M-EGCH Link Management

7/28/2019 M-EGCH Link Management

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All rights reserved 2005, Alcatel

Alcatel BSS B9 release

M-EGCH link management / August 2005


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All rights reserved 2005, AlcatelM-EGCH link management / August 2005

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Agenda

M-EGCH link management

TRX capability

M-EGCH link size

M-EGCH link establishment

M-EGCH link capacity increase

Unused GCHs

M-EGCH link release or capacity decrease

Periodical GCH establishment process


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M-EGCH link managementTRX capability

Hardware PS capability of a TRX is determined accordingto the generation of the BTSs TRE to which the TRX ismapped (that TRX-to-TRE mapping being done by theBSC)

TRE generation HW PS capability of the TRX

G2 (TRE in a DRFU BTS) CS1/2

G3 (TRE in an Evolium BTS) CS1/4

G4 (TRE in an Evolium BTS) CS1/4 + MCS1/9


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M-EGCH link managementTRX capability

TRX capabilities for GPRS (maximum CS) and for EGPRS(EGPRS possible or not, and maximum MCS) aredetermined at MFS side by taking into account thefollowing information received from the BSC

Hardware PS capability for each TRX (cf. previous slide)

Max_GPRS_CS O&M parameter

En_EGPRS O&M parameter

Max_EGPRS_MCS O&M parameter

Max_EGPRS_MCS

O&M

GPRS capability

(CS2/CS3/CS4)

Max_GPRS_CS

TRX GPRS

capability

HW PS

capability

BSC

EGPRS capability(MCS1-MCS9)

En_EGPRS

TRX EGPRS

capability


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M-EGCH link managementM-EGCH link size

Size of the M-EGCH link of a TRX is expressed by anumber of GCHs, which is computed with the followingvariables

Established_Nb_GCH

Current_Nb_GCH

Target_Nb_GCH

Min_Nb_GCH


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Established_Nb_GCH Definition Established_Nb_GCH is the number of GCHs that are activated in

the M-EGCH link and that will keep being activated during a certaintime.

Established_Nb_GCH = Nb_GCH_ Activated - Nb_GCH_Reserved_For_Release

On a G4 TRX, the upper value of Established_Nb_GCH is 36

On a G3 TRX, the upper value of Established_Nb_GCH is 14


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Established_Nb_GCH Depends on Nb_GCH_ Activated

the number of GCHs which are currently activated in the M-EGCH link of the TRX(i.e. an Activate-Ack message was received on those GCHs).

Note: the GCHs wich are reserved for release are counted in Nb_GCH_ Activated.

Nb_GCH_Reserved_For_Release: the number of GCHs which are currently

activated in the M-EGCH link of the TRX and which verify one of the followingconditions:

the GCH has been marked to be released (i.e. a Release message will be sent onthat GCH as soon as it becomes possible according to all the constraints)

the GCH is being released (i.e. a Release message has been sent on that GCH, oran abnormal release was reported for that GCH through a GCH-Release-Indicationmessage from PTU),

the GCH has been reserved for another TRX (the GCH preemption having not been

performed yet). The TRX which has reserved the resources of the GCH can be inthe same cell (intra-cell GCH preemption for PS traffic) or in another cell of the sameBTS (inter-cell GCH preemption for PS traffic)


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Current_Nb_GCH number of GCHs that are already activated or that will be activated in

the future in the M-EGCH link.

Current_Nb_GCH =Established_Nb_GCH + Nb_GCH_Reserved_For_Establishment

Established_Nb_GCH: cf. previous slides

Nb_GCH_Reserved_For_Establishment

number of GCHs which are not yet activated in the M-EGCH link of theTRX, but which will be activated in the future (as soon as it becomespossible according to all the constraints). Those GCHs will be activated

with free Abis and Ater nibbles, or with intra-cell or inter-cell GCHpreemptions. The resources of those GCHs have been reserved but theestablishment/preemption requests have not been sent yet, or theestablishment/preemption requests have been sent but the confirmationmessages are still awaited


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Target_Nb_GCH Definition Estimation of the number of GCHs necessary in a given M-EGCH

link to carry the signalling and data PS traffic induced by:

TBFs established on the TRX (best-effort or RT TBFs)

MPDCHs established on the TRX

One-UL-blocks allocated to some MSs on the TRX (in case of UL 2 phaseaccess)

Target_Nb_GCH is only a targeted numberof GCHs, which may ofcourse not be reached in transmission resource (Abis and/or Ater)congestion situations


