Mobile networks can stop working during emergencies like earthquakes due to network congestion. When too many users simultaneously try to make calls or use data, the network becomes overloaded. To prioritize emergency calls, mobile networks implement congestion control through techniques like access class barring that restrict access for most users during congestion while allowing emergency calls to connect. Admission control is also used to only allow call connections when sufficient network resources are available. These measures help ensure emergency calls can connect even when networks face excessive demands in disaster scenarios.

1. Why do mobile networks stop
working in case of
emergencies?
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2. The Problem
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Couple of questions on Quora:
• Why cell phones as I noticed today don't connect during/after
mild earthquake tremor?
• Why don't phone calls connect after the earthquake even if there
is no damage to network towers?

3. Lets look at an example of a bank
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EXIT

4. Lets look at an example of a bank
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EXIT

5. Lets look at an example of a bank
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EXIT

6. Lets look at an example of a bank
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EXIT

7. Lets look at an example of a bank
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EXIT

8. Lets look at an example of a bank
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EXIT

9. The Congestion Problem
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Nobody can get served due to the congestion
Congestion control should be used here to manage too many users
trying to get access to voice/data services from the mobile network

10. Congestion Control (or Load Control)
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Mechanism to ensure that in case of congestion, priority users and
emergency calls can still get served
Access Class (AC)
0 – 9: Randomly assigned to each normal user
11: For PLMN Use
12: Security Services
13: Public Utilities (e.g. water/gas suppliers)
14: Emergency Services
15: PLMN Staff
3GPP TS 22.011 (Service accessibility)

11. Access Class Control in 3GPP Releases
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(1) Access Class Barring (ACB)
(2) Service Specific Access Control (SSAC)
(3) Smart Congestion Mitigation (SCM)
(4) Extended Access Barring (EAB)
(5) Access Control for general Data Connectivity (ACDC)

12. Another Scenario in the bank
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EXIT
X

13. Admission Control
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Users get served only if there are enough resources available. This is
also often referred to as Call Admission Control (CAC) procedure.
• User admission procedure: This is done during RRC Connection
Establishment and Handover procedures. This looks at the CPU
resources as well as available radio resources and channel quality
for this particular user
• Service admission procedure: This is done when RAB is being
established or modified. This looks at bearer type (GBR/non-
GBR), priority, QCI, packet delay budget, admissible packet loss
rate, ARP, etc.

14. Thank You
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