Re: message distribution at ASP

Dario,

Dario wrote:                                                                         (Wed, 30 May 2007 09:56:36)
> 
> Hi,
> 
> I have a simple question regarding message distribution at ASP.
> 
> The RFC 4666 says about message distribution the following:
> 
> - at SGP (section 1.4.2.4.): "....by comparing elements of the incoming SS7
> message to currently defined Routing Keys in the SGP"
> 
> - at ASP (section 1.4.2.5.): "by observing the Destination Point Code (and
> possibly other elements of outgoing message, such as the SLS value). The ASP
> must also take into account whether the related Routing Context is active or
> not"
> 
> Do these descriptions converge to the same thing?
> 
> Here is one example where I am unsure:
> An ASP processes traffic for two ASs:
> 
> AS1 ~ RK1 = (DPC X, OPC Y, SI=3)
> AS2 ~ RK2= (DPC X, OPC Y, SI=5)
> 
> ASP is connected to two SGs, namely SG1 and SG2.
> Both SGs have available connection to SS7 destination Y.
> 
> ASP is registered and active for AS1 and AS2 at SG1.
> ASP is registered and active for AS1 at SG2.
> 
> My question is the following:
> how message with routing label DPC=Y, OPC=X, SI=5 can be routed from ASP:
> 
> a) if we observe Destination PC only, it can be send to either SG1 or SG2
> b) if we observe Routing Label and match it to AS, it can be sent over SG1
> only 
> 
> what is the correct distribution?

Section 1.4.2.4 is for distributing messages from the SGP to an ASP.  Section
1.4.2.5 is for distributing messages from the ASP to the SGP, which is your
case.  Also note that in Section 1.4.2.5 it says, as you quote, the
"Destination Point Code (and possibly other elements of the outgoing message,
such as the SLS value)."   Note that SI is an element of the outgoing message.

In SS7 the local network, PC and SI value are associated with an MTP-SAP and thus
with a specific MTP-User (ISUP in your case).  All the messages you describe
are associated with AS2.  Therefore, the ASP should send the message to an SGP
for which it is fully active for AS2 (otherwise, it will risk message loss).
When active for multiple SGP within the same SG, it is typically to loadshare
over the SGP by SLS value, or to mirror the traffic mode of the AS, such as
sending the message to an SGP for which the ASP is active in Active/Standby
mode).  When there are multiple SG via which the message can be routed, as in
your AS1 above, the selection between SG for which the ASP is active should
normally be based on SLS value (to avoid requiring multiple SG acting as STPs
to pass message over C-Links under non-failure conditions).  For multiple SG,
the availability of the intended destination via the SG should also be
considered: see the implementation note under Section 1.4.2.5.

--brian

-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/