Technical Requirements

Participation in a NASA Digital Learning Network™ event is possible primarily through interactive videoconferencing. Some programs are available via webcast technology. In order to participate in a DLN interactive videoconference, you will need a video conference codec (coder / decoder) that is standards based operating in either or both of the following modes - over ISDN lines (H.320 standard) or over IP (the internet -H.323 standard). Standards based codecs are all compatible with one another in the same mode.

There are numerous manufacturers with these standards-based codec products including:

Tandberg               http://www.tandberg.net/products/index.jsp

Polycom                  http://www.polycom.com/home/

Sony                         www.sony.com/conferencesolutions

Aethra                      http://www.aethra.com/worldwide/home.asp

VTel                          http://www.vtel.com/

EmblazeVCON       http://www.vcon.com/

ISDN, which stands for Integrated Services Digital Network, is a system bonding together several digital phone connections that has been available for over a decade. This system allows voice and data to be transmitted simultaneously across the world using end-to-end digital connectivity. It uses the International Telecommunications Union (ITU) H.320 compression algorithm, a standard protocol for digital transmission across telephone lines. ISDN is a proven technology that has been refined over the last decade to the point that it delivers clear video and voice transmission with few limitations. A typical ISDN videoconference uses three ISDN pairs of lines (384 kbps rate), but other rates are also used.

IP, which stands for Internet Protocol is an identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route traffic based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address. IP is the protocol also used for sending emails across the Internet. The (ITU) H.323 data format, a compression algorithm that provides consistent packet transmission of audio, video, and data across networks, is the standard for videoconferencing over IP. Videoconferencing over IP eliminates per minute long distance calling charges (of ISDN) and is often preferred because it allows management of most or all communication technology on a single network.

Schools should consider:

• Videoconferencing equipment capable of connectivity over ISDN (H.320) and/or IP networks (H.323). A system that has both IP and ISDN is recommended so that participation in videoconferencing is not limited to providers using only one mode.
• The DLN uses a standard connection rate of 384kbps (kilobits per second) for both ISDN and IP connections. Your location may want to arrange for increased bandwidth of 512kbps or 768kbps (40% overhead from these rates should be allowed when requesting IP bandwidth).
• Ability to "Dial Out" and have others "Dial In" (place outbound and receive inbound) calls.
• Symmetrical bandwidth allocation (same bandwidth inbound & outbound).
• For the IP mode, location of the systems on a subnet outside the firewall. However, if using IP technology and the system will be placed behind a firewall, access should be allowed locally through the firewall. All firewalls must be protocol aware. Your system administrator should assist with this process. (Additional details are given below.)
• Multisite features, which are optional but may be necessary if you plan to collaborate directly with more than one site.
• Webcast participation, which is possible via RealPlayer and Web connectivity. One computer and a projection device or a computer lab allows for student interaction via chat forum or email.

A firewall is a set of related programs (located at a network gateway server) that protects the resources of a private network. Basically, a firewall, working closely with a router program, filters all network packets to determine whether to forward them toward their destination. A firewall is often installed away from the rest of the network so that no incoming request can access private network resources. There are a number of firewall screening methods. A simple one is to screen requests to make sure they come from acceptable (previously identified) domain names and IP addresses.

Your Systems Administrator or Network Supervisor should consult with the manufacturer of your specific videoconferening system to obtain port settings to allow access through your firewall for your IP video conference equipment.

Firewall port settings must be correctly set to allow H.323 videoconferencing over IP (this does not apply to ISDN or dial-up switched phone lines). The firewall settings are ports that must be opened in the network security system or "firewall". If these ports are not open, the connection that will be available over the IP network may not allow the videoconference data to pass properly. This could result in: (1) a failure to establish a connection, (2) a very brief connection and then loss of connection, or (3) freezing during the connection.  It is important to understand that by opening these ports, you are punching holes in your firewall, which reduces the protection the firewall provides. CAUTION: For this reason, we recommend that your network administrator review these settings and that only qualified IT personnel make these changes. You will be enabling access to ports 1024+. This puts almost all third party TCP based products in vulnerable mode.

Below is a list of minimum ports that must be enabled for H.323 videoconferencing to work.

Q. What is the difference between a test call and a connectivity check?

A. We refer to a Test Call Connection as a recommended test connection from your location to our equipment after we have confirmed your event with us. A connectivity check should only be requested if you have not yet registered for an event.

Q. What is the difference between a Webcast and a videoconference?

A. A videoconference provides real-time, two-way, audio/video connectivity via compatible hardware and software on both ends. A Webcast is a video stream over the Internet of a special event or a videoconference event with up to three schools. The schools and teachers involved give permission to the DLN to stream the event, and a link is provided for participants to interact with the NASA presenter through e-mail or message board.

Q. What does it mean to share the connection with another school?

A. To facilitate the large number of DLN requests, you may be asked to share the connection with one or two other schools. When you share the connection, you will be able to interact with NASA and students from other schools.

Q. What is a special event and how does it differ from a regular DLN event?

Q. Does my class have to be available for a test connection?

A. No, your technical contact should be able to handle the test connection with NASA without  class participation.