Today’s Agenda 1. Do Lab 8 – will help with Exam 3 (1110am-1210pm) 2 Today’s Agenda 1. Do Lab 8 – will help with Exam 3 (1110am-1210pm) 2. Take Exam 3 (1210pm-125pm) 3. Lectures 20_21_22 (Inclass & Online) Dr. Clincy Lecture

Chapters 1 and 2 (Part 1 of 2) Dr. Clincy Lecture

OSI Reference Model The networking part of the course will be structured around the OSI reference model We will focus on the bottom 2 layers – similar to computer architecture (physical, data link) The 3rd and 4th layers will be covered in more advanced networking courses (network, transport) Dr. Clincy Lecture

OSI Reference Model Why Study OSI? Still an excellent model for conceptualizing and understanding protocol architectures More granularity in functionality - more functional delineation Key points: Modular Hierarchical (chain of command, pecking order) Boundaries between layers (called interfaces) NOTE: the protocols or functionality with in the layer could change however, the interface remains the same – this facilitates the flexibility Dr. Clincy Lecture

Advantages of Layering Easier application development Network can change without all programs being modified Breaks complex tasks into subtasks Each layer handles a specific subset of tasks Communication occurs between different layers on the same node or stack (INTERFACES) between similar layers on different nodes or stacks (PEER-TO-PEER PROCESSES Dr. Clincy Lecture

OSI’s Layered Approach Example Network A Network B Actual commands invoked, presentation Top Layer Some Intermediate Layer Bottom Layer Top Layer Some Intermediate Layer Bottom Layer Facilitate the actual communications Network interfaces, raw bits How does peer-to-peer communication work ? Dr. Clincy Lecture

OSI Application Open Systems Interconnection Presentation Session Transport Network Data Link Physical Open Systems Interconnection Developed by ISO (International Organization for Standardization) Contains seven layers Dr. Clincy Lecture

OSI’s Layered Approach between different layers on the same node or stack (INTERFACE) between similar layers on different nodes or stacks (PEER-TO-PEER PROCESSES) Dr. Clincy Lecture

OSI Reference Model ? Bottom 3 layers Top 4 layers Bottom 3 layers responsible for getting letter to destination (Bottom 3 layers): at the lower levels of the model protocols define the electrical and physical standards (Bottom 3 layers) at the lower levels, the bit ordering, the transmission of the bits, and error detecting and correcting are defined Top 4 layers at the higher levels of the model, the protocols define the data formatting, message syntax, dialogue management, message sequences and info presentation Dr. Clincy Lecture

OSI Physical Layer Responsible for transmission of bits Always implemented through hardware Encompasses mechanical, electrical, and functional interfaces Encoding and Decoding issues: how 0’s and 1’s are converted to signals Signal translation (ie. electrical to optical) Signal Multiplexing and Demultiplexing Signal Modulation and Demodulation Transport medium: Coaxial, Twisted Pair, Optical, etc.. Transmission Rate/Data Rate – how fast to send bits Transmission mode: transmission direction (simplex, duplex) Physical Topology: network layout Dr. Clincy Lecture

OSI Data Link Layer Responsible for error-free, reliable transmission of data Framing, Flow control, Error control (detection/correction), Access Methods Makes use of physical address because with in the same network Network Layer Data Link Layer Physical Layer Actually sends the packets (groups of frames) from node to node using a routing algorithm Takes raw data (bits) and transform them into frames, error control, etc. Transmit and receive the raw data (bits) Dr. Clincy Lecture

OSI Network Layer Responsible for routing of messages through networks Concerned with type of switching used (circuit v. packet) Handles routing among different networks NOTE: with in the same network, only the DATA LINK layer is needed – amongst multiple networks, the NETWORK LAYER is needed No need for routing with in the same network (LAN) Routing across “internetworks” Makes use of logical address vs physical address because not with in same network Dr. Clincy Lecture

OSI Network Layer Dr. Clincy Lecture

OSI Upper Layers Application Presentation Session Transport Peer-to-Peer Processes ….. End-to-End nodes only Dr. Clincy Lecture

OSI Transport Layer Isolates messages from lower and upper layers Breaks down message size (segmentation) (down) and performs re-assembly (up) Monitors quality of communications channel (oversee all hops) Selects most efficient communication service necessary for a given transmission (could change over hops) Flow and Error control for Source and Sink Dr. Clincy Lecture

OSI Session Layer Establishes logical connections between systems (up/down) Manages log-ons, password exchange, log-offs (up/down) Terminates connection at end of session (up/down) Dr. Clincy Lecture

