You are here

Query for GTTT and SSN

2 posts / 0 new
Last post
FarazM
Query for GTTT and SSN

Hi Everyone,

Kind of new here, so please don't mind if I ask some absurd or stupid questions :)

We have a small problem for which we are Trying to find the solution. It involves following entities

1. HLR -> Vendor = NSN
2. STP -> Vendor = Huawie
3. USSD GW (This is us) -> SS7 stack Vendor = Tieto

Currently we are handing USSD requests coming from HLR. We have multiple nodes/machines each having it's own GT and PC.

The integration is such that HLR has our VGT [virtual GT: Virtual GT is mapped to the all USSDGW GTs , so that STP can load balance the traffic to USSGW] to which is sends the requests to STP. The STP then does the load balancing the sends the requests to USSGW with RI=SSN, this works fine till the USSD is not interactive. However when the requests are Interactive, i.e. involving multiple dialogues, the the above scenario fails because:

1. STP sends in calledPartyAddress RI= SSN and also sends GT which the VGT (not physical GT) of USSD GW
2. The USSDGW replies in callingPartyAddress with RI=GT and sends back the VGT; same one which is got from STP, does not replace it with physical GT.
3. The Next Dialogue of same session which HLR forwards to STP; STP send RI=SSN but ALSO does load balancing, and hence sends to other USSD GW, causing the dialogue to ABORT as that sessionID does not belong to that USSDGW node.

We have spoken to the Tieto support and they have said when RI=GT is sent, ONLY then the stack can return the physical GT in Callingparty Address forcing the HLR to send the next dialogue of the physical GT thus subsequent requests will land on same USSGW from which the initial response was given.

However, the operator is saying that they cannot sent RI=GT as then they cannot load Balance on STP end.

Can you some please guide here if this is possible on Huawei STP to load balance on GT rather than SSN & DPC?

Regards,
SFA

afink
afink's picture
RE: Query for GTTT and SSN

your problem is here:

>>2. The USSDGW replies in callingPartyAddress with RI=GT and sends back the VGT; same one which is got from STP, does not replace it with physical GT.

The USSDGW should reply with his very specific GT.
Alternatively the STP could do the loadsharing by replacing the virtual GT with any of the physical GT's upon reception and thus the USSDGW would get a physical GT and answer on that. The virtualGT should only be used in the first packet.

I would recommend to route on GT in this case and not on SSN because if you route on SSN, the GT is not required to be included.

-----------------------------------------------------------------
SS7 , Internet & Networking Expert.
Developed own SS7/Sigtran/GSM protocol stack