High-level differences between SBCs and SIP proxies
SIP proxies have operations defined in RFC 3261 and supporting extensions. Though no IETF RFC completely defines how SBCs must function, SBCs evolved over the years. Which two operations demonstrate the high-level differences between SBCs and SIP proxies? (Choose two.)
Community Votes
100% of anonymous learners picked answer CE. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The exam tests the understanding that SBCs are application-layer gateways capable of deep header manipulation and protocol conversion, whereas SIP proxies primarily route messages with minimal modification.
This question distinguishes Session Border Controllers (SBCs) from SIP proxies based on their protocol handling capabilities. The community consensus confirms that SBCs modify SIP headers and interwork different protocols, while standard proxies generally preserve message integrity.
Candidates often select B because it describes standard proxy behavior, but it is incorrect because proxies do more than just add Via/Record-Route headers (e.g., decrementing Max-Forwards), and the option implies they leave everything else untouched which is misleading in this context compared to the explicit power of an SBC.
Community Discussion (4 comments)
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Expert Analysis
Why the Answer Is Correct
SBCs operate at the application layer and are designed to be 'application-aware.' Option C is correct because SBCs frequently perform Network Address Translation (NAT) traversal by modifying Contact, From, To, and Call-ID headers to ensure media paths are correctly routed through firewalls. Option E is correct because a key function of an SBC is protocol interworking, allowing it to bridge networks using different signaling protocols like SIP, H.323, or MGCP, which a pure SIP proxy cannot do.Why the Other Options Are Wrong
Option A is incorrect because standard SIP proxies are typically not SDP-aware; they treat the SDP body as opaque data, whereas SBCs inspect and modify SDP for media security and compatibility. Option B is incorrect because, while proxies add Via headers, they also decrement the Max-Forwards header, making the statement 'rest of the headers are left untouched' factually inaccurate. Option D is incorrect because stateful proxies terminate sessions only after receiving final responses, they do not actively initiate or manage session teardown logic independently like an SBC might in a failover scenario.Community Comment Notes
Comment [1] provides a detailed breakdown, confirming that B is partially correct but flawed due to the Max-Forwards omission, and clarifying that proxies don't modify SDP. Comment [4] suggests B & C, which is a common trap, but the official answer CE is widely accepted as the most distinct functional differences.Official Reference
Exam Strategy
Focus on the 'Application Awareness' distinction: if the device modifies headers (To/From/Contact) or converts protocols (SIP/H.323), it is likely an SBC. If it merely routes based on URI without changing content, it is a Proxy.