Issue link: https://www.e-digitaleditions.com/i/1156106
October/November/December 2019 I 15 container. During decoding, the compressed video is de-encapsulated and decompressed using the same H.264/AAC codec to recover the RGB video. • Video Stream Transmission—When streaming video over Ethernet, unicast and multicast are two commonly used methods to transmit from source to destination (see Figure 6). Unicast transmission is point-to-point. The video stream is sent from one device IP address to another via standard TCP/IP network connection protocol based on where the content is going. The video stream is transported from the sending device directly to a user who has requested the stream. Each requesting user gets a separate iteration of the stream. Because unicast employs standard TCP/IP, it is easy to use and seldom requires modifications to TCP/IP network infrastructure. Unicasting works well for on- demand video streamed at a user's convenience. The user can play, pause or stop the stream at will. The downside of unicasting is that it does not scale well. If too many users request the stream simultaneously, network con- Unicast Delivery Multicast Delivery Server Network Switch Layer 3 Routing Layer 2 Switching 192.168.0.1 Server Network Switch Layer 3 Routing Layer 2 Switching IGMP Snooping and Query Enabled 192.168.0.1 192.168.0.2 192.168.0.3 192.168.0.4 192.168.0.2 192.168.0.3 192.168.0.4 gestion can occur because the stream is duplicated for each user. Also, TCP checks to ensure error-free data reception. When data slows from traffic or from error checking, buffering occurs on the unicast stream. This might be merely irritating when watching a movie or video clip, but it can ruin a video conference call or a live-streamed event. Multicast transmission is one-to-many or many-to- many. A single video stream sent from a device on the network is delivered to multiple reception points via the user datagram protocol (UDP). The video stream goes from the sending device to each user who has tapped into the stream at the network switch. Unlike unicast, all users share the same stream, so they cannot play, pause or stop the stream at will. Because UDP does not check to ensure error-free data reception, it uses less overhead than TCP and transmits data faster, making buffering less likely than with unicast. This makes multicasting attractive for real- time streaming applications, such as video conferencing and live streaming. The downside of multicasting is that UDP makes no guarantees that video stream data packets will reach the destination error free. It is up to the FIGURE 6: With unicast, the source sends a duplicate data stream to each requesting user; with multicast, one data stream is shared by multiple users wishing to receive the stream.