Cell Broadcast Service USER DESCRIPTION

Transcription

1 Cell Broadcast Service USER DESCRIPTION

2 Copyright Copyright Ericsson AB All Rights Reserved. Disclaimer No part of this document may be reproduced in any form without the written permission of the copyright owner. The contents of this document are subject to revision without notice due to continued progress in methodology, design and manufacturing. Ericsson shall have no liability for any error or damage of any kind resulting from the use of this document.

3 Contents Contents 1 Introduction Scope Target Groups Revision Information Concepts 1 2 Overview 2 3 Capabilities 3 4 Technical Description Cell Broadcast Service Area Start of CBS operation Reception of new CB messages Deletion of CB messages Scheduling of BMC messages over the Uu interface Iu-BC Transport Iub Transport 10 5 Parameters Descriptions Range and Default Values 11 6 Feature Management 12 Reference List 13

4 Cell Broadcast Service

5 Introduction 1 Introduction This document describes the feature Cell Broadcast Service (CBS) within the WCDMA Radio Access Network (RAN). Note: Cell Broadcast Service, FAJ , is an optional feature. 1.1 Scope The document describes the CBS feature including operator parameters and information about the activation and deactivation of the feature. 1.2 Target Groups The target groups for this document are the following: System operators who need a general understanding of the CBS feature in WCDMA RAN Personnel working on Ericsson products or systems 1.3 Revision Information Table 1 Revision History Revision Reason for Revision A This is a new document. 1.4 Concepts The following concepts are addressed in this document: Cell Broadcast (CB) message Cell Broadcast Service Area (CBSA) BMC CBS Message User data as transmitted from the CBC to the UE. A CBSA represents the smallest geographical area where CB messages can be broadcast. One CBSA contains one UTRAN cell. BMC CBS Messages are sent from WCDMA RAN to the UE using the BMC protocol. A BMC CBS Message contains one CB message. 1

6 Cell Broadcast Service CTCH occasion A radio frame on the Secondary CCPCH where CTCH data can be sent. For an explanation of terminology used in this document, see Glossary of Terms and Acronyms. 2 Overview This section provides an overview of the CBS feature in WCDMA RAN. The CBS feature enables broadcast of short text messages to defined geographical areas known as Cell Broadcast Service Areas (CBSAs). The messages are repeated over the air interface at a frequency and for a duration agreed by the content provider. CB messages are generated by the Cell Broadcast Center (CBC) and sent to WCDMA RAN via the Iu-BC interface, see Figure 1. The CBC is an external node provided by the operator, that is, the functionality is not integrated in the Ericsson Core Network. UE UE Uu WCDMA RAN Node B RNC Node B Iub IuBC Cell Broadcast Center (CBC) Figure 1 CBS Overview U A The Iu-BC interface is standardized by 3GPP and the protocol stack is illustrated in Figure 2 below. 2

7 Capabilities SABP (ASN.1) TCP/IP Ethernet SABP (ASN.1) TCP/IP AAL5/ATM Figure 2 IP Iu-BC protocol stack Iu-BC protocol stack Physical layer ATM Iu-BC protocol stack U A The Service Area Broadcast Protocol (SABP), specified in Reference [2], is used to distribute CB messages from CBC to a number of CBSAs in RNC. Each CBSA contains only one UTRAN cell. The lower layers of the Iu-BC interface are specified in Reference [3]. Both IP and ATM transport is supported in WCDMA RAN. The CB messages received from CBC are stored in WCDMA RAN and the Broadcast Multicast Control (BMC) protocol, specified in Reference [4], is used on the Uu interface to schedule and broadcast corresponding BMC CBS messages in the cell. Each BMC CBS message contains one CB message. The BMC CBS messages are sent on the logical channel CTCH using RLC unacknowledged mode. The CTCH is multiplexed on a FACH transport channel carried by a Secondary CCPCH. CB messages are received by UEs in Idle mode and in state URA_PCH. The UE will monitor the CTCH during time intervals which do not conflict with the UE specific paging occasions on PICH. 3 Capabilities A maximum of 20 CB messages, or a total payload of 2.5 kbyte, can be stored per CBSA in the RNC. When this limit is reached new CB messages addressed to the CBSA are discarded. If a CB message is discarded the cell counter pmnodiscardedcbsmsgorders is stepped, see Reference [6]. The maximum number of CBSAs is within a PLMN and 2304 within an RNC. The size of incoming SABP messages is limited to octets. This should be large enough to cover a SABP WRITE-REPLACE message containing 2304 CBSAs. If the size exceeds octets the message is not decoded and WCDMA RAN responds by sending an SABP ERROR INDICATION to CBC. 3

