SSCA Security, QoS & Regulatory Compliance 4 — Questions and Answers
Question 1: A SIP B2BUA (Back-to-Back User Agent) is deployed between two networks. What security role can it serve?
- It increases attack surface and provides no security benefit
- It acts as a Session Border Controller hiding network topology (Correct answer)
- It bypasses TLS termination for better performance
- It eliminates the need for SRTP
Correct answer: It acts as a Session Border Controller hiding network topology
A B2BUA or SBC (Session Border Controller) can hide internal network topology, enforce media anchoring, and terminate/re-establish TLS to protect the internal network.
Question 2: Which QoS mechanism prioritizes voice packets by placing them in a dedicated low-latency queue on network equipment?
- Traffic shaping
- Weighted Fair Queuing (WFQ)
- Low Latency Queuing (LLQ) (Correct answer)
- FIFO queuing
Correct answer: Low Latency Queuing (LLQ)
Low Latency Queuing (LLQ) combines Priority Queuing with Class-Based WFQ to give real-time voice traffic strict priority treatment while policing bandwidth.
Question 3: Under FCC regulations, which service must VoIP providers that offer interconnected VoIP make available to all subscribers?
- Toll-free number portability
- E911 (Enhanced 911) emergency calling (Correct answer)
- International call blocking
- Mandatory call recording
Correct answer: E911 (Enhanced 911) emergency calling
The FCC requires all interconnected VoIP providers to support E911, transmitting caller location information to emergency services automatically.
Question 4: What does the SIP option tag 'sips:' URI scheme indicate about a call route?
- The call uses SRTP for media encryption
- All hops in the signaling path must use TLS (Correct answer)
- The call is authenticated with Digest only
- The call bypasses proxy servers
Correct answer: All hops in the signaling path must use TLS
The SIPS URI scheme requires that every hop in the signaling path use TLS, ensuring end-to-end transport security for SIP messages.
Question 5: Which type of SIP attack involves sending CANCEL or BYE messages mid-call to terminate an ongoing session without authorization?
- Toll fraud
- Call teardown (BYE/CANCEL hijacking) (Correct answer)
- RTP injection
- SIP scanning
Correct answer: Call teardown (BYE/CANCEL hijacking)
An attacker who can send spoofed BYE or CANCEL messages matching the correct Call-ID, From-tag, and To-tag can forcibly terminate a legitimate SIP session.
Question 6: What is the primary purpose of a SIP firewall or Session Border Controller performing 'topology hiding'?
- To increase call setup speed by caching SIP routes
- To conceal internal IP addresses and infrastructure from external parties (Correct answer)
- To block all INVITE messages from untrusted domains
- To transcode audio codecs at the network border
Correct answer: To conceal internal IP addresses and infrastructure from external parties
Topology hiding prevents external parties from learning internal IP addressing, server identities, and routing paths, reducing the attack surface of the VoIP infrastructure.
Question 7: In SRTP, what is the role of the Master Key Identifier (MKI)?
- It identifies which SSRC stream the packet belongs to
- It allows multiple master keys to coexist, enabling key rollover (Correct answer)
- It sets the SRTP encryption algorithm version
- It carries the DTMF tone information securely
Correct answer: It allows multiple master keys to coexist, enabling key rollover
The MKI field in SRTP packets identifies which master key was used to derive session keys, enabling smooth key rollover without disrupting media streams.
SSCA Security, QoS & Regulatory Compliance 4
A SIP B2BUA (Back-to-Back User Agent) is deployed between two networks.
What security role can it serve?