SIP Session Initiation Protocol Certification Exam — Questions and Answers
Question 1: What is the purpose of the SIP SUBSCRIBE method?
- Establishes a permanent monitoring session
- Registers a UA with a registrar for a fixed duration
- Subscribes to a media multicast group
- Requests notification of events from a notifier (Correct answer)
Correct answer: Requests notification of events from a notifier
SUBSCRIBE is used in the SIP event notification framework (RFC 6665) to request that a notifier send NOTIFY messages when a specific event occurs.
Question 2: In a SIP 'call hijacking via re-INVITE' attack, what is the attacker's goal?
- Prevent codec renegotiation to degrade call quality
- Terminate the call by sending a spoofed BYE
- Steal authentication credentials from the re-INVITE transaction
- Redirect the media stream to an attacker-controlled endpoint by modifying SDP in a re-INVITE (Correct answer)
Correct answer: Redirect the media stream to an attacker-controlled endpoint by modifying SDP in a re-INVITE
By injecting a forged re-INVITE with modified SDP, an attacker can redirect the RTP media stream to their own endpoint, effectively intercepting the audio.
Question 3: What is the importance of communication skills in Security and NAT Traversal?
- Communication skills cannot be learned
- Clear communication prevents errors, builds relationships, and ensures understanding among all parties (Correct answer)
- Communication is only important for managers
- Technical skills are sufficient without communication
Correct answer: Clear communication prevents errors, builds relationships, and ensures understanding among all parties
Effective communication is essential for coordination, error prevention, and stakeholder relationships.
Question 4: What is the effect of an INVITE glare condition in SIP session management?
- A proxy resolves the conflict by choosing one re-INVITE
- Both UAs send a re-INVITE simultaneously, causing each to receive a 491 and retry after a random delay (Correct answer)
- The session terminates automatically when glare is detected
- Both re-INVITEs are queued and processed sequentially
Correct answer: Both UAs send a re-INVITE simultaneously, causing each to receive a 491 and retry after a random delay
Glare occurs when both endpoints send re-INVITEs at the same time; each responds 491, and both must back off and retry after randomized timers.
Question 5: Which SIP response code does a UAS return when a session timer refresh interval is too short?
- 422 Session Interval Too Small (Correct answer)
- 480 Temporarily Unavailable
- 416 Unsupported URI Scheme
- 491 Request Pending
Correct answer: 422 Session Interval Too Small
422 Session Interval Too Small (RFC 4028) is returned with a Min-SE header indicating the minimum acceptable refresh interval.
Question 6: How does a UAC properly terminate a confirmed SIP dialog (active call)?
- By sending a BYE request within the existing dialog (Correct answer)
- By closing the underlying TCP or UDP connection
- By sending a CANCEL request to the UAS
- By sending a REGISTER with an Expires header value of 0
Correct answer: By sending a BYE request within the existing dialog
A confirmed dialog is terminated by sending a BYE request within the dialog; CANCEL can only be used to terminate a pending INVITE transaction before confirmation.
Question 7: What role does continuing education play in SIP Architecture?
- Keeping practitioners current with evolving best practices and new developments (Correct answer)
- It is optional and rarely helpful
- Only beneficial for management
- Only required for new practitioners
Correct answer: Keeping practitioners current with evolving best practices and new developments
Continuing education ensures practitioners stay current with advances in their field.
Question 8: What makes a professional competent in Call Setup and Teardown?
- Only certifications matter
- Only experience matters
- A combination of education, practical experience, ongoing learning, and adherence to professional standards (Correct answer)
- Only formal education matters
Correct answer: A combination of education, practical experience, ongoing learning, and adherence to professional standards
Competence requires the integration of knowledge, skills, experience, and professional conduct.
Question 9: How does technology impact modern practices in SIP Architecture?
