CS 4622 Computer Networks

1. CS 4622 Computer Networks Dr. Clincy Professor of CS • The prerequisite for CS4622 was recently removed from CS3503 with no replacement – will need to cover the prerequisite in this course (scientific fundamentals versus applied) (i.e. like you did in CS3503 as it relates to computers) • As a result of the above bullet item, no group project and some CS4622 topics will not be covered Intro and Lecture

2. Kick Off Behrouz Forouzan, Data Communications & Networking 4th Edition (handouts provided) Intro and Lecture

3. Tentative Course Outline:Subject to Change Intro and Lecture

4. Tentative Course Schedule:Subject to Change • Explain how the lectures after exams are online • Explain Blue represent lectures online • Explain last week – attending conference Intro and Lecture

5. Assessment • will curve GRADES if the SCORE AVERAGE is lower than 70 (curving vs bell-curve approach, TCP/IP new topic) (give example of curving concept – next bullet) • No make-up exams – last exam will count for missed exam – can miss only 1 exam • If last exam is missed, replaced with 70% of the average of the first three exams Intro and Lecture

6. Lesson in Stats – Example of Curving Grades – Raw Score to Final Grade What is an Avg ? What is the SD ? This is the curve Fitting raw scores to a curve ? = 90 + (RS-77)/1.4 ? = 80 + (RS-63)/1.4 ? = 70 + (RS-49)/1.4 ? = 60 + (RS-35)/1.4 Intro and Lecture

7. General Policies and Expectations: • Attendance at all classes is highly encouraged but NOT required. Concepts and ideas discussed in one class are used as building blocks for more concepts and ideas in the next class. • Any class session missed by the student is the student's responsibility to make up. • Makeup exams will NOT be given; instead, the last exam will count in place of the missed exam. If last exam missed, replaced with 70% of average of other exams. • Exams should be returned to the Professor in class right after the review for the student to receive a grade. Grades are not logged until the students have reviewed the exams for grading mistakes. If students take the exam from the classroom, a grading penalty of 50% will be used due to the fact the Professor has no real way of determining if the exam was tampered with or not. • Project assignments MUST be turned in on time to receive full credit. Late project assignments will be graded severely – for each day the assignment is late, the assignment’s grade will be reduced by 20%. • Students will not be allowed to makeup missed project assignments. • It’s hard to teach a subject like TCP/IP from a single source. The Professor will use multiple sources to teach various concepts – multiple sources such as (1) text book, (2) lecture notes, (3) handouts, (4) URL’s, and (5) project assignments. Every topic detail WILL NOT necessarily be found in the our text. • Students are expected to read the text and any other supporting documentation the Professor distributes. Intro and Lecture

8. General Policies and Expectations: • In being successful in this subject, expect a minimum of 2-3 hours of study per hour of lecture (6-9 hours per week) • The Professor expects students to take advantage of office hours when needing clarification or help. • The Professor greatly supports students sending emails at any time – it will be the goal of the Professor to reply to emails within a 24-hour time span (not counting weekends). • Be sure and provide the Professor a functioning personal email address for you (on your Sign-up List) – already has KSU address • Lecture notes purpose: serve as a guide to the Professor – help organize and time lecture • Guarantee: current lecture notes will be posted before the next up-and-coming lecture (ie. lecture notes 1 will be posted before lecture 2 occurs) • See syllabus for withdrawal policy, enrollment policy, and the Academic Integrity Statement. Be sure and give me the signed copy at the next class meeting • Go to my website for a syllabus and lecture notes Intro and Lecture

9. Chapter 2 (handout 1– only sections 2.1, 2.2 and 2.3) Dr. Clincy Professor of CS Intro and Lecture

10. Why Study OSI? Open Systems Interconnection (OSI) Reference Model • An excellent model for conceptualizing and understanding data communications • More granularity in functionality - more functional delineation • Key points: • Modular • Hierarchical (chain of command, pecking order) • Boundaries between layers (called interfaces) NOTE: the protocols or functionality with in the layer could change however, the interface remains the same – this facilitates the flexibility Intro and Lecture

11. Advantages of Layering • Easier application development • Network can change without all programs being modified • Breaks complex tasks into subtasks • Each layer handles a specific subset of tasks • Communication occurs • between different layers on the same node or stack (INTERFACES) • between similar layers on different nodes or stacks (PEER-TO-PEER PROCESSES) Intro and Lecture

12. Top Layer Top Layer Some Intermediate Layer Some Intermediate Layer Bottom Layer Bottom Layer OSI’s Layered Approach Example Network A Network B Actual commands invoked, presentation Facilitate the actual communications Network interfaces, raw bits How does peer-to-peer communication work ? Intro and Lecture

13. Open Systems Interconnection Developed by ISO (International Organization for Standardization) Contains seven layers Application Presentation Session Transport Network Data Link Physical OSI Intro and Lecture

14. OSI’s Layered Approach • between different layers on the same node or stack (INTERFACE) • between similar layers on different nodes or stacks (PEER-TO-PEER PROCESSES) Intro and Lecture

