Inquiry: Authentication in Reciever's Domain

[Couret Tabt]

Dear folks,

I have a question about SIP Authentication Mechanism below:

In inter-domain (e.g.proxy-proxy) we can use RFC4474(SIP Identity)
for user authentication, but, inside domain, how can a receiver
or a proxy in receiver side authenticate each other?

This means the followings:

CASE 1) Spoofing of Receiver:
After a Receiver's UA registered, without re-register
other user use the address that the former user registered.
(Then the former user is NOT unregistered by the proxy.)

Invite: Alice(in Atlanta) to Bob(in Biloxi)

Alice --->Atlanta--(RFC4474 Authentication)------>Biloxi---->Bob

*But actually,

this is spoofing user

(NOT Bob)

CASE 2)Spoofing of Proxy:
In attacks like Man-in-the-Middle, barge-in user spoof Receiver side Proxy.

Alice --->Atlanta--(RFC4474 Authentication)------>Biloxi---->Bob

*But actually,

this is spoofing proxy

(NOT Biloxi)


If you know it(how to authenticate), please let me know.

*I have studied about SIP more.
Is it appreciate that in this mailing list I have any above discussions?
Please let me know, too.

Thanks,
Tabt
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