Technology Fundamentals Chapter 2

Knowledge Checkpoints Types of transmissions Connections Data conversions Modem concepts Hardware associated with modems Analog-to-digital transmission Phone service and modems

In the Beginning There was data and it needed to move. Data was converted into a signal and the signal moved on a pathway.

Important Terms Circuit Port Two-wire, four-wire Analog Local loop PSTN Physical, logical Amplifier Attenuated Channel Line Trunk CPE PBX Local Exchange CO VC, SVC Interference Frequency Switched Dedicated Leased Line Communication band Hertz Wavelength Amplitude Phase Twisted pair Narrowband, broadband, wideband Codecs Modems Multiplexors Standards

Data and Signals are Building Blocks of a Network A signal is the transmission of data Signals are the electro-magnetic encoding of data Data moves as a signal To transfer data a physical wire/radio wave is used to convert into a signal Data and signals can be either analog or digital

Data and Signals Can Assume 2 Forms Analog Digital

Analog versus Digital Analog is a continuous waveform (variable by amplitude and frequency), with examples such as music and video.

Voice conversations are carried on a POTS network as analog data. Telephone switches connect calls at a Central Office (CO) Voice Concepts

Voice Traffic Voice traffic is either inter-LATA or Intra-LATA Competing phone companies maintain a POP for long distance calls Analog data is transmitted as an analog signal only within the local loop

Analog versus Digital Digital is a discrete or non-continuous waveform with examples such as computer 1s and 0s.

All Signals Have Three Components Amplitude Frequency Phase

Amplitude The amplitude of a signal is the height of the wave above or below a given reference point.

Frequency The frequency is the number of times a signal makes a complete cycle within a given time frame. Spectrum - The range of frequencies that a signal spans from minimum to maximum. Bandwidth - The absolute value of the difference between the lowest and highest frequencies of a signal. Attenuation - Loss of signal strength.

Phase The phase of a signal is the position of the waveform relative to a given moment of time or relative to time zero. A change in phase can be any number of angles between 0 and 360 degrees. Phase changes often occur on common angles, such as 45, 90, 135, etc.

Converting Digital Data into Digital Signals There are numerous techniques available to convert digital data into digital signals. Four techniques: NRZ-L NRZ-I Manchester Differential Manchester

Analog to Digital Analog signals work poorly over long distances on copper wire Signals require a boost which can distort the signal and introduce noise (it accumulates) Digitization converts audio signal to digital and avoids noise An A-to-D Converter makes an audio signal into a digital stream of numbers.

Pulse Code Modulation The analog waveform is sampled at specific intervals and the “snapshots” are converted to binary values.

Pulse Code Modulation When the binary values are later converted to an analog signal, a waveform similar to the original results. The more snapshots taken in the same amount of time, the better the resolution

PBX Concepts Provides shared use of voice circuits within a business organization Major players are telco-related Features are important in decisions to purchase

Signals on a Pathway

Transmitting a Signal Conducted (physical) Radiated (wireless)

The Physical Layer Responsible for establishing, maintaining and termination of physical connections between connecting devices Point-to-point links Transmits and receives a stream of bits--no data recognition Controlled by protocols defined by electrical, mechanical, and procedural specifications

Wire Propagation Effects Propagation Effects Signal changes as it travels If change is too great, receiver may not be able to recognize it Distance Original Signal Final Signal

Wire Propagation Effects: Attenuation Attenuation: Signal Gets Weaker as it Propagates May become too weak for receiver to recognize Signal Strength Distance

Wire Propagation Effects: Distortion Distortion: Signal changes shape as it propagates Adjacent bits may overlap May make recognition impossible for receiver Distance

Wire Propagation Effects: Noise Noise: Thermal Energy in Wire Adds to Signal Noise floor is average noise energy Random energy, so noise spikes sometimes occur Signal Strength Time Signal Noise Spike Noise Floor Error

Wire Propagation Effects Noise and Attenuation As signal attenuates, noise increases Noise errors increase with distance Signal Strength Distance Signal Noise Floor

Wire Propagation Effects: SNR Signal-to-Noise Ratio (SNR) Signal strength divided by average noise strength As SNR falls, errors increase Signal Strength Distance Signal Noise Floor SNR

Wire Propagation Effects: Noise & Speed Noise and Speed As speed increases, each bit is briefer Noise errors increase as speed increases One Bit Noise Spike Average Noise During Bit Low Speed (Long Duration) One Bit Noise Spike Average Noise During Bit High Speed (Short Duration) OK Error

Wire Propagation Effects: Interference Interference Energy from outside the wire Adds to signal, like noise Often intermittent (comes and goes), so hard to diagnose Signal Strength Time Signal Interference

ISDN Modem(Codec) Translates analog device signal into digital signal for propagation Constantly samples the intensity of the voice analog signal Sample 1/8,000 sec

Codec Divides each second into 8,000 sampling periods Only measures intensity of voice signal in each Sample 1/8,000 sec Sampling Period Intensity Value

Types of Transmission Lines Circuits (2 & 4-wire) Channel Difference between digital & analog conversations? Lines & Trunks What is different about the conversation? Switches CPE (within organizations) Connect trunks outside (part of a network) Connect exchanges Virtual Circuits Logical connections that act real (take different routes)

