Hello experts,
Could someone clarify how dialed numbers are identified as emergency numbers in mobile networks?
From my understanding, some emergency numbers like 112 and 911 are globally recognized and preconfigured in the handset itself. These can even be dialed without a SIM card.
In addition, many countries have their own local emergency numbers (such as 100, 101, 000, etc.), which are provided to the UE during location update procedures and defined as short codes in the MSC or MME.
My question is: when these locally defined emergency numbers are used, does the UE also tag them as emergency calls before initiating the call?
Your understanding is mostly correct. Numbers such as 112 and 911 are preprogrammed into the device, so the phone itself recognizes them as emergency numbers - allowing you to dial them even without a SIM card or network registration.
For country-specific emergency numbers (like 100, 101, or 000), the mobile network provides this information to the phone during location registration. This list is delivered through system information sent by the network - for example, from the MME in LTE or the MSC in 2G/3G systems -enabling the device to correctly tag those numbers as emergency as well.
Android has a DB for it, based on the country, you can find it here:
There’s also Emergency Calling Codes (ECC) on the SIM Card, and the MME broadcasts this info to the UE in the NAS messaging in the Emergency Number List
Tales from the Trenches – Emergency Calling when Roaming | Nick vs Networking
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I got the following information from 3GPP:
The numbers that the UE will tag as emergency numbers include both:
- The emergency numbers stored in the Mobile Equipment (ME), and
- The numbers communicated to the ME by the core network (via a defined process) that are stored on the SIM card.
Reference:
3GPP TS 22.101 V15.8.0 – Universal Mobile Telecommunications System (UMTS); LTE; 5G; Service aspects; Service principles
Section 10.1.1 – Identification of Emergency Numbers
The ME must recognize a dialed emergency number as valid and initiate emergency call establishment under one or more of the following conditions. If none apply, the ME should treat the dialed number as a normal call. Emergency number identification takes precedence over all other types of number analysis (e.g., for supplementary services).
a) 112 and 911 must always be available and stored in the ME.
b) Any emergency numbers stored on the SIM/USIM, when present.
c) 000, 08, 110, 999, 118, and 119, when no SIM/USIM is present; these must be stored in the ME.
d) Any additional emergency numbers downloaded by the serving network when the SIM/USIM is present.
There are 2 Scenarios:
1- UE Detected Emergency Calls:
Which means that UE knows already that this is an emergency calls, so UE send sos APN already in the contact header towards the network and as a result the network will treat it as an Emergency call.
2- Non-UE Detected Emergency Calls
In the non-UE detected the UE doesn’t know that this is an emergency call so it sends the call normally without sos APN, when it reaches the network which already know that this is an emergency number, it replies with 380 Alternative services and inserting inside the Contact header the sos urn (to let the UE knows that this is an emergency call), the UE replies afterwards with an INVITE including the sos so the emergency call starts from here.
AB Virtual Labs
So here we go.Emergency Number is specific to that particular country and may have more than one number for several services like police,fire and Ambulance.Usually if those countries are engaged with device manufacturers that countries OS build have emergency numbers hard coded.If not during initial registration or attach MSC or MME or AMF will deliver the configured emergency numbers to the handset.What it does is if someone dials one of those emergency numbers lets say 000 which is called UE detected Emergency number for IMS equipped network it is not the 000 which travels in Gm interface.It is a service urn.eg:urn:services:sos etc.which notify PCSCF this is an Emergency call.And there is SMS getting generated without user knowing to the emergency centre notifying that persons true location so a person who is in emergency dont have to repeat his or hers location.How each network handles emergency call for an example it supports 3G bases emergency call or volte based emergency call or both completely depend on the network preference and the important thing is call should connect all the time.
