UMTS protocols Different protocol stacks for user and control plane User plane (for transport of user data): Circuit switched domain: data within ”bit

UMTS protocols Different protocol stacks for user and control plane User plane (for transport of user data): Circuit switched domain: data within bit pipes Packet switched domain: protocols for implementing various QoS or traffic engineering mechanisms Control plane (for signalling): Circuit switched domain: SS7 based (in core network) Packet switched domain: IP based (in core network) Radio access network: UTRAN protocols

Data streams RLC MAC Phys. UE UTRAN 3G MSC GMSC UuUu IuIu GnGn User plane protocol stacks (CS domain) RLC MAC Phys. WCDMA TDM Frame Protocol (FP) AAL2 ATM Phys. AAL2 ATM Phys. TDM 2

User plane protocol stacks (PS domain) PDCP RLC GTP UDP IP GTP UDP IP GTP UDP PDCP RLC MAC Phys. MAC Phys. AAL5 ATM Phys. AAL5 ATM Phys. IP L2 L1 GTP UDP IP L2 L1 UE UTRAN SGSN GGSN UuUu IuIu GnGn WCDMA 3

UTRAN Model UTRAN OSI Model L2/MAC L1 L2/RLC L3/RRC UTRAN UE RRC RLC MAC PHY RRC MAC PHY RLC Signaling Radio Bearer Logical Channel Transport Channel Physical Channel CTRL USER DATA USER DATA 4

Uu (air, radio) interface protocols PHY MAC RLC RRC (Control Plane) Signalling radio bearers (User plane) radio bearers e.g. MM, CC, SM transparent to UTRAN Logical channels Transport channels PDCP L3 L2 L1 BMC Control Physical channels

Main tasks of RRC protocol Over the air interface, Radio Resource Control (RRC) messages carry all the relevant information required for setting up a Signalling Radio Bearer (during the lifetime of the RRC Connection) and setting up, modifying, and releasing Radio Bearers between UE and UTRAN (all being part of the RRC Connection). RRC also participates in the co-ordination of other Radio Resource Management (RRM) operations, such as measurements and handovers. In addition, RRC messages may carry in their payload higher layer signalling information (MM, CC or SM) that is not related to the air interface or UTRAN.

Main tasks of Uu L2 interface protocols PDCP (Packet Data Convergence Protocol): IP packet header compression (user plane only) BMC (Broadcast/Multicast Control Protocol): submission of messages to all or a group of UEs in a cell RLC (Radio Link Control): is often a transparent layer The RLC layer offers the following services to the higher layers: Layer 2 connection establishment/release Transparent data transfer, i.e., no protocol overhead is appended to the information unit received from the higher layer Assured and un assured data transfer The RLC layer comprises the following functions: Segmentation and assembly Transfer of user data Error correction by means of retransmission optimized for the WCDMA physical layer Sequence integrity (used by at least the control plane) Duplicate detection Flow control Ciphering

Medium Access Control (MAC) The MAC layer offers Data transfer to RLC and higher layers. The MAC layer comprises the following functions: Mapping between logical and transport channels Segmentation of data into transport blocks Selection of appropriate TF (basically bit rate), within a predefined set, per information unit delivered to the physical layer Service multiplexing on RACH, FACH, and dedicated channels Priority handling between data flows of one user as well as between data flows from several usersthe latter being achieved by means of dynamic scheduling Access control on RACH Address control on RACH and FACH Contention resolution on RACH 8

Physical Layer The physical layer offers information transfer services to the MAC layer. These services are denoted as Transport channels (TrChs). There are also special purpose Physical channels. Physical layer comprises following functions: Mapping of transport channels to physical channels Various handover functions Error detection and report to higher layers Multiplexing of transport channels Fast Close loop Power control Frequency and Time Synchronization Other responsibilities associated with transmitting and receiving signals over the wireless media. 9

RLC Logical / Transport / Physical channels MAC FP Phy FP UEBase stationRNC AAL 2 MAC AAL 2 Phy Logical channels Physical channels Transport channels :: WCDMA :: 10

Definition of Channels Logical Channel Type of information to be transmitted e.g., traffic or control logical channels. Transport Channel How and with what format data is transmitted through physical links. Physical Channel Unit of radio resource of a radio system e.g., frequency band, time slot, code, etc. RF Channel Fixed frequency band of a radio system. The MAC sublayer is responsible for mapping logical channels onto transport channels. The physical layer is responsible for mapping transport channels onto physical channels. 11

