SSCA Security, QoS & Regulatory Compliance 5 â Questions and Answers
Question 1: Which IETF standard defines the use of DTLS (Datagram TLS) for negotiating SRTP keys over the media path?
- RFC 4568 (SDES)
- RFC 5764 (DTLS-SRTP) (Correct answer)
- RFC 3711 (SRTP)
- RFC 6189 (ZRTP)
Correct answer: RFC 5764 (DTLS-SRTP)
RFC 5764 defines DTLS-SRTP, a method that uses a DTLS handshake over the RTP port to establish SRTP keying material without requiring keys in SDP.
Question 2: A VoIP provider is subject to PCI-DSS. Which scenario most directly triggers this compliance requirement?
- Carrying emergency 911 calls
- Processing credit card payments over the phone (IVR) (Correct answer)
- Offering toll-free numbers to customers
- Providing SIP trunking to a hotel
Correct answer: Processing credit card payments over the phone (IVR)
PCI-DSS applies when cardholder dataâincluding card numbers entered via DTMF in IVR systemsâis captured, stored, or transmitted, requiring call recordings and RTP streams to be protected.
Question 3: What is 'toll fraud' in the context of VoIP security?
- Charging customers incorrect call rates
- Unauthorized use of a VoIP system to make expensive calls at another party's expense (Correct answer)
- Stealing caller ID information for phishing
- Degrading call quality to force users to premium services
Correct answer: Unauthorized use of a VoIP system to make expensive calls at another party's expense
Toll fraud (also called IRSFâInternational Revenue Share Fraud) occurs when attackers compromise a PBX or SIP account and make international or premium calls billed to the victim.
Question 4: Which QoS parameter directly measures the percentage of RTP packets that do not reach the destination?
- Jitter
- Latency
- Packet loss (Correct answer)
- Mean Opinion Score (MOS)
Correct answer: Packet loss
Packet loss is expressed as a percentage of transmitted RTP packets that are lost in transit; even 1-3% loss can significantly degrade voice quality.
Question 5: Which SIP header field is specifically used to convey the reason a call is being redirected or terminated, commonly used for regulatory logging?
- Reason header (RFC 3326) (Correct answer)
- Warning header
- Alert-Info header
- Retry-After header
Correct answer: Reason header (RFC 3326)
The Reason header (RFC 3326) carries a cause code (SIP or Q.850) explaining why a request was forwarded or session terminated, supporting CDR and regulatory audit trails.
Question 6: What is the function of a 'jitter buffer' at a VoIP endpoint?
- To compress RTP packets before transmission
- To re-order and delay packets to smooth out arrival time variation (Correct answer)
- To encrypt RTP streams using SRTP
- To retransmit lost RTP packets automatically
Correct answer: To re-order and delay packets to smooth out arrival time variation
A jitter buffer holds incoming RTP packets briefly to compensate for variable network delay, presenting a smooth, consistent playout stream to the audio decoder.
Question 7: Under STIR/SHAKEN, which element signs the call attestation token to combat caller ID spoofing?
- The terminating carrier's SBC
- The originating service provider using an X.509 certificate (Correct answer)
- The ENUM server resolving the called number
- The subscriber's SIP UA endpoint
Correct answer: The originating service provider using an X.509 certificate
In STIR/SHAKEN, the originating service provider signs a PASSporT (Personal Assertion Token) using its X.509 certificate, attesting to its authority over the calling number.
SSCA Security, QoS & Regulatory Compliance 5
Which IETF standard defines the use of DTLS (Datagram TLS) for negotiating SRTP keys over the media path?