Understanding the components of a SIM card, its functions and working

Source: The post is based on the article “Understanding the components of a SIM card, its functions and working” published in “The Hindu” on 25th October 2023

What is the News?

Over the years, the SIM card has shrunk from the SIM to the mini SIM to the micro SIM to the nano SIM.The latest on this path is the eSIM card.

What is a SIM Card?

SIM stands for ‘subscriber identification module’.It is an integrated circuit or a microchip that identifies the subscriber on a given network.

In order for a mobile phone to connect to any cellular network that follows the Global System for Mobile Communications(GSM) standard, a SIM card is mandatory. 

This relationship is established using a unique authentication key — a piece of data that you need to ‘unlock’ access to the network. 

Every SIM card stores this data and it is designed such that you can’t access it through your phone. 

Instead, signals sent by your phone into the network are ‘signed’ by the key and the network uses the signature to understand whether your phone’s connection is legitimate.

Note: It is possible to duplicate a SIM card by accessing its key and putting it into another card.This is known as SIM cloning.

What information does a SIM card store?

The SIM card contains important information that identifies the user to the mobile network and allows the device to connect to the network. 

This information includes its own ID number (the integrated circuit card identifier), the International mobile subscriber identity(IMSI), the subscriber’s location area identity (i.e. their current location), a list of preferred networks (to whom the subscriber can connect when roaming) and emergency numbers.

What is eSIM?

An eSIM, or embedded SIM is a digital or electronic SIM card that is built into a device, such as a smartphone, tablet, or smartwatch, rather than being a physical, removable card. 

It serves the same purpose as a traditional SIM card, which is to identify a user to a mobile network and enable connectivity.

Advantages of eSIM: 

Firstly, it is considered to be environmentally friendlier than a physical SIM.Its reprogrammability means no need for more plastic and metal for a new SIM. 

Secondly, if a malicious person gains access to your phone, they won’t be able to separately access the SIM application nor be able to duplicate it.

Disadvantages of eSIM:

Firstly, in some countries, including the U.S, eSIMs can be programmed by subscribers themselves.But this process might be difficult for those with low digital literacy such as the elderly. 

Secondly, an eSIM can in theory allow network operators to track subscribers data including inside apps on the device, especially in the absence of data privacy laws.