Logical Channels Data DTCH (UL/DL) CTCH (DL) Control BCCH (DL) PCCH (DL) DCCH (UL/DL) CCCH (UL/DL) SHCCH (UL/DL) 12

Logical Channels MAC layer provides data transfer services on logical channels, control and traffic channels: Control channel to transfer control plane information Traffic channels to transfer user plane information Control channels Broadcast Control CHannel (BCCH) -downlink broadcast control Paging Control CHannel (PCCH) -downlink paging information Dedicated Control CHannel (DCCH) -dedicated between mobile & network Common Control CHannel (CCCH) -common between mobile & network Shared Channel Control information (SHCCH) -for UL & DL (TDD only) Data channels Dedicated Traffic CHannel (DTCH) -P2P ch. dedicated to one mobile (UL & DL) Common Traffic CHannel (CTCH) -P2MP ch. for unidirectional data 13

TrCh DCH (UL/DL) CCHs BCH (DL) FACH (DL) PCH (DL) DSCH (DL) RACH (UL) CPCH (UL) 14 DCH: Dedicated Channel CCHs: Common Channels BCH: Broadcast Channel FACH: Forward-Access Channel PCH: Paging Channel DSCH: Downlink Shared Channel RACH: Random Access Channel CPCH: Common Packet Channel Transport Channels [1/6]

Transport Channels [2/6] Dedicated Transport Channel Resources are reserved for a single user only (continuous and independent from the DCHs of other UEs) DCH Dedicated Channel Downlink/uplink Transport channel A point-to-point channel allocated to a specific user Carries information intended for the given user including data and higher layer control information Characterised by features such as: fast power control fast data rate change on a frame-by-frame basis in the uplink. In the downlink data rate variation is taken care of either with a rate- matching operation or with Discontinuous Transmission (DTX) instead of varying spreading factor frame-by-frame basis possibility of transmission to a certain part of the cell 15

Transport Channels [3/6] Common Transport Channels Resources are shared between users 1. BCH Broadcast Channel It is a downlink channel System and cell-specific information over the entire cell The terminal cannot register to the cell without the possibility of decoding the broadcast channel transmit with relatively high power in order to reach all users within a cell. low and fixed data rate 16

Transport Channels [4/6] 2. FACH Forward Access Channel It is a downlink channel Used to carry control information to a mobile station when the system knows the location cell of the mobile station May also carry short user packets 3. PCH - Paging Channel It is a downlink channel Used to carry control information to a mobile station when the system does not know the location cell of the mobile station It is used to inform the mobile station of incoming calls 17

Transport Channels [5/6] 4. RACH Random Access Channel It is an uplink channel Used to carry control information It is used for initiating a call (initial access to the serving BS) It may also carry short user packets must be heard from the whole desired cell coverage area, data rate is quite low. 5. CPCH Common Packet Channel It is an uplink channel used to carry infrequent medium sized packets the main differences to the RACH are: the use of fast power control a physical layer-based collision detection mechanism a CPCH status monitoring procedure 18

Transport Channels [6/6] 6. DSCH Downlink Shared Channel Used to carry infrequent medium and large sized packets It can be shared in time between several users It is always associated with a downlink DCH From the common channels DSCH was optional feature that was seldom implemented by the operators and later replaced in practice with High Speed Downlink Packet Access (HSDPA) 3GPP decided to take DSCH away from Release 5 specifications onwards Also CPCH has been taken out of the specifications from Rel5 onwards as it was not implemented in any of the practical networks 19

Logical / Transport channels mapping CCCH DCCH PCH DCH DSCH FACH BCH DCH CPCH RACH DCCH CTCH CCCH BCCH PCCH UplinkDownlink DTCH Logical channels Transport channels 20

Uplink Physical Channels Dedicated Physical Channels DPCCH DPDCH Common Physical Channels PRACH PCPCH 21 DPCCH: Dedicated Physical Control Channel DPDCH: Dedicated Physical Data Channel PRACH: Physical Random Access Channel PCPCH: Physical Common Packet Channel

