FACCH Call Set-up

2003330 Nokia BSC S10.5 ED, Vers. 2, Product Documentation

FACCH Call Set-up

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FACCH Call Set-up

The information in this documentation is subject to change without notice and describes only the product defined in the introduction of this documentation. This documentation is intended for the use of Nokia's customers only for the purposes of the agreement under which the documentation is submitted, and no part of it may be reproduced or transmitted in any form or means without the prior written permission of Nokia. The documentation has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia welcomes customer comments as part of the process of continuous development and improvement of the documentation. The information or statements given in this documentation concerning the suitability, capacity, or performance of the mentioned hardware or software products cannot be considered binding but shall be defined in the agreement made between Nokia and the customer. However, Nokia has made all reasonable efforts to ensure that the instructions contained in the documentation are adequate and free of material errors and omissions. Nokia will, if necessary, explain issues which may not be covered by the documentation. Nokia's liability for any errors in the documentation is limited to the documentary correction of errors. NOKIA WILL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THIS DOCUMENTATION OR FOR ANY DAMAGES, INCIDENTAL OR CONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use of this documentation or the information in it. This documentation and the product it describes are considered protected by copyright according to the applicable laws. NOKIA logo is a registered trademark of Nokia Corporation. Other product names mentioned in this documentation may be trademarks of their respective companies, and they are mentioned for identification purposes only. Copyright © Nokia Corporation 2003. All rights reserved.

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Contents

Contents Contents 3 List of tables 4 List of figures 5 Summary of changes 7 1 1.1

Introduction to FACCH Call Set-up feature 9 FACCH Call Set-up overview 9

2 2.1 2.2

Functional properties of FACCH Call Set-up 11 FACCH Call Set-up user interface 11 FACCH Call Set-up and mobile access 12

3 3.1

Channel required procedure of FACCH Call Set-up 15 Detailed description of channel required procedure of FACCH Call Setup 15

4

Channel reservation procedure of FACCH Call Set-up 19

5 5.1 5.2

Channel activation procedure of FACCH Call Set-up 21 CHANNEL_ACTIVATION message 21 CHANNEL_ACTIVATION_ACKNOWLEDGE message 22

6 6.1 6.2 6.3

Immediate assignment procedure of FACCH Call Set-up 25 IMMEDIATE_ASSIGN_COMMAND message 25 IMMEDIATE_ASSIGNMENT, SABM, UA messages 26 ESTABLISH_INDICATION message 27

7 7.1 7.2 7.3

Mode modify procedure of FACCH Call Set-up 29 ASSIGNMENT_REQUEST message 30 MODE_MODIFY in the BSS 32 CHANNEL_MODE_MODIFY in the BSS 33 Glossary 35

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List of tables

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List of figures

List of figures Figure 1.

CHANNEL REQUIRED procedure

Figure 2.

CHANNEL_REQUEST message, only one octet long

Figure 3.

CHANNEL ACTIVATION procedure

Figure 4.

IMMEDIATE ASSIGNMENT procedure

Figure 5.

MODE MODIFY procedure

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21 25

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Summary of changes

Summary of changes

Summary of changes

Changes between document issues are cumulative. Therefore, the latest document issue contains all changes made to previous issues. Changes made between issues 7 and 6

No major changes, only a note about AMR and FACCH Call Set-up added in chapter Introduction to FACCH Call Set-up feature . Changes made between issues 6 and 5

MODE_MODIFY in the BSS Multirate configuration added to MODE_MODIFY message.

CHANNEL_MODE_MODIFY in the BSS Multirate configuration added to CHANNEL_MODE_MODIFY message. The document has been revised throughout to comply with the latest documentation standards. Changes made between issues 5 and 4

No modifications in content; consistency of concepts and references checked and corrected. Changes made between issues 4 and 3

Purpose of this function class Removed information concerning phase 1 and phase 2 mobile stations.

References Added References Dual Band GSM/DCS Network Operation and Half Rate Telecom. Removed Reference ETR 09.09 Technical Report.

Detailed description Added Figure 2: CHANNEL_REQUEST message. Added Tables 1 and 2: NECI parameter is set to OFF/ON.

Channel reservation procedure

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Channel reservation principles changed.

Channel activation procedure Field changes in channel_activation message due to half rate and dual band.

