(Service Location Protocol) An IETF standard used to announce and discover services such as printers and file shares on an IP network. Apple used SLP prior to Mac OS 10.2, but migrated to its Bonjour technology. SLP is also used in SIP-based IP telephony applications. SLP addresses are formed like a URL, and SLP packets are typically transmitted over UDP. User, Service and Directory Agents An SLP "user agent" (UA) process runs in the client that queries a "service agent" (SA), which advertises its available service. In large networks, a "directory agent" (DA) caches services to improve performance, and user agents and service agents must use the directory agent if present. See SSDP and SIP.