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Midterm Review - Network Layers

Learn about the various layers in computer networks and how they enable communication between computers. Explore application architecture, session management, routing, and error control.

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Midterm Review - Network Layers

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  1. Midterm Review - Network Layers

  2. Computer 1 Computer 2 2

  3. Application Layer (Chapter 2) Applications (e.g., email, web, word processing) Application Layer Transport Layer Network Layer • The software that enables the user to perform useful work • Application architecture • The way in which the functions of the application layer software are spread among the clients and servers on the network • Functions of Application Layer 3

  4. 2.1 Application Architecture • Splitting the work across the client and the server • Basic Software Components: • Presentation Logic • Application Logic • Data Access Logic • Data 4

  5. 2.2 Various Architectures • Host-Based • Client-Based • Client-Server Based • Thin Client/Thick Client • Multi-Tier Architectures 5

  6. 2.3 Sending HTTP Request & Email • Web Transmission • 2-Tier network – Client/Server • Thin Client • HTTP Request, HTTP Response • Email Transmission • 2-Tier network – Client Server • Thick and Thin Clients • SMTP, POP, IMAP 6

  7. Computer 1 Computer 2 7

  8. Transport layer (Chapter 5) Application Layer Transport Layer NetworkLayer • Responsible for end-to-end delivery of messages • Responsible for segmentation and • reassembly • Breaking the message into several smaller pieces at the sending end • Reconstructing the original message into a single whole at the receiving end • Interacts with Application Layer 8

  9. Transmission Control Protocol (TCP) • Links the application layer to the network layer • Performs packetization and reassembly • Ensures reliable delivery of packets How many bytes does the TCP header add to a message? 24 bytes (if option used) or 20 bytes w/out option TCP Header 9

  10. Packetization and Reassembly Application layer sees message as a single block of data FTP FTP TCP TCP TCP packetization IP IP sender receiver TCP reassembly What size packet to use? Delivers incoming packets as they arrive (e.g., Web pages) or to wait until entire message arrives (e.g., e-mail) Done through negotiations 10

  11. … FTP SMTP HTTP 80 21 25 TCP 5.2.2 Linking to Application Layer Standards Non- Standard Port requiring further configuration (provides greater security • TCP may serve several Application Layer protocols at the same time • Problem • Solution • How do we know what number • the server uses? • What would be the other type of number used and why?

  12. 5.2.3 Session Management • A session can be thought of as a conversation between two computers. • Types of Session Management • Connection Oriented • What is connection oriented? How does it work? • What protocols use connection oriented? • Why? • Connectionless Routing • What protocols use connectionless? • Why?

  13. Computer 1 Computer 2 13

  14. Network Layer (Chapter 5) Transport Layer Network Layer Data Link Layer • Responsible for addressing and routing of messages • Selects best path from computer to computer until the message reaches destination • Performs encapsulation on sending end • Adds network layer header to message segments • Performs decapsulation on receiving end • Removes the network layer header at receiving end and passes them up to the transport layer 14

  15. IP Packet Formats: IPv4 (24 bytes) vs. IPv6 (40 bytes) IPv4 IPv6 15

  16. 5.1 Types of Addresses • Application Layer Address • Assignment • How do we get the URL’s IP address? • How do this work? • Address Resolution • Network Layer Address • Assignment (Subnets) • What is sent out to assign IP Address? • Data Link Layer Address • Assignment • What is sent out if MAC Address is unknown? Application Layer Transport Layer Network Layer Data Link Layer

  17. Dest. B C D E F G Next B B D D D B 5.2 Routing • Process of identifying what path to have a packet take through a network from sender to receiver • Routing Tables • Used to make routing decisions • Shows which path to send packets on to reach a given destination • Kept by computers making routing decisions • Routers • Special purpose devices used to handle routing decisions on the Internet • Maintain their own routing tables

  18. Network Layers Computer 1 Computer 2

  19. Data Link Layer (Chapter 4) Network Layer Data Link Layer Physical Layer • Responsible for moving messages from • one device to another • Controls the way messages are sent on media • Organizes physical layer bit streams into • coherent messages for the network layer • Major functions of a data link layer protocol • Media Access Control • Error Control • Message Delineation 19

  20. 4.1 Media Access Control (MAC) • Controlling when and what computer transmit • Why used • When to use • Two possible approaches • Controlled access • Contention based access 20

  21. 4.2 Major Functions of Error Control • Error prevention • Error detection (how do these work, which is better?) • Parity checks (Even and Odd) • Cyclic Redundancy Check (CRC) • Error correction • Retransmission 21

  22. 4.3 Automatic Repeat reQuest (ARQ) • Process of requesting a data transmission be resent • Main ARQ protocols • Stop and Wait ARQ (A half duplex technique) • Continuous ARQ (A full duplex technique) • Flow Control • Window 22

  23. 4.4 Data Link Protocols frame k frame k-1 frame k+1 • Classification • Asynchronous transmission • Synchronous transmission • Differ by • Message delineation • Frame length • Frame field structure 23

  24. Network Layers Computer 1 Computer 2

  25. Physical Layer (Chapter 3) Network Layer Data Link Layer Physical Layer • Includes network hardware and circuits • Types of Circuits • Physical circuits connect devices & include actual wires • Logical circuits refer to the transmission characteristics of the circuit • Physical and logical circuits may be the same or different. For example, in multiplexing, one physical wire may carry several logical circuits.

  26. 3.1 Circuits Physical connection (wire) • Configuration types (physical layout of the circuit): • Point-to-Point Configuration • Multipoint Configuration 26

  27. 3.1.2 Data Flow (Transmission) • How does data flow through the circuit (circuits can be designed to permit data flow) Configuration types: • Simplex • Half-Duplex • Full-Duplex 27

  28. 3.1.3 Multiplexing • Breaking up a higher speed circuit into several slower (logical) circuits • Several devices can use it at the same time • Requires two multiplexer: one to combine; one to separate • Main advantage: cost • Fewer network circuits needed • Categories of multiplexing: • Frequency division multiplexing (FDM) • Time division multiplexing (TDM) • Inverse Multiplexing

  29. 3.2 Media – Guided Media • Physical matter that carries the transmission • Types: • Guided Media • Radiated (Unguided) Media • http://whatis.techtarget.com/definition/0,,sid9_gci214198,00.html • http://www.iupui.edu/~ilight/index.html 29

  30. 3.2 Media Summary 30

  31. 3.3 Transmission of Data • Computers produce binary data (0 or 1) (i.e. discrete, predictable values) • Standards needed to ensure both sender and receiver understands this data • Codes • Signals • Digital • Bipolar, Unipolar • Analog • Frequency, Amplitude, Phase 31

  32. 3.3 Transmission Modes • Bits in a message can be sent on: • a single wire one after another (Serial transmission) • multiple wires simultaneously (Parallel transmission) • Two Modes of transmission: • Serial Mode • Parallel Mode 32

  33. Overall Efficiency of Transmissions 100 bytes (could be variable) 24 bytes 24 bytes 34 bytes EFF = [# of data bytes]/ [#data bytes + # of overhead] EFF = 500/(500+100+24+24+34) = 73% • You want to transmit a 500 byte email message. What would be the efficiency in transmitting this message? • Overhead: • SMTP: • TCP: • IP: • Ethernet: • What about an HTTP file of 4000 bytes? 33

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