Compressed Video Network Operation

August 17, 1999
Contact: Ron Olton

The easiest way to describe the operation of the new H.320 compressed video network is through something that all readers are familiar with, the Public Switched Telephone Network (PSTN). In order to place a telephone call, the caller dials the telephone number of the person that they wish to talk to. If the caller does not know the telephone number of the person that they wish to talk to, they first call the information number (a well known number) to get it.

If a call is required among more than two telephones (a conference call), an audio bridge is used to connect the telephones. Someone must schedule the audio bridge prior to the conference call, and notify all of the participants of the upcoming conference call.

The new compressed video network technology works the same way. The operator "calls" the remote codec by "dialing" its number from the originating codec. If the operator does not know the address of the remote codec, the originating codec must be able to call a well known number ("information") to get it and then "dial" it.

If a conference is required among more than two codecs, a video bridge is used to connect the codecs. As with the telephone network, someone must schedule the video bridge prior to the conference and notify all of the participants of the upcoming conference.

The ability for any college codec to conference directly with any suitably equipped site on Net.Work.Virginia.

The video bridges also have new features. Since these are functions of the video bridge, a video bridge must be used for the conference, even if it is a point to point conference.

Features:

• Sites in the same conference to run at different speeds
• Sites in the same conference to use different audio algorithms
• Sites in the same conference to run at different frame rates
• Courseware to incorporate standards based (T.120) data sharing

There are three elements provided to simplify codec installation and network operation. The first is the assignment of an ATM address (telephone number) to the college codec. This is an automated process where the address assigned to the codec is a combination of the address of the ATM switch that the codec is connected to and the unique hardware address of the codec ATM NIC. The codec is plugged into the ATM switch and the power is turned on. The codec and the ATM switch resolve the address and it is stored in the codec. The full address assigned to the codec can be viewed by selecting the codec "Set Configuration" window on the tool bar and clicking on the "ATM" tab.

The second element is the "information" mechanism used to resolve unknown codec addresses. The network provides two name resolution servers for the colleges (a primary and a backup). Each has a "well known" network address that is configured in the college codec. This gives the codec the ability to automatically look up and "dial" remote codec addresses without operator intervention. The VCC Utility staff provides the name server addresses, and instructions on how to configure the codec with them as part of the college codec installation and test process. The college completes the process by giving the VCC Utility the ATM address assigned to each codec, so that it can be placed in the servers. Non VCCS sites may also be included in the name servers. Colleges wishing to conference with a non-VCCS Net.Work.Virginia site may do so. The colleges need to provide the VCC Utility with the ATM address of the site or the name and phone number of a contact at the site that can provide the ATM address, so that it can be placed in the name resolution servers. The VCCS name resolution servers define a virtual VCCS compressed video network because they contain all of the sites that the colleges can conference with. Given that the VCCS name resolution servers will contain all of the sites that the colleges wish to conference with and are redundant, the use of any non-VCCS name resolution server is both unnecessary and not recommended.

The third element is caused by a limitation in the name resolution servers. The servers cannot accept anything but numbers to identify entries. Therefore, a pseudo telephone number that represents the site is assigned to each entry. This pseudo telephone number has to be configured in the codecs to identify the remote codec. These pseudo telephone numbers are assigned by the VCC Utility to ensure that each codec has one and only one entry in the name servers.

The complete the codec configuration process is as follows:

1. The codec is powered up and its address is given to the VCC Utility.

2. The Utility provides the name resolution server addresses, which are configured in the codec.

3. The VCC Utility provides the pseudo telephone numbers for each codec, which are configured in the codec "Address" window.

4. The codec "Speed Dialer" window is configured with a common name for each remote codec, and the entry is associated with the entry in the "Address" window.

The operator can now start a conference by opening the "Speed Dialer" window and clicking on the name for any remote site.

Given the prerequisites that each codec and video bridge has been configured with the addresses of the name servers, and that the name servers have been configured with the addresses of all of the codecs, the network operates as follows.

Any campus may call any other campus directly (point to point), at any time, by turning on their codec and clicking on the remote site name that they wish to conference with. Though this is possible without calling the VCC Utility to make an actual reservation (as is required for a multipoint conference), it is not recommended. The reason is that there may be something else already scheduled for one of the sites and without attempting to reserve both sites, conflicts in room use can occur. Conference between sites using only the old technology or between sites using the old and new technologies must be scheduled with the VCC Utility, because they can only be connected through a video bridge.

Multipoint conferences are scheduled through the VCC Utility staff. It does not matter whether the sites in a conference are using the old technology or the new technology; the VCC Utility will schedule whatever video bridge resources are needed by the conference. Conferences with the sites that belong to the Southside Virginia consortium network will also be scheduled through the VCC Utility.

Prior to making any reservation, all sites should check to make sure that their conference room has not already been scheduled for another conference or some other purpose.