Know about your SIM(Subscriber Identity Module)

GSM (Global System for Mobile Communication) and CDMA (Code Division Multiple Access) are two dominant technologies for mobile communication.

GSM:-

Technically GSM (Global System for Mobile communications, originally from Groupe Spécial Mobile) is a specification of an entire wireless network infrastructure. GSM operates on the wedge spectrum called a carrier. This carrier is divided into a number of time slots and each user is assigned a different time slot so that until the ongoing call is finished, no other subscriber can have access to this. GSM uses both Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) for user and cell separation.

CDMA:-

CDMA relates only to the air interface — the radio portion of the technology. The CDMA is based on spread spectrum technology which makes the optimal use of available bandwidth. It allows each user to transmit over the entire frequency spectrum all the time. 

DIFFERENCE BETWEEN CDMA AND GSM:-

	CDMA	GSM
Stands for	Code Division Multiple Access	Global System for Mobile communication
Storage Type	Internal Memory	SIM (subscriber identity module) Card
Global market share	25%	75%
Dominance	Dominant standard in the U.S.	Dominant standard worldwide except the U.S.
Data transfer	EVDO/3G/4G/LTE	GPRS/E/3G/4G/LTE
Network	There is one physical channel and a special code for every device in the coverage network. Using this code, the signal of the device is multiplexed, and the same physical channel is used to send the signal.	Every cell has a corresponding network tower, which serves the mobile phones in that cellular area.
International roaming	Less Accessible	Most Accessible
Frequency band	Single (850 MHz)	Multiple (850/900/1800/1900 MHz)
Network service	Handset specific	SIM specific. User has option to select handset of his choice.

HANDSETS SWAPPING IN GSM AND CDMA:-

You can swap GSM SIM(Subscriber Identity Module) cards between handsets when a new one is necessary, which enables you to carry all of your contact and calendar information over to a new handset with no hassle. CDMA operators answer this flexibility with their own service that stores user dataa, including phone book and scheduler information, on the operator’s database. This service makes it possible to not only swap over to a new handset with little trouble, but it also gives users the ability to recover contact date even if their phone is lost or stolen.

 Interaction between GSM and CDMA

In CITIES and densely populated areas, there are often high concentrations of GSM and CDMA connection bases. In THEORY, GSM and CDMA are invisible to one another and should "play nice" with one another. In practice, however, this is not the case. High-powered CDMA signals have raised the "noise floor" for GSM receivers, meaning there is less space within the available band to send a clean signal. This sometimes results in dropped calls in areas where there is a high concentration of CDMA technology. Conversely, high-powered GSM signals have been shown to cause overloading and jamming of CDMA receivers due to CDMA’s reliance upon broadcasting across its entire available band.

source:- diffen.com