7/25/2019 Sb Elab Trapezoid Model

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3G IMS Illustrated ( 2nd Level )

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The SIP trapezoid model is a classic model, in which a SIP user calls another SIP user, and the casetup occurs via two SIP proxy servers, that act on behalf of both users (respectively to facilitatethe session establishment!"or instance SIP user, #lice, in the domain $atlanta!com%, calls Bob, in the domain $billoxy!com%,and the call setup &oes throu&h both the proxy server in #lice%s domain ($atlanta!com% and the oin Bob%s domain ($billoxy!com% !

This is a SIP classic model, and may be used for instance when #lice uses the proxy in atlanta!comdomain as her local outbound proxy server , and Bob uses the proxy in billoxy!com domain asincomin& proxy server! 'hen #lice%s proxy receives her INVITE re uest, it examines the Request-URI headers, and based on that forwards the invitation to Bob%s proxy, i!e!, the proxy, which is in char&e of the domain $billoxy!com%! #s shown in the fi&ure below, this call setup model follows the &eometric forms of trapezoid andhence is called that way! It is classic, in a sense it is expected to be widely used and it enables fullcontrol (e!&!, services, security of both ends of the call (dialo& !

#tlanta!com proxy billoxy!com proxy

#lice

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