OSI Presentation Layer Provides format and code conversion services Examples File conversion from ASCII to EBDIC Invoking character sequences to generate bold, italics, etc on a printer The source and sink could operate using different encoding schemes – the presentation layer makes the translations Security Compression Dr. Clincy Lecture

OSI Application Layer Provides access to network for end-user (end-user being a human being or software application) User’s capabilities are determined by what items are available on this layer (ie. remote log-in, file transfer, email service, directory service, etc.) Dr. Clincy Lecture

Recap: What happens at the Intermediate Nodes ? Rx Tx 7 Intermediate Nodes 3 1 1 B C Q T A Z Dr. Clincy Lecture

COMPLEXITY TO CONSIDER Any particular node in an internetwork can be functioning as follows simultaneously: Tx to other internetwork nodes Rx from other internetwork nodes Intermediate node to some other internetwork nodes Dr. Clincy Lecture

OSI in Action: Outgoing File Transfer The File Transfer Program issues a command to the Application Layer Application passes it to Presentation, which may reformat, encrypt, compress, passes to Session (adds overhead) Session requests a connection, passes to Transport (adds overhead) Transport breaks file into chunks, adds error-checking and flow-control info, process-to-process, passes to Network (adds overhead) Network selects the data’s route (internetworking), passes to Data Link (adds overhead) Data Link adds error-control and flow-control info, passes to Physical (adds overhead) Physical translates bits to signal and transmits the signal, which includes information added by each layer Dr. Clincy Lecture

OSI in Action: Incoming File Transfer Physical receives signal and translates to bits, passes to Data Link Data Link checks for errors and performs flow control on bits, formulates bits into some formation (frames), passes to Network Network verifies routing (if intermediate node, determines next hop), passes to Transport Transport checks for errors and performs flow control on the chunks, reassembles the chunks, passes to Session Session determines if transfer is complete, may end session, passes to Presentation Presentation may reformat, perform conversions, decode, decrypt, decompress, pass to Application layer Application presents results to user (e.g. updates FTP program display) Dr. Clincy Lecture

US Postal System Analogy Illustrate how the US Postal System is very similar to how networking works Will help students better understand (versus memorize) networking Upper Layers – creating and interpreting the signal, data or info Lower Layers – getting the signal from one place to the next Dr. Clincy Lecture

Chapter 3 Physical Layer and Media Dr. Clincy Lecture

Data Vs Signal Fully explain the difference between signal and data before getting into the details Dr. Clincy Lecture

Data vs Signals We have talked about digital and analog signals – what about analog and digital data ?? Analog data Voice Images Digital data Text Digitized voice or images Dr. Clincy Lecture

Electromagnetic Signals - Time Electromagnetic signal can be expressed as a function of time or frequency Function of time Analog (varies smoothly over time) Digital (constant level over time, followed by a change to another level) ie. sound ie. bits Dr. Clincy Lecture

Periodic Signal Characteristics If the signal’s pattern repeats over and over, we called these signals Periodic Signals Periodic Signals can be either Analog or Digital Dr. Clincy Lecture

Analog Periodic Signal Case Amplitude (A): signal value, measured in volts Frequency (f): repetition rate, cycles per second or Hertz Period (T): amount of time it takes for one repetition, T=1/f Phase (f): relative position in time, measured in degrees General sine wave is written as S(t) = A sin(2pft + f) Dr. Clincy Lecture

Varying S(t) = A sin(2pft + f) Dr. Clincy Lecture Note: 45 degrees because p is 180 degrees

What is Wavelength ? The distance an electromagnetic wave can travel in the amount of time it takes to oscillate through a complete cycle Wavelength (w) = signal velocity x period or propagation speed x period Recall: period = 1 / frequency Another perspective of Wavelength: how far did this signal travel AS the signal goes through a FULL cycle ? Dr. Clincy Lecture

Electromagnetic Signals Electromagnetic signal can be expressed as a function of time or frequency Function of frequency (more important) Dr. Clincy Lecture

Electromagnetic Signals - Frequency Electromagnetic signal can be expressed as a function of time or frequency Function of frequency (more important) Spectrum (range of frequencies) Bandwidth (width of the spectrum) When we talk about spectrum, we mean the range of frequencies the electromagnetic signal takes on In the example, the signal has a Frequency range of f to 3f Therefore, a electromagnetic signal can be a collection (addition) of periodic analog Signals (Composite Signal) Dr. Clincy Lecture

Composite Periodic Signal According to FOURIER ANALYSIS, a composite signal is a combination of sine waves with different amplitudes, frequencies and phases. Could converged to a square wave 3rd harmonic 9th harmonic Dr. Clincy Lecture

