BLE Major/Minor functionality

Question

Can anyone tell me what major and minor (contained within the advertisement packet of BLE signals) are used for? I've heard that it's used for differentiating signals with the same UUID, but that raises questions like "why use two" and "is that just how certain receivers use it". It would be useful to have a decent explanation of it.

Answer 1

As per @Larme's comment, I presume you are asking about iBeacon advertisements - these are a special use of BLE. Bluetooth Low Energy service advertisements have a different format and don't include the major/minor.

The iBeacon specification doesn't say how to use major and minor - this is defined by the people that implement solutions using iBeacon. Two numbers just gives more flexibility.

A lot of effort went into making BLE use very little power. Accordingly the iBeacon advertisement has to be quite small in order to minimise the transmission time. I guess the designers decided two 16 bit numbers was a reasonable compromise between power consumption and a useable amount of information.

A typical retail use case could use the major to indicate a store (New York, Chicago, London etc) and the minor to indicate the department (shoes, menswear etc). The app that detects a beacon can then pass this information to a server which can send back relevant information - the user's location on a map or specials for that department etc. This was discussed in the guide that @Larme linked to.

A solution that presented information on museum exhibits might just use the major number to determine which exhibit the person was near and ignore the minor number. The minor number would still be in the advertisement, of course, the app just wouldn't use it for anything.