The general utility of IP and Ethernet networks is well-known. IP/Ethernet is the backbone of the Internet and is at the core of convergence — the blending of telecommunications with real-time voice, video and data. Despite its successes, however, IP/Ethernet also is the source of delays, lost data and best-effort transport. Within the broadcast industry, dedicated circuits are used to guarantee the delivery of content from the initial source to the final destination. This guarantee of delivery does not currently exist within the IP/Ethernet circuit technology. Therefore, when looking at how to change the delivery of broadcast and TV content, the question is, “Will there ever be a means to reconcile the dedicated circuits used in television distribution and the broadcast studio with IP networks?” The answer is yes. This article will look at the unique requirements for broadcast-video networking, problems associated with real-time content delivery over IP and solutions to these difficulties, including Ethernet.
 Broadcasters must develop new methods of maintaining QoS over IP networks. Technology from Leitch/Path1 has allowed coast-to-coast broadcasts over IP with quality comparable to satellite or ATM. |
IP protocol is by far the most common networking protocol in use by any computer or LAN due to its low cost, widespread installation, and ease of use.
Network services including networking of audio/video/metadata content, control, monitoring, interactivity and statistics gathering, have differing requirements for speed (data throughput) and latency (delay). Each function has its own requirements, but the one area placing the greatest demand on the network is live audio and video delivery.
Live interactive video services and video teleconferencing are intolerant of the buffering that is commonly used in today’s Internet video applications. Networks can avoid buffering delays by creating a virtual circuit (channel) that dedicates a portion of a network link to a video stream. Such a dedicated virtual channel, that guarantees the regular and periodic delivery of data and signals, is called an “isochronous channel.”
Traditional IP is unable to provide the dedicated real-time data paths or circuits that are essential to live broadcast video applications such as synchronizing voice and audio. Guaranteeing Quality of Service (QoS) is key to overcoming the shortcomings of IP.
Various methods have been adopted to tie the advantages of isochronous (dedicated) links with the advantages of IP networking. One method is to utilize a hybrid system such as IP over ATM, Fibre Channel or IEEE-1394.
ATM and SONET were developed for backbone transport of data. They establish a logical circuit from end to end, which guarantees quality of service (QoS). They are expensive solutions, however, and unwieldy in a rapid setup or take-down mode such as that often found in a TV studio or broadcast environment. For the foreseeable future, ATM and SONET will be utilized in the WAN environment coexisting with Ethernet IP.
Another method for adding a guaranteed quality of service element to IP/Ethernet is to utilize large amounts of bandwidth and keep the data-transport rate within reasonable bounds to avoid data collisions, traffic jams and lost data.On a small LAN with tightly controlled transmission rates, this queuing is reasonable. On a larger LAN, instabilities quickly develop and “pile-ups” occur at contention points, with unforeseen results.
Fortunately these problems are being addressed with the next generation of switches and routers. These evolving QoS protocols and mechanisms include:
RSVP/SBM: Part of the IntServ signaling protocol for requesting QoS guarantees on a per-flow basis. Often used in conjunction with a designated Subnet Bandwidth Manager (DSBM) to control admissions.
DiffServ: Protocol for offering differentiated services categorizes and prioritizes network traffic by tagging IP packet headers. In contrast with Intserv, DiffServ provides a means for simplifying QoS management on a bulk basis through aggregation.
MPLS: Multi-Protocol Labeling Switching is a protocol for specifying a fixed route through an IP network.
COPS: Common Open Policy Service for managing admission policy across networks. COPS is becoming the higher-level network policy management protocol from which a local RSVP/SBM would obtain network policy and admissions information.
The latest technology to enable guaranteed Quality of Service over IP/Ethernet is TrueCircuit from Path 1 Network Technologies, Inc.
TrueCircuit gives IP/Ethernets ATM-level Quality of Service by allocating virtual isochronous channels at Layers 1, 2 and 3 under the management of a network operating system. TrueCircuit interacts with all the protocols listed above to actually implement QoS guarantees across a network.
This system was demonstrated at the NAB and Networld/Interop trade shows, where an Ethernet LAN and wide-area network (WAN) with TrueCircuit moved multiple, simultaneous streams of MPEG-2 compressed and 270Mb/s uncompressed digital video. One of the benefits of the mechanism is that it interfaces seamlessly with SONET/ATM.
TrueCircuit over Gigabit Ethernet is so powerful that it is capable of precisely synchronizing video equipment to the level that genlocks can be distributed throughout the network domain.
Path 1, in conjunction with Leitch Technology, is developing equipment such as switches, routers, gateways, network appliances, embedded controllers, and control/monitoring software with the TrueCircuit technology embedded. TrueCircuit networks offer inherently secure virtual circuits and synchronization to allow products to be video phase aware. The networks are compatible with standard and evolving IETF and IEEE QoS protocols, such as, IEEE 802.1D, 802.1Q, IETF DiffServ, RSVP/SBM, COPS and SIP. Networks with TrueCircuit allow simple net management functions, with expanding capabilities and a comprehensive control toolset expected soon. The cost of the network is expected to fall to normal Ethernet/IP prices in a few years.
Today, the bulk of video content moves from the producer to the consumer via storage media (tape formats such as VHS, DVD, etc.), radio frequency, cable, satellite downlink or microwave link. In five years or so, the Internet will probably carry the majority of video programming. Because of the huge bandwidths involved in transmitting audio and video, video content will dominate all other Internet traffic volumes. Also, because of new interactive broadcasting services and the ever-present “channel surfer” sitting at the receiving end, rapid delivery will be crucial to user acceptance. IP/Ethernet is an evolving standard that is rapidly moving into every industry, at higher speeds and lower costs. Gigabit Ethernet is already available over ordinary CAT-5 cabling as well as single- and multimode fiber and coax. New standards-compliant QoS mechanisms are to be released this year to ensure low-latency, low-jitter channel transport of real-time data — with guaranteed QoS standards comparable to ATM. As shown at NAB, IP/Ethernet will soon become the de facto standard within the broadcast industry to bring quality content delivery at an affordable price.
For more information about the Path 1/Leitch TrueCircuit QoS technology visit www.leitch.com. Dr. Douglas Palmer is the chief scientist and Dr. Ronald Fellman is the CTO of Path 1 Network Technologies, Inc., San Diego, CA. Stan Moote is CTO of Leitch Technology Corp., Toronto.