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CONTENTS
1 PURPOSE OF THIS DOCUMENT 4
2 INTRODUCTION 5
2.1 SDCCH channel and "service setup" 5
2.2 Logical meaning of the indicator 5
2.3 Two different approachs 6
2.3.1 SDCCH Success Rate for call 6
2.3.2 SDCCH Success Rate in overall case 6
2.4 Analysis method 7
3 MAIN CALL PHASES 8
4 CALL SIGNALLING AND COUNTERS INCREMENTED 9
4.1 Overview 9
4.2 Signalling analysis 9
4.2.1 PART 1: channel request (#1) and channel required
(#2) 13
4.2.2 PART 2: from channel activation (#3) to immediate
assignment (#6) 16
4.2.2.1 Automatic retransmission of the RACH 17
4.2.3 PART 3: from CM service request (#7) to physical
context confirm (#39) 19
4.2.4 PART 4: TCH activation (#40) and assignment
command (#42) 23
4.2.5 PART 5: TCH seizure 23
5 SMS SIGNALLING 24
6 SDCCH Blocking 26
7 SDCCH Success Rate for call 27
7.1 Notes 29
8 SDCCH success rate in overall case 30
8.1 Overview 30
8.2 Counter 1075 "sdcch_abis_fail_call" 31
8.3 Ghost random accesses 32
8.4 Double reservations: RACH repetition (congestion or
coverage problem) 33
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8.5 BCCH frequency-BSIC reuse 35
8.6 Bursts of random accesses (HO access), frequency-BSIC
reuse distance 35
8.7 "channel activation not acknowledgement" message failure 36
8.8 FORMULA 37
9 APPENDIX: Counter 1078 "sdcch_a_if_fail_call" and A interface
blocking 41
10 Table 2: Counters involved in the SDCCH Success Rate for call 42
11 Table 3: Counters involved in the SDCCH Success Rate in the
overall case 43
12 Table 4: Counters indicated in the flowchart of the SDCCH
assignment with the features dynamic SDCCH allocation andFACCH call setup 46
13 References 48
14 DOCUMENT REVISION HISTORY 49
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1 PURPOSE OF THIS DOCUMENT
This document is aimed at analysing the behaviour of BSC statisticalcounters concerning the SDCCH signalling during a service. The purpose is
to define an indicator that can be utilized to monitor the performance of the
network during the signalling on the SDCCH channel, providing a proposal
of new formulas aimed at getting near the subscriber viewpoint as much as
possible.
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2 INTRODUCTION
2.1 SDCCH channel and "service setup"
The signalling transported on the SDCCH channel is aimed at
reaching the service requested by the Mobile Station; in some cases this
represents only the setup of the service, in other cases the service is
completely performed on the SDCCH channel.
Considering a call for example, the SDCCH signalling contains the
messages for the setup of the service required, that is the exchange of
information between the Mobile Station and the network in order to create
the call scenario; considering a SMS, all the signalling during the service istransported on the SDCCH channel. In both of the cases the initial signalling
for accessing the network by a Mobile Station requiring a service is
transported on the SDCCH channel.
In this document the expression "service setup" is referred generally to
the phase of signalling in which the information between the MS and the
BTS is transported on the SDCCH channel.
The percentage of service dropped during the setup is an important
indicator to monitor the quality of a network because it can show how well
the network is able to lead the subscriber to access the service. Many
scenarios may occur to a mobile subscriber hampering the access to the
network; the coverage, the interference level and the efficiency of the
equipment in the signalling are the main responsible of the value assumed
by the indicator.
The indicator is reliable if it shows what the subscriber perceives. In
the present document the estimation of the drops occurred during the service
setup phase is made; the aim is to evaluate the goodness of the accessibility
as perceived by the subscriber. Not a unique definition is found for this
indicator because of the different observation points of view.
2.2 Logical meaning of the indicator
The logical meaning of the indicator is the ratio between the amount
of service setups correctly terminated in the network and the amount of
service requests:
requestsserviceof N.
correctlyperformedsetupsserviceof N.=indicator
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The service setup leads to access the service requested by the
subscriber and it consists of the signalling on SDCCH channel. This is
always the first step for accessing the network by a Mobile Station.
The indicator that will be defined measures the successful transactions
on SDCCH channel allocated for the request of a new service.
2.3 Two different approachs
The SDCCH phase is a wide part of the signalling because it is the
first step for accessing the network for all the services requested by a MS.
Considering the performance of the network during the setup of a
service, it is possible to distinguish between the success of the setup in case
the service is a call or in case it is whatever service. By this way it is
possible to monitor the failure rate perceived only by the subscribersrequiring a call rather than all the subscribers independently of the service
they required.
In this document two different formulas will be defined in order to
monitor the SDCCH signalling in the two mentioned cases.
2.3.1 SDCCH Success Rate for call
The first case will consider the performance of the SDCCH signalling
only when the service is a call, that is the MS requires the service for a call
and the aim of the SDCCH transaction is the setup of the call. The indicatormonitoring this case will be named "SDCCH Success Rate for call":
requestscallof N.
callforsactionsSDCCH transuccessfulof N.
requestscallof N.
setupscallsuccessfulof N. callfor
=
== SSR
2.3.2 SDCCH Success Rate in overall case
The second case will consider the SDCCH signalling working for all
the possible services (call included); in this case the MS could require a
service as call, SMS, Location Update, IMSI detach and Supplementary
Service.
The name of the indicator that will be defined in this case is "SDCCH
Success Rate in overall case" or, simply, "SDCCH Success Rate":
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requestsserviceof N.
sactionsSDCCH transuccessfulof N.
requestsserviceof N.
setupsservicesuccessfulof N.
=
==SSR
2.4 Analysis method
In order to implement the definition and make operative the indicator,
it will be necessary to "translate" its definition into a formula composed by
the counters of the NMS database. In order to understand the meaning of a
counter it is necessary to know the condition incrementing the counter.
It is necessary to find a formula counting all events in a certain points
of the signalling phase of the service.
For this purpose an analysis concerning the signals exchanged during
the SDCCH phase among the equipment MS, BTS, BSC and MSC will be
performed (chapter 4); the counters triggered in correspondence of the
meaningful (for the definition of the indicator) signals will be described.
Moreover, the description of the critical cases incrementing the
SDCCH failure counters will be provided (chapter 8.2 and 9) in order to
make clearness about the inputs of the formula.
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3 MAIN CALL PHASES
Our analysis will start considering the signalling related to a call,because it is the service required by the subscriber most frequently.
Considering the call service, it is possible to divide it in logical phases
in order to monitor the performance of the network in correspondence of the
most critical steps.
In Figure 1 these phases are reported together with the name of the
related statistic monitoring the performance in the specific phase. The call
phases reported in the figure concern the SDCCH and TCH blocking, the
success rate during the SDCCH signalling related to a call and the drop call
rate.
Figure 1: Main call phases
As mentioned above, purpose of this document is to define the
SDCCH success rate both considering only the SDCCH related to a call(SDCCH Success Rate for call) and considering all the SDCCH channels
managed by the Radio Resource Manager in obtaining the service (SDCCH
Success Rate in overall case).
In order to achieve the aim, the signalling of the phase marked by dark
grey in Figure 1 (indicated as "establish SDCCH connection") will be
analysed in detail in chapter 4.
For completeness, also the definition of the indicator SDCCH blocking
(related to the phase "get SDCCH", marked by clear grey) will be provided
during the analysis in chapter 6.
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4 CALL SIGNALLING AND COUNTERS INCREMENTED
4.1 Overview
In order to define the SDCCH indicators mentioned in the chapter 3,
our investigation starts from the analysis of SDCCH signalling flow during
the Mobile Originated.
