Universal Mobile Telecommunications System(UMTS)

What is the UTMS?Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies. Currently, the most common form uses W-CDMA as the underlying air interface, is standardized by the 3GPP, and is the European answer to the ITU IMT-2000 requirements for 3G cellular radio systems.
To differentiate UMTS from competing network technologies, UMTS is sometimes marketed as 3GSM, emphasizing the combination of the 3G nature of the technology and the GSM standard which it was designed to succeed.UMTS combines the W-CDMA, TD-CDMA, or TD-SCDMA air interfaces, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs. In the most popular cellular mobile telephone variant of UMTS, W-CDMA is currently used. Note that other wireless standards use W-CDMA as their air interface, including FOMA.
UMTS over W-CDMA uses a pair of 5 MHz channels. 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 acted relatively slowly in allocating new frequencies specifically for 3G services (such as the United States).
The specific frequency bands originally defined by the UMTS standard are 1885-2025 MHz for the mobile-to-base (uplink) and 2110-2200 MHz for the base-to-mobile (downlink). In the US, 1710-1755 MHz and 2110-2155 MHz will be used instead, as the 1900 MHz band was already utlized.Additionally, in some countries UMTS operators use the 850 MHz and 1900 MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by AT&T Mobility.
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 (GeRAN). It can be connected to various backbone networks like the Internet, ISDN, GSM or to a UMTS network. GeRAN 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.