If the DID blocks are bound to each PRI you cannot say 120 Concurrent call in total.
If my first PRI_01_(038316xxxx)_IP_172.15.x.x is down then there is no call (incoming/outgoing) to this pilot number associated with this PRI or E1?
In such scenarios we ask ISP to route all 4 blocks on all 4 PRI lines so in case one PRI is down, the call will be routed ( both incommig and outgoing) through Other PRI lines.
For incoming this is handled by your ISP. if you want to test this, remove one PRI and call the block and see if it lands on your VG through other active PRI. But i dont recommend doing this and Instead of that i would recommend to talk to your ISP.
Other way is if you debug the gateway, you can see if ISP is hunting through the PRI.
Both of your questions rely to configuration on your service provider end. You need to check with them how they route calls to your circuits. If they route calls to any number to all of your circuits you would have the ability to get the number of calls that equate to the total number of channels of your the combined E1s. However if they send some numbers to only one E1 circuit then the total amount of calls to this number is limited to the number of channels that this circuit has and you would not get any calls if that specific circuit is non operational.
