When you connect to the Internet, what you are really doing is obtaining an IP address and DNS, which are basically the data that are assigned to your operator so that you can exchange information over the Internet. The problem is that, to save costs, the operators don't always assign the same IPs and DNS, they vary them, so if you always need to have total access to and from the Internet, it will be essential that you use a program like Dynamic DNS.
Get a fixed IP
There are many services that offer us the possibility to manage a fictitious fixed IP or DNS installing an application on our computer that periodically indicates if our IP and DNS have changed and updated, as Dynamic DNS is one of these applications. Thus, you will be able to have a mail, web or FTP server on your own computer, accessible from anywhere in the world.
With Dynamic DNS you will be able to configure any fixed IP service, to help you avoid the restriction of the operators, accomplishing a stable connection and the possibility to have servers of almost any service in your own house.