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Radio Resource Pre-emption and
Queuing in BSC
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# Nokia Siemens Networks 1 (41)
BSC3119
Nokia BSC/TCSM, Rel. S12, Product
Documentation, v.3
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Contents
Contents 3
List of tables 4
List of figures 5
Summary of changes 7
1 Overview of Radio Resource Pre-emption and Queuing 9
2 Technical description of Radio Resource Pre-emption and
Queuing 132.1 Queuing 132.2 Pre-emption 152.3 Interworking 18
3 Functionality of Radio Resource Pre-emption and Queuing 213.1 Pre-emption management in the BSC 223.2 Queue management in the BSC 223.3 Forced release 243.4 Forced handover 263.5 Queuing 29
4 User interface of Radio Resource Pre-emption and Queuing 39
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Contents
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List of tables
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List of figures
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List of figures
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Summary of changes
Changes between document issues are cumulative. Therefore, the latest
document issue contains all changes made to previous issues.
Changes made between issues 10-2 and 10-1
Priority level related information has been moved from section Storing
forced release requests to section Storing forced handover requests in
chapter Technical description of Radio Resource Pre-emption and
Queuing .
Changes made between issues 10-1 and 10
Editorial changes made.
Changes made between issues 10 and 9-1
BTS terminology use has been updated: the distinction between a BTS,
cell, and SEG has been clarified.
Some content related to pre-emption in chapter Functionality of Radio
Resource Pre-emption and Queuing has been moved to section Pre-
emption in chapter Technical description of Radio Resource Pre-emption
and Queuing.
The lowest priority value has been changed from 15 to 14 in chapters
Technical description of Radio Resource Pre-emption and Queuing, and
Functionality of Radio Resource Pre-emption and Queuing.
Interworking information on Dynamic Frequency and Channel Allocation
(DFCA), High Speed Circuit Switched Data (HSCSD), and Wireless
Priority Service (WPS) has been added to chapter Technical description of
Radio Resource Pre-emption and Queuing.
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1 Overview of Radio Resource Pre-
emption and Queuing
The purpose of the BSC pre-emption procedures (forced release andforced handover) is to offer a service of a guaranteed level to the
subscribers in a temporary cell congestion situation. The purpose of radio
resource queuing in the BSC is to increase the number of successfully
completed calls in a temporary congestion situation in the cell and, in
doing so, to increase radio network efficiency.
In a temporary congestion situation, the priority levels and the pre-emption
indicators may be used to determine whether the assignment or handover
request has to be performed unconditionally and immediately. This leads
to the triggering of the pre-emption procedure that causes the forced
release or forced handover of a lower priority connection if no freeresource is immediately available.
The seizure request that is allowed to cause forced release or forced
handover for a call in progress can be one of the following:
. call set-up
. mobile-originating call (MOC) set-up
. mobile-terminating call (MTC) set-up
.
handover attempt
Pre-emption is BSC-specific application software that contains specific
statistical functions.
Radio resource queuing in the BSC is always a cell-specific procedure.
Radio resource queuing is operating software that contains specific priority
management and statistical functions.
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Radio resource queuing enables the setting of the radio channel request to
the queue, and when a suitable radio resource is available again, theinterrupted call set-up can be continued. Consequently, there is no need to
cut off a started transaction caused by temporary radio channel congestion
in the cell.
The queued radio resource is always a traffic channel (TCH), never a
stand-alone dedicated control channel (SDCCH). The queued seizure
request can be one of the following:
. call set-up
. mobile-originating call (MOC) set-up
. mobile-terminating call (MTC) set-up
. handover attempt (all GSM-specified handover types)
Related topics in Radio Resource Pre-emption and Queuing in BSC
. Technical description of Radio Resource Pre-emption and Queuing
. Functionality of Radio Resource Pre-emption and Queuing
. User interface of Radio Resource Pre-emption and Queuing
Related topics in BSC/TCSM documentation
. Reference
. Commands
. MML Commands
. EE - Base Station Controller Parameter Handling
. EQ - Base Transceiver Station Handling in BSC
. Counters/Performance Indicators
. Call Control Measurements (CSW)
. 1 Traffic Measurement
. Parameters
. BSS Radio Network Parameter Dictionary
. Descriptions
. Functional Area Descriptions
. Radio Network Performance
. RF Power Control and Handover Algorithm
. Radio Channel Allocation
. Feature Descriptions
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. Radio Network Performance
.
