If you have a mobile phone (if you don’t, I have no idea how you survive), you will be on an HLR. This article will contain some of the essential parts of an HLR, and we’ll try to make it as simple and fun as possible.
A little disclaimer
Before we start, let’s establish that the concept of the HLR is incredibly technical, and I am not a particularly technical person. The primary purpose of my writing this article is so that other non-tech-bros can better understand what an HLR is.
If you’re after a super technical explanation that gets into all the nooks and crannies of HLRs, there’s no shortage of those articles online. Still, I want this one to be for the everyman, the people who squeal in fear at the sight of a circuit board, the ones who enjoy their technology but aren’t always aware of how it works.
What is an HLR?
HLR stands for “Home Location Register,” and it’s basically a giant database owned by your Telco that contains all sorts of relevant information based on your access to a global communications system. Within this database, you’ll find the information required to allow you to make a phone call, including your phone number, current location, IMSI, and MSISDN (we’ll get onto those later). While it might sound strange, the current location is essential for making a phone call. If the satellites don’t know where you are, they cannot receive the signal your phone sends out; if the satellites can’t find you, you can’t make a phone call.
What are IMSI and MSISDN?
IMSI, “International Mobile Subscriber Identity,” contains information about who owns which SIM card. So, when an HLR detects your SIM card, it will be able to say (not literally say, but you get the idea), “This SIM card is from John Smith, his phone number is xxxxxx. He’s with Amaysim, and can call anyone, but only in Australia”. MSISDM stands for Mobile Station Integrated Services Digital Network. This is just a big list of phone numbers. Your phone number will be on one of these lists.
How do HLRs work?
When you want to make a phone call, your phone will send out what is known as an MSC. To make it as simple as possible, an MSC is like a signal your phone sends to the HLR. I know tech bros will be throwing their socks at their screens after reading that, but thinking of the MSC as a signal sent by your phone makes it easier. The HLR detects if you’re at home or roaming.
What happens if you’re at home?
Your HLR will simply allow you to make the call if you’re at home. It will enable you to send the signal from your phone to the satellites, and you can make your call. Again, tech bros will probably be mad at that, but I’m just making it as simple as possible.
What happens if you’re roaming?
But what about if you’re out and about? Well, the same thing happens. Your phone sends an MSC to the HLR. But the HLR will detect that you’re roaming and get in touch with your local HLR. With the information provided by your HLR, the new HLR will set up a temporary profile for you, enabling you to use it as you would your regular HLR. Let’s say you get a set amount of 4G in your plan, but only in Australia. One day, you take a holiday to New Zealand.
The HLR in New Zealand detects you’re roaming and contacts your local HLR. This local HLR will tell the kiwi HLR, “This guy needs to pay $10 per MB when he’s out of Australia”. To which the Kiwi HLR will say, “Okie Dokie, I’ll make sure to bill him.”
Conclusion.
I won’t lie to you; HLRs are incredibly complicated and technical, and I have done my best to simplify it as possible. It almost felt like trying to explain quantum physics to a five-year-old. However, the basics are that an HLR is a database containing all the vital information about your phone and how it connects to the global communications system. Without them, phone calls would rely on older, far less efficient technology. In a nutshell, your phone sends a signal to an HLR which will enable you to make a call or get in touch with your HLR first.