The secrets you don't know about dual SIM dual standby

Do you think dual SIM functionality simply means inserting two SIM cards and using two phone numbers? However, behind this seemingly simple feature lie many secrets you may not know.

In 2000, Finland's Benefon company launched the world's first dual SIM card mobile phone, the Benefon twin.

However, due to the technological limitations at that time, the user experience of this phone was not very good.

It was the Chinese mobile phone manufacturers in the 2000s that really popularized the dual SIM functionality in the Chinese and even global markets.

Thanks to the low - cost chip solutions provided by domestic chip manufacturers such as MediaTek, the manufacturing cost of dual SIM phones was greatly reduced, which led to the rapid popularization of this feature.

At the end of 2005, China Unicom and Yulong Coolpad jointly launched the world's first dual SIM dual standby smartphone: the Coolpad 728.

Since then, more and more domestic and international brands have applied the dual SIM feature to mid - to high - end mobile phones, and it has gradually spread across all price segments.

This trend even contributed to the rise of some mobile phone manufacturers at that time, such as the well - known Longcheer Technology, Tianlong Mobile, and WNC Technology. They met the actual needs of a large number of users with the dual SIM feature and thus captured a considerable market share.

So, why has the dual SIM dual standby feature become a necessity and so popular in the Chinese market?

There are several important factors behind this.

First of all, there are huge differences in the package fees among domestic operators. For example, most of China Mobile's data packages are quite expensive, while those of China Telecom and China Unicom are much cheaper.

Many users choose to use two SIM cards simultaneously to save on phone bills. One card is used as the primary card for binding various information, and the other is used as a data card.

Another phenomenon is that many users need to separate their work and personal phone numbers. The dual SIM dual standby feature perfectly solves the convenience of number management, allowing users to better balance their personal and professional lives.

In addition, there are differences in signal quality and network coverage among different operators in different regions. The dual SIM feature enables users to have a more reliable network connection in different locations, avoiding the situation of being unable to access the Internet due to poor signal from a single operator. Under the combined effect of these factors, the dual SIM dual standby feature has become a widely accepted and strongly demanded feature among Chinese consumers. This strong market demand can even influence the decisions of global technology giants.

A typical example is Apple.

As we all know, Apple was relatively slow in implementing the dual SIM dual standby feature in iPhones. It wasn't until the iPhone XS in 2018 that Apple first added dual SIM card support to its phones.

More interestingly, to cater to the huge demand in the Chinese market, the Chinese version of the iPhone XS even offers two physical SIM card slots, while iPhones sold in other countries mostly use a combination of a physical SIM card and an eSIM.

This fully demonstrates the huge demand and influence of the Chinese market for the dual SIM dual standby feature, which can even make a giant like Apple, known for its design consistency, make localized adjustments for market share.

So, what is the technical principle of dual SIM dual standby, and how does it enable communication and Internet access?

Actually, what we've always called the SIM card is an abbreviation of a long English name, which, when translated, means Subscriber Identity Module.

Don't be deceived by the small size of the SIM card; it has a very high level of internal integration. Structurally, it mainly consists of three parts: the outermost metal contacts, which are responsible for physical connection with the phone's circuit and serve as the interface for data transmission; the middle protective hard rubber, which protects the internal core components; and the most crucial part, a tiny integrated circuit chip.

This chip is the core of the SIM card, storing the user's unique identity information. This information includes the International Mobile Subscriber Identity (IMSI), which is a globally unified code that can uniquely identify a user. It is used by the network to identify which country, which telecom operator, and even which mobile service area the user belongs to, as well as a 128 - bit encryption key for network authentication.

When the phone needs to access the network, it goes through a series of complex authentication processes with the chip via the metal contacts. The phone sends the IMSI to the network, and the network responds with a random number. The SIM card chip then encrypts this random number using its internal key and returns the result to the network to prove its legitimate identity.

