3CX Basic Certification Exam Prep Document
2026/2027 | PBX Administration, VoIP, SIP
Trunking & System Configuration | 30 Verified
Questions with Detailed Rationales
This exam contains verified questions taken from actual 3CX Basic Certification content, covering PBX
fundamentals, VoIP and SIP trunking, 3CX system administration, and troubleshooting. Questions reflect
real-world business communication scenarios, deployment requirements, and the administrative tasks
that system administrators, IT support staff, and telecom professionals must master for the 2026/2027
certification cycle.
Section 1: PBX Fundamentals, VoIP Protocols & SIP Trunking – Questions 1–10
Q1: A network administrator is configuring a new 3CX PBX for a 50-user office. The administrator needs
to understand which protocol is responsible for establishing, modifying, and terminating real-time
communication sessions such as voice and video calls. Which protocol serves this function?
A. RTP (Real-time Transport Protocol), which carries the actual audio and video media streams.
B. SIP (Session Initiation Protocol), which handles call setup, modification, and teardown between
endpoints. [CORRECT]
C. SDP (Session Description Protocol), which describes the media capabilities of endpoints but does not
manage sessions.
D. TCP (Transmission Control Protocol), which provides reliable data delivery but is not designed for real-
time session management.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because SIP is the signaling protocol that does
exactly what the question describes—it initiates sessions, negotiates parameters, handles call transfers,
and tears down connections when the call ends. RTP carries the media, SDP describes what media types
are supported, and TCP is a general transport protocol, but SIP is the one that manages the session
lifecycle.
,Q2: A company is selecting codecs for their 3CX deployment and wants to minimize bandwidth usage
while maintaining acceptable voice quality for internal calls. Which codec would typically offer the best
balance of low bandwidth and reasonable quality for standard business voice?
A. G.711, which provides excellent quality but uses approximately 64 kbps per call direction without
compression.
B. G.729, which compresses voice to approximately 8 kbps while maintaining acceptable quality for most
business conversations. [CORRECT]
C. G.722, which offers wideband HD voice quality but uses more bandwidth than narrowband codecs.
D. Opus, which is highly flexible but may use more bandwidth than G.729 when configured for high
quality.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because G.729 was specifically designed for
bandwidth-constrained environments like VoIP over WAN links, compressing voice down to 8 kbps while
still sounding decent for business calls. G.711 sounds great but eats bandwidth, G.722 is HD quality and
uses even more, and while Opus is versatile, G.729 remains the go-to when bandwidth minimization is
the priority.
Q3: A technician is troubleshooting a SIP trunk that is not registering with the provider. The technician
reviews the SIP trace and sees that the REGISTER request is being sent, but the provider is responding
with a 401 Unauthorized message. Which of the following is the most likely cause?
A. The RTP port range is blocked by the firewall, preventing media from flowing.
B. The authentication credentials (username and password) configured in the 3CX trunk settings do not
match what the provider expects. [CORRECT]
C. The SIP domain name is resolving to the wrong IP address in DNS.
D. The codec priority list on the 3CX system does not include any codecs supported by the provider.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because a 401 Unauthorized response from a SIP
registrar specifically means the authentication attempt failed. The REGISTER request reached the
provider, so basic connectivity is working, but the credentials didn't pass muster. It's almost always a
typo in the username, password, or authentication ID—double-checking those fields against what the
provider supplied is the first troubleshooting step.
, Q4: A call center manager wants to ensure that incoming calls are distributed evenly among available
agents rather than always ringing the same phone first. Which 3CX feature should the administrator
configure?
A. A ring group set to "Ring All," where all phones ring simultaneously and the first to answer gets the
call.
B. A queue with "Longest Idle" or "Round Robin" distribution strategy to evenly spread calls across
agents. [CORRECT]
C. A direct dial extension that forwards to a single agent's mobile phone.
D. An IVR menu that asks callers to press 1 for sales and 2 for support without any agent assignment
logic.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because a queue with distribution strategies like
"Longest Idle" or "Round Robin" is specifically designed to spread the workload fairly. "Ring All" just
creates a race to the phone, a direct dial goes to one person, and an IVR without queue logic just routes
calls to departments without managing agent distribution.
Q5: A company is deploying a 3CX system and needs to ensure that voice traffic receives priority over
email and web browsing on their network. Which networking concept should the administrator
implement?
A. VLAN segmentation, which separates voice and data traffic onto different virtual networks.
B. Quality of Service (QoS) markings, which prioritize VoIP packets to reduce latency, jitter, and packet
loss during network congestion. [CORRECT]
C. Network Address Translation (NAT), which allows multiple devices to share a single public IP address.
D. Dynamic Host Configuration Protocol (DHCP), which automatically assigns IP addresses to devices on
the network.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because QoS is exactly the tool for prioritizing
voice traffic—by marking VoIP packets with higher priority (DSCP values like EF for voice and AF for
signaling), routers and switches know to handle them first when bandwidth gets tight. VLANs help with
organization and security but don't inherently prioritize traffic, and NAT and DHCP have nothing to do
with call quality.
