H.323 Multipoint Conference Unit (MCU)

The Multipoint Conference Unit (MCU) is an important part of an H.323 video conferencing infrastructure, allowing three or more parties or persons to get together in a virtual meeting room.

PRIMARY QUESTIONS

• What is an MCU?
• Why do we need an MCU?
• Can an MCU create conferences with endpoints using different protocols?
• Should I use a third-party scheduler or an internal scheduling device on the MCU?

ANSWERS

What is an MCU? Like the more familiar audioconference bridge, an MCU essentially creates a point-to-point videoconference with each endpoint within a given conference. An MCU uses sophisticated software and hardware to combine these inputs into a shared environment very like a physical meeting space.

Why do we need an MCU? An MCU is required to link three or more endpoints.

Can an MCU create conferences with endpoints using different protocols? Depending on the type of MCU purchased, this can be accomplished. The Accord MCU is able to transcode between protocols. Other MCUs require the assistance of an external gateway to transcode between protocols.

Should I use a third-party scheduler or an internal scheduling device on the MCU? Depending upon the particular vendor’s MCU, the scheduler function may not have everything that the scheduling operator wants or needs. Not all internal schedulers can control other types of MCUs, whereas a third party scheduler can do so. As with most every technology, the more a product can do, the more expensive it is.

Multipoint Conference Unit Testing

IHETS tested four H.323 MCUs from February through March 2001: Accord – MGC-100; Cisco – 3540 MCU; Ezenia – Encounter 3000; CUSeeMe – Whitepines. Each MCU was tested over a three-day period with participants from higher education, K-12 education, and libraries. The participants were:

Higher Education:

• Ball State University
• Indiana State University
• Indiana University
• Ivy Tech State College – Ft. Wayne
• Purdue University

K-12 Schools:

• East Central Educational Service Center
• Northern Indiana Educational Service Center
• Northwest Indiana Educational Service Center
• Southern Indiana Educational Service Center
• Southwest Allen County Schools
• West Central Educational Service Center

Libraries:

• Indiana Cooperative Library Services Authority (INCOLSA)
• Indiana State Library
• Jennings County Public Library

Tests were all conducted at 2:00 p.m. to represent peak traffic loads and the Task Force wanted to test under worst-case bandwidth conditions. Each MCU was tested on three different days of the week, and all conferences were conducted at 384 kbps. Each MCU vendor provided an engineer to assist with testing, and it should be noted that no Quality of Service had been implemented on ITN at that time. Polycom, VCON, VTEL, and Microsoft NetMeeting endpoints participated in the testing, and several H.321 (ATM) endpoints also participated via a First Virtual Communications V-Gate gateway. In some cases, the NetMeeting participants had to be dropped in order to keep other participants from being dropped; this seemed to be related to the particular version of NetMeeting and the Microsoft operating system being used by those participants.

Table 3 lists functionality by vendor for the MCUs that were evaluated.

Recommendation: The IPVTF recommends the Accord MGC-100 MCU for the following reasons:

• It supports H.323 (IP), H.321 (ATM), and H.320 (ISDN) protocols.
• Participants in the tests rated Accord highest for audio and video quality.
• Implementation of the Accord will allow for unified scheduling across IP and ATM video. Other bridges would require third-party software to achieve this.
• The Accord MCU was designed for carrier or service providers.
• The Accord provides for more continuous presence options.
• Continuous presence on the Accord is symmetric. For example, four 384 kbps calls input are output as one 384 kbps call. On other MCUs, four 384 kbps calls input are output as one 1.344 Mbps call. This would use the entire bandwidth of a T1 link and significantly increase the cost of providing bridging service.
• Overall, the Accord has more functionality features than the other MCUs. This allows for greater flexibility in the provision of services.

Figure 2 illustrates how the Accord MGC-100 fits into the ITN infrastructure. ATM and IP calls reach the Accord through the ITN cloud; ISDN calls will be routed directly into the MCU, allowing all three protocols to be used in the same conference on the same MCU.

Figure 2

Table 3

*Transcoding is the capability to automatically change video and/or audio from one protocol to another.