UMTS supports up to 1920 kbit/s data transfer rates (and not 2 Mbit/s as frequently seen), although at the moment users in the real networks can expect performance up to 384 kbit/s - in Japan upgrades to 3 Mbit/s are in preparation. However, this is still much greater than the 14.4 kbit/s of a single GSM error-corrected circuit switched data channel or multiple 14.4 kbit/s channels in HSCSD , and - in competition to other network technologies such as CDMA-2000, PHS or wLAN - offers access to the World Wide Web and other data services on mobile devices.
UMTS combines the W-CDMA air interface, GSM 's Mobile Application Part (MAP) core, and the GSM family of speech codecs.
Note that many wireless technologies use W-CDMA as their air interface, including FOMA and J-Phone .
Like other real-world W-CDMA implementations, UMTS uses a pair of 5 MHz channels, one in the 1900 MHz range for uplink and one in the 2100 MHz range for downlink. In contrast, the competing CDMA2000 system uses one or more arbitrary 1.25 MHz channels for each direction of communication. UMTS and other W-CDMA systems are widely criticized for their large spectrum usage, which has delayed deployment in countries that have not allocated new frequencies specifically for UMTS (such as the United States).
The specific frequency bands originally defined by the UMTS standard are 1885-2025 MHz for uplink and 2110-2200 MHz for downlink.
For existing GSM operators, it is a simple but costly migration path to UMTS: much of the infrastructure is shared with GSM, but the cost of obtaining new spectrum licenses and overlaying UMTS at existing towers can be prohibitively expensive.
A major difference of UMTS compared to GSM is the air interface forming Generic Radio Access Network (GRAN). It can be connected to various backbone networks like the Internet , ISDN , GSM or to a UMTS network. GRAN includes the three lowest layers of OSI model . The network layer (OSI 3) protocols form the Radio Resource Management protocol (RRM). They manage the bearer channels between the mobile terminals and the fixed network including the handovers.