The SDCCH analysis that will be performed considering the MOC
signalling could be done also by considering the Mobile Terminated Call
protocol; the only difference is the paging message sent from the BTS to the
MS before the channel request (Figure 2, signal 1) is sent from the MS, but
this kind of message doesn't affect the SDCCH logical channel because it is
transported on the PCH channel.By this way the indicator related to the SDCCH success rate during the
call setup will be defined.
Some messages of the call protocol are common to the signalling of
the other services; starting from the signalling related to the call, it will be
possible to mark these signals and the related counters in order to introduce
also the definition of the indicator related to the overall case (i.e. not only
call related).
4.2 Signalling analysis
In the following three figures (Figure 2, Figure 3, Figure 4) theprotocol of the MOC signalling from the SDCCH up to the seizure of the
TCH is reported.
The signalling has been divided in five logical parts in order to
individuate the most meaningful signals depending on the indicator to be
defined and on the counters we want to study. The five parts include:
PART 1: radio access part up to SDCCH blocking
PART 2: radio access part after SDCCH blocking
PART 3: establishment part, authentication, ciphering and encryption
PART 4: TCH request
PART 5: TCH seizure
The meaning of the logical parts individuated within the signalling
(PART 1, .., PART 5) is described in the following sections (from 4.2.1 to
4.2.5).
The counters involved in the definition of the indicators are reported
in correspondence of the signal in which they are incremented. The counters
are indicated by the name and the number of the NMS2000 database.
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Figure 2: Signalling of Mobile Originated Call
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PART 3
Figure 3: Signalling of Mobile Originated Call
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Figure 4: Signalling of Mobile Originated Call up to "TCH seized" phase
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4.2.1 PART 1: channel request (#1) and channel required (#2)
The PART 1 of the signalling reported in Figure 2 consists of the
beginning of the radio access to the network required by the MS. Thechannel request message is sent from the MS to the BTS and the BTS sends
the channel required message to the BSC.
This is always the first step for accessing the network. This part of
signalling is performed for every MS accessing a service, independently
on the kind of service required, meaning that it is valid also for all the
other services (not call) the MS can ask: SMS, Location Update, IMSI
detach, Supplementary Service.
The channel request (#1) message is used by the MS for requesting a
dedicated signalling channel SDCCH. The MS sends the channel request
message to the BTS on the RACH channel, and then this message is notinvolved in the SDCCH signalling. Its content will be described because
needed in order to understand the "ghost rach" during the definition of the
SDCCH blocking (chapter 6).
The content of this message consists of 8 bits; 3 bits are reserved for
the establishment cause and 5 bits for the random reference:
• establishment cause (3 out of 8 bits)among the 8 possible combinations of these 3 bits, 5 are valid as
establishment causes:- answer for paging (Mobile Terminated Call)
- emergency call- call re-establishment
- user requests (Mobile Originated Call, Short Message Service,
supplementary services)
- other services (Location Update, IMSI detach indication)
the other 3 combinations are not valid and then refused by the
network;
• random reference selected by the MS (5 out of 8 bits)- these 5 bits are randomly selected by MS. The usage of random reference
is when two MSs access the network exactly the same time; they can be separated
by using the random reference.
After the channel request has been received, the BTS forwards the
channel request generated by MS to the BSC sending the channel required
message (#2). The channel required contains the same information as
channel request with additional information added by the BTS.
The channel required message from the BTS includes the following
data:
- message discriminator: common channel management;
- message type: channel required;
- channel nr: uplink CCCH (RACH);
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- request reference: establishment cause, random reference received in the access
request and the frame number on which it was received;
- access delay: delay of the access burst as measured by the BTS.
After the BSC received the channel required message it proceeds inthis way:
• if the establishment cause is valid (5 valid cases out of 8 casesmentioned above) the BSC starts searching for a SDCCH channel
and the counters sdcch_seiz_att #1000 is incremented:
• if the channel is available in the cell where the originalaccess came from, it is reserved; the counter sdcch_assign
#1007 is triggered and the signalling described in the PART
2 starts;
• if the SDCCH channel is not available, the MS cannot accessthe service, the immediate assignment rejected message (see
PART 2) will be sent to the MS (if SDCCH dynamic
allocation and/or FACCH call setup are active, see Figure 5),
and the counter sdcch_busy_att #1001 is incremented;
• if the establishment cause is not valid (3 cases out of 8 casesmentioned above) the BSC doesn't proceed with the signalling and
the counter ghost_ccch_res #3030 is incremented.
If the SDCCH channel is not available, the research can be extended
by using the two features SDCCH dynamic allocation (S7) and FACCH call
setup (S5). The flowchart describing the steps followed by the process incase these features are activated is reported in Figure 5. On the arrows the
most important counters incremented after the signals moving to a new
condition of the flowchart are indicated. The logical steps performed by the
signalling described in this section are within the dashed block named
"PART 1". The block of the flowchart named "PART 2, PART 3" means
that all the signalling of the logical parts 2 and 3 of Figure 2 is performed in
that point.
Note that in case queuing and/or direct retry started, no SDCCH HO is
possible for leaving the cell.
Considering the signalling and the counters analysed in this section it
is possible to define the SDCCH blocking indicator; in the chapter 6 the
formula evaluating the block on the SDCCH channel met by the MS
accessing the network is provided.
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est. cause
valid?
RACH is a
ghost detected
SDCCH
available?
dyn. SDCCH
allocation?FACCH?
FACCH
successful?
OUT
TCHPART 2,
PART 3TCH
congestion?
queuing or/and
DirRetry?queuing or DR
successful?
dyn. SDCCHallocation
successful?
RACH
3004
YES1000
NO
3030
NO
YES
1007
NO
1001
YES
1154
YES
1007
NO
1001,1155
NO
YES
1010,1043,
1098
YES1099,
1125(fullrate)
1126(halfrate)
NO
NO1009
YES
NO
YES
NO
YES
1010,
1026
PART 1
SDCCH HO not possible
at this point
Figure 5: Flowchart of the call setup with SDCCH dynamic allocation and FACCH call
setup
Here the name of the counters indicated by the number in the
flowchart is reported, a more accurate explanation is provided in the chapter
12.
COUNTER NUMBER COUNTER NAME
1000 sdcch_seiz_att
1001 sdcch_busy_att
1009 tch_norm_seiz
1010 tch_request1026 tch_call_request
1125 tch_succ_full_seiz_fast_call
1126 tch_succ_half_seiz_fast_call
1043 tch_fast_req
1154 sddch_dynamic_reconf_att
1155 sdcch_unsucc_imm_assign_att
1098 tch_seiz_att_due_sdcch_con
1099 tch_seiz_due_sdcch_con
3004 ch_req_msg_rec
3030 ghost_ccch_res
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4.2.2 PART 2: from channel activation (#3) to immediate assignment (#6)
In this section the signals included in PART 2 of Figure 2, needed for
concluding the radio access to the network, will be described.After a successful reservation of a new SDCCH channel, the BSC
activates it by sending the channel activation message (#3) to the BTS
including the following data:
- message discriminator: dedicated channel management;
- message type: channel activation;
- channel number;
- activation type;
- channel mode: DTX control and channel type;
- MS power: maximum MS power level authorised in the cell.
Three events may happen:
1) A successful case is acknowledged by the BTS with channel
activation acknowledgement message (#4). The BTS will starts the
transmission and reception on the associated SACCH using the power levels
and the timing advance received in the channel activation message.
2) The BTS refuses to activate the new channel, it sends the channel
activation not acknowledgement message to the BSC with the reason of the
failure. Possible failure causes are the following:
- radio resource not available;
- radio channel already activated/allocated;
- protocol error and subclause, such as mandatory information error;
- O&M intervention in cases when the channel cannot be used for O&M
reasons;
- ciphering algorithm not supported;
- Equipment failure;
- Service or option not available.
