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Network Misconceptions

Jul 11, 2014 3:22 PM, By Kevin Gross

Working with IT on AV networking projects

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VoIP is the most demanding network application

Through the use of voice over IP (VoIP), today most phone systems are connected to a computer network instead of using dedicated wiring and equipment. The network used for the telephone system is often the same one used for computers and other IT. Telephone calls over the network require higher performance than is demanded by other IT applications such as email delivery and web browsing. This performance requirement has been simplified in some corners of the IT industry to an understanding that VoIP requires the highest level of network performance available. This simplification leaves no room for applications that require higher performance than VoIP.

The good news is that while network performance has improved over the two decades since VoIP was first introduced, the performance requirements for VoIP have not changed significantly. The improved performance provided by networks is now available to applications requiring higher performance than VoIP. The highest tier of network performance should no longer be reserved for VoIP. Higher performance needs to be allocated to higher performance applications including media networking.

AV has no special requirements

A typical network configuration starts with all services and devices given equal access to network resources. Network engineers may not fully appreciate that media networking is a network application and deserves, if not requires, special configuration considerations.

IT pros have received little or no training and are generally unfamiliar with professional media networking. The network applications IT professionals are familiar with originate from PCs and servers, and include email delivery, web browsing, file transfers, and remote system and database access. Most of these applications are not particularly time sensitive. They also consume bandwidth on a sporadic basis—when an email comes in, when a web page is requested, when a file transfer is initiated. Most of these applications use TCP and are resilient to variable network performance.

Acceptable audio latency for some media networking applications is less than 1 millisecond—100 times lower than are required for VoIP. Packet loss is sometimes tolerable in VoIP and does not severely impact other IT services. Packets delayed in transit through the network may arrive too late to be useable at the media network receiver. Any dropped data will result in audible artifacts and in some media networking applications; no packet loss is acceptable.

In short, the assumptions that network designers are accustomed to making about network applications do not serve media networking. Network designers need to be made aware of these special requirements early in the design process.

This AV traffic is going to trash my network

Professional networked audio can continuously use 1Mb to 2Mb per channel, up to 100 times the bandwidth used by VoIP calls which typically aren’t run continuously. A multichannel audio device such as a mixing console can saturate a Gigabit Ethernet link. The bandwidth consumed by media networking may dwarf that used by all other applications on some networks. Some networks are only capable of supporting the more modest and elastic requirements of computer network applications.

IPTV and some other media networking systems use multicast messaging. Because multicast is often used only lightly, many networks lack intelligence for handling multicast traffic and will disruptively distribute multicast to all devices on the network or within the immediate vicinity of the multicast source.

Some media networking systems use Layer 2 Ethernet traffic. Much of the IT infrastructure and tools are geared towards Layer 3 IP traffic. The Ethernet traffic produced by these systems may be less visible, more difficult to control and manage, and dealing with it may be considered anywhere from an inconvenience to an unacceptable security risk.

So maybe AV traffic trashing a network isn’t a misconception in some cases. Media networking definitely pushes networks to a degree that may be surprising to IT pros not accustom to supporting high-performance networking. Fortunately, there are well-established IT techniques, standards, and technologies for addressing these issues. The distance between media network requirements and affordable network capabilities has been closing quickly. The gap between capabilities and requirements is less of an issue for newer network installations or moderate-sized media networks.

All necessary information is available in the documentation

Documentation for IT systems is typically extensive. The manual for a typical enterprise-grade network switch can run more than 1,000 pages. Technical features are defined in similarly extensive standards published by the IEEE, IETF, and others. There is a rich array of information and training for IT pros to draw upon when working with network systems.

Media network technology has only recently begun to conform to published standards. Protocol details may not be published in AV product documentation. These systems are supported by AV companies who may not speak the same language as the IT pros.

Despite their girth, product documentation for networking equipment may not contain the information needed to determine whether and how to make these systems support one another. Few switches, for instance, give a usable latency specification. Most network equipment supports QoS capabilities, but the exact nature of these capabilities and their compatibility with media networking systems can be impossible to ascertain without testing. In short, due to a lack of information, incompatibility, or difficulty interpreting specifications, it may be very difficult to determine whether media networking system B is compatible with network A.

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