15. OSI Reference Model ? • Bottom 3 layers (Data Comm Layers) • Responsible for getting data or info to destination • Routing and switching occurs • Define the electrical and physical standards • Performs bit ordering, transmission of the bits, and error detecting and correcting • Top 4 layers • Creation and interpretation of the data • Protocols for data formatting, message syntax, dialogue management, message sequences and info presentation are used Intro and Lecture

16. OSI Physical Layer (Old CS3501) • Responsible for transmission of bits • Always implemented through hardware • Encompasses mechanical, electrical, and functional interfaces • Encoding and Decoding issues: how 0’s and 1’s are converted to signals • Signal translation (ie. electrical to optical) • Signal Multiplexing and Demultiplexing • Signal Modulation and Demodulation • Transport medium: Coaxial, Twisted Pair, Optical, etc.. • Transmission Rate/Data Rate – how fast to send bits • Transmission mode: transmission direction (simplex, duplex) • Physical Topology: network layout Intro and Lecture

17. Actually sends the packets (groups of frames) from node to node using a routing algorithm Network Layer Data Link Layer Takes raw data (bits) and transform them into frames, error control, etc. Transmit and receive the raw data (bits) Physical Layer OSI Data Link Layer (partially Old CS3501/3503 and CS4622) • Responsible for error-free, reliable transmission of data • Framing, Flow control, Error control (detection/correction), Access Methods • Makes use of physical address because with in the same network Intro and Lecture

18. OSI Network Layer (CS4622) • Responsible for routing of messages through networks • Concerned with type of switching used (circuit v. packet) • Handles routing among different networks • NOTE: with in the same network, only the DATA LINK layer is needed – amongst multiple networks, the NETWORK LAYER is needed • No need for routing with in the same network (LAN) • Routing across “internetworks” • Makes use of logical address vs physical address because not with in the same network Intro and Lecture

19. OSI Network Layer (CS4622) Intro and Lecture

20. Bottom 3 layers – Data Comm Layers Application Presentation Session Transport Network Data Link Physical OSI Lecture

21. OSI Upper Layers • Application • Presentation • Session • Transport • Peer-to-Peer Processes ….. • End-to-End nodes only Lecture

22. OSI Transport Layer • Isolates messages from lower and upper layers • Breaks down message size (segmentation) (down) and performs re-assembly (up) • Monitors quality of communications channel (oversee all hops) • Selects most efficient communication service necessary for a given transmission (could change over hops) • Flow and Error control for Source and Sink Lecture

23. OSI Session Layer • Establishes logical connections between systems (up/down) • Manages log-ons, password exchange, log-offs (up/down) • Terminates connection at end of session (up/down) Lecture

24. OSI Presentation Layer • Provides format and code conversion services • Examples • File conversion from ASCII to EBDIC • Invoking character sequences to generate bold, italics, etc on a printer • The source and sink could operate using different encoding schemes – the presentation layer makes the translations • Security • Compression Lecture

25. OSI Application Layer • Provides access to network for end-user (end-user being a human being or software application) • User’s capabilities are determined by what items are available on this layer (ie. remote log-in, file transfer, email service, directory service, etc.) Lecture

26. Recap: What happens at the Intermediate Nodes ? Rx Tx 7 Intermediate Nodes 3 1 1 B C Q T A Z Lecture

27. COMPLEXITY TO CONSIDER • Any particular node in an internetwork can be functioning as follows simultaneously: • Tx to other internetwork nodes • Rx from other internetwork nodes • Intermediate node to some other internetwork nodes Lecture

28. The File Transfer Program issues a command to the Application Layer Application passes it to Presentation, which may reformat, encrypt, encode, compress, passes to Session (adds overhead) Session requests a connection, passes to Transport (adds overhead) Transport breaks file into chunks, adds error-checking and flow-control info, process-to-process, passes to Network (adds overhead) Network selects the data’s route (internetworking), passes to Data Link (adds overhead) Data Link adds error-control and flow-control info, passes to Physical (adds overhead) Physical translates bits to signal and transmits the signal, which includes information added by each layer OSI in Action: Outgoing File Transfer Lecture

29. Physical receives signal and translates to bits, passes to Data Link Data Link checks for errors and performs flow control on bits, formulates bits into some formation (frames), passes to Network Network verifies routing (if intermediate node, determines next hop), passes to Transport Transport checks for errors and performs flow control on the chunks, reassembles the chunks, passes to Session Session determines if transfer is complete, may end session, passes to Presentation Presentation may reformat, perform conversions, decode, decrypt, decompress, pass to Application layer Application presents results to user (e.g. updates FTP program display) OSI in Action: Incoming File Transfer Lecture

30. US Postal System Analogy • Illustrate how the US Postal System is very similar to how networking works • Will help students better understand (versus memorize) data comm and networking Upper Layers – creating and interpreting the signal, data or info Lower Layers – getting the signal from one place to the next