ETSI TR 144 901 V13.0.0 (2016-01)

ETSI TR 1144 901 V13.0.0 (201616-01)






TECHNICAL REPORT
Digital cellular telecocommunications system (Phahase 2+);
External Netwoorrkk Assisted Cell Change (NAACCC)
(3GPP TR 44.9.901 version 13.0.0 Release 13 13)

R
GLOBAL SYSTTEME FOR
MOBILE COMMUUNNICATIONS

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3GPP TR 44.901 version 13.0.0 Release 13 1 ETSI TR 144 901 V13.0.0 (2016-01)



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3GPP TR 44.901 version 13.0.0 Release 13 2 ETSI TR 144 901 V13.0.0 (2016-01)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
http://webapp.etsi.org/key/queryform.asp.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI

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3GPP TR 44.901 version 13.0.0 Release 13 3 ETSI TR 144 901 V13.0.0 (2016-01)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 7
4 Introduction and Motivation . 7
4.1 Task Description . 7
4.2 GPRS Cell Reselection pre-Release 4 . 7
4.3 NACC in GERAN Release 4, Short description . 7
4.3.1 System Information Reception . 8
4.3.2 Cell Change Notification (CCN) Mode Procedures . 8
4.4 Extension of NACC in Release 5 . 8
4.4.1 General . 8
4.4.2 Short Technical Description . 10
5 Requirements . 10
5.1 Architectural Requirements . 10
5.1.1 Case 16 - Intra-UTRAN case . 11
5.1.2 Case 4, 8, 12: GERAN UTRAN . 11
5.1.3 Case 13 - 15: UTRAN GERAN . 12
5.2 Node Requirements . 12
5.2.1 BSC . 12
5.2.2 RNC . 12
5.2.3 SGSN . 13
5.2.4 MSC . 13
5.3 Interface Requirements . 13
5.3.1 Gb interface . 13
5.3.2 A interface . 13
5.3.3 Iu interface . 13
5.3.4 Iur-g (Iur) interface . 13
5.3.5 Gn interface . 14
5.3.6 Uu interface . 14
5.3.7 Um interface . 14
6 Generic mechanism for exchange of RAN information . 14
6.1 General . 14
6.2 Generic RIM procedures for exchange of RAN information . 15
6.2.1 General . 15
6.2.2 RAN Information Request procedure . 15
6.2.3 RAN Information Send procedure . 15
6.2.4 RIM support in CN/RAN nodes. . 16
6.3 Messages for RAN information . 16
6.3.1 Message format . 16
6.3.2 Message Type . 16
6.3.3 Addressing and routeing . 17
6.3.4 Container Prefix and Container Units . 18
6.3.4.1 General . 18
6.3.4.2 Container Prefix . 18
6.3.4.3 Container Unit . 18
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3GPP TR 44.901 version 13.0.0 Release 13 4 ETSI TR 144 901 V13.0.0 (2016-01)
7 Exchange of RAN information for external NACC . 18
7.1 Principles for use of the generic mechanism for exchange of RAN information for NACC application . 18
7.1.1 General . 18
7.1.2 Container Unit Disposition for NACC. 19
7.1.3 Error Handling . 19
7.1.4 External NACC software support in RAN nodes . 19
8 Interface load . 19
9 Phased approach for the implementation . 20
10 Open Issues . 20
11 Specification Impact and Associated Change Requests . 20
11.1 General . 20
11.2 3GPP TS 23.060 GPRS; Stage 2 description . 20
11.3 3GPP TS 44.018 Mobile radio interface layer 3 specification . 21
11.4 3GPP TS 44.060 GPRS RLC/MAC Protocol . 21
11.5 3GPP TS 48.018 BSS GPRS Protocol (BSSGP) . 21
11.6 3GPP TS 29.060 GPRS Tunneling Protocol (GTP) . 21
11.7 3GPP TS 25.41x UTRAN Iu interface . 21
Annex A: Change History . 22
History . 23

ETSI

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3GPP TR 44.901 version 13.0.0 Release 13 5 ETSI TR 144 901 V13.0.0 (2016-01)
Foreword
rd
This Technical Report has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
ETSI