Soft Channel Capacity in BSC . Directed Retry in BSC
. Intelligent Underlay-Overlay
. Value Added Services
. Wireless Priority Service in BSC
. Trunk Reservation
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2 Technical description of Radio Resource
Pre-emption and Queuing
2.1 Queuing
The BSC has a cell-specific queue for every queue type. Three different
queue types are implemented:
. call queue
Used when mobile-originating call (MOC) or mobile-terminating call
(MTC) attempts are queued for.
. handover queue for urgent handovers
Used when an urgent handover attempt is queued for. The initial
cause of the handover determines the urgency.
. uplink/downlink interference
. uplink/downlink quality
. uplink/downlink level
. handover initiated because of a rapid field drop
. MS-BTS distance exceeding cell boundaries
. MS-BTS distance causing handover from extended range cell
to inner cell. MS-BTS distance causing handover from inner cell to
extended range cell
. forced handover to empty a cell
. handover from super-reuse to regular frequency area because
of a bad carrier-to-interference ratio (C/I)
. handover initiated to switch the A interface circuit pool
. handover of fast-moving MS from lower layer cell to upper
layer cell
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For more information, see Intelligent Underlay-Overlay and RF
Power Control and Handover Algorithm.. handover queue for non-urgent handovers
Used when a non-urgent handover attempt is queued for. The
handover causes treated as non-urgent are:
. power budget handover
. umbrella handover
. handover of slow-moving mobile station (MS) from upper layer
cell to lower layer cell
. MSC-controlled traffic reason handover
.
BSC-controlled traffic reason handover
These three logical queues form one cell-specific physical queue.
The handover attempt can be an internal intra-cell, internal inter-cell, or
external handover. However, external handovers are always treated as
urgent handovers when the target BSC has not received the handover
cause information from the A interface.
Note
The following handover attempts are not queued:
. handovers from regular to super-reuse frequency area
corresponding to the cause 'Good C/I ratio'
. handovers related to Directed Retry or Intelligent Directed Retry
. handovers initiated by the pre-emption procedure
You can handle the queuing parameters and management using Nokia
NetAct or the local MMI. With the parameters, it is possible to manage the
queuing on a cell-by-cell basis and to determine the queuing
characteristics. The following parameters are used:
. allowed queue length
. queuing time of the call queue type (the same for both MOC and
MTC)
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. queuing time of the handover queue type (the same for urgent and
non urgent handovers). priority management
. queue type priority: possibility to prioritise between the queue
types
. call queue
. handover queue for urgent handovers
. handover queue for non-urgent handovers
. MSC informed priority (MS priority): possibility to prioritise
between queue elements
The queue type priority and MSC informed priority can be set on or
off.
2.2 Pre-emption
The BSC has two ways to perform call pre-emption: forced handover and
forced release. In both cases, there is a separate queue for calls which are
waiting for the target call to be released or handed over. It depends on the
priority of the call which of the queues is chosen (forced handover or
forced release).
Priority of the request
The priority of the request is received with the request in a special priority
element. In pre-emption handling, the most important information
concerning seizure requests is the Priority information element (PIE). The
PIE contains the following information:
. MS priority
. pre-emption capability indicator (PCI)
.
pre-emption vulnerability indicator (PVI). queuing allowed indicator (QA)
With these indicators, different services can be offered to certain prioritylevels. Priority 0 is defined as spare and it does not initiate pre-emption
procedures.
. PCI=YES, QA=YES, PRIO=0
Does not initiate the pre-emption procedure because the priority
level 0 is specified as spare.
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. PCI=YES, QA=YES, PRIO=1
The highest possible priority. Initiates forced release for avulnerability call in progress.
. PCI=YES, QA=YES, PRIO=2...PRIO=14
Initiates forced handover for a vulnerability call in progress.
. PVI=YES, QA=no relevance, PRIO=0
Not chosen to be the target of the forced release or forced handover
because priority 0 is spare.
. PVI=YES, QA=no relevance, PRIO=1...PRIO=14
The lowest priority is chosen to be the target of the forced release or
forced handover. Priority 1 is the highest and 14 the lowest.
Forced release
Forced release queue
Forced release queue is the queue for the calls which are waiting for the
target call to be released. This is equipped with a higher priority than the
calls in the forced handover queue.
Storing forced release requests
The seizure request which is allowed to cause a forced release to another
call in progress is stored in the BTS forced release data structure
(BFRFIL). The seizure request is stored, provided that there is free space.
A maximum of eight seizure requests can be stored at the same time for
one cell.
When the seizure request is stored in the BFRFIL, the BSC sends the
QUEUING INDICATION message to the MSC. If Directed Retry is in use,
the BSC checks from the QUEUING INDICATION message in which
queue or data structure the call attempt is stored. If the call attempt iswaiting for forced release in the BFRFIL, Directed Retry is not initiated. If
the seizure request cannot be stored (that is, the BFRFIL is full), the
channel allocation is given a negative acknowledgement.
