Why SCCP and MTP3 both are considered as network layer?

Question

I see a high number of SCCP CREFs(Connection Refusal) in the logs. None of the calls are successful as observed from PM Counter statistics. The application has refused with the cause 7.From ITU-T Q.713 it indicates 00000111 network resource QoS unavailable/transient.

SCCP stack has logged unsolicited status indication with the event "Connection request failure" and cause "connection threshold exceeded".

Please let me know,

1.) What does this "connection threshold exceeded" indicate? Is this the SCCP connections ? Is it configurable ?
2.) What does "network resource" QoS unavailable/transient mean" ? Can "connection threshold exceeded" be the cause behind "network resource QoS unavailable/transient".

Please give me your valuable inputs on how to debug this further. Whether congestion can be the reason?

Answer 1

Both SCCP and MTP3 does the routing. MTP does the point code base routing where as SCCP does PC-SSN or GT based routing. So in short both the layers are doing the routing hence both are considered as network layer.

Answer 2

On behalf of Bart -
I find it a very strange question to ask.. No one would ask why IPv6 and IPv6 are both considered a network layer. This is why they were made for.

I believe the question should be what is the difference between SCCP and MTP3. So the SCCP was developed with MTP3, obviously after the MTP was developed. MTP was designed to carry circuit call related signaling, where with the SCCP it is capable to handle the noncircuit as well.

The main difference I would say is that SCCP is doing end to end routing where MTP3 is doing point to point routing. While MTP L3 can only identify and distribute messages to specific points and user parts, SCCP can route messages to specific applications that reside at signaling points.

On top of that SCCP is OSI Layer 3 compliant, in theory it can be transmitted over any OSI-compliant network.