- Technology improves efficiency, accuracy, and access to information while requiring new skills (Correct answer)
- Technology has no impact on this field
- Technology replaces all human judgment
- Technology is only useful for record keeping
Correct answer: Technology improves efficiency, accuracy, and access to information while requiring new skills
Technology enhances capabilities while also requiring practitioners to develop new competencies.
Question 10: Which SIP security mechanism uses the 'Identity' header to provide cryptographic proof of caller identity?
- TLS mutual authentication
- S/MIME signing
- RFC 8224 (STIR) (Correct answer)
- Digest Authentication
Correct answer: RFC 8224 (STIR)
RFC 8224 (STIR - Secure Telephone Identity Revisited) uses the Identity header containing a JWT token to cryptographically assert caller identity.
Question 11: What does a SIP response code of 180 Ringing indicate?
- The destination endpoint is currently ringing (Correct answer)
- The call has been successfully established
- The request cannot be fulfilled due to an error
- The request has been received and is being processed
Correct answer: The destination endpoint is currently ringing
A SIP response code of 180 Ringing is a provisional response indicating that the called party's user agent has received the INVITE and is currently alerting the user. It informs the calling party that the call is progressing and the destination is being notified, often accompanied by a ringback tone. This response does not establish the call but signals that the recipient is being alerted.
Question 12: What does the SIP 'To' header field represent in an initial request?
- The logical recipient or callee of the request (Correct answer)
- The transport protocol to use
- The IP address of the proxy server
- The session expiration time
Correct answer: The logical recipient or callee of the request
The 'To' header identifies the logical recipient of the request, typically the callee's address-of-record (AOR).
Question 13: When a SIP proxy performs Record-Routing, what is the primary reason?
- To encrypt all subsequent requests in the dialog
- To cache media packets for quality monitoring
- To remain in the signaling path for all subsequent requests within the dialog (Correct answer)
- To prevent REGISTER requests from leaving the domain
Correct answer: To remain in the signaling path for all subsequent requests within the dialog
Record-Routing ensures the proxy stays in the signaling path for all in-dialog requests such as re-INVITEs and BYEs.
Question 14: Which component of a SIP transaction is responsible for maintaining state between a client request and the server response?
- SIP Dialog (Correct answer)
- SIP Registrar
- SIP Proxy
- SIP Gateway
Correct answer: SIP Dialog
A SIP Dialog is a peer-to-peer relationship between two SIP user agents that persists for the duration of a call or session. It maintains state information, such as sequence numbers and route sets, between a client request and subsequent server responses. This stateful connection ensures that related messages are correctly associated and processed within the context of an ongoing session, providing continuity.
Question 15: What is the primary purpose of a SIP transaction?
- To establish a persistent connection between two endpoints
- To represent a single request and all responses to that request (Correct answer)
- To maintain session state for the duration of a call
- To route SIP messages across multiple proxies
Correct answer: To represent a single request and all responses to that request
A SIP transaction consists of a single request and any responses to that request, terminated by a final response, as defined in RFC 3261.
Question 16: What role does continuing education play in Call Setup and Teardown?
- Keeping practitioners current with evolving best practices and new developments (Correct answer)
- Only required for new practitioners
- Only beneficial for management
- It is optional and rarely helpful
Correct answer: Keeping practitioners current with evolving best practices and new developments
Continuing education ensures practitioners stay current with advances in their field.
Question 17: What is the role of a 'Back-to-Back User Agent' (B2BUA) from a security perspective?
- It relays SIP messages transparently without inspecting content
- It provides end-to-end encryption between two UACs
- It terminates and re-originates SIP calls, providing a security policy enforcement point (Correct answer)
- It authenticates users using certificate-based identity
Correct answer: It terminates and re-originates SIP calls, providing a security policy enforcement point
A B2BUA terminates and re-originates SIP sessions, allowing it to enforce security policies, strip sensitive headers, normalize content, and prevent malformed messages from propagating.
