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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)