Downlink Physical Channels Dedicated Physical Channel DPCH Common Physical Channels CPICH P-CPICHS-CPICH CCPCH P-CCPCHS-CCPCHSCHPDSCHAICHPICH 22 DPCH: Dedicated Physical Channel CPICH: Common Pilot Channel P-CPICH: Primary Common Pilot Channel S-CPCH: Secondary Common Pilot Channel CCPCH: Common Control Physical Channel P-CCPCH: Primary Common Control Physical Channel S-CCPCH: Secondary Common Control Physical Channel SCH: Synchronisation Channel PDSCH: Physical Downlink Shared Channel AICH: Acquisition Indication Channel PICH: Page Indication Channel

Transport & Physical Channels Transport ChannelPhysical Channel (UL/DL) Dedicated Channel DCHDedicated Physical Data Channel DPDCH Dedicated Physical Control Channel DPCCH (UL) Random Access Channel RACHPhysical random access channel PRACH (UL) Common packet channel CPCHPhysical common packet channel PCPCH (DL) Broadcast channel BCHPrimary common control physical channel P-CCPCH (DL) Forward access channel FACH (DL) Paging channel PCH Secondary common control physical channel S-CCPCH (DL) Downlink shared channel DSCHPhysical downlink shared channel PDSCH Signaling physical channels Synchronization channel SCH Common pilot channel CPICH Acquisition indication channel AICH Paging indication channel PICH CPCH Status indication channel CSICH Collision detection/Channel assignment indicator channel CD/CA-ICH 23

Transport / Physical channels mapping PCH DCH DSCH FACH BCH DCH CPCH RACH PRACH PCPCH S-CCPCH P-CCPCH DPDCH DPCCH SCH CPICH AICH PICH CSICH Physical channels Transport channels DPCH CD/CA- ICH UplinkDownlink PDSCH 24

WCDMA Uplink (FDD) Rel 99 Logical Channels (Layers 3+) Transport Channels (Layer 2) Physical Channels (Layer 1) Uplink RF Out UE Scrambling Code I+jQ I/Q Mod. Q I Ch c II Filter CCCH Common Control Ch. DTCH (packet mode) Dedicated Traffic Ch. RACH Random Access Ch. PRACH Physical Random Access Ch. DPDCH #1 Dedicated Physical Data Ch. CPCH Common Packet Ch. PCPCH Physical Common Packet Ch. Data Coding DPDCH #3 (optional) Dedicated Physical Data Ch. DPDCH #5 (optional) Dedicated Physical Data Ch. DPDCH #2 (optional) Dedicated Physical Data Ch. DPDCH #4 (optional) Dedicated Physical Data Ch. DPDCH #6 (optional) Dedicated Physical Data Ch. QQ DPCCH Dedicated Physical Control Ch. Pilot, TPC, TFCI bits Ch d GcGc GdGd j Ch d,1 GdGd Ch d,3 GdGd Ch d,5 GdGd Ch d,2 GdGd Ch d,4 GdGd Ch d,6 GdGd Ch c GdGd Ch d GcGc GdGd j RACH Control Part PCPCH Control Part j DCCH Dedicated Control Ch. DTCH Dedicated Traffic Ch. N DCH Dedicated Ch. Data Encoding DTCH Dedicated Traffic Ch. 1 DCH Dedicated Ch. Data Encoding MUXMUX CCTrCH DCH Dedicated Ch. Data Encoding 25

WCDMA Downlink (FDD) Rel.99 BCCH Broadcast Control Ch. PCCH Paging Control Ch. CCCH Common Control Ch. DCCH Dedicated Control Ch. DTCH Dedicated Traffic Ch. N BCH Broadcast Ch. PCH Paging Ch. FACH Forward Access Ch. DCH Dedicated Ch. P-CCPCH(*) Primary Common Control Physical Ch. S-CCPCH Secondary Common Control Physical Ch. DPDCH (one or more per UE) Dedicated Physical Data Ch. DPCCH (one per UE) Dedicated Physical Control Ch. Pilot, TPC, TFCI bits SSC i Logical Channels (Layers 3+) Transport Channels (Layer 2) Physical Channels (Layer 1) Downlink RF Out DPCH (Dedicated Physical Channel) One per UE DSCH Downlink Shared Ch. CTCH Common Traffic Ch. CPICH Common Pilot Channel Null Data Data Encoding PDSCH Physical Downlink Shared Channel AICH (Acquisition Indicator Channel) PICH (Paging Indicator Channel ) Access Indication data Paging Indication bits AP-AICH (Access Preamble Indicator Channel ) Access Preamble Indication bits CSICH (CPCH Status Indicator Channel ) CPCH Status Indication bits CD/CA-ICH (Collision Detection/Channel Assignment ) CPCH Status Indication bits S/P C ch S/P Cell-specific Scrambling Code I+jQ I/Q Modulator Q I C ch C ch 256,1 C ch 256,0 GSGS PSC GPGP Sync Codes(*) * Note regarding P-CCPCH and SCH Sync Codes are transmitted only in bits 0-255 of each timeslot; P-CCPCH transmits only during the remaining bits of each timeslot Filter Gain SCH (Sync Channel) DTCH Dedicated Traffic Ch. 1 DCH Dedicated Ch. Data Encoding MUXMUX MUXMUX CCTrCH DCH Dedicated Ch. Data Encoding 26