In this case the counter sdcch_act_fail_call #1072 is incremented;
note that this failure can occur before the SDCCH channel is obtained by the
MS, so it won't be included in the SDCCH failure causes.
3) The GSM timer T9103 is used for supervising the channel
activation procedure. If the BSC does not receive the channel activation
ack/nack message within the time limit of the timer T9103, the timer expires
and the counter sdcch_abis_fail_call #1075 will be incremented (see Figure
14). An accurate analysis of the cases incrementing this counter will be
performed in the chapter 8.2.
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If the timer T9103 expires or if it has received the channel activation
not acknowledgement message, it releases the allocated channel by sending
the procedure of assignment failure to the MSC.
After a successful SDCCH channel activation, the BSC sends the
immediate assignment command message (#5) to the BTS (see Figure 2).
The information transported in this message contains the complete
immediate assignment message (#6) which is sent by the BTS to the MS on
the AGCH channel containing the following data:
- SDCCH channel number.
- message header;
- page mode: normal paging;
- channel description of the SDCCH allocated and the associated SACCH and
hopping frequency;
- request reference as sent by the MS in the Channel Request;
- initial timing advance;- mobile allocation if frequency hopping is used;
- rest octet only for the GSM phase 2.
The BSS informs the MS on AGCH channel about the SDCCH
channel to be used by using immediate assignment message. In practice, this
message is an order from the network to the MS to move to the SDCCH
channel defined before.
The GSM timer T3101 is used to supervise the immediate assign
procedure. If the SDCCH channel reservation or activation has failed, the
BSC sends the immediate assignment reject message to the MS.
4.2.2.1 Automatic retransmission of the RACH
When the mobile has sent the channel request message (#1) on the
RACH channel, it expects an answer from the network within a certain
period. The MS starts the timer T3120 and waits for the answer ( immediate
assignment or immediate assignment reject ).
If the MS doesn't receive the answer within the time limit defined by
the timer T3120, the MS makes a new attempt and sends another channel
request message with a new random reference on the next time slot. A new
value of timer T3120 is computed and used. The MS repeats this process
either until it is granted access or until the maximum number of repetitionsis reached; the network broadcasts the maximum repetition number.
If the service has been requested by the user pressing the "request
button" on the phone (4th
case of the establishment cause mentioned in the
section 4.2.1), the subscriber doesn't perceive these retransmissions of the
RACH channel.
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For example, if the maximum number of automatic retransmissions is
5, after the user pressed the button on the MS in order to obtain the service,
the MS will try automatically to access the network (up to 5 consecutive
times) if it doesn't receive the answer on the AGCH (Access Grant Channel)
within the period fixed by the timer T3120.
The subscriber doesn't perceive the first four failures, he will have to
push again the button the phone only after the last failure.
This phenomenon leads to a big value of a counter related to SDCCH
failures in Abis interface that are not perceived by the subscriber. This
subject will be discussed also in the chapter 8.4 considering the issue of the
SDCCH failure in Abis interface.
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4.2.3 PART 3: from CM service request (#7) to physical context confirm (#39)
When the MS has performed the radio access phase (i.e. it received the
immediate assignment from the BTS), the signalling proceeds with theestablishment phase, the authentication procedure, the ciphering and
encryption reported in the PART 3 (Figure 2, Figure 3, Figure 4).
In this section the establishment part will be analysed in detail in order
to mark the messages and the counters needed for the SDCCH success rate
formula.
After receiving the immediate assignment (#6) message, the MS tunes
to the assigned SDCCH and starts to establish the signalling link across the
network. The MS sends the layer 2 SABM to the BTS on the SDCCH. The
SABM contains the layer 3 CM service request message (#7) in which the
MS specifies the service type required to the network.The service request message includes one of the following
informations:
1.CM Service Request - for Mobile Originated calls and Mobile originated SMS- header;
- CM service type: mobile originated call, short message service, supplementary
services, emergency call;
- Ciphering key sequence number;
- MS classmark 2;
- mobile identity.
2. Location Update Request
3. IMSI Detach Request
4. Paging Response - mobile terminated call or SMS mobile terminated:
- header;
- Ciphering key sequence number;
- MS classmark 2;
- mobile identity.
5. CM_Re-establishment Request
The BTS forwards the MS service request to the BSC in the establish
indication message (#8) which includes the following data:
- message discriminator - radio link layer management;
- message type - establishment indication;
- channel number - SDCCH + AGCH;
- link identifier - main signalling channel SDCCH;
- L3 Information - complete L3 service request as received from the MS.
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This message indicates to the BSC that MS is now on the SDCCH
channel. If this message is not received by the BSC, the counter
sdcch_abis_fail_call #1075 will be incremented and the setup of the service
will be interrupted. A depth study of this case will be performed in the
chapter 8.2.
The BSC decodes the cause of the service request from the content of
the establish indication message.
In Figure 6 the signalling chart with the counters incremented at the
establish indication message is reported.
MS BTS BSC MSC VLR
Figure 6: counters incremented at the establish indication message
(Nokia Electronic Documentation, S9)
In correspondence of this signal the BSC increments always one of the
following six counters indicating the reason of the service setup (the same
counters are indicated in Figure 2):
• 3013: call or SMS or suppl. service originated
• 3012: call or SMS or suppl. service terminated
• 3020: call re-establishment
• 3021: emergency call
• 3019: location update
• 3033: imsi detach (S7 release)
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In Figure 2 other three counters (3028, 3029, 3044) are indicated in
brackets because they are not triggered during the call setup but it is
important to remember their use further. These counters are incremented
later in the signalling (i.e. after the establish indication, see chapter 5) if the
service is a SMS (3028, 3029) or Supplementary Service (3044). This
allows extracting the number of SDCCH requested for call subtracting their
value from the counter 3013 and 3012.
That means, for example, that when a Mobile Originated Call service
or a originated SMS service is requested the counter "succ_seiz_orig
(3013)" is incremented; in case the service is a originated SMS the counter
"succ_sdcch_sms_est (3028)" or "unsucc_sdcch_sms_est (3029)" is also
incremented.
This will be the method followed during the definition of the SDCCH
success rate indicators in order to distinguish how many service requests are
aimed at creating a call.In the following step of the signalling the service request is forwarded
to the MSC by the CR (CM service request) message (#9), then the BSC
starts to initiate the signalling connection control part (SCCP) connection
for the MS for the SDCCH establishment from the BTS. The GSM timer
T9105 is used to supervise this procedure.
If the SCCP link establishment fails, the BSC releases all resources
related to this transaction.
The BTS acknowledges the SABM (CM_service_request) by sending
to the MS the layer 2 UA (establish_indication) frame (#10). UA
(unnumbered acknowledgement) is normal Layer 2 level acknowledgement
when setting up the Layer 2 level link in LAPDm -protocol.
By the process access request message (#11) the MSC forward the
MS request to the VLR for access management. After that the procedures of
authentication, ciphering and encryption are performed in sequence. We
omit to describe the signalling of these procedures because no counter is
involved in the indicator we are defining.
For the definition of the SDCCH Success Rate for call the next signals
to be considered are the last two of PART 3: the physical context request
(#38), with which the BSC requests the BTS for the timing advance of
mobile transmission used in the SDCCH required by the mobile to move
onto the new radio channel, and the physical context confirmation (# 39).On receiving the physical context confirm message the BSC searches
for the relevant TCH channel using channel reservation procedure; at this
point the following counters are incremented (see Figure 4):
• tch_req #1010 triggered when a TCH is requested in the BTS (calland HO);
• tch_call_req #1026 triggered when the TCH is requested for a call;this counter will be considered the goal of the SDCCH transaction in
the SDCCH success rate for call indicator formula;
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• tch_norm_seiz #1009 triggered when the TCH is reserved for acall (no for HO).
