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TUCoPS :: Phreaking Technical System Info :: we911.txt

Wireless E911 Service - Architecture and Future




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-->]OO[::[ Wireless E-9-1-1 ]::::::::[OO--[ by digiphreq ]-------------------
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Wireless Enhanced 9-1-1 Service- Architecture and future.
By Digiphreq <digiphreq@webcrunchers.com>
Darkcyde Communications 5/8/99
darkcyde.8m.com
		
		"A nerd is somebody who's life is focused on computers 
		and technology.  A geek is somebody who's life is focused
		on computers and technology and likes it that way."


Ye Ol'' Table of Contents
I. Introduction
II. A Bit of History
III. FCC Regulations on Wireless 9-1-1
IV. Common Wireline 9-1-1 Service
V. Issues on How to Make Wireless 9-1-1 Work
	1. Stage 1
	2. Stage 2
VI. Long Term & Conclusion

	I. Introduction:	
As you probably very well know Enhanced 9-1-1(E9-1-1) is the most common for
of 9-1-1 these days.  It is possible to find B9-1-1, if you live in the
middle of no where...  Anyway today wireline E9-1-1 relays all the important
info on you.  Location, name, and the telephone number to the dispatch
telecommunicator which then accurately routes your call to the proper
Emergency Dispatch Station.  In theory this makes the whole process faster,
as to get you help quicker.  Which is often not the case.  With the current
day workings of wireless networks, E9-1-1 isn't really possible. They have
begun to incorporate technologies to support it though.  This is all because
of a bunch of new regulations which the FCC placed on wireless
communications, which called for an improvement of the use of E9-1-1.
Originally in 1996 they created a two stage time line, which I will be
explaining later.  A quick overview is that Stage one will require wireless
networks to provide the user's call back number and the location including
which cell sector they are in.  Stage two allows for a more precise pin point
of the caller's location, which requires a bit more hardware and technology.
I will touch on a brief history of Wireline E9-1-1 service, Wireless E9-1-1
service operations(how it should work), and a more detailed overview of the
Two stage process involved in upgrading the current Wireless system.


	II. A bit of History:	
The first 9-1-1 service, was introduced in Alabama in 1968.  It's also known
as Basic 9-1-1 or B9-1-1.  This was a very primitive version of E9-1-1 which
only routed your call to a local police station.  In the 1980's B9-1-1 was 
enhanced and there was the introduction of E9-1-1.  	

                      Database             Automatic
          _           Management            Location
         / \          System               Info |   
        /   \              |                    |
        _____              |                    |
       :     :         Emergency                |
       :     :          Service                 |
       :_____:          Adjunct                 |
          |                 |                   |
          |                 |                   |
          |                 |                   |
          |            5ESS switch              |
       Central               E9-1-1             |  
        Office _________selective_____________PSAP    
                         router                   \
                       (routes Ani)                \___ Displays: 
                                                        Location
                                                        Call back #
                                                        Mapping Location

As you can see (sort of) when a residential or commerce line dials 911, there
call goes to the central office switch which routes their call to a E9-1-1
selective router.  Which then routes the call to the correct PSAP based on
the user's telephone number.  The phone number is passed from the PSAP to the
Customer Premises Equipment (CPE), which it uses to look up an Automatic
Location Information (ALI) database for the user's name and address.  On top
of all this the user's line number is then used as the call back number in
case the caller accidentally hangs up(Ex. the killer hangs up the phone for
them...) or the PSAP dispatcher needs to call the user back.


