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Very basic queries of GTT and related stuff

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Very basic queries of GTT and related stuff

Hi all.

I am trying to understand how a SS7 request reaches its destination, in an environment which may contain different permutations and combinations of Route-on-GT and Route-on-SSN.

I will put in my queries, with as much details of the setup as possible.

Case 1)
At node "Node1", the "Called-Party-Address" of a SCCP packet has "Route-on-GT".
Since "Route-on-GT" is present, GTT happens.
After GTT, the "Called-Party-Address" of the same SCCP packet at the same "Node1" is converted to the one with "Route-on-SSN"; and next point-code, say "Node2" is added in the SCCP packet. Also, "Node2" is added at the MTP3 layer, which would serve as the destination of the packet.

So, my queries are ::

In the above case, the packet will be sent to "Node2" (since "Node2" was added in the MTP3 layer); and then at "Node2", the packet/request routed to the proper application (since "Route-on-SSN" is present in the "Called-Party-Address")?

When the GTT took place at "Node1", was it necessary for "Node2" to be filled as the DPC in the Called-Party-Address (since really all that was needed was the DPC information to be passed to the MTP3 layer)?

I will be grateful to confirmations/rejections of my understandings; I will post further queries based upon the learnings from the answers to the above queries.

Looking forward to some pointers.

Thanks and Regards,

Edited by: AjayGarg on 03/10/2014 - 10:47
afink's picture
Re: Very basic queries of GTT and related stuff

1) is correct
for 2) well every entity in your setup needs to be addressable. So if node1 wants to send any packets to node2, it needs to know the address of it. Even if it knows the link of node2 and would send the packet, then node2 wouldnt know if the packet is for node2 itself or maybe node 3 behind node 2.
On Layer3, all packets are routed by pointcode
On Layer4 packets are routed by GTT from node to node or by SSN to a layer5 above SCCP.

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