Every question of this course

Q1.1 Which spelling of the group's name appears in front of every one of its document numbers?

• C1
• CN1
• CT1

Document numbers run C1-262074, C1-261459 and so on. The catalogue of specifications also uses C1, while the meeting calendar writes "3GPP CT 1" and the group's own long name starts CT1. CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1)

Q1.2 How many CT1 office holders currently have no end date on record?

• Four
• Forty-four
• Two

A chair, two vice chairs and a secretary. Forty-four is the number of terms of office in the whole file, current and past together. 4 CT1 office holders have no end date on record

Q1.3 What was CT1 before it was CT1?

• A subgroup of RAN2
• A group called CN1, which closed and became CT1
• A study item inside SA2

The group grew out of CN1. The old name still shows in the long form the tooling uses, which ends "ex-CN1". CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1)

Q1.4 When did the earliest CT1 meeting on record start?

• 1999-01-11
• 2005-04-25
• 2017-10-01

The meetings database has 184 CT1 meetings, and the earliest of them started on 25 April 2005. Anything before that is not in this data. the earliest CT1 meeting on record started 2005-04-25

Q1.5 Which of these does TS 24.501 say it applies to?

• The base station and the UE only
• Every network function in the 5G core
• The UE, the AMF, the SMF and the PCF

The scope names exactly four — the UE, the access and mobility management function, the session management function and the policy control function. §1

Q2.1 What does the reference list of TS 24.501 call TS 23.501?

• Service requirements for the 5G system; Stage 1
• System Architecture for the 5G System; Stage 2
• Procedures for the 5G System; Stage 3

The reference list writes each document's full title. TS 23.501 is stage 2, TS 23.502 is the other stage-2 document, and TS 22.261 is the stage-1 one. §2

Q2.2 Where does TS 24.501 say the sequences of its elementary procedures can be found?

• In TS 23.502
• In TS 38.331
• In its own clause 5

The overview says complete NAS transactions consist of specific sequences of elementary procedures, and that examples of such sequences are in TS 23.502. The elementary procedures themselves are TS 24.501's. §4.1

Q2.3 What does stage 3 add that stage 2 does not have?

• The business case for the feature
• The list of network functions
• {'The bits': 'which octet carries which field, and what value means what'}

A stage-3 document defines the message format down to the octet and the bit, as the message-type table and the message-format clause do. A stage-2 document names functions and shows sequences. §9.1.1

Q2.4 Between which two points does TS 24.501 say the NAS sits?

• The UE and the AMF
• The AMF and the SMF
• The UE and the base station

The overview says the NAS forms the highest stratum of the control plane between the UE and the AMF, at the reference point N1, for both 3GPP and non-3GPP access. §4.1

Q2.5 Which of these titles from CT1's own list ends in "Stage 3"?

• TR 24.860, the study on the 6G NAS protocol
• TS 24.007, general aspects of layer 3 signalling
• TS 24.369, the Ambient IoT NAS protocol

TS 24.369 is a stage-3 protocol specification. A TR is a study, not a protocol, and TS 24.007 sets out general aspects rather than one protocol. TS 24.369

Q3.1 How many CT1 specifications are active?

• 199
• 237
• 229

237 are listed against the group and 8 of them are no longer active, leaving 229. Of those 229, 199 are technical specifications and 30 are technical reports. 229 active CT1 specifications

Q3.2 Which specification has attracted the most CT1 change documents over the whole record?

• TS 24.501, at 15623
• TS 24.229, at 3413
• TS 24.301, at 5422

TS 24.501 leads the all-time count with 15623 against 5422 for the next document. Over the last twelve months alone the order changes — TS 24.301 edges ahead with 499 against 498. 15623 CT1 documents change 24.501 (Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3), over the whole record

Q3.3 How many of the 229 active CT1 specifications sit in the 24 number series?

