Internet Locator Service

Internet Locator Service. It was a client–server system developed by Microsoft to provide real-time user presence and location information, primarily for facilitating connections within its instant messaging and collaboration software ecosystems. The service functioned as a central directory where clients could register their status and query the availability of other users, enabling features like chat, application sharing, and whiteboarding in products such as Microsoft NetMeeting. Its architecture and protocols were foundational to Microsoft's early real-time communication platforms before being superseded by more modern presence information standards.

Overview

The primary role was to act as a dynamic directory service for locating users on a network and determining their readiness to communicate. It was a core component of Microsoft NetMeeting, allowing participants in a videoconferencing session to find each other and establish peer-to-peer connections for data exchange. The service maintained a database of online users, their network addresses, and supported capabilities, which clients could browse or search. This enabled seamless initiation of multimedia sessions, file transfers, and collaborative activities across corporate intranets and the wider Internet.

Technical operation

Operationally, clients communicated with a central server using a proprietary protocol over TCP port 389, which was also commonly used by the LDAP. Upon startup, a client would register its presence with the server, providing information such as its IP address, UDP ports for audio/video, and current status. The server, often running on Microsoft Windows NT Server, would aggregate this information into a searchable directory. Other clients could then query this directory to resolve a user's email address or alias to a current network location, enabling direct socket connections for RTP streams or T.120 data channels.

Historical development

It was introduced in the mid-1990s alongside Microsoft NetMeeting, which was itself derived from technology acquired from PictureTel and Intel. The service was integral to Microsoft's strategy for IP-based collaboration and competed with other early presence systems like those used in ICQ and AOL Instant Messenger. As part of the Microsoft Windows ecosystem, it was included in server products like IIS 4.0 and was later extended by the Exchange Server team. Its development culminated in the SIP-based Microsoft Office Live Communications Server 2005, which marked a transition towards IETF standards.

Related protocols and services

It was closely associated with the T.120 ITU standard for data conferencing and the H.323 suite for videotelephony. Its functionality was a precursor to and later integrated with the SIP for SIMPLE, which became the basis for Microsoft Lync and Skype for Business. Other related Microsoft services included the Active Directory, which handled authentication, and the Site Server ILS service. In the broader industry, similar concepts were implemented in the XMPP used by Jabber and the service records of the SLP.

Security and privacy considerations

The original design had significant security limitations, as registration and query traffic were typically unencrypted, exposing user IP addresses and online status to eavesdropping. This made it susceptible to harvesting attacks and could facilitate social engineering or network reconnaissance. The lack of strong authentication allowed for spoofing of user identities. In response, later implementations within corporate firewalls often used NTLM authentication and were placed behind proxy servers. These concerns directly influenced the development of more secure presence protocols with TLS encryption and end-to-end privacy controls in successor platforms.

Category:Microsoft services Category:Instant messaging Category:Directory services