* How video over IP works
Today, we’ll continue our primer on how video over IP networks works with a discussion about the options for video transmission. We’ll start with video conferencing. Once encoded into digital format, video for conferencing can be sent over a private network using either private (non-IP) lines, private IP or IP-VPN connections, the public Internet (not recommended), VDSL, or via radio transmission to mobile devices.
For video conferences, the video is treated as a real-time transmission, and session control for IP connections is provided by either H.323 or Session Initiation Protocol (SIP). QoS is controlled by setting IP bytes to differentiate the video from data transmissions that may be sharing the same line, and audio-visual quality will vary based on the compression techniques and bandwidth allocation. Video on demand can also be shared within the enterprise using the same video compression and control protocols used for video conferencing. Click here for a discussion on video compression.
Video over IP can also be sent over VDSL. IPTV deployments like AT&T’s U-verse use VDSL to deliver standard broadcast quality and HDTV to the mass market. VDSL speeds can theoretically reach 56Mpbs, but in real networks it currently provides about half of the theoretical limit. IPTV differs from cable broadcast television in how it is delivered to the subscriber, but broadcast and IPTV use video compression. Cable TV broadcasts every channel via a hybrid fiber-coax network to every subscriber, but the set top box in the home authorizes what each subscriber can see based on their subscription package. When IPTV is delivered, each channel is a “switched” session so the network delivers each individual channel as an IP session – saving bandwidth across the VDSL network by providing the user one channel at a time.
Video to mobile handsets is delivered on the cellular phone network’s data channel using one of two techniques: Digital Multimedia Broadcasting (DMB) or Digital Video Broadcasting (DVB). Both techniques can be deployed on GPRS and UMTS networks, both can use H.264 for audio-video encoding, and both offer satellite and terrestrial modes for operation. As is the case with the landline delivery, mobile video quality will vary depending on the compression techniques and bandwidth allocated. While today’s mobile video is typically not delivered over IP, most mobile providers plan to send their mobile video over IP in the future.
