Elementary Procedures for Circuit-Switched (CS) Call Control (CC) in 3GPP

Presented by Louis K. H. Kuo

Outline

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

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).

• Layer 2 is split into following sublayers: – 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)

U-plane C-plane

Introduction of Related Backgrounds (1/2)• Radio Interface Protocol Architecture (Service

Access Points (SAPs) are marked by circles.)• “Logical” SAPs

– P2P Communication• Three Types of SAPs in RLC

– Acknowledged Mode (AM)– Unacknowledged Mode (UM)– Transparent Mode (TM)

• The Service provided by L2– Radio Bearer– Signaling Radio Bearers

• Between RRC and RLC

L3

cont

rol

cont

rol

cont

rol

cont

rol

LogicalChannels

TransportChannels

C-plane signalling U-plane information

PHY

L2/MAC

L1

RLC

DCNtGC

L2/RLC

MAC

RLCRLC

RLCRLC

RLCRLC

RLC

Duplication avoidance

UuS boundary

BMC L2/BMC

control

PDCPPDCP L2/PDCP

DCNtGC

RadioBearers

RRC

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.

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

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• NAS• MS side

RABM: RAB ManagerREG: REGisterSM: Session ManagementMN: Mobile NetworkSMS: Short Message ServiceGSMS: GPRS SMSSS: Supplementary ServicesPDP: Packet Data Protocol TI: Transaction IDMM: Mobility ManagementGMM: GPRS MMPD: Protocol Discriminator

GMMSM-SAP

MM-sublayer

GMM GMM coord

MNSMS-SAP

GMMREG -SAP

MMSMS-SAP

MMCC-SAP MMSSSAP

PMMSMS -SAP

MNSS-SAP MNCC-SAP

GMMSMS-SAP

TI TI PDP TI

CM

CC SS GSMS

TI

PD

MM MM coord

PD

SMREG-SAP

RA

BM

SM

-SA

P

RABM

RAB1-SAP

RAB Entity

1

RAB Entity

2

RAB Entity

n

RAB Control

RABn-SAP RAB2-SAP

SM

GM

MR

AB

M-S

AP

Access Stratum sublayer

RABMAS-SAP GMMAS-SAP

RRC PDCP

PDCPn-SAP

BMC

PDCP2-SAP PDCP1-SAP RR-SAP

GMMSSSAP

TI

GMMSS2SAP

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

Standard L3 Messages (1/9)• A standard L3 message [6]

– (1) Imperative part• 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.

Example: General message organization

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.

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.

• 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 sub-

protocol discriminator, and called skip indicator otherwise.

Example: General message organization

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).

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.

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,• Bit 8 is encoded as "0“

– 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.

GCC: Group CCBCC: Broadcast CCLCS: Location Services

8 7 6 5 4 3 2 1

0 octet 1Message typeN (SD)or 0

8 7 6 5 4 3 2 1

octet 1Message type

Standard L3 Messages (7/9)• Message Type Octet (Cont.)

– When accessing Rel.99 and newer networks– For MM, CC, and SS,

• bits 7 and 8 are used for send sequence number

– For GCC, BCC, and LCS,• only bit 7 is used for send sequence number • and bit 8 is set to the default value.

– 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– bit 7 is set to 1 while bit 8 is 0 for the EMM and 1 for the ESM.

EMM: EPS Mobility ManagementESM: EPS Session Management

8 7 6 5 4 3 2 1

octet 1Message type

8 7 6 5 4 3 2 1

0 octet 1Message typeN (SD)or 0

8 7 6 5 4 3 2 1

octet 1Message typeN (SD) or 0

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)

Standard L3 Messages (9/9)• Sub-Protocol Discriminator (SPD)

– 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.

