You have many options, depending on what you would like to accomplish in your conferences and of course, your budget.
You have two basic types of systems: H.320 (ISDN), and H.323 (video over IP). If you would like two systems to have a point-to-point conference, you simply dial the phone number or IP address of the far end system.
If you would like to implement a dialing plan or AAA (authentication, authorization, and accounting), you would need to implement Cisco's MCM. The dialing plan is for your end users ease of use. We typically use a dialing plan similar to the phone system, in which we give each end-point a unique telephone style number, better referred to as an E.164 address. The gatekeeper function of the MCM resolves the E.164 address to either an IP address, or directs it toward the gateway.
The purpose of the gateway is to bridge an H.323 network to an H.320 network. Cisco's 3520 or 3525 Gateway will allow your ISDN end-points to confer with your IP end-points. In order to have a conference with three or more end-points you would need to implement Cisco's 3510 or 3540 MCU, depending on your needs and future scalability. This allows you to have multiple end-points in a conference, as well as multiple presence, which is a quad screen showing your speaker and three other sites.
There are also many options for sharing data during your conferences. Bandwidth requirements depend on the video quality, and number of end-points you use. You also have many ways to "fine tune" your network by implementing QOS.
We have tested Cisco's 3525 Gateway, 3540 MCU, and two 2610 routers running the MCM software and HSRP for redundancy. In our lab we connected a PictureTel 900, Polycom Viewstation 512, VTEL Galaxy, Tandberg 6000, Tandberg 1000, and two Vcon Escorts together in a conference, utilizing both H.320 and H.323 end-points. Everything worked well together and I was very pleased. I hope this helps.