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3GPP TR 44.901 version 13.0.0 Release 13 6 ETSI TR 144 901 V13.0.0 (2016-01)
1 Scope
This Technical Report provides background information, motivations, concepts and requirements regarding an extended
Network Assisted Cell Change (NACC) feature for external cell change support. Cell change between GERAN and
UTRAN cells is outside the scope of this report, although consideration has been taken in order to allow an easier
extensibility to that case. The extension is based on the Release 4 version of the NACC feature where the mobile station
is only supported by the NACC when performing internal cell re-selection, i.e. within a BSC. The extension of the
feature is for GERAN just affecting BSS and for the core network the SGSN and signalling links between these network
nodes. To support cell changes between GERAN and UTRAN, also the Um and the Uu interfaces are affected.
The evolved Release 4 NACC proposal as described in this TR provides the basis for the detailed Stage 2 and stage 3
specification work. The feature will be developed in a phased approach and a longer-term vision is presented in the
report.
The focus of the TR is to:
- Define the requirements on different nodes
- Specify the requirements for the interfaces
- Propose a plan for the work item project
- Evaluation of what does and does not need to be standardised
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
• References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TD GP-010361, 'Network Assisted Cell Change; Concept document'
[2] 3GPP TS 48.018: "General Packet Radio Service (GPRS); BSS GPRS Protocol (BSSGP)".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following definitions apply:
External cell change: Change of cells where old and new cell do not belong to the same BSC.
External neighbouring cells: Cells listed in the BA-lists within a BSC that belongs to other BSCs.
Extended neighbouring cell list: List of System information received from the external neighbour cells to be used in
the Network Assisted Cell Change procedure.
Service outage time: The time between the last received uplink RLC block from the mobile station in the
old cell and the mobile station's first uplink RLC block received in the new cell.
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3GPP TR 44.901 version 13.0.0 Release 13 7 ETSI TR 144 901 V13.0.0 (2016-01)
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:

CCN  Cell Change Notification
EDGE  Enhanced Data rates for GSM Evolution
GERAN  GSM/EDGE Radio Access Network
GPRS  General Packet Radio Service
NACC  Network Assisted Cell Change
NC  Network Control mode (can be NC0, NC1 or NC2)
O&M  Operations and Maintenance
PACCH  Packet Associated Common Control Channel
PS  Packet Switched
QoS  Quality of Service
RN  Radio Network
RAN  Radio Access Network
RIM  RAN Information Management
UE  User Equipment
UTRAN  Universal Terrestrial Radio Access Network
4 Introduction and Motivation
4.1 Task Description
The purpose of this new work task is to shorten the service outage time at cell reselection in packet transfer mode when
the originating and the target cells belong to different BSCs/RNCs. This will improve the delivered quality of service
for most QoS classes.
4.2 GPRS Cell Reselection pre-Release 4
A pre-Release 4 GPRS/EDGE mobile station shall in modes NC0 and NC1 perform cell reselection purely based on
neighbour cell measurements and independent of whether a packet transfer is ongoing or not. The cell change is
performed without notifying the network. The MS is then not allowed to make random access in order to restart the data
transfer in the new cell until a consistent set of system information for that cell has been correctly received. This
behaviour is also used in Release 4 for the cases when a GPRS mobile station moves between GSM cells belonging to
different BSCs or from a GSM to a UMTS cell.
If the MS is trying to collect the target cell system information before the cell change, the MS may lose downlink data,
which then has to be retransmitted in the new cell. If on the other hand the system information is collected after entering
the target cell, the MS must first synchronise to the system information broadcast cycle and then collect the required
system information before starting to re-establish the data transfer. In both cases the MS will lose a certain amount of
time and downlink data when collecting the system information. There is also a risk that one or more RLC SDUs have
to be completely retransmitted in the new cell as the cell change can be performed anytime during an ongoing transfer.
For these reasons the Network Assisted Cell Change feature was introduced in Release 4 for MSs performing cell
changes between cells belonging to the same BSC. The feature reduced the service outage time for an MS in packet
transfer mode from a couple of seconds down to 300-700 ms by giving the network a possibility to assist the MS before
and during the cell change. The assistance is given both as sending of neighbouring cell system information and with
introduction of new procedures.
4.3 NACC in GERAN Release 4, Short description
NACC, the Network Assisted Cell Change feature introduced in Release 4 is a tool to minimize the service outage time
for all QoS classes when a GPRS MS in packet transfer mode moves between GSM cells belonging to the same BSC.
An overview of the Release 4 behaviour is described in GP-010361.
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3GPP TR 44.901 version 13.0.0 Release 13 8 ETSI TR 144 901 V13.0.0 (2016-01)
NOTE: In the Release 4, NACC is not implemented to support cell reselections between GERAN and UTRAN
or between BSCs. In this technical report a possible introduction of these cases is outlined.
The NACC procedures are introduced as a mandatory feature for an Release 4 MS to speed up the cell re-selection.
There are two main set of procedures specified for NACC, independent from each other:
- One set which supports the mobile station with neighbouring cell system information and
- One set which prepares the MS and puts the MS into Cell Change Notification mode (CCN mode) during a short
period of time before the cell change.
4.3.1 System Information Reception
In the first set of procedures the network may - independent of the NC and the CCN modes - send neighbouring cell
system information to an MS. The information is sent on the PACCH and is required for initial access after a cell
change. An MS in Packet Transfer mode, which receives this information, shall store the information for 30 seconds.
The MS may then use this information in the new cell. In the new cell the MS may then initiate access and receive
missing system information from BCCH or PBCCH on PACCH by using the Packet PSI/SI Status procedures.
4.3.2 Cell Change Notification (CCN) Mode Procedures
In the second set of procedures a Release 4 MS in packet transfer mode enters CCN mode when a cell reselection is
determined and if the network has ordered the MS to use CCN within the cell and towards the target cell. This order can
either be generally given by the network in system information or be individually addressed to a certain mobile.
When in CCN mode the MS informs the network with a Cell Change Notification message that the MS wants to
reselect cell. The message contains the identity of the target cell. After sending the message to the network the mobile
station continues the ongoing packet transfer for either a maximum time of about 1 second or until the network responds
with a Packet Cell Change Continue or Packet Cell Change Order message. The Packet Cell Change Order message
may indicate another target cell than the one proposed by the mobile station. After the delay, the MS leaves CCN mode.
The MS also leaves CCN mode if it returns to Packet Idle mode, if it enters NC2 mode or if the criteria for camping on
the old cell are no longer fulfilled.
In CCN mode the network also has an opportunity to send neighbouring cell system information required for immediate
initial access in the new cell when the re-selection has been performed. In CCN mode, the network may also terminate
the ongoing packet transfer before sending the Packet Cell Change Continue or the Packet Cell Change Order message
to the MS.
4.4 Extension of NACC in Release 5
4.4.1 General
In Release 4 of the GERAN specifications, the NACC procedures cover only cell re-selection to other GERAN cells
within the same BSC where the BSC has system information available for the target cell.
This limits the value of NACC, as external BSC cell changes and also cell changes between GERAN and UTRAN cells
in some network configurations are of frequent occurrence. Extensions of the NACC feature to handle also external cell
changes will therefore be of a certain value. For cell changes between Gb and Iu mode within GERAN and between
GERAN A/Gb mode and UTRAN Iu-mode it is not obvious that the service for the user is improved by NACC. These
cases might require rather heavy signalling to re-establish the RRC, the radio access bearers and the MM connections
before the user service can be restarted in the target cell.
A rough estimation of the occurrence of inter BSC cell changes in an assumed scenario where the BSC area consists of
a regular hexagonal area surrounded by other BSC areas (Figure 4.1.1.a) and subdivided into smaller, hexagonal
clusters is shown in Table 4.1.1.a. The traffic between these areas is then assumed to be equal distributed.
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3GPP TR 44.901 version 13.0.0 Release 13 9 ETSI TR 144 901 V13.0.0 (2016-01)
White = External cells belonging to other BSCs
Dark = Internal cells within a BSC Area

