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There is a fundamental difference between addresses and identifier of devices. Addresses determine the communication endpoint within a certain system. For example in the Internet Protocol an IP address is needed to establish a socket, a connection between devices. While an address is unique at a given point in time, addresses need not be permanent. A device can have its address changed. A new device can take on the address of a previous device. And a device can have more than one IP address.
Identifiers can be understood as a dedicated, publicly known attribute or name for an identity, a person or a device. Typically, identifiers are valid within a specific domain. A device can have more than one identifier, but it requires at least one unique identifier within any domain through which it can be accessed.
In the classic Web we have a Domain Name Service (DNS) mapping human readable Uniform Resource Identifier (URI) to IP-addresses. A browser for example resolves a website URI www.telekom.com first. The actual connection between the browser and the Web server is then established by using the returned IP-address.
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