Question 18: What is the most important foundational concept in Call Setup and Teardown?
- Memorizing all rules without understanding
- Ignoring established guidelines
- Understanding core principles and their practical application in Call Setup and Teardown (Correct answer)
- Only following instructions from supervisors
Correct answer: Understanding core principles and their practical application in Call Setup and Teardown
Core principles provide the foundation for all decision-making and practice in Call Setup and Teardown.
Question 19: What is the primary purpose of standardized procedures in SIP Architecture?
- To slow down work processes
- To benefit only management
- To create unnecessary bureaucracy
- To ensure consistency, safety, and quality across all practitioners (Correct answer)
Correct answer: To ensure consistency, safety, and quality across all practitioners
Standardized procedures ensure that all practitioners deliver consistent, safe, and high-quality outcomes.
Question 20: How does SIP interoperability with H.323 typically get managed?
- By using a SIP proxy server
- By avoiding the use of H.323 in SIP environments
- Through a protocol gateway that translates between SIP and H.323 (Correct answer)
- By direct communication between SIP and H.323 endpoints
Correct answer: Through a protocol gateway that translates between SIP and H.323
SIP and H.323 are two distinct and complex signaling protocols for multimedia communication, each with its own architecture, message formats, and call flow procedures. Direct communication between endpoints using these different protocols is not possible without translation. Therefore, a protocol gateway is required to translate the signaling messages and media parameters between SIP and H.323, enabling interoperability between the two environments.
Question 21: A SIP B2BUA differs from a SIP proxy primarily because:
- A B2BUA only modifies the Via header
- A B2BUA operates only on UDP transport
- A B2BUA terminates and re-originates each SIP dialog, maintaining full control of both legs (Correct answer)
- A B2BUA cannot handle INVITE transactions
Correct answer: A B2BUA terminates and re-originates each SIP dialog, maintaining full control of both legs
A B2BUA (Back-to-Back User Agent) acts as a UAS on one side and a UAC on the other, terminating and re-originating dialogs, giving it full control over both call legs.
Question 22: To ensure secure communication in SIP, which of the following practices is recommended?
- Use SIP over plain UDP for faster communication
- Implement SIP over TLS and use secure authentication methods (Correct answer)
- Avoid using authentication to reduce complexity
- Disable encryption to simplify configuration
Correct answer: Implement SIP over TLS and use secure authentication methods
To ensure secure communication in SIP, the recommended practice is to implement SIP over TLS (Transport Layer Security) and utilize robust authentication methods like Digest Authentication. TLS encrypts the SIP signaling messages, protecting them from eavesdropping and tampering, while secure authentication verifies the identity of communicating parties. This combined approach significantly enhances the confidentiality, integrity, and authenticity of SIP communications.
Question 23: When a SIP trunk interconnects two enterprises with overlapping private numbering plans, which element typically resolves number translation?
- DNS SRV record
- STUN server
- Session Border Controller with dial plan translation (Correct answer)
- SIP Registrar
Correct answer: Session Border Controller with dial plan translation
A Session Border Controller (SBC) with dial plan translation rewrites numbers to avoid conflicts between overlapping private numbering plans.
Question 24: What are the key regulatory requirements affecting Call Setup and Teardown?
- There are no regulations
- Regulations are optional guidelines
- Only federal regulations apply
- Compliance with applicable laws, industry standards, and licensing requirements specific to the field (Correct answer)
Correct answer: Compliance with applicable laws, industry standards, and licensing requirements specific to the field
Practitioners must comply with all applicable regulations, which may include federal, state, and industry-specific requirements.
Question 25: Which combination of headers uniquely identifies a SIP dialog?
- From URI and To URI only
- Call-ID and CSeq number
- Via branch parameter and Call-ID
- Call-ID, From tag, and To tag (Correct answer)
Correct answer: Call-ID, From tag, and To tag
RFC 3261 defines a SIP dialog as uniquely identified by the three-tuple of Call-ID, From tag, and To tag.
