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Collaboration, Voice & AV · Intermediate

Telephony Denial of Service (TDoS)

An attack that floods a phone system or number with calls to make it unavailable to legitimate callers.

Definition

TDoS uses autodialers, botnets or compromised SIP systems to overwhelm trunks, IVRs or contact centers, sometimes targeting emergency services or hospitals for extortion. Mitigations include SBC call rate limiting, CAC, caller reputation services, STIR/SHAKEN validation, and carrier-level filtering.

Example

Thousands of short spoofed calls per minute exhaust a hospital's inbound SIP trunk sessions.

Exam tip

TDoS targets call capacity rather than network bandwidth; SBCs provide rate limiting.

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