RIP, OSPF, BGP
IP Multicast
University of Delaware CPEG 419

7. University of Delaware CPEG 419
Outline (cont’d)
Transport Layer
UDP
TCP
End-to-end argument
Error control
Flow and congestion control
Security
University of Delaware CPEG 419

8. University of Delaware CPEG 419
Outline (cont’d)
Layer 5 and above
DNS
FTP
SNMP
HTTP
Wireless networks (time permitting)
University of Delaware CPEG 419

9. Administration Issues
How late can we start next Tuesday?
Probably no class on Oct 3.
University of Delaware CPEG 419

10. University of Delaware CPEG 419
Introduction
Basic concepts
Layers
OSI
TCP/IP
University of Delaware CPEG 419

11. University of Delaware CPEG 419
Ubiquitous Computing
Computers everywhere.
Also means ubiquitous communication
Users connected anywhere/anytime.
PC, laptop, palmtop, cell phone, etc.
University of Delaware CPEG 419

12. University of Delaware CPEG 419
Computer Network
WHY?
Provide access to local and remote resources (data/information, computing, etc.).
Provide efficient communication ( , voice over IP, chatting, etc.)
HOW?
Collection of interconnected end systems:
Computing devices (mainframes, workstations, PCs, palm tops)
Peripherals (printers, scanners, terminals, sensors).
Applications: location and platform transparency.
University of Delaware CPEG 419

13. Computer Networks (cont’d)
Physical Components:
Nodes
End systems (or hosts),
Routers/switches/bridges, and
Links
twisted pair,
coaxial cable,
fiber,
radio,
etc.
University of Delaware CPEG 419

14. Computer Networks (cont’d)
Protocols – Protocols define a way for the physical components to work together.
Applications – The final result and end product of the network.
University of Delaware CPEG 419

15. The Internet: Some History
Late 1970’s/ early 1980’s: the ARPANET (funded by ARPA).
Connecting university, research labs and some government agencies.
Main applications: and file transfer.
Features:
Decentralized, non-regulated system.
No centralized authority.
No structure.
Network of networks.
University of Delaware CPEG 419

16. University of Delaware CPEG 419
The Internet (cont’d)
Early 1990’s, the Web caused the Internet revolution: the Internet’s killer app!
Today:
Almost 60 million hosts as of
Doubles every year.
University of Delaware CPEG 419

17. How the Internet is designed
Internet Society
IAB
IETF
IRTF
Internet draft -> RFC -> Internet standard
There are many other standards that are also used, e.g., IEEE, ISO, ITU-T
University of Delaware CPEG 419

18. Network Architecture (chapter 2)
Protocol layers: divide and conquer.
Main idea: each layer uses the services from lower layer and provide services to upper layer.
Higher layer shielded from the implementation details of lower layers.
Interface between layers must be clearly defined: services provided to upper layer.
University of Delaware CPEG 419

19. Network Layers in Action: An Example
Goal: Send a file from a web server (e.g. yahoo.com) to a web client (e.g. your PC).
Application
e.g. http server
Application
e.g. http client
Transport Layer
e.g. TCP source
Transport Layer
e.g. TCP receiver
Network Layer: IP
Network Layer: IP
Network Layer
Network Layer
Link Layer
e.g., CSMA/CD
Link Layer
e.g., CSMA/CD
Link Layer
Link Layer
Link Layer
Physical Layer
e.g., twisted pair
Physical Layer
e.g., twisted pair
Physical Layer
Physical Layer
Physical Layer
University of Delaware CPEG 419

20. Approach 1: ISO OSI Model
ISO: International Standards Organization
OSI: Open Systems Interconnection.
Application
Presentation
Session
Transport
Network
Data link
Physical
University of Delaware CPEG 419

21. University of Delaware CPEG 419
OSI ISO 7-Layer Model
Physical layer: transmission of bits/bytes. Deals with electric properties and encoding.
Data link layer: reliable transmission over physical medium; synchronization, error control, flow control; media access in shared medium.
Network layer: routing and forwarding; congestion control; internetworking.
University of Delaware CPEG 419

22. OSI ISO 7-Layer Model (cont’d)
Transport layer: error, flow, and congestion control end-to-end.
Session layer: manages connections (sessions) between end points.
Presentation layer: data representation.
Application layer: provides users with access to the underlying communication infrastructure.
University of Delaware CPEG 419

23. University of Delaware CPEG 419
Example 2: TCP/IP Model
Model employed by the Internet.
TCP/IP
Application
ISO OSI
Application
Presentation
Session
Transport
Transport
Internet
Network
Network
Access
Data link
Physical
Physical
University of Delaware CPEG 419

24. TCP/IP Protocol Suite:
Physical layer: same as OSI ISO model.
Network access layer: medium access and routing over single network.
Internet layer: routing across multiple networks, or, an internet.
Transport layer: end-to-end error, congestion, flow control functions.
Application layer: same as OSI ISO model.
University of Delaware CPEG 419

25. Physical Layer (Stallings Chap. 3-6)
Sending raw bits/bytes/words across “the wire”.
Point to point. No routing, no error correction (link layer).
Objective: Transmit a frame from a transmitter to receiver.
University of Delaware CPEG 419

