DTM Planning Training

DTMEric Kroon
The basic (theoretical) understanding of DTM
Planning issues that arise with DTM
How to monitor DTM
This training should be self supporting
This training is written from a perspective that the student has already basic knowledge about planning and optimization issues of EGPRS as well as the terminology
* © NOKIA BSS_12_FUD_v2_1.PPT / 13-09-2005 /
Nokia Customer Confidential
GPRS Transparent Transport Protocol (GTTP)
Coordination of PS and CS paging
Signaling
What is DTM?
Dual Transfer Mode is a subset of Class A mode of operation, only possible if there is radio resource allocation co-ordination in the network
In DTM mode the MS is simultaneously in dedicated and packet transfer mode but the CS and PS timeslots allocated in each direction are contiguous and within the same frequency
In DTM mode the CS part consists of a single-slot connection while PS part may be a multi-slot connection
DTM is an optional feature for the mobile station as well as for the network
New applications like WAP browsing / emailing with ongoing CS call, Video sharing and Mobile Net meeting can be supported
In multislot operation, the GPRS data is sent on a PDCH
What is DTM
DTM is an application software product in BSS12.
It affects only BSC software
It requires a valid license in the BSC
HW requirements in BSS12:
UltraSite (CX5.0), MetroSite (CX5.0), and Talk Family (feature candidate S12) BTSs support DTM, no SW changes are required
Requirements for other Network elements:
DTM capable terminals are required
OSS4.1 SW needed at NetAct
MSC needs to support IMSI delivery to BSC (M11).
GPRS territory is mandatory (DTM resources will be in the PS territory)
System Configuration:
Other requirements
Network must have GPRS or EDGE activated and active in the network where DTM is to be rolled out
Preferable the PS territory should have at least have 2 TS dedicated (this will minimize extra signaling for territory upgrade for DTM calls)
Supported bands
GSM 800
GSM 900
GSM 1800
GSM 1900
The CS connection is controlled in the BSC and handles:
Speech codec mode selection for DTM-CS
Handover control
The PC connection is controlled by the PCU (PCU2) and handles:
Admission control to PS territory
Channel allocation for both CS as PS DTM connection
PS territory management
Not supported in DTM
Queuing and pre-emption
Soft channel capacity
NCCR and NACC
New DTM classes
For DTM three new MS classes have been defined. These are
Class 5,
Class 9,
Class 11
Box colors
The following figure represents examples of timeslot allocation for different classes
DTM - GPRS Transparent Transport Protocol
GPRS mobility management and session management signaling can be send on main DCCH, i.e. signaling channel when MS is on dedicated mode (FACCH or SACCH)
New protocol layer: GPRS Transparent Transport Protocol (GTTP)
Short signaling messages
GTTP will be used
GTTP signaling provides fast signaling link for GMM/SM messages (no TBF needed).
Long signaling messages and user data
The PDCH (i.e. TBF in DTM mode is needed) is used
New message on the radio interface: GPRS INFORMATION
DTM - GPRS Transparent Transport Protocol
GTTP is only used when the MS is in DTM dedicated mode
GTTP signaling is only used in the following cases
The DL LLC PDU contains signaling
The size of the DL LLC PDU (in bytes) is less then
18 * MAX_LAPD_LENGTH – 8
A brief look on the information flow with GTTP signaling
IMSI coordination
Coordination of PS and CS resources requires that the IMSI is know in both territories i.e. BSC (CS part) and PCU (PS part).
The MSC provides the IMSI to BSC on common ID message in
Call establishment cases
External handover cases
RA update
NOM I (Gs-interface) has to be used for paging coordination
DTM does not change the CS paging procedure
The MS is always (if not attached to GPRS) is paged on the PCH
PS paging
CS paging co-ordination means that CS Paging Request is sent to the MS on PACCH when the MS is having PS data transmission (MS is in packet transfer mode)
Signaling principles
Current implementation: Class A mode of operation MSs must be able to listen to different frequencies in the same TS. E.g. to listen to the (P)BCCH while in dedicated mode
New procedures have been implemented to support MSs which cannot listen to different frequencies in the same TS
Small overview of signaling principles in different conditions is presented below
DTM/PS channels can be multiplexed similar to normal GPRS/EDGE
Two DTM/CS HR connections can share a timeslot
DTM/CS HR support is BSS13 feature candidate
DTM - Multiplexing Examples
DTM/CS in FR mode, DTM-PS timeslot shared with other GPRS users.
