Networking H15 Analog and Digital Data Data, Signal, Transmission Encoding and Decoding ( Amplitude Shift, Frequency Shift, PCM etc.) Transmission Simplex, Half - Duplex, Duplex Serial and Parallel Transmission Synchronous + Asynchronous Transmission impairments Attenuation and Attenuation Distortion

Networking H15 Media (twisted pair etc.) Switching Techniques Why do we need to switch? Switching Concepts(Crossbar, Multi-Stage) Message, Packet, Circuit Switching Multiplexing Frequency Division, Time Division, Statistical Time Division

Networking H15 8LANS and WANS 8Network Topologies Bus, Star, Ring 8Media Access Control Techniques 802.3, 802.4, Protocols 8Why would you want Protocols in the first place? 8OSI Model 8Interconnection Repeaters, Bridges, Routers, Hubs, Gateways

Networking H15 8TCP/IP Protocol and Addressing +WWW 8Frame Relay, Cell Relay, FDDI etc 8X Step Approach to Network Design 8Wireless Networks 8Distributed Computing 8Client Server 8Technologies in Client Server 8Middleware 8Groupware

Communication considerations 1)AHHH!! What do those electrical signals mean? 2)How can I send a bit, what signal do I use for 0 and which for 1? 3)How do devices make use of the wire? 4)How do I derive meaningful information from all of these bits 5)How are transmission errors discovered and dealt with? 6)How do packets get from one system to another?

Communication Considerations 1)How do I send large amounts of data and how do I ensure that I receive all of my data? 2)How do machines keep track of who there are talking to? 3)What language is this, how can I the computer understand different formats? 4)How does a user gain access to the network? 5)How do programmers write programs to use the network?

Our solution the OSI model 8Application 8Presentation 8Session 8Transport 8Network 8Data link 8Physical

What is a Protocol? 8Allows entities (i.e. application programs) from different systems to communicate 8Shared conventions for communicating information are called protocols 8Includes syntax, semantics, and timing

Why Use Protocol Architecture? 8Data communications requires complex procedures 8Sender identifies data path/receiver 8Systems negotiate preparedness 8Applications negotiate preparedness 8Translation of file formats 8For all tasks to occur, high level of cooperation is required

Modular Approach 8Breaks complex tasks into subtasks 8Each module handles specific subset of tasks 8Communication occurs 8between different modules on the same system 8between similar modules on different systems

OSI Lower Layers 8Physical 8Data Link 8Network

OSI Physical Layer 8Concerned with transmission of unstructured bit stream over physical medium 8Deals with accessing the physical medium 8Mechanical characteristics 8Electrical characteristics 8Functional characteristics 8Procedural characteristics

OSI Data Link Layer 8Responsible for error-free, reliable transmission of data 8Flow control, error correction

OSI Network Layer 8Responsible for routing of messages through network 8Concerned with type of switching used (circuit v. packet) 8Handles routing between networks, as well as through packet-switching networks

OSI Upper Layers 8Transport 8Session 8Presentation 8Application

OSI Transport Layer 8Isolates messages from lower and upper layers 8Breaks down message size 8Monitors quality of communications channel 8Selects most efficient communication service necessary for a given transmission

OSI Session Layer 8Establishes logical connections between systems 8Manages log-ons, password exchange, log- offs 8Terminates connection at end of session

OSI Presentation Layer 8Provides format and code conversion services 8Examples 8File conversion from ASCII to EBDIC 8Invoking character sequences to generate bold, italics, etc on a printer

OSI Application Layer 8Provides access to network for end-user 8User’s capabilities are determined by what items are available on this layer

OSI in Action: Outgoing File Transfer 8Program issues command to Application Layer 8Application passes it to Presentation, which may reformat, passes to Session 8Session requests a connection, passes to Transport 8Transport breaks file into chunks, passes to Network 8Network selects the data’s route, passes to Data Link 8Data Link adds error- checking info, passes to Physical 8Physical transmits data, which includes information added by each layer

OSI in Action: Incoming File Transfer 8Physical receives bits, passes to Data Link 8Data Link checks for errors, passes to Network 8Network verifies routing, passes to Transport 8Transport reassembles data, passes to Session 8Session determines if transfer is complete, may end session, passes to Presentation 8Presentation may reformat, perform conversions, pass to Application layer 8Application presents results to user (e.g. updates FTP program display)

Data Communication Terms 8Data - entities that convey meaning, or information 8Signals - electric or electromagnetic representations of data 8Transmission - communication of data by the propagation and processing of signals

Examples of Analog and Digital Data 8Analog 8Video 8Audio 8Digital 8Text 8Integers

