Assessment 1 Review Network Layers

Computer 1Computer 2 2

Application Layer (Chapter 2) 3 Application Layer Network Layer Transport Layer Applications (e.g., , web, word processing) 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

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

Network Layers 7 Computer 1Computer 2

Data Link Layer (Chapter 4) 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 Data Link Layer Physical Layer Network Layer 8

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 9

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 10

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 11

4.4 Data Link Protocols Classification  Asynchronous transmission  Synchronous transmission Differ by  Message delineation  Frame length  Frame field structure frame k frame k+1frame k-1 12

Network Layers 13 Computer 1Computer 2

Physical Layer (Chapter 3) 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. 14 Physical Layer Network Layer Data Link Layer

3.1 Circuits 15 Physical connection (wire) Configuration types (physical layout of the circuit):  Point-to-Point Configuration  Multipoint Configuration

3.1.2 Data Flow (Transmission) 16 How does data flow through the circuit (circuits can be designed to permit data flow) Configuration types:  Simplex  Half-Duplex  Full-Duplex

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 17

3.2 Media – Guided Media 18 Physical matter that carries the transmission Types: Guided Media Radiated (Unguided) Media

3.2 Media Summary 19

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 20

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 21