DTM/CS in HR mode, DTM-PS timeslots shared with other GPRS users.
2 DTM/CS calls packed on the same timeslot in HR mode, DTM/PS timeslots shared with other GPRS users.
4 DTM users sharing the same PDTCH.
DTM/PS
Accessing DTM mode principles
DTM can be ONLY entered via (CS) dedicated mode (see next slide)
IF the PS call is dropped then the MS returns to “normal CS” call
If the CS call is dropped then the MS returns to packet idle mode and the network will re-establish the PS connection
In a MO call establishment DTM request is send over DCCH and both PS as CS resources are coordinated
In a MT call establishment either the CS resources are aligned to the PS resources or the both of the resources are coordinated
Inter-cell handover causes the DTM allocation to be terminated and after the handover took place the PS resources are re-established
Call assignment
When the MS is in dedicated mode the resources will change territory (CS to PS) or be dropped
A closer look on what happens during call assignment
The BSC selects a suitable speech codec for the DTM-CS connection based on the existing speech codec selection rules
The BSC configures the target DTM-CS timeslot to CS use, if needed (in PS territory)
The BSC will assign the new allocation to the MS
The BSC will move the CS connection to the target DTM-CS timeslot.
After the MS has moved to the new resources the source DTM-CS timeslot will be configured back to CS use
MO DTM call
MS requests the resources via the SDCCH (not supported in 1st release)
This happens when the MS is in dedicated mode without a CS traffic channel
This is not supported in the first release of S12 -> PCU will reject the setup of the call
The MS can request directly DTM resources on the SDCCH before having a dedicated channel
A new penalty timer for call setup : DTM SDCCH CALL PENALTY TIMER
MS requests the resources via the FACCH
This happens when the MS is in dedicated mode (CS channel allocated)
The BSC first examines the following DTM related issues before allocation
Network examinations
Examine if the MS has an other DTM establishment ongoing
The BSC will receive from the MSC information on the radio link (speech codec, type of call)
MO DTM call network examinations
A MO DTM call can be established if the following conditions are fulfilled:
Cell supports DTM
MS supports DTM
A TCH is allocated for a CS speech call
MS is not already in the process of establishing a DTM call
There is no other handover procedure ongoing for the MS
CS connection release is not started
IMSI of the MS is known by the BSC
DTM request is received from the normal area of the cell
MO call assignment
If the call can be established then the establishment timer is started (t_dtm_request_timer, new UTPFIL timer)
This timer controls the DTM call setup time
Before continuing with the assignment the BSC waits for a certain number of Rxlevel measurements or until the timer has expired before continuing with the DTM call assignment
The Rxlevel measurements provide the “BTS list”
If the timer expires the call assignment will be aborted
PCU receives the “BTS list” and selects the best BTS for setting up of the call and the PDM checks the availability for the DTM connection
If the DTM call can be established the resources are allocated and the CS call will have an intra cell handover to the PS territory
MO call setup exceptions
If there is an UL TBF ongoing or being established for the MS when the PCU receives an allocation request then the PCU will release the UL TBF. This could be the case if the MS abandons the ongoing PS data transfer, enters dedicated mode and requests a DTM call before the PCU realizes that the MS is no more using the UL TBF.
If there is a DL TBF ongoing or being established for the MS when the PCU receives an allocation request, then the PCU will delete the DL TBF. The untransmitted DL LLC PDUs will be kept in the buffer so that they can be transmitted to the MS later when the MO DTM call establishment has been completed. This means that the PCU will continue with the MO DTM call establishment in this case and the DL TBF establishment procedure will be started when the MO DTM call establishment has been completed.
MT DTM call
A MT DTM call case applies when the PCU receives DL LLC PDUs from the SGSN and
The PCU does not have any resource reservation or
The MS has a DTM allocation but no TBFs ongoing
Two methods for an MT call establishment to start
without a DTM allocation for the MS
with a DTM allocation for the MS (ONLY with EQoS)
Perform BTS specific selection
Allocate resources for the DTM call
Establish a DL TBF for the mobile (if the channel allocation procedure is successful)
Request resource allocation and TBF allocation from the call serving BSC
Create a new PFC
Perform BTS specific selection
If the PCU is already having the corresponding PFC context for the MS, then the admission control check is not needed
Allocate resources for the DTM call
Establish a DL TBF for the mobile (if the channel allocation procedure is successful)
Request resource allocation and TBF allocation from the call serving BSC
In this case the PCU will start a call establishment procedure unless GTTP can be used
The following steps are taken for an MT call with and without EQoS
With EQoS
Without EQoS
When receiving the request for establishment the BSC will start the DTM assignment
procedure. All the signaling will be send on the DCCH to the MS.
