Question

2. As pointed out in the textbook, port numbers of are unique within a system. For example, TCP port 1433 is the default port for SQL Server default instance and UDP port 1434 is used for SQL Server Browser service, both SQL Server default instance and SQL Server Browser service are 'local process' to Windows or Windows Server. These examples also explain that the local process (i.e., port number) implies the protocol, which is also stated in the textbook. If this is true, when used as an API, why a socket needs to be identified by the triple (protocol, local address, local process) instead of (local address, local process)?

Answer 1

Yes, port numbers are unique but some time and this will be unique only in the case when only one instance is running and if there are more than one instances running then the port number for the remaining processes would be chosen from the range: (49152–65535).
Thus it is crucial for us to specify the protocol along with the local address and local process. Because when there would be more than one processes of the same application running then it would be necessary to specify the protocol it is using.

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