Facch Setup

8/6/2019 Facch Setup

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Nokia Siemens Networks

GSM/EDGE BSS, rel.

RG10(BSS), operatingdocumentation, issue 04

Feature description

BSC3015: FACCH Call Set-up

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Table of ContentsThis document has 19 pages.

Summary of changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1 Overview of FACCH Call Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2 Procedures of FACCH Call Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1 Channel required procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 Channel reservation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 Channel activation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.4 Immediate assignment procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.5 Mode modify procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3 User interface of FACCH Call Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . 18



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List of FiguresFigure 1 Channel required procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 2 CHANNEL REQUEST message, only one octet long. . . . . . . . . . . . . . . . 9

Figure 3 Channel activation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 4 Immediate assignment procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 5 Mode modify procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15



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List of TablesTable 1 NECI parameter is set to OFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Table 2 NECI parameter is set to ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10



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BSC3015: FACCH Call Set-up Summary of changes

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Summary of changesChanges between document issues are cumulative. Therefore, the latest document

issue contains all changes made to previous issues.

Changes made between issues 12-0 and 11-0

Editorial Changes.


In section Channel activation procedure, ACCH control information has been added.


The lists of supported establishment causes in CHANNEL REQUEST message have

been updated in section Channel required procedure.


A note has been added to section Channel request message about HR/FR data.

Specification references have been updated.

Multirate configuration information has been removed from the document.



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Overview of FACCH Call Set-up

1 Overview of FACCH Call Set-upWhen a MS requests a dedicated resource by sending a random access, the BSC tries

to allocate an SDCCH for the MS. If there are no SDCCHs available at that moment, the

BSC tries to allocate a TCH instead of rejecting the resource request.

If there are free TCHs, FACCH Call Set-up is used to assign the MS from the CCCH to

the TCH - instead of the SDCCH - with the immediate assignment procedure. The

FACCH is used for call set-up signalling instead of the SDCCH. The TCH is used for sig-

nalling and thus no assignment procedure is needed in the radio interface. Instead, only

the mode modify procedure is required to change the channel mode from signalling to,

for example, speech or data.

Note that circuit pool change is not supported with FACCH call setup.

Related topics in FACCH Call Set-up

•Procedures of FACCH Call Set-up

• User interface of FACCH Call Set-up

Other related topics

• Functional Area Descriptions

• Operability

• Radio Network Configuration Management

• Reference

• Commands

• MML Commands

• EE - Base Station Controller Parameter Handling in BSC

• EQ - Base Transceiver Station Handling in BSC

• Parameters

• BSS Radio Network Parameter Dictionary

• PRFILE and FIFILE Parameter List

http://general_glossary.pdf/



http://dn9813999.pdf/















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BSC3015: FACCH Call Set-up Procedures of FACCH Call Set-up

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2 Procedures of FACCH Call Set-upThe procedures of FACCH Call Set-up are described in more detail in the following sec-

tions.

The causes presented in the procedures are BSSMAP causes. For more information on

the corresponding DX causes, see Call Related DX Causes in BSC.

2.1 Channel required procedure

The channel required procedure offers the MS the means to start the establishment of

a mobile originating call or to answer the PAGING REQUEST message.

The channel required procedure is presented in the following figure.

Figure 1 Channel required procedure

CHANNEL REQUEST message

The MS requests for a dedicated signalling channel SDCCH by sending the CHANNEL

REQUEST message (a) to the BTS on the RACH. The message is sent in random mode

and consists of two different information elements that are coded as follows:

Figure 2 CHANNEL REQUEST message, only one octet long

The establishment cause information field indicates the reason for requesting the estab-

lishment of a connection. This field has a variable length (from 3 bits up to 6 bits). The

random reference is an unformatted field with variable length (from 5 bits down to 2 bits).

The establishment cause information field length is 3 when the MS is GSM phase 1 level

or when the MS is GSM phase 2 level and the new establishment causes

support (NECI) parameter is set to OFF.

The following establishment causes are supported (the random reference field is

marked with x s):

MESSAGE

8 ... 1 Meaning of establishment cause

000xxxxx Location updating (SDCCH)

100xxxxx Answer to paging (SDCCH, TCH/H or TCH/F)

101xxxxx Emergency call

Table 1 NECI parameter is set to OFF

MS BTS BSC MSC

a)

CHANNEL REQUESTb)CHANNEL REQUIRED

Bit

Octet 1

8 7 6 5 4 3 2 1

ESTABLISHMENT

CAUSERANDOM

REFERENCE







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Procedures of FACCH Call Set-up

Note that HR data call is not supported in the BSC. FR is the preferred rate for data call

request and re-establishment call request. If a call request based on the establishmentcause can be either data or speech, counter 001124 TCH FACCH CALL CH RATE NOT

DEF is incremented and FR is set as the preferred rate.