26. University of Delaware CPEG 419
Basic Concepts
Signal: electro-magnetic wave carrying information.
Time domain: signal as a function of time.
Analog signal: signal’s amplitude varies continuously over time, ie, no discontinuities.
Digital signal: data represented by sequence of 0’s and 1’s (e.g., square wave).
University of Delaware CPEG 419

27. Digital vs. Analog Signals
Digital signals don’t really exists. We interpret analog signals as digital
digital
signal
analog
signal 1 1
University of Delaware CPEG 419

28. Bandwidth vs. Data Rate
Q. What is the bandwidth of 10base-T ethernet?
The data rate is 10Mbs (mega bits per second).
The bandwidth maybe larger than 10Mhz.
Let x(t) be the analog signal broadcast.
The Fourier transform of x is
X(f) is the component of x that has frequency f
The bandwidth of x is the fBW such that
|X(f)| is small for f > fBW
University of Delaware CPEG 419

29. University of Delaware CPEG 419
Bandwidth vs. Data Rate 2
time
domain signal
1.5 1
0.5 10 20 30 40 50 60 70 80 90
2.5
frequency
domain
signal 2
1.5 1
0.5
-0.5
0.98
0.99 1
1.01
1.02
1.03
x 10 4
A single pulse contains all frequencies!
University of Delaware CPEG 419

30. University of Delaware CPEG 419
Bandwidth vs. Data Rate
Band-limited approximation of the digital signal 1 1 1 1 1 1 1 1
sample times
threshold
0.3 time the bit-rate
0.5 time the bit-rate 1 1 1 1 1 1 1 1 1 1 1 1
0.75 times the bit-rate
1 times the bit-rate
2 times the bit-rate
University of Delaware CPEG 419

31. University of Delaware CPEG 419
Bandwidth vs. Data Rate
Suppose the digital signal is … …
And a bit is sent every T seconds.
University of Delaware CPEG 419

32. Fourier Series (Fourier Transform for periodic signals)
Let x be periodic with period 2T
where
University of Delaware CPEG 419

33. University of Delaware CPEG 419
Bandwidth vs. Data Rate
Suppose the digital signal is … …
And a bit is sent every T seconds.
The lowest frequency component is at ½ the data rate.
What is the lowest bandwidth of the signal that might be able to approximate x?
Hence, to transmit a binary signal with data rate 1/T, one must use an analog signal
that contains frequencies up to ½1/T.
University of Delaware CPEG 419

34. Multi-level Signals Bit Rate and Baud Rate
The number of bits transmitted can be increased by transmitting more than one bit in one time slot
Baud rate: number of times per second signal changes its value (voltage).
Each value might “carry” more than 1 bit.
Example: 8 values of voltage (0..7); each value conveys 3 bits, ie, number of bits = log2V.
Thus, bit rate = log2V * baud rate.
For 2 levels, bit rate = baud rate.
University of Delaware CPEG 419

35. University of Delaware CPEG 419
Last slide
University of Delaware CPEG 419

36. University of Delaware CPEG 419
Data Transmission 1
Analog and digital transmission.
Example of analog data: voice and video.
Example of digital data: character strings
Use of codes to represent characters as sequence of bits (e.g., ASCII).
Historically, communication infrastructure for analog transmission.
Digital data needed to be converted: modems (modulator-demodulator).
University of Delaware CPEG 419

37. University of Delaware CPEG 419
Digital Transmission
Current trend: digital transmission.
Cost efficient: advances in digital circuitry (VLSI).
Advantages:
Data integrity: better noise immunity.
Security: easier to integrate encryption algorithms.
Channel utilization: higher degree of multiplexing (time-division mux’ing).
University of Delaware CPEG 419

38. University of Delaware CPEG 419
Communication Model
Network
Source
Destination
University of Delaware CPEG 419

39. University of Delaware CPEG 419
Example
PTN
Modem
Modem
Source
Destination
Source System
Destination System
PTN: Public Telephone Network
University of Delaware CPEG 419

40. Connecting End Systems
Dedicated link
Multiple access / shared medium
University of Delaware CPEG 419

41. Connecting End Systems (cont’d)
Router
Switched network
Router: switching element; a.k.a., IMPs (Interface
Message Processors) in ARPAnet’s terminology.
University of Delaware CPEG 419

42. Shared Communication Infrastructure
Shared medium:
Examples: ethernet, radio.
How to acquire channel: medium access control protocols.
Switched networks:
Shared infrastructure consisting of point-to-point links.
Circuit- versus packet-switching.
University of Delaware CPEG 419

43. University of Delaware CPEG 419
Circuit Switching
Establish dedicated path (circuit) between source and destination.
Example: telephone network.
+’s: predictable usage of resources(stream-oriented).
-’s: lower resource utilization (e.g.,bursts).
University of Delaware CPEG 419

44. University of Delaware CPEG 419
Packet Switching S1 D1 S2 D2
Data split into transmission units, or packets.
Routers: store packets briefly store packets and forward them: store-and-forward.
Efficient resource use: statistical multiplexing.
Ability to accommodate bursts.
University of Delaware CPEG 419

45. (Switched) Network Topologies
Ring
Tree
Star
Irregular
University of Delaware CPEG 419

46. University of Delaware CPEG 419
Protocol
Set of rules that allow peering entities to communicate.
Example: 2 friends talking on the phone.
Peering entities or peers: user application programs, file transfer services, services, etc.
University of Delaware CPEG 419