1. Elementary Procedures for CircuitSwitched (CS) Call Control (CC) in
3GPP
Presented by Louis K. H. Kuo

2. Outline
•
•
•
•
•
•
•
Introduction of Related Backgrounds
Overview on Call Control
Standard L3 Messages
Service State Diagram
Service Arrow Diagram
System Log
References

3. Introduction of Related Backgrounds (1/2)
• The radio interface is layered into three protocol layers [1]:
– the physical layer (L1);
– the data link layer (L2);
– the network layer (L3).
U-plane
• Layer 2 is split into following sublayers:
C-plane
– Medium Access Control (MAC), Radio Link Control (RLC), Packet
Data Convergence Protocol (PDCP) and Broadcast/Multicast
Control (BMC).
• PDCP and BMC exist in the U-plane only.
• Layer 3 and RLC are divided into Control (C-) and User (U-) planes.
• In the C-plane, Layer 3 is partitioned into sublayers (e.g., CC, MM).
– Access Stratum (AS): from RRC (Radio Resource Control) to L1
– Non-Access Stratum (NAS): AS and from NAS to the NAS of
Mobility Management Entity (MME)

4. Introduction of Related Backgrounds (1/2)
• Radio Interface Protocol Architecture (Service Access
Points (SAPs) are marked by circles.)
• “Logical” SAPs
GC
– P2P Communication
GC
• Between RRC and RLC
Nt
DC
UuS boundary
U-plane information
C-plane signalling
L3
control
Radio
Bearers
control
control
control
control
RRC
PDCP
PDCP
L2/PDCP
BMC
• The Service provided by L2
– Radio Bearer
– Signaling Radio Bearers
DC
Duplication avoidance
• Three Types of SAPs in RLC
– Acknowledged Mode (AM)
– Unacknowledged Mode (UM)
– Transparent Mode (TM)
Nt
RLC
RLC
RLC
L2/BMC
L2/RLC
RLC
RLC
RLC
RLC
RLC
Logical
Channels
MAC
L2/MAC
Transport
Channels
PHY
L1

5. Overview on Call Control (1/4)
• Call Control (CC) Protocol [2] or Call Control Function (CCF)
– One of the protocols of the Connection Management (CM)
sublayer
• Each CC entity is independent from each other and shall communicate
with the correspondent peer entity using its own MM connection.
– The present document describes the call control protocol only
with regard to two peer entities.
• Certain sequences of actions of the two peer entities compose
"elementary procedures“.
– These elementary procedures may be grouped into the
following classes:
•
•
•
•
call establishment procedures;
call clearing procedures;
call information procedures;
miscellaneous procedures.

6. Overview on Call Control (2/4)
• Three Basic Types of Calls
– MO Call
• The terms "mobile originating" or "mobile originated" are used to
describe a call initiated by the mobile station (MS).
– MT Call
• The terms "mobile terminating" or "mobile terminated" are used to
describe a call initiated by the network (NW).
– NW Initialed MO Call [3]
• A feature allows the NW to ask the MS to establish a MO connection.
• The serving PLMN provides the MS with the necessary information
which is used by the MS to establish the connection.
• It is mandatory for CCBS ME and is used in the case of a CCBS recall.
– Completion of Calls to Busy Subscriber (CCBS) [4]: CCBS is evoked when a
called party is busy, this supplementary service (SS) enables the calling party
to be connected to a called party

7. Overview on Call Control (3/4)
• Example [5]: To make a phone call.
– From MOC to PTC; from POC to MTC
• Protocol Architecture [6]
– Eight defined architectures
– Example: A MS supporting the PS mode of operation
UMTS service
RABM: RAB Manager
REG: REGister
SM: Session Management
MN: Mobile Network
SMS: Short Message Service
GSMS: GPRS SMS
SS: Supplementary Services
PDP: Packet Data Protocol
TI: Transaction ID
MM: Mobility Management
GMM: GPRS MM
PD: Protocol Discriminator
RABn-SAP
MNCC-SAP
MNSMS-SAP
SMREG-SAP
CM
MNSS-SAP
RABM
RAB
Entity RAB
1
Entity RAB
2
Entity
n
RABMSM-SAP
SM
RAB
Control
GSMS
PDP
TI
CC
TI
GMMREG
PMMSMS
GMMSMSGMMSM- -SAP
-SAP
SAP
SAP
SS
TI
TI
MMSMSSAP
MMCC-SAP GMMSS2SAP
TI
GMMSSSAP MMSSSAP
MM-sublayer
MM
GMM
GMMRABM-SAP
• NAS
• MS side
RAB1-SAP RAB2-SAP
PDCP1-SAP
PDCP2-SAP
PDCPn-SAP
RABMAS-SAP
GMM
coord
MM
coord
PD
PD
RR-SAP
GMMAS-SAP
Access Stratum sublayer
PDCP
BMC
RRC

