Advanced metering infrastructure (AMI) is the radio or mobile network, and the software behind it, that collects readings from millions of smart meters and sends commands back to them. The meter measures the power. AMI is the system that carries those measurements to the utility.
The main problem is scale. A city can have lakhs of meters, and each sends a reading many times a day. Some meters sit in basements or narrow lanes where mobile signal is weak. So many AMI systems use a mesh network. In a mesh, each meter passes the messages of its neighbours along, until they reach a device that has a good connection. That device is called a data concentrator. Other utilities give every meter its own mobile connection instead. That is simpler, but it needs a SIM or a similar link in every meter and a monthly cost for each.
Consider a meter on the ground floor of an old apartment block in Coimbatore. The walls are thick, and the meter cannot reach the mobile tower. A meter on the top floor of the next block can. So the ground-floor meter hands its reading to that meter, which forwards it. If that meter loses power, the first meter finds another neighbour, so the reading still gets through.
The software at the utility is called the head-end system. It collects the readings, checks them, and fills any gaps. It passes the data to a meter data management system, which stores it for billing, and to the grid control room. In the other direction, it sends commands to the meters, such as a request to read now or to disconnect a prepaid meter. Because a disconnect command can cut off a home's supply, each command is encrypted and checked before the meter obeys it.
The readings are a kind of time series data. Because there are so many, utilities need to store and process very large volumes. A mistake in AMI shows up directly in customers' bills, so reliability matters more than speed.
AMI is only the transport. What the data is used for, such as energy disaggregation, is a separate job.