When the seizure request is stored in the BFRFIL, the BSC's BTS state
data structure (BSTAFI) is updated with the information on the number of
forced release seizure requests in that cell and time supervision is started.
The time limit is a BSC-specific fixed parameter (which means that it
cannot be changed by the user).
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The seizure requests are removed from the BFRFIL in a chronological
order.
Successful forced release
If the BSC detects seizure requests in the BFRFIL when a traffic channel
(TCH) is released, the first seizure request is removed. The number of
forced release seizure requests in the BFRFIL in that cell is updated in the
BSTAFI.
Time-out for the forced release
The number of TCH requests which are allowed to cause a forced releaseis updated in the BSTAFI. Unsuccessful assignments or handover attempts are reported to the BSC as a negative acknowledgement to the
channel seizure request with the cause 'no resource available'.
Forced handover
Forced handover queue
Forced handover queue is the queue for the calls which are waiting for the
target call to be handed over.
Storing forced handover requests
The seizure request which is allowed to cause a forced handover to
another call in progress is stored in the BTS forced handover data
structure (BFHFIL). The seizure requests are stored to BFHFIL according
to the priority levels of subscribers. The seizure request is stored in the
BFHFIL, providing that there is free space. If there is no free space in the
BFHFIL, a request of lower priority is removed to make room for a request
of higher priority. Up to eight seizure requests can be stored at the same
time for one cell. When the seizure request is stored in the BFHFIL, the
BSC sends the QUEUING INDICATION message to the MSC. If Directed
Retry is in use, the BSC checks from the QUEUEING INDICATIONmessage in which queue or data structure the call attempt is stored. If thecall attempt is waiting for forced handover in the BFHFIL, directed retry is
not attempted. If the seizure request cannot be stored (that is, the BFHFIL
is full and it is not possible to remove any lower priority requests), the
channel allocation is given a negative acknowledgement.
When the seizure request is stored in the BFHFIL, the BSC's BTS state
data structure (BSTAFI) is updated with the information on the number of
forced handover seizure requests in that cell and time supervision is
started. The time limit is a BSC-specific fixed parameter.
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The seizure requests are removed from the BFHFIL in a chronological
order.
Successful forced handover
When a TCH is released in the actual cell, the BSC first checks the
BFRFIL. If the BSC does not detect a seizure request in the BFRFIL, it
then checks the BFHFIL. If the BSC detects seizure requests in the
BFHFIL, the first seizure request is removed. The number of forced
handover seizure requests in the BFHFIL in that cell is updated in the
BSTAFI.
Time-out for forced handover
The number of TCH requests which are allowed to cause a forced
handover is updated in the BSTAFI. Unsuccessful assignments or
handover attempts are reported to the BSC as a negative
acknowledgement to the channel seizure request with the cause 'no
resource available'.
2.3 Interworking
Directed Retry
If Directed Retry is used simultaneously with pre-emption forced release
and forced handover, the value of the min time limit directed retry
parameter has to be smaller than the time limit for pre-emption (fixed value
10 seconds).
If Directed Retry is used simultaneously with queuing, the value of the min
time limit directed retry parameter has to be smaller than the
value of the time limit call parameter.
For more information on Directed Retry, see Directed Retry in BSC.
Trunk Reservation
Pre-emption is applied to those pre-emption capable subscribers that have
been rejected by the trunk reservation algorithm.
By combining Pre-emption and Trunk Reservation, it is possible to define
different service grades to the network.
For more information on the service grades, see Trunk Reservation and
radio resource allocation in Trunk Reservation.
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WPS and pre-emption cannot co-exist in the same network. If WPS is
used in the network, pre-emption cannot be used.
For more information on WPS, see Wireless Priority Service in BSC.
Related topics
. Overview of Radio Resource Pre-emption and Queuing in BSC
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3 Functionality of Radio Resource Pre-
emption and Queuing
MCMU switchover during pre-emption and queuing
The marker and cellular management unit (MCMU) is duplicated. The
state of the BSC in the spare unit can be changed to active in any situation
without affecting the active calls. Calls at set-up phase can break.
The pre-emption and queued transactions are set-up phase connections,
and, therefore, not updated and maintained in the spare unit. If an MCMU
switchover occurs during pre-emption or queuing, there is no real time pre-
emption or queuing data available in the new working unit. This means that
the BSC cannot send an acknowledgement concerning the pre-emption
attempt or queuing. The process instances that have requested pre-emption or queuing services are released autonomously when the time
supervision for the acknowledgement from the BSC expires. The pre-
emption call attempts and queued call attempts are then cleared. The pre-
emption handover attempts and queued handover attempts are
interrupted, and calls continue on the original radio channels.