Question 26: Which SIP extension supports the exchange of instant messages between users?
- SIP-INVITE
- SIP-IM (Correct answer)
- SIP-OPTIONS
- SIP-CALL
Correct answer: SIP-IM
SIP is a versatile protocol that can be extended beyond traditional voice and video calls to support other real-time communication features. The SIP-IM (Instant Messaging) extension specifically defines how text-based instant messages are encapsulated and exchanged using SIP signaling. This allows for integrated messaging capabilities within the SIP framework.
Question 27: How should ethical dilemmas be handled in Call Setup and Teardown?
- Make decisions based solely on personal preference
- Ignore ethical concerns
- Follow established ethical guidelines, consult with supervisors, and prioritize stakeholder welfare (Correct answer)
- Always choose the cheapest option
Correct answer: Follow established ethical guidelines, consult with supervisors, and prioritize stakeholder welfare
Ethical decision-making requires following professional guidelines and prioritizing the welfare of all stakeholders.
Question 28: How does technology impact modern practices in Call Setup and Teardown?
- Technology is only useful for record keeping
- Technology has no impact on this field
- Technology improves efficiency, accuracy, and access to information while requiring new skills (Correct answer)
- Technology replaces all human judgment
Correct answer: Technology improves efficiency, accuracy, and access to information while requiring new skills
Technology enhances capabilities while also requiring practitioners to develop new competencies.
Question 29: In SIP, what does 'SPIT' stand for and what threat does it represent?
- SIP Protocol Interception Technique — call eavesdropping
- Spam over Internet Telephony — unsolicited bulk voice calls (Correct answer)
- Session Protocol Integrity Testing — security auditing
- Secure Peer Identity Token — caller verification
Correct answer: Spam over Internet Telephony — unsolicited bulk voice calls
SPIT (Spam over Internet Telephony) refers to unsolicited bulk calls over VoIP, analogous to email spam but for voice communications.
Question 30: What does a SIP 302 Moved Temporarily response instruct the UAC to do?
- Authenticate with the proxy
- Terminate the session immediately
- Resend the request to an alternate URI provided in the Contact header (Correct answer)
- Retry the request after a delay
Correct answer: Resend the request to an alternate URI provided in the Contact header
302 Moved Temporarily provides an alternate Contact URI and instructs the UAC to retry the request at that new address.
Question 31: How should risk be managed in SIP Architecture?
- By avoiding all risk entirely
- Risk management is not necessary
- By ignoring potential problems
- Through identification, assessment, mitigation strategies, and ongoing monitoring of potential risks (Correct answer)
Correct answer: Through identification, assessment, mitigation strategies, and ongoing monitoring of potential risks
Effective risk management involves a systematic process of identifying, evaluating, and addressing potential threats.
Question 32: Which SIP authentication mechanism involves sending a challenge-response pair to verify user credentials?
- Digest Authentication (Correct answer)
- OAuth Authentication
- Basic Authentication
- Kerberos Authentication
Correct answer: Digest Authentication
Digest Authentication is a common SIP authentication mechanism that involves a challenge-response process to verify user credentials without sending the password in plain text. The server sends a challenge, and the client responds with a hash of the password, nonce, and other information. This method provides a more secure alternative to Basic Authentication by protecting credentials from eavesdropping.
Question 33: Which SIP mechanism allows a UA to detect if a session is still active when no media is flowing?
- Registration refresh
- 180 Ringing keepalive
- Session timers (RFC 4028) (Correct answer)
- PRACK retransmission
Correct answer: Session timers (RFC 4028)
RFC 4028 session timers use periodic re-INVITEs or UPDATE requests to verify both sides are still alive.
Question 34: When integrating SIP with Microsoft Teams Direct Routing, the Session Border Controller must support which audio codec mandatorily?
