Managing a Video Network

Video quality for external users, such as visitors to your Web site, is usually out of your control. And these users won't likely call you when they can't receive a video feed, nor will they come knocking on your office door asking for a better frame rate. You can control video only up to the point it leaves your network; beyond that, you're at the mercy of the service providers that transport it to the user.

The type of video carried on your network can be varied and unpredictable. It can travel all at once as heavy traffic, or it can come in bits and pieces. On your enterprise backbone, video likely will be streamed for corporate news or training. This can be either scheduled broadcasts or VoD (video on demand). The advantage of scheduling video is that you know when it's coming, so you can prepare for the increased traffic by designing the broadcast so your network can accommodate it.

VoD, however, can kill your network. Most video is streamed in multicast (one-to-many), but VoD is almost always one-to-one. If one person occasionally streams video across your network, it's no big deal. But if 500 users suddenly hop on the network to watch a training video, your data and other traffic--including some of the video streams--can come to a standstill under the heavy load. Such traffic can put a lot of stress on your servers, which have to pull data for each feed from the drives and push it over the network interface.

Videoconferencing, meanwhile, has grown from its premium-priced ISDN service days to riding over the public Internet for little or no cost. It's typically a one-to-one or one-to-few internal application. Videoconferencing equipment has been limited to the enterprise market because of high cost and lack of wide acceptance, but that's changing. Today, any size organization can conduct videoconferences, thanks to outsourced services such as GlowPoint, one of the first networks designed to make videoconferences as high-quality and reliable as long-distance voice calls.Quality Time

So, what type of video quality do you need? You can decrease the video traffic over your network and allow more video streams to be sent simultaneously if you sacrifice the clarity of the feed. Newer codecs such as H.264 provide compression at lower bandwidth rates, which lets the network carry more streams.

Codecs are becoming more efficient on the desktop: Apple and Microsoft are running neck and neck in the quality/bandwidth race. Both of their codecs (H.264 and VC-1, respectively) will be included in the next generation of DVDs, which support HD (high definition) and run at the desktop through QuickTime or Windows Media Player. H.264 was designed as an open standard that can provide the same or better quality at less than half the bandwidth of an MPEG-2 stream.

Another piece to the quality puzzle is video resolution. Standard full-screen video has a resolution of 640x480 pixels, but you might not need that level for your video traffic. Streamed video is typically, at best, 25 percent of full-screen--320x240. Many codecs can make video appear at a higher resolution than it really is by softening or algorithmically doubling the resolution.

Servers may not be part of the physical cabling, but they're an integral part of how you deliver video content to your customers. They capture video from the source and encode it. You can build your own video server or buy a turnkey system. Rolling your own includes the server, capture card or FireWire connection to a digital camera. Video can be captured and encoded in a variety of formats, then distributed in near-real time or stored for later transmission.The trade-off with real-time encoding is that it sacrifices quality because it must finish encoding one frame before the next frame gets to the processor. And with video running at 30 frames per second, the CPU could easily be overtaxed. If you want the best video quality, delay distribution until it can be encoded properly, which will result in higher-quality video at a lower bit rate--albeit at a longer turnaround time.

Turnkey systems come with embedded processors designed to encode video, so you get higher encoding performance. They are better suited for encoding in real time or near-real time and can deliver video to the desktop in a variety of formats, including WMV (Windows Media Video) and MPEG-1, 2 and 4. If you must deliver content both inside and outside your organization, you can create at least two different versions of the video with these systems--higher bandwidth/better quality for internal use and lower bandwidth/lesser quality for external use.

You also can configure turnkey systems to perform storage and VoD services when you want to archive video for later playback. Companies such as Kasenna and VBrick Systems offer hardware products that perform both encoding and storage and distribution services, including a streaming media server. Another plus: These systems provide a one-stop shop for support.

A less expensive option is to combine off-the-shelf video products. Beyond the hardware, the actual distribution method is important: For one-to-one distribution, you need plenty of bandwidth and horsepower to support the maximum number of expected streams. Each video feed takes "A" amount of bandwidth, so the total bandwidth needed is the number of streams multiplied by A.Your distribution server will not only need fast processors, but fast disk, too, to pull the video as quickly as possible. SCSI and SATA (Serial ATA) alone won't cover multiple video streams, so you need a RAID of SCSI or SATA drives to push several hundred megabits per second. And depending on the number of streams supported, you may need Gigabit Ethernet or multiple Gigabit Ethernet interfaces.

If your video is scheduled, you can replace a one-to-one distribution with a one-to-many multicast, which reduces the horsepower and bandwidth your server requires. One stream is transmitted, replicated and distributed to each client.

It all comes down to the distribution backbone--the network itself. The biggest obstacle to enterprise video is the lack of QoS. Most enterprise networks aren't designed to deliver video effectively, and some IT departments treat all data equally, without prioritizing types of traffic. (If your department operates this way, it's time for a change of attitude.)

Although video may be just one small chunk of traffic traversing your network, its impact can't be ignored. The same switch and router devices you use for transmitting voice over IP are necessary for video. You also need Layer 3 QoS (DiffServ) and VLANs (virtual LANs). DiffServ provides traffic shaping for your network and maintains priorities among packets, which will ensure that your users receive each video frame. And splitting your network into VLANs keeps traffic where it needs to be, not roaming where it shouldn't go. You don't want video traffic clogging your accounting VLAN and vice versa.

If you control your WAN, MPLS (Multiprotocol Label Switching) is a good solution for maintaining QoS. There are plenty of service providers that transport video data, some with other traffic and others. purely video. Akamai, for instance, can place data and video close to the end user with its nationwide network that replicates data at various servers around the country. This works well with prerecorded video or if you've scheduled live video in a one-to-many broadcast.To provide the highest-quality video to outside users or customers, you need multiple network connections for backup in case of WAN failure. And get network connections from more than one IP provider, which will decrease the chance of a failure preventing your video from getting through. Routing your traffic with BGP (Border Gateway Protocol) gives traffic the best (and usually shortest) route to its destination.

No Free Lunch

Billing for VoD services is still in its infancy. You can create your own method and integrate it into your existing accounting system if you have an internal development team, or you can hire some outside help. Many turnkey delivery systems include billing software, and billing solutions come packaged with products such as Elitecore Technology's eStream software. Billing and setup are a little easier with videoconferencing--Forgent and VCON, for example, sell software that schedules calls and ensures that network and video resources are available for a videoconference. They also set up and place the call, as well as maintain data on the call for billing purposes.

You can't just add video traffic to your network without proper planning and preparation. Know your strategy and goals for video, then build out your network so it delivers the content reliably and predictably.

Darrin Woods is a Network Computing contributing editor. He has worked as a WAN engineer for a telecom carrier. Write to him at [email protected].1. Determine user locations. Are they internal (local to your company) or external (accessing your network over the Internet)?

2. Define the type of video traffic you will transmit: videoconferencing, scheduled, streamed or video-on-demand, or a combination.

3. Set the required video quality. If you need full-screen and high-resolution video, it must be the highest quality. But if you'll be transmitting talking-head video, you won't require the same level of quality.

4. Choose your encoding system. You can go with existing or off-the-shelf video hardware/software or a turnkey system.

5. Select your decoding and delivery system. Do you need to stream the video to one person at a time or to multiple users simultaneously?6. Design your network to deliver the video, but leave plenty of bandwidth for all other traffic. This may entail deploying QoS.

7. Set up a billing system. Make sure you have the methods and software in place to bill your users or departments.