Networking Ch. 3

logical circuit

refer to the transmission characteristic of the circuit....It is an idealized or physical device implementing a logical operation on one or more logical inputs, and produces a single logical output.

Switch

switching a transmission from being on the local loop to the telephone network

Parabolic Reflectors

Used to send/receive microwaves. Since microwave's signal approach a frequency similar to light, they can be reflected, focused, and refracted (similarly to light)

Graded-Index Multimode fiber optic cable

Type of Fiber Optic cable that improved upon Multimode. GIM changed the refractive properties of the glass fiber so that as the light approaches the outer edge of the fiber, it speeds up, which compensates for the slightly longer distance it must travel compared with light in the center of the fiber. --these improvements double effective distance of multimode to about 1,000 meters

Multimode fiber optic cables

Type of Fiber optic cable (earliest) that allowed light to shine within the cable in any direction. Problems: (1) plagued by excessive signal weakening (attenuation) and (2) dispersion (spreading of the signal so that different parts of the signal arrive at different times at the destination). --due to problems, it was limited effective distance to about 500 meters

Single-Mode fiber-optic cable

Type of fiber optic cable that transmits a single direct beam of light through a cable that ensure the light reflects in only one pattern (in part because the core diameter was reduced from 50 microns to 5/10 microns. --smaller diameter allows for faster and longer transmission (100 kilometers) --due to small diameter, light must be perfectly aligned with the fiber, so it can only use lasers (not LEDs) making this cable more expensive

Symbol Rate

number of symbols sent over the circuit per second

Analog transmission

occurs when the signal sent over the transmission media continuously varies from one state to another in a wave like patter much like the human voice

DC

Direct current - travels in only one direction

Phase

Direction in which a wave begins --measured in number of degrees

6 major considerations in choosing a transmission media

(1) TYPE OF NETWORK - WANs (microwaves), LANs (twisted pair cable), and MANs (2) COST - costs in wireless can vary on distance of transmission...Guided is more based on production cost (3) TRANSMISSION DISTANCE - Twisted pair, coaxial, and radio can only go certain distances before message needs to be retransmitted (4) SECURITY - wireless (less secure) and Guided (more secure) (5) ERROR RATES - (From Best to worst) Fiber Optic, Coaxial, Twisted Pair, and Wireless (6) TRANSMISSION SPEEDS - can vary within media type and with vendor but....Fiber optic = 1-40gbps, twisted pair/coaxial = 1mbps - 1gbps, and wireless = 10-100mbps

channels

(FDM) a separate logical circuit, and the devices connected to them are unaware that their circuit is being multiplexed --similar to on different radio frequencies`

Guardbands

(FDM) the unused portions of the circuit that separate the frequencies from each other

Character

(In coding) A symbol that has a common, constant meaning

Simplex transmission

(data flow) A one way transmission, ie. radio and TV

Half-duplex transmission

(data flow) A two way transmission that only allows one direction to transmit at a time. ie. walkie talkies

Control Signals

(data flow) computers use control signals to negotiate which will send and which will receive data in Half-duplex transmissions

Codec

-->Data can be sent over a circuit as Digital Data (computer--binary) or as Analog Data (human voice--wave shape). -->A Codec translates Analog Data to Digital Data -->You need two modems for transmission (sender/receiver) Codec = COde/DECode

Modem

-->Data can be sent over a circuit as Digital Data (computer--binary) or as Analog Data (human voice--wave shape). -->A Modem translates a computers Digital Data to Analog -->You need two modems for transmission (sender/receiver) modem = MODulator/DEModulator

Coding Scheme

--AKA Code --The specific language standard that computers use to represent binary data --the group of bits (binary) that are the "alphabet" of any given system 3 Predominant Coding Schemes: (1) United States of America Standard Code for Information Interchange (USASCII or ASCII), (2) ISO 8859, and (3) Unicode

bit rate

--AKA Data Rate --number of bits transmitted per second. --bit is a unit of information --This is calculated by n*Max Symbol Rate (n=number of bits sent on each symbol)

Turnaround time

--AKA Retrain time or Reclocking time --The amount of time half duplex communication takes to switch between sending and receiving

baud rate

--AKA Symbol Rate --The number of times per second the signal on the communication circuit changes. --NOT interchangeable with bit rate --baud is a unit of signaling speed

Point-to-Point (circuit configuration)

--AKA dedicated circuits --goes from one point to another (eg. one computer to another computer)

Multipoint (circuit configuration)

--AKA shared circuit --many computers are connected on the same circuit. Each must share the circuit with the others, and only one computer can use the circuit at a time.

Unicode

--Many different versions exists UTF-8 = 8 bit version UTF-16 = 16 bit per character version (2 bytes is called a "word"). Used in Microsoft computers. More bits = can represent Cyrillic or chinese characters

ISO 8859

--Standardized by the International Standards Organization --an 8 bit code --ISO 8859 = ASCII but with many non-english characters used by Europeans

bandwidth

--The maximum symbol rate in any circuit depends on the bandwidth available and signal-to-noise ratio --calculated: Difference between highest and lowest frequencies in a band or set of frequencies

signal-to-noise ratio

--The maximum symbol rate in any circuit depends on the bandwidth available and signal-to-noise ratio --strength of signal compared with the amount of noise in the circuit

What numbered layer is the physical Layer?