PVCs and SVCs Private Virtual Circuits are permanently available Routes may differ to destinations Switched Virtual Circuits Routes vary but connection is “on-demand”

Three Types of Connections Switched (dial-up) Leased Line (private) Dedicated (owned)

Spectrum Influences Services Wideband >64Kbps Broadband >2Mbps (optical) Narrowband <64Kbps Media influences frequency & spectrum Wire = 1MhZ Cable = 1GhZ

Mutliplexors Reduces number of links between 2 points Condensing multiple conversations to travel on a single channel Methods can be used to divide up the multiple conversations to travel on a single line: FDM, TDM, STDM, WDM

Modems Computers are digital & the telephone line is analog The translation device called a modem Digital Signal Modem Analog Signal

Modems Devices are digital;Transmission line is analog The line is analog the short distance to the CO (Central Office) Digital Device Analog Transmission Line

Modulation A Modem is a Modulator and Demodulator Modulation is converting outgoing digital device signals into analog transmission line signals Demodulation is converting incoming analog transmission line signals into digital device signals Digital Signal Modem Analog Signal

Modem Types Internal Modem On printed circuit board inside PC Does not take up desktop space Internal modems do not require a serial cable but instead require an IRQ to be assigned.

Home Connections

Modem Types External Modem Easy to install (just plug into serial port) Takes up desk space Needs wire to serial port (adds to wiring clutter)

Modem Types PC Card Modems Fit in PC Card slots on notebooks Easy to install Expensive

Modem Connection for Internal Modem Phone Line to Telephone Phone Line to Wall Jack

Modem Connection for External Modem Phone Line to Telephone Wall Power: usually uses “brick” transformer Serial Cable to Serial Port Phone Line to Wall Jack

Modem Standards Two Modems Must Follow Same Standards Speed standards (modulation method) Error correction and compression standards Facsimile standards Modern modem standards are created by the ITU-T

Modem Standards Training Period When two modems first start talking, they negotiate standards to use; settle on highest common standards

Modem Speed Standards (ITU-T) V.90 Receive at 56 kbps but send at only 33.6 kbps Fall back to 33.6 kbps if cannot support V kbps send and receive V.32 bis 14.4 kbps send and receive bis means second (version of the standard)

V.90 Modems Telephone Bandwidth is Limited Bandwidth limits speed Limits speed to about 35 kbps When you transmit, limited to 35 kbps 35 kbps

V.90 Modems Telephone Bandwidth is Limited Limits occur when you transmit in analog to the phone company Analog-to-digital converter (ADC) at the telephone company limits you to about 35 kbps Telephone Network Telephone Network ADC PC V.34 modem 33.6 kbps

V.90 Modems Receive at 56 kbps ISP connects with digital line to the Telco Sends at 56 kbps No analog-to-digital converter to limit speed Telephone Network Telephone Network DAC PC 56 kbps modem ISP Digital Link No ADC! 56 kbps

V.90 Modems Receive at 56 kbps 56 kbps digital channels inside phone network Only local loop is analog today Trunk lines and switches support 56 kbps transmission Telephone Network Telephone Network DAC PC 56 kbps modem ISP Digital Switches and Trunk Lines 56 kbps

V.90 Modems Receive at 56 kbps Telephone company transmits in analog to subscriber at 56 kbps Digital to audio converter (DAC) does not limit speed to less than 56 kbps Telephone Network Telephone Network DAC PC 56 kbps modem ISP Digital Link 56 kbps

V.90 Modem Telephone Company Does Not Have to Do Anything Differently ADCs and DACs are already in place for ordinary voice service Lack of change in phone system allowed fast implementation Telephone Network Telephone Network ADC PC 56 kbps modem ISP Digital Link DAC

V.90 Modem ISP Does Have to Do Things Differently Digital line to telephone network Special equipment at ISP Does not use a V.90 modem If used V.90 modem, could only send at 33.6 kbps Telephone Network Telephone Network DAC PC 56 kbps modem ISP Digital Link No V.90 Modem!

Modern modems use combinations of amplitude, frequency, and phase modulation to achieve high data rates. The fastest dial-up modem at the moment is 56 Kbps. Modems can support auto answer, auto dial, auto disconnect, and auto redial. Modems

Connection negotiation is the ability of a modem to automatically fall forward or fallback to faster or slower speeds, respectively. Modems can perform data compression and error correction and support the MNP 1-5 protocols. Most modern modems can support the fax standards. Modem Characteristics

Internal and External Modems

Why Your Dial up is Slow

Modem Pools A relatively inexpensive technique that allows multiple workstations to access a modem without placing a separate modem on each workstations. Modem pools can also be used to allow external users to dial into a business or corporate network via a modem in the modem pool.

The Reason Your ISP is Slow

Important Figures & Tables to Study Figure 2.8, p. 33 Table 2, p. 37 Table 2.1, p. 38 Figure 2.11, p. 38 Figure 2.13, p. 42

Knowledge Checkpoints Describe current voice technologies How is a PBX used? Give an example of a business application of a voice technology What problems can data encounter during transmission? How does a modem work?