Dual SIM phone call waiting on one SIM when using other SIM?

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.

Replies

  • Harshad Italiya
    Harshad Italiya
    gwendollen
    In our dual sim mobiles,suppose we are in call via 1st sim..if another person calls to the 2nd sim why cant that person hear the ring or atleast call waiting??i know we cant hear ring practically....but theoritically the two sim's are independent to each other and also each sim and phone are not connected physically...sim is just an interface....then what is it the reason that the service providers cant able to provide this compatibility to the mobiles???
    Dual SIM capability is not handled by SIM provider it is handled by the Processor used in mobile. So there is no any relation between two GSM provider you are using. If your processor is smart enough to sense that there is incoming call on other SIM then they can give you acknowledge on same. In this case both GSM modem running in parallel (Samsung phone is example of such).
  • Sindhu Chowdary
    Sindhu Chowdary
    do you mean that samsung phones have such facility...i mean their processors are smart enough to recognize another call on another sim?
  • lal
    lal
    Not all samsung phones have this ability. Those phones termed 'dual sim stand-by' cannot connect to two calls at the same time. When at stand by they can recieve signal in both networks(sims). But once a call is initiated or gprs connection is attached in one sim, the other network will be disconnected. If the phone is termed 'dual sim active', the device will be able to make calls in both networks at the same time.

    This gives information on all the dual sim varieties Dual Sim
  • neha samant
    neha samant

    Is there any way that if i am using sim 1 and i am on call and any other person calls me either on sim 1  or sim2 then both the numbers say not rechable or switched off so that other person dont come to know that phone was busy

  • Amol Jain
    Amol Jain

    It happens with Xiaomi dual SIM phones. But the other person does get a busy tone. I myself have experienced this several times. 

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