1

Transmission requires the sender and receiver to agree on two key parameters

1 - what symbols will be used (what pattern of electricity, light, or radio wave will be used to represent a 0 and 1 2 - Once these symbols are set, the sender and receiver have to agree on the symbol rate (number of symbols sent over the circuit per second)

5 reasons Digital Transmission > Analog

1) FEWER ERRORS - Digital is binary (only two distinct values) making it easier to detect and correct errors 2) Digital offers HIGHER MAXIMUM TRANSMISSION RATE - ie. Fiber-optics is designed for digital 3) Digital is MORE EFFICIENT - can send more data with digital than analog 4) Digital is MORE SECURE - it's easier to encrypt 5) Integrating voice, video and data on same circuit is more simple with digital

Formula for binary total binary combinations

2^n n = number of bits 2 = each bit has 2 options: 1 or 0

Geosynchronus

A satellite stays stationary over one point of the earth

Serial Transmission

A Transmission mode. A stream of data is sent over a communication circuit sequentially in a bit by bit fashion --slower than parallel transmission

Parallel Transmission

A Transmission mode. The way the internal transfer of binary data takes place inside a computer --eg. if there are 8 bits, then all 8 bits of the data element are transferred between main memory and the central processing unit simultaneously on 8 separate connections

Unipolar Signaling

A digital transmission technique where voltage is always either positive or negative (like a DC current)

Byte

A group of consecutive bits that is treated as a unit or character --1 byte usually equals 8 bits

Carrier Wave

A simple sound wave transmitted through the circuit that conveys data in terms of amplitude, frequency, and phase. --you can assign multiple bits to amplitudes, frequencies, or phases (or a combination of the 3)

ADPCM

Adaptive Differential Pulse Code Modulation. alternative to PCM that is used by voice services over lower speed digital circuits. --transmits the difference between the last time interval sample, and the current one. (samples 8,000 times per second and sends 4 bits due to differential)

AC

Alternating Current - Travels first in one direction and then in the other direction

AM or ASK

Amplitude Modulation, AKA Amplitude shift keying. Changing height of wave when symbols are determined by wave amplitude

Microwave transmission

An extremely high frequency radio communication beam that is transmitted over a direct line-of-sight path between any two points (usually between two parabolic reflectors stationed on radio antennas ). --Uses very short (micro) wave lengths --Perform same functions as cables

Lempel-Ziz encoding

As a message is being transmitted, this coding builds a dictionary of 2/3/4 character combinations that occur in the message. Anytime the same character pattern reoccurs in the message the index to the dictionary entry is transmitted rather than the actual data

BONDING standard

Bandwidth on Demand Interoperability Networking Group. A standardization of IMUX. --used to be that to use IMUX, you had to ensure you bought IMUX circuits from the same vendor so both clients or hosts could communicate --Now, and IMUX circuit that conforms to BONDING standards can communicate with any other IMUX circuit that conforms to the same standard

DWDM

Dense Wavelength Division Multiplexing. A variant of WDM that adds TDM to WDM.

DSL

Digital Subscriber Line. An approach to better utilizing the capacity of twisted pair wires in the local loop. DSL combines analog transmission with FDM and partially TDM. --A DSL Modem (Customer Premises Equipment (CPE)) is set up at customer's home and at telephone company's switch closet (to customers home). --The modem functions as an FDM device which splits circuit into 3 logical circuits (analog voice channel for phone, upstream data circuit from home to telephone company switch, and downstream data circuit). --TDM is then used to combine the digital channels

Bipolar signaling

Digital transmission technique where voltage can be both positive or negative --(like AC)

FDM

Frequency Division Multiplexing (FDM) divides circuit into multiple channels (and guard bands) which multiple computers can use simultaneously. --Think of the circuit being split up horizontally --a logical circuit is permanently assigned to a device look at picture p. 83

FM or FSK

Frequency Modulation, AKA Frequency Shift Keying. Changing length of wave when symbols are determined by wave frequency

Watt

Fundamental unit of electrical power. A rate unit, not a quantity

Amplitude

Height of a wave (volume) --measured in decibals (db)

V.44

ISO standard for data compression, uses Lempel Ziv encoding

Fiber-Optic Cable

Instead of carrying telecommunication signals in the traditional electrical form, this technology uses high speed streams of light pulses from lasers or LEDs (Light emitting diodes) that carry information inside hair thin strands of glass called optical fibers. Fiber optic systems: Multimode, Graded-index multimode, and single mode

Twiste Pair Cable

Insulated pairs of waries that can be packed close together. --One of the most common types of guided media

ISP

Internet Service Provider

IMUX

Inverse Multiplexing. Combines several low speed circuits to make them appear as one high speed circuit to the user

Satellite Transmission

Is similar to microwave transmission except instead of transmission involving another nearby microwave dish antenna, it involves a satellite many miles up in space

