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Modem. Modem connection. PC. PC. modem. modem. 110011. 110011. DCE. DCE. DTE. DTE. Modem type. Asynchronous, Synchronous Half-Duplex, Full-Duplex. Modulation method. FSK 1 bit per baud. max speed =2400 bps PSK, DPSK up 3 bit per baud

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Modem connection
Modem connection

PC

PC

modem

modem

110011

110011

DCE

DCE

DTE

DTE


Modem type
Modem type

  • Asynchronous, Synchronous

  • Half-Duplex, Full-Duplex


Modulation method
Modulation method

  • FSK 1 bit per baud. max speed =2400 bps

  • PSK, DPSK up 3 bit per baud

  • QAM combines ASK and PSK, encoding 4-7 bits per baud

  • TCM same as QAM, but adds extra bits for error correction


Signal constellation
Signal Constellation

distance = sqrt(C2+D2)

point defines a legimate signal change

C

C

angle = sin-1

sqrt(C2+D2)

D

  • distance defines signal抯 amplitude

  • angle defines phase shift


Constellation samples
Constellation samples

V.22

600 baud 1200 bps

PSK

V.22bis

600 baud 2400 bps

QAM

V.32

2400 baud 9600 bps

TCM


V 29 signal constellation
V.29 Signal Constellation

90

  • 8 phases with 4 amplitudes QAM

  • 2400 baud, 9600 bps

1010

3*sqrt(2)

0010

1000

1011

sqrt(2)

0011

5

0000

3

0

180

0111

1111

0001

1001

0101

0110

1101

0100

1110

1100

270


Some standards
Some standards

  • V.32bis

    • 2-dimensional TCM with 128 pts.

    • transmission rate up to 14,400 bps

  • V.32ter

    • 2-dimensional TCM with 512 points

    • Transmisiion rates up to 19,200 bps

  • V.34

    • 4-dimensional TCM with 768 points

    • Transmisiion rates up to 28,800 bps


Error correcting
Error correcting

  • LAPD (Link Access Protocol D) based on HDLC sychronous protocol

  • MNP (Micrcom Networking protocol)trademark of Microcom

  • TCM modulation with error detecting code

  • V.42CRC error correcting standard


Mnp protocol
MNP protocol

  • Microcom Networking Protocol (MNP)Modem protocol developed by Micocom, Inc.

  • Divided into classes 1-10 MNP modems negotiate to operate at the highest supported class

  • Considered a de facto industry standard


V 42 recommendation
V.42 Recommendation

  • V.42

    • Defines error-checking standard

    • uses CRC for each data block

  • V.42bis

    • Defines modem compression using the Lempel Ziv method


Fallback

9,600 bps

modem

modem

Down

speed

7,200 bps

modem

modem

4,800 bps

modem

modem

Fallback


Smart modem
Smart modem

  • Introduces by Hayes Microcomputer Products

    • known as Hayes-comptible modems

  • Properties

    • standard modem with microprocessor

    • automatic dialling

    • provides command in ASCII form

  • Hayes command

    • known as Hayes-comptible modems

    • AT DT 9,9985800


Hayes response codes
Hayes Response Codes

  • 0 OK

  • 1 CONNECT

  • 2 RING

  • 3 NO CARRIER

  • 4 ERROR

  • 5 CONNECT 1200

  • 6 NO DIALTONE

  • 7 BUSY

  • 8 NO ANSWER

  • 10 CONNECT 2400


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