• 16
• 175
• 149

175 are in the 24 series and 16 in the 23 series. 149 is a different number entirely — the count of active specifications that have a Rel-18 version. 175 active CT1 specifications in the 24 series

Q3.4 What is the difference between a TS and a TR?

• A TS is newer, a TR is retired
• A TS tells you what to build, a TR studies a question
• A TS is CT1's, a TR belongs to the parent group

A technical specification is the buildable document; a technical report studies a question. CT1 has 199 of the first kind and 30 of the second, and both are its own. 30 active CT1 technical reports (TR)

Q3.5 How many active CT1 specifications have a Rel-20 version?

• 229
• 31
• 154

31 have a Rel-20 version, against 154 for Rel-19 and 149 for Rel-18. A Release is an edition of the whole system, and only a fraction of the list has been carried into the newest one so far. 31 active CT1 specifications have a Rel-20 version

Q4.1 What are the two protocols defined inside TS 24.501?

• EPS and 5GS
• 5GMM and 5GSM
• NAS and RRC

5GS mobility management runs between the device and the AMF; 5GS session management runs between the device and the SMF. Both live in the same document and both are called NAS. §1

Q4.2 If a session management message is piggybacked on a mobility management message and the session part fails, what happens to the mobility part?

• It is retried automatically
• It fails too, because they travel together
• It can still succeed — its success does not depend on the piggybacked part

The document says in as many words that the success of the 5GMM procedure is not dependent on the success of the piggybacked 5GSM procedure. The two run in parallel. §4.2

Q4.3 When may a device start a session management procedure?

• At any time after the radio connection is up
• Only when a 5GMM context exists and secure exchange of NAS messages has been started
• Only during registration

Session management procedures can be performed only if a 5GMM context has been established and the AMF has started the secure exchange of NAS messages. Mobility management comes first, always. §6.1.1

Q4.4 What is an N1 NAS signalling connection made of?

• A single radio bearer between the device and the base station
• An access stratum connection joined to an NG connection over the N2 reference point
• A TCP connection between the device and the AMF

The definition calls it the concatenation of an access stratum connection and an NG connection via the N2 reference point. The NAS does not have a link of its own; it borrows two. §3.1

Q4.5 Besides mobility and session management, what third thing does the scope of TS 24.501 say the document specifies?

• The charging records for a session
• The UE policy delivery service between the device and the PCF
• The radio measurement reports

The scope names it explicitly, for both 3GPP and non-3GPP access, and the procedures for it sit in an annex rather than in the main clauses. §1

Q5.1 How many types of 5GMM procedure does the document distinguish?

• Three — common, specific, and connection management
• Five, one per message pair
• Two — network-initiated and UE-initiated

The split is by how a procedure can be started, not by who starts it. Common procedures can always run in connected mode; specific procedures are limited to one at a time per access; connection management covers service request, paging and notification. §5.1.2

Q5.2 In which state has no 5GMM context been established, leaving the device unreachable?

• 5GMM-REGISTERED-INITIATED
• 5GMM-NULL
• 5GMM-DEREGISTERED

In 5GMM-DEREGISTERED the location is unknown to the network. In 5GMM-NULL 5GS services are disabled altogether, and 5GMM-REGISTERED-INITIATED means a registration is already under way. §5.1.3.2.1

Q5.3 How many main 5GMM states does the network side have?

• One per PDU session
• Six, the same as the device
• Four

The network has DEREGISTERED, COMMON-PROCEDURE-INITIATED, REGISTERED and DEREGISTERED-INITIATED. The device has six, because it also has REGISTERED-INITIATED, SERVICE-REQUEST-INITIATED and NULL. §5.1.3.2.3

Q5.4 What does the error handling clause say about the order of its own subclauses?

• They may be applied in any order
• They shall be applied in order of precedence
• Only the first one that matches applies

The clause states plainly that clauses 7.1 to 7.8 shall be applied in order of precedence, so a message failing an early check never reaches the later ones. §7.1

Q5.5 Which annex of TS 24.501 records every version the document has ever had?