- Opus
- G.729
- G.722
- G.711 (PCMU/PCMA) (Correct answer)
Correct answer: G.711 (PCMU/PCMA)
Microsoft Teams Direct Routing requires the SBC to support G.711 (PCMU and PCMA) as a mandatory baseline codec for interoperability.
Question 35: What SIP method is typically used to modify an existing session, such as changing media parameters?
- BYE
- OPTIONS
- ACK
- RE-INVITE (Correct answer)
Correct answer: RE-INVITE
The RE-INVITE method is a special form of the INVITE method used to modify an existing, established SIP session without tearing it down. It allows endpoints to change session parameters, such as adding or removing media streams, changing codecs, or updating IP addresses. This provides flexibility for dynamic session management, enabling adjustments to an ongoing call's characteristics.
Question 36: What quality metrics are most important in Call Setup and Teardown?
- Measurable outcomes, process compliance, and stakeholder satisfaction (Correct answer)
- Only financial metrics
- Only speed of completion
- No metrics are needed
Correct answer: Measurable outcomes, process compliance, and stakeholder satisfaction
Quality in Call Setup and Teardown is measured through multiple dimensions including outcomes, processes, and satisfaction.
Question 37: Which approach is most effective for problem-solving in Call Setup and Teardown?
- Always asking someone else
- Ignoring the problem until it resolves itself
- Random trial and error
- Systematic analysis followed by evidence-based decision making (Correct answer)
Correct answer: Systematic analysis followed by evidence-based decision making
Systematic, evidence-based approaches lead to more reliable solutions than ad hoc methods.
Question 38: What is the importance of communication skills in Call Setup and Teardown?
- Clear communication prevents errors, builds relationships, and ensures understanding among all parties (Correct answer)
- Communication is only important for managers
- Communication skills cannot be learned
- Technical skills are sufficient without communication
Correct answer: Clear communication prevents errors, builds relationships, and ensures understanding among all parties
Effective communication is essential for coordination, error prevention, and stakeholder relationships.
Question 39: A SIP UA sends an INVITE to a PSTN gateway that supports only G.711. The UA's SDP offer includes G.729 and G.711. What determines which codec is used?
- The UA always wins the codec negotiation
- RTCP negotiates the codec after the call is established
- SDP answer from the gateway selects the mutually supported codec (Correct answer)
- The gateway selects the first codec in the offer
Correct answer: SDP answer from the gateway selects the mutually supported codec
The gateway's SDP answer selects one or more codecs from the offer that it supports, finalizing the codec choice.
Question 40: In SIP, what is an 'address-of-record' (AOR)?
- A SIP URI that serves as a public address for a user (Correct answer)
- The FQDN of the SIP proxy
- The MAC address bound to a SIP phone
- The IP address of the UA's NIC
Correct answer: A SIP URI that serves as a public address for a user
An AOR is a SIP URI (e.g., sip:alice@example.com) that represents a user's persistent public identity, independent of their device location.
Question 41: What is the SIP loose routing mechanism and which header does it use?
- Source routing via the Via header
- Strict routing via the Request-URI
- Loose routing via the Route header with 'lr' parameter (Correct answer)
- Policy routing via the P-Asserted-Identity header
Correct answer: Loose routing via the Route header with 'lr' parameter
Loose routing (RFC 3261) uses the Route header with the 'lr' parameter, allowing proxies to forward requests without replacing the Request-URI.
Question 42: What are the key regulatory requirements affecting SIP Architecture?
- There are no regulations
- Compliance with applicable laws, industry standards, and licensing requirements specific to the field (Correct answer)
- Only federal regulations apply
- Regulations are optional guidelines
Correct answer: Compliance with applicable laws, industry standards, and licensing requirements specific to the field
Practitioners must comply with all applicable regulations, which may include federal, state, and industry-specific requirements.
Question 43: What is Timer B in SIP INVITE client transactions?