The network uses the random reference and the MS access slot number to identify and

to address the MS.

The MS starts the GSM timer T3120 and waits for its access acceptance, which is the

IMMEDIATE ASSIGNMENT message on the AGCH.

If the MS is not granted access within the time limit defined by the GSM timer T3120,

the MS makes a second attempt and sends another CHANNEL REQUEST message with

a new random reference on the next time slot. A new value of the GSM timer T3120 is

computed and used. The MS repeats this procedure either until it is granted access or

until the number of repetitions reaches the maximum.

110xxxxx Call re-establishment (TCH/F)

111xxxxx Originating call (TCH/F)

0010xxxx Answer to paging, dual rate MS and TCH/F is

requested

0011xxxx Answer to paging, dual rate MS and TCH/H or

TCH/F is requested

MESSAGE


0000xxxx Location updating (SDCCH)

0001xxxx Other procedures which can be completed with an

SDCCH

100xxxxx Answer to paging (SDCCH, TCH/H or TCH/F)

101xxxxx Emergency call

110xxxxx Call re-establishment, TCH/F was in use (TCH/F)

111xxxxx Originating call and TCH/F is needed

0010xxxx Answer to paging, dual rate MS and TCH/F is

requested

0011xxxx Answer to paging, dual rate MS and TCH/H or TCH/F is requested.

0100xxxx Originating speech call from dual rate MS when

TCH/H is sufficient (TCH/H)

0101xxxx Originating data call from dual rate MS when

TCH/H is sufficient (TCH/H)

011011xx Call re-establishment, TCH/H was in use (TCH/H)

Table 2 NECI parameter is set to ON

MESSAGE


Table 1 NECI parameter is set to OFF (Cont.)





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CHANNEL REQUIRED message

After receiving the CHANNEL REQUIRED message (b) from the BTS, the BSC starts to

allocate a relevant channel.

The CHANNEL REQUIRED message includes the following data:

• message discriminator: common channel management

• message type: channel required

• channel number: uplink CCCH (RACH)

• request reference: establishment cause, random reference received in the channel

request and the frame number on which it was received

• access delay: delay of the access burst as measured by the BTS.

2.2 Channel reservation procedure

After receiving the CHANNEL REQUIRED message, the BSC begins to search for an

SDCCH. If there are no SDCCHs available, the BSC starts to search for a TCH. If there

is a TCH available in the cell from which the original access was granted, the BSC

reserves it and the immediate assignment procedure starts.

If all the SDCCHs and TCHs are reserved in the cell in question, the BSC sends an

IMMEDIATE ASSIGNMENT REJECT message to the MS.

The BSC can allocate TCHs or SDCCHs as follows:

• TCH/F or TCH/H due to the CHANNEL REQUIREDmessage, if there are no SDCCHs

available and FACCH Call Set-up is allowed

• SDCCH due to the CHANNEL REQUIRED message, if there are SDCCHs available

and FACCH Call Set-up is allowed

• SDCCH due to the CHANNEL REQUIRED message, if FACCH Call Set-up is not

allowed.

The number of TCHs and SDCCHs depends on the radio configuration.

2.3 Channel activation procedure

After a new TCH has been successfully reserved, the BSC activates the channel by

sending the CHANNEL ACTIVATIONmessage to the BTS. The GSM timer T9103 super-

vises the channel activation procedure. The channel mode for the TCH channel is sig-

nalling.

The channel activation procedure is presented in the following figure.

Figure 3 Channel activation procedure

MS BTS BSC MSC

a)CHANNEL ACTIVATION

b)CHANNEL ACTIVATION ACK



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CHANNEL ACTIVATION message

The BSC sends the CHANNEL ACTIVATIONmessage (a) to the BTS in order to activate

the new TCH channel.

The CHANNEL ACTIVATION message includes the following data:

• message discriminator: dedicated channel management

• message type: channel activation

• channel number

• activation type

• channel mode: DTX control and channel type (signalling, TCH/F or TCH/H, no

resources required)

• BS power: maximum BS power level authorised in the cell (optional)

• MS power: maximum MS power level authorised in the cell (optional)

• timing advance to be used by the MS in subsequent communications (optional)

• SACCH information (optional)• ACCH control information (optional).