• Annex D
• Annex F
• Annex C

Annex F is the change history. Annex C is about storing mobility management information, and Annex D holds the UE policy delivery service. §Annex F

Q5.6 What does the 5GS update status value 5U2 mean?

• Roaming is not allowed
• The last registration attempt was successful
• The last attempt failed procedurally, for example no answer came back

5U1 is UPDATED, 5U2 is NOT UPDATED — a procedural failure such as no response or reject arriving — and 5U3 is ROAMING NOT ALLOWED, where the network did answer and the answer was negative. §5.1.3.2.2

Q6.1 Who can start a registration procedure?

• Only the device
• Only the AMF
• Either side

The document says the registration procedure is always initiated by the UE. De-registration, by contrast, can be started by either side. §5.5.1.1

Q6.2 What happens to a PDU session when its radio and network resources are released?

• The session is torn down and has to be established again
• The session can remain established
• The device is de-registered

The document states that PDU sessions can remain established even when the resources between the device and the SMF are temporarily released. That is what makes a service request possible later. §6.1.1

Q6.3 Which of these is a PDU session type in TS 24.501?

• Bluetooth
• Ethernet
• MPLS

The five types are IPv4, IPv6, IPv4v6, Ethernet and Unstructured. For an Ethernet session the core network allocates neither a MAC nor an IP address to the device. §6.2.2

Q6.4 How many primary authentication methods does the document define, and must a device support them?

• Three, and the network picks one
• One, and it is mandatory
• Two, and both the device and the AMF shall support both

The two are the EAP based method and the 5G AKA based method, and the document says the UE and the AMF shall support both. Neither side may offer only one. §5.4.1.1

Q6.5 Which timer controls periodic registration update in the device?

• T3510, 15 seconds
• T3512, default 54 minutes
• T3502, default 12 minutes

T3512 is the periodic timer; when it expires the device starts a registration for mobility and periodic registration update. T3510 guards a registration in flight and T3502 spaces out attempts after repeated failure. §10.2

Q6.6 What does the SUCI conceal?

• The SUPI, the permanent subscription identifier
• The device's IMEI
• The network's identity

The identification procedure describes the SUCI as a privacy preserving identifier containing the concealed SUPI. The IMEI and IMEISV are formats of the PEI, a separate identifier. §5.4.3.1

Q7.1 What is in the first octet of every 5GS NAS message?

• The sequence number
• The message type
• The extended protocol discriminator

Bits 1 to 8 of the first octet carry the extended protocol discriminator, which says whether this is a mobility management or a session management message. Everything else depends on knowing that first. §9.2

Q7.2 A 5GMM message arrives with the security header type set to 0000. What is it?

• An integrity protected message whose code is missing
• A malformed message to be discarded
• A plain message, not security protected

The document says a message received with security header type 0000 shall be treated as a plain, not security protected message, and that a sender of an unprotected message shall encode it that way. §9.3

Q7.3 How long is the message authentication code in a security protected NAS message?

• Four octets
• Sixteen octets
• One octet

The content table of the security protected message gives it four octets, after one octet of protocol discriminator and a half octet each of security header type and spare, and before one octet of sequence number. §8.2.28

Q7.4 What does a receiver send back when it gets a message type it does not recognise?

• A status message with cause #97, message type non-existent or not implemented
• A registration reject
• Nothing — it ignores the message

The device shall return a 5GMM STATUS or 5GSM STATUS with cause #97. Cause #98 is the neighbouring case, a message type that exists but does not fit the current protocol state. §7.4

Q7.5 Can the same information element identifier mean two different things?

• Yes — the same IEI can be used for different element types in different messages of the same protocol
• Only in the session management protocol
• No, identifiers are unique across the document

A note in the message definitions clause says so directly. An identifier is only meaningful inside the message it appears in. §8.1

Q7.6 What does the sequence number field of a security protected message carry?