Call release general
By having a DTM call released is meant that the MS is having a DTM allocation ongoing which is going to be released
Call release can be initiated by:
by MS or MSC
by PCU
Without EQoS : The BSC will be notified with the release and a handover from PS territory to CS territory is going to be made
With EQoS: when the last PFC context of an MS is deleted and the MS is having a DTM allocation
by BSC
Different cases can cause the BSC to release the DTM connection
MS or MSC initiated CS call release
CS side initiated DTM call release
a case where the DTM-CS channel should be changed but the reallocation within the PS territory is not possible
PS side initiated DTM call release
The CS resources are moved back to the CS territory
PCU initiated call release
Without EQoS the BSC is notified that the PS resources will be released
The call release will be rejected if
The MS is in handover interval state or other handover cases are ongoing
MS or BTS power control is used
The CS-DTM call will have an intra-cell handover to the CS territory and continue as a “normal” CS call
With EQoS the call will be release when the last PFC context is deleted
The PFC life-time determines how long a CS connection is kept in the PS territory once the data flow has ceased for a DTM MS (there is a DTM specific upper limit for the PFC life-times, DTM PFC Packet Flow Timer )
After the PCU tells the BSC that the resources will be released, the BSC initiates an intra-cell handover.
Note 1: if there is no room to move the CS resources they will stay in the PS territory until the MS can be moved to the CS territory
Note 2: the inter-cell handover procedure the DTM allocation is released by the BSC before the FLUSH-LL arrives at the PCU
BSC initiated call release
In the following cases the BSC will initiate a call release
The CS connection is released if there is another DTM allocation ongoing for the MS.
If the MS is having an inter cell handover
The BSC has detected an assignment failure during an initial DTM call establishment procedure.
DTM is being deactivated in the cell and GPRS remains enabled. In this case the BSC initiates a DTM call release procedure for all the ongoing DTM calls in the cell.
The BSC initiated DTM intra-cell handover procedure is rejected. The CS call will be moved to the CS territory.
The BSC receives a request for in-call modification where the CS call needs to be moved to the CS territory.
The call is released in 2 phases
BSC informs the PCU that the MS is leaving DTM
BSC informs the PCU that the DTM-CS resources are not longer in use
Call rejection
If the PCU cannot make the connection the following procedure will be valid:
Resources
Available?
No
Yes
Make
connection
1. The target cell supports DTM.
2. The target cell is not overloaded or the traffic load in the target cell is less than the traffic load in the source cell
3.The target cell fulfils the required signal level thresholds:
AV_RXLEV_NCELL (n) > RxLevMinCell (n) + MAX (0, Pa) and PBGT (n) > DtmMarginPBGT (n), where DtmMarginPBGT (n) is given by the new parameter DTM Power Budget Margin.
Abort
DTM
connection
Call abortion procedures
The BSC can abort an initial MO/MT DTM call establishment procedure in the following situations:
The MS is not in the cell where the PCU made the DTM allocation.
The DTM allocation is made for an MS whose TCH channel is assigned for other purpose than CS speech call.
The BSC considers the made DTM allocation as unsuitable for the MS.
The Soft Channel Capacity feature prevents the assignment of HR speech codec mode in a situation where the PCU has packed the DTM call on a timeslot that is already having one DTM call in HR mode (possible only in MO case).
The DTM call establishment is aborted due to ongoing inter-cell HO procedure.
The DTM call establishment is aborted due to ongoing DTM call release procedure.
The DTM assignment failure is detected
The DTM call establishment fails due to some abnormal situation at the BSC side.
DTM call counters
Assignment
failures
Request
rejects
Assignment
attempts
Release
106000
Updated also in RT PFC creation case
105000
Territory upgrade cases
Territory downgrade cases
In DTM the following new territory issues apply
The CS-DTM call belongs to the PS territory (and it is handled by the PCU)
When the dedicated GPRS capacity is considered, then only the PS configured timeslots will be taken into account
The default GPRS capacity will be considered as a default size of the PS territory
The CMAX parameter will be considered as an upper limit for the size of the PS territory
PS perspective:
The PCU will keep a record about the DTM-CS timeslots and the allocations therein.
The PCU will not allocate any TBFs on the timeslots that are reserved for DTM-CS connections.
When computing the traffic load or capacity on the PS channels, the PCU will exclude the DTM-CS timeslots.
