Supporting PC-based video over a single fiber network
PC-based video systems differ sharply from those based on telephony. Here`s what to look for when choosing one.
Pete Ianace Intelect Network Technologies
From the multinational conglomerate to the emerging company, many of the enterprise`s daily operations now take place over video. Video applications thrive in the typical corporation, ranging from a broadcast-quality videotaped message from management to a product-planning videoconference among engineering, product development, and marketing staffs. Now that video runs on data networks, the data-communications manager--not the telecommunications manager--is responsible for installing the video network and delivering video services.
The corporate or technical manager wants an integrated video solution that supports the three major business applications for video: videoconferencing, video broadcast, and video surveillance. In fact, the technologies required for video integration already exist. Managers can integrate even a high volume of traffic into a single video network, which, in turn, is part of a corporate network that also supports voice, data, and local area network (lan) applications.
This article reviews the manager`s technological options for PC-based video systems and suggests what he or she should look for in an enabling technology. The appropriate underlying technology gives the enterprise immediate access to critical, time-sensitive visual information. The right technology features high-resolution, low-bandwidth consumption, and digital image recording and storage. The ideal video-enabling technology offers the enterprise both cost-efficiency and compatibility with installed networks, hardware, and software.
Welcome to the maze
Selecting the right PC video-enabling technology is not straightforward. The manager who carries that responsibility enters a maze of standards, technologies, and solutions. PC-based video systems differ sharply from telephony-based video systems used in such applications as large "help desks." Similarly, business video services sharply differ from those in the consumer video market. New products from large vendors such as Microsoft and Intel blur the distinctions between PC- and telephony-based video and between the business and consumer marketplaces. For smaller vendors, however, it is impossible to provide solutions for both consumers and businesses, and for both PC- and telephony-based applications. These market differences require that the manager carefully think through the video services and applications he or she needs to support before selecting a video-enabling technology.
The lack of industrywide standards for PC-based video creates another twist in the maze. The public network adopts and follows industry standards for network architectures, interfaces, and other technologies. For example, the International Telecommunication Union (itu) governs standards for telephony-based video. The itu established H.261/H.263 as video-compression algorithms under the umbrella of its H.320 wide area network (wan) standard.
In the private-network environment, however, compression standards vie for dominance. These standards range from the itu`s H.261 and H.263 to the newer Wavelet compression technology. Unlike the public network market, there is no single industry standard in the private-network environment. Vendors select the standard upon which to base their systems, just as enterprises choose which equipment to buy.
The fact that not all video implementations support each application further complicates the choice of a PC video-enabling technology. Some video-compression techniques do not provide the bandwidth and signal clarity necessary for vhs-quality video. For instance, consider the H.261 and H.263 protocols that support videoconferencing over wans. The two protocols provide very high-compression, low-bandwidth consumption over Integrated Services Digital Network (isdn) lines. H.261 and H.263 conserve bandwidth but compromise picture quality. Images sent with these protocols lose detail, blur noticeably at high speeds, and suffer visible pixelization. The quality of an H.261/H.263 signal rapidly degrades if the packet drops during transport and loses data. The signal quality also degrades if the image contains rapid movement.
On the other hand, another compression technique, known as Motion jpeg (m-jpeg), sends video signals with a clearer image than is achievable with H.261 and H.263. m-jpeg`s image contains more data than H.261/H.263 images. Compare m-jpeg`s luminance and chrominance sampling of 4:2:2 to H.261/H.263`s 4:1:1 (see table on page 60). m-jpeg compresses each full video frame, further enhancing the images it sends.
Despite its advantages, m-jpeg, along with H.261/H.263, encounters image problems at higher compression rates. The block structures of m-jpeg, H.261, and H.263 often produce images where square pixels appear as artifacts. By using high-bandwidth lines, however, an enterprise can eliminate the need for such high compression rates and thus avoid these image problems.
The underpinnings: compression and architecture
Wavelet, the newest video-compression technique, combines m-jpeg`s advantages with superior data handling and excellent picture quality. Like m-jpeg, Wavelet offers 4:2:2 luminance and chrominance sampling. Both Wavelet and m-jpeg compress each full frame of video, which permits each frame to be located for editing and more thorough recompression. Wavelet, however, achieves superior picture quality and greater compression without m-jpeg`s noticeable artifacts. This highly scalable new compression technique allows the user in a bandwidth- sensitive application to select a higher compression and lower frame rate. In applications that require high quality rather than low bandwidth, the user can select a higher frame rate but lower compression rate.