• The number of information elements in the message
• A counter that restarts at every procedure
• The eight least significant bits of the NAS COUNT

The full NAS COUNT is longer; only its lowest eight bits travel, and both sides reconstruct the rest. The same eight bits also appear in the transparent containers used at handover. §9.10

Q8.1 What does the second digit of a 3GPP version number mean?

• The number of change requests in that version
• The Release the document belongs to
• It is incremented for all changes of substance

The Foreword sets out x.y.z. The first digit says how far through approval the document is, the second is incremented for changes of substance, and the third only for editorial changes. §Foreword

Q8.2 What does a first digit of 3 or greater mean in a 3GPP version number?

• The document has been presented for information
• The document is in its third Release
• The document has been approved and is under change control

1 means presented for information, 2 means presented for approval, and 3 or greater means an approved document under change control. Version 20.0.0 of TS 24.501 is therefore an approved one. §Foreword

Q8.3 How many of the 4235 CT1 documents of the last twelve months were change requests?

• 2835
• 4235
• 563

2835 were change requests and 563 were pCRs, which change a document still being drafted rather than one already published. 2835 CT1 documents of kind 'CR' uploaded on or after 2025-08-04

Q8.4 What was the outcome word on the largest group of documents at meeting C1-161?

• postponed, with 70
• agreed, with 174
• revised, with 259

More documents were revised than agreed. A revision comes back with a new number, so one problem can occupy several document numbers before it settles. 259 documents came out of C1-161 as 'revised'

Q8.5 What is in the "Tdoc" column of the rows that produced version 20.0.0 of TS 24.501?

• Document numbers beginning CP-
• The change request numbers only
• Document numbers beginning C1-

The change history records a CP- number and the meeting CT#112 for those rows. CT1's own C1- numbers appear in the early rows, from when the document was still a draft. §Annex F

Q9.1 How many documents were put to meeting C1-161?

• 174
• 617
• 4235

617 documents at one meeting. 174 is how many of them came out agreed, and 4235 is the whole group's document count for the year. 617 documents were put to C1-161

Q9.2 What is the state of the C1-161 meeting report?

• Approved
• Draft
• Not written

The C1-161 report is a draft, so its numbers can still change. The C1-160 report is approved. CT1 meeting report C1-161

Q9.3 How many people are listed as taking part in C1-161?

• 415
• 165
• 172

172 at C1-161 and 165 at C1-160. 415 is a different number — the organisations that filed at least one document across the whole year. 172 people are listed as taking part in C1-161

Q9.4 How many new or revised work items were agreed at C1-161?

• Five
• Nine
• Nineteen

Nine at C1-161, against five at the meeting before it. Nineteen is the number of documents withdrawn at C1-161. 9 new or revised work items were agreed at C1-161

Q9.5 Where is CT1 meeting C1-164 planned to be held?

• Calgary
• Valletta
• Prague

C1-162 and C1-163 are both planned for Prague; C1-164 is Calgary. Valletta is where C1-160 was held in April 2026. C1-164

Q10.1 Which group received the most outgoing liaison statements from CT1 in the last twelve months?

• RAN2, with 44
• CT4, with 8
• SA2, with 19

RAN2 is the busiest destination, with 44 letters against 19 to SA2. In the other direction SA2 is the busiest source, with 39 incoming letters against RAN2's 15. 44 outgoing liaison statements to RAN2 in the twelve months to 2026-08-04

Q10.2 Over the whole record, has CT1 sent more letters than it has received?

• No — 2507 sent against 3002 received
• The counts are equal
• Yes — 3002 sent against 2507 received

3002 out and 2507 in over the whole record. In the last twelve months the balance runs the other way — 108 out and 135 in. 3002 CT1 documents of kind 'LS out' over the whole record

Q10.3 A group does not appear in the liaison tables. What does that mean?

