What is PTT or PoC?

PTT PoC or Push to Talk over Cellular is a service option for a cellular phone network which permits subscribers to use their phone as a walkie-talkie. A typical Push to Talk connection connects almost instantly. One significant advantage of PoC is that it allows a single person to reach an active talk group with a single button press; users no longer need to make several calls to coordinate with a group. Push-to-talk cellular calls are half duplex communications — while one person transmits, the other(s) receive. Traditional mobile phone networks and devices utilize full-duplex communications, allowing customers to call other persons on a mobile or land-line network and be able to simultaneously talk and hear the other party. Such communications require a connection to be started by dialing a phone number and the other party answering the call, and the connection remains active until either party ends the call or the connection is dropped due to signal loss or a network outage. Therefore, telephone communication protocol does not allow for casual and immediate transmissions to be sent to other parties on the network. Whereas telephone calls require the lengthy process of dialing, network switching and routing, call setup, and waiting for the other party to answer, a two-way radio has a much quicker protocol because of the immediacy of push to talk communication. Full-duplex operation on mobile phone networks is made possible by using separate frequencies for transmission and reception. Mobile Push-to-Talk service, offered by some mobile carriers, adds functionality for individual half-duplex transmissions to be sent to another party on the system without needing an existing connection to be already established. Since the system is half-duplex, only one user can transmit by PTT at a time; the other party is unable to transmit until the transmitting user unkeys their PTT button. Currently, PTT service is supported only between parties on the same mobile carrier service, and users with different carriers will be unable to transmit to each other by PTT.

What is CDMA?

Definition: CDMA, or Code Division Multiple Access, is a competing cell phone service technology to GSM, which is the world’s most widely used cell phone standard. CDMA uses a “spread-spectrum” technique whereby electromagnetic energy is spread to allow for a signal with a wider bandwidth. This allows multiple people on multiple cell phones to be “multiplexed” over the same channel to share a bandwidth of frequencies. With CDMA technology, data and voice packets are separated using codes and then transmitted using a wide frequency range. Since more space is often allocated for data with CDMA, this standard became attractive for 3G high-speed mobile Internet use. The CDMA standard was originally designed by Qualcomm in the U.S. and is primarily used in the U.S. and portions of Asia by other carriers. Sprint, Virgin Mobile and Verizon Wireless use CDMA while T-Mobile and AT&T use GSM. While CDMA and GSM compete head on in terms of higher bandwidth speed (i.e. for surfing the mobile Web), GSM has more complete global coverage due to roaming and international roaming contracts. GSM technology tends to cover rural areas in the U.S. more completely than CDMA. Over time, CDMA won out over less advanced TDMA technology, which was incorporated into more advanced GSM.