	III. FCC Regulations on Wireless 9-1-1
(This Was Borrowed)
Points of Interest in the FCC Ruling Over Wireless 9-1-1
-Wireless carriers must support call routing based on cell sector,
and they must also convey information sufficient to enable the PSAP to call
back the 9-1-1 caller(that is transmit the calling party number) within 18
months of the ruling's effective date.  This requirement is sometimes called
Stage 1.
-Carriers must support deployment of technology to determine a caller's 
location within 125m of accuracy for 67% of all wireless 9-1-1 calls  
within five years effective date.  Support of a specific location 
determination, which will require PSAPs to be able to handle coordinates 
rather than street addresses, is sometimes called Stage 2.
-The FCC will entertain waivers on a case by case basis for not complying                
with the rules. 
-Any call from a handset having a MIN must be transmitted to 9-1-1 even if 
the handset no longer has valid service.  The call may not be intercepted 
or blocked.  The local PSAP may decide whether or not to receive calls from 
non-MIN telephones, for example phones that were never service activated.  
if a    PSAP requests these calls, the carrier is supposed to provide them.
-The ruling applies to cellular, broadband PCS, and geographic area SMR 
providers (meaing SMRs that provide mass market services).  Systems 
provided 
by movile satellite communications vendors, such as Motorola's Iridium, are 
not covered by this ruling.Because it is not a federal issue, the FCC has 
determined that localities and states should plan for cost recovery at           
their levels.  Details of subsidization for deployment and nonsubscriber         
calls must      be negotiated on local level (State or municipality, similar 
landline 9-1-1 subsidization).  Funding should be available for both basic       
and enhanced 9-1-1.
Conditions for Compliance:
1. PSAPs must request and be ready to handle wireless location information.
2. A cost recovery mechanism (negotiated at the local level) must be in place.
PSAP Choices:
Because of the two conditions for compliance PSAPs effectively choose 
implementation dates.  
PSAPs also get to choose whether they want to handle calls from handsets
without MINs.
Further Rulings for the Future:
- Tightening of location accuracy requirements to 40 feet 90% of the time,
- Availability of altitude information,
- Performance criteria on time for calling completion,
- Consumer Education programs for wireless 9-1-1,
- Possible reconsideration of issues of PSAP choice, and
- Possible requirement that the strongest signal must carry the 9-1-1 call.
		
	IV. Common Wireline 9-1-1 Service
Today in most areas wireless communication networks have the ability to run
off of B9-1-1.  This is because of the AUTOPLEX 1000 System.  Basically a
caller can dial 9-1-1 and be connected to the proper ASAP based on the
location of the serving cell.  Location routing is accomplished with a digit
by digit method.  Which allows Automatic Number Identification (ANI) for
Centralizing Automatic Message Accounting (CAMA) signaling to field a number
corresponding to the serving cell.  Upon arrival at the E9-1-1 selective
router the field issued to show the PSAP for that area.  The call is then
routed.  An alternative to this would be to populate the ANI field with a
7-digit dial-back number as opposed to the location information.  The E9-1-1
selective router then assigns the incoming trunk one of four NPAs.  The
remaining seven NPAs complete the 10-digit dial-back number.  

