HLR & VLR

HLR and VLR are two important components in mobile network environment where the basis of mobility depends on these two elements. HLR is the Home Location Register whereas VLR is the Visitor location register.

The main purpose of HLR is to find the location information of a mobile subscriber. For a simple example it is like checking the address of a letter where it should be sent. In this case the problem is, address of the subscriber is not static but dynamic. It changes all the time. So HLR contains the location information of subscribers which helps operators to find where he/she is.

VLR contains information about users in a particular area at a given time. So it is not a permanent storage since the users in a particular area can be switched constantly. This VLR is attached to a particular Mobile Switching Center (MSC) which receives Short Messages (SM) or Calls from operator and distribute it to the final user.

When these two elements are compared and contrasted, HLR is a permanent data storage whereas VLR is a temporary storage. HLR contains all the data about the entire subscriber base of a particular operator whereas at a given time VLR contains information about a subset of the subscriber base unless all the subscribers are in one geographical area. And HLR is built as optimized reading is capable whereas in VLR both the processes reading and writing is optimized.

In conclusion both these elements are vital in mobile networks since the mobility depends on HLR and VLR, specially using HLR.