Cell Broadcast Service in RAN P7

Overview

FAJ 121 1326 Cell Broadcast Service

• P7 Feature Scope (Optional)

• Enables broadcast of short text messages to UEs in idle mode and URA_PCH state

• CB messages are generated by an external Cell Broadcast Centre (CBC) and sent to UTRAN via the new Iu-BC interface.

UuRRC: SIB5BMC signalling (25.324)Logical ch: CTCHTransport ch: FACH1Physical ch: S-CCPCH

Uu

Cell

BroadcastCenter

(CBC)

UTRAN

RNC

Node B

Node B UE

UE

Iub

IuBC

Iu-BCSABP signalling (25.419)Signalling transport (25.414)-TCP/IP (port: 3452)-IP or ATM transport

Concepts• Cell Broadcast (CB) message

– User data as transmitted from the CBC to the UE

• Cell Broadcast Service Area (CBSA)– A CBSA represents the smallest geographical area where CB messages

can be broadcast. One CBSA contains one UTRAN cell

• BMC CB message– BC CB messages are sent from WCDMA RAN to the UE using the BMC

protocol. – A BMC CB message contents one CB message

• CTCH occasion – A radio frame on the S-CCPCH where CTCH can be sent

CBS in Ericsson RAN P7 (1/2)Restrictions & Limitations CBS Level 2 Scheduling (DRX mode) is not supported in P7 Max CB messages stored per cell: 20 Max CBS payload stored per cell: 2.5 kbyte

References CPI: Cell Broadcast Service, 126/1553-HSD 10102/7 3GPP SoCs:

– BMC (25.324), 44/17402 - HSD10102/7– SABP (25.419), 45/17402 – HSD 10202/7– Iu interface data transport & signalling (25.414), 02/17402 – HSD

10102/7

Feature preparation CN requirements:

– None Hardware requirements:

– R4 HW for the RANAP/RNSAP MP in RNC UE requirements:

– Support for CBS according to 3GPP Rel-99 Initial tuning:

– Not applicable

Feature Activation SW license for FAJ 121 1326 installed and activated in RNC MO IuBcLink created and unlocked Cell Broadcast Service Area defined per UtranCell (parameter cellBroadcastSac) Note: Activation of this feature will impact UE battery consumption in idle mode

and state URA_PCH

CBS in Ericsson RAN P7 (2/2)

Radio Protocol

BMC protocol model & functions

L2/BMC sublayer

RRC BMC-SAP

user-plane

L2/RLC sublayer

BMC

RLC

UM

CTCH-SAP

CBMC-SAP

Storage of Cell Broadcast Messages Scheduling of BMC messages Transmission of BMC messages to UE

Note : E/// P7 will not support Traffic volume monitoring and radio resource request

Functions

Cell Broadcast Service AreaCBSA (Cell Broadcast Service Area) definition

PLMN id + Location Area Code (LAC) + CB Service Area Code

• Only used towards the CBC and contained one cell• CB SAC is configured in RNC and set as cellBroadcastSac • OSS provide consistency check rule

– To verify CBSAs are unique in all the network• Existing SA towards CN (CS and PS domain) is not affected.

Start of CBS operation• Criteria to start CBS operation

1. The CBS feature activated and the license is loaded 2. The Iu-BC link is configured 3. The cells in which CB messages are to be broadcast are enabled and a CBSA is defined for

each cell

• RNC send a SABP RESTART message to CBC– Contains a list of all defined CBSAs within the RNC.

• SABP RESTART Message is also sent– When

• Disable cell was recovered and trigger to the RNC• And periodic timer of 30seconds is expired

– Timer is implemented to avoid frequent messages

– Message contains a list of all CBSAs that have triggered within last 30second

Broadcasting the message(Write and Replace)

Note: E/// P7 doesn’t support BMC schedule message

Write-Replace Message from CBC (1)

• Message type – Identify the type of message (e.g. Write-Replace)

• Message identifier – RNC uniquely identify the CB message by this identifier with the 12 left most bits of

the Serial number• New serial number and old serial number

– Indicate new and old message• Service Area identifier

– Identifies Service area – Max 2304 Service Areas are supported

• Category– “High priority” : Broadcast immediately– “Background” : Broadcast when No High priority or Normal Traffic broadcast – “Normal” : Broadcast according to the repetition period IE

Note : In Ericsson’s implementation RNC will not use the Category information. All CB messages are sent immediately after reception of a Write-Replace message.