Only when the network verification is passed can the phone officially access the network for calls and data communication. Thus, the SIM card is the key for the phone to connect to the mobile network.

The dual SIM dual standby feature has two main modes: DSDS and DSDA. Understanding them is the key to uncovering the principle of dual SIM dual standby.

DSDS, which is what we commonly call dual SIM dual standby single call, as the name implies, means that two SIM cards can be on standby simultaneously and can both receive calls and text messages.

However, its core lies in the single call aspect, which means that when one SIM card is in a call or using data, the other will be temporarily offline or disabled.

For example, when you are making a call with SIM card 1, SIM card 2 cannot receive calls or access the Internet at this time. Data traffic can only be processed by one SIM card selected by the user at a time.

Phones in DSDS mode usually only need one set of radio frequency modules and baseband chips. They achieve the alternate standby of two SIM cards through very fast software switching, which is hardly noticeable in daily use.

Then there is the second mode: DSDA, which is dual SIM dual call.

This is a more advanced mode that allows the phone to use two SIM cards for communication simultaneously. For example, one card can be used for making a call while the other can be used for accessing the Internet, or both cards can perform high - speed data transmission at the same time.

Compared with DSNS, the implementation of DSDA requires more complex hardware support, usually two sets of independent radio frequency modules to process the data streams of the two SIM cards respectively.

It also needs to meet specific frequency band combinations and network conditions. It can only be activated when the frequency bands of the two SIM cards form a DSDA combination supported by the device.

The biggest advantage of the DSDA mode is that it can significantly improve the communication rate, especially in scenarios that require high - speed data transmission, such as downloading large files or conducting high - definition live broadcasts. By using two SIM cards to transmit target service data simultaneously, the communication rate can be increased.

To avoid excessive power consumption and data waste, the DSDA function may also be intelligently turned on or off in combination with various conditions such as network status, device temperature, and battery level.

There are two crucial factors that contribute to our smooth dual SIM dual standby experience today: VoLTE and VoNR. They are the keys to achieving high - quality calls.

VoLTE is voice call based on the 4G LTE network. Before VoLTE, when we used 4G to access the Internet, the phone would automatically fall back to the 2G or 3G network when making a call, resulting in mediocre call quality and network interruption during the call.

The emergence of VoLTE has completely changed this situation. It enables high - definition voice and video calls to be made directly over the 4G LTE network, greatly improving call quality with clearer and more realistic sound.

It allows calls and data to be used simultaneously, which means you can continue to watch videos, play games, or send WeChat messages over the 4G network while making a call, and the data service will not be interrupted. This solves the pain point of DSDS to a certain extent, which is especially important for dual SIM users. For example, when you make a call with the secondary SIM card, the data network of the primary SIM card can remain unobstructed.

VoNR is the 5G version of VoLTE.

It provides higher - quality voice and video calls directly over the 5G SA network. The advantage of VoNR is that it allows users to use 5G data during a voice call, ensuring an uninterrupted high - speed experience.

After talking about SIM cards, let's talk about the corresponding card slots. In the era of feature phones, you had to open the back cover of the phone and even remove the battery to see the SIM card slot, and then insert the SIM card like inserting a battery.

At that time, the card slots were usually fixed inside the phone without the convenient card tray design we have now. Although this design was relatively sturdy, it was very troublesome to replace the SIM card, and it was also more complicated to repair if the card slot was damaged.

Then, with the development of technology, SIM cards started a "slimming campaign".

They gradually shrank from the size of a credit card. First, they became Mini - SIM cards, and then shrank further into Micro - SIM cards, which are smaller than Mini - SIM cards and look like small stamps.

The most common SIM card in our phones now is the Nano - SIM card, which was introduced in 2012. It has become so small that it almost only consists of the chip and a plastic border. It is the continuous reduction in the size of SIM cards that has freed up valuable space inside the phone, making the physical implementation of dual SIM dual standby possible.