Video networks

SMPTE 2022

In order to stream video over IP, a scheme was needed that could counter the issues of transmission errors. The Video Services Forum (VSF) and SMPTE developed a group of standards to define such a scheme, SMPTE 2022.

First video data must first be mapped into IP packets. In the case of constant bit rate MPEG-2, this is detailed in SMPTE 2022-2. The video data is encapsulated in Real-Time Protocol (RTP, IETF standard 3350), which deals with the transfer of real-time data. The datagrams use User Datagram Protocol (UDP) over IP, rather than the more common TCP/IP.

RTP, which deals with the transfer of real-time data, includes timestamps (for synchronization) and sequence numbers so that the receiver can restore out-of-order packets to the correct order.

Packet loss is managed through forward error correction (FEC). Redundant data is added to the video stream so that the receiver can detect and recover missing information. The downside of FEC is it adds to the overall data rate.

The initial standards defined the FEC and means of transmitting MPEG-2 video (2022-1). Variable-bit-rate MPEG-2 is covered in 2022-3 and 2022-4. Later work added an FEC standard and mapping for High Bit Rate Media Signals over IP Networks (HBRMT), including 270Mb/s, 1.5Gb/s and 3Gb/s video (SMPTE 2022-5, 2022-6). The standards do not detail JPEG 2000, but this is expected to be covered by a recommended practice from the VSF.

File transport

Several products now exist that manage the transport of video files over long-haul circuits. The vagaries of insecure FTP circuits are now replaced with encrypted (if needed) and fast links.

Application layer protocols like FTP run over TCP/IP. TCP was conceived back when office networks ran at 10Mb/s and remote access used dial-up modems running at tens of kilobits. The algorithms to manage congestion are just not suited to the networks of today. Several vendors now offer alternative transport control technology that can fully utilize the available bandwidth.

Such data transport applications can be integrated as Web services in wider broadcast systems in order to provide automated deliver of files between workflow processes. (See Figure 1.) The wide area transfer of files is essential to the smooth operation of dispersed broadcast operations.

With many broadcasters leasing long-haul fiber connections for live video contribution and distribution links, spare capacity can be used for this non-real-time data exchange.

Summary

The introduction of Carrier Ethernet over fiber networks has lowered the cost per bit on metro and long-haul connections. This, in turn, opens up new possibilities for broadcasters. Group stations are able to consolidate operations into a central hub. Satellite stations can be operated from the hub as if they were on the next block. Sportscasters can provide the same quality of coverage with fewer staff on site. Many operations can remain at network HQ, with fiber connecting the remote venue with studio operations back at base. The 2012 Olympics saw many applications of fiber to save onsite operations costs.

Fiber also enables the mass transport of files from producer to distributor, cutting out the costs of tape transport. Directors and producers are no longer tied to the post house; remote collaboration can use a mix of live proxy viewing and file exchange to facilitate more efficient program production.

Video networks are helping the globalization of content provision and revolutionizing the offering to viewers from sportscasters. They underlie centralcasting operations. The affordability of video networks is enabling broadcasters to do more with less. The technology for video networks is driven by the video traffic over the World Wide Web and by the data transport needs of enterprise corporations. Broadcasters can take advantage of this low-cost connectivity to offer new services and streamline workflows across multiple sites.

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—David Austerberry is editor of the world edition of Broadcast Engineering.