Queuing possibility
The target cell used for queuing can vary depending on the request type.
One queuing target cell is possible in the following cases:
. call attempt: the actual cell is used as the queuing target
. internal intra-cell handover: the actual cell is used as the queuing
target
. external cell handover (target BSC): the cell identified by the MSC in
a HANDOVER REQUEST message is used as the queuing target
In an internal inter-cell handover, it is possible to use more cells (up to
sixteen) as alternative target cells in radio resource allocation. Thehandover candidate cells for the channel search are chosen from the
candidate cell list created by the handover algorithm and forwarded to the
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BSC. From these cells, the BSC searches for a free radio resource in the
order of their superiority over each other. If all the cells in the list arecongested, the queuing possibility in the candidate cells is checked using
the same order as in the allocation procedure.
Consequently, in this handover type choices are given to the BSC to
increase the chance of getting the required free radio resource, either
immediately or after queuing.
3.1 Pre-emption management in the BSC
Pre-emption is used when the BSC receives an assignment request or a
handover request from the MSC and no suitable channel is available in the
cell.
Note
You can deny the use of pre-emption in the case of a handover attempt
with the BSC-specific parameter pre-emption usage in handover.
The BSC checks the Priority information element (PIE) and, on the basis of PIE's flags, it may initiate a forced release or forced handover. Only one of
these two is allowed for one subscriber on the basis of the PIE. In other
words, it is not possible to try a forced handover first and then initiate a
forced release if the forced handover is unsuccessful. If the forced
handover is unsuccessful, a new forced handover attempt is initiated if the
time supervision has not expired and there is a suitable vulnerability
candidate to be handed over. The MSC must support queuing for the pre-emption procedure to work.
3.2 Queue management in the BSC
Queuing is used when the BSC receives an assignment or a handover
request from the MSC, and all traffic channels are busy or there are no
traffic channels (TCHs) of the requested kind available. If this seizure
request is not allowed to pre-empt an existing connection, the BSC checks
the Priority information element (PIE) and, on the basis of the 'queuing
allowed' indicator, can initiate queuing.
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Use of the priority element in queuing
In queue handling, one of the most important pieces of information
concerning the queued seizure request is the priority of the queue
element. This queue element priority consists of the mobile station (MS)
priority and the queue type priority.
The SEIZURE REQUEST messages to the BSC contain the MS priority
information, which is the priority value determined by the MSC. The queue
type priority is a SEG queue parameter that also affects the queuing
algorithm function considerably. In general, the handover queue type is set
to have a higher priority than the call queue type, because handovers deal
with existing call connections.
Cell queue length
Every created transceiver (TRX) builds up to eight possible queue
positions in the cell. If the TRX contains half rate resources, the queue
length is doubled. The maximum queue length in a cell is 32. Everydeleted TRX removes eight/sixteen possible queue positions.
The actual queue length is calculated by using the number of the possible
queuing positions (all created TRXs in the cell) and the SEG parameter
maximum queue length given in percentage format. Recalculation is
performed when you change the value of the maximum queue lengthparameter or when the number of the active TRXs changes (TRXs are
created or deleted).
The calculated actual queue length in the cell specifies the number of call
and handover attempts that can queue for a TCH release in that cell.
In the BSC, every cell has the same maximum data area (same number of
queuing positions) on which the maximum queue length can have an
effect. The data area gives the maximum value to the actual queue length
for every cell. The size of the data area can be changed, but it is fixed in a
certain software package.
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3.3 Forced release
Forced release possibility checks
When the BSC receives an ASSIGNMENT or a HANDOVER REQUEST
message and all traffic channels (TCHs) are busy, it checks whether the
assignment is allowed to cause a forced release to another call in progress
on the cell. The forced release transaction is allowed, if the 'pre-emption
capability' indicator is set on, the MS priority is set to 1, and the 'queuing
allowed' indicator is set on.
In a call attempt which is allowed to cause a forced release, the Priority
information element (PIE) received from the MSC in the ASSIGNMENTREQUEST message is used. The MSC can prevent the use of the forced
release procedure for a call in progress by setting the pre-emption
vulnerability indicator off.
In an internal handover, the original PIEs used. The PIE is stored in the
BSC during the call set-up phase. If the MSC has prevented the forced
release in the original call attempt, the forced release is also denied in all
handover attempts during the ongoing call.
In an external handover, the PIE received from the MSC and in the
HANDOVER REQUEST message is used.
