1. Signals
   1. Analog
      1. Simple (sine wave
         1. wavelength
            1. distance between repeating units of a propagating waves of a given frequency
            2. Wavelength=propagation speed x period = propagation speed/frequency
         2. Characteristic
            1. Amplitude
            2. -Strength of a signal -period; time taken to complete 1 cycle -T=1/f
            3. Phase
            4. -position of waveform relative to time 0 -measure in degree/radians
            5. Frequency
            6. -rate of change respect to time -change in short span =high frequency -change in long span =low frequency -f=1/T
         3. Time and frequency domain
      2. Composite
         1. -Consist of many sine wave with different frequency, phase and amplitude(Fourier analysis) -if composite signal is periodic, the decomposition is a series of signal with discrete frequency - if composite signal is nonperiodic, the decomposition is a series of signal with continuous frequency
         2. Bandwidth
            1. -range of frequencies that a medium can pass without losing one-half of power contained in the signal
   2. Digital
      1. Bit interval- time required to send single bit bit rate- no of bit interval/second
      2. Advantages – cheaper, less susceptible to noise Disadvantages – greater attenuation
      3. Topic
   3. Transmission impairment
      1. Noise
         1. - thermal noises induced noise, crosstalk and impulse noise may corrupt signal
      2. Distortion
         1. Signal change form of shape Can be occurred in composite signal with different frequencies Will affect delay in arriving time
      3. Attenuation
         1. Signal loses strength when traverse through medium
   4. Performance
      1. Bandwidth-delay product
         1. 2 performance metric of link Determine the amount of data that can be in transit in the network
      2. Latency
         1. Queuing time
            1. Time needed for each intermediate/end device to hold message before it can be process
         2. Processing Delay
            1. Time router takes to process packet header
         3. Transmission time
            1. Time required for a bit to traverse to a destination Message size/bandwidth
         4. Propagation time
            1. Time required for a bit to traverse to a destination Distance/propagation speed
      3. Throughput
         1. Amount of data moved successfully from one place to another Time of a request and receive is called response time
      4. Bandwidth
         1. In hertz; Range of frequencies that a channel can pass In bit/second; speed of a bit transmission
   5. Baseband vs Broadband
      1. Topic
2. Transmission Modes
   1. Parallel
      1. allows transfers of multiple data bits at the same time over separate media used with a wired medium that uses multiple, independent wires the signals on all wires are synchronized so that a bit travels across each of the wires at precisely the same time
      2. Advantage
         1. High speed: it can send N bits at the same time a parallel interface can operate N times faster than an equivalent serial interface Match to underlying hardware: Internally, computer and communication hardware uses parallel circuitry
   2. Serial
      1. sends one bit at a time There are two main reasons why using a serial. serial networks can be extended over long distances at less cost using only one physical wire means that there is never a timing problem caused by one wire being slightly longer than another
      2. Topic
      3. Asynchronous Transmission
         1. It is asynchronous if the system allows the physical medium to be idle for an arbitrary time between two transmissions The asynchronous style of communication is well-suited to applications that generate data at random (e.g., a user typing on a keyboard or a user that clicks on a link) The disadvantage of asynchrony arises from the lack of coordination between sender and receiver
      4. Synchronous Transmission
         1. A synchronous mechanism transmits bits of data continually with no idle time between bits after transmitting the final bit of one data byte, the sender transmits a bit of the next data byte The sender and receiver constantly remain synchronized which means less synchronization overhead
      5. Isochronous Transmission
         1. Isochronous transmission is designed to provide steady bit flow for multimedia applications Delivering such data at a steady rate is essential because variations in delay known as jitter can disrupt reception (cause pops or clicks in audio/make video freeze for a short time)
