[SIPForum-discussion] Outbound and inbound proxy

Dipan Kumar m.dipan1987 at gmail.com
Mon Dec 22 16:49:13 UTC 2014

Thanx to all for your earliest response.

But If think of a scenario where 6 proxies in between

A  ------>P1->P2->P3->P4->P5->P6-------->B

Then according to all of you P1 is outbound proxy and P6 is inbound proxy
if call is from A to B.

Then how can we define outbound/inbound proxy for  P2 ,P3,P4,P5 ?

On what  basis we define a proxy as outbound and inbound?

On Sat, Dec 20, 2014 at 9:31 PM, Paul Kyzivat <pkyzivat at alum.mit.edu> wrote:

> On 12/18/14 6:35 AM, Dipan Kumar wrote:
> > Hi All
> >
> > 1.Can anybody clarify what is the diffrence between outbound and inbound
> > proxy
> > 2.If there are multiple proxy in between then how to define which one is
> > inbound and which one is outbound
> > 3.How many outbound and how many inbound proxy are possible between two
> > endpoints in case of multiple proxy scenario.
> These things aren't formally defined (with the exception of rfc5626) -
> they are terms for things that are observed in deployed systems.
> Loosely, an outbound proxy is one that a UAC uses when sending out of
> dialog requests.
> And an inbound proxy is one that is inserted in front of the UAS for
> out-of-dialog requests coming to a UAS.
> Quite often a single proxy will serve both purposes.
> Once you establish a dialog, the set of servers on the path is largely
> determined by the Record-Route of the dialog establishing request. If
> there were outbound and inbound proxies during the dialog establishing
> request, and they Record-Route themselves, then they will be there for
> subsequent requests within the dialog. And they can still be considered
> to be inbound and outbound proxies in that case.
> It is also possible for a UAC to insert a proxy in in-dialog requests
> even though it isn't in the route set for the dialog. If so, that would
> also be an outbound proxy.
> If you consider a consider a call between alice at atlanta.com and
> bob at biloxy.com using the typical trapezoid topology for sip calls where
> alice's UA has registered with atlanta.com and bob's has registered with
> biloxy.com:
> alice at alanta.com ----- atlanta.com ----- biloxy.com ----- bob at biloxy.com
> then any proxies between alice and atlanta.com can be considered in-
> and/or out-bound proxies for alice, and any proxies between biloxy.com
> and bob to be in- and/or out-bound proxies for bob.
>         Does that help?
>         Paul
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Dipan Kumar
Sr.Software Engineer
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