Interconnect HLRs

Hi,Ace.
If an HLR's have Sigtran you can connect it to Core as you wish. It can be direct connections, connections over GMSC, over STP etc.
But rules are defined by operator network, i.e. CN arhitecture. If all nodes of operator are already connected through STP, HLRs wiil be connected the same way.

Being a critical component in the Core network(CN), it is always recommended for the HLR to be connected with an STP.
Below are some of the reasons:-

1) If the no of Network elements are higher in numbers(e.g if the network is having many NEs in the order of ~10 MSCs, Few more SGSNs, Several IN/SCPs etc.), then without STP, the HLR has to establish a direct link with each of the nodes (i.e. MSC, MSS, SMSC, IN/SCP etc.) which requires Sigtran configuration for so many direct nodes and may become tough to manage(i.e. traffic routing etc.) over a period of time.

2) Certain STPs(actually many) have features like SS7 firewall and SCCP filtering based on CallingParty/CalledParty etc.
From this point of view, if HLR is connected via STP, then STP can perform all the necessary filtering to avoid the unnecessary messages to reduce the load in the HLR end.
[i.e. due to messages from the networks(Point codes, GTs) which are not supposed to send any signaling traffic towards the specific Network(HLR)].