适用于AV over IP的线缆选择

While Ethernet technology started with computer networks, it has expanded to encompass voice, security, building automation and now commercial AV. 

 

In the graphic below, the green rings indicate how much of each technology segment has embraced Ethernet connectivity so far.

There are many reasons for this shift—easy-to-use infrastructure and high-bandwidth capabilities, for starters—but the low cost of Ethernet switches has led this charge. Traditional AV switches can cost tens of thousands of dollars while an Ethernet switch to support AV over IP requires only a few hundred dollars.

 

Ethernet relies primarily on two cable types:

1. Category twisted-pair copper cables

2. Fiber cables

Category cables are designed to be backward compatible with lower-speed Ethernet signals. This allows you to install a better-performing cable to support future technology while also being able to support existing systems.
  

For example: If you install a Category 6A cable, it can support your existing gigabit network. When the time comes to upgrade, it will also support next-level 10G systems. This saves you from having to reinstall cabling.  

 

Category is often abbreviated as “Cat” or “CAT” followed by a number. In terms of performance, CAT 6A is better than CAT 6 and CAT 5e; CAT 6 is better than CAT 5e. Lower and higher category cables exist (Category 3 and Category 8, for example), but they aren’t often used in AV or enterprise environments.

 

When you add fiber into the mix, you can achieve even more distance and bandwidth. 

 

IP Challenges to Consider

One of the biggest challenges presented by AV signals is latency (delay in time of signal). Most AV signals demand a constant stream of information, so delays can cause sync issues or signal loss. This can create problems—especially when you’re controlling interactive content or viewing a live performance, where delays as small as 15 ms can be noticed.  

 

To address this, some Ethernet gear prioritizes packets through QoS (quality of service) and special switching that lets “more important” traffic pass. These features can add another layer of complexity to your system and require a specialized AV network design.  

 

Another concern is bandwidth—especially for video. We’ve seen video bandwidth explode, with HDR 4K video signals requiring 18 Gb/s of uncompressed data. Unless you run fiber or multiple category cables, you’ll have to compress your signal. This compression takes time and runs the risk of errors during signal encoding or decoding. The more compression, the longer it takes and the more latency and errors introduced into the system.

 

HDMI 2.1 calls for bandwidth capabilities of 48 Gb/s, and some video gaming systems are talking over 100 Gb/s. Where will bandwidth stop? And how can you be prepared?

 

What Speed Do You Need?

Should you base your cabling system on today’s requirements or on a safety margin for futureproofing? IEEE standards allow you to upgrade cabling as systems because they’re backward compatible with lower speeds; the cabling infrastructure is usually the hardest item to change within the system.

 

Compare unplugging a switch and device to the labor involved in running a new cable through the ceiling and wall. If you’re putting in new cabling, consider a minimum of Category 6 and, if possible, upgrade to Category 6A—even if you’re currently supporting only a 1 Gb/s network. It will save you time, money and frustration in the long run.

 

Same Network, Your Own Network or Virtual Networks?

Should your AV system be on its own network or a separate network? Or maybe a virtual network? The answer to this fairly complex question depends on the situation. Here are some factors to consider:

• Programming and operation: Some AV systems require special program settings. An AV integrator will program and test the system to make sure these adjustments are working. If a system is upgraded or changed, then someone needs to make sure those changes did not negatively affect the AV system. How often do you receive notices for software upgrades?

   

• Security: AV systems can present a weakness to a company’s IP security plan.  

   

• Enough bandwidth: Does your AV system require the same bandwidth as the rest of the network? Does the current network have enough bandwidth for the AV system?

   

• Always-available bandwidth: AV systems don’t typically do well when they have to share bandwidth. For the most part, if they’re on, then they constantly need information.  
  
  

How Does This Effect Cabling? 

The most effective way to wire an Ethernet system is by using a star topology: Every device is directly cabled (“horizontally”) back to a switch. These switches then connect with a backbone cable, which is typically a fiber cable. Note: Horizontal cabling does not have to run horizontally but needs to be at or under 330 ft (100 m). This cable length includes patch cords.

 

Computer and telecom switches are usually located in telecom rooms. Where does your AV equipment live? If it lives in the telecom room, then all cabling runs to that point. If the Ethernet switch lives in AV equipment racks, then the cabling runs there instead. You can connect AV equipment racks to telecom rooms with backbone cabling, which gives you access across campus. 

 

If you choose the telecom room for equipment, then there are some advantages: These rooms are typically more secure, have limited access and offer better environmental controls. You can use the same switches for multiple systems, including AV, networks, phones, etc.

 

You might be able save a little money on cables if your AV Ethernet switch is located in the same room as your AV equipment, but you’ll also lose flexibility and control. In addition, some AV equipment might be required to be in the room (for example, you might need to load a DVD into a player).

 

How Do You Want to Connect?

Traditional network cabling runs category cable from patch panels in telecom rooms to faceplates in work areas. Patch cords are used at each of these ends: one from the faceplate to the device and one from the patch panel to the switch. This creates a universal cabling system in which changes can be made in the telecom room and work area based on what device connects to what switch.  

 

AV equipment, on the other hand, has traditionally been connected directly. You plug a cable into an output device and plug the other end into the receiving device. For example: You plug a TV into a Blu-ray player with an HDMI cable.

 

Just recently, network cabling standards were changed to allow devices to be connected directly at the work area without a faceplate or patch cord. This change is called modular plug terminated link (MPTL) topology.

 

As Ethernet expanded to include more devices, like cameras and wireless access points, the standards group realized that, in some of these locations, flexibility wasn’t needed to change devices at the work area: You could connect directly with an RJ45 plug. Back in the telecom room, you still have your patch panel so you can adjust which switch it plugs into.

 

When cabling your AV system, you can choose how you want to connect: directly or with patch cords—or using a combination? Do you want a system that complies with network standards? Switch and equipment location dictate this choice. 

 

You may decide to use different methods for different projects. Our recommendation is to use MPTL where devices won’t change; it gives you more flexibility within racks. If the device might change, then a traditional patch cord on both sides will give you flexibility. If it’s likely that nothing will change, then you can directly connect the switch and equipment. 

 

Bringing AV systems onto the Ethernet network can support scalable switching, long distances and new opportunities to merge communications and data. In an upcoming blog, we’ll discuss your cabling options in more detail: copper and fiber.