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E911 Hosted Solutions: What the Heck is ELIN and Who is ERL?


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August 12, 2009

E911 Hosted Solutions: What the Heck is ELIN and Who is ERL?

By Amy Tierney, TMCnet Web Editor

When it comes to safety, there’s no question that more and more enterprises understand the growing significance of implementing enhanced 911, or “E911 services.” The bottom line is E911, which uses location-based technology to pinpoint the location of 911 callers, can help save lives, officials with Everett, Wash.-based hosted solutions provider 911 ETC said during an E911 hosted solutions panel interview, printed in full below.

While dozens of businesses are moving toward IP-based systems for voice communications and are rolling out the technology, the fact remains that few people really know the ins and outs of the solution, which uses terms such as “ELIN” and “ERL.” To me, the acronyms look like nothing more than alphabet soup. It’s nothing an E911 dictionary can’t solve, but what does it all really mean?
To find out, TMCnet turned to a team of industry experts – Mark J. Fletcher, product manager, E911 Emergency Services for Nortel, Guy Clinch, senior solutions manager for Avaya, a VoIP equipment provider, and Ted Mallires, manager in the technology consulting and solutions group of Plante & Moran – to chat about the definitions and the meaning behind them.
TMCnet: How do you define ELIN and ERL?
Clinch (pictured left): An Emergency Location Identification Number, or “ELIN” is a North America Dialing Plan telephone number that may be used to represent one or more telephone extensions for the purpose of locating a caller who has dialed 911 from a Multi-Line Telephone System, or “MLTS extension. A Multi-line Telephone System is one typically used by businesses, government, and universities whereby a PBX (News - Alert) supports many phone extensions within a building, campus, or in some cases, over multiple locations.  

The concept is that a single number can represent several telephone extensions when the deployment of the extensions is fairly uncomplicated, such as where many telephones are used in an open office where there are no obstructions. In these instances, there is no need to identify the location of each individual device. One telephone number, or ELIN, may be automatically substituted by the MLTS for each of the extensions in that logical area.
The logical area in which the telephone extensions exist is called the Emergency Response Location, or “ERL.” A 911 operator who receives the call at the Public Safety Answering Point PSAP must be able to call back the ELIN in case the caller is disconnected. The MLTS must then deliver the return call back to the original extension or some covering extension that would make it possible to get back in touch with the person experiencing the emergency.
Mallires (pictured right): When a telephone system has been set up to run its E911 application, any user making a 911 call will out-pulse a pre-assigned DID number rather than their actual DID number. As part of the set up of the E911 applications, all telephone users are grouped into logical zones - by floor, by wing, by department, etc. These groupings are known as “ERL’s.” Each ERL is assigned an ELIN. Some manufacturers use the term “CESID” or “Customer Emergency Service Identification.”  Using ELINs/CESIDs to serve a proximate group of users reduces the number of records needed in the PS-ALI database thereby reducing cost, simplifies set up of the E911 database, and can simplify 911 Move/Add/Change administration.      
TMCnet: Why is there a lack of understanding regarding E911 operations?
Fletcher (pictured left):Although the concepts of E911 are not difficult, they are used once by customers during the deployment, and then are rarely called upon again. Many administrators simply cannot warrant the expense of training and time out of the office required to get up to speed. Consulting is an efficient and affordable solution.
Clinch: The 911 system is complicated. Part of the problem is that the basic concepts behind the system originated more than 40 years ago in a time when telecommunications technology was very different. The 911 system today, is in many ways, anachronistic to the modern telecommunications model. For instance, even though modern telecommunications protocols are often in digital formats, substantially of the network that supports the public 911 system is still based on analog.

An example is the information that accompanies a 911 emergency call. Even though modern telecommunications protocols can carry significant amounts of information, the 911 system is typically only capable of delivering only one piece of information - a 10- digit telephone number - across the entire communication. Unfortunately, almost every 911 call, at some point between the caller to the PSAP, is downgraded in the PSTN to an analog circuit known as Centralized Automatic Message Accounting. (CAMA). This fact is not well known and causes an intellectual disconnect for the owner/operator of a modern MLTS.

