Port 728 Unassigned - System Port

Port 728 is a System Port. Transport Protocol , Port 728 Service Name , Service Name Description: Unassigned.

Port	Protocol	Description	Source
728		Unassigned	IANA
728	TCP UDP	Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com
728	TCP UDP	Unassigned	bekkoame

Port	Service Name	Description
67	bootps	Bootstrap Protocol Server
764	omserv
1899	mc2studios	MC2Studios
2158	touchnetplus	TouchNetPlus Service
3631	cs-services	C&S Web Services Port
4612		Unassigned
6922		Unassigned
7028		Unassigned
7672	imqstomp	iMQ STOMP Server
8115	mtl8000-matrix	MTL8000 Matrix

A port is an endpoint of communication in an operating system. While the term is also used for hardware devices, in software it is a logical construct that identifies a specific process or a type of service.

Port numbers are assigned in various ways, based on three ranges: System Ports (0-1023), User Ports (1024-49151), and the Dynamic and/or Private Ports (49152-65535);

The Well Known Ports are assigned by the IANA and on most systems can only be used by system (or root) processes or by programs executed by privileged users. Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port. The contact port is sometimes called the "well-known port". To the extent possible, these same port assignments are used with the UDP [RFC768]. The range for well-known ports managed by the IANA is 0-1023.
DYNAMIC AND/OR PRIVATE PORTS Registered Ports are those from 1024 through 49151.
The Dynamic and/or Private Ports are those from 49152 through 65535