Cisco 7920 Wireless IP Phone
Cordless telephones
Cordless telephones consist of a base unit that connects to the land-line system and also communicates with remote handsets by low power radio. This permits use of the handset from any location within range of the base. Initially, cordless phones used the 1.7 MHz range to communicate between between base and handset. Because of quality and range problems, these units were soon superseded by systems that used frequency modulation in higher frequency ranges (49 MHz, 900 MHz, 2.4 GHz, and 5.8 GHz). The range of modern cordless phones is normally on the order of a few hundred yards.
Wireless phone systems
Most wireless phone systems are cell-structured. Wireless communication is used between the handsets and the cell. Communication between cells can be wireless, or over ground cables. When an active handset moves from one cell to another, the call is automatically transferred to the next cell without interrupting the call.
There are now multiple standards for common carrier wireless telephony, often with multiple incompatible standards used in the same nation:
- First generation – Analog
- marine and mobile radio telephony
- AMPS
- CDPD data service on AMPS
- NMTS
- Second generation (2G) – Digital
- CDMA IS-95A
- GSM, (different frequencies for different continents: see GSM article)
- iDEN
- TDMA IS-136
- 2.5G
- CDMA IS-95B
- GPRS
- EDGE
- i-Mode
- Third generation (3G)
- CDMA 2000
- UMTS, also called W-CDMA
- TD-SCDMA
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
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