The PCU will note the DTM allocations in the territory downgrade procedure as well as the permission request procedure.
CS perspective:
The BSC will handle the traffic on the DTM-CS connections.
The BSC will not allocate any other CS connections on the DTM-CS timeslots than the DTM related CS connections.
When computing the BTS load for speech codec mode selection purposes the DTM-CS timeslots will be considered as ‘occupied CS channels’.
When the BSC triggers a territory downgrade procedure in order to reduce the size of the PS territory, the affected DTM-CS timeslots need to be downgraded too.
What does not change
The PCU should request a territory upgrade procedure if the load on the PS configured timeslots exceeds the current thresholds
The BSC should trigger a territory upgrade procedure if the size of the PS territory is smaller than the default PS territory size
Territory upgrade procedure will be triggered if the PS territory is too small for a DTM allocation
What is new
The BSC should trigger a territory upgrade procedure if the number of PS configured timeslots in the PS territory goes below the dedicated GPRS capacity due to DTM allocations
Territory downgrade
The PCU requests a territory downgrade procedure if the load on the PS configured timeslots goes below the current thresholds
New constraint: The PCU will ensure that the number of PS configured timeslots in the PS territory does not go below the dedicated GPRS capacity (smallest amount of TS will be MIN { (size – default_size), (size - dedicated – dtm_cs) }
The BSC may trigger a territory downgrade (permission request) procedure if the CS load situation requires an extension of the CS territory
New constraint: The BSC will ensure that the number of PS configured timeslots in the PS territory does not go below the dedicated GPRS capacity (smallest amount of TS will be MIN { (size – default_size), (size - dedicated – dtm_cs) }
Needless handovers
A DTM call is having a handover
DTM call reallocation
106017
DTM_IMSI_NOT_
AVAILABLE
105008
DTM_TBF_ASSIGNMENT_
FAILURES
004195
DTM_HO_DUE_LACK_
OF_RESOURCE
Drop
001233
DROP_AFTER_DTM_
TCH_ASSIGN
001234
DROP_DTM_TCH_
ASCMPL_RFCH_REL
105025
DTM_ALLOC_3_DL_
PS_TSL
105021
DTM_ALLOC_1_UL_
PS_TSL
Detailed
The PCU
The BSC
But what always happens is that the PS call will be dropped and the CS call will be handover to the CS side before changing the cell
Different kind of handovers
Intra cell handover
This type of handover mostly happens when an MS is entering or leaving DTM mode
Both BSC as PCU can initiate handover
When the Intra cell handover succeeds the same procedure as DTM call assignment is used and the TBF scheduling is started
PCU initiated intra cell handover
The PCU may initiate an intra-cell handover for a DTM allocation due to the following reasons
A territory downgrade permission request procedure triggers a DTM-CS reallocation procedure for a DTM allocation
A territory downgrade procedure triggers a DTM-CS reallocation procedure for a DTM allocation
The Quality Control (QC, does not require EQoS) function at the PCU triggers a DTM-CS reallocation procedure for a DTM allocation
A PFC creation (needs EQoS), modification or deletion procedure triggers a DTM-CS reallocation procedure for a DTM allocation
Once the PCU has found new resources for the DTM call the PCU will
Stop scheduling the PS resources belonging to the old DTM allocation
Inform the BSC about the new DTM allocation. The DTM allocation consists of a CS resource and possibly a PS resource reservation
BSC initiated intra cell handover
The BSC controls the handovers
The BSC can initiate an intra-cell handover for a DTM allocation due to the following reasons:
The speech codec mode of the ongoing DTM-CS connection needs to be changed
The DTM-CS connection needs to be moved to another timeslot due to quality reasons. The existing quality monitoring algorithms at the BSC shall be used to trigger this.
The BSC cannot select the target timeslot for the DTM-CS connection because the PCU takes care of the DTM channel allocation. Therefore, the handover due to quality reasons might not always bring the required result.
A BTS specific indication is used whether it is allowed or forbidden to apply HR speech codec mode in the DTM reallocation procedure.
Same procedure when resources have been found
Inter BSC handover
The BSC will perform an inter-cell handover procedure for a DTM MS, as currently done in S11.5, without consulting the PCU
This means that the BSC moves the DTM-CS connection to the target cell’s CS territory without reserving DTM resources in the target cell until a request for a DTM allocation is received from the MS or from the SGSN
After the handover procedure has been completed the BSC will send the DTM INFORMATION message to the MS on the main DCCH (if MS was in DTM mode and new cell supports DTM)
After the cell change the DTM MS can perform a Cell Update or a Routing Area Update procedure via the GTTP signaling procedure or via a DTM allocation.
