V.90 Modems

1
V.90 Modems

• Telephone Bandwidth is Limited (Chapter 4)
• Bandwidth limits speed
• Limits speed to about 35 kbps
• When you transmit, limited to 35 kbps

35 kbps
2
V.90 Modems

• Telephone Bandwidth is Limited
• Limits occur when you transmit in analog to the
  phone company
• Analog-to-digital converter (ADC) at the
  telephone company limits you to about 35 kbps

Telephone Network
PC
V.34 modem
ADC
33.6 kbps
3
V.90 Modems

• Receive at 56 kbps
• ISP connects with digital line to the Telco
• Sends at 56 kbps
• No analog-to-digital converter to limit speed

Digital Link
Telephone Network
PC
ISP
56 kbps modem
DAC
No ADC!
56 kbps
4
V.90 Modems

• Receive at 56 kbps
• 56 kbps digital channels inside phone network
• Only local loop is analog today
• Trunk lines and switches support 56 kbps
  transmission

Digital Switches and Trunk Lines
Telephone Network
PC
ISP
56 kbps modem
DAC
56 kbps
5
V.90 Modems

• Receive at 56 kbps
• Telephone company transmits in analog to
  subscriber at 56 kbps
• Digital to audio converter (DAC) does not limit
  speed to less than 56 kbps

Digital Link
Telephone Network
PC
ISP
56 kbps modem
DAC
56 kbps
6
V.90 Modem

• Telephone Company Does Not Have to Do Anything
  Differently
• ADCs and DACs are already in place for ordinary
  voice service
• Lack of change in phone system allowed fast
  implementation

Digital Link
ADC
Telephone Network
PC
ISP
56 kbps modem
DAC
7
V.90 Modem

• ISP Does Have to Do Things Differently
• Digital line to telephone network
• Special equipment at ISP
• Does not use a V.90 modem
• If used V.90 modem, could only send at 33.6 kbps

Digital Link
Telephone Network
PC
ISP
56 kbps modem
DAC
No V.90 Modem!
8
V.90 Modem

• User Needs a V.90 Modem
• Does not need a new phone line
• Not all phone lines will work, but it is never
  worth the cost to install a new line for V.90
  modems