The SACCH information is used in a dual band cell or when IMSI Based Handover is

enabled in the BSC. For more information, see Dual Band Network Operation or IMSI-

Based Handover .

ACCH control information indicates whether the MS is capable of ACCH repetition if

Robust AMR Signalling is activated. For more information, see Robust AMR Signalling.

The other optional elements are always present.

CHANNEL ACTIVATION ACKNOWLEDGE message

The BTS acknowledges a successful activation with the CHANNEL ACTIVATION

ACKNOWLEDGE message (b). The BTS starts the transmission and reception on the

associated SACCH, using the power levels and the timing advance received in the

CHANNEL ACTIVATION message.

Correspondingly, the BTS acknowledges a failure with the CHANNEL ACTIVATION

NACKmessage. The possible causes for a failure are listed below. For more information,

see 3GPP TS 48.058.

• radio resource not available

• radio channel already activated or allocated

• protocol error and subclause, such as mandatory information error

• O&M intervention when the channel cannot be used for O&M reasons

• encryption algorithm not implemented• equipment failure

• service or option not available

• not implemented unspecified

• mandatory IE error

• general IE error.

If the BSC does not receive the CHANNEL ACTIVATION ACKNOWLEDGE or CHANNEL

ACTIVATION NACK message within the time limit of the GSM timer T9103, or if it

receives the CHANNEL ACTIVATION NACK message, it releases the allocated channel

and sends an IMMEDIATE ASSIGNMENT REJECT message to the MS.













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2.4 Immediate assignment procedure

The IMMEDIATE ASSIGNMENT message facilitates the assignment of the MS onto a

TCH. Correspondingly, the IMMEDIATE ASSIGNMENT REJECTmessage facilitates the

refusal of the access: if the TCH reservation or activation fails, the BSC sends theIMMEDIATE ASSIGNMENT REJECT message to the MS. The GSM timer T3101 super-

vises the immediate assignment procedure.

The figure below shows the immediate assignment procedure.

Figure 4 Immediate assignment procedure

IMMEDIATE ASSIGN COMMAND message

After a successful TCH activation, the BSC sends the IMMEDIATE ASSIGN COMMAND

message (a) to the BTS. This message contains the IMMEDIATE ASSIGNMENT

message, which the BTS sends to the MS.

TheIMMEDIATE ASSIGN COMMAND

message includes the following data:• message header

• message type

• channel number

• immediate assignment information.

The immediate assignment information contains the complete IMMEDIATE

ASSIGNMENT message:

• message header

• page mode: normal paging

• channel description of the TCH allocated, the associated SACCH and frequency or

hopping sequence• 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 phase 2.

IMMEDIATE ASSIGNMENT message, SABM, UA frame

After receiving the IMMEDIATE ASSIGNMENT message, the MS tunes to the assigned

TCH and starts to establish the signalling link across the network. The MS sends the

layer 2 SABM (Set Asynchronous Balanced Mode) to the BTS on the TCH. The SABM

(c) contains a layer 3 service request message. The MS specifies to the network the

required service type with the service request message.

MS BTS BSC MSC

a)IMMEDIATE ASSIGN COMMAND

b)IMMEDIATE ASSIGN

SABM c) d)ESTABLISH INDICATION

e)UA



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The service request message contains one of the following:

1. CM SERVICE REQUEST - for mobile originating calls and for a mobile originating

SMS (Short Message Service) - contains:

• header • CM service types

• ciphering key sequence number

• MS classmark 2

• mobile identity.

2. PAGING RESPONSE contains:

• header

• ciphering key sequence number

• MS classmark 2

• mobile identity.

3. CM RE-ESTABLISHMENT REQUEST

4. Emergency setup.

The BTS acknowledges the SABM by sending the UA frame (e) to the MS. The MS

expects this acknowledgement within time T; otherwise it acts as described in 3GPP TS

44.018.

ESTABLISH INDICATION message

The BTS forwards the MS service request to the BSC in the ESTABLISH INDICATION

message (d), which includes the following data:

• message discriminator: radio link layer management

• message type: establishment indication

• channel number: TCH + SACCH• link identifier: main signalling channel TCH

• L3 Information - complete L3 service request as received from the MS.

Having received the ESTABLISH INDICATION message, the BSC starts the power

control and handover algorithm.

2.5 Mode modify procedure

The mode modify procedure changes the channel mode from signalling to speech or

data. The procedure is presented in the figure below.





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Figure 5 Mode modify procedure

ASSIGNMENT REQUESTmessage

The MSC sends an ASSIGNMENT REQUESTmessage (a) to the BSC for the assignment

of channels on the A interface and the radio interface.