Mapping logical/Transport/Physical 27

Physical channels in WCDMA Bit sequences from different physical channels are multiplied with a channelization code (spreading) multiplied with a scrambling code (scrambling) multiplexed in code domain modulated using QPSK. Downlink channels: conventional QPSK modulation DPCH = Dedicated physical channel Uplink channels: Dual-channel QPSK moduation DPDCH = Dedicated physical data channel DPCCH = Dedicated physical control channel 28

Uplink Physical Channels [1] Two dedicated and two common physical uplink channels: Dedicated Channels: Dedicated Physical Data (DPDCH) Control (DPCCH) Channel Common Channels: Physical Random Access (PRACH) Physical Common Packet (PCPCH) Channel 29

Uplink Physical Channels [2] Dedicated Uplink Physical Channel 1. DPDCH - Dedicated Physical Data Channel Used to carry dedicated data i.e. the dedicated transport channel (DCH) There may be zero, one, or several uplink DPDCHs 2. DPCCH Dedicated Physical Control Channel Used to carry control information generated at layer 1 consists of: pilot bits to support channel estimation+ SIR estimate for PC. transmit power-control (TPC) commands feedback information (FBI): transmission diversity in the DL. an optional transport-format combination indicator (TFCI): bit rate, channel decoding, interleaving parameters for every DPDCH frame. One DPCCH and up to six parallel DPDCHs can be transmitted simultaneously

DPDCH / DPCCH structure in uplink (Dedicated Physical Data/Control Channel) Data Pilot TFCI FBI TPC DPDCH (I-branch) 10 ms radio frame (38400 chips) 01214 2560 chips DPCCH (Q-branch) Dual-channel QPSK modulation:

32 WCDMA Uplink Frame Structure DPDCH I: data channel Q: sync & control DPCCH Pilot TFCI FBI TPC TFCI = transmit format combination indicator FBI = feedback information TPC = transmit power control DPDCH = dedicated physical data channel DPCCH = dedicated physical control channel slot 0 slot 1slot i slot 14 radio frame = 10 ms 10 bits SF for DPCCH is 256 Spreading factor SF: SF = 256/2 k DPDCH spreading factor may thus range from 256 down to 4 DPCCH spreading factor fixed at 256

Uplink DPCCH Slot Format 33

Uplink Variable Rate 1-rate 10 ms Variable rate 1/2-rate 1/4-rate 0-rate : DPCCH : DPDCH (Data) R = 1R = 1/2R = 0 R = 1/2

35 WCDMA Uplink Modulator Structure pulse shape filter (SRC) pulse shape filter (SRC)) DPDCH 1 DPDCH 2 DPDCH 3 DPCCH I Q + + + - + + Odd Even Up to six DPDCH per UE can be Multiplexed and one DPCCH DPDCH C ch,SF,j DPCCH C ch,256,0

Common Uplink Physical Channel 1. PRACH - Physical Random Access Channel It is used to carry RACH A contention-based uplink channel; thus, no scheduling is performed. Slotted ALOHA approach with fast acquisition indication A UE can start the transmission at a number of well-defined time-slots called access slots Consist of one or several preambles of length 4096 chips and a message of length 10 or 20 ms No power control is supported. RACH Operation: First, UE sends a preamble. The SF of the preamble is 256 and contain a signature sequence of 16 symbols a total length of 4096 chips. Wait for the acknowledged with the Acquisition (AICH) from the BS. In case no AICH received after a period of time, the UE sends another preamble with higher power. When AICH is received, UE sends 10 or 20 ms message part. The SF for the message is from 32 to 256. 36 Uplink Physical Channels [3]