If the BSC fails to receive the physical context confirmation message
within the T9108, or the message does not contain all the information
expected, the BSC returns an assignment failure message to the MSC with
the cause "equipment failure". The MSC either aborts with a clear command
or retries.
If the request cannot be acted on because all radio channels are
reserved, the queue is full, the request has been in the queue for too long, or
because of exceptional conditions such as restart/reset, then the BSC returns
an assignment failure with the cause "no radio resource available".
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4.2.4 PART 4: TCH activation (#40) and assignment command (#42)
The PART 4 of the signalling includes the last message transported on
the SDCCH channel toward the MS.After a successful TCH reservation, the BSC sends the channel
activation message (#40) to the BTS. In this message it tells the BTS to
activate the radio channel required. The message contains the following
data:
- message type;
- channel number = Lm/Bm + AGCH;
- activation type = normal assignment;
- channel mode = DTX indication and channel type. The channel type is either a
speech or data channel. If it is a speech channel, GSM speech encoding algorithm
is included; if it is a data channel, the transparent or the non-transparent mode isincluded. The data rate is also given.
The BSC starts the timer T9103 waiting for the channel activation
acknowledgement message (#41). If no response is received from the BTS
within the timer T9103, the BSC will send the MSC an assignment failure
message with the cause "equipment failure". The MSC either aborts or
retries.
For the TCH radio channel to be assigned, the BSC sends the
assignment command message (#42) to the MS.
This command is transparent to the BTS and it is the last command on
the SDCCH channel. It gives the MS all the information necessary for it tochange over to the TCH. The message consists of:
- header- channel description
- power command - max. MS power
- channel mode - speech full rate or data
- mobile allocation
On receiving the Assignment Command over the Air Interface, the MS
changes over from the SDCCH to the TCH it has been assigned to.
After a successful assignment procedure, the BSC releases theSDCCH channel.
4.2.5 PART 5: TCH seizure
The signals reported in PART 5 of Figure 4 represent the TCH seizure
oriented to create the conversation on the TCH channel.
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5 SMS SIGNALLING
In this section we consider the signalling in case the service requested
is a SMS. The setup of the SMS service is the same of the call until the
setup message sent from the MS to the network (signal #31 of call
signalling, Figure 3).
In case of a Mobile originated SMS the setup message is not sent by
the MS and it is replaced with a layer 2 message, a SABM containing the
message SAPI=3. The BTS acknowledges the MS with the Unnumbered
Acknowledgement signal of layer 2.
After that the BTS sends to the BSC a second establish indication (the
first est. ind. has been described as message #8 in the call signalling) by
which the BSC decodes the cause as "SMS". The final step is the
transmission of the data.
In the following three figures the signalling in case of Mobileoriginated/terminated SMS is represented. In case of success the counter
succ_sdcch_sms_est #3028 is incremented, in case of failure the counter
incremented is uns_sdcch_sms_est #3029. As mentioned in the section
4.2.3, in case of SMS service also the counters 3012 or 3013 are triggered
after the establish indication message (signal #8) of Figure 2.
Figure 7: successful Mobile originated SMS signalling
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Figure 8: successful Mobile terminated SMS signalling
Figure 9: unsuccessful Mobile originated SMS
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6 SDCCH Blocking
Before studying the SDCCH success rate, for completeness another
formula is provided which takes into account the number of SDCCH
channels not allocated because of lack of resources.
The definition of the SDCCH blocking formula is based on the
signalling and on the counters described in the section 4.2.1 (PART 1);
considering the signalling of Figure 2 this indicator is related to the first two
signals, until channel required message.
The SDCCH request is the first step during the service setup, if the
SDCCH is not obtained the subscriber cannot access the service.
As mentioned in the section 4.2.1, the signalling related to this phase
is common for all the services required. Therefore the formula will evaluate
the overall SDCCH blocking, meaning that the result is not referred only to
the SDCCH channels requested for a call but to all the SDCCH requests.Further than the cases mentioned in the section 4.2.1, the counter
#1000 sdcch_seiz_att is incremented also during SDCCH HO attempt.
This indicator calculates the percentage of SDCCH requests blocked
because of lack of resources on the total number of SDCCH requests (MOC,
MTC, call re-establishment, emergency call, SMS, location update, IMSI
detach, supplementary service, HO).
The denominator will be the sum of the SDCCH requests and the
numerator will be the sum of the SDCCH not seized because of lack of
resources. In the numerator the number of SDCCH busy channel has been
reduced by the number of successful FACCH call setup (Figure 5), because
in this case the MS reaches the service (i.e. TCH for call) after passing
through the SDCCH blocking.
The formula of the SDCCH blocking indicator is the following:
1001000
1099
1001
*)_att (sdcch_seiz
)con (due_sdcch_-tch_seiz_
)_att (sdcch_busy
king %SDCCH bloc+
+
=
Formula 1: SDCCH blocking formula
The description of the counters involved in this formula is provided in
the chapter 12 together with the counter description of the Figure 5.
If the dynamic SDCCH allocation feature is active, the FACCH
feature operates only in case of dynamic SDCCH allocation failure.
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7 SDCCH Success Rate for call
The formula of the SDCCH success rate for call is defined as the ratio
between the number of successful transactions on SDCCH channel during
call setup and the number of transactions started for a call request.
The numerator will be the number of traffic channel requests, because
the goal of the SDCCH signalling for call is the reservation of the TCH; the
denominator will be the number of times that the BSC decodes as type of
service request a call plus the difference between the incoming and outgoing
SDCCH HO.
Considering the five parts individuated in dividing the SDCCH
signalling of a call in the chapter 4, this definition is related to the PART 3
(section 4.2.3).
The transaction is defined as successful if it reaches the physical
context confirmation, signal #39 in Figure 4.The causes originating the service are counted with the establish
indication message, signal #8 in Figure 2. These causes are:
• Mobile Originated Call
• Mobile Terminated Call
• Call Re-establishment
• Emergency Call
The following causes are excluded:
• Location Update
• Short Message Service
• IMSI detach
• Supplementary Service
The signalling PART 2 is not involved in the definition of this
indicator because in that part it is not possible to isolate the factors related to
a call and, moreover, it includes the signals exchanged during the possible
RACH retransmission procedure mentioned above (section 4.2.2.1). This
part will be considered during the definition of SDCCH Success Rate in the
overall case.With the comments described in the chapters 4 and 5 it is now
possible to define the indicator monitoring the SDCCH Success Rate for call
by the following formula:
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100
4066
4051
4058
4045
3044sup
3029
3028
3021
3020
3013
3012
1026
100
*
)ch (-bsc_o_sdc
)ch (-msc_o_sdc
)h (bsc_i_sdcc
)h (msc_i_sdcc
)ce ( plem_servi_-succ_seiz
)t (cch_sms_es-unsucc_sd
)(h_sms_est-succ_sdcc
)g_call (sdcch_emer
)_re_est (sdcch_call
)orig (succ_seiz_
)term (succ_seiz_
)eq (tch_call_r
* H HOs)(net SDCC new calls) zures for(SDCCH sei
requests)(TCH call
%e for callsucc. rat SDCCH
+
+
+
+
+
+
+=
=
+
=
=
Formula 2: SDCCH success rate for call
At the denominator the counters 3028, 3029, 3044 are subtracted
because, as explained in section 4.2.3, their increments are already included
in the counters 3012, 3013. By this way only the number of SDCCH
requested for call is taken into account.
