Recap of Layers Application, Data Link and Physical

Network Layers Computer 1Computer 2 2

Application Layer 3 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

Application Layer Characteristics 4 * From Business Data Communications (Manish Agrawal)

Application Architecture Splitting the work across the client and the server Basic Software Components: Presentation Logic Application Logic Data Access Logic Data Types of Architectures: Host (or Server) Based Client Based Client/Server Based 5

How the web and work: Web: HTTP Request sent from a client to a server What is included in the request? Server responds back with an HTTP Response What is included in the response? SMTP Packet sent from client to server POP IMAP 6

Network Layers Computer 1Computer 2 7

Introduction - Transport layer 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 Transport Layer Application Layer Network Layer 8

Network Layers Computer 1Computer 2 9

Introduction – Network 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 Network Layer Transport Layer Data Link Layer 10

Network Layers Computer 1Computer 2 11

Data Link Layer - Introduction 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 12

4.1 Media Access Control (MAC) Controlling when and what computer transmit  Important when more than one computer wants to send data at the same time over the same, shared circuit Point-to-point half duplex links Multipoint configurations Two possible approaches  Controlled access  Contention based access 13

Source of Error What causes itHow to prevent it Line Outages Faulty equipment, Storms, Accidents (circuit fails) White Noise Movement of electrons (thermal energy) Increase signal strength (increase SNR) Impulse Noise Sudden increases in electricity (e.g., lightning, power surges) Shield or move the wires Cross-talk Multiplexer guard bands are too small or wires too close together Increase the guard bands, or move or shield the wires Echo Poor connections (causing signal to be reflected back to the source) Fix the connections, or tune equipment Attenuation Gradual decrease in signal over distance (weakening of a signal) Use repeaters or amplifiers Intermodulation Noise Signals from several circuits combine Move or shield the wires Jitter Analog signals change (small changes in amp., freq., and phase) Tune equipment Harmonic Distortion Amplifier changes phase (does not correctly amplify its input signal) Tune equipment Error Control - Sources of Errors and Prevention mostly on analog More important 14

Major Functions of Error Control Error prevention Error detection Parity checks Check Sum Cyclic Redundancy Check (CRC) Error correction Retransmission Stop and Wait ARQ (A half duplex technique) Continuous ARQ (A full duplex technique) Forward Error Correction 15

Network Layers Computer 1Computer 2 16

Physical Layer - Overview 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. 17 Physical Layer Network Layer Data Link Layer

Circuit Configurations & Data Flow 18 Configuration: Basic physical layout of the circuit Configuration types:  Point-to-Point Configuration  Multipoint Configuration Data Flow (Transmission): Simplex Half-Duplex Full-Duplex Multiplexing

Media 19 Physical matter that carries the transmission Signal transmitting properties of chosen media are important Types: Guided Media Radiated (Unguided) Media

Data Transmission Data - Representation of facts in a formalized manner suitable for communication, interpretation, or processing by humans or by automatic means Signal - Detectable transmitted energy that can be used to carry information Bits in a message can be sent on:  a single wire one after another (Serial transmission)  multiple wires simultaneously (Parallel transmission) Modes of transmission: Serial Mode Parallel Mode 20

Transmission Types Digital Transmission (Digital Data) – Voltage Encoding Unipolar Bipolar NRZ Bipolar RZ Analog Transmission (Digital Data) – Modulation Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM) Digital Transmission (Analog Data)  Requires a pair of special devices called Codec - Coder/decoder A device that converts an analog voice signal into digital form Converts it back to analog data at the receiving end Used by the phone system 21