UNDERSTANDING PS-ALI SERVICE & VPCs
As mentioned earlier, the telephone system's E911 application does nothing to populate the actual carrier ALI databases that exist strategically throughout the public network. In order to populate the "custom" ALI records into the public network, a carrier offering needs to be purchased. This offering is typically referred to as Private Switch ALI Service (PS-ALI Service) and allows the customer to build their custom ANI/ALI database and then upload it to the public 911 database network. Once this is completed, calls from the enterprise to 911 will display the custom information to the PSAP receiving the call. It is important to note that there are two primary methods of interfacing to the PS-ALI service when using conventional trunks--either by using ISDN-PRI or by using CAMA (Centralized Automatic Message Accounting) trunks. The preferred method is almost always to use PRI, since it can be used to make and receive calls, while CAMA trunks (a minimum of two must be installed) do nothing but support the PS-ALI functionality at a cost similar to T1/PRI.
The major providers of PS-ALI service are the local carriers (ILECs/CLECs) such as AT&T, Verizon, QWEST, XO, Cincinnati Bell, etc. Typically, there is a one-time cost to set up the PS-ALI database that may range from approximately $2,000 for a 50-record database to $8,000 for a 2,000 record database. Likewise, there is typically a recurring cost to maintain the records in the regional ALI database that may range from approximately $30 for a 50 record database to $150+/month for a 2,000 record database. Service offerings can vary to include unlimited access by the customer to make updates to their PS-ALI database; or the service may limit them to submitting their changes to the carrier who then charges a fee for each update required.
A brief summary of some PS-ALI service offerings:
AT&T: AT&T offers PS-ALI products across its 22 state footprint, but the product name, pricing, and precise feature functionality vary according to its legacy RBOC areas.
* AT&T (SBC region): PS-ALI service comes in two versions: "9-1-1 Locator ID" and "9-1-1 Locator ID Lite" service. The "9-1-1 Locator ID" service allows the customer a direct interface with the E911 database to make changes as needed, and it scales to handle many records. The "Lite" service is priced to accommodate those with a need for relatively few records (
* AT&T (Bell South region): PS-ALI service is called "911 Pinpoint."
* AT&T (PAC Bell and Southwestern Bell region): PS-ALI service is called "PS-ALI."
VERIZON: Verizon's PS-ALI product is called "PS/ALI." Verizon recently dropped monthly recurring charges for this service--there is now just a $2,500 non-recurring fee to set the customer up in Verizon's E-911 database.
QWEST: Qwest's PS-ALI product is called "PS/ALI."
Embarq: Embarq's PS-ALI product is called "PS/ALI."
Intrado: Primarily provides 911 operations support systems services to incumbent local exchange carriers, competitive local exchange carriers and wireless carriers but will also offer services to enterprises on an individual case basis.
It is important to note that if SIP trunks are used, standard PS-ALI service will not suffice. IP-based trunking requires the services of a VoIP Positioning Center (VPC). VPC’s are the E911 service providers for VoIP service providers (VSPs). Some of the major VPCs are:
* 911 Enable
* Intrado
* Red Sky
* TeleCommunication Systems
* Vixxi
Interestingly, SIP trunks paired with VPC services can allow for even more detailed information to be loaded into the data fields sent to the PSAP than those found with conventional trunks.
DESIGN CONSIDERATIONS
When moving forward with an E911 deployment, a key step is planning out what will ultimately make up the PS-ALI database. A number of questions will need to be answered and will require the review of building floor plans, and may even require on-site walk-throughs. These include:
* What should make up the geographic "zones" (Emergency Response Locations/ERLs) that will be associated with each ELIN?
* How granular do we want to be--how big or small should each ERL be?
* How many PS-ALI records will we ultimately require to support all of our ERLs?
When defining zones it is helpful to think about what location information the emergency responders will receive versus what they will see when they arrive on-site. Is it reasonable that they could quickly find the caller? Or is the space so large--or so partitioned--that it would be time consuming to comb through it? Sometimes fire alarm zones can be used as a guide to defining reasonable ERLs. The local Police or Fire department may also offer helpful assistance and guidance when working through some of these decisions. A helpful resource is the National Emergency Number Association’s website--go to "For 911 Professionals" then "MLTS/PBX;" once there you will have access to technical documents including the PDF: "Model Legislation: E9-1-1 for MLTS."
It should be noted that certain E911 instances can be particularly challenging, and though they are beyond the scope of this article, they should be on your radar:
* Soft Phones: Passing proper ANI/ALI for soft phone users within the enterprise is generally not a problem for the E911 application but when soft phones are used outside of the enterprise (e.g., home, hotel, coffee shop, etc.) significant difficulties arise that are not easily accommodated by most E911 solutions.
* Networked Sites: When dealing even with small metropolitan networks, you may be faced with sites that cross boundaries and are served by different PSAPs as well as even different carrier ALI databases. This can require multiple PS-ALI services with multiple connections to these services. It is important to understand up front what PSAPs serve each site and which carriers are responsible for providing the ALI database serving these PSAPs.
* SIP Phones: In cases where SIP phones are being used instead of the manufacturer’s IP phones, E911 capabilities found in the telephone system may not carry over and provide full functionality to SIP phone users due to limitations associated with supported SIP feature sets.
By understanding the implications that current design capabilities can pose for 911 calling, system designers can identify in advance scenarios that pose potential for trouble, and can inform their customers as to additional steps that might be needed to fully protect the integrity of those calling 911. By understanding the tools that are available and how they are used, enterprises are able to take reasonable, economical steps to overcome design issues and protect their personnel and any others using their telephone system. Helping organizations understand how to protect employees while minimizing risk and liability is good business - it is also doing our part to help emergency personnel meet their challenge of responding effectively when that 911 call comes in.
Ted Mallires is a Manager in the Technology Consulting & Solutions group of Plante & Moran, PLLC, an accounting and management consulting firm with offices located throughout the Great Lakes region. He specializes in telecommunications and networking projects and is a member of the Society of Telecommunications Consultants.
