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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.
-
-
-