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Target_Nb_GCH Depends on Nb_PDCH_EGPRS: the number of PDCHs on the TRX on which

radio resources have been allocated for at least one EGPRS TBF

Nb_PDCH_GPRS: the number of PDCHs on the TRX on which radioresources have been allocated only for GPRS TBFs

Nb_MPDCH: the number of MPDCH(s) that the BSC has requestedthe MFS to establish on the TRX

One-UL-blocks allocated on some RTSs of the TRX, i.e.T_One_Block timer is running on at least one RTS of the TRX

Fast Initial PS Access feature is enabled or not in the cell

The Max_GPRS_CS and Max_EGPRS_MCS O&M parametervalues.

alpha_HiAter values associated to the different PDCHs of the TRX


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Target_Nb_GCH Depends on

Number of GCHs needed to send one radio block

coded with CSi or MCSi

Number of required GCHsCSi(i 1,4) UL DL

Nb_GCH(CSi)

CS-1 0,73 0,73 0,73

CS-2 1,00 1,00 1,00

CS-3 1,25 1,22 1,25

CS-4 1,64 1,60 1,64

Number of required GCHsMCSi(i 1,9) UL DL

Nb_GCH(MCSi)

MCS-1 0,89 0,86 0,89

MCS-2 1,00 1,00 1,00

MCS-3 1,33 1,28 1,33

MCS-4 1,50 1,47 1,50

MCS-5 1,86 1,81 1,86

MCS-6 2,36 2,31 2,36

MCS-7 3,49 3,39 3,49

MCS-8 4,14 4,00 4,14

MCS-9 4,49 4,39 4,49


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Target_Nb_GCH Formula

1) Target_Nb_GCH =

GPRSPDCHNBi

i

__

1

_GPRS_CS)Nb_GCH(Maxer(i)alpha_HiAt

+

EGPRSPDCHNBi

i

__

1

)_EGPRS_MCSNb_GCH(Maxer(i)alpha_HiAt

+ Nb_MPDCH ,Note: xmeans x rounded up to the next higher integer.

where Nb_GCH(Max_GPRS_CS) and Nb_GCH(Max_EGPRS_MCS) are defined accordingto the table in the previous slide.

2) If Target_Nb_GCH < Min_Nb_GCH, then

Target_Nb_GCH = Min_Nb_GCH, with Min_Nb_GCH defined in the next slides.


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Target_Nb_GCH Examples Assuming there is no MPDCH to establish on the considered TRX,

that the Fast Initial PS Access feature is disabled, and that the Aterusageof the GPU is normal

Target_Nb_GCH = 1*4.49 = 5 GCHs for the MEGCH link of a TRX

supporting one 1-TS best-effort EGPRS TBF (if the Max_EGPRS_MCSparameter is set to MCS-9),

Target_Nb_GCH = 1*4.49 + 1*4.49 + 1*4.49 + 1*4.49 = 18 GCHs for theMEGCH link of a TRX supporting one 4-TS best-effort EGPRS TBF (if theMax_EGPRS_MCS parameter is set to MCS-9),

Target_Nb_GCH = 1*1.64 = 2 GCHs for the M-EGCH link of a TRX

supporting one 1-TS best-effort GPRS TBF (if the Max_GPRS_CSparameter is set to CS-4),

Target_Nb_GCH = 1*1.64 + 1*1.64 + 1*1.64 + 1*1.64 = 7 GCHs for theM-EGCH link of a TRX supporting one 4-TS best-effort GPRS TBF (if theMax_GPRS_CS parameter is set to CS-4)


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Target_Nb_GCH Examples Assuming there is no MPDCH to establish on the considered TRX,

that the Fast Initial PS Access feature is disabled, and that the Aterusageof the GPU is high(GCH_RED_FACTOR_High_Ater_Usage parameter is set to 0.75)

Target_Nb_GCH = MAX (0.75*4.49 , Min_Nb_GCH )= Min_Nb_GCH = 5 GCHs

for the MEGCH link of a TRX supporting one 1-TS best-effort EGPRSTBF (if the Max_EGPRS_MCS parameter is set to MCS-9)

In this case, Target_Nb_GCH is forced to Min_Nb_GCH

Target_Nb_GCH = 0.75*4.49 + 0.75*4.49 + 0.75*4.49 + 0.75*4.49

= 14 GCHs

for the MEGCH link of a TRX supporting one 4-TS best-effort EGPRSTBF (if the Max_EGPRS_MCS parameter is set to MCS-9)


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Min_Nb_GCH Definition Estimation of the minimum number of GCHs necessary in a given M-

