1CMPE 150- Introduction to Computer Networks

CMPE 150

Fall 2005Lecture 1

Introduction to Computer Networks

2CMPE 150- Introduction to Computer Networks

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:– 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.– 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.

• Internetworking and IP.• IP Routing and Control.• Transport Layer.• Application Layer.• Putting It All Together!

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Other Networking Courses• CE 151 Network Administration• CE 152 Protocols• CE 156 Network Programming• CE 107 Stochastic System Analysis • EE 103 Signals and Systems • CE 154 Data Communication • CE 153 Digital Signal Processing• EE 151 Communications Systems• CE 108 Data Compression• CE 163 Multimedia• CS 111 Operating Systems

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Grading• Mid-term 35%• Assignments 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– 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

– E2E communication..– Types of transport service.– Connectionless versus connection-oriented.– UDP.– TCP.

• Application layer– DNS, ssh, telnet, ftp, news, e-mail.– The Web.

• 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.– 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 inter-switch trunks simultaneously.

• At some point, there were too many connections between switching offices!

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• Thus, a second-level hierarchy was added.

• The current telephone system has at least five levels of hierarchy.

The Telephone Network (cont’d)

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Addressing

• Uniquely identifies users.• Examples: – Postal address, telephone number.

• Types of addresses:– 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 voice-band communications.

• The PSTN is well designed and engineered for the transmission and switching of voice– 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 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