Computer Networks Class Notes - Class #1 CSC Computer Networks and Open Systems Villanova University Computer Science Department Fall 2001

2Villanova UniversityComputer Networks Agenda 4 Introductions 4 Objectives? 4 Review Syllabus (courtesy of Dr. Cassel) 4 Administrative Stuff 4 Overview of Computer Networks (see syllabus) 4 HTML (see syllabus) 4 Simple Web Forms (see syllabus) All students are expected to prepare for class, show up and participate.

3Villanova UniversityComputer Networks General Stuff 4 Syllabus available online at, – 4 Office Hours: Thursday’s from 4:00 - 6:00, room ? unix accounts have been setup on the CSC cluster and Doyle (G50) –See me after class for userid/passwd if not known 4 Network logins setup on PC’s in G50 4 Teaching Assistant - Hongyi Li

4Villanova UniversityComputer Networks General Stuff 4 Grading –No tests! –Class attendance/participation –Assignments –Extra effort 4 Text: –Computer Networks and Open Systems - An Application Development Perspective, Cassel and Austing 4 Feedback/questions?

5Villanova UniversityComputer Networks Additional Information 4 Computer Networks, Third Edition –Andrew S. Tannenbaum, Prentice Hall, Internet Request For Comments (RFC) –

6Villanova UniversityComputer Networks Overview of Computer Networks 4 Peer-to-peer networking only 4 Networking Benefits? –Shared resources, reliability, incremental growth, performance 4 Network issues affect every aspect of computing 4 Data Communications –Control/sharing of communications channel, message encoding, error handling, re-transmission, packetizing, packet ordering, etc. –Network Applications typically unaware of these lower-level issues/activities - TRANSPARENCY

7Villanova UniversityComputer Networks Overview of Computer Networks 4 Network requires 3 components: –Transmission medium; network interface; network software –Network software is similar to operating system software - assists user in gaining access to system resources and protects the system 4 Networks provide interoperability between processes –Cooperative operation depends on common understanding - agree on format/meaning of messages and conditions - called a PROTOCOL

8Villanova UniversityComputer Networks Overview of Computer Networks 4 Protocol Example (ConfirmAndDisplay) 4 Protocol Conflicts 4 Resolving conflicts (standards) –Select one of the competing protocols (de facto) –Drop existing protocols and develop a new one –Support multiple protocols –Keep original and support new global protocol

9Villanova UniversityComputer Networks Overview of Computer Networks 4 Layered Architecture –Services built from simpler services –Layer N makes services available to layer N+1 Services: a set of primitives that a layer provides to the layer above –Layering Principles: Each layer should, Represent a different level of abstraction Perform a well-defined function Be chosen to minimize information flow across interfaces Be reasonably sized - enough layers to allow for separating functions that do not below together but not too many layers that the architecture becomes unwieldy

10Villanova UniversityComputer Networks Overview of Computer Networks –Layers communicate Protocol Data Units (PDUs) between their peers - each layer encapsulates the previous layer’s PDU within the data section of its own PDU

11Villanova UniversityComputer Networks Overview of Computer Networks 4 Layering and the OSI model 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical 4 User-oriented services - layers 5 thru 7 Appl. PDU Presentation PDU Session PDU Transport PDU Network PDU Data Link PDU Data

12Villanova UniversityComputer Networks (insert slides with descriptions of each layer)

13Villanova UniversityComputer Networks Overview of Computer Networks 4 Protocol Suites –ARPA protocols - also called DoD, DDN or TCP/IP protocol suite. –SNA (hierarchical, generally not scalable) –APPN (IBM’s peer-to-peer protocol suite) –ISODE (ISO compliant, also supports ARPA) 4 Network Classifications –Local Area Networks (LAN) - “802” protocols –Wide Are Networks (WAN) - –Metropolitan Area Networks (MAN)

14Villanova UniversityComputer Networks Overview of Computer Networks 4 Topology (transparent to user) - LAN’s only –Daisy-chain –Bus –Ring –Star (or hub and spokes) –Tree 4 Internetworking –Repeaters - Physical layer –Bridges - Data Link layer –Routers - Network Layer –Gateways - Any layer

15Villanova UniversityComputer Networks HTML Documents 4 See syllabus

16Villanova UniversityComputer Networks Simple Web Forms 4 See syllabus

17Villanova UniversityComputer Networks Coming Up Next 4 Read chapters 1 & 2 4 Web Search exercise - due 9/6 4 Begin web design - due 9/20 4 Web Applications (2 of them) - due 11/8 and 12/6

Questions/Comments ???

19Villanova UniversityComputer Networks Class Feedback On a scale of 1 to 5, how helpful were the following: ___ Course material ___ Course exercises ___ Instructor’s presentation of material ___ Facilities General Feedback: __________________________________________________ _________________________________________________________________