8 Cell Broadcast Service 4 Technical Description 4.1 Cell Broadcast Service Area The CBS feature includes the area concept Cell Broadcast Service Area (CBSA) which represents the smallest geographical area where a CB message can be broadcast. The CBSA is only used towards the CBC node and it contains one UTRAN cell. The service area identity (SAI) for a CBSA is defined as: PLMN id + Location Area Code (LAC) + CB Service Area Code The CB Service Area Code is configured in the RNC and the value is set by the cell parameter cellbroadcastsac. For PLMN id and LAC the already configured values for the cell are used. In order to avoid configuration mismatch OSS provides a consistency check rule for verifying that the CBSAs are unique in all cells in the network. Warnings will be issued in case on non-unique SAI as same SAI in different cells may cause broadcasting of CB messages in the wrong area. If the cellbroadcastsac parameter is set to undefined no CB messages can be broadcast in the cell. 4.2 Start of CBS operation This section describes the prerequisites for CBS operation as well as the functionality triggered in WCDMA RAN at feature activation. In order to start CBS operation the following criteria must be fulfilled: 1. The CBS feature is activated and the license is loaded, see Section 6 on page The Iu-BC link is configured, see Section on page The cells in which CB messages are to be broadcast are enabled and a CBSA is defined for each cell, see Section 4.1 on page 4. As soon as criteria 1 and 3 are fulfilled, the CTCH configuration is included in system information, SIB5, and the UE will start monitoring the CTCH occasions on S-CCPCH in cells where a CBSA has been defined. However, no CB messages can be broadcast in the cells as long as the Iu-BC link is not configured. 4

9 Technical Description Once all criteria 1, 2 and 3 above are fulfilled, RNC informs CBC about the service areas that are operable by sending a SABP RESTART message. The SABP RESTART message contains a list of all defined CBSAs within the RNC. If a cell with a defined CBSA becomes disabled the broadcast is stopped in that cell and all stored CB messages are cleared. As soon as the cell is up again a restart indication is triggered for the cell. To avoid that SABP RESTART messages are sent too often over the Iu-BC interface a periodic timer of 30 seconds is implemented in the RNC to monitor the restart indications. Whenever the timer expires RNC will send a SABP RESTART message to CBC containing a list all CBSAs that have triggered a restart indication during the last 30 seconds. If there were no restart indications when the timer expires, no SABP RESTART message is sent for that period. 4.3 Reception of new CB messages Broadcast of a new CB message, or replacement of an old CB message, is initiated by CBC with SABP message WRITE-REPLACE. In addition to the actual CB payload the SABP WRITE-REPLACE message contains the following information Message Identity and Serial Number Old Serial Number Data Coding Scheme Service Areas List Repetition Period Number of Broadcasts Requested Category The Message Identity and the 12 left-most bits of the Serial Number uniquely identifies a CB message within a CBSA. This information is optional and only included in the SABP WRITE-REPLACE message if there is a need to replace an already stored CB message for a given Message Identity. This information is transferred transparently to the UE. List of CBSAs where the CB message is to be broadcast. Information about how often the CB message is to be broadcast. Information about how many times the CB message is to be broadcast. The broadcast can be either finite or infinite. This information indicates the priority of the CB message. Figure 3 illustrates the steps performed in WCDMA RAN at reception of a SABP WRITE-REPLACE message. 5