Random Access in the Uplink 37 1.25msec

38 Access Preamble Control Part Data Part Message Part 4096 chips (1msec) Structure of the random access transmission MS IDReq. Serv.Optional user packetCRC Structure of the random access message Data part 0.25msec I-branch Q-branch

Structure of Random Access Message part 39

2. PCPCH Physical Common Packet Channel Carries CPCH Its transmission is based on CSMA/CD approach with fast acquisition indication Access slot and timing structure is same as for RACH In addition to Access Preamble it also has one Collision Detection Preamble (CD-P) Different from RACH, channel can be reserved for several frames and it uses fast power control. In RACH, one RACH message is lost, whereas in CPCH an undetected collision may lose several frames and cause extra interference. 40 Uplink Physical Channels [4]

PCPCH operation: After receiving CPCH AICH from BS, UE sends a CPCH CD preamble (CD-P) with the same power from another signature. If no collision after a certain time, the BS echo this signature back to the UE on the CD Indication Channel (CD-ICH). Then, the UE sends data over several frames with fast power control. The CPCH status indicator channel (CSICH) carries the status of different CPCH information. 41 Uplink Physical Channels [5]

42 Structure of the CPCH random access transmission Access Preamble Collision Resolution Preamble (CD-P) Control Part Data Part Message Part 4096 chips BS UE AICH CD-ICH

Downlink Physical Channels Dedicated Physical Channel DPCH Common Physical Channels CPICH P-CPICHS-CPICH CCPCH P-CCPCHS-CCPCHSCHPDSCHAICHPICH 43 DPCH: Dedicated Physical Channel CPICH: Common Pilot Channel P-CPICH: Primary Common Pilot Channel S-CPCH: Secondary Common Pilot Channel CCPCH: Common Control Physical Channel P-CCPCH: Primary Common Control Physical Channel S-CCPCH: Secondary Common Control Physical Channel SCH: Synchronisation Channel PDSCH: Physical Downlink Shared Channel AICH: Acquisition Indication Channel PICH: Page Indication Channel

Downlink Physical Channels [1] Dedicated Downlink Physical Channels DPCH - Dedicated Physical Channel The dedicated transport channel is transmitted time multiplexed with control information generated at layer 1 spreading factor SF: SF = 512/2 k In the downlink the spreading factors range from 4 to 512, with some restrictions on the use of spreading factor 512 in the case of soft handover. The downlink DPDCH consists of QPSK symbols. Each symbol consists of two bits while in the case of uplink the DPDCH consists of BPSK symbol (one symbol corresponds to one bit). When the total bit rate to be transmitted exceeds the maximum bit rate for a downlink physical channel, multicode transmission is employed (i.e., several parallel downlink DPCHs are transmitted using the same spreading factor). In this case, the layer 1 control information is put on only the first downlink DPCH. 44

DPCH structure in downlink Data TPC TFCI Data 10 ms radio frame 01214 2560 chips Pilot QPSK modulation, time multiplexed data and control information: (DPCH = Dedicated Physical Channel)

46 WCDMA Downlink Frame Structure DPDCH DPCCH TFCIPilotTPC slot 0 slot 1 slot i slot 14 radio frame = 10 ms DPDCH DPCCH Data1 Data2

Downlink DPCH Slot format 47

Common Downlink Physical Channels 1. CPICH - Common Pilot Channel (C 256,0 ) Fixed rate carries a pre-defined bit/symbol sequence Channel estimation Two types of CPICH Primary Common Pilot Channel Secondary Common Pilot Channel 48 Frame structure for Common Pilot Channel Downlink Physical Channels [2] Pilot Symbol Data (predefined symbols sequence) 12345678910111213140 1 Frame = 15 slots = 10 mSec 1 timeslot = 2560 Chips = 10 symbols = 20 bits = 666.667 uSec

1.1 Primary CPICH Same channelization code always used Scrambled using primary scrambling code One per cell Broadcast over entire cell 1.2 Secondary CPICH Uses either primary or secondary scrambling code Zero, one or several per cell May be transmitted over a part of cell 49

