Depends on the vendor. The VLR is “bolted” to the MSC, hence MSC/VLR.
Generally, it is a parameter that is set as a part of the deployment of the MSC/VLR.
Can be configured using MML – Man Machine Language – commands.
It should not be a “hard-coded” parameter.
You will need to consult your MSC/VLR’s vendor manual, e.g. Ericsson, Huawei, Nokia, ZTE, etc..
VBR/ Wallis Dudhnath