[Asterisk-Users] RE:911, networks of * servers, etc. (was: VOIP Dialtone?)

John Todd jtodd at loligo.com
Thu Aug 21 16:34:48 MST 2003


This is excellent data; thank you.  I'll review before harrassing the 
E911 folks at VON.

However, this only seems to solve problems for local PSAP 
connectivity to your * server.  Or am I mistaken?

I think a larger and simpler (read: less hardware and no "custom" 
circuits) system needs to be developed to hand information to the 
PSAP.  I know that none of my customers would ever, EVER consider 
purchasing a dedicated circuit into the 911 system until they were 
forced to by some sort of laws.  With VoIP providers all over the 
nation, I think this is an unworkable solution.  I may be whistling 
in the wind, but that's the reality of the situation.

JT



At 7:15 PM -0400 8/21/03, Tom Zimnicki wrote:
>
>Which brings me to an application at hand:
>
>We currently have an * box connected to a SIP Media Gateway which is
>connected to the PSTN via SS7.
>
>We have MF FG-C 911 trunks connected to a DMS and can bring an MF T-1 into
>the * box if we buy a T400P card.
>
>
>The question is how do you support ringback with SIP devices? (i.e. the PSAP
>operator keeps the 'trunk' siezed and forces ringing on the SIP phone that
>is on-hook. It should also generate a 'howler' tone on an off-hook set)
>
>(There was a list for SIP 911 issues, but it appears to be dormant:
>http://lists.cs.columbia.edu/mailman/listinfo/911 )
>
>There was a reference to using re-invites and suspend/resume via RFC 3064
>and that T1.628 - 2000 might have been looking into it. Does anyone have a
>current copy they could check to see if this issue has been addressed?
>
>(Also GR-529
>http://telecom-info.telcordia.com/site-cgi/ido/docs.cgi?ID=159801680D000801&KEYWORDS=529&TITLE=&DOCUMENT=&DATE=&CLASS=&COUNT=1000
>
>&
>
>ANSI T1.628a-2001. http://www-comm.itsi.disa.mil/t1/628.html will probably
>be of interest.)
>
>Does anyone here have the interest or experience to try and make this happen
>on * ?
>
>(And although the world is moving to E911 and there are folks working on SS7
>for *, is anyone interested in getting the Digium cards and * to intereface
>with the Emergency Service Feature Group C trunks that a Nortel 911-DMS
>Tandem uses? )
>
>Regards,
>
>Tom Zimnicki
>
>----- Original Message -----
>From: "Michael Kane" <mkane at to-talk.com>
>To: <asterisk-users at lists.digium.com>
>Sent: August 21, 2003 3:25 PM
>Subject: Re: [Asterisk-Users] RE:911, networks of * servers, etc. (was: VOIP
>Dialtone?)
>
>
>>  There are TDM interfaces higher end PBX's use to interconnect to the
>PS/ALI.
>>  I beleive it's a CAMA trunk that signals using MF.
>>
>>
>>
>>  ----- Original Message -----
>>  From: "John Todd" <jtodd at loligo.com>
>>  To: <asterisk-users at lists.digium.com>
>>  Sent: Thursday, August 21, 2003 3:00 PM
>>  Subject: [Asterisk-Users] RE:911, networks of * servers, etc. (was: VOIP
>>  Dialtone?)
>>
>>
>>  >
>>  > Yes, I'm familiar with the E911 platforms and their requirements to
>>  > some degree.  The trick is that the people running Asterisk PBX
>>  > systems have no visibility into SS7, and that is an unreasonable
>>  > expectation, so some other out-of-band method for moving caller
>>  > location to the PSAP is required.
>>  >
>>  > As far as geographic location tracking is concerned: that is the
>>  > user's problem.  If they don't have the correct information in their
>>  > device, then they're SOL.  There is _no way_ to develop lat/lon/alt
>>  > coordinates from an IP address, despite what any .com
>>  > flash-in-the-pan company says they can do with their clever
>>  > databases.  Thus, the PBX/switch provider will have to enforce their
>  > > own database of device-to-geographic-coordinates.  (As mentioned,
>  > > maybe a SIP header is a reasonable thing to use for the UA to relay
>  > > this data to the proxy.)  I am not concerned so much about the
>>  > ability of the devices to send their data to the proxy: I am VERY
>>  > concerned about how the proxy then looks up the appropriate PSAP, and
>>  > then relays the data for the call to that PSAP.
>>  >
>>  > JT
>>  >
>>  >
>>  >
>>  >
>>  > >911 through the phone system is tricky business. e911 which is the
>  > > >automated process of handing the address to the 911 center uses the SS7
>>  > >database to do it's work (the database is created when the LEC runs
>>  > >physical lines to locations not by people filling anything out). Cell