   3. modes of operation
      1. Simplex
         1. a simplex mechanism can only transfer data in a single direction
      2. Half-Duplex
         1. A half-duplex mechanism involves a shared transmission medium
      3. Full-Duplex
         1. : allows transmission in two directions simultaneously
3. Digital Transmission
   1. LINE CODING
      1. UNIPOLAR (NRZ)
      2. POLAR (NRZ,RZ,BIPHASE:MANCHESTER AND DIFFERENTAL MANCHESTER
      3. BIPOLAR (AMI AND PSEUDOTERNARY)
      4. MULTILEVEL (2B/1Q,8B/6T,4D-PAM5)
      5. MULTITRANSITION (,LT-3)
   2. ANALOG TO DIGITAL CONVERSION
      1. PULSE CODE MODULATION (PCM)
         1. Most common techniques to change an analog signal to digital data. -The first step is sampling.
      2. DELTA MODULATION
         1. Find the changes from the previous sample. -Modulator and demodulator
4. Analog Transmission
   1. Digital to Analog conversion is the process of changing one of the characteristic of an analog signal based on the information in digital data.
   2. Types of Digital-to-Analog Transmission
      1. Amplitude shift keying (ASK)
         1. In ASK, the amplitude of the carrier signal is varied to create signal elements. Both frequency and phase remain constant while the amplitude changes.
      2. Frequency shift keying(FSK)
         1. In FSK, the frequency of the carrier signal is varied to represent data. The frequency of the modulated signal is constant for the duration of one signal element, but change the next signal if the data element changes. Both peak amplitude and phase remain constant for all signal elements.
      3. Quadrature amplitude modulation(QAM)
         1. QAM is a combination of ASK and PSK. QAM use two carriers, one in phase and the other quadrate, with different amplitude levels for each carrier.
      4. Phase shift keying(PSK)
         1. In PSK, the phase of the carrier is varied to represent two or more different signal elements. Both peak amplitude and frequency remain constant as the phase change.
   3. Bit Rate versus Baud Rate
      1. Bit rate is the number of bits per second.
      2. Baud rate is the number of signal elements per second.
   4. Analog to analog conversion is the representation of analog information by an analog signal.
      1. Analog to Analog
         1. Amplitude modulation
            1. In AM transmission, the carrier signal is modulated so that its amplitude varies with the changing amplitudes of the modulating signal. The frequency and the phase of the carrier remain the same, only the amplitude change to follow the variations in the information.
         2. Frequency modulation
            1. In FM transmission, the frequency of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal. The peak amplitude and phase of the carrier signal remain constant, but as the amplitude of the information signal changes, the frequency of the carrier changes correspondingly
         3. Phase modulation
            1. In PM transmission, the phase of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal. The peak amplitude and frequency of the carrier signal remain constant, but as the amplitude of the information signal changes, the phase of the carrier changes correspondingly
5. Transmission Media
   1. Guided (wired)
      1. Fiber-optic cable
         1. Topic
         2. Fiber Optic Cable : Adv & Disadv
            1. Topic
      2. Twisted-pair cable
         1. Topic
      3. Coaxial cable
         1. Topic
   2. Unguided (wireless)
      1. Wireless Transmission
         1. Radio
            1. Typically radio waves ranging from 3 KHz and 1 GHz Omnidirectional Can travel long distances Can penetrate walls Uses omnidirectional antenna
         2. Microwave
            1. Typically radio waves ranging from 1 and 300 GHz Line-of-sight Repeater required for long distance Uses unidirectional antenna Application – Unicasting Communication
         3. Infrared
            1. Frequency from 300 GHz and 400 THz Unidirectional, line-of-sight Short range communication Cannot penetrate walls Advantage : not effected by other system Susceptible to interference from the sun, so cannot be used outdoors
      2. Propagation Method
         1. Ground Propagation
            1. Radio wave travel through the lowest portion of atmosphere Low frequency omnidirectional signal follows the Earth’s curvature Distance depends on power of the signal
         2. Sky Propagation
            1. HF radiates upwards into the atmosphere, reflected back to Earth Allow greater distance with low power signal
         3. Line of Sight Propagation
            1. Very HF transmitted in straight lines from antenna to antenna (directly) Radio transmission cannot completely focused