Instead of using the Internet scheme of using a protocol port number as part of an address to deliver data to a process on a given host, consider an alternative scheme where the process is located using a unique process ID (PID), such as that assigned to each active process by the Unix operating system. Note that a PID is assigned dynamically to a process when the process is started so that it is not possible to know ahead of a program's execution what the ID will be at runtime. The range of values for PIDs also varies from system to system. What, if any, is the problem with such an addressing scheme?

Also, A naming scheme is said to allow location transparency [community- ml.org, 25] if the scheme allows objects to be addressed without explicit knowledge of their physical location. For example, the U.S. phone number system is location transparent, since a caller does not need to know the whereabouts of the callee when dialing up. The U.S. Postal Service address system, on the other hand, does not allow location transparency, since you must address the recipient with his/her physical address (excluding post office box numbers, that is).

Consider each of the following naming schemes. For each, determine whether it is location transparent. Justify your answer.

1 - The Domain Name System (DNS)

2 - Uniform Resource Locator (URL)

3 - Uniform Resource Name (URN)

4 - Extensible Name Service (XNS)