2. P-CCPCH - Primary Common Control Physical Channel (C 256,1 ) Used to carry BCH SF=256 P-CCPCH is not transmitted during first 256 chips -that time is reserved for primary and secondary synchronization channels (SCH) 50 Frame structure for Primary Common Control Physical Channel Downlink Physical Channels [3] Broadcast Data (18 bits) SSC i BCH Spreading Factor = 256 1 Slot = 0.666 mSec = 18 BCH data bits / slot 12345678910111213140 1 Frame = 15 slots = 10 mSec 2304 Chips 256 Chips SCHBCH PSC PSC used for slot synchronization, SSC used for frame synchronization and scrambling code group (16 SSCs in 64 different combinations)

3. S-CCPCH - Secondary Common Control Physical Channel carry FACH and PCH SF = 256/2 K FACH and PCH can be mapped to same secondary CCPCH Primary CCPCH has fixed pre-defined rate while secondary CCPCH has variable rate Primary CCPCH is continuously transmitted over entire cell while secondary CCPCH is only transmitted only when there is data available 51 Downlink Physical Channels [4] Spreading Factor = 256 to 4 1 Slot = 0.666 mSec = 2560 chips = 20 * 2 k data bits; k = [0..6] 12345678910111213140 1 Frame = 15 slots = 10 mSec 20 to 1256 bits0, 2, or 8 bits DataTFCI or DTXPilot 0, 8, or 16 bits

52 Downlink Physical Channels [5]

SCH (Cont.) Both the P-SCH and the S-SCH are bursty and transmitted by the base station in the first 256 chips of every slot. It transmits no power for the remainder of the slots. 53

SCH (Cont.) The P-SCH is a fixed 256 chip sequence that is repeated at the start of every slot by every WCDMA cell; it is used by mobiles to detect the presence of a WCDMA cell at a specific point in code space. Correlating the received signal with a copy of the P-SCH sequence yields a correlation peak indicating the time of a slot start for each cell within reach of the mobile. The primary and secondary SCH differ in that the S-SCH encodes information by transmitting a series of fifteen 256 chip sequences per frame. This series of fifteen S-SCH bursts signals the cells scrambling code group, and is repeated every frame. The S-SCH can also be used to identify the frame start of the downlink transmission of the transmitting cell. Neither the P-SCH nor the S-SCH are scrambled with the cells scrambling code. 54

5. PDSCH Physical Downlink Shared Channel Carry DSCH Shared by users based on code multiplexing As DSCH is always associated with DCH, PDSCH is always associated with DPCH Spreading factor may vary frame-to-frame (SF = 256 to 4) Control information is transmitted on the DPCCH part of the associated DPCH 6. AICH Acquisition Indicator Channel Used to carry Acquisition Indicators (AI) Either corresponds to an access preamble or a CD preamble Access preamble is an AP-AICH and CD preamble is a CD-AICH 55 Downlink Physical Channels [6]

7. PICH Page Indicator Channel Used to carry Page Indicator (PI) PICH is always associated with a S-CCPCH to which PCH is mapped 56 Downlink Physical Channels [7]

57 WCDMA Downlink Modulator Structure pulse shape filter (SRC) Primary Sync Code Secondary Sync Code sum dedicated traffic channels primary & secondary common pilot channels primary & secondary common control channels other channels s/p Primary CPICH C ch,256,0 Primary CCPCH C ch,256,1 Others are assigned by UTRAN GsGs

Uplink DPDCH bit rates 256 128 64 32 16 8 4 SFChannel bit rate (kb/s)User data rate (kb/s) 15 30 60 120 240 480 approx. 7.5 approx. 15 approx. 30 approx. 60 approx. 120 approx. 240 960approx. 480 58

Downlink DPDCH bit rates 256 128 64 32 16 8 4 SFChannel bit rate (kb/s)User data rate (kb/s) 15 30 60 120 240 480 approx. 1-3 approx. 6-12 approx. 20-24 approx. 45 approx. 105 approx. 215 960approx. 456 512 1920approx. 936 59

User data rate vs. channel bit rate Channel bit rate (kb/s) User data rate (kb/s) Channel coding Interleaving Bit rate matching Interesting for user Important for system 60

Documents

UMTS protocols Different protocol stacks for user and control plane User plane (for transport of user data): Circuit switched domain: data within ”bit