DCN286 Notes

1. 4 International Standardization Groups
A) IEEE (Institute of Electrical and Electronics)
Develops standards for LANS
802.3 is IEE standard for Ethernet  defines data access to network CSMA/CD
B) TIA (Telecommunications International Alliance)
Physical layer standards
TIA 568Cabling standard
C) ITU (International Telecommunications Union)
Standards for telecommunications
V.90 Modem was a standard
D) ISO (International Organization for Standardization)
Standards for LAN, MAN, WAN, and ISDN
ISO Model is standards in communication
2. How does Analog Transmission Work?
A) Available Bandwidth The available bandwidth is 200-3400Hz
Modem can only handle frequencies within range 200-3400Hz
B) Carrier Wave
Sent before any transmission
Fixed amplitude and sign wave
C) How do modems modify carrier waves to represent data?
Amplitude Shift Keying  Change in amplitude (voltage)
Frequency Shift Keying  Change in frequency
Phase Shift Keying  Change in Phase
D) How do modems get faster transmission (QAM)
QAM is a modulating scheme by changing the amplitude shift keying or amplitude modulation
Higher modulation allowing more information to be sent per baud
Carrier wave contains more information per baud being sent
E) Difference between baud rate and bits per second
Baud Rate number of times modem sends a new signal
Bits Per Second  Amount of data sent in a unit of time (per second)
F) V.90 Modem is not truly analog because the analog signal is converted to digital for transmission

3. How does Digital Transmission Work?
A) How Does PCM Work?
Sampling rate is sample of waves at regular intervals
Samples are taken and voltage is measured
Measurement is stored in a digital number
Numbers are digitally transmitted, and converted back to analog once received
Higher the frequency of sampling rate, more accurate the analog waves can be reconstructed
Sampling rate must be at least twice the highest frequency of analog wave for accurate