903 self documenting Telnet Panic Door - System Port

903 is a System Port. Transport Protocol TCP , 903 Service Name ideafarm-panic, Service Name Description: self documenting Telnet Panic Door.

Port	Protocol	Service Name	Description	Source
903	TCP	ideafarm-panic	self documenting Telnet Panic Door	IANA
903	UDP	ideafarm-panic	self documenting Panic Door: send 0x00 for info	IANA
903	TCP		VMware Remote Console ,Unofficial	wikipedia
903	TCP UDP		Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com
903			Net-Devil	simovits.com
903	TCP UDP	ideafarm-catch	IDEAFARM-CATCH	bekkoame

Port	Service Name	Description
158	pcmail-srv	PCMail Server
845		Unassigned
2537	upgrade	Upgrade Protocol
3019	resource-mgr	Resource Manager IANA assigned this well-formed service name as a replacement for "resource_mgr".
3054	amt-cnf-prot	AMT CNF PROT
3382	fujitsu-neat	Fujitsu Network Enhanced Antitheft function
5177		Unassigned
5857		Unassigned
6084	reload-config	Peer to Peer Infrastructure
6192		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