CS 438 - Xiao - Computer Networks - Ch2 - Exam 1

Persistent storage

magnetic or SSD storage

Full duplex link

used for transmission in both directions at once. Ex) twisted pair wires, one for each direction

Half-duplex link

both directions but not at same time

simplex link

only one fixed directions at all times (not common)

Coaxial Cable (Coax)

one central wire surrounded by insulation, a metallic shield, and a covering of insulation. longer distances at better speed and noise than twisted pairs

frequency equation

lambda *f = c

FHSS

(frequency hopping spread spectrum), hops from frequency to frequency hundreds of times /s. popular for military: hard to detect & difficult to jam

CDMA

(Code Division Multiple Access): use different codes (introduce later)

DSSS

(direct sequence spread spectrum), uses a code sequence to spread the data signal over a wider frequency band. Widely used to let multiple signals share the same frequency band.

UWB

(Ultra-WideBand): sends a series of rapid pulses, varying their positions to communicate information. The rapid transitions lead to a signal that is spread thinly over a very wide frequency band. high rates, tolerate interference

Digital modulation

process of converting between bits and signals

Basebase transmission

signal occupies frequencies from zero up to a maximum; particularaly for wire

Passband Transmission

signal occupies a band of frequencies around the frequency of the carrier signal.

Multiplexing

multiple signals share the channel

NRZ

non return zero. use a positive voltage to represent a 1 and a negative voltage to represent a 0.

Manchester drawback

requires twice as much bandwidth as NRZ because of the clock

NRZI

(Non-Return-to-Zero Inverted): 1 as transition & 0 as no transition, e.g. USB as an application

4B/5B

Every 4 bits is mapped into 5-bit pattern with table. adds 25% overhead, better than 100% overhead of Manchester

Bipolar encoding

use two voltage levels to represent a logical 1, (e.g. +1V or −1V) with 0V representing 0.

ASK

Amplitude Shift Keying. Two different amplitudes are used to represent 0 and 1 ex) nonzero and zero levels

FSK

Frequency shift keying

PSK

Phase shift keying

BPSK

Binary phase shift keying. Wave is shifted 0 or 180 degrees at each symbol period

QPSK

quadrature phase shift keying. uses 4 shifts to key 2 bits of information per symbol

FDM

Frequency Division Multiplexing

Frequency Division Multiplexing

frequency spectrum divided into frequency bands and each user has exclusive possesion of some band

TDM

Time Division Multiplexing

Time Division Multiplexing

users take turns in round robin fashion

Sideband

band of frequencies higher or lower than the carrier frequency that are the result of the modulation process

Subcarrier

sideband of radio frequency carrier wave which is modulated ot send additional information. ei color in a b&w television system

CDMA explanation

Code Division Multiple Access. Assigns a unique code to each voice call or data transmission to uniquely identify it from all other transmissions sent over cell network. "spread spectrum" network, calls are spread throughout the entire RF band.

TDM analogy

all people in middle of room, take turns to speak

FDM analogy

people divided into groups (high pitch, low pitch, normal talking etc) such that each pair can hold its own coversation at the same time independently of everyone else

CDMA analogy

everyone talks in different languages (Chinese, English, French etc), can only understand what is in your language, treat everything else as noise

Local Loop

analog twisted pairs going to houses and businesses

Trunks

digital fiber optics connecting the telephone switch offices

telephone switching office

where calls are moved from one trunk to another

How many Bell Operating Companies did AT&T split

23

How many regional BOC

7

LATA

Local Access Transport Area. USA is divided into 164. Contains a few area codes

LEC

Local Exchange Carrier. A telephone company that provides local telephone service inside a LATA

IXC

InterXchange Carrier. Carries inter-LATA traffic (Sprint, Verizon, etc)

POP

Point of Presence. IXC switching office inside each LATA

End Office Code

Has up to 10,000 local loops

First 6 digits of phone number

end office (ie 513-673)

Dial up modem

early way to connect to internet by using analog signals over existing telephone infrastructure

Digital Subscriber Lines

operate over existing telephone lines to carry voice, data, and video.

Asymmetric DSL

Any version of DSL in which downstream throughput is higher than upstream throughput.

DSL bonding

achieve higher speeds by using multiple telephone lines

FTTH

Fiber to the Home, an ultimate goal

FTTN

Fiber to the Neighborhood. Gets within at least a few miles of a home.

FTTdp

Fiber to the Distribution Point. To within a few meteres of customer premise (ie to apartment building but not individual apartment)

FTTC

in between FTTdp and FTTN

FTTX

Fiber to the (X ie home, curb, neighborhood)