350-801 CLCOR: Implementing and Operating Cisco Collaboration Core TechnologiesDemo

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QuestionQ190

Voice Gateways and Session Border Controllers

SIP proxy operations are defined in RFC 3261 and its supporting extensions. Although no IETF RFC fully specifies how SBCs must operate, SBCs have evolved over time. Which two operations illustrate the high-level differences between SBCs and SIP proxies?

Choose two
  • A SIP proxies are SDP-aware and can change the SDP bodies.
  • B SIP proxies add a Via header and optionally a Record-Route header, and the rest of the headers are left untouched.
  • C SBCs can modify headers such as To, From, Contact, and Call-ID. It can introduce new headers into the SIP message.
  • D Stateful proxies are context-aware and can terminate communication sessions by themselves.
  • E SBCs are capable of interworking completely different protocols to set up, modify, and tear down communication sessions. It includes SIP, H.323, and MGCP protocols.
Explanation

An SBC can act as a back-to-back user agent, allowing it to modify SIP dialog headers such as To, From, Contact, and Call-ID, and to add headers. SBCs can also interwork distinct signaling protocols for establishing, changing, and ending communication sessions, whereas a SIP proxy primarily forwards SIP requests according to SIP routing rules. RFC 3261 specifies that proxies do not modify message bodies during forwarding and focuses their core processing on routing-related fields such as Via and Record-Route.

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