688 ApplianceWare managment protocol - System Port

688 is a System Port. Transport Protocol TCP UDP , 688 Service Name realm-rusd, Service Name Description: ApplianceWare managment protocol.

Port	Protocol	Service Name	Description	Source
688	TCP UDP	realm-rusd	ApplianceWare managment protocol	IANA
688	TCP UDP		REALM-RUSD (ApplianceWare Server Appliance Management Protocol),Official	wikipedia
688	TCP UDP		Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com
688	TCP UDP	realm-rusd	ApplianceWare managment protocol	bekkoame

Port	Service Name	Description
1084	ansoft-lm-2	Anasoft License Manager
1524	ingreslock	ingres
2359	flukeserver	FlukeServer
2639	aminet	AMInet
3723	sychrond	Sychron Service Daemon
4695		Unassigned
5292		Unassigned
6696		Reserved
8280	synapse-nhttp	Synapse Non Blocking HTTP
8548		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