MIS 140 Chapter 3

One commonly used VoIP standard

G.722 wideband audio a version of ADPCM that operates at 64 Kbps - samples at 8,000 per second and produces 8 bits per second

Time division multiplexing (TDM)

a communication circuit is shared among two or more computers by having them take turns, dividing the circuit "vertically" A character is taken from each computer in turn doesn't require guardbands

Coaxial cable

a type of guided media that is quickly disappearing copper core as an inner conductor with an outer cylindrical shell for insulation - outer shield, just under the shell, is the second conductor way more costly than twisted pair cable with no extra benefit

Circuit configuration

the basic physical layout of the circuit

Symbol

the pattern of electricity, light, or radio wave that is used to represent a 0 and a 1

In clean, error free, and interference free analog transmission, what three basic factors could be changed to obtain a higher data rate?

--Boost frequency range on the transmission line --Go from two waves per symbol to one wave per symbol --Increase our modulation to send more bits per symbol

Gigabit Ethernet

--SymRate = 125 MHz --Bits/Symbol = 2 (x 4 lines parallel) ---Detection = Voltage levels ---Data Rate = "1Gbps" (Actually 800 Mbps because every 5th bit is a control bit with no actual data)

When sending four bits at a time using frequency modulation, the number of different frequency levels that would be needed would be _______.

16?

4B5B encoding

4 bits are mapped into 5 bits no more than 4 1s or 0s in a row - 5th bit will be the opposite in order to delineate each 4 bit section - helps detect errors

Bandwidth of a standard telephone line

4000 Hz

How many bits are required to sample an incoming signal 4000 times per second using 64 different amplitude levels?

6 bits

Multipoint circuit

AKA *shared circuit* Many computers on the same circuit - only one can use circuit at a time

Customer premises equipment (CPE)

A DSL modem It is first an FDM device that splits the physical circuit into three logical circuits: a standard voice circuit for phone calls, an upstream data circuit, and a downstream circuit

Point to point circuit

AKA *dedicated circuit* Goes from one computer to another used when computers generate enough data to fill the capacity of the circuit

Baud rate

A unit of signaling speed used to indicate the number of times per second the signal on the communication circuit changes AKA symbol rate

Fast Ethernet

AKA -* 100Base-T* --SymRate = 125 MHz --Bits/Symbol = 0.8 (4B5B encoding) ---Detection = Change in voltage level ---Data Rate = 100Mbps --Binary 0 = no voltage change --Binary 1 = step voltage

Manchester

AKA -* 10Base-T* --SymRate = 10 MHz --Bits/Symbol = 1 ---Detection = Direction of voltage change ---Data Rate = 10Mbps

Bandwidth on Demand Interoperability Networking Group

AKA BONDING an IMUX standard that allows clients and hosts to communicate using IMUX most common use of BONDING is room-to-room video conferencing

Amplitude modulation (AM)

AKA amplitude shift keying (ASK) the amplitude is changed - one wave height representing 1 and another representing 0 most suseptible to noise (errors)

Data rate

AKA bit rate calculated by multiplying the number of bits sent on each symbol by the maximum symbol rate

Frequency modulation (FM)

AKA frequency shift keying (FSK) A different wave length is used for a 1 and a 0

Phase modulation (PM)

AKA phase shift keying (PSK)

Local loop

AKA the last mile The wires that run from your home or business to the telephone switch that connects your local loop into the telephone network

Statistical time division multiplexing (STDM)

Allows more computers on a circuit than TDM or FDM selection of transmission speed for the multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be mutliplexed

Three important characteristics of sound waves that are transmitted through the voice circuit

Amplitude - the height(and depth) of the wave measured in decibles Frequency - length of the wave, measured in waves per second (Hertz or Hz) Phase - refers to the direction in which the wave begins, measured in the number of degrees

What are the two types of data that can flow through the circuit

Analog and digital

Sending multiple bits simultaneously in analog form

Can assign different amplitudes, frequencies, or phase degrees to different bits Can only go so far before differences become too small to distinguish from noise Can also combine modulation techniques in same transmission