10 Cell Broadcast Service UE RNC CBC Check list of service areas 2. For all defined service areas in the list: -Store new data -Stop broadcast of old CB message (optional) -Start broadcast of new CB message 1. SABP WRITE-REPLACE 1. SABP WRITE-REPLACE COMPLETE CTCH: BMC CBS Message... CTCH: BMC CBS Message 3. For finite broadcast: Clear CB message and stop broadcast. Figure 3 WRITE-REPLACE U A 1. At reception of the SABP WRITE-REPLACE message RNC checks that all service areas included in the message are defined as CBSAs and responds with a SABP WRITE-REPLACE COMPLETE message. 2. For each defined CBSA listed in the SABP WRITE-REPLACE message the following steps are performed: If the cell contained in the CBSA is enabled, the new CB message is stored. If the SABP WRITE-REPLACE message contains an Old Serial Number, the previously stored CB message is replaced with the new information. Broadcast of the old CB message is stopped. The new CB message is broadcast on CTCH using the BMC protocol. The BMC CBS messages are broadcast with the repetition period requested by CBC. 3. For finite broadcast, the CB message is cleared when it has been repeated the number of times requested by CBC. For infinite broadcast, the CB message is repeated until it is deleted by CBC, see Section 4.4 on page Deletion of CB messages An active CB message can be deleted by request from CBC using one of the SABP procedures KILL or RESET. The KILL procedure is used to stop broadcast of one CB message in one or several CBSAs whereas the RESET procedure is used to stop broadcast of all CB messages stored in one or several CBSAs. Both procedures are supported in WCDMA RAN. 6

11 Technical Description 4.5 Scheduling of BMC messages over the Uu interface The logical channel CTCH is multiplexed on FACH1, carried by the existing S-CCPCH used for 32 kbps Interactive PS RB and SRBs. The CTCH is scheduled on S-CCPCH during predefined CTCH occasions. The CTCH occasions are fixed on the SFN cycle and thus repeated cyclically. CTCH occasions are defined as the radio frames in which the following equation is true: SFN = K + m*n, m = 0, 1, 2,... M (Reference [5]) K is the offset to the first CTCH occasion on the SFN cycle. The value is hard coded to 0. N is the period of CTCH occasions on S-CCPCH. The value is set by the parameter ctchoccasionperiod. M is chosen so that K + M*N 4095 (Max SFN) Note that the TTI for FACH1 is 10 ms, that is, each CTCH occasion corresponds to one TTI on FACH1. S-CCPCH (SFN) CTCH (SFN 0) (SFN 1) (SFN 2) CTCH (SFN N) (SFN N+1) ctchoccasionperiod Figure 4 Scheduling of CTCH occasions on Secondary CCPCH U A The CTCH will share existing S-CCPCH resources used for SRB signalling and PS Interactive data on FACH. However, transmission of BMC CBS messages will have highest priority in the RNC during a CTCH occasion. Thus the parameter ctchoccasionperiod can be used to control the maximum bandwidth of the CTCH channel that can vary from 0.18 kbps (ctchoccasionperiod = 256) up to 30.4 kbps (ctchoccasionperiod = 1). If there are no BMC CBS messages to transmit in a CTCH occasion, the TTI can be used by RNC to send other FACH1 or FACH2 data. Note that if the CTCH occasions are scheduled frequently, and the CBS load is high in the cell, the transmission of SRB signalling and PS Interactive data on FACH1 and FACH2 might get delayed. A UE in idle mode and state URA_PCH must listen to every CTCH occasion scheduled on S-CCPCH even if it does not contain any CTCH data. If the CTCH occasions are scheduled frequently on S-CCPCH it will impact the UE battery consumption in idle mode and URA_PCH state. Thus the setting of the parameter ctchoccasionperiod is a trade off between maximum CTCH bandwidth and UE standby time. 7

12 Cell Broadcast Service If a CTCH occasion conflicts with a paging occasion, the UE will prioritize paging before reading CTCH. The paging occasions are calculated based on the IMSI and the DRX cycle length coefficient. Different DRX cycle length coefficients can be configured for UEs in idle mode and in state URA_PCH, see Idle Mode and Common Channel Behavior. In order to avoid that the same UE will miss all CTCH occasions it is important to make sure that the ctchoccasionperiod is not set to a multiple of the DRX cycle length coefficient. Note: Changing the attribute ctchoccasionperiod will affect any ongoing traffic in the cell. Whenever its value is set, the cell is disabled automatically and then re-enabled. 4.6 Iu-BC Transport Network Aspects Overview 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, see Figure 5. The CBC node must be connected using IP/Ethernet to O&M Router. Cell Broadcast Center (CBC) IP transport (Iu-BC) RNC ATM transport (Mur + Iu-BC) O&M Router COMINF Figure 5 Iu-BC using ATM transport U A For IP case Iu-BC can be carried over IP/Ethernet straight to the CBC node from RNC, see Figure 6. 8

