The final test

E1 Which of the three stages does TS 23.501 belong to?

• Stage 2, the architecture
• Stage 3, the protocols
• Stage 1, the requirements

E2 A reference is written without a date or version number. Which version applies?

• The latest version of that document in the same release as TS 23.501
• The version current when TS 23.501 was first published
• Any version, at the implementer's choice

E3 How may two control plane functions in the 5G core talk to each other?

• Either, depending on the vendor
• Only over a point-to-point reference point
• Only over a service-based interface

E4 The AMF carries session management messages between the phone and the SMF. What does it do with them?

• It passes them on without acting on them
• It rewrites them into a service-based API call
• It reads them and decides which UPF to use

E5 Why does the same piece of behaviour need two different reference point names when it sits between two different pairs of functions?

• Because 3GPP ran out of short names
• Because the protocol differs on each
• Because a reference point is named after the pair it joins, not after what it does

E6 What has to happen before a function can be found through the NRF?

• It has to be listed in the DNS
• It has to register its NF profile with the NRF
• It has to be named in the subscription data

E7 Why does a phone almost never send its SUPI to the network?

• Because the SUPI is only created after registration
• Because the SUPI is too long for a radio message
• Because the UE provides the SUPI in concealed form instead

E8 What sits directly under NGAP on N2, between the access network and the AMF?

• GTP-U
• TCP
• SCTP

E9 A registered phone is in your pocket overnight, sending nothing. Which pair of states is it in?

• RM-DEREGISTERED and CM-IDLE
• RM-REGISTERED and CM-IDLE
• RM-REGISTERED and CM-CONNECTED

E10 A device is in CM-CONNECTED with RRC_INACTIVE and a packet arrives for it. Who pages it?

• The AMF, over N2
• The NG-RAN, inside the RAN Notification Area
• Nobody — the device is unreachable until it speaks first

E11 A phone registered on the same network over both radio and Wi-Fi wants a multi-access session. How many establishment requests does it send?

• Two, one over each access
• Three — one per access and one to bind them
• One, over either access

E12 Which attribute of a PDU session may change while the session is alive?

• The SSC mode
• The S-NSSAI of the serving PLMN
• The DNN

E13 Which N4 rule decides whether a packet is forwarded, dropped or buffered?

• The Packet Detection Rule
• The Forwarding Action Rule
• The QoS Enforcement Rule

E14 What is the finest thing 5G can give a separate quality treatment to?

• A PDU session
• A QoS Flow
• A single IP packet

E15 Clause 5.14 of TS 23.501 is one sentence. What does it say?

• That the AMF decides all policy
• That policy control is out of scope for the 5G System
• That the policy and charging control framework is defined in TS 23.503

E16 Where are the authentication methods and key derivations of 5G defined?

• In TS 23.502, with the procedures
• In clause 5.10 of this document
• In TS 33.501

E17 How many S-NSSAIs may the Allowed NSSAI carry in signalling between the device and the network?

• As many as the subscription holds
• Sixteen
• Eight

E18 In Local Break Out, where does the packet leave the mobile network for the internet?

• In the home network, always
• In the visited network — the anchor and its SMF are both there
• Wherever the phone asks for

E19 What does the N26 interface join together?

• The MME in the 4G core and the AMF in the 5G core
• The 4G Serving Gateway and the 5G User Plane Function
• The 4G radio network and the 5G radio network

E20 Why does the core pick a user plane function close to the device for edge computing?

• To shorten the end-to-end delay and take load off the transport network
• To save IP addresses
• Because the radio cannot reach a distant server