Aha, here is my take.
I am almost certain others will have their own interpretations.
>From 2616:
"transparent proxy" is a proxy that does not modify the request or
response beyond what is required for proxy authentication and
identification.
A "non-transparent proxy" is a proxy that modifies
the request or response in order to provide some added service to
the user agent, such as group annotation services, media type
transformation, protocol reduction, or anonymity filtering.
To my understanding, a Proxy as defined in RFC 3261, should be considered
as a 'transparent' entity
(with certain implementation details from what 2616 categorized as one).
A 'B2B' who looks like a Proxy may be considered transparent or
non-transparent depending on what
he does with the messages.
To my opinion, this confusion of transparent vs. non transparent entites
stem from the following facts in SIP:
a) There is a standard element called a 'Proxy' in the RFC which
authenticates and routes calls.
In its purest form, he could be classified as a transparent proxy.
There are some differences between what 2616 defines as a
'transparent proxy' vs. what SIP
means it to be. (For example, SIP proxies may rewrite reqURIs
without restriction while
2616 imposes certain restrictions. As another example, I
understand HTTP proxies cannot
change Expires which SIP entities -actually its a registrar here
can and some others.
There may be others - experts on HTTP could add things here.
b) We have an element called a 'B2BUA'. Unlike a 'Proxy', this guy
has full control over
a call including origination, termination and is capable of
changing many elements of the
messages to suit specific services (eg. a Media Proxy for NAT,
anonymizer etc)
However, to the external world, a B2B *may* appear as a
transparent proxy. See
http://www1.ietf.org/mail-archive/working-groups/sipping/current/msg01855.html
for the
now TradeMarked "Dean's 10" transparency points.
Thanks to the B2B, the proxy space is confused to a point where I
recently encountered
a statement implying that a true proxy is a 'B2B proxy' -> and if
a proxy provider does
not implement his proxy as a B2B, he obviously did not read the
specs right :-)
Oh Well !
regds
Arjun
--
Arjun Roychowdhury @ Hughes Software Systems
11717 Exploration Lane, Germantown MD 20876
(O): 301 212 7860 (M): 240 997 [EMAIL PROTECTED]
"Rajesh R A" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
02/25/2003 07:16 AM
To: <[EMAIL PROTECTED]>
cc:
Subject: [Sip-implementors] Transparent SIP Proxy
Hi,
I am looking for some documents on the usage of Transparent Proxy for
handling SIP. How different, if any, is the SIP Transparent Proxy
different from HTTP Transparent proxy.
Thanks in Anticipation.
Regards,
Rajesh
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