2026/2027 | PBX Administration, VoIP, SIP
Trunking & System Configuration | 30 Verified
Questions with Detailed Rationales
This exam contains verified questions taken from actual 3CX Basic Certification content, covering PBX
fundamentals, VoIP and SIP trunking, 3CX system administration, and troubleshooting. Questions reflect
real-world business communication scenarios, deployment requirements, and the administrative tasks
that system administrators, IT support staff, and telecom professionals must master for the 2026/2027
certification cycle.
Section 1: PBX Fundamentals, VoIP Protocols & SIP Trunking – Questions 1–10
Q1: A network administrator is configuring a new 3CX PBX for a 50-user office. The administrator needs
to understand which protocol is responsible for establishing, modifying, and terminating real-time
communication sessions such as voice and video calls. Which protocol serves this function?
A. RTP (Real-time Transport Protocol), which carries the actual audio and video media streams.
B. SIP (Session Initiation Protocol), which handles call setup, modification, and teardown between
endpoints. [CORRECT]
C. SDP (Session Description Protocol), which describes the media capabilities of endpoints but does not
manage sessions.
D. TCP (Transmission Control Protocol), which provides reliable data delivery but is not designed for real-
time session management.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because SIP is the signaling protocol that does
exactly what the question describes—it initiates sessions, negotiates parameters, handles call transfers,
and tears down connections when the call ends. RTP carries the media, SDP describes what media types
are supported, and TCP is a general transport protocol, but SIP is the one that manages the session
lifecycle.
,Q2: A company is selecting codecs for their 3CX deployment and wants to minimize bandwidth usage
while maintaining acceptable voice quality for internal calls. Which codec would typically offer the best
balance of low bandwidth and reasonable quality for standard business voice?
A. G.711, which provides excellent quality but uses approximately 64 kbps per call direction without
compression.
B. G.729, which compresses voice to approximately 8 kbps while maintaining acceptable quality for most
business conversations. [CORRECT]
C. G.722, which offers wideband HD voice quality but uses more bandwidth than narrowband codecs.
D. Opus, which is highly flexible but may use more bandwidth than G.729 when configured for high
quality.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because G.729 was specifically designed for
bandwidth-constrained environments like VoIP over WAN links, compressing voice down to 8 kbps while
still sounding decent for business calls. G.711 sounds great but eats bandwidth, G.722 is HD quality and
uses even more, and while Opus is versatile, G.729 remains the go-to when bandwidth minimization is
the priority.
Q3: A technician is troubleshooting a SIP trunk that is not registering with the provider. The technician
reviews the SIP trace and sees that the REGISTER request is being sent, but the provider is responding
with a 401 Unauthorized message. Which of the following is the most likely cause?
A. The RTP port range is blocked by the firewall, preventing media from flowing.
B. The authentication credentials (username and password) configured in the 3CX trunk settings do not
match what the provider expects. [CORRECT]
C. The SIP domain name is resolving to the wrong IP address in DNS.
D. The codec priority list on the 3CX system does not include any codecs supported by the provider.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because a 401 Unauthorized response from a SIP
registrar specifically means the authentication attempt failed. The REGISTER request reached the
provider, so basic connectivity is working, but the credentials didn't pass muster. It's almost always a
typo in the username, password, or authentication ID—double-checking those fields against what the
provider supplied is the first troubleshooting step.
, Q4: A call center manager wants to ensure that incoming calls are distributed evenly among available
agents rather than always ringing the same phone first. Which 3CX feature should the administrator
configure?
A. A ring group set to "Ring All," where all phones ring simultaneously and the first to answer gets the
call.
B. A queue with "Longest Idle" or "Round Robin" distribution strategy to evenly spread calls across
agents. [CORRECT]
C. A direct dial extension that forwards to a single agent's mobile phone.
D. An IVR menu that asks callers to press 1 for sales and 2 for support without any agent assignment
logic.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because a queue with distribution strategies like
"Longest Idle" or "Round Robin" is specifically designed to spread the workload fairly. "Ring All" just
creates a race to the phone, a direct dial goes to one person, and an IVR without queue logic just routes
calls to departments without managing agent distribution.
Q5: A company is deploying a 3CX system and needs to ensure that voice traffic receives priority over
email and web browsing on their network. Which networking concept should the administrator
implement?
A. VLAN segmentation, which separates voice and data traffic onto different virtual networks.
B. Quality of Service (QoS) markings, which prioritize VoIP packets to reduce latency, jitter, and packet
loss during network congestion. [CORRECT]
C. Network Address Translation (NAT), which allows multiple devices to share a single public IP address.
D. Dynamic Host Configuration Protocol (DHCP), which automatically assigns IP addresses to devices on
the network.
Correct Answer: B
Rationale: The best answer is B. This choice is correct because QoS is exactly the tool for prioritizing
voice traffic—by marking VoIP packets with higher priority (DSCP values like EF for voice and AF for
signaling), routers and switches know to handle them first when bandwidth gets tight. VLANs help with
organization and security but don't inherently prioritize traffic, and NAT and DHCP have nothing to do
with call quality.
