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Midterm Review - Network Layers Computer 1 Computer 2 2 Application Layer (Chapter 2) Applications Application Layer (e.g., email, web, word processing) 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 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 2.2 Various Architectures Host-Based Client-Based Client-Server Based • Thin Client/Thick Client Multi-Tier Architectures 5 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 Computer 1 Computer 2 7 Transport layer (Chapter 5) Responsible for end-to-end delivery of messages Application Layer Responsible for segmentation and reassembly Transport Layer Breaking the message into several smaller Network Layer pieces at the sending end Reconstructing the original message into a single whole at the receiving end Interacts with Application Layer 8 Transmission Control Protocol (TCP) • Links the application layer to the network layer • Performs packetization and reassembly • Ensures reliable delivery of packets TCP Header How many bytes does the TCP header add to a message? 24 bytes (if option used) or 20 bytes w/out option 9 Packetization and Reassembly Application layer sees message as a single block of data TCP packetization FTP FTP TCP TCP IP IP receiver sender TCP reassembly What size packet to use? Done through negotiations Delivers incoming packets as they arrive (e.g., Web pages) or to wait until entire message arrives (e.g., e-mail) 10 5.2.2 Linking to Application Layer TCP may serve several Application Layer protocols at the same time Problem Solution How do we know what number the server uses? HTTP FTP SMTP 80 21 25 TCP Standards What would be the other type of number used and why? Non- Standard Port requiring further configuration (provides greater security 5 - 11 … 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? 5 - 12 Computer 1 Computer 2 13 Network Layer (Chapter 5) Responsible for addressing and routing of messages Selects best path from computer to computer until the message reaches destination Transport Layer Performs encapsulation on sending end Adds network layer header to message segments Network Layer Data Link Layer Performs decapsulation on receiving end Removes the network layer header at receiving end and passes them up to the transport layer 14 IP Packet Formats: IPv4 (24 bytes) vs. IPv6 (40 bytes) IPv4 IPv6 15 5.1 Types of Addresses • Application Layer Address • Assignment • How do we get the URL’s IP address? • How do this work? • Address Resolution Application Layer Transport Layer Network Layer • Network Layer Address • Assignment (Subnets) • What is sent out to assign IP Address? Data Link Layer • Data Link Layer Address • Assignment • What is sent out if MAC Address is unknown? 5 - 16 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 a given destination Kept by computers making routing decisions Dest. Next B B C B D D E D F D G B to reach Routers Special purpose devices used to handle routing decisions on the Internet Maintain their own routing tables 5 - 17 Network Layers Computer 1 Computer 2 18 Data Link Layer (Chapter 4) Responsible for moving messages from one device to another Network Layer Controls the way messages are sent on media Data Link Layer Physical Layer 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 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 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 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 4.4 Data Link Protocols Classification Asynchronous transmission Synchronous transmission Differ by frame k-1 frame k frame k+1 Message delineation Frame length Frame field structure 23 Network Layers Computer 1 Computer 2 24 Physical Layer (Chapter 3) Includes network hardware and circuits Network Layer Data Link Layer Physical Layer 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. 25 3.1 Circuits Physical connection (wire) Configuration types (physical layout of the circuit): Point-to-Point Configuration Multipoint Configuration 26 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 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 28 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 3.2 Media Summary 30 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 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 Overall Efficiency of Transmissions You want to transmit a 500 byte email message. What would be the efficiency in transmitting this message? Overhead: • SMTP: 100 bytes (could be variable) • TCP: 24 bytes • IP: 24 bytes • Ethernet: 34 bytes EFF = [# of data bytes]/ [#data bytes + # of overhead] EFF = 500/(500+100+24+24+34) = 73% What about an HTTP file of 4000 bytes? 33