Technical data

www.westermo.com Theoretical and general applications 69
Some standards
*) The symbol rate is negotiated during handshaking
V.90
V.90 is an interesting modem standard as it offers potentially high data rates. This is
achieved by making use of a partially digital communication standard PCM (Pulse
Code Modulation). The standard was developed particularly for users to connect to
the internet and is consequentially not a symmetric data transfer. Although under good
circumstances download speeds of 56.0 kbit/s are possible the upload speed is only
9600 bit/s. The other complication is that the internet service providers have to use
special modems to allow a V.90 modem to connect. What this means is that two stan-
dard V.90 modems connected together do not connect at V.90, but more likely at
V.34bis, thus providing a link of 33.6 kbit/s in both directions.
Standard Bitrate Half/Full Baudrate No of bits Modulation
V.21 300 bit/s FDX 300 baud 1 bit/baud FSK
V.22 1200 bit/s FDX 600 baud 2 bit/baud DPSK
V.22bis 2400 bit/s FDX 600 baud 4 bit/baud QAM
V.23 1200 bit/s FDX 1200 baud 1 bit/baud FSK
V.32 9600 bit/s FDX 2400 baud 4 bit/baud TCM
V.32bis 14400 bit/s FDX 2400 baud 7 bit/baud TCM
V.34 Up to FDX Up to *) TCM
33600 bit/s 3429 baud
V.90 Up to FDX Up to *) PCM
56000 bit/s FDX 8000 baud
B A C K