Codec

Code/Decode used to send analog voice data over a digital circuit in the same way that a pair of modems is used to translate data to send across the circuit

Data compression and the ISO standard for data compression

Data compression can be used to compress data in order to increase throughput rates in modems V.44 - uses Lempel-Ziv encoding ---Lempel-Ziv encoding produces a dictionary of 2, 3, and 4 character combinations ---every time a repeated character combination occurs, the encoding sends an index to the dictionary, rather than the actual characters ---averages a compression of around 6:1

Take-aways for management

Digital is better (see reasons at beginning of chapter) Because analog and digital data is able to converge in physical networks, voice telecommunications is increasingly under the purview of IS organizations Consolidation of manufacturers of networking equipment for organizations and for telephone companies

5 advantages to digital transmission over analog

Fewer errors Higher maximum transmission rates More efficient More secure Simpler to integrate voice, video, and data on same circuit

Two ways to reduce Quantizing error

Increase the number of amplitude levels, which minimizes the differnce between the levels and results in a smoother signal Sample more frequently, which reduces the "length" of each "step", resulting in a smoother signal

3 levels of Ethernet transmission schemes

Manchester Fast Ethernet Gigabit Ethernet *see lecture notes for more detail*

Guided media

Media in which the message flows through a physical media such as a twisted pair wire, coaxial cable, or fiber-optic cable The media "guides" the signal

Wireless media

Media in which the message is broadcast through the air, such as microwave or satellite

Modem

Modulator/Demodulator converts a digital signal into an analog signal that can be transmitted over phone lines

Symbol rate

Number of symbols sent over the circuit per second

Analog transmission

Occurs when the signal sent over the transmision media continuously varies from one state to another in a wave-like pattern modems translate digital data from a computer into analog signals to be transmitted over telephone circuits

Digital Subscriber Line (DSL)

One approach to changing the way data are transmitted in the local loop to provide higher-speed data transfer combines analog transmission and FDM to provide a set of voice and data circuits

Simplex transmission

One-way transmission, such as that with radios and TVs

Modulation

To represent digital information, a *carrier wave* is sent down the circuit and then *modulated*, or changed in shape to represent a 1 or a 0

POTS

Plain Old Telephone Service Refers to the telephone system

Logical circuit

Refers to the transmission characteristics of the connection

Quadrature amplitude modulation (QAM)

Splitting the symbol into eight different phases (3 bits) and two different amplitudes (1 bit) for a total of 16 possible values This 64-QAM can represent 4 bits in one symbol - 256 QAM can represent 8 bits commonly used in digital TV services and cable modem Internet services

Serial transmission

Stream of data is sent over a circuit sequentially in a bit-by-bit fashion - only one physical wire slower than parallel transmission

Physical circuit

The actual wire used to connect devices

Adaptive differential pulse code modulation (ADPCM)

The alternative used by Instant Messaging and many other applications that provide voice services over low-speed digital circuits Samples voice data at 8,000 times per second and uses same 8 bits per sample that PCM does Difference is that it transmits the *difference* between the current 8 bit value and the previous 8 bit value The slowness of change of voice signals means that they can be represented using only 4 bits

Turnaround time

The amount of time half-duplex communication takes to switch between sending and receiving AKA *retrain time*

Bandwidth

The difference between the highest and the lowest frequencies in a band or set of frequencies

Quantizing error

The difference between the smooth flow of a sound wave and the approximated digital representation - produces a metallic sound

Symbol rate

The frequency at which symbols, representing bits, are sent through a circuit - 64 Hz sends 64,000 symbols per second

Coding Scheme

The language that computers use to represent data

Pulse code modulation (PCM)

The standard used by the North American telephone network input voice signal is sampled 8,000 times per second (2X the 4000 Hz bandwidth) each time the input voice is sampled, 8 bits are generated, making transmission speed 64 Kbps (8 bits per sample x 8,000 samples per second)

