Modem Standards

1
Modem Standards

• Two Modems Must Follow Same Standards
• Speed standards (modulation method)
• Error correction and compression standards
• Facsimile standards
• Modern modem standards are created by the ITU-T

2
Modem Standards

• Training Period
• When two modems first start talking, they
  negotiate standards to use settle on highest
  common standards

3
Modem Speed Standards (ITU-T)

• V.90
• Receive at 56 kbps but send at only 33.6 kbps
• Not all phone lines, ISPs support 56 kbps
• Fall back to 33.6 kbps if cannot support
• V.34
• 33.6 kbps send and receive
• V.32 bis
• 14.4 kbps send and receive
• bis means second (version of the standard)

4
Modem Standards Error Correction and Compression

• ITU-T
• V.42 Error detection and correction
• V.42 bis Compression (up to 41)
• Most newer modems have both
• MNP Level 5
• Proprietary standard of Microcom
• Once widely used
• Provides both error correction and compression
• Now largely superceded by V.42 and V.42 bis

New
5
Modem Standards

• Facsimile Modem Standards
• Most modems also act as fax modems
• Facsimile requires different modulation than data
  transmission
• V.14 14.4 kbps
• V.29 9.6 kbps