EGCH link for the TBF and MPDCH traffic supported by the TRX, byconsidering a stabilised situation where the Max allowed (M)CSvalue of the TBFs established on the TRX has reached theMAX_GPRS_CS or the MAX_EGPRS_MCS O&M parameter value

Min_Nb_GCH

=

Nb_MPDCH + Nb_GCH_For_Max_Allowed_(M)CS


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Min_Nb_GCH Depends on Nb_GCH_For_Max_Allowed_(M)CS is computed as follows:

If the TRX supports no radio resources

Nb_GCH_For_Max_Allowed_(M)CS = 0,

Else, if the TRX only supports radio resources for GPRS TBFs

Nb_GCH_For_Max_Allowed_(M)CS = Nb_GCH(Max_GPRS_CS),

with Max_GPRS_CS the O&M parameter value, and Nb_GCH(x) definedin the previous slides

Else, if the TRX supports radio resources for at least one EGPRS TBF

Nb_GCH_For_Max_Allowed_(M)CS = Nb_GCH(Max_EGPRS_MCS),

with Max_EGPRS_MCS the O&M parameter value, and Nb_GCH(x)defined in the previous slides


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Min_Nb_GCH Example In this example, it is assumed that there is no MPDCH allocated on

the TRX.

If there is one GPRS TBF and one EGPRS TBF established on theTRX, and if Max_EGPRS_MCS = MCS-9, then:

Min_Nb_GCH = 0 + MAX (0, Nb_GCH(MCS-9) ) = 4.49 = 5


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Particular cases The values of

Target_Nb_GCH

Min_Nb_GCH

have to be recomputed in the following cases

Case of a TRX only supporting one-UL-block(s) allocations

Case of a TRX currently used for the Fast Initial PS Access feature


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Particular caseTRX only supporting one-UL-block(s) allocations

In case there is neither TBF nor MPDCH resources on the TRX (i.eM-EGCH not established), and in case the TRX is not currently usedfor the Fast Initial PS Access feature

If some one-UL-blocks are allocated on some RTSs of the TRX (i.e.the T_One_Block timer is running on at least one RTS of the TRX),then the following variables shall be forced to 1:

Target_Nb_GCH = 1

Min_Nb_GCH = 1


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Particular caseTRX currently used for the Fast Initial PS Access feature

If En_Fast_Initial_GPRS_Access = enabled in the cell, and if theconsidered TRX is currently used for the Fast Initial PS Accessfeature, then the M-EGCH link of that TRX shall contain

N_GCH_FAST_PS_ACCESS GCHs If, on the TRX currently used for the Fast Initial PS Access feature,

one of the variables Target_Nb_GCH or Min_Nb_GCH is greaterthan or equal to N_GCH_FAST_PS_ACCESS, then this variable isvalid.

But if one of those variables is strictly less thanN_GCH_FAST_PS_ACCESS, then this variable shall be forced toN_GCH_FAST_PS_ACCESS

GC


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Particular caseTRX currently used for the Fast Initial PS Access feature

The following rules will always be respected on this TRX

Target_Nb_GCH N_GCH_FAST_PS_ACCESS,

Min_Nb_GCH N_GCH_FAST_PS_ACCESS

Among others, updating the variables on the TRX currently used for theFast PS Access feature guarantees that the GCHs of that TRX will not

be preempted by some other TRXs (intra-cell or inter-cell GCHpreemptions)

M EGCH li k


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M-EGCH link managementM-EGCH link establishment

Conditions to establish an M-EGCH link: An M-EGCH link is established each time there is some new PS

traffic (TBF, MPDCH or one-UL-block) on a TRX which has currentlyno established M-EGCH link

It can also be established due to the Fast Initial PS Access feature

M-EGCH link establishment: For the sequence of BSS events to establish an M-EGCH link, cf.

scenarios

GCH establishments with free Abis and Ater resources

inter-cell or intra-cell GCH preemptions

A certain number of GCHs (up to Target_Nb_GCH, and inthe limit of the available Abis and Ater transmissionresources) will be attempted to be established, either inone or in several successive steps

M EGCH li k t


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M-EGCH link managementM-EGCH link capacity increase

Conditions to increase M-EGCH link capacity: The number of GCHs of an existing established M-EGCH link may

have to be increased each time there is some new PS traffic (TBF orone-UL-block) on this TRX

It can also be increased due to the Periodical GCH establishment

process featureM-EGCH link capacity increase:

For the sequence of BSS events to establish some new GCHs in anexisting M-EGCH link, cf. scenario GCH establishments with free