This formula involves measurements from Traffic Measurements,
Resource Access Measurements and HO Measurements. A summary
description of the counters is reported in the chapter 10.
The previous formula is defined on BTS basis. On BSC basis the
terms 4058 and 4066 (SDCCH HOs controlled by the BSC) have to beremoved from the denominator and, on PLMN level, also the terms 4045
and 4051 (SDCCH HOs controlled by the MSC) have to be removed.
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7.1 Notes
In the following two notes the considerations about the impact in the
formula of the SDCCH HO during SMS signalling are described. For
simplicity we consider the originated SMS and the SDCCH HO BSCcontrolled. The observations are valid also in case of terminated SMS and
SDCCH HO MSC controlled.
• NOTE 1: SMS signalling in the cell
If an originated SMS signalling is dropped before the establish
indication message for SMS (see Figure 7), the counter succ_sdcch_sms_est
#3028 (or #3029) will not be incremented in the cell but the counter
succ_seiz_orig #3013 or bsc_i_sdcch #4058 has been triggered.
In this case the denominator of the formula will be incremented of one
unit because of an establish indication not related to call, decreasing the
value of the indicator (i.e. of the success rate) in comparison to the reality.
Therefore the result of the indicator will fluctuate around the real
value depending on the weight of this phenomenon.
• NOTE 2: SMS signalling during HO
The SDCCH HO can be performed for every kind of service, and it is
not possible to distinguish between handovers related or not related to call.In this note we want to consider the impact of that on the indicator
when SDCCH HO is performed during SMS signalling (i.e. from establish
indication message #8 of Figure 2 up to establish indication message for
SMS of Figure 7):
• in the source cell the counters succ_seiz_orig #3013 andbsc_o_sdcch #4066 will be triggered: they cancel their effect in the
formula above; this doesn't affect the indicator;
• in the destination cell the counters bsc_i_sdcch #4058 andsucc_sdcch_sms_est #3028 (or #3029) will be triggered: they
cancel their effect in the formula above; also in this case thismeans that it doesn't affect the indicator.
The conclusion is that the value of SDCCH success rate for call has no
fluctuation around the real information if SDCCH HO is performed
successfully during SMS service.
Note that if the outgoing SDCCH HO during SMS has been successful
in a cell and then the signalling is dropped in the new cell, we are in the case
of the previous NOTE 1.
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8 SDCCH success rate in overall case
8.1 Overview
Aim of this indicator is to evaluate how many SDCCH transactions
started at the establish indication message (signal #8 in Figure 2) arrive
successfully at the end of the SDCCH signalling.
In this case all the SDCCH transactions will be considered, that is all
the SDCCH signalling originated with every establishment cause or by
incoming SDCCH HO.
In order to evaluate the performance in this case, counters for the
failures on SDCCH channel will be used in the formula. If a message is lost
or corrupted during the SDCCH signalling phase, a failure counter related tothe SDCCH part will be incremented. All the counters counting the failures
during the SDCCH phase are described in the chapter 11.
The SDCCH success rate will be obtained as complement of the
failure rate. The failure rate is calculated as ratio between the total number
of SDCCH failures and the total number of establishment causes plus the
incoming SDCCH HOs.
Among the SDCCH failures, a specific analysis will be performed in
the next sections regarding the SDCCH failures counted in the Abis
interface. Concerning the causes incrementing the number of these failures,
there is a part of signalling in which a wide number of Abis failures is
counted but the subscriber doesn't perceive them.
The part of signalling involved in this analysis is the PART 2 of
Figure 2; this part is the end of the radio access part. The most critical point
will be the immediate assign message sent from the BTS to the MS on
AGCH channel and the answer from the MS in the cm_service request
message on SDCCH.
As already mentioned in the section 4.2.2.1, the causes incrementing
the counter related to the failure in the Abis interface need an accurate
analysis in order to understand how many of the failures counted are really
detected by the user. This is very important for defining an indicator
showing what the subscribers are really perceiving.
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8.2 Counter 1075 "sdcch_abis_fail_call"
The purpose of this section is to explain the possible reasons for thecounter 1075 sdcch_abis_fail_call being updated and when the subscriber
perceives the failure. In the real statistics it is common that this counter
makes up most of the failures in the SDCCH signalling.
In the following table the DX causes composing this counter are
reported.
Cause name Cause number
abis_fail_block_c 304
abis_msg_corrup_to_bts_c 305
block_slave_c 307
ch_act_fail_c 314
data_ind_corrup_c 319
estab_ind_fail_c 321
estab_conf_fail_c 322
mode_mod_ack_fail_c 326
no_meas_result_c 327
no_resp_from_copro_c 328
phy_cont_conf_fail_c 329
rcs_alg_start_ack_fail_c 330
rcs_alg_cl_ack_fail_c 331
rf_ch_rel_ack_fail_c 333rel_ind_fail_c 335
signalling_error_c 336
sapi_3_fail_c 343
sub_timer_c 367
estab_ind_corrupted_c 370
has_state_conflict_c 505
Table 1: DX causes of the counter 1075
One of the reasons why counter 1075 is incremented is when the BSC
receives an establish indication which contents have been corrupted (DX
cause 370), or more commonly when a timer (T3101, default 3 sec) expires
while waiting for the establish indication (DX cause 321). In the real
statistics it has been found that the biggest contribution to the value of the
counter 1075 is exaclty in the DX cause 321.
Purpose of the following sections is to analyse when the failure due to
missed establish indication is really perceived by the subscriber.
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The establish indication is the first message sent from the BTS to the
BSC after the MS has successfully accessed the SDCCH (signal #8 in Figure
2).
The reasons because the MS would not appear on the granted SDCCH
are multiple; the following issues will be covered in the next paragraphs:
• ghost random accesses
• double reservations: RACH repetition (congestion or coverage problem)
• BCCH frequency-BSIC reuse
• bursts of random accesses (HO access)
• "channel activation not acknowledgement" message failure
8.3 Ghost random accesses
The BTS is continuously monitoring the UL Random Access Channel
slots in order to find whether or not there has been a random access from a
mobile. The information contents of a random access burst are rather
limited, thus it is possible the BTS detects a random access from
background noise. This kind of a "ghost random access" contains a random
Establishment Cause, and it is detected with a random timing advance.
There will always be a certain number of ghost accesses in the
network. If the number of SDCCH seizures per site is very small, then it is
possible that the majority of the accesses are ghost accesses. If this is the
case, then the result will be a high failure rate, and nothing can really be
done except to ignore the SDCCH Abis fail on sites where there is very little
traffic.One would expect (after BTS SW B9/D2) to receive maximum
somewhere around a few tens of ghost seizures per day per site. The amount
of ghost seizures can be studied with the counter ghost_ccch_res #3030; this
counter is incremented each time a ghost reservation is rejected on the
CCCH. The rejection is based on the Establishment Cause. Since the
Establishment Cause is random, in some cases the Establishment Causes in
the ghost random accesses will not be valid. Since this request is rejected it
will not result in 1075 being augmented. However we can expect a random
distribution of Establishment causes on ghost random accesses, thus a
certain amount of ghost random accesses will contain a valid establishment
cause and be granted a SDCCH. This SDCCH reservation will eventually
time out (timer T3101) and result in sdcch_abis_fail_call. The counter 3030
contains also accesses rejected due to excessive timing advance in the
random access (feature Distance verification in resource allocation), but
these can be subtracted by the counter rej_seiz_att_due_dist #3031.
