Migrating from GPRS to UMTS

From GPRS network, the following network elements can be reused:

Home location register (HLR)
Visitor location register (VLR)
Equipment identity register (EIR)
Mobile switching centre (MSC) (vendor dependent)
Authentication centre (AUC)
Serving GPRS Support Node (SGSN) (vendor dependent)
Gateway GPRS Support Node (GGSN)
From Global Service for Mobile (GSM) communication radio network, the following elements cannot be reused
Base station controller (BSC)
Base transceiver station (BTS)
They can remain in the network and be used in dual network operation where 2G and 3G networks co-exist while network migration and new 3G terminals become available for use in the network.

The UMTS network introduces new network elements that function as specified by 3GPP:
Node B (base station)
Radio Network Controller (RNC)
Media Gateway (MGW)
The functionality of MSC and SGSN changes when going to UMTS. In a GSM system the MSC handles all the circuit switched operations like connecting A- and B-subscriber through the network. SGSN handles all the packet switched operations and transfers all the data in the network. In UMTS the Media gateway (MGW) take care of all data transfer in both circuit and packet switched networks. MSC and SGSN control MGW operations. The nodes are renamed to MSC-server and GSN-server.
Security

3G networks offer a greater degree of security than 2G predecessors. By allowing the UE to authenticate the network it is attaching to, the user can be sure the network is the intended one and not an impersonator. 3G networks use the KASUMI block crypto instead of the older A5/1 stream cipher. However, a number of serious weaknesses in the KASUMI cipher have been identified.

In addition to the 3G network infrastructure security, end to end security is offered when application frameworks such as IMS are accessed, although this is not strictly a 3G property.
Issues

Although 3G was successfully introduced to users across the world, some issues are debated by 3G providers and users:

Expensive input fees for the 3G service licenses & agreements
Numerous differences in the licensing terms
Large amount of debt currently sustained by many telecommunication companies, which makes it a challenge to build the necessary infrastructure for 3G
Lack of member state support for financially troubled operators
Expense of 3G phones
Lack of buy-in by 2G mobile users for the new 3G wireless services
Lack of coverage, because it is still a new service
High prices of 3G mobile services in some countries, including Internet access (see flat rate)
Current lack of user need for 3G voice and data services in a hand-held device