Signaling System 7


SS7/C7 is a complex and important part of the PSTN architecture today. For packet voice to truly be an option for service providers, packet telephony and the SS7 network must integrate.

This chapter covered in detail the four layers of SS7. It also covered the detailed message flows of a common call in SS7.

The details in this chapter can help those who are deploying SS7 and packet voice networks to better understand how SS7 works. Also, this chapter shows how many details must be covered for packet telephony and the PSTN to successfully integrate. Some of the key areas in which VoIP must inter-work with SS7 include:

  • Physical link interconnection of MTP1

  • Signal unit termination and acknowledgments of MTP2

  • L4 user data extraction from MSUs (for ISUP and TCAP)

  • L4 protocol support for call completion- and transaction-based services (ISUP and TCAP, respectively)

These key areas must be addressed for VoIP networks to fit seamlessly into or interface to the PSTN.

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