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Figure 10: RACH ghosts
Considering the 8 bits of information in the RACH burst, 3 bits are
related to the establishment cause and 5 bits are related to the random
reference (see section 4.2.1). Among the 8 combinations obtained by the 3
bits of the establishment cause, 5 are legal (valid est. cause) and 3 are not
valid. Supposing the same probability for every establishment cause in a
ghost RACH, it can be deduced that the 3/8 part of the ghost are recognised
by the network incrementing the counter 3030. Therefore the amount of
ghost accesses that finally result in sdcch_abis_fail_call #1075 can be
estimated around 5/3*(3030-3031).The subscriber does NOT perceive all these failures.
Since the distribution is random, this is only estimation and should
only be used with relatively large sample numbers.
8.4 Double reservations: RACH repetition (congestion or coverageproblem)
This phenomenon is based on the procedure described in section
4.2.2.1 about the automatic RACH retransmission by a MS.
When the mobile has sent a random access, it will expect an answer
from the network within a certain time period. If the answer (ImmediateAssignment or Immediate Assignment Reject) is not received, the mobile
will repeat the random access. The repetition timers are explained in GSM
specification 04.08. The maximum amount of repetitions is defined in the
BCCH information, BSC parameter RET (max number of retransmission). If
the MS has to send multiple random accesses for a call or location update, it
is possible that there will be multiple reservations of SDCCH for one
mobile; naturally the mobile can use only one of these and the rest will
eventually time out and result in sdcch_abis_fail_call counter.
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Figure 11: automatic RACH retransmission
The MS can send multiple random accesses in the following
situations:
• The mobile could not receive the immediate assignment (signal #6in Figure 2). This can be due to several reasons: either the BTS has
not received the random access, or it has problems sending the
Immediate Assignment, or the MS is not capable of receiving the
Immediate Assignment.
• If there is UL interference, or the coverage is weak, the RandomAccess may be lost. In this case the SDCCH will not be seized,
and counter 1075 will not be augmented.
• If there is overload on the Access Grant channel, the ImmediateAssignment may be deleted by the BTS. The amount of deleted
Immediate Assignments (and Immediate Assignment Rejects) can
be found from counter del_ind_msg_rec #3005. In case the
immediate assignment is deleted, the MS will send a new Random
Access after timer expiration – the first seizure of SDCCH will
result in sdcch_abis_fail_call. In case the Immediate Assignment
Reject is deleted, the SDCCH was not reserved because of
congestion, and sdcch_abis_fail_call will not be augmented.
• If there is interference on the DL access grant channel, or coverageis weak, it is possible that the MS can not receive the Immediate
Assignment, and thus will make repetitions. For all the sent and
not received Immediate Assignments, sdcch_abis_fail_call will be
augmented.
The subscriber does not perceive the increments of the
sdcch_abis_fail_call due to RACH retransmission by the MS.
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8.5 BCCH frequency-BSIC reuse
If there are two sites with the same BCCH frequency and the same
BSIC, then the training sequence codes used in the random access message
by the MS and the decoding process at the BTS will be identical for thesesites. Limited only by the radio propagation environment, the random
accesses from one MS will be heard on both sites. Based on the frame
timing differences between the two sites, some of these accesses may result
in SDCCH reservations on two sites simultaneously. The MS will receive
the Immediate Assignment for one of these reservations, and access the
SDCCH. The second reservation will time out and sdcch_abis_fail_call will
be augmented but the subscriber does not perceive the failure.
Figure 12: same RACH detected by two BTSs
8.6 Bursts of random accesses (HO access), frequency-BSIC reusedistance
Sometimes burst like occurrences of sdcch_abis_fail_call have been
evidenced, together with sudden SDCCH congestion, and possibly also
Access Grant channel overflow. So far the only explanation found for thisphenomena is the frequency-BSIC reuse distance.
Consider that we have (Figure 13):
BTS1 as serving cell;
BTS2 with TCH on TRX1 frequency 1, BSIC 1;
BTS3 with BCCH frequency 1, BSIC 1.
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Now, limited only by signal attenuation, the handover access bursts to
BTS2 TRX1 will be overheard on BTS3 BCCH frequency 1. The handover
access burst is exactly like a random access burst (as electromagnetic
shape); the fields in the handover access burst may be interpreted as the
Establishment Cause and the random reference of the Random Access burst.
Most probably some of the timeslots of BTS2 TRX1 will overlap the RACH
of BTS3. So, if we do not have adequate distance between BTS2 and BTS3,
some of the handovers to BTS2 may result in sudden bursts of random
accesses to BTS3, resulting in sdcch_abis_fail_call, SDCCH congestion and
possibly also access grant channel overflow. The distance between BTS2
and BTS3 may easily be tens of kilometres, depending on the radio
propagation environment, and is not limited by the GSM specific 35 km
timing advance limits (the frame timing of BTS2 and BTS3 not being
synchronised).
Figure 13: HO access confused with the RACH by a third BTS
8.7 "channel activation not acknowledgement" message failureAfter the BSC has sent the channel activation message (#3) to the
BTS, it waits for the answer; three different events may happen:
1. the BTS sends the channel activation acknowledgement ,successful case (Figure 2);
2. the BTS sends the channel activation not acknowledgement because of a failure; in this case the counter sdcch_act_fail_call
#1072 is incremented;
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3. the BSC doesn't receive any signal from the BTS; in this case(after the timer T9103 expires, Figure 14) the counter
sdcch_abis_fail_call #1075 is incremented.
Figure 14: Channel activation acknowledgement not received by the BSC
8.8 FORMULA
Considering the previous issues it is clear that a big part of the failuresmapped in the counter 1075 are not perceived by the subscriber; therefore it
is reasonable to introduce a factor in order to weight the value of the
"sdcch_abis_fail_call" in the formula of the SDCCH failure rate.
The critical point is the establish indication (see Figure 2) message
sent from the BTS to the BSC. All the failures in Abis happened after this
message (both during a call and HO) are detected by the subscriber because
the SDCCH signalling is dropped. Considering the failures in Abis
happened before this message, only a small part of them will be perceived
by the user; in fact a lot of them are generated by ghost RACHs, RACH
repetitions, HO access bursts or RACH felt by more than one BTS.
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From real statistics it has been found that the value of the failure
mapped as Abis failure before the establish indication message is around the
95% of the whole value of the counter 1075 sdcch_abis_fail_call.
All the messages lost between the channel activation and the establish
indication (except the negligible number of "channel activation not
acknowledgement" message, described in par. 8.7) are represented by the
following difference:
)ach (i_-sdcch_ims
)_upd (-sdcch_loc
)rg_call (-sdcch_eme
)l_re_est (-sdcch_cal
)_orig (-succ_seiz
)_term (-succ_seiz
)gn (sdcch_assi
3033det
3019
3021
3020
3013
3012
1007+
This is the number of failures mapped as Abis failures collected
because of missed establish indication message (signal #8 of Figure 2).