8. Overview on Call Control (4/4)
• The CC service class consists of the following services [6]:
– MS side
•
•
•
•
•
MO and MT call establishment for normal calls;
MO call establishment for emergency calls;
call maintaining;
call termination;
call related SS Support.
– NW side
•
•
•
•
call establishment;
call maintaining;
call termination;
call related SS support.
• Three matrices to understand CC protocol
– L3 massage structure, service state diagram, and service arrow diagram

9. Standard L3 Messages (1/9)
• A standard L3 message [6]
– (1) Imperative part
Example: General message organization
• A header
• The rest of imperative part
– (2) Non-imperative part
– (Note: Both the non-header part of the imperative part and
the non-imperative part are composed of successive parts
referred as standard Information Elements (IEs).)
• A standard IE may have the following parts, in that order:
– an Information Element Identifier (IEI);
– a Length Indicator (LI);
– a value part.

10. Standard L3 Messages (2/9)
• A standard IE has one of the formats as follows.
– LV-E and TLV-E are used for EPS Mobility Management
(EMM) and EPS Session Management (ESM) only.
• Seven types of standard IEs are defined:
– format V or TV with value part consisting of 1/2 octet;
– format T with value part consisting of 0 octets;
– format V or TV with value part that has fixed length of at least one octet;
– format LV or TLV with value part consisting of zero, one or more octets;
– format LV-E or TLV-E with value part consisting of zero, one or more octets and
a maximum of 65535 octets. This category is used in EPS only.

11. Standard L3 Messages (3/9)
• Example: Type 4 IE of format TLV
– A type 4 standard IE has format LV or TLV. Its LI precedes the
value part, which consists of zero, one, or more octets; if
present, its IEI has one octet length and precedes the LI.
Example: General message organization
• The header of a standard L3 message is composed of two
octets, and structured in three main parts. [6]
– The Protocol Discriminator (PD) (1/2 octet)
– A message type octet
– A half octet used in some cases as Transaction Identifier (TI), in some other cases as a subprotocol discriminator, and called skip indicator otherwise.

12. Standard L3 Messages (4/9)
• For the EPS protocols (EMM and ESM), a standard L3 message can be
either a plain NAS message or a security protected NAS message:
– A plain NAS message
• which is composed of two or three octets, and structured in four main parts.
– A PD (1/2 octet)
– A half octet used in some cases as security header type and in other cases as an EPS
bearer identity (1/2 octet)
– A message type octet
– One octet included in some cases and used as a Procedure Transaction Identity (PTI)
– A secure protected message
• which is composed of six octets, and structured in four main parts.
–
–
–
–
The PD (1/2 octet)
A half octet used as security header type
A message authentication code of four octets
A sequence number of one octet
• This header is followed by a complete plain NAS message (i.e. including the
header of this plain NAS message).

13. Standard L3 Messages (5/9)
• Protocol Discriminator (PD)
(Note that the following contents focus on the standard L3 message which is not for the usage of EPS.)
– Bits 1 to 4 of the first octet of a standard L3 message
– The PD identifies which the standard L3 message
belongs.
– For future evolution to an extension mechanism
• The use of protocol discriminators with one octet length,
where bits 4 to 1 are coded as 1 1 1 0.
– Messages of such protocols may be not standard L3 messages.

14. Standard L3 Messages (6/9)
• Message Type Octet
– The second octet in a standard L3 message
– When a standard L3 message is expected,
• a message is less than 16 bit long, then this message shall be
ignored.
– When accessing Rel.98 and older networks,
GCC: Group CC
BCC: Broadcast CC
• Bit 8 is encoded as "0“
LCS: Location Services
– Further, value "1" is reserved for possible future use as an extension
bit.
– If “1” is detected, a protocol entity shall diagnose a "message not
defined for the PD" error and treat the message accordingly.
• Bit 7
– For RR messages including MM, CC, SS, GCC, BCC and LCS,
» bit 7 is used for send sequence number.
– For all other standard L3 messages (i.e. the protocols other than MM, CC, SS, GCC, BCC and LCS),
» bit 7 is set to a default value.
8
0
7
N (SD)
or 0
6
5
4
3
Message type
2
1
8
octet 1
7
6
5
4
3
Message type
2
1
octet 1