- The retransmission interval for INVITE requests over UDP
- The time a server waits before sending a 100 Trying response
- The maximum time a UAC waits for a final response to an INVITE before timing out (Correct answer)
- The interval between sending ACK and cleaning up the transaction
Correct answer: The maximum time a UAC waits for a final response to an INVITE before timing out
Timer B is the INVITE client transaction timeout set to 64*T1 (32 seconds by default), after which the transaction is abandoned if no final response is received.
Question 44: Which header uniquely identifies a SIP transaction?
- From tag
- Via branch parameter (Correct answer)
- Call-ID
- CSeq number
Correct answer: Via branch parameter
The Via branch parameter (starting with 'z9hG4bK') uniquely identifies a SIP transaction per RFC 3261.
Question 45: Which attack targets SIP infrastructure by sending a high volume of crafted SIP messages to exhaust server resources?
- Eavesdropping
- SPIT (Spam over Internet Telephony)
- Toll fraud
- SIP flooding (DoS) (Correct answer)
Correct answer: SIP flooding (DoS)
SIP flooding attacks send massive volumes of SIP messages to overwhelm a server's processing capacity, constituting a Denial of Service attack.
Question 46: In SIP digest authentication, what is the purpose of the 'nonce' value?
- Prevents replay attacks by ensuring each challenge is unique (Correct answer)
- Encrypts the user password
- Identifies the authentication realm
- Specifies the hashing algorithm to use
Correct answer: Prevents replay attacks by ensuring each challenge is unique
The nonce is a server-generated unique value included in the WWW-Authenticate challenge to ensure each authentication response is unique and cannot be reused.
Question 47: What makes a professional competent in SIP Architecture?
- A combination of education, practical experience, ongoing learning, and adherence to professional standards (Correct answer)
- Only certifications matter
- Only formal education matters
- Only experience matters
Correct answer: A combination of education, practical experience, ongoing learning, and adherence to professional standards
Competence requires the integration of knowledge, skills, experience, and professional conduct.
Question 48: What does the SIP 'Expires' header control when used in a REGISTER request?
- The duration for which the contact binding is valid (Correct answer)
- The timeout before a re-INVITE must be sent
- The lifetime of the SIP dialog
- The maximum session duration for voice calls
Correct answer: The duration for which the contact binding is valid
The Expires header in a REGISTER request tells the registrar how long (in seconds) to keep the AOR-to-contact binding before it expires.
Question 49: Which SIP timer governs how long a UAC waits for a final response before retransmitting an INVITE?
- Timer D
- Timer A
- Timer B (Correct answer)
- Timer C
Correct answer: Timer B
Timer B is the INVITE transaction timeout timer; if no final response is received within 64*T1, the transaction times out.
Question 50: What is the purpose of the 'opaque' route set maintained by a UAC after dialog establishment?
- To record the authentication credentials for the dialog lifetime
- To cache the IP address of the remote UAS for direct media delivery
- To store the codec list negotiated during SDP offer/answer
- To ensure subsequent requests within the dialog are routed through the same set of proxies (Correct answer)
Correct answer: To ensure subsequent requests within the dialog are routed through the same set of proxies
The route set, built from Record-Route headers received during dialog establishment, ensures all subsequent in-dialog requests follow the same proxy path as the initial INVITE.
Question 51: Which SIP method is used to send mid-session information that does not change the session state?
- UPDATE
- MESSAGE
- INFO (Correct answer)
- NOTIFY
Correct answer: INFO
INFO carries application-level information (e.g., DTMF tones) within an established session without modifying the session state.
Question 52: Which SIP header limits the number of proxies that can forward a request?
- Max-Hops
- TTL
- Route-Limit
- Max-Forwards (Correct answer)
Correct answer: Max-Forwards
The Max-Forwards header starts at a value (typically 70) and is decremented by each proxy; reaching 0 causes a 483 Too Many Hops response.
