[Keefe]

Short for Realm-Specific Internet Protocol, an IP address translation technique that is an alternative to NAT. RSIP lets an enterprise safeguard many private Internet addresses behind a single public Internet address.
RSIP functions by leasing public IP addresses and ports to RSIP hosts located in private addressing realms. The RSIP client requests registration with an RSIP server, or gateway. The server in turn delivers either a unique public IP address or a shared public IP address and a unique set of TCP/UDP ports and attaches the RSIP host’s private address to this public address. The RSIP host uses this public address to send packets to public destinations. The packets contain both the public and private addresses, and the RSIP server strips off the private address header and sends the packet on with a public IP header.

RSIP can also be used to relay traffic between several different privately addressed networks by leasing several different addresses to reach different destination networks.