Cisco Certified ExpertSS7 Upper Layer Protocols
To this point, this chapter has covered much of what makes up the infrastructure of the SS7 network. It has detailed the transporting functions that allow for communication between SS7 nodes. Now take a look at what makes your calls work. Within the upper layer of the SS7 stack (Layer 4), there are several protocols that you can use for call messaging functions. DUP, TUP, National User Part (NUP), and ISUP are all used for call messaging.
DUP and TUP are legacy protocols that were used prior to the latest messaging advances created by ISUP. Although this chapter does discuss them, it is important to remember that they are not typically used within the SS7 network. However, some countries, such as China, still employ them to some degree.
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