Finally, Wavelet supports a diverse range of video-compression options for different applications. Distance-learning applications, for example, require high-quality video if students are to read what the instructor writes on the blackboard. The typical videoconference, though, does not require such a high-quality signal.
These varying standards may confound or frustrate the manager; however, proper forethought will help. The following are additional tips of what to look for in a video networking architecture:
An advanced switching design--This consumes less bandwidth and frees network resources for other data, voice, or multimedia applications.
Onboard switching, encoding, and decod- ing--These features reduce the need for external equipment and cut the costs and time of installation.
Digital video encoding, which unifies the video network with data, voice, and lan traffic--The corporation, consequently, has a single, unified network to manage. A single network simplifies network management tasks and streamlines operations without com- promising the quality of applications.
By selecting a technology that uses Wavelet video compression, the manager gets superior picture quality and data handling as well as the best features of earlier compression methods. In addition, the manager should look for a PC video-enabling technology that uses the classical Internet protocol (IP) within the lan. An IP-based technology offers clear advantages to the corporation. Operating at the network layer, the IP works with another communications protocol known as transmission control protocol (tcp). Most popular lan technologies use tcp/ip, including T1/E1, Asynchronous Transfer Mode (atm), frame relay, Fast Ethernet (100 Mbits/sec), Ethernet (10 Mbits/sec), and Token Ring. An IP-based PC video-enabling technology works with the enterprise`s existing tcp/ip-based lan hubs, switches, and routers. This compatibility lets the enterprise cost-effectively meet demand for new video-based applications and maximize use of its installed lans, PCs, and other equipment.
Besides contending with competing industry standards, the manager charged with selecting a PC-based video-enabling technology must identify the enterprise`s initial applications for video. Organizations universally use voice and data. Voice and data are not application-sensitive, but video is. Without well-defined applications, video at first seems like a luxury rather than a necessity. Once an enterprise recognizes the value of video, though, video usage soars and unanticipated applications proliferate.
Originally, business video applications involved "talking heads"-- meetings or videoconferences where the only video was of the participants. Now, video involves data collaboration, in which participants share computer-aided designs, word processing documents, spreadsheets, contents of white boards, and other kinds of documents over the network. Several vendors offer data collaboration software, which facilitates this document sharing. Participants share the documents, live and interactively, over the network without interrupting ongoing video transmissions.
The medical and legal fields today rely upon video for telemedicine and litigation-support applications. Radiologists compare notes while viewing CT scans and other medical images over video. Jurisdictions increasingly arraign prisoners via video to reduce costs and increase security.
In business, popular video applications include videoconferencing, video broadcasting, and video surveillance. The chief executive records a television-quality video message on his or her vcr or PC, and employees then view the video from their PCs at their convenience. Alternatively, an enterprise provides training sessions to multiple parties simultaneously. Other organizations conduct multipoint-processing and continuous-presence videoconferences. Recent advancements in lan-based video systems brought about the growing applications for video in today`s corporation. The first advancement was the development of PC video systems that run over tcp/ip. New video systems now take full advantage of a corporation`s installed data lans, PCs, atm, Fast Ethernet and Ethernet, frame relay, and Synchronous Optical Network networks (see Fig. 1).
Newer video switches represented a second technological advancement. These switches allow multiple parties to participate in a video call--the multipoint- processing and continuous-presence videoconference mentioned earlier. Before the development of the newer video switches, video was possible only point-to-point, where Point A communicated with Point B over a dedicated line. Now a PC-based multipoint-processing, continuous-presence videoconference can include up to four people. Each person, seated at a PC, interactively shares the same video, information, and discussion.
Multicast, broadcast, and unicast
Many new Internet applications, including the multipoint-processing videoconference, involve communications from one to multiple parties, or from many senders to many recipients. To support such multiparty transmissions, the industry developed the IP multicast extension to the standard IP.
IP multicast allows the source of the message to send a single copy to recipients who want the information. The multicast extension sends the message to as many recipients as necessary. To receive a message, the party joins a multicast session group. Membership in these dynamic groups changes frequently. The IP message is transmitted to a host group, which is identified by a single IP destination address. This transmission method ensures that only one copy of the message passes over any single link in the network.