Write-Replace Message from CBC (2)

• Repetition Period– Indicates the periodicity of message broadcasts– Set from once per one second to once per -1 hour

• Number of Broadcast requested– Indicates the number of the times a message to be broadcast 0 – 65535: – 0 indicates “until other command received from CN”

• Data Coding Scheme– Identifies the alphabet or coding employed for the message characters

and message handling• Broadcast message content

– Bit string (1….9968) ,,, The size shall be multiple of 8

Write-Replace RNC action

• Checks all service areas are defined as CBSA then responds Write-Replace complete message– If not, responds Write-replace failure message

• If the cell contained in the CBSA is enabled – The new message is stored

• If the Message contains old serial number– The previously stored message replaced with the new message

• New message is broadcast on CTCH – With the repetition period requested by CBC– For infinite Broadcast the CB message is repeated until it is deleted by

CBC

Deletion of CB messages

• Kill Procedure– Used to stop broadcast of one CB message in one

or several CBS’s

• Reset Procedure– Used to stop broadcast of all CB messages stored

in one or several CBS’s

CTCH mapping on S-CCPCH

• The logical channel CTCH is multiplexed on FACH1

• Then carried by exiting S-CCPCH for 32kbps Interactive PS RB and SRB’s

• The CTCH is scheduled on S-CCPCH during predefined CTCH occasion i.e. timing of CTCH transmission is fixedCTCH

SFN 0

CTCH

SFN NSFN 1S-CCPCH

ctchOccasionPeriod

......

10mS

SFN 2......

SFN N+1

SFN cycle : 0…..4095

CTCH Occasions• CTCH occasions are defined as SFN=K+m*N, m=0,1,2….M

K: Offset of the first CTCH, Hard coded to 0

N: Period of CTCH occasion, ctchOccasionPeriod:1-256 M: Chosen so that SFN=K+m*N <=4095 (Max SFN)

SFN cycle : 0…..4095

CTCH

SFN 0

CTCH

SFN NSFN 1S-CCPCH

N:ctchOccasionPeriod

......

10mS

SFN 2......

SFN N+1

Maximum BW of CTCH Channel can vary from 0.18kbps to up to 30.4kbps

CTCH occasion impact

• Impact on SRB and PS interactive, UE power consumption– BMC CB messages will have the highest priority in frames defined as CTCH occasions

• Other FACH1 or FACH 2 data can be sent if no CTCH data

– Frequent CTCH occasion and high CBS load cause delay of SRB and PS interactive on FACH 1 and FACH2

– UE (In idle and URA_PCH) must listen to every CTCH occasion• Trade off between Max CTCH BW and UE power Consumption

Need to select CTCH occasion period carefully Confliction with paging occasion

– UE will prioritize paging occasion if paging occasion conflict with CTCH occasions in idle and URA_PCH state

– Paging occasions are calculated based on the IMSI and the DRX cycle length coefficient

Need to make sure CTCH occasion period is not set to a multiple of DRX cycle length coefficient to avoid same UE will miss CTCH occasion

IuBC Interface

Iu-BC protocol stack and precondition

• The Iu-BC interface is standardized by 3GPP.• The CBC node must be connected to the O&M IP network • The O&M IP network must allow the TCP port for SABP

3452 and will compete for bandwidth with the O&M traffic

IP Iu-BC protocol stack ATM Iu-BC protocol stack

Iu-BC using ATM transport

• Iu-BC and O&M traffic will share the same IP host in RNC. • For ATM case, Iu-BC traffic is carried to O&M router using ATM.• The CBC node must be connected using IP/Ethernet to O&M Router.

IP transport (Iu-BC)

ATM transport(Mur + Iu-BC)

Iu-BC using IP transport

• For IP case Iu-BC can be carried over IP/Ethernet straight to the CBC node from RNC • all IP Routing configuration in RNC for Mur can be reused for Iu-BC as the Iu-BC interface is

connected to the same O&M IP network as Mur. • There is no need to add or modify routes as all traffic is sent to the O&M Router.