The bottom line is that MLTS owners need to understand a lot of complexity. They then need to make decisions based on their deployment as to how to configure their systems and to what level of granularity they wish to provide location information to public safety officials. These decisions involve not just technology. They need to be done in conjunction with those responsible for organizational risk tolerance, human resources, local public safety officials and other technology and non-technology decision makers.
Mallires: First, even among telecommunications professionals, the 911 network is not typically well understood.  Second, E911 takes two components to work: a) You must have the E911 application equipped and activated within the telephone system (this may be provided by the manufacturer as a standard offering, or it may be an optional offering. and b), You must subscribe to a “PS-ALI” service, or Private Switch – Automatic Location Information most usually procured through the local telco. 
The PS-ALI service is the “bridge” that connects the customized ALI records built within the premise telephone system to the public 911 network. This is how the custom location information sitting in the telephone system makes its way to the receiving Public Safety Answering Point, or dispatch center. We have found that even vendors selling the E911 application as part of their telephone system solution often do not understand the requirement to have a PS-ALI service the first time they propose this application to their customers. 
TMCnet: What problems exist with the E911 system?
Fletcher: The E911 system, as it stands today, is one that was built over 40 years ago when we lived in a hard wired fixed environment that was under explicit control of Ma Bell and her cousins. In those days, and up until the past few years, a phone number represented a fixed physical location.
The requirements of today's dynamic and mobile workforce simply cannot be met with the legacy E911 system. Number portability is the norm instead of the exception, and telephone numbers and physical locations are not even distant cousins.
The Next Generation 911 promises a data centric environment, easily adaptable to the needs of users today and in the future, but it is reliant on security, location aware call servers and devices. Although all of this is technically possible today, the economical constraints placed on enterprises, public safety and the carrier networks create a challenge to make it a reality.
Clinch: In today’s MLTS world, people can be in constant movement. The PS/ALI process will never catch up to somebody, for instance, who is using a wireless VoIP phone and moving across a campus or within a large building.
The problem gets deeper when you talk about people like me who use applications or devices that authenticate to an MLTS  in one location, but can be calling from virtually anywhere on the planet. For, example, my single-access phone number exists as an extension in an Avaya (News - Alert) office in Waltham Mass. I haven’t been there in months, but if I dialed 911 from my phone, and if my administrator had not taken the appropriate programming steps, the fire trucks would arrive in Waltham. That won’t do me a heck of a lot of good next week when I am in Montgomery, Ala.
TMCnet: What programs are in place to entice clients/customers to learn about the concept of E911?
Mallires: Currently, 16 states have legislation with the potential to impact business telephone system design: Alaska, Arkansas, Colorado, Connecticut, Florida, Illinois, Kentucky, Louisiana, Maine, Massachusetts, Minnesota, Mississippi, Texas, Vermont, Virginia and Washington.
Regulation is an enticement to learn about this. Many manufacturers have been working diligently to educate their staff, channel partners, and customers with product sheets, white papers, and even videos explaining their E911 capabilities. We would also recommend anyone who wishes to know more explore the National Emergency Number Association’s Web site.
Clinch: Avaya has a Professional Service E911 Consulting Offer to help our customers work through this process. We also provide training and during the implementation of our systems work with our customer to set up their original configuration.The thing is it is up to the customer to make the decisions about how granular they want to track, how often they want to update the ALI database and other important decisions. We can advise, but it is their responsibility.

Fletcher: Last year Nortel created a whole series of videos and podcasts on YouTube (News - Alert). This series was designed to be simple and easy to understand for both technicians and customers explaining the important concepts administrators need to understand. In addition, because some environments warrant full an E911 risk assessment and remediation project, Nortel (News - Alert) put together a complete consulting and services practice to provide both channel partners and customers the expertise required.
TMCnet: What other terms should people know that are important related to E911?
Fletcher: “PS-ALI,” or Private Switch Automatic Location Identifier database - the database that contains the ELIN to ERL mapping.
MSAG, or Master Street Address Guide database - maintains the ELIN to servicing PSAP mapping, which is based at the E911 Selective Router.
OSN, or On Site Notification - the mechanism to provide internal first responders with critical 911 call information
Mallires: “MLTS,” or Multi-Line Telephone System/PBX – used by NENA to describe telephone systems that may have state legislation with 911 impact.
ISDN-PRI: A type of shared, digital trunk compatible with PS-ALI service.
CAMA trunk: A type of dedicated trunk compatible with PS-ALI service if ISDN-PRI cannot be used.
“VPC,” or Voice over IP Positioning Center – a newer version of PS-ALI service that supports Session Initiation Service trunks, as well as providing enhanced capabilities to deliver location information to PSAPs across North America.
TMCnet: Why is E911 important today?
Clinch: In the MLTS environment today, E911 is especially important. Organizations driven by competition and costs are rapidly deploying IP telephony-based systems. This means that the traditional assumption about where a call enters the PSTN is where the caller is located has been completely blown away. MLTS systems today exist within vast private networks that are no longer tied to specific geographies and governmental jurisdictions. The information so important to the rapid response by public safety officials to an emergency is limited to what the owners/operators of the MLTS systems provide. MLTS owners/operators incur potential liability if harm comes to someone using their systems because delay resulted in bad, missing or insufficient information.
The bottom line is this: Because this issue is not well understood or cared for, people who might have lived have died. If the owners/operators of the MLTS that is used to dial 911 understood and dealt with E911 appropriately, the situation might have been different.
Fletcher: As systems grow larger, cover more geographical territory, and provide more virtual services users become more nomadic in nature. Location is the most critical piece of 911, and the days of a phone number representing a physical location are dwindling fast. Although 16 states now have some law in place for E911, an enterprise needs to be concerned with employee safety and corporate liability no matter where the employee is, or what type of device they are using. Ignoring E911 in any implementation unnecessarily exposes the enterprise. In most systems today, E911 can be implemented for little to no extra cost, and the advancements in On Site Location Notification, such as screen pop maps of the callers’ location and e-mail, or pager alerts are becoming the standard deployment.
Mallires: Since it is easier than ever before with current WAN and telecommunications technology to network disparate sites together and centralize trunking, organizations may have a legal, but also an ethical responsibility to understand the impact of their technical designs as it relates to the processing of emergency phone calls for their staff, customers, and occupants.

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Amy Tierney is a Web editor for TMCnet, covering unified communications, telepresence, IP communications industry trends and mobile technologies. To read more of Amy's articles, please visit her columnist page.

Edited by Amy Tierney

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