Why do mobile networks stop working in case of emergencies?

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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?

Lets look at an example of a bank

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Lets look at an example of a bank

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Lets look at an example of a bank

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Lets look at an example of a bank

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Lets look at an example of a bank

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Lets look at an example of a bank

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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

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)

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)

Another Scenario in the bank

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X

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.

Thank You

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