Switch

The switch that connects your local loop the the telephone network it contains a codec that converts the analog signal to a digital signal

Digital transmission

The transmission of binary electrical or light pulses in that it only has two possible states, a 1 or 0

Parallel transmission

This is the way the internal transfer of binary data takes place inside a computer Each bit is transferred on its own circuit

Multiplexing

To break one high-speed physical communication circuit into several lower-speed logical circuits so that many different devices can simultaneously use it but still "think" that they have their own separate circuits

Codec

Translates analog voice data into digital form for transmission over digital computer circuits

Modem

Translates the computer's digital data into analog data that can be transmitted through the voice communication circuits, then a modem on the other end translates the analog back to digital

Full-duplex transimission

Transmit in both directions simultaneously, with no turnaround time

Half-duplex transmission

Two-way transmission, but can transmit in only one direction at a time similar to a walkie-talkie computers use *control signals* to negotiate which will send and which will receive data

6 Factors in deciding which type of media to use

Type of network Cost Transmission distance Security Error Rates Transmission speeds

5 types of digital transmission

Unipolar - always positive/0 or negative/0 volts Bipolar (NRZ) - positive voltage = 1, negative voltage = 0 - never returns to zero Bipolar (RZ) - voltage returns to zero in between each symbol, which provides an error checking opportunity Bipolar: Alternate Mark Inversion (AMI) - Manchester encoding - used by ethernet - signal is changed from high to low or low to high in the middle of a time splice - less susceptible to errors going unnoticed

3 predominant coding schemes in use today

United States of America Standard Code for Information Interchange (USASCII, or more commonly, ASCII) - most popular for data communications ISO 8859 - includes ASCII codes plus non-English letters - HTML often uses this scheme Unicode - UTF-8 and UTF-16 are two different versions

Guardbands

Unused portions of a FDM circuit that separate the channels from each other to avoid interference

PAM-5 encoding

Used by 1000Base-T 5 diff voltage levels - 4 to send data and 1 as a control bit --00 = -1.0 V --01 = -0.5 V --10 = +0.5 V --11 = +1.0 V More susceptible to noise (finer differences) so some opt for 100Base-T instead

Wavelength division multiplexing (WDM)

a version of FDM used in fiber-optic cables transmit multiple channels using different wavelengths of light Dense WDM (DWDM) is a variant that further increases capacity by adding TDM to WDM

Inverse multiplexing (IMUX)

combines several low-speed circuits to make them appear as one high-speed circuit to the user a common usage is to provide T1 circuits for WANs (T1 combines 24 64 Kbps circuits to transmit at 1.544 Mbps)

Radio transmission

common form of wireless communication a radio receiver/transmitter uses a specific frequency range that does not interfere with commercial radio stations

Voice over Internet Protocol (VoIP)

commonly used to transmit phone conversations over digital networks uses digital telephones w/ built-in codecs - so can be directly connected into a LAN Must be able to operate in emergencies to call 911 ---must have uninterrupted power supplies (UPS)

Frequency division multiplexing (FDM)

dividing the circuit "horizontally" so that many signals can travel a single communication circuit simultaneously divided into channels transmitting at different frequencies - each channel is separate logical circuit

Microwave transmission

extremely high-frequency radio communication beam that is transmitted over a direct line-of-sight path between any two points stations can be place approx. 25 - 50 miles apart

Fiber optic cable

high-speed streams of light pulse from lasers or LEDs and carry information inside hair-thin strands of glass

Twisted pair cable

insulated pairs of wires that can be packed quite close together the wires are usually twisted to minimize the electromagnetic interference between one pair and any other pair in the bundle

Bit rate

number of bits transmitted per second

Satellite transmission

similar to microwave, except instead of transmission involving another nearby microwave dish antenna, it involves a satellite many miles in space (low-earth orbit [LEO]) *raindrop attenuation* is an issue in heavy rains