Introduction to Computer
Networks
CMPE 150
Fall 2005
Lecture 1
CMPE 150- Introduction to Computer Networks
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Class Information
• Class time and location:
– M, W, F from 2:00 – 3:10.
– E2 180
• Class Web page:
– http://www.cse.ucsc.edu/classes/cmpe150/Fall05
• Instructor:
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Katia Obraczka
E2 323
Office hours: TBD
katia@soe.ucsc.edu
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Class Information
• Teaching Assistant
– Sudharsan Rangarajan
• E-mail: sudrang@soe.ucsc.edu.
• Lab Assistants
– Jay Boice (boice@soe.ucsc.edu).
– Todd Nagengast (todd@soe.ucsc.edu).
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Textbook
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Pre-requisites
• CMPE 16
• CMPE 12C/L
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Focus
• Intro to data networks from an engineering
perspective.
• Broad coverage.
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Network architectures.
Network protocols,
Layered design.
Protocol stack.
TCP/IP and the Internet,
• Hands-on aspect.
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Topics Covered
• Introduction and
Overview.
• Physical Layer.
• Medium Access Control
(MAC).
• Link Layer.
• Network Layer.
• Routing.
CMPE 150- Introduction to Computer Networks
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Internetworking and IP.
IP Routing and Control.
Transport Layer.
Application Layer.
Putting It All Together!
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Other Networking Courses
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CE 151
CE 152
CE 156
CE 107
EE 103
CE 154
CE 153
EE 151
CE 108
CE 163
CS 111
Network Administration
Protocols
Network Programming
Stochastic System Analysis
Signals and Systems
Data Communication
Digital Signal Processing
Communications Systems
Data Compression
Multimedia
Operating Systems
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Grading
• Mid-term
• Assignments
35%
25%
– Homework
– Labs
• Final
40%
No credit for work that is not your own.
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Academic Integrity
• Academic integrity policies will be strictly
enforced!
• Academic integrity policy violations will NOT
be tolerated!
• http://www.ucsc.edu/academics/academic_integrity/policy.html
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Course Outline
• Introduction
– History, basic concepts, terminology.
– More, “not-so-basic” concepts:protocols, layering,, etc.
• Physical layer
– Transmitting data.
• Data link layer
– Reliable transmission.
– Accessing the communication medium
• Medium access control protocols.
• LANs
– Ethernet, token ring, wireless LANs.
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Course Outline (cont’d)
• Network layer
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Types of network services.
Circuit- vs. packet switching.
Virtual circuits and datagrams.
Routing.
Addressing.
Unicast and multicast.
• Internetworking
– IP.
– The Internet.
– IP Routing and Control.
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Course Outline (cont’d)
• Transport layer
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E2E communication..
Types of transport service.
Connectionless versus connection-oriented.
UDP.
TCP.
• Application layer
– DNS, ssh, telnet, ftp, news, e-mail.
– The Web.
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HTTP.
HTML.
Search engines.
Proxy and caches
– Peer-to-peer.
– Security.
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What’s a network?
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What’s a network?
• Merriam-Webster Dictionary:
– “|A fabric or structure of cords or wires that
cross at regular intervals…”
– “A system of computers, terminals and
databases connected by communication lines”
• “A computer network is defined as the
interconnection of 2 or more independent
computers.” [Ramteke,”Networks”, pg. 24].
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Why network?
• Before networks:
– One large computer (mainframe) used for all
processing in businesses, universities, etc.
• Smaller, cheaper computers…
– Personal computers or workstations on
desktops.
– Interconnecting many smaller computers is
advantageous! Why?
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Ubiquitous Computing
• Computers everywhere.
• Also means ubiquitous communication.
– Users connected anywhere/anytime.
– PC (laptop, palmtop) equivalent to cell phone.
• Networking computers together is critical!
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Computer Network
• Provide access to local and remote resources.
• Collection of interconnected end systems:
– Computing devices (mainframes, workstations,
PCs, palm tops)
– Peripherals (printers, scanners, terminals).
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Why network?
• Resource sharing!
– Hardware: printers, disks, terminals, etc.
– Software: text processors, compilers, etc.
– Data.
• Robustness.
– Fault tolerance through redundancy.
• Load balancing.
– Processing and data can be distributed over
the network.
• Location independence.
– Users can access their files, etc. from
anywhere in the network.
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Problems?
• Security!
– It’s much easier to protect centralized
resources than when they are distributed.
– Network itself as the target..
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Some History
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Before the Internet
• Postal network.
– Delivers different types of objects (letters,
packages, etc.) world-wide.
– Relatively high delay but relatively cheap.
– Sender and receiver identified by their postal
address (name, number, street, city, etc.).
• Telephone network.
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Engineered to deliver real-time voice.
Also world-wide.
Low delay but more expensive.
Users identified but telephone number.
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The Telephone Network
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The Telephone Network
• Telephone was patented by G. Bell in 1876.
• For one telephone to be able to talk with
another telephone, a direct connection
between the two telephones was needed.
– Within one year, cities were covered with a
wild jumble of wires!
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The Telephone Network (cont’d)
• In 1878, the Bell Telephone company opened
its first switching office (in New Haven, CT).
• Each user would connect to the local
switching office.
– When a user wanted to make a call, s/he rang
to the office, and would be manually
connected to the other end.
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The Telephone Network (cont’d)
• To allow for long-distance calls, switching
offices (switches) were connected .
• Several connections can go through interswitch trunks simultaneously.
• At some point, there were too many
connections between switching offices!
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The Telephone Network (cont’d)
• Thus, a second-level hierarchy was added.
• The current telephone system has at least
five levels of hierarchy.
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Addressing
• Uniquely identifies users.
• Examples:
– Postal address, telephone number.
• Types of addresses:
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Flat.
Hierarchical.
Are postal addresses flat or hierarchical?
And phone numbers?
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POTS or PSTN
• For over 100 years, the POTS (Plain Old
Telephone System) a.k.a. PSTN (Public
Switched Telephone Network) handles voiceband communications.
• The PSTN is well designed and engineered for
the transmission and switching of voice
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Real-time.
Low latency.
High reliability.
Moderate fidelity.
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Evolution of Communications
Networks
• About 30 years ago, a second communications
network was created with the goal of providing a
better transport mechanism for data.
• In this class, we will study the technology
underpinning data networks.
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Communication Model
Network
Source
CMPE 150- Introduction to Computer Networks
Destination
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Simplified Communication Model
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Components
• End systems (or hosts),
• Routers/switches/bridges, and
• Links (twisted pair, coaxial cable, fiber, radio,
etc.).
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Components (cont’d)
• Source
– generates data to be transmitted
• Transmitter
– Converts data into transmittable signals
• Transmission System
– Carries data
• Receiver
– Converts received signal into data
• Destination
– Takes incoming data
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Simplified Data Communications
Model
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Key Tasks
• Transmission.
• Signal Generation.
• Synchronization.
• Error detection and correction.
• Addressing and routing
• End-to-end Recovery.
• Security.
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Networking
• Point to point communication not usually
practical
– Devices are too far apart.
– Large set of devices would need impractical
number of connections.
• Solution is a communications network.
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Simplified Network Model
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