Frequency

Length of wave (number of waves per second). --expressed in Hertz

LEO

Low Earth Orbit. A way to combat propagation delay in satellite transmission

Guided Media

Medium types which the message flows through a physica media; the media "guides" the signal

PM or PSK

Phase Modulation, AKA Phase Shift Keying. Changing direction of wave when symbols are determined by wave phase

POTS

Plain Old Telephone Service - enables voice comunication between any two telephones within a telephone system's network --converts the analog voice to digital data in the network, and then back to analog data when reaching the receiver 3 important characteristics of sound waves in a voice circuit: Amplitude, Frequency, and Phase

PCM

Pulse Code Modulation. A form of modulation used by North American Telephone Network. --each time the voice signal is sampled (8,000 times per second), 8 bits are generated

QAM

Quadrature Amplitude Modulation. Splits a symbol into 8 phases (3bits) and 2 amplitudes (1bit) for a total of 16 different possible values

STDM

Statistical Time Division Multiplexing (STDM). --Logic behind it: If a circuits max transmission rate is 256 kpbs and it is multiplexed amongst 4 computers, each computer's max transmission rate is 64 --...however, computers are generally not working at max capacity 100% of the time, so STDM limits the max transmission rate based on a Statistical analysis of the usage requirements of the circuit to be multiplexed --PROS: provides more efficient use of the circuit and is less expensive --CONS: (1) If all computers operate above the statistically set max, there will be delays (2) logical circuits aren't assigned to devices, so each computers' data is interspersed together, so you have to include an address in the data packets

Hertz (Hz)

Symbol rate on a circuit 64 Hz = 64,000 symbols per second

Quantizing Error

The difference of error between an analog signal and a digitized signal --Two ways to reduce this: increasing the number of amplitude levels, and decreasing the frequency of each step

Radio transmission

The most commonly used form of wireless media. --Each device in your network has a radio receiver/transmitter that uses a specific frequency range that is designed to transmit a signal only a short distance

Digital transmission

The transmission of binary, electrical, or light pulses in that it only has two possible states: 1/0 --All Digital transmission techniques require (1) a set of symbols (defines how to send 1s/0s, and (2) symbol rate

TDM

Time Division Multiplexing (TDM) is when two or more computers share the same circuit...The circuit can only transmit one 1 at a time --generally more efficient than FDM because circuit doesn't waste space on guard bands --a logical circuit is permanently assigned to a computer look at picture p. 83

Multiplexing

To break on 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 --often done in multiples of 4 --2 multiplexers are needed for each circuit: one to combine the original circuits into the one multiplexed circuit and one to separate them back into the four separate circuits --4 types of multiplexing: Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Statistical Time Division Multiplexing (STDM), and Wavelength Division Multiplexing (WDM)

USASCII or ASCII

United States of America Standard Code for Information Interchange (USASCII or ASCII). There are two types. One 7 bit version with 128 valid character combinations, and an 8 bit version (256 options)

VoIP

Voice Over Internet Protocol. Transmits phone conversations over digital networks. Uses digital phones with built in Codecs. --because Codec is built into phone, the phone can be connected into a LAN. Thus, VoIP only needs one network opposed to the usual two (voice network, data network)

WDM

Wavelength Division Multiplexing (WDM) is a version of FDM used in fiber optic cables. WDM works by using lasers to transmit different frequencies of light (ie. colors) into fiber optic cables. The light multiplexes the the physical circuit and devices are assigned different frequencies

Modulation

When transmitting data through a telephone line, you can the shape of the carrier wave (in terms of amplitude, frequency, and phase) to represent different data values (0s and 1s)

Propagation delay

a disadvantage of satellite transmission that occurs because the signal has to travel out into space and back...causing a delay

Coaxial Cable

cable with a copper core (inner conductor) with an outer cylindrical shell for insulation. Has an outer shield that is used as a second conductor. --guided media that is quickly disappearing

Voltage

electrical pressure - the amount of electrical force pushing electrons through a circuit

Current

movement or flow of electrons, normally from positive (+) to negative (-) --Direct Current (DC) & Alternating Current (AC)

Data Compression

literally compressing data to increase the rate of throughput data over a communication link

Wireless media

media where message is broadcast through the air

Circuit

path over which the voice, data or image transmission travels. Can be a twisted wire pairs, coaxial cables, fiber-optic cables, microwave transmissions, and so forth

Manchester Encoding

special type of bipolar signaling in which the signal is changed from high to low (or low to high) mid signal

physical circuit

the actual wire-used to connect two devices....It's the physical media that carry the message we transmit

Circuit Configuration

the basic physical layout of the circuit. Two configurations: Point-to-Point & multipoint

Medium

the physical matter or substance that carries the voice or data transmission Types of transmission media: Copper (wire), glass/plastic (fiber optic), and Air (radio, microwave, or satellite)

Polarity

the plus (+) or minus (-) measurements of current

Local Loop

the wires that run from your home/business to the telephone switch that connects your local loop into the telephone network

Amperes (amps)

units of electrical flow, or volume

Raindrop attenuation

when satellite transmissions are absorbed by heavy rain. (not a major problem)