Building Telephony Systems with OpenSIPS - Second Edition

Summary

In this chapter, we explained the different NAT types and devices. Then, you learned about the available methods to traverse NAT. After discovering the pros and cons of the different methods, we suggested the use of STUN and detected cases where STUN does not work properly and so switched to the traversal of UDP over Relay NAT. We also saw what algorithms are in use to traverse NAT and its corresponding code. Finally, we published the entire call flow for a call behind a NAT device. In the next chapter, we are going to cover phone features implemented as SIP services.