What redundancy mechanism does SIP use for call setup?

• A. DNS SRV
• B. H.323
• C. SIP INFO
• D. STUN

Answer: (B)

SIP call setup relies on DNS SRV records to locate the signaling servers for a domain. DNS SRV lets a domain publish multiple SIP endpoints (with assigned priority and weight), so a user agent can contact the highest-priority server first and automatically fail over to the next one if that server is unavailable. This provides redundancy and load balancing for establishing calls, helping ensure availability even if a specific SIP server goes down.

Other options don’t serve this purpose: H.323 is a separate VoIP protocol not used to support SIP signaling redundancy; SIP INFO is a signaling message type for mid-call information and not a mechanism for locating or failover of signaling servers; STUN helps with NAT traversal for media paths, not with signaling server redundancy.