819 Unassigned - System Port

819 is a System Port. Transport Protocol , 819 Service Name , Service Name Description: Unassigned.

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

Port	Service Name	Description
738		Unassigned
1575	oraclenames	oraclenames
1926	egs	Evolution Game Server
2200	ici	ICI
3339	anet-l	OMF data l
5843		Unassigned
5913	ads-c	Automatic Dependent Surveillance
6485	sun-sr-iiop	Service Registry Default IIOP Domain
6518		Unassigned
7008	afs3-update	server-to-server updater

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