Abis and Ater resources and inter-cell or intra-cell GCH

preemptions (Target_Nb_GCH - Established_Nb_GCH) GCHs (in the limit of the

available Abis and Ater transmission resources) will be attempted tobe established, either in one or in several successive steps

M EGCH li k t


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M-EGCH link managementUnused GCHs

T_GCH_Inactivity timer An inactivity timer called T_GCH_Inactivity is introduced per M-

EGCH link (instead of per PDCH in B8). It allows to

anticipate the arrival of new PS traffic on a given TRX (PS trafficinterruption followed by a PS traffic resumption on a given TRX),

provide some time for the radio defragmentation process to be completedin the cell (cf. T3 TBF reallocations),

optimise ping times (cf. the T_GCH_Inactivity_Last timer),

make the Ater nibbles of the released GCHs (on T_GCH_Inactivity timerexpiry) usable by other BTSs, or by other DSPs (if all the 4 nibbles of the64k Ater TS are freed),

if there is some PS traffic on another TRX in the BTS while theT_GCH_inactivity timer is running, the unused GCHs can be preemptedto meet the GCH needs of that other TRX (that avoids an Abis-Aterdeswitching operation followed by a reswitching operation in the BSC)

M EGCH li k t


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T_GCH_Inactivity timer Each time Established_Nb_GCH becomes strictly higher than

Target_Nb_GCH, the T_GCH_Inactivity timer of the M-EGCH link isstarted (if it was not running). Some GCHs are indeed considered tobe no more needed by the M-EGCH link

The established GCHs that are considered to be no more needed inthe M-EGCH link are said to be unused. The other GCHs are saidto be used

When the T_GCH_Inactivity timer of the M-EGCH link expires,(Established_Nb_GCHTarget_Nb_GCH) unused GCHs areattempted to be released (except if the conditions to launch theT_GCH_Inactivity_Last timer are verified)

M EGCH li k t


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T_GCH_Inactivity timer

M EGCH li k t


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Order with which the GCHs are released in an M-EGCH link

1. Basic Abis nibbles mapped to RTSs out of the non preemptable PSzone of the cell

2. Extra Abis nibbles and bonus basic Abis nibbles

3. Basic Abis nibbles mapped to RTSs within the non preemptable PSzone of the cell

4. Basic Abis nibbles mapped to RTSs supporting MPDCHs (case ofMPDCH release only)

M EGCH li k t


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If, for any reason, Established_Nb_GCH becomes equal to or lessthan Target_Nb_GCH, then the T_GCH_Inactivity timer shall bestopped if it was running.

While the T_GCH_Inactivity timer is running, a decrease of theTarget_Nb_GCH value may imply that there are some new unusedGCHs in the M-EGCH link. In that case, T_GCH_Inactivity timer shallnot be restarted (to avoid that some transmission resources are keptestablished for a too long time while not being effectively used for PStraffic)

M EGCH li k t


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T_GCH_Inactivity_Last timer(case of the release of the last TBF in a cell):

An inactivity last timer called T_GCH_Inactivity_Last is introducedper M-EGCH link (instead of per PDCH in B8).

The behaviour related to the T_GCH_Inactivity_Last timer is only

applicable if En_Fast_Initial_GPRS_Access = disabled If En_Fast_Initial_GPRS_Access = enabled, the T_GCH_Inactivity_Last

timer shall never be launched.

N_GCH_FAST_PS_ACCESS is an O&M parameter indicating thenumber of GCHs that shall be kept established when there is nomore (E)GPRS traffic in a cell. The goal is to allow keepingN_GCH_FAST_PS_ACCESS established GCHs for a while (duringthe T_GCH_Inactivity_Last timer) after the release of the last TBF ofthe cell

Those GCHs will be useful in case of (E)GPRS traffic resumption in thecell (when the Fast Initial PS Access feature is not enabled).

M EGCH li k t


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T_GCH_Inactivity_Last timer When the last TBF in the cell is released, and the TRX supporting that TBF

is the last established PS-capable TRX of the cell , the values ofTarget_Nb_GCH and of Min_Nb_GCH of the TRX are updated as usual(they become both equal to 0, except if the TRX is supporting some one-UL-blocks or MPDCHs). Then, the T_GCH_Inactivity timeris launchedaccording to the traffic type of the last TBF.