The Cell Update procedure is done if the MS is GPRS attached and in Ready state and if the RA has not changed during the handover procedure.
The Routing Area Update procedure is done if the MS is GPRS attached and if the RA has changed during the handover procedure
After handover BSC uses normal DTM allocation procedure
Things that can go wrong in inter BSC handover
If the inter-cell handover procedure fails so that the MS returns to the source DTM-CS channel the CS call continues on the source DTM-CS timeslot. But the PS call does not.
If the timer T3103 expires during the DTM intra-cell handover procedure the BSC will release the CS resources allocated for the MS and inform the PCU that the MS has left dedicated mode
Avoiding needless handovers
When a DTM MS is having a DTM allocation in the cell, the BCS will avoid doing needless inter-cell handovers for the DTM MS. Therefore, the following inter-cell handovers will be avoided when a DTM MS is having a DTM allocation:
MSC controlled traffic reason handover
BSC controlled traffic reason handover
Umbrella handover
Inter-cell direct access
IUO to child cell (super reuse frequencies are not supported by DTM)
In addition, the following intra-cell handovers will be avoided when a DTM MS is having a DTM allocation:
An AMR FR speech codec packing to AMR HR speech codec
Handovers between regular and super re-used TRXs
Load based handovers between segment’s BTSs
A closer look to procedures
When an intra-cell handover is triggered the following procedure is followed:
Search for and order neighbor cells according to search method (depending on reason for handover)
Order neighbor cells according to DTM capability (ADJ_DTM_ENABLED)
Check if which cells are overloaded and exclude them from potential candidate. The cells with the lowest load will be put higher on the list
Moving a DTM initiated call to a DTM cell
When a DTM capable MS is establishing a CS call on a non-DTM capable cell the BSC will try to move it to a DTM capable cell (increase of handovers)
The BSC will initiate an eased PBGT handover to a DTM capable cell as soon as the coverage of at least one DTM capable adjacent cell is available. The following formula applies
AV_RXLEV_NCELL (n) > RxLevMinCell (n) + MAX (0, Pa) and
HoMarginPBGT (n) > PBGT (n) > DtmMarginPBGT (n)
After a successful intra-BSC PBGT handover the PBGT handover back to the non-DTM capable source cell is allowed only if :
PBGT (SERV_CELL) < DtmMarginPBGT (SERV_CELL) - 2dB
PBGT (SERV_CELL) = (A - AV_RXLEV_NCELL (SOURCE_CELL)) –
(B - AV_RXLEV_DL_HO - (BsTxPwrMax - BS_TXPWR))
B = MsTxPwrMaxGSM (BTS) or MsTxPwrMaxGSM1x00 (BTS)
A = MsTxPwrMaxGSM (ADJ) or MsTxPwrMaxGSM1x00 (ADJ)
After a successful inter-BSC PBGT handover the BSC will set PBGT handover back to the non-DTM capable source cell on the penalty bench
And if it fails the connection will not be setup / continued
Inter system handovers
When the PCU receives information that a DTM MS that is in dedicated mode in a DTM capable cell (DTM co-ordination indicates this) can move to UTRAN, then the PCU will do the following:
If the WCDMA FDD NCCR Enabled parameter indicates that ISNCCR procedures are enabled in the BSC and a ISHO will be performed
If the WCDMA FDD NCCR Enabled parameter indicates that ISNCCR procedures are disabled in the BSC, then the PCU will ignore the request to make an ISHO.
The NCCR specific parameters NCCR Control Mode and WCDMA FDD NCCR Preferred will be ignored in this context (the NCCR procedures are not applied in DTM)
Non-DTM but WCDMA capable MSs will be handed over to WCDMA as soon as the necessary information for the decision is available and the operator has so indicated by the new parameter, ISHO Preferred For non-DTM MS.
DTM handover counters
Dedicated mode
Updated only in BSC internal inter-cell HO; not in external HO (inter BSC HO)
NON_DTM_BASED_ISHO_SUCCESS
NON_DTM_BASED_ISHO_ATTEMPT
LA and RA updates
Cell Update procedure in dedicated mode, packet idle mode and Ready state; performed on the main DCCH
Cell Update procedure in dedicated mode, packet idle mode and Ready state; performed on a TBF
SGSN
MS
BSS
MSC
Speech codec selection
The BSC will use the existing algorithms for channel quality monitoring on the DTM-CS timeslots.
