a and transmit it in IP www.TechnicalPDF.com packets. This is a significant improvement in spectral efficiency that eliminated the need to set aside separate spectrum for voice calls. All 3rd generation and newer cellular services are digital. This improves privacy as eavesdropping on digital transmissions is more difficult because the digital bits are encrypted (encryption uses mathematical algorithms to reorder bits, making them unreadable to unauthorized people) before they are transmitted over the open air between handsets and an operator's equipment. See Table 7-1 for a list of the main mobile protocols along with the various implementations within each generation. Unlike 3rd generation protocols, which used different technologies in Europe and parts of the United States, 4G LTE is for the most part is implemented uniformly throughout the United States and Europe, as well as in Asia and parts of Africa. All current mobile services including 2G (second- generation) services are digital. Digital mobile protocols use codecs to code analog voice into digital bits and decode them to analog at the receiving user device. Digital transmissions enable features such as caller ID, speed dialing, and voicemail message notifications. Signals for these features are carried separately in the signaling channel. 3G standards had various releases or revisions, which improved upon and increased capacity and suitability for mobile networks capable of carrying voice, video, and data. However, even in these revisions, voice is transmitted using the less-efficient circuit switching where spectrum that could be shared with data is set www.TechnicalPDF.com aside for voice. More information on 3G and 3G standards are in Table 7-6 and Table 7-7 in the "Appendix." In 4G networks, voice is carried in Internet Protocol (VoIP) packets on the same spectrum as data. 3G protocols are still available in even advanced networks because there are still older phones that are compatible with only 3G and not 4G protocols. Once mobile providers find