15. Standard L3 Messages (7/9)
• Message Type Octet (Cont.)
– When accessing Rel.99 and newer networks 4 3
6
7
5
8
N (SD) or 0
Message type
– For MM, CC, and SS,
• bits 7 and 8 are used for send sequence number
– For GCC, BCC, and LCS,
8
0
7
6
N (SD)
or 0
• only bit 7 is used for send sequence number 6
7
8
• and bit 8 is set to the default value.
5
4
1
2
octet 1
2
3
1
octet 1
Message type
5
4
3
2
1
Message type
– For all other standard layer 3 messages,
• Non-RR messages
– bits 7 and 8 are set to the default value. (The default values are both 0.)
– Exception: For SM protocol, bit 7 is set to 1.
• RR messages [7]
– bit 8 is set to the default value. (No default value for bit 7)
• EPS
EMM: EPS Mobility Management
ESM: EPS Session Management
– bit 7 is set to 1 while bit 8 is 0 for the EMM and 1 for the ESM.
octet 1

16. Standard L3 Messages (8/9)
• Transaction identifier (TI in PS NAS Msg.; TIO in CS NAS Msg.)
– Bits 5 to 8 of octet 1 of a standard L3 message
– The TI allows to distinguish up to 16 bi-directional messages
flows for a given PD and a given SAP.
• Such a message flow is called a transaction.
– An extension mechanism is also defined.
• which allows to distinguish up to 256 bi-directional messages flows for
a given PD and a given SAP.
• which shall not be used unless explicitly stated in the core spec.
– TI flag
• 0: The message is sent from the side that originates the TI.
• 1: The message is sent to the side that originates the TI.
– TIO (Bits 7 to 5 in octet 1)
– TIE (Bit 7 to 1 in octet 2)

17. Standard L3 Messages (9/9)
• Sub-Protocol Discriminator (SPD)
CTS: Cordless Telephony System
– Bits 5 to 8 of octet 1 of a standard L3 message
– which allows to identify between protocols inside one sublayer.
• Skip indicator
–
–
–
–
Bits 5 to 8 of octet 1 of a standard L3 message
The content of skip indicator depends on the protocol and the SAP.
The use of this half-octet is consistent for a given PD and SAP.
Unless been specified in the protocol, the skip indicator IE is a spare
field.

18. Service State Diagram [6] (1/2)
• Service graph of Call Control entity - MS side
• Three partitions: MO call, call clearing, MT call

19. Service State Diagram (2/2)
• Service graph of Call Control entity - NW side
• Three partitions: MO call, call clearing, MT call

20. Primitive: inter-layer info. in one node
Message: inter-node info.
Service Arrow Diagram (1/3)-MO call setup (Successful case)
Setup Request from MS
Mobile Station
CC
MNCC-SETUP-REQ
MM
MMCC-EST-REQ
RR
RR-EST-REQ
(CM SERV REQ)
L2
L2
RR
MM
Network
CC
DL-RANDOM-ACC-REQ/IND (CHANN REQ)
DL-UNIT-DATA-IND/REQ(IMM ASS)
DL-ASS-REQ
RR-EST-CNF
SABM (CM SERV REQ)
DL-EST-CNF
DL-EST-IND
UA (CM SERV REQ)
RR-EST-IND
(CM SERV REQ)
AUTH REQ
Authentication &
Ciphering
AUTH RES
CIPH MODE CMD
MMCC-EST-CNF
RR-SYNC-IND
(ciph)
CIPH MODE COM
RR-SYNC-REQ
(ciph)
RR-SYNC-CNF
(ciph)
MMCC-EST-IND
(SETUP)
SETUP
MNCC-CALLPROC-IND
CALL PROC
MNCC-CALLPROC-REQ
ASSIGN CMD
MMCC-SYNC-IND
(res ass)
MNCC-ALERT-IND
MNCC-SETUP-CNF
RR-SYNK-IND
(res ass)
RR-SYNC-REQ
(res ass)
ASSIGN COM
RR-SYNC-CNF
(res ass)
ALERT
CONNECT
CONN ACK
MNCC-SETUP-IND
MMCC-SYNC-REQ
(res ass)
MMCC-SYNC-CNF
(res ass)
MNCC-ALERT-REQ
MNCC-SETUP-RSP
MNCC-SETUPCOMPL-IND
MO Call Setup
DATA FLOW