>>  phone
>>  > >service providers have the simuliar problems as VoIP service providers
>>  are
>>  > >facing are realizing with call forwarding and call following it will
>get
>>  > >worse.. Congress has mandated that the cell phone industry make it
>>  possible
>>  > >to track a cell phone users within 300yards via cell sites and
>>  > >triangulation. By 2005 every cell phone will be required to have a GPS
>>  and
>>  > >send GPS information to the 911 system when they call 911. If you want
>>  more
>>  > >information on e911 try http://www.fcc.gov/911/enhanced/ . As the cell
>>  > >phone industry grows there will be a need for a national 911 call
>routing
>>  > >center. I bet it won't be free.
>>  > >
>>  > >
>>  > >Original Message:
>>  > >-----------------
>>  > >From: John Todd jtodd at loligo.com
>>  > >Date: Thu, 21 Aug 2003 01:32:24 -0700
>>  > >To: asterisk-users at lists.digium.com
>>  > >Subject: [Asterisk-Users] 911, networks of * servers, etc. (was: VOIP
>>  > >Dialtone?)
>>  > >
>>  > >
>>  > >
>>  > >OK, that "VOIP dialtone?" thread was getting really out of hand, so
>>  > >I'll condense my answers into one big ugly message:
>>  > >
>>  > >
>>  > >1) 911 service.  Yes, that is one of three reasons to keep your PSTN
>>  > >line.  The other two reasons are:   Inbound calls from local callers
>>  > >still should work on a POTS line, for now.  You can't find VOIP
>>  > >providers in most area codes, so you'll most likely need to have a
>>  > >"local" number that finds it's way to you for "local" tasks.
>>  > >Secondly, the Internet is not as reliable as the phone system.
>>  > >Sorry, folks, it just works that way right now despite what your
>>  > >network engineer might tell you.  That's not to say it's unreliable,
>>  > >but those last two nines are very expensive... Besides, any good
>>  > >network engineer will tell you that you should have multiple paths
>>  > >for your IP connectivity.  With few exceptions, most homes do not
>>  > >have multipath connectivity.  (note: businesses may in fact have
>>  > >better uptime on their IP network than their phone network, if they
>>  > >have competent engineers and a reasonable budget.)
>>  > >
>>  > >1.5) There are reasonable technical solutions to this problem, but
>>  > >for the life of me I can't figure out why the 911 centers haven't
>>  > >gotten their act together and solved this.  There are two halves to
>>  > >this problem: "What PSAP do I call? (and what phone number)"  and
>>  > >"How do I get my location data to the PSAP once I call them?"
>>  > >C'mon, this is not difficult.  The first question can be answered
>>  > >trivially: there _must_ be a database of address-to-PSAP mappings.
>>  > >Any PBX administrator (or SIP phone owner, for that matter) should be
>>  > >able to figure out their address.  Methods for associating the PSAP
>>  > >number with the phone are numerous, and trivially implemented - if
>>  > >people don't keep their address information updated, they're SOL
>>  > >(though you can remind them in an automated fashion to keep it
>>  > >updated - just forbid them from using the service unless they verify
>>  > >the address every month or so.)
>>  > >
>>  > >The second question is more difficult, but certainly possible.  There
>>  > >may be kludge ways of doing it, and there should be more elegant ways
>>  > >of doing it.  A SIP header with lat/lon/alt data that gets sent from
>>  > >the UA only on 911 (or other programmable string) calls might be
>>  > >reasonably elegant... maybe.  But that only gets the data to the SIP
>>  > >proxy.  That doesn't solve the issue of how you get that data from
>>  > >the SIP proxy to the PSAP, which at some point will be almost
>>  > >certainly through a PSTN connection... ADSI FSK, maybe?  Ugly, and
>>  > >PSAPs would not want to invest in equipment.  A national caller-id to
>>  > >location clearinghouse in which your proxy could participate (any 911
>>  > >calls would create a temporary mapping)?  Maybe, but probably not.
>>  > >Non-standard, and I doubt PSAP operators would want another tool,
>  > > >even if it is web-based and so easy a monkey could use it.  I don't
>>  > >know.  I guess I'll grill the PSAP people at the panel next month at
>>  > >VON.  :-)
>>  > >
>>  > [snip]
>>  > _______________________________________________
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>>  >
>>
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