A solution could be to include in the sum of the SDCCH failures only
the Abis failure occurred after the establish indication, defining a coefficient
C in order to modify the impact of the counter sdcch_abis_fail_call #1075
with the following weight:
)1075(___
3033det
3019
3021
3020
3013
3012
1007
1call failabissdcch
)ach (i_-sdcch_ims
)_upd (-sdcch_loc
)rg_call (-sdcch_eme
)l_re_est (-sdcch_cal
)_orig (-succ_seiz
)_term (-succ_seiz
)gn (sdcch_assi
C
+
−=
With the comments described in the previous sections it is possible to
define the SDCCH Success Rate formula which seem to match the
perception of the subscriber:
ure rate %SDCCH failrate %essSDCCH succ −= 100
where:
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100
4058
4045
3033det
3019
3021
3020
3013
3012
1079
1078
1076
1075
1039
1038
1037
1036
1035
1004
1003
100*min
*
)h (bsc_i_sdcc
)h (msc_i_sdcc
)ach (_sdcch_imsi
)upd (sdcch_loc_
)g_call (sdcch_emer
)_re_est (sdcch_call
)orig (succ_seiz_
)term (succ_seiz_
)(_fail_oldsdcch_a_if
)(_fail_callsdcch_a_if
)(_fail_oldsdcch_abis
)ll (is_fail_caC*sdcch_ab
)_act (sdcch_netw
)_reset (sdcch_bcsu
)_act (sdcch_user
) fail (sdcch_bts_
)_fail (sdcch_lapd
)ld_ho (sdcch_rf_o
)o_fail (sdcch_radi
sg SDCCH HOincosindicationestablish
uresSDCCH fail ure rate %SDCCH fail
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
=
=
+
=
Formula 3: SDCCH failure rate in the overall case
where C is the coefficient (between 0% and 100%) introduced for the
failure in Abis interface during the SDCCH signalling in order to consider
how many Abis failures mapped in this counter are really detected by the
subscriber.This formula involves measurements from Traffic Measurements
(failures), Resource Access Measurements and HO Measurements.
The counters involved in this formula are described in the chapter 11.
Another comment (see chapter 9) must be added regarding the counter
"sdcch_a_if_fail_call" (1078). Between the causes incrementing this
counter, that is all the signalling failures in the A interface, there is also the
block in the A interface. This condition is verified when the MSC doesn't
find the resource on the PCM link.
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The previous formula is defined on cell basis. On BSC basis the terms
4058 (SDCCH HOs controlled by the BSC) have to be excluded from the
denominator and, on PLMN level, also the term 4045 (SDCCH HOs
controlled by the MSC) have to be excluded.
At the denominator the counters for SMS and supplementary services
are subtracted for the reason described in the SSR for call and in the section
4.2.3 .
In the following figure the scenario of the counters involved in the
SDCCH request is reported; the Abis failures are divided in the ghost
contribute and in the failures after the establish indication (small part of abis
failures).
Figure 15: scenario and counter relations during SDCCH request
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9 APPENDIX: Counter 1078 "sdcch_a_if_fail_call" and A interfaceblocking
The counter 1078 is defined as the number of SDCCH transaction
failures due to an A interface failure during call attempt. By definition, in
these failures the block in the A interface is also included.
Considering the signalling between MSC and BSC defined in the
specification ETSI 08.08 ver 8.5, one of the possible message type (08.08,
3.2.2.1) is the "overload " message (3.2.1.26). This message is sent from the
BSS to the MSC or from the MSC to the BSS. There can be several causes
for sending this message (the cause values are listed in 08.08 – 3.2.2.5);
typical cause values are: processor overload, O&M. For example, when the
processor is overload at the MSC, the MSC can indicate to the BSS that it is
in a congested state and it is not able to process new service requests. One of
the cause value for the "overload " message is "Requested terrestrial resourceunavailable", that is sent as overload cause from the MSC to the BSC when
the MSC doesn't find the resource in the A interface. This can happen if no
free slot is found in the PCM line.
This event is included in the DX causes of the counter 1078 (NED S9)
as "m_req_terr_res_unava_c" (DX cause number 916). This means that a
congestion in the A interface is mapped as a failure in the A interface by the
SDCCH BSS counter failure 1078.
Considering the same call between two MSs, if no resources in the A
interface are free on the both sides it is not possible to have two increments
of the sdcch_a_if_fail_call (related to the two cells in which the MS are
located); the counter 1078 will be incremented only in the source cell.
In fact, in order for the MSC to be able to perform the pre-analysis
(i.e. dialled number validity check), in the source cell the resource in the A
interface has been already allocated. Without this condition (free PCM slot
in the A source side) the process cannot proceed, the routing with the
destination number doesn't start and the resource in the destination A if is
not requested.
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10 Table 2: Counters involved in the SDCCH Success Rate for call
Database NMS counter
name and number
Description Table
tch_call_request1026
Number of TCH requests for normal assignment(successful + unsuccessful). Updated when the Radio
Resource Manager receives a TCH request in a call attempt.
Traffic
succ_seiz_term
3012
Successful SDCCH seizures for a mobile terminated
call (MTC). This counter is increased by one every time that
an ESTABLISH INDICATION containing a paging
response is received on SDCCH from the BTS.
succ_seiz_orig
3013
Successful SDCCH seizures for a mobile originating
call (MOC). This counter is increased by one every time that
an ESTABLISH INDICATION containing a CM service
request is received on SDCCH from the BTS.
sdcch_call_re_est
3020
The number of successful SDCCH seizures for call
re-establishment. This counter is augmented by one every
time that an ESTABLISH INDICATION containing a call
re-establishment is received on the SDCCH from the BTS.
sdcch_emerg_call
3021
The number of successful SDCCH seizures for an
emergency call. This counter is augmented by one every time
that an ESTABLISH INDICATION containing a emergency
call is received on the SDCCH from the BTS.
succ_sdcch_sms_est
3028
Number of the SMSs successfully established on an
SDCCH.
UPDATED: When an ESTABLISH INDICATION
message (mobile originating SMS) or an ESTABLISH
CONFIRM message (mobile terminating SMS) is received
on SDCCH from the BTS.
unsucc_sdcch_sms_est3029
Number of the unsuccessful establishments of SMSson an SDCCH.
UPDATED: When establishment of SMS fails on
SDCCH.
succ_seiz_supplem_serv
3044
Number of the successful seizures of SDCCHs for
supplementary service (S9).
UPDATED: When an ESTABLISH_INDICATION
message with CM service request and service type
supplementary service is received on SDCCH from the BTS.
ResourceAccess
msc_i_sdcch
4045
Number of the successful incoming SDCCH to
SDCCH HOs controlled by the MSC.
UPDATED: When the HO is completed.
bsc_i_sdcch
4058
Number of the successful incoming SDCCH to
SDCCH HOs controlled by the BSC.
UPDATED: When the HO is completed.
msc_o_sdcch
4051
Number of the successful outgoing SDCCH to
SDCCH HOs controlled by the MSC.
UPDATED: When the HO is completed.
bsc_o_sdcch
4066
Number of the successful outgoing SDCCH to
SDCCH HOs controlled by the BSC.
UPDATED: When the HO is completed.
Handover
BSC
Table 2: Counters involved in the SDCCH Success Rate for call
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11 Table 3: Counters involved in the SDCCH Success Rate in the overallcase
Database NMS
counter name andnumber
Description Table
sdcch_assign 1007 Successful SDCCH seizures for immediate assignment
UPDATED: When the Radio Resource Manager allocates
an SDCCH for immediate assignment (call attempt).
sdcch_radio_fail 1003 Number of the SDCCH transactions ended due to a
radio failure.
UPDATED: When an SDCCH transaction ends due
to a radio failure (radio link timeout) and the RRM releases
the SDCCH. Also if MS user clears the call during the
SDCCH phase, this counter will be updated.
sdcch_rf_old_ho
1004
Number of the SDCCH transactions ended due to a
radio failure on the source channel during HO betweenSDCCH-SDCCH or SDCCH-TCH.
UPDATED: When an SDCCH transaction ends due
to a radio failure (HO failure) on the source channel during
HO attempt and the RRM releases the SDCCH.
sdcch_user_act
1037
Number of the SDCCH transactions ended due to
user actions. (The TRX/TSL is in substate blocked by the
user.)
UPDATED: When the user disconnects a busy
SDCCH by blocking the TSL/TRX with an MML
command. The transaction ends and the SDCCH is
released.
sdcch_bcsu_reset
1038
Number of the SDCCH transactions ended due to a
BCSU restart.UPDATED: When an SDCCH transaction ends due
to a TRX blocked by a BCSU restart and the RRM releases
the SDCCH.
sdcch_netw_act
1039
Number of the SDCCH transactions ended due to
reconfiguration of the radio network. (The TRX blocked is
in substate blocked by the system.)
