How to Connect: Choosing the Best Connection Method for Your Videoconference

The use of H.323 technology offers considerable flexibility to Videoconference Administrators for creating videoconference connections. In the CalREN Video Services (CVS) environment, connection options for your videoconferences include:

Schedule your videoconference using the CVS Scheduling Desk.

This method is generally required if you have more than 2 sites participating, or if any sites require ISDN dial-in access. It is optional if you have only 2 participating sites. Choose this option if:

• There are more than 2 sites participating in your conference, or you have one or more sites who will dial in via ISDN.
• You want the CENIC Network Operations Center to be able to disconnect and reconnect participants in case of problems.
• You want your videoconference to appear in the online schedule at the CVS Scheduling Desk.

Bypass the CVS Scheduling Desk.

This method is possible if you have only 2 participating sites, and both sites have H.323 capabilities. You might choose this option if:

• There are only 2 sites, and both have equipment manufactured by the same company (e.g., both Polycom or both Tandberg codecs). In this case, there are often proprietary features designed to enhance the videoconference quality when making a direct, point-to-point connection.
• One of the 2 sites is an H.323-capable non-CVS site. In this case, you may prefer to connect using IP addresses rather than asking the site to dial in via ISDN. In this case, especially if the sites will connect over the commercial Internet, quality is not assured, but you may discover through testing that the quality is adequate for your purposes.

Should you decide to bypass the CVS Scheduling System, you may connect using Dial Strings or IP Addresses.

If you choose to use Dial Strings for videoconferencing, you are sending the videoconference media stream through your CVS gatekeeper/proxy device. This is illustrated below:

Using Dial Strings provides two major benefits:

1. Media streams sent through the gatekeeper are given priority over other data on the network. That means that if network demand is high, your videoconference is less likely to be affected.
2. On some campuses, videoconferences will only work if you use Dial Strings because their videoconferencing equipment is behind a firewall, and all calls must go through the CVS gatekeeper/proxy device.

There are, however, situations in which IP Addresses are preferable over Dial Strings. These are as follows:

If you are attempting to take advantage of proprietary features because both endpoints are the same brand, you will need to experiment with Dial Strings and IP addresses. There may be some features that will be supported only if you connect with IP addresses.

If you are connecting to an H.323-capable non-CVS site, you will almost always need to use IP addresses to make the point-to-point connection. The exception is that: if the site you want to connect to has a Global Dial String issued by Vide.net and is registered with the North American Root Gatekeeper. In that case, you can dial them directly, but you must ensure your device's dial string is GDS-compliant. (For more information about Internet2 connectivity, please send a request for information via e-mail to SchedDesk@cenic.org.

When you use IP Addresses for videoconferencing, the media stream goes directly from your videoconferencing endpoint to the other site's endpoint. This is illustrated below:

There are many factors to consider, and this document does not constitute an exhaustive examination of all of them. However, the following matrix represents our advice for most situations:

	Schedule on CVS	Point-to-Point via Dial String	Point-to-Point via IP Address
My videoconference has more than 2 participants.*
One or more of the participants in my videoconference will be dialing in via ISDN
I do not want the end users to have to initiate the videoconference call.
I want my videoconference to appear in the online schedule.
My videoconference has only 2 participants who are both CVS sites and one of the sites has a firewall that only allows traffic to and from the gatekeeper.
My videoconference has only 2 participants who are both CVS sites.
My videoconference has only 2 participants, both have the same kind of equipment, and both are CVS sites.
My videoconference has only 2 participants, one of which is a site with a GDS dial string registered with the North American Root Gatekeeper.
My videoconference has only 2 participants but one of them is not a CVS site, even though they are both H.323-capable.
My videoconference has only 2 participants, both have the same kind of equipment, but one is not a CVS site.

* This applies to codecs that support only one connection at a time. Some codecs have the ability to make two or three simultaneous direct connections. When using a codec with this option, any of the three methods of connection may be used.