Electromagnetic Spectrum for Transmission Media Tell them how to study this chart Dr. Clincy Lecture

Digital Signaling represented by square waves or pulses Refers to transmission of electromagnetic pulses that represents 1’s and 0’s 1 cycle amplitude (volts) time (sec) frequency (hertz) = cycles per second Dr. Clincy Lecture

Digital Signal Rate Each bit’s signal has a certain duration Example, given a data rate of 50 kbps (or 50,000 bps) Each would have a 0.02 microseconds duration Duration (or bit length) = 1/50000 = .00002 sec = .02 msec Dr. Clincy Lecture

Digital Signal # bits per level = log2 x (#oflevels) Sending 1 bit per level Sending 2 bits per level How many levels needed to send 5 bits at a time ???? # bits per level = log2 x (#oflevels) Dr. Clincy Lecture

Baseband Transmission In sending the digital signal over channel without changing the digital signal to an analog signal Use low-pass channel – meaning the bandwidth can be as low as zero Typical: 2 computers directly connected Dr. Clincy Lecture

Digital Text Signals In transmitting text, the text is first converted to binary information (1’s and 0’s) Then the binary info in converted to voltage pulses Voltage pulses are then transmitted across the transport medium How do we represent letters, numbers, characters in binary form? Most common current forms: ASCII, EBCDIC Dr. Clincy Lecture

ASCII Dr. Clincy Lecture

EBCDIC Dr. Clincy Lecture

Channel Capacity As we know, impairments limits the actual data rate realized The actual rate realized at which data can be transmitted over a given path, under given conditions is called Channel Capacity Four concepts Data rate – the rate, in bps, the data can be communicated Bandwidth – constrained by the Tx and transport medium – expressed in cycles per second or Hertz Noise – average level of noise over the communication path Error rate – the rate in which erroneous bits are received Dr. Clincy Lecture

Impairments Dr. Clincy Lecture

Attenuation Loss of energy – the signal can lose energy as it travels and try to overcome the resistance of the medium Decibel (dB) is a unit of measure that measures a signal’s lost or gain of strength – can be expressed in power or voltage dB = 10 log10 [P2/P1] = 20 log10 [V2/V1] Samples of the power or voltage taken at times 1 and 2. Dr. Clincy Lecture

Distortion Distortion is when the signal changes its form. The each signal that makes up a composite signal could have different propagation speeds across the SAME medium – because of this, the different signals could have different delays (arriving at the receiver) – this causes a distortion. Dr. Clincy Lecture

Noise Thermal Noise - the uncontrollable or random motion of electrons in the transport medium which creates an extra signal (not sent by the transmitter) Induced Noise – undesired devices acting as a transmitting antenna and those signals being picked up Cross Talk Noise – effect of one wire crossing another wire Impulse Noise – spikes in energy (ie lightning) Dr. Clincy Lecture

Signal to Noise Ratio SNR = avg-signal-power/avg-noise-power High SNR – good (less corruption) Low SNR – bad (more noise than good power) SNR is described in Decibels (dB) SNRdB = 10 log10 SNR Dr. Clincy Lecture

Shannon Equation Shannon’s equation is used to determine the actual capacity of a channel given noise exist C = B log2 (1 + SNR) B = Bandwidth C= Channel Capacity SNR = Signal-to-noise ratio Dr. Clincy Lecture

Nyquist Equation Given noise, determine the maximum bit rate BitRate = 2 x B x log2 L B is the bandwidth of the channel L is the # signal levels used BitRate unit is bps (bits per second) Having 2 levels is reliable because a Rx can interpret 2 levels – suppose you had 64 levels – less reliable or more complex to interpret Dr. Clincy Lecture

Bandwidth Bandwidth is a measure of performance Bandwidth in hertz – range of frequencies Bandwidth in bps – bps a channel can handle (D/A case here (ie. Modem)) Dr. Clincy Lecture

Throughput Throughput is a measure of performance – how fast data can flow through a network Bandwidth could be what the channel could handle however, Throughput would be the amount that actually flowed through Bandwidth – potential Throughput – actual Dr. Clincy Lecture

Latency Latency is a performance measure – how long it takes an message to completely arrive to the receiver Latency consist of propagation time (time for a bit to travel from Tx to the Rx) Propagation time = distance/propagation-speed transmission time (time for a message to be sent) Transmission time = message-size/bandwidth queuing time (time each intermediate node holds the message) processing time (time each node spends processing the message) Note: if message is small, more bandwidth exists and therefore, the latency is more of propagation time versus transmission time Dr. Clincy Lecture