704 errlog copy/server daemon - System Port

704 is a System Port. Transport Protocol TCP UDP , 704 Service Name elcsd, Service Name Description: errlog copy/server daemon.

Port	Protocol	Service Name	Description	Source
704	TCP UDP	elcsd	errlog copy/server daemon	IANA
704	TCP UDP		Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com
704	TCP UDP	elcsd	errlog copy/server daemon	bekkoame

Port	Service Name	Description
515	printer	spooler
546	dhcpv6-client	DHCPv6 Client
604	tunnel	TUNNEL
1214	kazaa	KAZAA
1421	gandalf-lm	Gandalf License Manager
2277	bluectrlproxy	Bt device control proxy
2334	ace-client	ACE Client Auth
2345	dbm	dbm
3964	sasggprs	SASG GPRS
4448	asc-slmd	ASC Licence Manager

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