The BSC expects to receive the following fields in the ASSIGNMENT REQUEST

message:

• message type

• channel type: speech, TCH/F or TCH/H, speech algorithm

• L3 header information

• priority (optional)

• circuit identity code indicating the channel to be used on the A interface

• downlink DTX flag (optional)

• radio channel identity (optional)

• interference band to be used (optional).

The BSS responds to the ASSIGNMENT REQUEST message by sending the MSC the

ASSIGNMENT COMPLETE or ASSIGNMENT FAILURE message. On receiving an

ASSIGNMENT FAILURE message, the MSC can either issue a CLEAR COMMAND or

retry.

The MSC runs a supervisory timer for the assignment procedure: if the MSC fails to

receive a response from the BSS within the defined time limit, it clears the call with a

CLEAR COMMAND message. The BSS releases the MS connection with the channel

release procedure.

If the BSC identifies any of the following situations on analysing the ASSIGNMENT

REQUEST message, it rejects the request by sending the ASSIGNMENT FAILURE

message to the MSC, without taking any action towards the BTS:

MS BTS BSC MSC

a)

DT1(ASSIGNMENT REQUEST)

b)MODE MODIFY

c)MODE MODIFY ACKNOWLEDGE

d)DATA REQUEST(CHANNEL MODE MODIFY)

e)CHANNEL MODE MODIFY

f)

CHANNEL MODE MODIFY ACK

g)DATA INDICATION(CHANNEL MODE MODIFY ACK)

h)DT1(ASSIGNMENT COMPLETE)



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1. If the BSC is not able to use the A channel indicated in the CIC (Circuit

Identification Code) because it is used for another call, the BSC rejects

the request with the cause requested terrestrial circuit already allo-

cated.

2. If the BSC is not able to use the A channel indicated in the CIC because

the channel has been marked as faulty, the BSC rejects the request with

the cause requested terrestrial resource unavailable.

3. If the CIC is blocked, the BSC rejects the request with the cause

requested terrestrial resource unavailable. The BSC also sends a

BLOCK message to the MSC. For more information on reasons which

can cause a circuit to be blocked by the BSC, see 3GPP TS 48.008.

4. If there is no circuit pool on the A interface which is able to support the

requested TCH type, the BSC rejects the request with the cause

requested transcoding/rate adaption not available.

5. If there is a circuit pool on the A interface which is able to support the

requested TCH type but the pool implied by the CIC is totally contradic-

tory with the TCH type requirement, the BSC rejects the request with the

cause circuit pool mismatch.

6. If the circuit pool implied by the CIC is at least partially compliant with

the requested TCH type, changing the circuit pool may be required.

Reasons for the change include the actual traffic channel resource sit-

uation of the cell and the attempt to allocate the resources in the most

optimal way. In this case the BSC rejects the request with the cause

switch circuit pool.

7. If the requested speech coder versions are not supported, the BSC

rejects the request with the cause requested speech version unavail-

able.

8 If the radio interface data rate requirement is totally contradictory with

the requested TCH rate, the BSC rejects the request with the cause

invalid message contents.

If the MSC receives an ASSIGNMENT FAILURE message with a cause indicating a CIC

problem, the MSC may choose to send another ASSIGNMENT REQUEST for the same

call using a different circuit.

MODE MODIFYmessage

If the ASSIGNMENT REQUEST message is valid, the BSC proceeds to perform the mode

modify procedure.

The BSC first sends the MODE MODIFY message (b) to the BTS to change the channel

mode from signalling to speech or data. At this point the BSC connects the Abis channel

to the A channel and the speech path is switched through.

Synchronization with the transcoder starts as described in 3GPP TS 44.018.

The MODE MODIFY message includes the following data:

• message discriminator: dedicated channel management

• message type: mode modify

• channel number

• channel mode: DTX control and channel type (speech, TCH/F or TCH/H, speechalgorithm)





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When the BSC receives the MODE MODIFY ACKNOWLEDGE message (c) as a response

from the BTS, it starts to change the MS channel mode. If the BSC fails to receive the

MODE MODIFY ACKNOWLEDGE message within the defined time limit, 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 message or retries.

If the BSC receives the MODE MODIFY NEGATIVE ACKNOWLEDGE message from the

BTS, the BSC sends an ASSIGNMENT FAILURE message to the MSC either with the

cause equipment failure or requested transcoding or rate adaption unavailable. The

cause value is mapped from the cause value received in the MODE MODIFY NEGATIVE

ACKNOWLEDGE message. The MSC either aborts with a CLEAR COMMAND message or

retries.