13 Technical Description Cell Broadcast Center (CBC) COMINF RNC IP transport (Iu-BC) IP transport (Mur + Iu-BC) IP/Ethernet O&M Router Figure 6 Iu-BC using IP transport U A QoS Dimensioning For IP over ATM case, 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. The fact that the Iu-BC interface will be connected to the same O&M IP network as Mur implies the following: QoS must be considered as the Iu-BC traffic will compete for bandwidth with the O&M traffic Iu-BC interface and traffic will experience the same level of network security as O&M traffic and as provided by the O&M IP network 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 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. 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: 9

14 Cell Broadcast Service Security 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 octets. nummsgs/second is the number of SABP messages sent over the Iu-BC interface per second. IP network security must be considered when adding Iu-BC traffic to the O&M IP network. This network has many access points compared to the networks for user traffic and is potentially exposed to greater security threats. To improve security it is recommended to turn on the Filter for IP source address validation in the RNC by setting parameter sourceipaddressvalidation to TRUE. This filter will avoid the establishment of connections from other IP source addresses than the configured IP address for the CBC. It is possible to turn this filter off if there is a need to establish connections from more than one IP address. Note: If the filter is not used the security level may need to be increased for the entire O&M IP network Configuration In order to start CBS operation the MO IuBcLink has to be created in RNC. The recommended configuration of the IuBcLink can be found in Table 2 below. Table 2 Iu-BC configuration MO:<Type> = <Name> <attribute> = <value> Comment IuBcLink=1 administrativesta UNLOCKED will te = UNLOCKED activate CBS cbcipaddress [0..15] sourceipaddressva lidation = TRUE IP address of the CBC according to IP address plan It is recommended to set the parameter to TRUE 4.7 Iub Transport The new logical channel CTCH is carried over the existing transport bearer established for FACH1. 10

15 Parameters 5 Parameters This section describes all parameters that the operator can configure to control the CBS feature in WCDMA RAN. Further parameter information can be found in Radio Network Parameters. 5.1 Descriptions cellbroadcastsac ctchoccasionperio d cbcipaddress sourceipaddressv alidation Cell Broadcast Service Area Code within a location area. The parameter can be set per cell. Period of CTCH allocations on S-CCPCH. The parameter can be set per cell. IP address of the CBC. The input format used by the operator is four fields of digits, separated by dots. Each field may consist of three digits. The value of each field shall be in the range Indicates if the source IP address shall be validated when the CBC establishes a connection. When set to TRUE, only a source IP address equal to cbcipaddress is accepted. 5.2 Range and Default Values Table 3 WCDMA RAN Cell Broadcast Parameters Parameter Name Default Value Value range Unit of Measurement cellbroadcastsac [undefined] [undefined, ] ctchoccasionperiod ms cbcipaddress - Four fields of digits, separated by dots. Each field may consist of three digits. The value of each field shall be in the range sourceipaddressvalidation TRUE FALSE, TRUE

16 Cell Broadcast Service 6 Feature Management This section describes how features are managed, that is, how status is read, and how a feature is activated or deactivated. The following features are covered: Cell Broadcast Service Parameter Check To check the status of any of the parameters listed for the features below, use the latest revision of the OSS-RC, OSS Parameter Check User Guide 1/1553-APR /2. Activation and Deactivation Activation or deactivation of a feature is done in a variety of ways using OSS Network Explorer and other Ericsson proprietary tools. Customer tools may also be used, but this is not described by Ericsson. Switching the parameters either on or off activates or deactivates the feature. Activation and deactivation of the Cell Broadcast Service feature is made using the RNC parameter featurestate, for designation cellbroadcastservice, in the generic MO class RncFeature. 12

17 Reference List Reference List [1] OSS-RC, OSS Parameter Check User Guide, 1/1553-APR /2 [2] 3GPP TS , UTRAN Iu-BC Interface: Service Area Broadcast Protocol (SABP) [3] 3GPP TS , UTRAN Iu interface data transport and transport signalling [4] 3GPP TS , Broadcast/Multicast Control (BMC) [5] 3GPP TS , Radio Resource Control (RRC) Protocol [6] Managed Object Model RNC, AXD10503/1 [7] Idle Mode and Common Channel Behavior, 71/1553-HSD10102/6 [8] Glossary of Terms and Acronyms, 1/0033-HSD10102/7 [9] Radio Network Parameters, 86/1553-HSD10102/7 13