Technical Q&A NW12

Static Socket Numbers

Q: We created an application that allows many users to communicate and send files on a common socket number. Inside Macintosh: Networkingstates on page 7-6that 64-127 socket numbers are available for program development, but not for a released product. We want to use a static socket number, since opening a different dynamic socket for each machine to send duplicate information is pointless, and it would have excessive overhead.

We want to apply for a socket number within the range of 1-63 (Inside Macintosh: Networking states these are reserved for use by Apple) so that there is no chance that Apple or another developer could create a product that tries to use the same socket. If we can obtain an assigned socket number, all future applications that we create will use the same socket number.

A: We understand your need for a well-known, static DDP socket number, since your application multicasts/broadcasts to a well-known number. Unfortunately, however, Apple does not assign static socket numbers.

Your best bet would be to pick an arbitrary number (in whatever range you feel safest) and use it, but allow the user (or the network administrator) to modify that number via a control panel (possibly an administrative panel that uses a preference file that the administrator distributes, or an administrative server that provides this number).

While this method doesn't guarantee that you'll have sole use of a socket number, it does allows you to have some centrally administered options.