Member • Jan 11, 2013
Dual SIM phone call waiting on one SIM when using other SIM?
In dual-SIM mobile devices, suppose we are engaged in a call via the first SIM. If another person calls on the second SIM during this period, why can't the caller hear a ring or at least receive a call waiting notification?
While I understand that we, as users, can't hear a ring due to practical constraints, isn't it theoretically possible since the two SIM cards operate independently of each other and are not physically connected to the phone?
They serve merely as interfaces. So, what is the underlying reason that prevents service providers from providing this compatibility to mobile devices?
Answer:
Have you ever found yourself puzzled about the peculiar functioning of dual SIM phones? Specifically, have you ever wondered why a caller can't hear a ring or receive a call waiting notification when they dial your second SIM while you're on a call using the first SIM?
You might logically conclude that since SIM cards operate independently and serve simply as interfaces rather than physical components of the phone, there should be no hindrance to such functionalities.
Well, this confusion is something I've pondered too, and after delving deeper into the matter, I've found some enlightening answers.
To understand why this occurs, we need to unravel the technological fabric of our modern smartphones, particularly dual-SIM devices.
The essence of this issue lies within the design of the phone and the functionality of the telecommunication networks, rather than with the service providers themselves.
The first point to consider is that while both SIM cards can be in standby mode simultaneously, generally, only one can be active at a time.
This is especially true for devices that employ Dual SIM Dual Standby (DSDS) technology. When you are engaged in a call on one SIM card, the other SIM card essentially goes into a "passive" state.
This means it can't receive calls or messages because all the resources of the device are channeled towards maintaining the active call on the first SIM.
Now, you may wonder, why can't the second SIM simply stay active as well, allowing for call waiting notifications or at least a ring?
This leads us to the second factor at play - the telecommunication networks.
Calls are facilitated via the cellular network's radio resources. When you're on a call, your phone is using these resources to maintain the connection.
The issue arises from the fact that a single phone generally has only one radio transceiver, which can handle one call at a time.
This is a hardware limitation and has nothing to do with the SIM cards themselves or the service provider.
To put it simply, imagine the radio transceiver as a single lane road. You can only drive one car (or call) down it at a time. If another car (or call) comes from the opposite direction, it has to wait until the road is clear before it can proceed.
In theory, you could have a phone with two or more radio transceivers, each connected to a different SIM card. This would indeed allow each SIM to handle calls independently of the other.
But this approach has its challenges. More transceivers would mean a higher cost for the device, increased power consumption, and likely a larger physical size to accommodate the additional hardware.
Consequently, most phone manufacturers opt for a single radio transceiver to balance functionality, cost, and battery life.
In conclusion, the inability to receive a call on the second SIM while engaged in a call on the first is due primarily to device design and network limitations rather than any restrictions imposed by the service provider.
With advancements in technology, these limitations could potentially be overcome. Until then, our dual-SIM devices will continue to operate one call at a time.