981 Unassigned - System Port

981 is a System Port. Transport Protocol , 981 Service Name , Service Name Description: Unassigned.

Port	Protocol	Description	Source
981		Unassigned	IANA
981	TCP	SofaWare Technologies Remote HTTPS management for firewall devices running embedded Check Point FireWall-1 software,Unofficial	wikipedia
981	TCP UDP	Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com

Port	Service Name	Description
194	irc	Internet Relay Chat Protocol
659		Removed
997	maitrd
1230	periscope	Periscope
1349	sbook	Registration Network Protocol
1655	dec-mbadmin	dec-mbadmin
2984	hpidsadmin	HPIDSADMIN
4544		Unassigned
6432	pgbouncer	PgBouncer
6874		Unassigned

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