RE: [Sip] Back-to-Back User Agent Ttransparency Top 10 list

["Dean Willis" <dean.willis@softarmor.com>]

By the way, 3GPP proxies are much more conformant now than they were
when I first posted this, so please don't beat them up about anything
here. They've done a great job improving the transparency of their
system. Thank you, 3GPP!

--
Dean

> -----Original Message-----
> From: sip-admin@ietf.org [mailto:sip-admin@ietf.org] On 
> Behalf Of Dean Willis
> Sent: Wednesday, December 04, 2002 7:23 PM
> To: sip@ietf.org
> Subject: [Sip] Back-to-Back User Agent Ttransparency Top 10 list
> 
> 
> 
> Apologies to those of you who have seen this before. It's a 
> couple of years old, which explains my frustration with this 
> particular topic.
> 
> Note that "conformant" proxies satisfy all 10. Strict UAs 
> satisfy none.
> 
> ----------------------------
> 
> 1) Dialog transparency: The call-ID is the same on "both 
> sides" of the 
> B2BUA. Proxies have this characteristic. A B2BUA that actually 
> terminates a dialog on one side and generates a new dialog on 
> the other 
> doesn't. Some 3GPP AS functions fall into this category, as do 3PCC 
> controllers.
> 
> 2) Identity transparency: The user appears to have the same 
> identity on 
> both sides of the B2BUA. A proxy has this property. An identity 
> anonymizer doesn't.
> 
> 3) CSEQ transparency: The B2BUA does not alter CSEQ numbers. A 
> traditional proxy has this property. A 3GPP P-CSCF does not, 
> as it can 
> generate a BYE message and then have to manage disjoint CSEQ 
> spaces on 
> each side.
> 
> 4) Header transparency: The B2BUA doesn't change headers that transit 
> it. Proxies have mostly this property, changing onlya few 
> headers that 
> are specifically changed by the proxy function. Proxies don't change 
> headers they don't understand. 3GPP "proxies" are likely to 
> go to town 
> changing all SORTS of headers. All with the best of intentions, mind 
> you.
> 
> 5) Body transparency: The MIME bodies on the SIP message are not 
> altered by the B2BUA. Real SIP proxies have this property. Firewall 
> proxies that modify SDP, and most everything in 3GPP, doesn't.
> 
> 6) Media transparency: AS with body transparency, but 
> considering only 
> the media aspects. The 3GPP P-CSCF breaks this transparency rule by 
> editing one's SDP to meet operator preferences.
> 
> 7) Topology transparency. Via, Route, Record-Route, Path, 
> P-Service-Route, and other headers that reveal topology are 
> roughly the 
> same on both sides of the B2BUA, save for any which uniquely identify 
> that B2BUA. Proxies have this characteristic. Topology hiding devices 
> like the dynamicosft "firewall proxy in edge proxy mode" or the 3GPP 
> THIG don't.
> 
> 8) Security transparency: The B2BUA doesn't alter security aspects, 
> such as encryptions, authorization headers, etc. Proxies 
> generally have 
> this property, but 3GPP stuff  doesn't.
> 
> 9) Accounting transparency: Stuff used to generate records or track 
> usage is not altered by a B2BUA with this property. Proxies have this 
> property. 3GPP is trying to define a P-header (P-original-dialog-ID, I
> believe) to provide for accounting transparency across 3GPP 
> AS elements 
> operating at a low level of transparency.
> 
> 10) Functional transparency: The task that the user of the UA 
> wants to 
> accomplish actually works across the B2BUA, rather than being 
> blocked/distorted by it. Proxies generally have this 
> property, with the 
> caveat the proxy can reject a request if needed. Some 3GPP 
> entities can 
> mutate functionality beyond all recognition. This is probably the 
> single most important transparency concept. The rules of a "proxy" as 
> defined in RFC3162 are there to preserve functional transparency, and 
> anything that "breaks" those rules is likely to compromise 
> functionality in some way.
> 
> _______________________________________________
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> 
> 

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