Hi SIP Experts!
I was wondering wether anyone could help me clarify the specific
requirements for a B2BUA.
I know it is supposed to act just like two UA's back to back, just
like the name says, but when stumbling on the notes regarding 3GPP's Rel
5
and its CSCF's I find my self slight fuzzy on the differences.
These CSCFs are "SIP-incompliant" because they send messages on account
of the endpoint, behaving as if the _were_ that specific endpoint. (they
can send BYE i think one of the examples were)
Now I understand why they shouldnt, if we talk S/MIME security and so
on,
but I cant exactly understand the finer details of what the proxy would
do
differently if it did implement/use all the requirements of a B2BUA.
My other question is a simple one regarding via-headers and their use.
One of the benefits of having the via-header route the response
"backwards",
towards the originator, is that of redundancy the rfc says. (apart from
not needing
state for remembering where it came from)
So if the host in the via-example below doesnt answer, the proxy could
try
doing more DNS lookups, trying to find an alternative right?
My simple question is...should this be done on the full name
"server42.betelgeuse.com", or just the domain name "betelgeuse.com" ?
Should each server have extra NAPTR records for all the possible
backupservers?
What about the recieved=x.x.x.x line?
And then I final check..this redundancy can only work properly in
non-stateful
environments right? Since the backup proxy wouldnt have neither dialog
nor transactional
state, unless conveyed by outofbounds means?
Via: SIP/2.0/UDP server42.betelgeuse.com
;branch=z9hG4bKnasads8;received=192.0.1.2
Very thankful for any and all helpful clarifications
Regards
Taisto Qvist
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