Eliot,
So, it would seem that you want to enable any two H.323 devices to transparently convey a CAP message from point A to point B. For example, assume that the NWS detects the tornado. By what means is it expecting to send the CAP message to the Weather Channel? If H.323 had the facility, would the NWS perhaps send the CAP message directly to a receive using H.323? (This is akin to placing a phone call, but rather than delivering a voice message, the system delivers a text message and gets acknowledgement of receipt.)
Or, is it expected that the Weather Channel would fetch these CAP messages through other means?
I don't expect to see H.323-enabled sirens and such, so let's consider a user's PC-based softphone or IP phone: would you expect the NWS or Weather Channel or other entity to transmit the CAP message directly to the end user of such devices? Or, would you expect the CAP message to be translated in the network into something that is "human decipherable" (e.g., a formatted text message, video message, or voice message) that gets "played" to the user? In that case, the user's equipment would never see or process a CAP message.
Any further clarification you can provide would be greatly appreciated.
Thanks, Paul
-----Original Message----- From: Eliot Christian [mailto:echristian@usgs.gov] Sent: Monday, May 28, 2007 9:56 AM To: simao.campos@itu.int; paulej@packetizer.com; s.horne@packetizer.com; Christian.Groves@nteczone.com Cc: itu-sg16@lists.packetizer.com; Art Botterell Subject: RE: [itu-sg16] Instant Messaging in H.323 & Common Alerting Protocol (CAP)
Please forgive me diving into the middle of this discussion.
I would like to make a distinction here: a CAP message is a special case of emergency messages generally. We all know that just about any medium can be used to communicate emergency messages: sirens, police with bullhorns, voice over radio or telephone, text over news wire, text crawl over television, fax, e-mail, and so on. I would say that the underlying source of any emergency message may include, but is not limited to, a CAP message.
I'd also note that CAP only standardizes the information content of emergency messages as they are being communicated digitally and electronically. A CAP message must be delivered entirely and without corruption, and in its specific structured format (transformable to the prescribed XML or ASN.1 syntax and encodings).
Human receivers of emergency messages rarely deal directly with underlying CAP messages. A person who hears a siren blaring does not know or care if the siren is a TCP/IP device programmed to process CAP messages. The same is true of a warning given by a policeman based on a CAP message to his squad car, or a warning given by a radio announcer reading a CAP message off of a news wire service.
Yet, the relaying, filtering, and routing of CAP messages is a very important aspect as CAP messages do traverse a wide range of communications paths. From a communications architecture perspective, our key consideration is whether traversal of a given path segment preserves the content and structural integrity of the CAP message and any associated authority, authenticity and security assertions. Where such integrity is not preserved, we should say that delivery of the CAP message is finished although the emergency message itself may continue to be relayed.
For example, let's say the National Weather Service sends out a CAP message for a tornado alert. This CAP message is then picked up by the Weather Channel and inserted into television news. Seeing that message on television, local police trigger the public address system at a shopping mall in the threatened area. Here, a complex relay of the emergency message is occurring. The emergency messages were triggered by the original CAP message but the derivative emergency messages are not preserving the full integrity of the underlying CAP message.
Expanding on the example, it is also possible for a local police system to pick up the CAP message directly from the National Weather Service. The police system can then automatically relay that message to an automated system at the shopping mall, programmed to process the CAP alert directly. In a similar vein, commercial wireless service providers in the U.S. will soon be required to process CAP messages and send such a tornado alert directly to their subscribers. Because these more automated communications paths can be much quicker and less error- prone, we look forward to deeper penetration of CAP-enabled communications over time. But, multiple communications paths for emergency messages will be commonplace for the foreseeable future.
Eliot