or data traffic to flow is established. 17. The SMF then sends a PDU Session Update SM Context Response to the AMF as an acknowledgment of Step 15. 18. The SMF may send an optional PDU Session SM Context Status Notify (release). If any of the steps after Step 5 have failed, the SMF informs the AMF and tells it that it has released any resources that it had allocated to the UE PDU session. 19. The SMF sends an IPv6 Router Advertisement to the UE via the UPF in case the Session type is IPv6 or IPv4v6. After this step, the uplink path of the traffic is established. 20. If the PDU Session establishment fails after Step 4, the SMF will unsubscribe from notifications about modifications to the UDM and will also deregister the given PDU Session. This concludes the PDU establishment procedure. After this procedure, the user device can access the network resources, browse data, and surf the internet. We learned about the different types of PDU Establishment procedures in detail in Chapter 6, which showed us not only how a UE attaches for data calls but also voice calls and Wi-Fi. All these messages are transported over HTTP/S and TCP. Hence, the underlying IP backbone network must be built robustly. If there is a delay or loss of packets in the backbone, messages would be retransmitted and timeouts in the TCP window would occur. This might lead to a signaling storm and high call failure rates. 5G SA network design fundamentals Designing a macro network Designing a macro (public) 5G network entails planning and architecting its subcomponents, as listed here: Data center design: One of the most defining aspects of the usability and reliability of a network is its data center design. There are many ways to design a data center. One of the popular high- level design templates is shown here: ((g)) ((g)) ((g)) ((g)) North Zone West Zone East Zone Central Data Center ((g)) ((g)) South Zone ((g)) ((g)) ('A') Figure 11.10 - Data center layout in a network In the preceding diagram, the geographic area where the network is supposed 