IP transport (Iu-BC)

IP transport(Mur + Iu-BC)

QoS

• From RNC to CBC node the Iu-BC traffic will get the same QoS characteristics as O&M traffic.

• For the traffic from the CBC to the RNC, QoS separation in the IP network using different settings of the DSCP (DiffServ Code Point) can be done if the CBC node supports it.

• The QoS characteristics currently recommended for O&M traffic is assumed to be adequate for Iu-BC traffic.

• An operator may choose to implement an O&M IP network with a higher QoS level.

Dimensioning• The dimensioning of the O&M IP network should take into account Iu-BC

traffic. • The Iu-BC traffic volume is expected to be low and the impact on the

dimensioning should be small. • The Iu-BC capacity demand can be calculated using the formula below:

C Iu-BC = Msglength * numMsgs/second

• Msglength is the length of the SABP message. Note that the maximum length of a SABP message that can be processed in WCDMA RAN is limited to 18000 octets.

• numMsgs/second is the number of SABP messages sent over the Iu-BC interface per second.

O&M Network (IP)

RNC3810

<Network example>

ET-M4

O&M Router<ATM/IP Converter>

Mur

OSS Server

CBC Network (IP)

CBS

Core

MP

Backplane

Mur

O&M Network (IP)

RNC3810

<Network example>

ET-M4

O&M Router<ATM/IP Converter>

Mur

OSS Server

O&M Router

X

Core

MP

Backplane

CBC Network (IP)

CBS

Redundant example with ET-MFXET-MFX board redundancy

Some Iu-BC Network Example

IuBCHost

IuBCHost

IuBCHost

IuBCHost

IuBCHost

IuBCHost

CBS

NW Address TranslationNW Address Translation

Area 1 Area N

O&M

New/Modified MO structure

LA

SA

UtranCell

RncFunction

0..47

0..2304

0..2304

0..2304

1

1 1

# …... # ctchOccasionPeriod # cellBroadcastSac # …..

1

0..1

# administrativeState # operationalState # availabilityStatus # cbcIpAddress #sourceIpAddressValidation

0..2304 1 1

IubcLink

• Each UtranCell can be associated with a new Cell Broadcast Service Area used towards the CBC node.– SAC for the CB SA is set by parameter cellBroadcastSac– Existing SA towards CN (CS and PS domain) is not affected.

Parameter setting (1/3)

cellBroadcastSac

• Scheduling of CTCH on S-CCPCH is controlled by parameter ctchOccasionPeriod.

• The setting of ctchOccasionPeriod is a trade off between max CBS throughput and UE battery usage in idle mode and URA_PCH state.

ctchOccasionPeriod

CTCH CTCHS-CCPCH

ctchOccasionPeriod

......

Parameter setting (2/3)

cbcIpAddress

• Four field of digits, separated by dots.• Each field may consists of three digits.• The value of each field shall be in the range 0….255

sourceIpAddressValidation Filter for IP source address validation in the RNC If it set to “true” filter will avoid the establishment of connections from

other IP addresses

Parameter setting (3/3)

• No impact on KPIs• New pm counters

– pmNoReceivedSABPMsgs: Number of received SABP messages over Iu-Bc– pmNoSentSABPMsgs: Number of sent SABP messages over Iu-Bc– pmNoRejectedTcpConnections: Number of rejected TCP connections because

of disallowed source IP address– pmNoDiscardedCbsMsgOrders: Number of discarded CB message orders per

cell– pmNoDiscardedBmcMsgs: Number of discarded BMC PDU’s per cell. Each BMC

PDU contains one BMC CB message.– pmBmcTrafficVolume: Accumulated BMC payload (bytes) per cell

Observability (1/2)

• New GPEH events– CBS_MESSAGE_ORDER_DISCARDED – triggered each time counter

pmNoDiscardedCbsMsgOrders is stepped.

– New events for all SABP messages transmitted over Iu-BC:• SABP_WRITE_REPLACE• SABP_WRITE_REPLACE_COMPLETE• SABP_WRITE_REPLACE_FAILURE• SABP_KILL• SABP_KILL_COMPLETE• SABP_KILL_FAILURE• SABP_RESET• SABP_RESET_COMPLETE• SABP_RESET_FAILURE• SABP_RESTART• SABP_ERROR_INDICATION

Observability (2/2)