987 Unassigned - System Port

987 is a System Port. Transport Protocol , 987 Service Name , Service Name Description: Unassigned.

Port	Protocol	Description	Source
987		Unassigned	IANA
987	TCP	Microsoft Corporation Microsoft Windows SBS SharePoint,Unofficial	wikipedia
987	TCP UDP	Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com

Port	Service Name	Description
936		Unassigned
1051	optima-vnet	Optima VNET
4278	vrml-multi-use	VRML Multi User Systems
4446	n1-fwp	N1-FWP
4559	hylafax	HylaFAX
4707		Unassigned
5711		Unassigned
5758		Unassigned
6676		Unassigned
7399		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