Question 53: What quality metrics are most important in SIP Architecture?
- Only financial metrics
- No metrics are needed
- Measurable outcomes, process compliance, and stakeholder satisfaction (Correct answer)
- Only speed of completion
Correct answer: Measurable outcomes, process compliance, and stakeholder satisfaction
Quality in SIP Architecture is measured through multiple dimensions including outcomes, processes, and satisfaction.
Question 54: Which threat does the 'Record-Route' header manipulation pose in SIP security?
- An attacker can modify codec negotiation during the session
- An attacker can reroute the initial INVITE to a different destination
- An attacker can insert themselves as a persistent on-path proxy for all in-dialog requests (Correct answer)
- An attacker can prevent BYE messages from terminating a call
Correct answer: An attacker can insert themselves as a persistent on-path proxy for all in-dialog requests
By injecting a malicious URI into the Record-Route header, an attacker can ensure all subsequent in-dialog requests (like re-INVITEs and BYE) pass through their proxy.
Question 55: What is the function of the CSeq header in SIP session management?
- Identifies the transaction method and sequence number within a dialog (Correct answer)
- Stores the session expiration time
- Encrypts the session media stream
- Routes requests through proxy servers
Correct answer: Identifies the transaction method and sequence number within a dialog
CSeq provides a command sequence number paired with the method name, used to order requests and match responses within a dialog.
Question 56: What is the significance of documentation in SIP Architecture?
- Only management needs to document
- Documentation is unnecessary busy work
- Only required during audits
- It provides a record for accountability, quality assurance, and legal compliance (Correct answer)
Correct answer: It provides a record for accountability, quality assurance, and legal compliance
Proper documentation supports accountability, enables quality review, and satisfies legal requirements.
Question 57: Which transport protocol is recommended for SIP interoperability when traversing firewalls and NATs due to its reliable delivery?
- UDP
- SCTP
- TCP (Correct answer)
- RTP
Correct answer: TCP
TCP is preferred for firewall and NAT traversal because stateful firewalls track TCP connections, and TCP ensures reliable SIP message delivery.
Question 58: Which IETF RFC defines the SIP-T framework for carrying ISUP information within SIP messages?
- RFC 4474
- RFC 3711
- RFC 3261
- RFC 3372 (Correct answer)
Correct answer: RFC 3372
RFC 3372 defines SIP-T, which enables ISUP signaling to be encapsulated within SIP for PSTN interworking.
Question 59: In SIP, what does a 491 Request Pending response indicate?
- A re-INVITE or UPDATE was rejected because another transaction is already in progress within the dialog (Correct answer)
- Authentication credentials are pending verification
- The proxy queue is full and the request must be retried
- The requested URI cannot be resolved
Correct answer: A re-INVITE or UPDATE was rejected because another transaction is already in progress within the dialog
491 is returned when a UA receives a re-INVITE while it has a pending unacknowledged re-INVITE, preventing overlapping transactions.
Question 60: What is the importance of communication skills in SIP Architecture?
- Technical skills are sufficient without communication
- Clear communication prevents errors, builds relationships, and ensures understanding among all parties (Correct answer)
- Communication is only important for managers
- Communication skills cannot be learned
Correct answer: Clear communication prevents errors, builds relationships, and ensures understanding among all parties
Effective communication is essential for coordination, error prevention, and stakeholder relationships.
SIP Session Initiation Protocol Certification Exam
The SIP Session Initiation Protocol Certification Exam validates expertise in SIP protocol fundamentals, session management, security, interoperability, architecture, and call setup and teardown procedures for VoIP and unified communications professionals.
Exam Rules
- You can skip questions and return to them later
- Flag questions for review before submitting
- No feedback shown until you submit the entire exam
- Unanswered questions count as wrong — answer everything
- 10 pretest questions are mixed in and don't affect your score
- Timer auto-submits when time runs out
- Your progress is auto-saved every 30 seconds