5 General issues

29.3053GPPInterWorking Function (IWF) between MAP based and Diameter based interfacesRelease 17TS

5.1 Message Routing Mechanism

The principles for IWF message routing are:

– For the same user, the messages shall go to and come back through the same route with the same IWF(s) for the duration of a MAP dialog.

– To ensure the correct message routing for the interworking scenarios, the IWFs in the network shall be able to map the SS7 number and the Diameter identity of the MME/SGSN 1-to-1. This may be achieved by static or dynamic configuration.

– To ensure the parallel multiple request messages can get their correct response messages, the IWFs in the network shall be able to map the MAP Dialogue Id and the Diameter Session Id 1-to-1.

The overall message routing mechanism for the scenario is described as below:

1. The MME/SGSN may not be able to identify whether there is an IWF or not on the route to an HSS. The routing of the first message from the MME/SGSN to the IWF/HSS is the same as for a normal Diameter message routing. If the MME/SGSN knows the address/name of the IWF/HSS for a certain user, both the Destination-Realm and Destination-Host AVPs shall be present in the request. Otherwise, only the Destination-Realm AVP shall be present and the command shall be routed to the next Diameter node based on the Diameter routing table in the client.

When the MME/SGSN receives an answer message from the IWF/HSS, it should store the identity of the IWF/HSS for each IMSI for future reference to be able to send messages for the same IMSI.

2. The IWF shall assign an SS7 number for the Diameter node MME/SGSN and shall assign a Diameter identity for the SS7 node HSS. This may be achieved by static configuration or dynamic assignment when the first signalling exchange occurs between the Diameter/SS7 nodes and the IWF. The IWF shall maintain a mapping table (address mapping table) for the assignment relationship.

When a Diameter message reaches the IWF to set up a new Diameter session, the IWF(s) shall allocate a MAP Dialogue Id for the Diameter session. The IWF(s) shall maintain a mapping table (session mapping table) between the MAP Dialogue Id and the Diameter Session Id.

The IWF shall then process messages as described below:

a. When the IWF receives a Diameter message from a Diameter node, it shall map the Diameter message to a MAP message. It shall obtain a MAP Dialogue Id from the Diameter Session Id in the received message according to the session mapping table. The IWF shall obtain the source/destination SS7 Number from the source/destination Diameter Identity in the received message according to the address mapping table.

b. When the IWF receives an SS7 message from an SS7 node, it shall map the MAP message to a Diameter message. It shall obtain the Diameter Session Id from the MAP Dialogue Id in the received message according to the session mapping table. The IWF shall obtain the source/destination Diameter Identity from the source/destination SS7 Number in the received message according to the address mapping table.

3. When the HSS/HLR receives the first message from IWF/SGSN, the HSS/HLR shall record the SS7 number of the source for future message handling.

5.2 Void

5.3 Security Consideration for IWF

To support the full EPS-AKA security level for the related IWF scenarios, the Pre Rel8 HLR shall be upgraded so that E-UTRAN authentication vector requests from nodes serving E-UTRAN can be identified. The detailed mechanism is described in 3GPP TS 33.401 [2].