Videoconferencing: How to Step Up From Skype
A Dive Into Protocols
In a perfect world, you would never need to think about the protocols in a videoconferencing product. Unfortunately, you still have to do so in a few cases, such as when you're trying to connect to someone who has an older system. Knowing which protocol a system uses (or which protocols it can translate) can be critical. However, protocol information tends to be available in a table in a user-manual appendix rather than on the product box--not easy to stumble across, but worthwhile to look for.
Self-hosted small-business videoconferencing systems--whether offered as a stand-alone appliance, software running on a server, or a service provided across the Internet--will generally be based on one of two technologies: SIMPLE (Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions) or XMPP (Extensible Messaging and Presence Protocol), the protocol that underlies Jabber. SIMPLE and XMPP are both open protocols, though each approaches the challenges of videoconferencing from a different direction.
SIMPLE grew out of SIP (Session Initiation Protocol), an audio protocol employed in many Voice-over IP systems. Its two major benefits are its use of XML for presence information--letting a caller know whether the receiving party is available--and its support for various messaging protocols for collaboration.
XMPP also uses XML to define its data structures for features including presence, VoIP, and rich messaging types (such as audio and video). It grew out of an instant messaging protocol developed as an open alternative to AOL Instant Messenger, and its standards are still being finalized. Neither SIMPLE nor XMPP is intrinsically better.
Large enterprise videoconferencing and telepresence systems--which provide audio and video of such high quality that the effect is almost like being in the same room--make use of a component called an MCU (Multipoint Control Unit) that plays traffic cop and bandwidth manager. In these systems, the MCU initiates the connections to multiple sites, opening connections with the various ports and protocols required.
An MCU also serves as a universal translator, allowing videoconference clients using different compression techniques and protocols to communicate. In unified communications systems, the server contains the MCU function, simplifying both configuration and administration. Stand-alone MCUs tend to support more users and provide higher quality, while those provided as software in a server tend to be less expensive.
Relative processing requirements and quality come into play with another layer of protocols seen in specifications for videoconferencing system software. The H.261 and H.263 video compression standards that have been used in videoconferencing for many years are being supplanted by another pair of standards: H.264/AVC and MPEG-4 AVC. Like the higher-level SIMPLE and XMPP, these standards are two approaches to the same set of problems from two separate organizations.
It's often not obvious from the packaging or marketing material which standard a particular system uses; look in the technical specifications of any device to find out which standard is inside.
A Case for Dedicated Hardware?
The availability of dedicated processing power and silicon-based (rather than software-based) compression and decompression are the primary advantages of stand-alone, hardware-based videoconferencing systems, which offer quality up to telepresence levels.
Enterprise-class systems base multipoint videoconferencing systems on hardware MCUs and gateways that handle connection and presence tasks. For most small organizations, on the other hand, a software-based system based on SIMPLE or XMPP is more affordable.
In particular, the capability to provide Quality of Service (QoS) for network traffic of specific types or from particular network addresses is necessary to ensure that video and audio remain smooth and high-quality while normal business tasks take place across the network.
Videoconferencing is a high-bandwidth, demanding application for end-point clients, servers, and networks. Although the Star Trek holodeck isn't yet possible on a small-business budget, technology has evolved to a point at which you can have a professional-quality videoconferencing presence without busting your IT budget.