Practice Test Geeks(SSCA) Sip School Certified Associate Practice Test
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Proxy Servers Flashcards

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  1. In the SIP trapezoid model, how many proxies are typically involved in a call between two different domains?

    Answer: Two

    The SIP trapezoid involves two proxies — one in the caller's domain (outbound proxy) and one in the callee's domain (inbound proxy).

  2. What does a SIP proxy do when it performs 'sequential forking'?

    Answer: It tries each destination in order, waiting for a failure response before trying the next

    Sequential forking tries potential destinations one at a time, moving to the next only after receiving a failure or timeout from the current attempt.

  3. Which DNS record type does a SIP proxy typically query first to resolve the next-hop server for a SIP URI?

    Answer: NAPTR record

    A SIP proxy queries NAPTR (Naming Authority Pointer) records first to determine the transport protocol and then uses SRV and A records to find the server address.

  4. What happens to the Via header when a SIP proxy forwards a request?

    Answer: The proxy adds its own Via header on top of the existing ones

    Each forwarding proxy pushes its own Via header to the top of the Via header stack so responses can be routed back along the same path.

  5. What is a B2BUA (Back-to-Back User Agent) and how does it differ from a standard SIP proxy?

    Answer: A B2BUA terminates and re-originates SIP dialogs, maintaining full control, unlike a proxy which only forwards

    A B2BUA acts as both a UAS and UAC, terminating the incoming dialog and creating a new outgoing dialog, giving it full call control unlike a proxy which merely forwards.

  6. Which SIP response code does a proxy return when the Max-Forwards header value reaches zero?

    Answer: 483 Too Many Hops

    When Max-Forwards reaches 0, the proxy returns 483 Too Many Hops to prevent infinite routing loops.

  7. In SIP, what is the role of an 'outbound proxy' for a SIP UA?

    Answer: It receives all outgoing requests from the UA and routes them toward the destination

    An outbound proxy receives all outgoing SIP requests from the UA and is responsible for routing them toward the appropriate destination.

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