In a successful forced release, the BSC sends a pre-emptive TCH request
for a new call or handover attempt. This request causes the forced release
for another call in progress and the new call receives the released TCH.
The BSC then initiates channel allocation signalling.
If no channel has been released within the time limit, the forced release is
unsuccessful.
Selection of the candidate for forced release
After the BSC has stored the information of the seizure request to the BTSforced release data structure (BFRFIL), it selects the candidate to be
released. The following main principles apply to the candidate selection:
. the candidate has the pre-emption vulnerability indicator set on
. the call in progress is not an emergency call
. the lowest priority of the calls in progress is chosen
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The TCH channel rate requirement of the resource request makes the
candidate selection procedure more complicated, especially when the cellcontains dual rate resources and a full rate TCH is requested. In that case,
the following three cases are possible:
. the MS of lowest priority is found among the full rate MSs
. the MS of lowest priority is found from a half occupied dual rate radio
timeslot (RTSL)
. the MS of lowest priority is found from a dual rate RTSL, both halves
of which are occupied
The MSs of the first two cases are accepted as candidates but the thirdcase is exceptional when forced release is requested.
The following rules are applied when the candidate for forced release is
selected:
. the MS of lowest possible priority is allocated
. only one call is allowed to be released for an incoming call
When the BSC has found the best suitable candidate for the release, it
starts the required signalling procedures concerning forced release.
Successful and unsuccessful forced release
. successful forced release
The successful assignment or handover is reported to the BSC,
including the data concerning the radio resource information
allocated to it. After that, the BSC starts the required signalling
procedures concerning the assignment or handover attempt.
. unsuccessful forced release
If no TCH has been released within the time limit, the TCH servicerequest is rejected because of lack of resources.
Time-out for the forced release
When the forced release seizure request is stored to the BFRFIL, time
supervision is started. The time limit is a BSC-specific fixed parameter.
If the time supervision expires and no TCHs have been released, the BSC
receives a time-out message. The seizure request is removed from the
BFRFIL.
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Statistics counters for forced release
When the BSC receives a seizure request attempt which is allowed to
cause a forced release for another call in progress, statistical counters are
updated. Assignment request attempts and handover request attempts
have their own counters.
When a TCH request which is allowed to cause a forced release for
another call in progress is rejected because of lack of released channels,
the statistics counters are updated. Assignment request failures and
handover request failures have their own counters.
When the seizure request that caused a forced release for another call in
progress receives a TCH, a statistics counter is updated.
If TCH allocation is based on the RX level and the assignment request is
rejected because of too low an RX level, a specific statistical counter is
updated.
The counters are BTS-specific. For more information on the counters, see
1 Traffic Measurement.
For an overview, see Overview of Radio Resource Pre-emption and Queuing in BSC.
3.4 Forced handover
Forced handover possibility checks
When the BSC receives an ASSIGNMENT or a HANDOVER REQUEST
message and all traffic channels are busy, it first checks from the Priority
information element (PIE) of the seizure request if the assignment or
handover is allowed to cause a forced release. If a forced release is not
allowed, the BSC then checks if the seizure request is allowed to cause aforced handover for another call in progress on the cell. The forced
handover transaction is allowed if the 'pre-emption capability' indicator is
set on, the MS priority is set to 2-14 in the PIE, and the 'queuing allowed'
indicator is set on.
In a call attempt which is allowed to cause a forced handover, the priority
element received from the MSC in the ASSIGNMENT REQUEST
message is used. The MSC can prevent the use of the forced handover function for the call in progress by setting the pre-emption vulnerability
indicator off.
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In an internal handover, the original PIE is used. The PIE is stored during
the call set-up phase in the BSC. If the MSC has prevented the forcedhandover in the original call attempt, the forced release is also denied in all
handover attempts during the ongoing call.
In an external handover, the priority element received from the MSC in the
HANDOVER REQUEST message is used.
In a successful forced handover, the BSC sends a pre-emptive TCH
request for a new call or handover attempt. This request causes a forced
handover for another call in progress and the new call receives the
released TCH. The BSC then initiates channel allocation signalling.
If no channel has been released within the time limit, the forced handover
is unsuccessful.
Selection of candidate for forced handover
After the BSC has stored the information of the seizure request to the BTS
forced handover file (BFHFIL), it selects the candidate for forced handover.