	V. Issues on How to Make Wireless 9-1-1 Work:
There are several wireless problems which limit the use of E9-1-1.  First
CAMA trunk signaling transmits one 8-digit telephone number to the PSAP. This
causes problems because it can only have 4 NPAs, and therefore cannot give
caller identification while wireless subscribers are roaming.  Second the
caller's telephone number cannot be used to route a wireless E9-1-1 call
since the caller's location depends on the Mobile Directory Number (MDN).
Since a real street address cannot be associated with a MDN, the dispatcher
cannot dispatch emergency services.  So while this could seem kind of
hopeless its really not.  A lot of other ways have been devised to handle
this all.  Which commonly involve in band analog MultiFrequency (MF)
signaling.  I'll start out with some bad idea's then explain the good one.
There was the Group D signaling solution.  It was first intended for equal
access upon long distance calls.  It was able to support both a 10-digit ANI
and a 10-digit dialed-digits field.  Essentially the dialed-digits field
could be used for the location information. The problem with this method(and
you knew the would be a problem...) is that it cannot support an interface
between a Mobile Switching Center (MSC) to the selective router as does
Signaling System 7 (SS7).  Next there was a method which used a conversion to
CAMA from Group D signaling.  This method is fairly complicated and really is
degrading with performance, which makes it a bad choice... here goes an
explanation.  With the idea that MSC cannot provide SS7 connectivity with the
PSTN and the 9-1-1 selective router cannot support SS7 or Group D signaling
for 9-1-1 call processing.  With a Group D to CAMA translation device between
MSC and the selective router, it could provide signaling conversion. The
translation device has a third field which sends the 10-digit dial-back
number and location information to the ALI database during call set up.  The
device send s a special 7-digit key value in the ALI field to the selec
tive router.  Basically then this key would represent the cell from which the
call was placed to the router.  Then the 7-digit key field is routed to the
PSAP during the setup.  Meanwhile the ALI runs a check by the PSAP using this
keys value or field, then it would return the real 10-digit MDN.  Next we
have a expanded CAMA signaling solution which has no practical reason for
existing.  It just won't work.  I'll explain it anyway.  The existing CAMA
interswitch 9-1-1 signaling maybe built upon to support a 10-digit ANI and
10-digit location number.  This requires some modifications to be made to the
current PSAP hardware and the 9-1-1 selective router.  This would cause a
degradation of the performance due to extra MF signaling involved.  Finally
we have the practical solution which is what was used mainly for the Stage 1
process.  Which is a solution through SS7, which should make hybrid's day.
He just can't seem to get enough on SS7.  The use of SS7 will be explained in
my explanation of what Stage 1 was.
Stage 1:
	Basically an entirely new architecture is needed.  The common setup
was to distribute the service processing across the AUTOPLEX System 1000
MSC, 5ESS-2000 Switch, Emergency Services Adjunct (ESA), ALI database,
associated database management system, and the PSAP CPE.  The MCS used ISDN-
UP Signaling to convey a 10-digit dial-back number in the charge number
parameter, as well as location information in the caller party number.  The
9-1-1 selective router uses the location information to route the call to the
appropriate PSAP.  An ISDN PSAP is required to receive and use both the 10-
digit dial-back number and the location information.  Some major improvements
to the AUTOPLEX System 1000 were put in to affect for Stage 1.  The CAMA
signaling is replaced with ISDN-UP which has the obvious advantages of being
able to transmit both dial-back number and the location information as
opposed to CAMA signaling 8-digit information.  Also CAMA signaling only
supported a 7-digit calling party number unique with one of four area codes,
where as ISDN-UP will support the full 10-digit calling party number.
Another major change was in MSC, which was to then use ISDN-UP signaling as
well.  Which could convey a 10-digit dial-back number in the charge field and
a 10-digit routable Directory Number (DN) which represents the cell location
and originating service provider in the called party number field.  Basically
this is used to reach roaming customers.  The use of a DN allows a call to be
routed through the PSTN to the E9-1-1 selective router grouped with the PSAP
without direct connection trunks.  The E9-1-1 selective router then selects
the appropriate PSAP based on the serving cell, call type, and some other
less important criteria.  To support this, the dialed-digit routing
capability must be integrated with the 5ESS-2000 switch E9-1-1 feature, thus
allowing these calls to be routed using the called party number rather than
the ANI.  Location information, dial back number, and service provider are
forwarded to the PSAP via ISDN during call setup.  An ISDN PSAP is required
to receive and use both the dial back number and location information encoded
in the dialed digits.  In the case where the PSAPs cannot support ISDN and
enhanced adjunct processor interface (API) will provide the ability to
support existing PSAP CPE, which uses CAMA in-band signaling.  The
information received via enhanced SS7 ISDN-UP from the MSC to the 5ESS-2000
will be forwarded over the API when the ESA queries made for routing
information.  The information will then be forwarded to the ALI over a new
ESA to ALI interface.  The 5ESS switch will then pass a unique 7-digit key
value to the PSAP in the ANI field.  When the ALI is queried by the PSAP with
this value, the location, service provider and dial back number is returned
to the PSAP.  The PSAP equipment would need to be enhanced to provide the
caller's location to the telecommunicator using a textual method whereby the
called party number is used to query the ALI database, which provides
location and identification of the cell/sector.  Alternatively, Geographic
Information Systems (GIS) can be used to provide a geographic representation
of a caller's approximate location on a computer-generated map.  The PSAP GIP
map displays provide the dispatcher with visual identification of the
caller's location (their cell/sector) in perspective of other important
geological locations.  The displays can pinpoint roads, addresses, buildings,
houses, ems dispatch vehicles, fire hydrants, cell sites, and the service
boundaries to emergency services.  Ok so since this was originally put to use
back in 96 and was to last as a period for approximately 18 months, it has
for the most part gone in to affect in most areas.  It's hard to say though,
depending on the area....