UPDATED: When an SDCCH transaction ends due
to a TRX blocked by a failure which leads to TRX
reconfiguration. The failure may occur both during call and
HO attempts.
sdcch_bts_fail
1036
Number of the SDCCH transactions ended due to a
BTS failure. (The TRX blocked is in one of thesesubstates: FU fault, CU fault, BTS reset, BCF reset, both
CU and FU fault, BCF fault.)
UPDATED: When an SDCCH transaction ends due
to a TRX blocked by a BTS failure and the RRM releases
the SDCCH.
sdcch_lapd_fail
1035
Number of the SDCCH transactions ended due to
an LAPD failure. (The TRX blocked is in one of these
substates: signalling link fault or PCM fault.)
UPDATED: When an SDCCH transaction ends due
to a TRX blocked by an LAPD failure and the RRM
releases the SDCCH.
Traffic
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sdcch_abis_fail_call
1075
Number of the SDCCH transactions ended due to a
failure in the Abis interface during a call in progress. There
is no acknowledgement of channel activation, no indication
of call establishment received, i.e., ghosts.
UPDATED: When an SDCCH transaction ends dueto signalling problems in the Abis interface and the RRM
releases the SDCCH.
Reasons that trigger the counter: see chapter 8.2):
Phantom RACHs that have a valid establihment
cause.
The BTS can hear the MS, but the MS cannot hear
the BTS, and so the MS does not respond to the
IMMEDIATE ASSIGNMENT message with a SABM.
MS is accessing the network at the limit of
sensitivity and messages are lost.
Poor Radio conditions.
MS is accessing network through another BTS (co-
channel, co-BSIC interference).sdcch_abis_fail_old
1076
Number of the SDCCH transactions ended due to a
failure in the Abis interface on the source channel during
SDCCH-SDCCH or SDCCH-TCH HO.
UPDATED: When an SDCCH transaction ends due
to a failure in the Abis interface on the source channel
during an HO and the RRM releases the SDCCH.
sdcch_a_if_fail_call
1078
Number of the SDCCH transactions ended due to a
failure in the A interface during call attempt.
UPDATED: When an SDCCH transaction ends due
to signalling problems in the A interface during a call
attempt and the RRM releases the SDCCH.
sdcch_a_if_fail_old
1079
Number of the SDCCH transactions ended due to a
failure in the A interface failure on the source channel
during an SDCCH-SDCCH or SDCCH-TCH HO.
UPDATED: When an SDCCH transaction ends due
to signalling problems in the A interface during an
SDCCH-SDCCH or SDCCH-TCH HO and the RRM
releases the SDCCH.
sdcch_loc_upd
3019
Number of the successful seizures of SDCCHs for
location update.
UPDATED: When an ESTABLISH INDICATION
message with request for a location update is received on
SDCCH from the BTS.
imsi_detach_sdcch
3033
Number of the successful seizures of SDCCHs for
IMSI detach (S7).UPDATED: When an ESTABLISH INDICATION
message for an IMSI detach is received on SDCCH from
the BTS.
succ_seiz_term
3012
See Table 2 description.
succ_seiz_orig
3013
See Table 2 description
sdcch_call_re_est
3020
See Table 2 description
sdcch_emerg_call
3021
See Table 2 description
Resource
Access
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msc_i_sdcch
4045
See Table 2 description
bsc_i_sdcch
4058
See Table 2 description
Handover BSC
Table 3: Counters involved in the SDCCH Success Rate in the overall case
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12 Table 4: Counters indicated in the flowchart of the SDCCHassignment with the features dynamic SDCCH allocation and FACCH
call setup
Database NMS counter name
and number
Description Table
sdcch_seiz_att
1000
Number of the times when an MS attempts to
seize an SDCCH.
UPDATED: When the RRM receives requests
for SDCCH from an MS as the MS needs a channel
for either a call or a HO.
sdcch_busy_att
1001
Number of the times when an MS attempts to
seize an SDCCH unsuccessfully because all SDCCHs
are busy.
UPDATED: When the RRM has no SDCCHs
to allocate for a call or HO attempts.
tch_norm_seiz1009
Number of the successful requests for a TCHin a normal assignment.
UPDATED: When the RRM allocates a TCH
as a response to a TCH request in a call attempt.
tch_request
1010
Total number of the requests for a TCH
(successful and unsuccessful).
UPDATED: When the RRM receives a
request for a TCH either in a call or an HO attempt.
tch_call_request
1026
Number of TCH requests for normal
assignment (successful + unsuccessful)
UPDATED: When the Radio Resource
Manager receives a TCH request in a call attempt.
tch_succ_full_seiz_fast_call
1125
Number of the successful Full Rate TCHs
seizures for a FACCH call setup.
UPDATED: When the RRM allocates an FR
TCH as a response to an SDCCH request as part of
the FACCH call setup during SDCCH congestion.
tch_succ_half_seiz_fast_call
1126
Number of the successful Half Rate TCHs
seizures for a FACCH call setup.
UPDATED: When the RRM allocates an HR
TCH as a response to an SDCCH request as part of
the FACCH call setup during SDCCH congestion.
tch_fast_req
1043
Number of the TCH requests for FACCH call
setup during SDCCH congestion (both successful and
unsuccessful).
UPDATED: When the RRM receives arequest for an SDCCH but there are no SDCCHs idle
and a TCH is tried to be allocated as part of the
FACCH call setup. It is indicated in the received
SDCCH request whether FACCH setup is allowed or
not.
Traffic
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sddch_dynamic_reconf_att
1154
Number of the SDCCH reconfiguration
attempts for immediate assignment.
UPDATED: When a SDCCH channel is
needed for an immediate assignment and no free
SDCCH is available and the request is sent forreconfiguring a TCH channel to a SDCCH channel.
This counter is not updated if reconfiguration is done
from SDCCH to TCH channel.
sdcch_unsucc_imm_assign_att
1155
Number of the unsuccessful SDCCH
allocation attempts for immediate assignment.
UPDATED: When the SDCCH channel
allocation does not succeed due to lack of SDCCH
resources at the time of the immediate assignment.
When SDCCH is released with the dx-cause
rtsl_reconf_fail_c.
tch_seiz_att_due_sdcch_con
1098
Number of the attempts to seize a TCH due to
SDCCH congestion.
UPDATED: When the RRM attempts toallocate a TCH as a response to a request for an
SDCCH seizure during SDCCH congestion. The
RRM does this if the TCH allocation (=FACCH
setup) is allowed in the message carrying the request
for the SDCCH seizure.
tch_seiz_due_sdcch_con
1099
Number of the successful TCH seizures due to
congestion on the SDCCH.
UPDATED: When the RRM allocates a TCH
as a response to a request for SDCCH seizure during
congestion on the SDCCHs. The RRM allocates a
TCH if the TCH allocation (=FACCH setup) is
allowed in the message carrying the request for the
SDCCH seizure.
ch_req_msg_rec
3004
Number of CHANNEL REQUIRED messages
received from the BTS.
UPDATED: When a CHANNEL REQUIRED
message is received from the BTS.
ghost_ccch_res
3030
Number of the ghost reservations on a CCCH.
UPDATED: When a ghost reservation is
detected on a CCCH because the establishment cause
is not valid. This kind of random access can be
caused by, for example, white noise or co-channel
interference.
Resource
Access
Table 4: Counters indicated in the flowchart of the SDCCHassignment with the features dynamic SDCCH allocation and FACCH call
setup
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