The following main principles apply to the candidate selection:
. the candidate has the pre-emption vulnerability indicator set on
.
the call in progress is not an emergency call. the lowest priority call of the calls in progress is chosen
The TCH channel rate requirement of the resource request makes the
candidate selection procedure more complicated, especially when the cell
contains dual rate resources and a full rate TCH is requested. The
following three cases are then possible:
. the MS of lowest priority is found among the full rate MSs
. the MS of lowest priority is found from a half occupied dual rate
RTSL. the MS of lowest priority is found from a dual rate RTSL which also
has the other half occupied
The following rules apply in the selection of the candidate for forced
handover:
. the MS of lowest possible priority is allocated
. only one forced handover is permitted
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In some circumstances, a forced handover can be performed within the
cell that maintains the candidate call - a kind of call packing featuregenerated by pre-emption:
. a full rate call can be handed over from a dual rate RTSL to a free
permanent full rate RTSL
. a half rate call can be handed over from a half occupied dual rate
RTSL to a free permanent half rate RTSL
. a half rate call can be handed over from a half occupied dual rate
RTSL to another half occupied dual rate RTSL
. if channel rate changes are allowed, a full rate call can be handed
over to a free half rate resource
Consequently, a half rate call can be handed over to a free
permanent full rate resource. In these cases, the handovers are
performed externally and controlled by the MSC if the A interface
circuit pool does not support the channel rate changes. Note that thefull rate call must have half rate capabilities before it can be moved
to a half rate traffic channel.
When the BSC has found the best suitable candidate for a handover, a
decision on whether the handover is going to be performed intra-cell or notis made. The BSC starts the required signalling procedures concerning
forced handover.
If the handover attempt is rejected, the BSC checks if the seizure request
is still waiting for a free resource in the BFHFIL. If the seizure request is in
the BFHFIL, the BSC selects another candidate for a forced handover. If
the seizure request is not in the BFHFIL, the forced handover procedure
ends.
Successful and unsuccessful forced handover
. successful forced handover
The BSC starts the required signalling procedures concerning the
assignment or handover attempt.
. unsuccessful forced handover
If no TCH has been released within the time limit, the TCH service
request is rejected because of lack of resources.
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Time-out for forced handover
When the forced handover seizure request is stored to the BFHFIL, time
supervision is started. The time limit is a BSC-specific fixed parameter.
If the time supervision expires and no TCHs have been released, the BSC
receives a time-out message. The seizure request is removed from the
BFHFIL.
Statistics counters for forced handover
When the BSC receives a seizure request attempt which is allowed to
cause a forced handover for another call in progress, statistical counters
are updated. Assignment request attempts and handover request attemptshave their own counters.
When a TCH request which is allowed to cause a forced handover for
another call in progress is rejected because of lack of released channels,
the statistics counters are updated. Assignment request failures and
handover request failures have their own counters.
The counters are BTS-specific. For more information on the counters, see
1 Traffic Measurement.
3.5 Queuing
Queuing possibility checks
When all TCHs are busy or there are no TCHs of the requested kind
available and the seizure request is not allowed to cause a forced release
or a forced handover for another call in progress, the BSC checks whether
the queuing of this assignment or handover is allowed. The queuing
transaction is allowed if the following requirements are met:
. the 'queuing allowed' indicator in PIE is set on
. the cell channel configuration contains channels capable of the
requested channel rate
. the SEG specific queue parameters make queuing possible in the
cell
In call attempt queuing, the priority element that has been received fromthe MSC and contained in the ASSIGNMENT REQUEST message,
contains the 'queuing allowed' indicator. This priority element is used. If the
MSC prevents the queuing, the call attempt cannot be placed in the queue.
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In an internal handover, the original PIE is used and stored in the original
call set-up in the BSC. If the MSC has prevented the original call attemptqueuing, the queuing is also denied in all handover attempts during the
ongoing call.
In external handover queuing, the PIE received from the MSC in the
HANDOVER REQUEST message, contains the 'queuing allowed'
indicator. This priority element is then used. If the MSC prevents queuing,
the handover attempt cannot be placed in the queue.
Queuing possibility in the cell: If this transaction queuing is allowed, the
BSC checks that the queue is available, that is, that the actual queue
length is not zero, and the queue type is activated in this cell so that the
time limit value of the queue type is not zero. If queuing is not allowed in
the cell in general, or for this kind of attempt only, the call attempt cannot
be placed to the queue.
. successful queue set-up
In a call attempt queuing and an external handover attempt queuing
in the target BSC, if there is no TCH of the requested kind available
in the cell and the queue set-up is successful, the BSC sends a
QUEUING INDICATION message to the MSC.
.
successful queuing
When the queue element receives a TCH, queuing is successful. In
that case, the BSC starts the required signalling procedure
concerning the attempt.
. unsuccessful queuing
In all radio channel request cases, if no TCH of the requested kind is
available in the cell and the queue set-up is not successful, the BSC
starts the required clearing or interruption procedure concerning the
attempt.