When the T_GCH_Inactivity timer expires, provided there is still no TBFtraffic in the cell, Max(0, Established_Nb_GCHN_GCH_FAST_PS_ACCESS) GCHs shall be released (instead ofEstablished_Nb_GCH Target_Nb_GCH GCHs for a classicalT_GCH_Inactivity timer expiry). The GCHs to release are determined withthe same priority rules as the ones defined for a classical T_GCH_Inactivitytimer expiry apply

The T_GCH_Inactivity_Last timershall then be launched if the new valueof Established_Nb_GCH is still strictly greater than Target_Nb_GCH (and,as in B8, the value of the timer to launch shall be set toT_GCH_Inactivity_Last - T_GCH_Inactivity). If not, theT_GCH_Inactivity_Last timer shall not be launched (because the establishedGCHs are useful for some MPDCH(s))

on a given TRX, the timers T_GCH_Inactivity_Last and T_GCH_Inactivity are neverrunning at the same time

M EGCH link management


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T_One_Block timer Unlike T_GCH_Inactivity, the T_One_Block timer is related to a RTS.

The T_One_Block timer is activated as soon as a one-UL-block isallocated on the RTS, whether the RTS supports some TBFs or not,and whether the T_GCH_Inactivity timer is running or not on theTRX.

The T_One_Block timer shall be restarted each time a new one-UL-block is allocated on the RTS.

Notes:

The T_One_Block timer remains running even if some TBFs areestablished on the RTS,

At least one GCH will remain established while the T_One_Block timer isrunning on at least one RTS of the TRX thanks to the definitions ofTarget_Nb_GCH and of Min_Nb_GCH,

Contrary to B8, the T_One_Block and T_GCH_Inactivity timers are notexclusive of each other (i.e. the two timers can be running at the sametime)



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M-EGCH link managementM-EGCH link release or capacity decrease

Conditions to release an M-EGCH link or decrease itscapacity

In the nominal case, an established M-EGCH link has to be released,or its number of GCHs decreased, each time the T_GCH_Inactivityor T_GCH_Inactivity_Last timer of the M-EGCH link expires,

following a reduction of the PS traffic (TBF or one-UL-block traffic) onthe TRX.

The M-EGCH link release or capacity decrease is subsequent to thedecrease of the Target_Nb_GCH value of the TRX.

An M-EGCH link release or capacity decrease can also be due to inter-cellGCH preemptions or intra-cell GCH preemptions

An M-EGCH link release or capacity decrease can also be due to the fillingof the GPU Ater TS margin or of the DSP GCH margin

At last, some abnormal GCH releases can also occur (cf. next slides)

Some GCH may be released due to CS pre-emption



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M-EGCH link managementPeriodical GCH establishment process

Goals of the periodical GCH establishment process periodically attempt to increase the M-EGCH link size of TRXs which

have not yet reached their Target_Nb_GCH (i.e. the TRXs for whichCurrent_Nb_GCH < Target_Nb_GCH) in the cell. It allows

the usage of the recently freed Abis/Ater transmission resources in the

BTS/GPU due to GCH releases (no free couple of Abis and Ater nibble willremain unused for more than T_CANDIDATE_TBF_REALLOC seconds ifthere currently exists some GCH needs in the GPU),

the usage of the free basic Abis nibbles mapped to RTSs out of the nonpreemptable PS zone of the cell. Indeed, those basic Abis nibbles may betemporarily unused due to the Abis nibble selection priorities which defavorthem



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Goals of the periodical GCH establishment process It allows (contd)

to guarantee that, following some abnormal GCH releases, new GCHs willbe established in the impacted M-EGCH links (either with free Abis andAter resources, or with inter-cell or intra-cell GCH preemptions).

to guarantee a balance between the M-EGCH link sizes of the TRXs of agiven cell after some TBFs (established on those TRXs) have beenreleased. Some intra-cell GCH preemptions are indeed allowed to betriggered by the periodical GCH establishment process.

to guarantee that some GCHs are inter-cell preempted towards (the M-EGCH links of) the cell, if it is allowed according to the fairness constraintsdefined between the cells of the BTS. This can be useful for example

following the release of an RT PFC in another cell of the same BTS.

to guarantee that some GCHs are always established for the Fast InitialPS Access feature



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Conditions to launch the periodical GCH establishmentprocess

Transmission ResourceAvailability (2)

TRX selection (3)

Available_Nb_GCH

Cell TransmissionEquity (4)

Transmission resourcereservation (5)

GCH ESTABLISHMENT PROCESS (6)

"target" TRX

T_CANDIDATE_TBF_REALLOC timer expiry

Available_Nb_GCH_With_Equity

Were some T3 or T4 TBF reallocation requests successfully played? (1)

No

Yes

End of the process

(nothing is done) (7)


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