CTS: Cordless Telephony System

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

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

Service Arrow Diagram (1/3)-MO call setup (Successful case)CC MM RR L2 L2 RR MM CC

Mobile Station Network

MNCC-SETUP-REQ DL-RANDOM-ACC-REQ/IND (CHANN REQ)

DL-UNIT-DATA-IND/REQ(IMM ASS)

DL-ASS-REQ DL-EST-IND

DL-EST-CNF UA (CM SERV REQ)

AUTH REQ

AUTH RES

CIPH MODE CMD

CIPH MODE COM

SETUP

CALL PROC

ASSIGN CMD

ASSIGN COM

ALERT

CONNECT

CONN ACK

MNCC-CALL-PROC-IND

MNCC-ALERT-IND

MNCC-SETUP-CNF

MMCC-EST-CNF

MMCC-SYNC-IND (res ass)

RR-EST-CNF

RR-SYNK-IND (res ass)

RR-EST-IND(CM SERV REQ)

RR-SYNC-REQ (c iph)

RR-SYNC-CNF (c iph)

RR-SYNC-REQ (res ass)

RR-SYNC-CNF (res ass)

MMCC-EST-IND (SETUP)

MMCC-SYNC-REQ (res ass)

MMCC-SYNC-CNF (res ass)

MNCC-SETUP-IND

MNCC-CALL-PROC-REQ

MNCC-ALERT-REQ

MNCC-SETUP-RSP

MNCC-SETUP-COMPL-IND

DATA FLOW

MMCC-EST-REQ RR-EST-REQ(CM SERV REQ)

RR-SYNC-IND (c iph)

SABM (CM SERV REQ)

Primitive: inter-layer info. in one nodeMessage: inter-node info.

Setup Request from MS

Authentication &Ciphering

MO Call Setup

Service Arrow Diagram (2/3)-MT call setup (Successful case)

Mobile Station Network

DATA FLOW

DL-RANDOM-ACC-REQ/IND (CHANN REQ)

DL-UNIT-DATA-IND/REQ (IMM ASS)

DL-EST-REQ DL-EST-IND

DL-EST-CONF UA (PAG RES)

AUTH REQ

AUTH RES

CIPH MODE CMD

CIPH MODE COM

SETUP

CALL CONF

ASSIGN CMD

ASSIGN COM

ALERT

CONNECT

CONN ACK

RR-EST-IND

RR-SYNC-IND (ciph)

RR-SYNC-IND (res ass)

MMCC-EST-IND (SETUP)

MMCC-SYNC-IND (res ass)

MNCC-SETUP-IND

MNCC-CALL-CONF-REQ

MNCC-ALERT-REQ

MNCC-SETUP-RES

MNCC-SETUP-COMPL-IND

RR-EST-REQ (mob id)

RR-EST-CNF

RR-SYNC-REQ (res ass)

RR-SYNC-CNF (res ass)

RR-SYNC-REQ (res ass)

RR-SYNC-CNF (res ass)

MMCC-EST-REQ (mob id)

MMCC-SETUP-REQ

MMCC-EST-CNF

MNCC-CALL-CONF-IND

MMCC-SYNC-REQ (res ass)

MMCC-SYNC-CNF (res ass)

MNCC-ALERT-IND

MNCC-SETUP-CNF

MNCC-SETUP-COMPL-REQ

SABM (PAG RES)

DL-UNIT-DATA-IND/REQ (PAG REQ)

MMCC RR L2 L2 RR MM CC

Setup Request from NW

Authentication &Ciphering

MT Call Setup

Service Arrow Diagram (3/3)-MO, call and channel release (Successful case) Mobile Station Network

DATA FLOW

MNCC-DISC-REQ

MNCC-REL-IND

MMCC-REL-REQ

RR-REL-IND

DISCONNECT

RELEASE

RELEASE COM

CHANN REL

DL-REL-REQ

DL-REL-CNF

DISC

UA

DL-REL-IND

RR-REL-REQ MMCC-REL-REQ

MNCC-DISC-IND

MNCC-REL-REQ

MNCC-REL-CNF

CC RRL2 CCMM MMRR L2

Disconnect

Release

Channel Release

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.

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)

PresenceM: MandatoryC: ConditionalO: Optional

System Log (3/5)

• Messages for CS CC in Ex.1 (Cont.)– CC/Call Proceeding (NW to MS)

– CC/Facility (NW to MS)

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)

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)

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)