The BSC will use the existing algorithms and thresholds to change the speech codec mode when needed with the following exception:
The BSC will not trigger an intra-cell handover procedure for a DTM call in the purpose of changing the speech codec mode from FR to HR (intra-cell HO due to HR -> FR change is OK and the FR -> HR change is OK if the intra-cell HO is triggered by some other reasons).
The first DTM release the BSC will always use the FR speech codec mode for a DTM call but in the later DTM releases (possibly CD release for S12) it will be possible to use also HR mode.
Since the change in the speech codec mode requires a change in the CS timeslot, the BSC will trigger an intra-cell handover procedure for the DTM allocation, when the speech codec mode needs to be changed from HR to FR during the DTM call.
Deployment of DTM
The territory deployment strategy will most likely not change in the beginning of DTM rollout.
When investigating the current territory situation the following guideline can be followed. 4 TSs can have 2 simultaneous users. Together with the dtm_1 KPI a good overview can be achieved about if the territory is not too small.
All BTSs or SEGs should have GPRS territory
When planning DTM on top of existing network typical dimensioning process should be followed
DTM requires at least 2 TS (one for PS and one for CS TSL)
Operator should not require to make changes on territory size due to DTM
Coverage planning
Uplink coverage might be reduced regarding uplink multislot allocation. The coverage of DTM does not differ from the coverage of speech calls and EDGE connections
Otherwise DTM has comparable coverage to speech calls and EDGE connection
More planning issues
Transmission
No extra E1 / T1 required initially (if not needed in the first place)
1 DTM CS allocation will take 1 RTSL from PCU2 connectivity
If EDGE has been implemented, number of connected RTSLs is not typically limiting PCU connectivity (EDAP is limiting factor)
DTM will have some influence for both CS and PS traffic
Blocking in CS will prevent DTM handovers and establishment (mobility)
Blocking in PS will prevent DTM connections
The use of DTM should not add blocking for normal speech users
All RNW counters are updated in the same way as normal CS allocations (like handover, Dropped call, SDCCH, etc)
Deployment possibilities with DTM
PCU 2 first release does not support separated GPRS and EDGE territory, next release might support this (PCU2 will not support separate territories for GPRS and EDGE!!!)
Capacity planning for DTM is influenced by the following factors:
TS allocation (all DTM TS, both CS and PS, are allocated from the GPRS territory)
Used DTM applications and the typical DTM traffic profile
GPRS territory fragmentation (a DTM CS TS cannot be multiplexed with a PS TS)
DTM call allocations and reallocations
Because of the simultaneous CS and PS connection, DTM influences both CS and PS traffic
The penetration of DTM-capable MSs
Used DTM applications
DTM traffic profile
DTM service pricing
CS traffic/blocking rate
Fragmentations
A high number of simultaneous DTM users create PS territory fragmentation.
if the expected number of DTM users at service launch is considered to be large, re-dimensioning of the existing network is recommended
If the DTM user locations can be identified, some single cells that have simultaneous DTM users may require more CS and PS TSs
Especially the GPRS territory may need to be increased if the other data services in the BTS require high data rates or multislot allocations
The PCU allocates PS resources for the DTM users far from the CS-PS territory border
In highly-loaded PS territories the PS resources can be allocated from the middle of the PS territory. This causes fragmentation to the PS timeslots which decreases the PCU capability to give multislot allocations for other data connections
Power control issues
The BSC will limit the range of the transmission power of a CS connection when the CS connection is part of a DTM allocation.
the DL transmission power of a DTM-CS connection will be between [PMAX – 10 dB, PMAX], where PMAX is the maximum transmission power that can be used in the given TRX.
Since the GPRS specific DL power control is not supported in BSS12, the PCU will apply the same transmission power to DTM related DL TBFs as is used in normal GPRS/EGPRS operation.
Signaling
The signaling load generated by the DTM co-ordination is dependent on the penetration of DTM mobiles.
when the large majority of the mobiles are DTM capable, then the DTM co-ordination will generate a considerable signaling load at the PCUSIG interface
In the overload situation the BSC is perhaps not able to handle all the DTM co-ordination messages generated and the message might be discarded. The following can happen
The PCU may not receive an indication that a DTM MS has entered dedicated mode.
If the PCU receives a data PDU for the MS in this case, the DL TBF establishment fails and the MS is considered as unreachable.
