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Subject: Re: [emergency] usage scenarios
"Separate automatic notifications of both the car crash and the HAZMAT carrier are sent using the Vehicular Emergency Data Set (VEDS), contained in the Distribution Element, and in addition, a video clip taken from a live transmission is transmitted as a properly mimeTyped non-xml mpeg file for a time-stamped reference." It concerns me that the EDXL framework is being used in this example as a transport mechanism to deliver MPEG video - something it clearly is not. I've brought this up a few times and it has largely gone ignored. Base64 encoding adds quite a lot of overhead to data, and embedding this type of content can easily lead to situations where a decoder is hammered because it cannot deal with the size of the payload, or the message is rendered useless because it cannot be delivered in a timely fashion over bandwidth-starved and/or error-prone transmission links. If the transmission link is unicast, you can quite easily cap out the bandwidth on the link if multiple recipients are retrieving the content at the same time (in which case the EDXL delivery system is for all intent purposes rendered useless). Content of this nature should be delivered to recipients via out-of-band delivery on the same base transport mechanism (be that HTTP or whatever). That way you can receive the message immediately and parse the video content when it arrives. Server operators can also then apply QoS settings to the traffic to prioritize delivery of EDXL messages. In these situations it may also be advantageous to support multiple content URI references, i.e. a reference to a download URI for the content, a local disk reference if another mechanism handles delivery of assets, and alternate methods for access such as streaming (in which case the streaming metadata file (SDP, etc.) is inserted into the content as a derefuri chunk). Cheers Kon
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