Figure 4.1.1.a: Example of internal/external cells for a BSC
Table 4.1.1.a: Relation between External to Total number of cell changes
BSC Area Size No of possible Relation External/Total no of cell
(in # of cells) external cell changes changes (in %)
1 6 100
7 18 43
19 30 26
37 42 19
61 54 15
91 66 12
127 78 10
169 90 9
271 114 7
397 138 6
547 162 5
721 186 4
1141 234 3

The case with a network composed of a mixture of BTSs and BSCs from different vendors will also give much higher
figures (approximately30 - 50% of external cell changes) as the cell clusters for a certain BSC will look like islands
among cell clusters from other vendors BSCs. This will also be the case having overlapping GERAN and UTRAN
coverage.
This is a simplified network where cell reselection is assumed to be possible only to the 6 closest neighbours. In normal
case the neighbouring cell lists can contain cells not directly close to the serving cell. So the figures for external cell
changes will probably be higher.
There is also the case when UTRAN and GERAN overlay, which means that the two access technologies have different
nodes in the access network.
Based on the reasons described above this study considers an extension of NACC to cover also cell changes to a cell
managed by another BSC/RNC where the origin BSC/RNC does not have system information available for the target
cell. This requires new signalling between BSCs/RNCs. The signalling may then be performed via the A, Gb, Iu and/or
Iur-g interfaces to inform each BSC/RNC of the neighbouring cell system information.
NOTE: the exchange of information between BSCs/RNCs via A and Iu-cs interfaces is out of the scope of this
document, although care has been taken in order to allow an easy extension for other features using inter
BSC/RNC communication.
The Table 4.1.1.b below indicates scenarios to be considered for cell reselection between different BSCs/RNCs and the
possibility to add the NACC feature to each case is then further discussed in this document. GERAN Gb indicates a
BSC connected to SGSN only via Gb; GERAN Iu indicates a BSC connected to SGSN only via Iu and GERAN Iu/Gb
indicates a BSC connected to SGSN via both Iu and Gb. This paper does not consider cell reselection scenarios
involving CDMA 2000 cells.
Table 4.1.1.b: Possible combinations of cell changes
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3GPP TR 44.901 version 13.0.0 Release 13 10 ETSI TR 144 901 V13.0.0 (2016-01)
Case No From To Traffic via
1 GERAN Gb GERAN Gb SGSN
2 GERAN Gb GERAN Iu/Gb SGSN
3 GERAN Gb GERAN Iu SGSN
4 GERAN Gb UTRAN SGSN
5 GERAN Iu GERAN Gb SGSN
6 GERAN Iu GERAN Iu/Gb SGSN or Iur-g
7 GERAN Iu GERAN Iu SGSN or Iur-g
8 GERAN Iu UTRAN SGSN or Iur
9 GERAN Iu/Gb GERAN Gb SGSN
10 GERAN Iu/Gb GER
...