Do MCUs Make Sense?

The MCU, or multi-point control unit, has been the heart of modern videoconferencing. Historically, it's the only way for more than two sites to join a single videoconference. MCUs are typically specialized DSP-based systems often charged by port capacity.

MCUs are more than a switch, but rather an active participant in the conversation - at least technically. The MCU decodes the video streams and then encodes an appropriate mix of video streams for each participant into a single stream. All this decoding/encoding, or transcoding, makes MCUs very CPU intensive. Additionally, MCUs also provide gateway services that improve interoperability between video systems.

But there are several factors that threaten the future of MCU hardware. It's becoming questionable if they still make sense.

1. Multi-Stream Endpoints. The traditional MCU architecture assumes a highly capable multi-stream MCU and simpler single-stream endpoints. Like many other aspects of IP networking, more capabilities are being pushed to the endpoints. Multi-stream endpoints means that each video session gets sent to each endpoint, effectively eliminating the need for an MCU to recode all the content into a single stream. This is largely enabled by Scalable Video Coding (SVC), which allows a stream to be sent in layers. Often the active speaker is larger in HD, and other participants are miniature, thus requiring less bandwidth. Multi-stream capable endpoints and SVC allow local control over the size/quality of each stream. This approach puts more emphasis on the endpoints and less on the infrastructure.

2. Software-based MCU. Moore's Law has made it possible for software to now perform many functions previously performed by hardware. The key advantage of software is it is easier to upgrade. That's important because things are changing quickly. The MCU role may still be necessary, but perhaps not the DSP specialized hardware that gives it a shorter useful life. By separating the hardware, MCUs can be dynamically distributed across data centers and even run on virtual infrastructure.

3. Appliances. That might not be the right term, but more and more devices and applications support entry level MCU functionality. IBM Sametime will soon offer built-in MCU services. Mitel's UC360 endpoint has a built-in four-port video bridge. Microsoft Lync now supports limited MCU functions. Video isn't always about three-screen conference rooms, and increasingly more about on-the-go personal communications. These shifts in processing reduce the requirements for dedicated platforms.

4. Cloud. There are an increasing number of providers and solutions for cloud-based MCU services. The cloud solutions address gateway, transcoding, and bandwidth requirements needed for video. As with many cloud-scale solutions, the prices are compelling - often lower than enterprises using internal resources. Many cloud operators also offer ongoing upgrades, wider means of interoperability, and a low cost means to spike utilization.

MCUs will remain a mainstay for the enterprise for quite some time supporting existing systems, but their appeal as new devices is thinning. However, MCUs offer no per-minute charges, no scheduling conflicts, and potentially greater security over private networks. Customers that already have major MCU investments should maintain them, but evaluate technology shifts and their long term plans. Video usage is growing, particularly among mobile devices, many of which are capable of supporting multi-stream sessions. Sites with major investments may want to consider a hybrid approach between premises and cloud solutions to accommodate increased demand.

Perhaps the biggest reason organizations continue to purchase hardware-based MCUs is to support an installed base of equipment; self-perpetuating logic. Video systems are changing quickly: SVC, WebRTC, VP8/VP9, H.265 are examples of reasons to question long-term hardware commitments that support today's technologies.