CHANNEL MODE MODIFY message

After receiving the MODE MODIFY ACKNOWLEDGE message from the BTS, the BSC

sends the CHANNEL MODE MODIFY message to the MS and starts a timer. The

CHANNEL MODE MODIFY message (e) is transparent to the BTS and is transferred as

the DATA REQUEST message (d) over the Abis interface.

The CHANNEL MODE MODIFY message includes all the information necessary for the

MS to change the channel mode from signalling to speech or data. The message

consists of the following:

• header

• channel description

• channel mode: speech full rate, speech half rate or data full rate.

On receiving the CHANNEL MODE MODIFY message over the radio interface, the MS

changes the channel mode and acknowledges this by sending the CHANNEL MODE

MODIFY ACKNOWLEDGE message (f) to the BSC. This message is transparent to the

BTS and is transferred over the Abis as a DATA INDICATION message (g).

The BSC checks the channel mode element of the CHANNEL MODE MODIFY

ACKNOWLEDGE message. The procedure has failed if the old channel mode is returned

instead of the one that was ordered. If the ordered channel mode is returned, the BSC

sends the ASSIGNMENT COMPLETE message (h) to inform the MSC of the successful

completion of the mode modify procedure. See 3GPP TS 44.018 for more details.

If the timer used to supervise the receival of the CHANNEL MODE MODIFY

ACKNOWLEDGE message expires, the BSC returns an ASSIGNMENT FAILUREmessage

to the MSC with the cause radio interface message failure. The MSC either aborts or

retries.



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User interface of FACCH Call Set-up

3 User interface of FACCH Call Set-upYou can set the FACCH Call Set-up for each BSC via the man-machine interface (MMI).

Similarly with the MMI, you can set the New Establishment Causes Support (NECI) fieldon or off for an individual cell. The field allows the MSS to use the new establishment

cause values: when an MS requests for a channel, the request can include more

accurate information about the establishment cause and channel type needed for the

requested service.

The following calls and channel types are possible:

• emergency call (SDCCH or TCH/F)

• call re-establishment (SDCCH, TCH/F or TCH/H)

• answer to paging (SDCCH, TCH/F or TCH/H)

• answer to paging (SDCCH, dual rate)

• mobile originating speech/data call (SDCCH, TCH/F or TCH/H)

• location updating (SDCCH)

• other procedures on SDCCH.

The following channel request values can be set in FACCH call set-up:

• emergency call

• answer to paging

• ordinary call

• re-establishment.

The channel request values in the NECI field also include an indication of the suggested

rate, such as the half rate support for the call. The BSC will allocate a suitable resource

for a transaction according to the SDCCH or the TCH. For more details, see Half Rate

in BSC.

Parameters

The parameters used in connection with FACCH Call Set-up are described below:

• FACCH_CALL_SET_UP : with this parameter you can activate or deactivate FACCH

Call Set-up. The parameter can be input from the Parameter Handling MML or

NetAct.

For more details, see PRFILE and FIFILE Parameter List.

• new establishment causes support (NECI): with this parameter you can

set the value of the NECI field. This parameter can be operated via the Base Trans-

ceiver Station Handling MML.

For more details, see Radio Network Configuration Management and BSS Radio

Network Parameter Dictionary.

• enable emergency call on FACCH: with this parameter you can activate or

deactivate an emergency call to use FACCH Call Set-up. This parameter can be

found in the radio network database and it can be operated via the Base Station

Controller Parameter Handling MML or NetAct.

• enable call re-establishment on FACCH: with this parameter you can

activate or deactivate call re-establishment to use FACCH Call Set-up. This param-

eter can be found in the radio network database and it can be operated via the Base

Station Controller Parameter Handling MML or NetAct.

• enable ordinary calls on FACCH: with this parameter you can activate or

deactivate a mobile originating call to use FACCH Call Set-up. This parameter can















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be found in the radio network database and it can be operated via the Base Station

Controller Parameter Handling MML or NetAct.

• enable answer to paging call on FACCH: with this parameter you can

activate or deactivate the mobile terminated call to use FACCH Call Set-up. This

parameter can be found in the radio network database and it can be operated via

the Base Station Controller Parameter Handling MML or NetAct.

For more details on parameters enable emergency call on FACCH, enable

call re-establishment on FACCH, enable ordinary calls on FACCH and

enable answer to paging call on FACCH, see BSS Radio Network Parameter

Dictionary and Base Station Controller Handling in MSC in MSC/HLR Product Docu-

mentation.





Facch Setup

Documents

Transcript of Facch Setup