Video networks for broadcast

Last month's column covered basic networking. This month we will look at the requirements for video networks for broadcast and how you can use technology to meet these needs. Planning a video network for broadcast can be a little trickier than planning for a conventional network. If you are designing a conventional business network, the traffic, applications and bandwidth requirements are well-known; people have been building these types of networks for years. But, if you are building a network for broadcast, things are not as clear. Most broadcast facilities include some post production. Just how much of the network is used for post can greatly affect the design of the network; the files moved around in post tend to be large. Broadcast facilities also frequently include news applications. If the news workflow supports server-based editing and collaborative workflow, then the network requirements can be quite demanding. If, on the other hand, your broadcast facility is still primarily tape-based, then a phased approach that allows you to expand capacity as network demands increase may be best.

Engineers who design video networks for broadcast might do well to start with a list of requirements for their facility. Some possible considerations are: number of simultaneous connections, mix of clients and servers, video application types, criticality of network, age of connected devices, operating systems supported, equipment lifetime, and Internet connectivity.

Number of connections

Figure 1. Networks with a large number of simultaneous connections may require two or more switches. Note the high-bandwidth connection between the switches. Click here to see an enlarged diagram.

Consider the maximum number of network-interface cards (NICs) you expect to have connected to the network at one time. Include all desktop computers and servers of course, but you might also want to include temporary connections for laptops, demonstration equipment and special-event requirements. The number of connections needed, and how widely they're distributed, will determine the number of switches needed (see Figure 1).

Mix of clients and servers

It is important to know the mix of clients and servers because servers will require high-bandwidth connections. In conventional networks, there are many clients and a few servers. Broadcast networks may be the same, but the number of servers can be higher. Also, the placement of central servers in your network topology is critical if you are to avoid bandwidth bottlenecks.

You should also think about whether the client-to-server ratio is likely to change radically in the near future, so you can plan accordingly.

Video application types

We are fortunate to have a wide variety of network-aware video applications available these days. Many do not significantly impact network performance. However, if you have a news department that wants to use a centralized storage facility with network editing, you must take into account the extra demand these applications will place on your network. Opening video files across a network for editing requires a huge amount of bandwidth, especially if multiple clients are involved. You may be better off keeping the content local, and only exchanging edit information across the network.

Criticality of network

When building a broadcast video network, one of the most important issues to be addressed is the criticality of the network. It is easy to say, “Of course this network is critical; it serves my broadcast facility.” But are you willing to pay 10 or 20 times more for your network? If you use off-the-shelf, consumer-networking hardware, costs can be extremely low. But, if you use so-called enterprise hardware from top-of-the-line manufacturers, the costs can be staggering.

To make an informed decision, you must know what functionality and reliability you get for an order-of-magnitude price increase. Generally speaking, a step up to enterprise technology gets you 1) greater throughput through switching components, 2) better remote monitoring, 3) advanced failure and automatic recovery features, and 4) higher-quality components. While these features may be critical to you, bear in mind that you may be able to purchase 10 or 20 backup switches for the price of an enterprise switch. Situations will vary, and there are some facilities that absolutely need the features that more-expensive device provides. You will need to make that decision.

Age of connected hardware

What is the age of the computers you are connecting to the network? Are they all older computers with 10Base-T NICs? Do they have NICs at all? Is it realistic to connect these computers to the network, or would it be less expensive and less problematic to purchase new computers that are network-ready? The time and effort required to get old computers ready to connect to a network may exceed the value of the computers themselves. It is now possible to buy powerful computers for under $500, and older network-ready computers are available on E-BAY and from local sources at low cost.

Flexibility of network hardware

These days, Ethernet hardware has advanced to the point that a single piece of equipment can support 10Base-T, 100Base-T and Gigabit Ethernet. The equipment can auto-switch between these different technologies without any user configuration, and you can mix different speeds without any problem. This is good news because your new network will be able to support old equipment as well as your newest high-speed server. The price of Gigabit switches has also started to drop dramatically.

Operating systems

It is a fact that some operating systems are easier to connect to a network than others. Also, it is well-known that particular versions of operating systems are prone to networking difficulty. Without getting into specifics, the author has had good networking experiences with Windows 95, 2000 and XP. He has also found various forms of *NIX including Red Hat and Free BSD to be extremely stable networking platforms. Mac OS9 and OSX also seem to be stable and reliable.

Equipment lifetime

When planning your network, you should be realistic about how long the equipment will last. You should face the fact that, the day after you purchase network components, something else will be available that is faster, less expensive and has more features. Networking hardware remains functional for a long time. The author still has some old pre-Ethernet networking cards that work just fine, but they certainly are not usable today. So go ahead and purchase new equipment when you need to and don't look back. Use old equipment when it makes sense, and throw out old technology if you suspect it will be more trouble than it's worth.

Internet connectivity

An increasingly key component of any video broadcast network is Internet connectivity. The author has found that people are of two minds on the subject, and the issue seems to be driven by user requirements. On one hand, there are many times when people need access to the Internet as part of their normal work processes in a broadcast facility. On the other hand, broadcasters are justifiably worried about security issues that come with an Internet connection. It might be simple to say that Internet connections should never be permitted on video networks for broadcast. But with the advent of commercial and program delivery over the Internet, the increasing use of the Internet in group-station environments through virtual private networks, and the general ubiquity of the Internet in everyday workflows, it seems that outlawing Internet connectivity altogether may not be practical.

Figure 1. Networks with a large number of simultaneous connections may require two or more switches. Note the high-bandwidth connection between the switches. Click here to see an enlarged diagram.

In your network planning, you should think about whether your Internet connection will be persistent (always available), or whether it on-demand (only available when required, or when someone in the facility enables it). In most cases, you will find that the demand for Internet connectivity will be so high that it may be easier to plan on a persistent connection from the beginning, even if this goes against your intuition from a security standpoint.

Given this need, your plan should include getting someone in your facility up to speed on firewall and router configuration, network-address translation (NAT), port-address translation (PAT) and other network-security issues (see Figure 2). Classes on these subjects are widely available, and well worth the investment. That said, in any plan including an Internet connection, you must include a firewall and proper anti-virus protection to keep people with malicious intent from causing problems on your network.

Brad Gilmer is executive director of the AAF Association, executive director of the Video Services Forum, and he is the president of Gilmer & Associates, a consulting firm.

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