Editing Enhanced 911 (section)

==Call routing==
===Landline routing===
Calls to 911 over the [[public switched telephone network]] (PSTN) are routed to a special router (known as Selective Router, or 9-1-1 Tandem).<ref>{{Cite news|url=https://www.fcc.gov/general/9-1-1-master-psap-registry|title=911 Master PSAP Registry|date=2011-02-14|work=Federal Communications Commission|access-date=2018-10-08|language=en}}</ref><ref>{{Cite news|url=https://www.fcc.gov/general/communications-route-diversity-public-safety|title=Communications Route Diversity for Public Safety|date=2011-02-11|work=Federal Communications Commission|access-date=2018-10-08|language=en}}</ref> The router looks for the address associated with the caller's telephone number in a database. The caller's phone number is known as an [[Automatic number identification]] (ANI). The database relating ANIs to addresses is known as Automatic Location Identification (ALI). The router then uses the address to search in the Master Street Address Guide (MSAG) for the Emergency Service Number (ESN) of the appropriate Public Safety Answering Point (PSAP) for that area and connects the call to it.<ref>{{Cite web|url=https://dps.mn.gov/divisions/ecn/programs/911/Pages/history.aspx|title=ECN 911 History|website=Minnesota Department of Public Safety|language=en-us|access-date=2018-10-08}}</ref><ref name=":3">{{Cite patent|country=US|number=20160337831A1|title=Real-time over the top 9-1-1 caller location data|status=|pubdate=2016-11-17|fdate=2015-05-16|gdate=|invent1=|inventor1-first=|url=https://patents.google.com/patent/US20160337831A1/en}}</ref>

====MSAG====
The Master Street Address Guide (MSAG) is a database of street addresses and corresponding Emergency Service Numbers (ESNs).<ref name=":0" /> ESNs represent one or more emergency service agencies (e.g. fire department, law enforcement) designated to serve a specific range of addresses in a geographic area, called an Emergency Service Zone.<ref>[https://dps.mn.gov/divisions/ecn/programs/911/Documents/NG911PSAP_Installation%20Guide_v3_8.pdf PSAP Installation Guide] (19 December 2011), ECN 911 Program, Minnesota Department of Public Safety</ref>

===Wireless routing===
Calls from cellular phones are received via [[Cell site|cell towers]] by [[Mobile switching centre server|mobile switching centers]] (MSC).<ref name=":3" /> The switching center automatically assigns a unique identifier to each cellular 911 call, known as a "pseudo ANI".<ref name=":3" /> The Selective Router connects the call to a PSAP based on the cell tower's location.<ref name=":3" />