Analog Signals 8A continuously varying electromagnetic wave that may be propagated over a variety of media, depending on frequency 8Examples of media: 8Copper wire media (twisted pair and coaxial cable) 8Fiber optic cable 8Atmosphere or space propagation 8Analog signals can propagate analog and digital data

Digital Signals 8A sequence of voltage pulses that may be transmitted over a copper wire medium 8Generally cheaper than analog signaling 8Less susceptible to noise interference 8Suffer more from attenuation 8Digital signals can propagate analog and digital data

Analog Signaling

Digital Signaling

Reasons for Choosing Data and Signal Combinations 8Digital data, digital signal 8Equipment for encoding is less expensive than digital- to-analog equipment 8Analog data, digital signal 8Conversion permits use of modern digital transmission and switching equipment 8Digital data, analog signal 8Some transmission media will only propagate analog signals 8Examples include optical fiber and satellite 8Analog data, analog signal 8Analog data easily converted to analog signal

Analog Transmission 8Transmit analog signals without regard to content 8Attenuation limits length of transmission link 8Cascaded amplifiers boost signal’s energy for longer distances but cause distortion 8Analog data can tolerate distortion 8Introduces errors in digital data

Digital Transmission 8Concerned with the content of the signal 8Attenuation endangers integrity of data 8Digital Signal 8Repeaters achieve greater distance 8Repeaters recover the signal and retransmit 8Analog signal carrying digital data 8Retransmission device recovers the digital data from analog signal 8Generates new, clean analog signal

About Channel Capacity 8Impairments, such as noise, limit data rate that can be achieved 8Channel Capacity – the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions

Impairments and Capacity 8Impairments exist in all forms of data transmission 8Analog signal impairments result in random modifications that impair signal quality 8Digital signal impairments result in bit errors (1s and 0s transposed)

Transmission Impairments: Guided Media 8Attenuation 8loss of signal strength over distance 8Attenuation Distortion 8different losses at different frequencies 8Delay Distortion 8different speeds for different frequencies 8Noise 8distortions of signal caused by interference

Transmission Impairments: Unguided (Wireless) Media 8Free-Space Loss 8Signals disperse with distance 8Atmospheric Absorption 8Water vapor and oxygen contribute to signal loss 8Multipath 8Obstacles reflect signal creating multiple copies 8Refraction 8Noise

Types of Noise 8Thermal (aka “white noise”) 8Uniformly distributed, cannot be eliminated 8Intermodulation 8When different frequencies collide (creating “harmonics”) 8Crosstalk 8Overlap of signals 8Impulse noise 8Irregular spikes, less predictable

Why Use Analog Transmission? 8Already in place 8Significantly less expensive 8Lower attentuation rates 8Fully sufficient for transmission of voice signals

Analog Encoding of Digital Data 8Data encoding and decoding technique to represent data using the properties of analog waves 8Modulation: the conversion of digital signals to analog form 8Demodulation: the conversion of analog data signals back to digital form

Modem 8An acronym for modulator-demodulator 8Uses a constant-frequency signal known as a carrier signal 8Converts a series of binary voltage pulses into an analog signal by modulating the carrier signal 8The receiving modem translates the analog signal back into digital data

Methods of Modulation 8Amplitude modulation (AM) or amplitude shift keying (ASK) 8Frequency modulation (FM) or frequency shift keying (FSK) 8Phase modulation or phase shift keying (PSK)

Amplitude Shift Keying (ASK) 8In radio transmission, known as amplitude modulation (AM) 8The amplitude (or height) of the sine wave varies to transmit the ones and zeros 8Major disadvantage is that telephone lines are very susceptible to variations in transmission quality that can affect amplitude

100 1 ASK Illustration

Frequency Shift Keying (FSK) 8In radio transmission, known as frequency modulation (FM) 8Frequency of the carrier wave varies in accordance with the signal to be sent 8Signal transmitted at constant amplitude 8More resistant to noise than ASK 8Less attractive because it requires more analog bandwidth than ASK

FSK Illustration

Phase Shift Keying (PSK) 8Also known as phase modulation (PM) 8Frequency and amplitude of the carrier signal are kept constant 8The carrier signal is shifted in phase according to the input data stream 8Each phase can have a constant value, or value can be based on whether or not phase changes (differential keying)

0011 PSK Illustration

011 Differential Phase Shift Keying (DPSK) 0

Analog Channel Capacity: BPS vs. Baud 8Baud=# of signal changes per second 8BPS=bits per second 8In early modems only, baud=BPS 8Each signal change can represent more than one bit, through complex modulation of amplitude, frequency, and/or phase 8Increases information-carrying capacity of a channel without increasing bandwidth 8Increased combinations also leads to increased likelihood of errors