1. Dr. ClincyLecture1 Chapter 2 (handout 1– only sections 2.1, 2.2 and 2.3) 1 of 10 Dr. Clincy Professor of CS Exam #3 Monday (3/14/16): Opened Book, No Computer, No Phone: All Chapter 4 (except 4.14) and sections 5.1 and 5.2 (and all related lectures) Lab 8 Posted on website

2. Dr. ClincyLecture2 Why Study OSI? 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) Open Systems Interconnection (OSI) Reference Model In understanding the “full scope” of data communications and networking is VERY COMPLEX (and convoluted) Packet Switch Versus Circuit Switch

3. Dr. ClincyLecture 23 Internet – Underlying Technologies The Internet is an interconnection of “backbone” networks JOINED together via routers, gateways and switches Internet is comprised of LANs, Point-to-Point WANs and Switched WANs LAN Examples: Ethernet, Token Ring (not in book), Wireless and FDDI Ring (not in book) Pt-to-Pt WAN Examples: Telephony Modem, DSL, Cable/Modem, T-Lines and SONET Switched WAN Examples: X.25, Frame Relay and ATM Routers, Gateways, Bridges, Brouters, Modems, Switches Domain also includes Tx Issues Rx Issues Networked Applications Servers Storage Systems

4. Dr. ClincyLecture4 OSI Model Open Systems Interconnection Developed by ISO (International Organization for Standardization) Contains seven layers Application Presentation Session Transport Network Data Link Physical Note 1: CS3501 focuses on layer 1 (Physical Layer) Note 2: CS4622 focuses on layers 2 – 4 (TCP/IP)

5. Dr. ClincyLecture5 OSI Reference Model ? Bottom 3 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

6. Dr. ClincyLecture6 OSI Physical Layer 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

7. Dr. ClincyLecture7 OSI Data Link Layer 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 Network Layer Data Link Layer Physical Layer Actually sends the packets (groups of frames) from node to node using a routing algorithm Takes raw data (bits) and transform them into frames, error control, etc. Transmit and receive the raw data (bits)

8. Dr. ClincyLecture8 OSI Network Layer 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 Fragmentation occurs at this layer - explain

9. Dr. ClincyLecture9 OSI Network Layer

10. Dr. ClincyLecture10 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

11. Dr. ClincyLecture11 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) Three-way handshake

12. Dr. ClincyLecture12 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

13. Dr. ClincyLecture13 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.)