Hi hlr.bless,

Following MAP messages flow in two networks, when a subscriber sends a message to another subscriber B, served by different network:
1. First message will be submitted to home SMSC of subscriber “A” (SMSC of Network A). MAP message from serving MSC to SMSC : MO Forward SM
2. SMSC of network A sends “Send Routing Info for SM Request” to HLR of network B. MAP message from SMSC A to HLR B : Send Routing Info For SM
3. HLR of Network B responds “Send Routing Info for SM” to SMSC of network A with Network node (serving MSC of subscriber B) and IMSI of subscriber B.
4. SMSC of network A forwards message to serving MSC (Network Node Address, received in Send Routing Info Response ) of subscriber B. MAP message from SMSC A to Serving MSC : MT Forward SM.
5. Serving MSC delivers message to Subscriber B and sends acknowledgement to SMSC of Network A (MT Forward SM Acknowledgement).

Thanks
Shri

Hi hlr.bless,

You are absolutely right and your understanding is correct. In my response of basic SMS flow, I did not involve all the network nodes coming in between SMSC, HLR and MSC. I only included originating and destination network nodes. Infect, different network nodes (HLR, SMSC, MSC and other VAS nodes) in a network connects each other through GMSC or STP for signalling purpose. So, even in same network HLR communicates to SMSC through GMSC or STP. Similarly, from one network to another network communication happens through GMSCs/STPs as you mentioned. In case of International Networks, communication happens from one network of a country to another network of another country through IGPs (International gateway providers). In this case, message from originating node of a network “A” first goes to GMSC/STP of network “A” followed by IGP of network “A”, IGP of network “B”, GMSC/STP of network “B”. Reverse message also follow the same format. Here IGP is either STP or GMSC. Hope this clarifies your question.

Thanks
Shri