If the queue set-up has been successful, but the queuing time-outtakes place, the BSC sends a normal negative radio resource
allocation acknowledgement to the MSC.
If the queue set-up has been successful, but the queue element has
to be removed from the queue, the BSC sends a normal negative
radio resource allocation acknowledgement to the MSC.
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Indicates whether the queued resource is requested from the
extended area or the normal area. The same queues are used byMSs of the normal area and the extended area. When a TCH is
released in the normal area, it is assigned immediately to the first MS
of a queue which is queuing for resources of the normal area. When
a radio channel is released in the extended area, it is assigned
immediately to the first MS of a queue which is queuing for resources
of the extended area.
In call attempt queuing, the type of the requested TRX is always the
same as the TRX type used for signalling.
In intra-cell and inter-cell handover, the TRX type request from the
HANDOVER REQUEST message is used.
In external handover queuing, the queued TRX type is always E-
TRX if the target cell is extended. The queued TRX type is N-TRX if
the target cell is normal.
Prioritisation of the request
In queue management, an important part of the queue element is the
priority. There are two queue priority elements:
. MS priority: possibility to prioritise between queue elements
. queue type priority: possibility to prioritise between the queue types
Queue management with different combinations of the priority elements
are the following:
. queue type priority off, MS priority off
In this most straightforward case of queue management, the priorityelements are not taken into account at all. The seizure request is
placed on the queue, providing that there is free space. If the queue
is full, the channel allocation is given a negative acknowledgement.
. MS priority on, queue type priority off
The seizure request, that is, the queue element, is placed on the
queue in a position that the MS priority entitles.
The MS priorities of the queue elements are checked. If the new
queue element has a higher priority than the previous ones, it is
placed on the queue so that it is located just before the lower priority
element. Other queue elements are transferred one position towards
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the end. In this case, the last queue element may have to be
removed from the queue. This is then informed to the requestedinstance as a negative acknowledgement to the radio channel
seizure request.
When the seizure request is placed on the queue, the timer service
corresponding to the queue type is attached, and the required BSC
file updating is performed. After that the queuing acknowledgement
is returned to the requested instance.
. MS priority off, queue type priority on
The new queue element is placed on the queue in the position that
the queue type priority entitles.
The queue type priorities of the queue elements are checked. If the
new queue element has a higher priority than the previous ones, this
new element is placed on the queue just before the lower priority
element. Other queue elements are transferred one position towards
the end. In this case, the last queue element may have to be
removed from the queue. This is then informed to the requested
instance as a negative acknowledgement to the radio channel
seizure request.
When the seizure request is placed on the queue, the timer service
corresponding the queue type is attached and the required BSC file
updating is performed. After that, the queuing acknowledgement isreturned to the requested instance.
. MS priority on, queue type priority on
In this case, the queue element priority consists of the MS priority
and the queue type priority.
The new queue element is placed on the queue in the position that
the queue element priority entitles.
The MS priority operates only within one single queue type. For
example, a higher MS priority call attempt is placed after a lower MS
priority handover attempt, if the handover queue type priority is set tobe higher than the call queue type priority.
In the queue setting analysis, only the MS priorities corresponding to
the same queue type as the requested one are checked, so that the
search is not performed on the whole cell queue. If the new queue
element has a higher MS priority than the previous ones within the
same queue type, the new element is placed on the queue so that itis located just before the lower MS priority element. Other queue
elements within the same queue type are transferred one position
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Transaction release during queuing
. queuing MS on SDCCH is released
When the queuing radio channel (source) is a stand-alone dedicated
control channel (SDCCH), the queuing data is stored in the BSC's
signalling channel state data structure (SCHSTA) record
corresponding to the SDCCH in question.
If the SDCCH is released during the queuing, the queue element is
removed from the queue. If the queuing SDCCH receives a TCH, the
queuing data in the SCHSTA has to be removed. Similarly, if the
queuing time runs out or the queue element is removed from the
queue, the queuing data in the SCHSTA is removed.
. queuing MS on TCH is released
When the queuing radio channel (source) is a TCH, the queuing
data is stored in the BSC's traffic channel status data structure
(TCHSTA) record corresponding to the TCH in question.
If this TCH is released during queuing, the queuing element is
removed from the queue files with the queuing data stored in the
TCHSTA.
If the queuing TCH receives a new TCH, the queuing data in the
TCHSTA has to be removed. Similarly, if the queuing time runs out or
this queue element is removed from the queue, the queuing data in
the TCHSTA is removed.
