or set-top box. Content is compressed by Video and audio codecs and then encapsulated in MPEG transport stream or Real-time Transport Protocol or other packets. IP multicasting allows for live data to be sent to multiple receivers using a single multicast group address. In standards-based IPTV systems, the primary underlying protocols used are: Service-provider-based streaming: IGMP for subscribing to a live multicast stream (TV channel) and for changing from one live multicast stream to another (TV channel change). IP multicast operates within LANs (including VLANs) and across WANs also. IP multicast is usually routed in the network core by Protocol Independent Multicast (PIM), setting up correct distribution of multicast streams (TV channels) from their source all the way to the customers who wants to view them, duplicating received packets as needed. On-demand content uses a negotiated unicast connection. Real-time Transport Protocol (RTP) over User Datagram Protocol (UDP) or the lower overhead H.222 transport stream over Transmission Control Protocol (TCP) are generally the preferred methods of encapsulation. Web-based unicast only live and VoD streaming: Adobe Flash Player prefers RTMP over TCP with setup and control via either AMF or XML or JSON transactions. Apple iOS uses HLS adaptive bitrate streaming over HTTP with setup and control via an embedded M3U playlist file. Microsoft Silverlight uses smooth streaming (adaptive bitrate streaming) over HTTP. Web-based multicast live and unicast VoD streaming: The Internet Engineering Task Force (IETF) recommends RTP over UDP or TCP transports with setup and control using RTSP over TCP. Connected TVs, game consoles, set-top boxes and network personal video recorders: Local network content uses UPnP AV for unicast via HTTP over TCP or for multicast live RTP over UDP. Web-based content is provided through either inline Web plug-ins or a television broadcast-based application that uses a middleware language such as MHEG-5 that triggers an event such as loading an inline Web browser using an Adobe Flash Player plug-in. Local IPTV, as used by businesses for audio visual AV distribution on their company networks is typically based on a mixture of: Conventional TV reception equipment and IPTV encoders TV gateways that receive live Digital Video Broadcasting (DVB) MPEG transport streams (channels) from terrestrial aerials, satellite dishes, or cable feeds and convert them into IP streams Via satellite Although IPTV and conventional satellite TV distribution have been seen as complementary technologies, they are likely to be increasingly used together in hybrid IPTV