An interesting scenario here. Basically here is what happened:
We have 4 cisco ITPs connected to several nodes via SIGTAN and TDM in our network. The ITP has logically been divided into 3 SGs (instance 0,1 and 2).
In this particular case we added a fourth instance (instance 4) for a test node, and we all know that by default, the Network Appearance is the same as the instance number. in this case any AS configured instance 4 had a NA of 4. thing is, this instance (4) has to comminicate with a HLR operating in instance 1. thus did not work. so I changed the NA on the AS in instance 4 to 1 and walaa! it worked! , in so doing i messed up whatever was in instance 1 NA 1. Funny enough a wireshark trace showed me it was now expecting INSTANCE 4 NA 1, and not INSTANCE 1 NA 1.
I get that the NA should be unique so that whatever is configured under a particular instance knows to what SS7 network it belongs to. What I dont understand is this: Each instance is a seperate SG and should NOT interfere with another one. So why did SG (instance 4) interfere with instance 1?
If anyone can help to shed some light onto this, i would be grateful.