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think that the short message originated from circuit switched/packet switched network(legacy network) has to terminate in the same network. if there is an IP-SM-GW, does the short message have to go through the IP-SM-GW anyway?

anonymous
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2 Answers2

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In general, IP-SM-GW is a kind of application server that acts as a bridge between 2G/3G networks and IMS. It helps to provide an interconnection at transport level and service level between 2G/3G and LTE by converting the SMS to SIP (or vice versa).

It determines the domain (CS/PS or IMS) for delivery of SMS. That is, the IP-SM-GW shall help in checking whether delivery can happen via IMS for the particular user. If the user is an authorized user, it shall extract the Short Message (SMS-SUBMIT) and forward towards SMS-SC via SMS-IWMSC. If it is an un-authorized user, the IPSM-GW shall not forward the message.

Hence, it is normally used by operators to gain the benefit of its interconnection functionalities unless the operator has a different light weight node, flow or requirement.

In a typical deployment architecture, the IPSM-GW interacts with IMS core, HSS, OCS, CDF and SMS-GMSC/SMS-IWMSC. The message is routed to the SMS-SC for delivery to the SMS-based user or the message is received from the SMS-SC of an SMS-based UE for delivery to an IP-based UE.

If SMS is sent from IMS towards legacy domain, it shall check that the sender and receiver addresses are correct in the SIP headers & service authorization. If SMS is sent from legacy domain towards IP based domain, it shall translate the MSISDN/IMSI to TEL URI or to SIP URI.

Transport Level Interworking : At transport level interworking, it helps in communication with the UE using IMS messaging as transport while maintaining the format and functionality of the Short Message and also to carry the SMS status messages as encapsulated bodies of IMS messages..

LTE to GSM -> The IP-SM-GW should interpret the SIP message that it receives along with the the Relay PDU by parsing the message in order to recover the type of SMS PDU that it is sending.

GSM to LTE -> The IP-SM-GW should interpret the SMS-PDU and populate it with necessary SIP headers and add the Relay PDU in the SIP payload.

Service Level Interworking : At service level interworking, it helps to determine whether to perform the transformation of the message format or not & realize the transformation accordingly.

LTE to GSM -> The IP-SM-GW should realize the transformation by translating the SIP headers in to SMS-PDU and placing of payload of SIP message in SMS-PDU(TP-User-Data). GSM to LTE -> It will extract the info as in above case.

Community
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Karthik Balaguru
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Operators may choose to design their networks so that message all go through some nodes if they had some driver for this, but it is definitely possible to send SMS messages within a network and between SS7 networks without going through an IP to SS7 gateway, if that is your question.

Mick
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