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CG-EWCG-001 Wireless E911 Guide
Issue 3, January 6, 2004 MSAG Maintenance and ESN Assignment
4. MSAG Maintenance and ESN Assignment
4.1 Overview
This section provides general information on ESN assignments and guidelines for working with BST,
BST’s data vendor, Intrado, and with the E911 Customer on MSAG maintenance. The Wireless Carrier
must meet with the E911 Customers in the wireless service area and agree on 911 call routing, default
routing, ESN assignments, and properly assigning MSAG valid street addresses to each ALI database
record. Intrado will be the point of contact for data processing and data issue resolution. All other issues
should be directed to the BST Wireless E911 Implementation Manager.
4.2 ESN Assignments
ESN mapping is necessary if calls are to be routed to more than one PSAP within an E911 service area.
The E911 Customer is responsible for providing boundary information to BST during the conversion to
E911 and, ongoing, as emergency districts change.
When an E911system is being implemented, the E911 Customer provides BST the boundaries depicting
each fire, police and EMS jurisdiction for the E911 service area. After all emergency service boundaries
have been defined, a different ESN is assigned to each geographical area with the same set of responding
agencies, i.e., police, fire, and EMS.
The ESN controls 911 call routing to the proper PSAP and provides emergency agency information
for each wireline 911 call. The ESN numbers are assigned to the E911 serving area based on the ESN
numbers available in the E911 tandem central office switch. The ESN for wireless 911 calls are used to
route the call to the proper PSAP. Due to the geographical variation in service areas of different cell sites,
it is not currently feasible to display specific emergency agency information for wireless calls. Cell site
service areas generally do not match existing emergency service boundaries. Creating additional ESN
boundaries for wireless service areas would be difficult for the E911 Customer and quickly exhaust
the ESN numbers available.
The Wireless Carrier must meet with each E911 Customer in the service area and provide wireless service
coverage areas for each cell site. The E911 Customers must agree on which PSAP should receive 911
calls based on the coverage area for each antenna face. This may require agreements between political
jurisdictions if the wireless service area crosses jurisdictional boundaries. In addition to deciding PSAP
routing, the E911 Customers must also decide on which PSAP should receive all 911 calls where the ANI
(pANI) is not delivered to the E911 tandem with the call. This condition is known as "ANI failure" and
must be default routed to a specific PSAP. The E911 Customers should agree and assign ESN numbers
for both normal and default routing. Wireless Carriers must provide BST the list of PSAPs identified to
receive default routed calls and the associated trunk groups.
Wireless Carriers must identify E911 Customers using premises based ALI systems. Premises based
systems may have special data and interface requirements to enable the dynamic wireless data to be
included in those systems.
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