Multicast transmits more efficiently than do the two other methods of transmission--point-to-point unicast or broadcast. Point-to-point unicast sends an individual copy of the message to each recipient; if there are 50 recipients, each receives an individual copy of the message. Accordingly, unicast devours bandwidth, and the sender`s bandwidth limits the number of recipients.
In addition, multicast achieves more efficiency than the broadcast method of transmission. Broadcast sends a copy of the message to all nodes on the subnet, even if those nodes do not want the message. In comparison, multicast selectively sends the message only to those nodes that want it.
To accommodate multicast in a lan or wan, end-node hosts must support IP multicast transmission and reception in the tcp/ip protocol stack. Multicast also requires network interface cards in the lan. These cards filter for lan data link-layer addresses that are mapped from network-layer IP multicast addresses. The multicast message readily travels beyond the lan to a wan, while broadcast messages transmit only within a single subnet. In addition to the equipment needed to support multicast in a lan, wan-multicasting requires IP multicast-capable intermediate routers between senders and recipients. Most new routers come equipped with these capabilities, but older routers usually need memory upgrades. wan-level multicasting also may require that the organization construct firewalls to allow IP multicast traffic.
Smooth lan-to-wan communications also necessitates an efficient video-bridging technology. One such bridge now on the market connects a PC video system to any standard H.320 videoconferencing system via isdn lines. The bridge converts m-jpeg video signals into H.320 signals, and vice versa. H.320 signals travel over isdn-bri (basic rate interface) to the video bridge, and then to the m-jpeg PCs over an IP-based lan. Video signals from the m-jpeg workstations, meanwhile, move from the video bridge over the isdn-bri to the H.320 workstation (see Fig. 2).
Selecting the right bridging technology calls for the manager to be sensitive to hidden costs. The bridging technology just described has two-way signal translation, from H.320 to m-jpeg and vice versa, which eliminates the need for isdn capabilities at every desktop. Most gateway solutions that connect lan videoconferencing systems to H.320 systems, however, require special equipment at each workstation. Typically, each desktop needs two codecs and two network connections. The enterprise must purchase two videoconferencing systems for each station--one for the wan and one for the lan. The manager should be on the lookout for such buried costs.
The end of stand-alone
The term "integration" describes business video applications today. The industry no longer can afford to regard videoconferencing, video broadcasting, and video surveillance as stand-alone, discrete applications. Newer PC-based video systems reflect this integration in their ability to support multiple, simultaneous applications. Only the imagination limits the applications of such an integrated video system.
Consider the following application of a four-window, PC-based desktop video system. A city police chief and mayor, each sitting at his or her PC, talk "live" to each other about the pending city budget. The two-way videoconference occupies one of the four windows on each PC. A second window broadcasts Cable News Network or another television network. A third window scans the 100 or more video surveillance cameras located throughout the city at major traffic signals. The fourth PC window allows for data collaboration as the two officials discuss a budget spreadsheet.
Suddenly, a major earthquake strikes the city. The video-surveillance window on the PCs switches immediately to live coverage of the disaster. To scrutinize the damage, officials can pan, zoom, or tilt any of the 100 video cameras located around the city. Within minutes, the second PC window broadcasts cnn`s coverage of the earthquake. The officials now use the data-collaboration window to bring the city fire chief on screen to discuss how to best respond to the disaster. Because all three officials view the same scene, they quickly develop an appropriate plan.
This application seamlessly integrates video surveillance, videoconferencing, and video broadcast for the user. The police chief responding to an emergency need not worry about the integration of his or her video applications. Instead, the chief concentrates on the work at hand--responding appropriately to a natural disaster.
A single video standard does not dominate the private-network environment, unlike the public network sector. Admittedly, most managers would cheer if the private-network environment selected a single standard. The private-network market, however, does offer innovative video-enabling and bridging technologies and competitive video network architectures. The manager charged with selecting a PC-based video system must first keep in mind the video applications the enterprise wants to use. Next, he or she should evaluate competing technologies. These steps ensure that the manager will choose a PC-based video system that is cost-effective, easy to use, and compatible with existing equipment. By carefully weighing the available technologies, the manager will be sure to select the right solution for his or her enterprise. u
Pete Ianace is president and chief executive of Intelect Network Technologies, Richardson, TX.