Roaming MT Call Flow

Hi Winmeeners,

Here i am going to explain about Roaming MT Call Flow. Roaming MT Call Flow is nothing but, when user is in roaming how he is receiving calls. Now we are going to see both MT (Mobile terminated) call flow and Roaming MT call flow.

MT Call Flow:

A and B are two users of one network.  A party is calling to B party. It is the MT call for B party.

The below diagram explains the MT Call flow.

1. When A Party calling to B party, GMSC sends SRI request to HLR.
2. HLR requests Provide roaming number in B Party MSC/VLR.
3. MSC/VLR sends Mobile station roaming number to HLR.
4. HLR sends SRI response to GMSC.
5. Finally GMSC connect the calls to B Party MSC/VLR.

Roaming MT Call Flow:

A and B are two users of one network.  B Party is in roaming. A party is calling to B party. It is the Roaming MT call for B party.

The below diagram explains the Roaming MT Call flow.

1. When A Party calling to B party, GMSC sends SRI request to HLR.
2. HLR knows B number is in Roaming, So HLR sends TCSI flag to GMSC (or A Party MSC)
3. GMSC sends MT Forward IDP to B Party SCP for billing purpose.
4. If B Party have sufficient balance. SCP sends IDP response to the GMSC.
5. GMSC sends TCSI suppressed SRI request to HLR
6. HLR requests Provide roaming number from B Party MSC/VLR.
7. MSC/VLR sends PRN Response – Mobile station roaming number to HLR.
8. Then HLR sends SRI response to GMSC.
9. Finally GMSC connects the call with B Party MSC/VLR.