The PCU may not receive an indication that a DTM MS has left dedicated mode. The PCU is not able to remove the MS from the IMSI record resulting in a ‘hanging’ record that consumes memory of the PCU.
DTM Fragmentation Penalty (DFP)
BTS/SEG parameters
PRFILE parameters
DTM PFC Packet Flow Timer (DPPFT)
Defines the maximum time accepted for a Packet Flow Timer (PFT) during a DTM allocation. A PFC life-time determines how long the CS connection of a DTM MS is kept in the PS territory after the data traffic has ceased for the MS.
High value = more resources taken, low value = slow PDP connection time
DTM Fragmentation Penalty (DFP)
This parameter defines the value of the fragmentation penalty. This parameter is used to balance the trade-off between searching for a DTM allocation that gives the optimal DTM-PS resources and for a DTM allocation that avoids fragmentation of PS resources in the PS territory.
High value = low fragmentation, low value = high fragmentation
ISHO Preferred For Non-DTM MS (IPND)
With this parameter the operator may determine whether an inter-system handover is to be triggered for a DTM incapable but WCDMA capable MS as soon as an appropriate WCDMA target cell is available.
DTM Segment parameter
DTM ENABLED (SEG)
Indicates if DTM is enabled in a SEGMENT.
Note that DTM feature can be activated only in segments that belong to a DTM capable PCU.
DTM adjacent cell parameters
ADJACENT DTM ENABLED (ADJ)
Indicates if adjacent cell supports DTM or not. Parameter can be given at Adjacent Cell creation when neighbour is external i.e. under another BSC.
If Adjacent Cell is created with BTS reference, the value is copied from the reference BTS (Master-BTS).
DTM POWER BUDGET MARGIN (DPM)
With this parameter you define a power budget handover threshold for inter-cell HOs:
a) DTM capable mobiles to DTM capable neighbour cell when the serving cell is not supporting DTM,
b) DTM call attempts to DTM capable neighbour cell when there is no free resources for a DTM allocation in the serving DTM capable cell,
c) DTM calls from DTM capable cell to non-DTM capable cell.
DTM PRFILE Parameters
DTM_CALL_ASSIGN_TIMER
Defines the length for a timer that is used to supervise the DTM call establishment procedure at the PCU.
The DTM call assignment is considered to be successfully completed when the PCU receives a valid RLC/MAC block from the mobile. The timer is then stopped.
The DTM call assignment is considered to be unsuccessfully completed when the supervising timer expires. The assigned TBF is then abnormally released
DTM_CALL_PENALTY_TIMER
This parameter defines the value for the Wait Indication.
When a MO DTM call establishment is rejected the Wait Indication timer is used. The rejection is sent with a DTM REJECT message. The Wait Indication within the message determines the time period during which the MS is not allowed to make a new packet access attempt to the same cell.
MAX_LAPD_LENGHT
DTM_MS_CL_11_SUPPORT_EDA
This parameter determines whether the PCU is allowed to assume that a DTM Multislot Class 11 mobile supports extended dynamic allocation mode.
With this assumption the PCU is able to allocate 2 UL PS timeslots for a DTM Multislot Class 11 at the MO DTM call establishment.
MS Capability
TCH RESERV BY DTM MS - Number of events where a CS speech connection is established for a DTM capable MS. Note that it is possible to estimate the DTM penetration (user activity affects this of course) when the value of this counter is compared with the one that counts the corresponding CS connection establishments for all MSs.
