Signal distribution: The costs of compression
Corporate networks are struggling to cope with the demands of video traffic. Should you plump for
high quality or low latency? 1GB or 10GB? Steve Montgomery explores the options.
Distribution of multichannel AV streams over IP networks is becoming commonplace, however limitations in network bandwidth place restrictions on the amount of video that any network can carry.
However, recent research report from Netgear found that most corporate businesses are rapidly migrating from 1GB to 10GB Ethernet networks. This is good news for vendors of AV equipment, allowing them to seize opportunities to provide equipment to distribute audio and video over these networks.
One of the main user requirements is to provide several video channels at once, and this requires a considerable amount of available network bandwidth.
Compression technology is used to reduce the data size of those streams and squeeze more channels onto a network. 1GB and 10GB networks cannot carry multiple video streams without some form of compression.
However compression comes at a cost in latency and image quality. A range of
compression techniques has been developed over the years allowing users to select a specific type that best meets their requirements.
Samuel Recine, director of sales, Americas and Asia Pacific at Matrox, believes that image quality of very low bitrate streams is good enough for most corporate applications: “Crestron and other brands manufacture exceptionally balanced products using JPEG 2000 compression. Other companies, like Matrox have achieved 4Kp60
4:4:4 quality and latency levels using H.264 that are good at bitrates even well below the 1 GB/s requirements of JPEG 2000. The majority of AV-over-IP applications can tolerate a small amount of latency in exchange for massive networks, a high degree of interoperability, ease of network set-up and maintenance and scalability. This is
the crux of the AV-over-IP market. No codec competes with H.264 for the balance of quality, latency, bitrate and interoperability with millions of other devices.
“In general the relationship with latency also has to do with the quality and sophistication of coupling the transmitter products with receiver products in AV-over-IP versus not just the choice of codec.”
Compression inevitably delays the signal. However some manufacturers claim zero latency. Recine believes this is a misunderstanding: “When vendors refer to zero latency, they are most often referring to latency levels not detectable in the application. Most end users are far more concerned about deploying real standards and designing AV networks that are interoperable and scalable versus latency levels between excellent and better than excellent.”
As Rob Muddiman, EMEA sales director, Zeevee, points out: “It is incredible how some vendors claim zero latency when using a JPEG2000 type compression, when in reality it introduces 20-30mS latency. ZeeVee has both compressed and uncompressed solutions. Our compressed solution uses JPEG2000 and has
only a 20mS latency.”
Justin Kennington, president, SDVoE Alliance, concurs: “Companies cannot realistically claim zero latency on compressed signals and quite often their technical publications indicate what their marketing fails to. High compression of the
type required to put 4K video onto a 1G network will always demand compromises in both latency and image quality. These technologies need to use a whole frame of video to make a reasonably good image quality in the low bandwidth environment. Just the act of waiting on a whole frame (16 milliseconds at 60 Hz)
takes time and in all cases the system delay is at least two frames.”
Crestron’s DigitalMedia NVX product is marketed as having no latency penalty, although this translates to an actual end-to-end latency of 30ms, as Rob Carter, technology manager, DigitalMedia, Crestron explains: “When we talk about no latency we are referring to our NVX technology that combines codec and scaling latencies. As a result, NVX has the same latency performance as our HDBaseT scaling products.
Some companies don’t include scaling, which typically adds a minimum of 30 ms on top of the quoted numbers. And, according to our internal tests, they can be significantly higher.”
Given that compression is needed to distribute multiple video streams over a single network, the choice of compression technology is crucial.
“Choosing the right one is critical, since it has a direct impact on end users,” says Carter. “JPEG 2000 can offer amazing quality with latency low enough to fit within our scaler latencies. Unfortunately not all JPEG2000 implementations are created equal, so there are other network video products on the market
that use it but still have quality and latency problems. VC2 is another codec out there but it sacrifices quality for latency.”
Commercial organisations are continually looking for ways to cut expenditure. Network infrastructure is a primary target, particularly with the high cost of cable installation around buildings. An attractive option is to combine AV and data networks into one, effectively piggy-backing the video distribution onto an existing IP data network. However, this is not always feasible. Muddiman: “Some vendors claim that
they work on a 1GB network, but in reality, they take up so much bandwidth they effectively have to sit on a dedicated stand-alone network. A product that takes 800MB operating on a 1GB link leaves very little for IT traffic. Our advice is, if you are putting in a separate network, do it properly and install 10GB.”
Carter agrees: “While true convergence makes the most efficient use of network resources, there are still significant advantages to network video even if you set up a separate network. Flexibility in design is probably the most important feature of network video. Network ports don’t need to be video inputs or outputs; they can be inputs or outputs or control systems or touch panels.
Given the port density of the network switches, the system can be easily expanded as needs change with time. Even if a separate network switch is used, users will still often want to take advantage of network runs that are already in the walls. Gigabit network video solutions can re-use Cat5e that’s already in the walls. 10G
Ethernet requires more expensive Cat6a cable that’s not as readily available.”
“Running networked AV systems over the same wiring and IT infrastructure as
the corporate IT networks can contribute to reducing the installation costs,” explains Bertalan Petrik, sales operation manager, Lightware Visual Engineering. He does, however, point to a potential drawback: “The optimal Ethernet switches for AV over IP are different from standard, corporate network switches, which could deteriorate the performance of an AV over IP system. On the other hand, using low
latency switches for emails would probably be overkill. To eliminate network security problems the separate AV network can be isolated from the corporate network, just like in the case of conventional matrix-based AV systems. Also, most AV over IP products offer multicasting, which is a problem on the corporate network.
Separating them can solve these issues too. A separate AV network enables the performance of the AV over IP products to be guaranteed.”
Martin Bonsoir, international applications engineering manager for Biamp highlights another reason that networks are kept apart. “Organisations separate their networks for several reasons, although cost-saving is rarely one of them. Arguably, the overall project has a higher cost when deploying two networks. But since those deployments are almost always done by different departments, each usually ends up
with a lower cost for their part of the job. It helps to step back and look at the overall cost.”
Once the AV distribution network has been installed, control and management generally becomes the responsibility of the end user.
Manufacturers will provide a suite of software tools to set up and configure the system, but most users will require a dedicated control interface. This comes at a cost. Kennington says it’s always been this way: “In the past, the manufacturer of a matrix switch would provide the software necessary to commission and operate the switch for free. Yet no one ever put this software in front of the end user as the final
solution. Instead, a professional AV programmer was brought in to build a user experience on top of the control system. Although billed as services, this person was really providing custom software for hire.
“In the AV over IP world, the model is just the same. If I buy encoders and decoders, I expect there to be some configurability included for free. But I still expect that I will pay extra for software tailored to my needs. This might come from a commercial software vendor, building on top of the API, or a traditional AV programmer, creating control software for a specific enterprise or other use case.”
With the wealth of products and technologies available, integrators need to consider the best solution for each project. These considerations must include the requirement for combination of the IT and AV networks, selection of compression technology and whether to source components for single, or multiple, vendors.
It is sensible for organisations to plan the network infrastructure with a view on future upgrades says Paul Harris of Aurora Multimedia
“Installing Cat6a cabling at the start saves cost as it will cost more later to pull new wire versus the cost difference. Fibre is a better choice as multimode will go about 1000ft (about 300m)and at 40G about 330ft. To be 8k60Hz or 4K120Hz ready you will need at least a 10G network. 40G will allow for minimal compression
of 8K when the time comes.”