[atoca] Proposal for gap analysis.
"'Mark Wood'" <mark.wood@drcf.net> Tue, 31 July 2012 14:13 UTC
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From: 'Mark Wood' <mark.wood@drcf.net>
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Subject: [atoca] Proposal for gap analysis.
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Friends, There are some similarities and some differences between EU-ALERT/CMAS, (now known as WEA) and IP multicasting. IP multicast has some strengths that Cell Broadcast does not have, and some apparent weaknesses that may be either solvable or at least we can mitigate them. I have an expert knowledge of cellular multicast but am new to IP technologies, but learning fast. I am humble enough to accept correction as needed. But fist, there is a step we need to take as soon as practical. After a lot of 'too-ing' and 'fro-ing', its now widely agreed that any multicast based system would be greatly simplified by having a standard block of addresses dedicated to the function of public warning. Now the latest version of the 3GPP standard on 023.041 V11.1, does indeed reserve a generous block of addresses for this purpose. This would make it very easy for administrated system (AS) administrators to open a specific block of multicast addresses on distribution routers by default, without any worry about torrents of broadcast data flooding his network nor worry about if the message were truly authentic (as the government gateway guaranties this). And yet this does not preclude the administrator from opening other non governmental gateways at the policy of the AS if she wants to. Proposal 1 I believe that a good place to start would be to reserve a block of 255 multicast addresses, both in IP4 and IP6, for future development for multicast based public warning systems, and other civic purposes at the discretion of the member state. Then we can take a look at two alternative protocols, and look for a good way to emulate the geo-specificity feature of CB. 1. Should we create a sort of 'Cell Broadcast over IP Encapsulation protocol' in which cell broadcast messaging is wrapped up in a package format suitable for transmission by IP networks, and then rely on an app at the host to present the result to the user? There are two advantages to this approach. Information presently created at the originator system has been created in such a way as to respect the limitations that the mobile networks have placed upon the emergency management community, that the message must have less than 90 characters (80 bytes). Therefore a separate message origination systems, separate gateways and separate trust protocol rule set in the aggregator gateway system is not needed. Furthermore the user will see the same message exactly and in the same format no matter what device he looks at. All of this helps in a confused and panicky situation. The university of Delft noted that people like to see three different confirmations of something before they believe it. Furthermore such a small message payload will not raise any broadcast storm worries. 2. Or should we create a separate format and protocol designed to exploit the fact that IP networks do not have the restraints that 2G cell broadcast systems have, and can send megabytes of data in very rich multi media formats? The advantage would be much more functionality for the solution, but at the cost of complexity at the message originator side because message inputs would now become a lot more involved with many more functions to choose from. Nevertheless I think in the future this should be the goal, a sort of EU-ALERT V2. Maybe we should work on both, as they are not incompatible with each other; there is no problem in running them both side by side. Clearly it will be a few years down the road before the emergency management profession are sufficiently familiar with EU-ALERT/WEA to be confident enough with something much more demanding. Proposal 2 I believe we should look at how we should create a CB over IP encapsulation protocol. Proposal 3 We should look at how a more flexible public messaging multicast format would need to be framed. Geo specificity One area of significance is that of geo specificity. CB is attractive also because it is natively and passively geo specific (well, bluntly, but good enough). In the present IPAWS OPEN system, the originators signal their proposals to a gateway unit, which analyses the polygon and distributes it to networks which have service area under the polygon. Within the networks, a Cell Broadcast Centre (CBC) analyses the polygon and send the message only to cells which have service area under the polygon. Since a cell is typically about a few KM across, we have resolution down to about a neighbourhood. *However this is normally good enough*. All this is done passively without any position reporting, polling, data base interrogation, paging, SS7 signalling or any network signalling at all. We need to find a way to passively emulate this. I think it may not be as tough as all that, here is what I propose. The administrator of any system knows the physical location of access level switches and access wireless access points. Typically the distribution layer of routers in located on one campus and subnets rarely cover more than one building (at least subnets go with LANs which are normally in one building due to Ethernet limitations). Since Protocol Independent Multicast protocol (PIM) requires the setting up of RV points at which administrators control access to subsequent multicast addresses and their distribution, it should be fairly easy for an administrator to associate all of the public warning range of multicast addresses with a collective location, such as a ZIP code provided by a CUG at that Gateway. A development of PIM would automate this if we know something of the location of the distribution router. Yes, it's not rocket science, but it is way good enough for this application as it matches the geo specificity of Cell Broadcast really quite well (in fact is normally better). It's optional for us to use Internet Gateway Multicast Protocol IGMP, because you can subscribe a subnet to a multicast address by informing the Ethernet port on the distributing router that it has subscribed this subnet to this range of addresses. So therefore IGMP may not be as big a problem as anyone thinks. Remember that civic messages are very short (80 bytes) and quite rare, (one every 20 minutes for maybe a few days a year). This is trivial amounts of data so an administrator is not opening himself up to broadcast storms by doing this as they sometimes fear, (BPDU's are much more but no one thinks of switching spanning tree off). If someone would like to tell me what text is needed to make this an official suggestion, I am quite ready to oblige. We could not have done this before the 3GPP finished its work (this march), but they have, so It is time to do this now. Warm regards Mark Wood DRCF. PS A FRIEND OF MINE RECENTLY GOT HIS VERY FIRST GENUINE REAL CMAS MESSAGE ON HIS BLACKBERY, SO IT IS RUNNING CODE!!
- [atoca] Proposal for gap analysis. 'Mark Wood'