UL TBF RELEASES DUE DTM - Number of cases where an ongoing UL TBF needs to be released due to a DTM procedure
DL TBF RELEASES DUE DTM - Number of cases where an ongoing DL TBF needs to be released due to a DTM procedure
DL RLC CS1 BLKS TO DTM MS - Number of RLC data blocks transmitted with CS-1 to mobiles having a DTM allocation
DL RLC CS2 BLKS TO DTM MS - Number of RLC data blocks transmitted with CS-2 to mobiles having a DTM allocation
LLC BYTES UL DTM - Number of bytes transmitted in UL direction in DTM mode. Includes both GPRS and EGPRS modes (EQoS counter)
LLC BYTES DL DTM - Number of bytes transmitted in DL direction in DTM mode. Includes both GPRS and EGPRS modes
DTM Handover counters
DTM MS HO ATT TO DTM CELL - Number of attempts where the handover for a DTM capable MS in dedicated mode is started to the DTM capable cell
DTM MS HO SUCC TO DTM CELL - Number of the successful handovers where a DTM capable MS in dedicated mode is handed over to the DTM capable cell
DTM MS HO ATT TO NON DTM CELL - Number of attempts where the handover for a DTM capable MS in dedicated mode is started to the NON-DTM capable cell
DTM MS HO SUCC TO NON DTM CEL - Number of the successful handovers where a DTM capable MS in dedicated mode is handed to the NON-DTM capable cell
DTM CALL HO FROM DTM CELL - Number of events where an MS that was having a DTM allocation in the source cell is handed over to the cell
DTM HO DUE LACK OF RESOURCE - Number of events where the BSC triggers an inter-cell handover procedure for a DTM MS due to lack of resources in the source cell
Key Performance Indicators
Dtm_2: DTM CS traffic ratio
Dtm_3: DTM PS payload ratio
Dtm_4: UL DTM PS payload
Dtm_5: DL DTM PS payload
Dtm_6: DTM allocation success ratio
Dtm_7: DTM initial allocation failure ratio due to lack of resources
Dtm_8: DTM CS connection establishment failure due to link failure
Dtm_9: DTM PS connection establishment failure due to link failure
Dtm_10: DTM CS drop call ratio
Dtm_11: DTM reallocation success ratio
Key Performance Indicators
Dtm_13: DTM CS traffic
Dtm_16: DTM HO attempts to non DTM cell ratio
Dtm_17: DL multislot soft blocking for DTM
Dtm_18: UL multislot soft blocking for DTM
Traffic counters (1/3)
DROP AFTER DTM TCH ASSIGN - Number of dropped DTM calls after the TCH is assigned
DROP DTM TCH ASCMPL RFCH REL - Number of DTM TCH drops between Assignment Complete and RF Channel Release Ack messages
M TRAFFIC LOAD - Number of messages received from the MSC reporting cause traffic_load
EXT IN DTM NO RES AVAIL - Number of successful external incoming handovers due to reason that there are no free PS resources available for a DTM call in the source cell
EXT IN DTM TRAFFIC - Number of successful external incoming handovers for DTM calls due to PCU quality control and due to reason that DTM is disabled in the source cell
INTER DTM NO RES AVAIL - Number of successful internal inter-cell handovers due to reason that there are no free PS resources available for a DTM call in the source cell
INTRA DTM MO CS TO PS - Number of successful internal intra-cell handovers due to mobile originated DTM call establishment
INTRA DTM MT CS TO PS - Number of successful internal intra-cell handovers due to mobile terminated DTM call establishment
INTRA DTM MT PS TO PS - Number of successful internal intra-cell handovers due to PCU initiated DTM call reallocation
INTRA DTM PS TO CS - Number of successful intra-cell handovers due to DTM call release
EXT OUT DTM NO RES AVAIL - Number of successful external outgoing handovers due to reason that there are no free PS resources available for a DTM call in the serving cell
EXT OUT DTM DISABLED - Number of successful external outgoing handovers for DTM calls due to reason that DTM is disabled in the serving cell
EXT OUT DTM HO TO DTM - Number of successful external outgoing handovers for DTM capable mobile stations due to reason that serving cell does not support DTM
EXT OUT DTM HO TO WCDMA - Number of successful external outgoing handovers for mobile stations that support WCDMA but does not support DTM
INTER DTM DISABLED - Number of successful internal inter-cell handovers for DTM calls due to reason that DTM is disabled in the source cell
Activation of DTM
1. Activate IMSI delivery on the MSC.
In a Nokia MSC, IMSI delivery is active when the value of the COMMON ID INFORMATION SUPPORTED BSSAP parameter is YES.
Check the value of the COMMON ID INFORMATION SUPPORTED parameter (EDB).
If necessary, change the value of the parameter to YES (EDT).
2. Activate DTM on the BSC.
Check that the PCU2 and DTM licences are active (W7I).
Check that the PCU2 and DTM feature states are ON (W7I).
Check that (E)GPRS is enabled in the segment (EQO).
Change the value of the DTM enabled parameter to Y (EQV).
3. Test the activation.
Start the measurements (TPS).
Wait until the measurements are enabled and check them (TPI).
Establish a voice call between two MSs, one of which is DTM capable.
Establish a PS connection with the DTM-capable MS.
Disconnect the calls.
3GPP release 4 TS 43.055 Dual Transfer Mode
3GPP TS 44.018, v 5.16.0, Mobile radio interface layer 3 specification, Radio Resource Control (RRC) protocol.
PS
PS
CS
PS1
PS2
PS2
PS1
CS2

Documents

DTM Planning Training