• Only that it is not among the four busiest in that direction
• Its letters were not counted
• It exchanged no letters with CT1

The register carries the four busiest partners in each direction and no more. Absence from the table is not a zero, and no number may be inferred for a group that is not listed. 5 outgoing liaison statements to SA1 in the twelve months to 2026-08-04

Q10.4 What does TS 24.501 say a device does when it is idle over 3GPP access and needs to send an initial NAS message?

• It sends the message straight to the AMF
• It asks the lower layer to establish an RRC connection
• It waits to be paged

The device asks the lower layers, and only when they report the connection is up does it consider the N1 NAS signalling connection established. The NAS depends on a layer it does not specify. §5.3.1.1

Q10.5 Where does TS 24.501 send a reader for the security requirements behind primary authentication?

• TS 33.501
• TS 23.502
• Its own clause 4.4

The purpose clause says the procedure provides keying material as specified in TS 33.501, and the security mode control clause points at that document again for restrictions on running procedures at the same time. §5.4.1.1

Q11.1 How many named work items received a CT1 document in the last twelve months?

• Six
• 219
• 415

219 distinct work item names. Six is the number the register carries a count for, and 415 is the number of organisations that filed something. 219 named work items received CT1 documents in the twelve months to 2026-08-04

Q11.2 Which work item took the most CT1 documents in the year?

• AmbientIoT-CT, with 420
• TEI19, with 200
• FS_6G_NAS_CT, with 170

AmbientIoT-CT leads with 420 against 200 for TEI19, the second item. The 6G study item is fifth with 170. 420 CT1 documents for the work item AmbientIoT-CT in the twelve months to 2026-08-04

Q11.3 What does the register say the name "MINT_Ph2" stands for?

• Mobile Internetworking, phase 2
• Minimization of service interruption, phase 2
• Nothing — it holds work item names exactly as documents spell them

The register carries the string and no expansion of it. TS 24.501 separately defines MINT in its own text, which is where an explanation has to come from. 172 CT1 documents for the work item MINT_Ph2 in the twelve months to 2026-08-04

Q11.4 What does TS 24.501 say MINT aims to enable?

• A device to minimise the time it spends registered
• A device to keep a session alive across a handover
• A device to obtain service from a PLMN offering disaster roaming services

The clause says MINT aims to enable a UE to obtain service from a PLMN offering disaster roaming services when a disaster condition applies to the UE determined PLMN with disaster condition. §4.24

Q11.5 Which specification took the third most change documents in the last twelve months?

• TS 24.379
• TS 24.229
• TS 24.369, the ambient IoT NAS protocol

TS 24.369 took 430, behind TS 24.301 with 499 and TS 24.501 with 498. It does not appear in the all-time top six at all, because it is young. 430 CT1 documents change 24.369 (Ambient IoT Non-Access-Stratum (AIoT NAS) protocol for 5G System (5GS); Stage 3), in the twelve months to 2026-08-04

Q12.1 Which working groups does the register list as CT1's siblings?

• CT2, CT3 and CT4
• CT3, CT4, CT5 and CT6
• RAN2, SA2 and SA3

The register lists four sibling CT groups by name, under a parent group called CT, and does not say which of them still meet. RAN2, SA2 and SA3 are CT1's busiest correspondents, but they are not CT groups. CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1)

Q12.2 How many liaison statements did CT1 send to CT4 in the last twelve months?

• None
• Eight
• Forty-four

Eight out and seven in, which makes CT4 the busiest of CT1's own sibling groups in both directions. Forty-four is the count for RAN2. 8 outgoing liaison statements to CT4 in the twelve months to 2026-08-04

Q12.3 What does the register say CT3 does?

• It handles interworking with external networks
• Nothing at all — it holds the name and no description
• It owns the charging specifications

The register was built for CT1 alone. It carries the sibling group names because they appear beside CT1 in the group table, and no description, count or specification list for any of them. CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1)

Q12.4 Which four things does TS 24.501 say it applies to?