Stage 2: 
	Stage 2 is basically just an architectural build on what was created
in Stage 1.  The implementation was to last near 5 years.  Stage 2 would
bring new GIS capabilities along which would work better with the wireless
E9-1-1 system. During this stage the geolocation system was required to meet
the FCC's 5 year requirements for wireless E9-1-1.  So the wireless system
could communicate with the geolocation system to determine the position of a
target mobile terminal (which has dialed 9-1-1).  Alternatively, if the
wireless system recognizes a mobile telephone equipped with GPS the mobile
terminal could provide its current location via new air interface messages.
Several technologies have been proposed to meet the FCC's long term mobile
locating requirements for wireless E-9-1-1 systems.  To meet the needs of the
9-1-1 community that is to those who provide the emergency response service
to the public, the existing base of mobile phones must be supported without
modification.  Promising technologies proposed for this purpose include time
difference of arrival and direction of arrival triangulation systems.  Each
has its advantages depending on the physical environment in which it is
targeted to be deployed.  In addition, advances in GPS receiver technology
have made it possible to integrate GPS with wireless telephones.  Which has
been recently brought somewhat into the commercial market.  If the mobile
terminal knows its location, it makes sense to use this information for the
E9-1-1 system because the GPS is potentially much more accurate than a
location determined by means of time difference of arrival and direction of
arrival triangulation.  The geolocation information (latitude, longitude,
altitude, and accuracy) will be integrated in an SS7/ISDN-UP and ISDN call
set-up message for the 9-1-1 call.  At this point in the evolution, SS7/ISDN-
UP and the Transaction Capabilities Application Part (TCAP) signaling
protocols will be modified to support transmission of the location
information from the wireless system to the selective router.  ISDN-UP will
be used for delivery of location information with call set-up while TCAP
messages will be used to support caller location tracking, which requires
location updates during a call.  Regardless of the location technology used
by a wireless service provider, the location information will be passed
through the network and used in a standard way.  Therefore, the E9-1-1
communications network infrastructure will remain implemented in the wireless
network.  Although not required by FCC rule making, the new location
information can be used to route a call to a PSAP accurately.  Upgrades to
support this capability include geolocation routing capabilities that will be
integrated into the 5ESS-2000 switch's E9-1-1 feature, the ESA, and the DBMS.
Once again, the information is delivered to the PSAP, and computer aided
dispatch systems with GIS mapping will used to portray the information in a
way that makes it easily understandable by the telecommunicator and
responding emergency personnel.  In turn, the improved location information
will be reflected in the GIS map display with a pinpointed location and
associated accuracy representation.  A GIS based service administration
capability will proceed the ability to define and dynamically change
municipal jurisdictional boundaries and emergency service zones via a
computerized map interface.  This administration system will indirectly
maintain the call routing data used by the 9-1-1 selective router.  The
process will simplify the administration of the 9-1-1 service by eliminating
the need to share cell/sector location data among wireless, local exchange,
and emergency service providers.  In this environment, base station
reconfigurations by a wireless service provider will no longer affect the
data maintained in the PSTN and PSAP providing the end-to-end E9-1-1 service.
Onward to my brief explanation of triangulation and geolocations.  Network
based triangulation methods of location (TDOA and DOA) require that at least
two DOA or three TDOA receivers locate the target mobile terminal and that
some technique be available to resolve ambiguities caused by multipath
propagation.  These requirements may be difficult to meet in many wireless
environments causing the accuracy of the locating system to be degraded or
making system deployment cost prohibitive.  For example, in rural
environments, cell sites cover very large geographical areas, often resulting
in marginal voice coverage on the fringes of the cells.  In such areas, it is
unlikely that receivers in multiple cell sites would "see" the mobile
terminal, thereby, making it difficult or impossible to establish the
caller's location.  This problem could be worked around by adding
supplementary location receivers, although such deployment might be very
costly for rural wireless service providers.  Furthermore, in dense urban
areas, the effect of multipath propagation becomes a dominant factor in
deterioration of the accuracy of the locating system.  Multipath propagation
refers to multiple copies of the same transmitted signal are received by an
antenna.  Usually, the first signal arrives via the most direct path from the
transmitter.  Additional copies of the signal are received at later times,
ranging from hundreds of nanoseconds to tens of microseconds later, and they
then overlap the first signal.  These copies result from the reflection of
the original signal from various objects, such as buildings and vehicles.
The effects of multipath propagation particularly in cities can degrade the
precision of the location estimate to such a point that no added benefit can
be gained over visually reporting the serving cell/sector location because
urban environments often have relatively dense micro cell grids for their
wireless networks.  These problems are difficult to overcome without some
assistance from the mobile telephone.  Whether or not the FCC requirement of
125m accuracy will be technically or economically feasible in such
environments is not clear.


	VI. Long Term & Conclusion
Although recent FCC ruling only requires location accuracy of 125m in 67% of
all cases, the public safety community often requires even more accurate
information.  Ideally an emergency unit responding to a 9-1-1 call would know
exactly in which room in a skyscraper which the incident is occurring or has
occurred(using for instance the ISDN-UP altitude parameter).  Clearly this
level of accuracy cannot be achieved cost effectively with unmodified
wireless phones and today's technology.  With new technology and assistance
from the mobile terminal, however future land based location systems will be
able to provide much better accuracy than that of the FCC Stage 2
requirements.  Although such systems are not available today, several
concepts have been proposed for example signpost location beacons and
specialized signaling schemes optimized for location purposes.  Whatever
scheme becomes dominant as the technology matures, the pursuit of standard
implementations is important.  This will insure that the cost as sociated
with an improved wireless E9-1-1 system are reduced. Basically really from a
safety stand point all this is really fine in my opinion.  It will help save
other people and possibly yourself one day.  Meanwhile this isn't really a
cell user's friend.  This gives the wireless service providers more control
over you with this type of technology, which can be looked at as a very bad
thing.  Anyway, peace.




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