Queue search
If the BSC detects queued seizure requests in the cell when the TCH is
released, the cell queue is scanned. The last updated interference level
information to be used for the released TCH can be found in the channel
state file record.
When TCH radio resources are deblocked and the BSC detects queuedseizure requests in the cell, the cell queue is scanned. The new available
TCH interference band is initialised for the worst interference band until a
real interference updating is received.
The cell queue is also scanned when the idle TCH interference levels are
changed and there are queued seizure requests in the cell. This is donebecause the queued elements may have just the kind of interference band
requirements that the new updated TCHs can now offer.
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Unsuccessful queuing, as well as the queuing time used, are marked to
the statistics counters. Call set-ups and handovers have their owncounters. The urgent and non-urgent handovers can also be picked out
using the counters. If TCH access is based on the RX level and call set-up
request is rejected because of too low an RX level, a specific statistical
counter is used.
Changing cell queue length
If you change the value of the parameter max queue length, the BSC
receives a parameter update from Nokia NetAct or the local MMI. You can,
for example, set the new maximum queue length definition to zero, so that
queuing is not possible in that cell. The actual queue length, that is, the
maximum queue length proportioned to the number of possible queuingpositions (all created TRXs in the cell), is recalculated after the parameter
change.
If there are queuing call or handover attempts not located within the newallowed area, the BSC removes them immediately from the cell queue and
negative acknowledgements for the queued channel seizure requests are
forwarded to the requested instances.
Every created TRX builds up to eight/sixteen (full rate TCH / half rate TCH)
queue positions. The maximum queue length in the cell is 32. When a TRX
is deleted, the same number of possible queue positions is removed. Theactual queue length is determined with the value of the max queue
length parameter (in percentage format) given by the user.
After the TRX deletion procedure, it is checked whether there are queuing
call or handover attempts not located within the new allowed area. If this is
the case, the BSC immediately removes them from the cell queue and
negative acknowledgements for the queued channel seizure requests are
forwarded to the requested instances.
Related topics
. Overview of Radio Resource Pre-emption and Queuing in BSC
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4 User interface of Radio Resource Pre-
emption and Queuing
User interface of pre-emption
Pre-emption activated in the BSC with the PREEMPT_USAGE parameter
using the local MMI. The SEG-specific queue parameters do not have any
influence on pre-emption.
The BSC-specific parameter pre-emption usage in handover defines
whether the pre-emption procedures (forced release and forced handover)
are applied in the case of a handover attempt. The parameter is handled
with the EEQ command (Base Station Controller Parameter Handling , EE
command group).
The pre-emption procedures are not applied to 'better cell' handovers. If a
pre-emption capable subscriber attempts a 'better cell' handover to a
congested cell, the pre-emption procedures are not applied, and the
subscriber remains in the source cell.
User interface of queuing
The queue characteristics are defined with SEG object class parameters.
The parameters are handled with the EQH command (Base Transceiver
Station Parameter Handling , EQ command group). The parameters can
also be handled using Nokia NetAct.
The following parameters are related to queuing:
. max queue length
The maximum queue length in the cell specifies the number of call
attempts and handover attempts waiting for a traffic channel (TCH)
release in the cell. If the value is set to zero, TCH queuing is not
possible in that cell.
. time limit call
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The maximum queuing time for call attempts (mobile-originating or
mobile-terminating) in the cell. If the value is set to zero, call attemptqueuing is not active in that cell.
. time limit handover
The maximum queuing time for handover attempts (all handover
types and handover reasons) in the cell. If the value is set to zero,
handover attempt queuing is not active in that cell.
. queueing priority call
The specified priority for the call queue type in the cell. Queue type
prioritisation enables different priorities between call attempt and
handover attempt queuing.. queueing priority urgent handover
The specified priority for the urgent handover queue type in the cell.
Queue type prioritisation enables different priorities between call
attempt and handover attempt queuing and between urgent and
non-urgent handovers queuing.
. queueing priority non-urgent handover
The specified priority for the non-urgent handover queue type in the
cell. Queue type prioritisation enables different priorities between
call attempt and handover attempt queuing and between non-urgentand urgent handovers queuing.
. MS priority used
Indicates whether the priority data for the message element priority
in the ASSIGNMENT REQUEST and HANDOVER REQUEST
messages from the MSC is taken into account in the queue
management of the cell.
. queue priority used
Indicates whether the queue type priority is taken into account in
queue management in the cell.
For more information on the parameters, see BSS Radio Network
Parameter Dictionary.
Counters
Traffic Measurement includes counters that are related to Radio Resource
Pre-emption and Queuing. For more information on the counters, see 1
Traffic Measurement.
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