• The UE, the base station, the AMF and the UPF
• Every function of the 5G core
• The UE, the AMF, the SMF and the PCF

Those four are named in the scope. Anything outside them is somebody else's document, which is why the reference list at the front is so long. §1

Q12.5 What is the effect of the reference list at the front of TS 24.501?

• The listed documents become provisions of TS 24.501 through the reference
• It lists the documents CT1 also owns
• It is a reading suggestion

The opening line says the referenced documents constitute provisions of the present document. A pointer in a 3GPP specification has force, and that is why dependencies between groups matter so much. §2

Q13.1 What does the prefix on the document number C1-262074 tell you?

• It was agreed
• It was written in 2026
• It is a CT1 document

Every CT1 document number begins C1-. The register separately records which meeting a document belongs to and what outcome it got; neither can be read off the number. CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1)

Q13.2 Which document kind arrived most often at CT1 in the last twelve months?

• Change requests, at 2835
• Discussion papers, at 197
• Liaison statements in, at 135

Change requests lead every other counted kind — 2835 in the year, against 563 for pCRs, the next largest. 2835 CT1 documents of kind 'CR' uploaded on or after 2025-08-04

Q13.3 When was the newest CT1 document on record uploaded?

• 2026-05-22, the last day of C1-161
• 2026-07-31 at 10:40:59, for meeting C1-162
• 2026-08-04

The newest upload is filed under a meeting that has not started. That is why nothing about C1-162 may be described as decided. the newest CT1 document on record was uploaded 2026-07-31 10:40:59, for meeting C1-162

Q13.4 How many of the 229 active CT1 specifications have parsed text on this machine?

• All 229
• 157
• 175

157 can have a clause quoted from them here. For the rest the register holds the number, the type, the title and the Releases, and nothing more. 157 of 229 active CT1 specifications have parsed text on this machine

Q13.5 A specification is at version 2.1.0. What does the first digit tell you?

• It is approved and under change control
• It belongs to Release 2
• It has been presented to the TSG for approval

1 means presented for information, 2 means presented for approval, and 3 or greater means approved and under change control. A first digit of 2 is not yet something to build against. §Foreword

Q14.1 How many CT1 meetings have an attendance figure in this data?

• Two
• None
• All 172 that have been held

Only C1-160 and C1-161, counted from the participant lists inside their reports. Three meeting folders are mirrored here and only two of them hold a report, so no trend in attendance can be described. 165 people are listed as taking part in C1-160

Q14.2 Why can no "in the last twelve months" figure be compared with an all-time figure?

• 7181 documents carry no upload date, so they are in the all-time counts and cannot be in the yearly ones
• The all-time figures stop in 2015
• The yearly figures are estimates

A yearly count is a count of dated rows. An all-time count includes the undated ones. The two are measured differently and a trend drawn between them is not supported. 7181 CT1 documents carry no upload date

Q14.3 Where can the meaning of an abbreviation used in TS 24.501 be found?

• In the document's own definitions and abbreviations clauses
• Nowhere
• In the source register, which expands every abbreviation

The register holds titles and work item names as strings and expands none of them. The specification has a definitions clause and an abbreviations clause, and anything explained in this course about the protocol comes from there. §3.2

Q14.4 What does the register hold about the 44 CT1 terms of office?

• Only that there are 44 — the four current holders are the only ones named
• Nothing at all
• The name, company and dates of every term

Four office holders with no end date are named. The other terms exist as a count, so no chapter here may name a past chair. The office holders page carries them term by term. 44 CT1 terms of office are on record

Q14.5 What can be said about what CT1 decided at meeting C1-162?

• That it approved the C1-161 report
• Nothing — the meeting has not happened
• That 69 documents were agreed there

C1-162 is planned for 2026-08-24. 69 documents are already filed under it, which is a count of paperwork, not of decisions. 69 documents are already filed under C1-162