21. Service Arrow Diagram (2/3)-MT call setup (Successful case)
Mobile Station
CC
Network
Setup Request from NW
MM
RR
RR
L2
L2
DL-UNIT-DATA-IND/REQ (PAG REQ)
MM
CC
MMCC-SETUP-REQ
RR-EST-REQ
(mob id)
MMCC-EST-REQ
(mob id)
DL-RANDOM-ACC-REQ/IND (CHANN REQ)
DL-UNIT-DATA-IND/REQ (IMM ASS)
DL-EST-REQ
RR-EST-IND
DL-EST-CONF
SABM (PAG RES)
DL-EST-IND
RR-EST-CNF
UA (PAG RES)
AUTH REQ
Authentication &
Ciphering
AUTH RES
CIPH MODE CMD
RR-SYNC-IND
(ciph)
MNCC-SETUPIND
RR-SYNC-REQ
(res ass)
CIPH MODE COM
RR-SYNC-CNF
(res ass)
MMCC-EST-CNF
SETUP
MMCC-EST-IND
(SETUP)
CALL CONF
MNCC-CALLCONF-REQ
ASSIGN CMD
MMCC-SYNC-IND
(res ass)
RR-SYNC-IND
(res ass)
ASSIGN COM
MNCC-ALERTREQ
ALERT
MNCC-SETUPRES
CONNECT
MNCC-SETUPCOMPL-IND
CONN ACK
MT Call Setup
DATA FLOW
MNCC-CALLCONF-IND
RR-SYNC-REQ
(res ass)
RR-SYNC-CNF
(res ass)
MMCC-SYNC-REQ
(res ass)
MMCC-SYNC-CNF
(res ass)
MNCC-ALERT-IND
MNCC-SETUP-CNF
MNCC-SETUPCOMPL-REQ

22. Service Arrow Diagram (3/3)-MO, call and channel release (Successful case)
Mobile Station
CC
Network
MM
L2
L2
RR
RR
MM
CC
DATA FLOW
Disconnect
DISCONNECT
MNCC-DISC-REQ
MNCC-DISC-IND
MNCC-REL-IND
RELEASE
MNCC-REL-REQ
RELEASE COM
Release
MNCC-REL-CNF
MMCC-REL-REQ
CHANN REL
RR-REL-IND
DL-REL-REQ
DL-REL-CNF
Channel Release
DISC
UA
RR-REL-REQ
DL-REL-IND
MMCC-REL-REQ

23. System Log (1/5)
• Environment - QXDM Prof.
>> Item type: Long packets (OTA)
>> Filter/Register on target for items: CC, MM, GSM RRM
– (Ex.1) The MO call is successful and disconnects by
calling user.
– (Ex.2) The MT call is successful and disconnects by the
calling user.

24. Presence
M: Mandatory
C: Conditional
O: Optional
System Log (2/5)
• Messages for CS CC [2] in Ex.1
– SETUP message content (MS to NW)
• Transaction ID (trans_id_or_skip_ind = 0x0)
–
TI values are assigned by the side of the interface initiating a transaction
.
• Protocol discriminator (prot_disc = 0x3)
– Call control; call related SS messages
• Message type (msg_type = 0x5)
– Call establishment message – SETUP
• Bearer capability 1 (bearer_cap_1_incl = 0x1)
• Called party BCD number (called_party_bcd_incl = 0x1)

25. System Log (3/5)
• Messages for CS CC in Ex.1 (Cont.)
– CC/Call Proceeding (NW to MS)
– CC/Facility (NW to MS)

26. System Log (4/5)
• Messages for CS CC in Ex.1 (Cont.)
– CC/Alerting (NW to MS)
– CC/Connect (NW to MS)
– CC/Connect Acknowledge (MS to NW)

27. System Log (5/5)
• Messages for CS CC in Ex.1 (Cont.)
– CC/Disconnect (MS to NW)
– CC/Release (NW to MS)
– CC/Release Complete (MS to NW)

28. References
• [1] 3GPP TS 25.301 V11.0.0 (2012-09) - 3GPP TSG RAN; Radio Interface
Protocol Architecture (Rel.11)
• [2] 3GPP TS 24.008 V12.3.0 (2013-09) - 3GPP TSG CT; Mobile Radio
Interface Layer 3 Spec.; CN protocols; Stage 3 (Re.12)
• [3] ETSI TS 100 906 v7.0.1 (1999-07) - Digital Cellular Telecom. System
(Phase2+); MS Features (GSM 02.07) ver. 7.0.1 (Rel. 98)
• [4] Asterisk 1.4/Call Completion on Busy Subscriber (CCBS)
• [5] WCDMA/UMTS第三代無線通訊系統(1)--核心網路架構介紹
• [6] 3GPP TS 24.007 V12.0.0 (2013-06) - 3GPP TSG CT; Mobile Radio
Interface Signalling Layer 3; General Aspects (Rel.12)
• [7] 3GPP TS 44.018 V12.0.0 (2013-09) – 3GPP TSG GERAN; Mobile
Radio Interface Layer 3 Spec.; RRC protocol (Rel.12)