Of course the devil is in the details, that is, can we implement this
scheme without doing too much violence to the architecture.
On Thu, 2008-10-16 at 10:01 -0400, Robert Joly wrote:
> - An optional three-digit location code;
Presumably the length of the location code is settable.
> #2 - Using network topology information: if the call did not carry a
> location code then the public IP address of the caller is compared
> against the optional network topology information of each configured
> location.
I don't see what you mean by "the caller's public IP address". What bit
of the SIP request are you examining?
> #3 - Using Location's configured users list: if the call did not carry
> a location code and the caller's IP address did not match any of the
> locations' topologies, the redirect server will look for a signed
> P-Asserted Identity header in the message. If one is found, the
> redirect server will try to find a location that contains the user
> identified by the header and use its gateway list as candidates to route
> the call.
Mention here the interaction of #3 with the current scheme of forcing
all calls that appear to be from a defined user in the domain to
providing auth credentials, from which a P-Asserted-Identity header is
constructed.
> Users that do not match any of the presented criteria are essentially
> location-less and will, by default, fall into the 'Default' location
> category.
Actually, that is "INVITEs that do not match any of ...".
> ---Deciding which gateways to use to route the calls---
>
> So far, we have seen the machinery used to generate a list of gateways
> that are _potential candidates_ to route the call based on the caller's
> location. That list of candidate gateways needs to be intersected with
> the list of gateways configured on the exercised dialplan to generate
> the final list of gateways that the request will be redirected to. This
> section details that intersection logic:
>
> Let A be a user making a call that will be routed using a PSTN gateway;
> Let Loc(A) be the location that A belongs to;
> Let DP(call) be the dialplan used to route the call;
> Let GW(Loc(A)) be the ordered list of gateways belonging to loc(A);
> Let GW(default) be the ordered list of gateways belonging to the
> 'default' location;
> Let GW(DP(call)) be the ordered list of gateways configured for
> DP(call).
>
> The list of gateways that the call will ultimately be redirected to is
> given by:
> ( GW(Loc(A)) LOGICAL_AND GW(DP(call)) ) LOGICAL_OR ( GW(default)
> LOGICAL_AND GW(DP(call)) )
>
> To state it in words, the list of gateways that the call will be
> redirected to will consist of all the gateways associated with the
> user's location that are also found in the dialplan followed by all the
> gateways belonging to the 'default' location that are also found in the
> dialplan. This means that if a user does not belong to any location
> then the list of gateways that the call will be redirected to will only
> consist of all the gateways belonging to the default location that are
> also found in the dialplan.
>
> So, for example, if a dialplan is configured to use the following
> gateways:
> GW_1_B
> GW_1_A
> GW_Elsewhere_A
> GW_SomewhereElse_A
> GW_Def_A
>
> ...and caller A's location includes the following gateways:
> GW_1_A
> GW_1_B
> GW_1_C
>
> ...and the 'Default' location includes the following gateway:
> GW_Def_A
> GW_Def_B
>
> ...then a call made by caller A using this dialplan will be sent to the
> following ordered list of gateways:
> GW_1_A
> GW_1_B
> GW_Def_A
>
> Note from the previous example that if there are order discrepancies
> between the dialplan and location gateway lists, the location's order
> takes precedence. This explains why the resulting ordered list of
> gateway in the example is {GW_1_A, GW_1_B, ...} even though the
> dialplan's ordered list was {GW_1_B, GW_1_A, ...}
So what you're really saying is (using operations that are aware of the
orderings involved):
Let C be a call that will be routed using a PSTN gateway;
Let Loc(C) be the effective location for C;
Let DP(C) be the dialplan used to route the call;
Let GW(Loc(C)) be the ordered list of gateways belonging to loc(C);
Let GW(default) be the ordered list of gateways belonging to the
'default' location;
Let GW(DP(C)) be the *set* of gateways configured for DP(call).
The list of gateways that the call will ultimately be redirected to is
given by:
( GW(Loc(C)) INTERSECT GW(DP(C)) )
FOLLOWED_BY
( GW(default) INTERSECT GW(DP(C)) )
Where the ordering of the result of an intersection is the ordering of
the elements in the first, ordered, argument.
I assume you also expect the 2nd and later occurrences of a single
gateway to be deleted from the final list.
A couple of questions come to mind:
- We probably want to be able to set the effective location of some
calls to be different from others. E.g., we may want emergency calls to
prefer the local gateways, but non-emergency outside calls to prefer a
central gateway.
- Do we have a decent solution to the "multiple gateway routing
problem"?
Dale
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