300-070 Question #83: Real Exam Question with Answer & Explanation

The correct answer is B: SIP provides support for third-party entities.. SIP (Session Initiation Protocol) is distinguished from H.323 and MGCP by its native support for third-party call control. (B) is correct - SIP defines mechanisms such as the REFER method that allow a third-party entity (like a proxy or another endpoint) to redirect or transfer a

Question

When comparing SIP H.323 and MGCP, which of the following is specific to SIP?

Options

AThe dial plan is directly on the gateway.
BSIP provides support for third-party entities.
CSIP defines Translation per the gateway.
DSIP has a centralized dial plan.

Explanation

SIP (Session Initiation Protocol) is distinguished from H.323 and MGCP by its native support for third-party call control. (B) is correct - SIP defines mechanisms such as the REFER method that allow a third-party entity (like a proxy or another endpoint) to redirect or transfer a call, enabling features like call transfer without requiring the originating server to remain in the media path. This peer-to-peer yet extensible model is unique to SIP. Option A (dial plan on the gateway) describes MGCP, where the gateway is 'dumb' and the call agent holds the dial plan - but MGCP gateways do process some digit collection. Option C (translation per gateway) is more characteristic of MGCP/H.323 gateway behavior. Option D (centralized dial plan) is the defining trait of MGCP, where a Media Gateway Controller (like CUCM) owns all call routing logic.

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