Mode modify procedure New failure reasons and field changes due to half rate added in the procedure. Sections removed: FACCH call set-up and other features Failure

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Introduction to FACCH Call Set-up feature

1

Introduction to FACCH Call Set-up feature This feature is optional. In FACCH call set-up, the MS is assigned from the CCCH to the TCH - instead of the SDCCH - with the IMMEDIATE ASSIGNMENT procedure. The TCH is used for signalling and thus no assignment procedure is needed in the Radio interface. Instead, only the MODE MODIFY procedure to the TCH channel is required to change the channel mode from signalling to speech. When an MS requests a dedicated resource by sending a random access, the BSC tries to allocate a 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, the FACCH call set-up is used. This means that FACCH is used instead of SDCCH for call set-up signalling and at the assignment phase of the call the channel mode is modified from signalling to, for example, speech.

Note The BTS must support AMR, otherwise the AMR with FACCH Call Set-up does not work.

1.1

FACCH Call Set-up overview The whole topic summary of FACCH Call Set-up

Functional properties of FACCH Call Set-up Channel required procedure of FACCH Call Set-up Channel reservation procedure of FACCH Call Set-up Channel activation procedure of FACCH Call Set-up

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Immediate assignment procedure of FACCH Call Set-up Mode modify procedure of FACCH Call Set-up

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Functional properties of FACCH Call Set-up

2 2.1

Functional properties of FACCH Call Setup FACCH Call Set-up user interface The network operator can set the FACCH call set-up for each BSC, via the manmachine interface (MMI). Similarly, with the MMI the operator can set the NECI field for new establishment cause values on or off for an individual cell The parameters used are described below. FACCH CALL SET UP

The network operator can activate or deactivate the whole FACCH Call Set-up feature by using parameter FACCH call set up . This parameter can be operated via Parameter Handling MML. For more details, see Parameter Administration . It is also available in the NMS. NEW ESTABLISHMENT CAUSES SUPPORT

The network operator can set the value of NECI field by using parameter new establishment causes support . This parameter can be operated via Base Transceiver Station Handling MML. For more details, see Radio network administration . EMERGENCY CALL ON FACCH

The network operator can activate or deactivate the emergency call to use FACCH Call Set-up by using parameter emergency call on FACCH . This parameter can be found from radio network database and it can be operated via Base Station Controller Handling MML. For more details, see Base Station Controller Handling in MSC (ED). It is also available in the NMS.

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RE-ESTABLISHMENT ON FACCH

The network operator can activate or deactivate the re-establishment to use FACCH Call Set-up by using parameter re-establishment on FACCH . This parameter can be found from radio network database and it can be operated via Base Station Controller Handling MML. For more details, see Base Station Controller Handling in MSC (ED). It is also available in the NMS. ORDINARY CALLS ON FACCH

The network operator can activate or deactivate the mobile originating call to use FACCH Call Set-up by using parameter ordinary calls on FACCH . This parameter can be found from radio network database and it can be operated via Base Station Controller Handling MML. For more details, see Base Station Controller Handling in MSC (ED). It is also available in the NMS. ANSWER TO PAGING CALL ON FACCH

The network operator can activate or deactivate the mobile terminated call to use FACCH Call Set-up by using parameter answer to paging call on FACCH . This parameter can be found from radio network database and it can be operated via Base Station Controller Handling MML. For more details, see Base Station Controller Handling in MSC (ED). It is also available in the NMS.

2.2

FACCH Call Set-up and mobile access The NECI field allows the mobile stations to use the new establishment cause values. The field also shows the half rate support for the call. (see Half Rate in BSC ). When a mobile station requests a channel, the request can include more accurate information about the establishment cause and channel type needed for the service requested. The following calls and channel types are possible:

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emergency call (SDCCH or TCH/F)

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

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answer to paging (SDCCH, TCH/F or TCH/H indicated by MS)

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

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location updating (SDCCH)

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other procedures on SDCCH.

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Functional properties of FACCH Call Set-up

The channel request values also include the indication of the suggested rate. The BSC will allocate a suitable resource for a transaction according to the SDCCH or the TCH. The following channel request values can be set in the FACCH call set-up:

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emergency call

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answer to paging

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ordinary call

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re-establishment.

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Channel required procedure of FACCH Call Set-up

3

Channel required procedure of FACCH Call Set-up The CHANNEL REQUIRED procedure offers the mobile station the means to start the establishment of the mobile originating call or the answering to the PAGING REQUEST message. The MS requests a dedicated signalling channel SDCCH with the CHANNEL_REQUEST message. Figure 1 shows the CHANNEL REQUIRED procedure.

MS

BTS

BSC

MSC

a) CHANNEL REQUEST b) CHANNEL REQUIRED

Figure 1.

3.1

CHANNEL REQUIRED procedure

Detailed description of channel required procedure of FACCH Call Set-up The MS requests access by sending the CHANNEL_REQUEST message (a) to the BTS on the RACH. It is sent in random mode and consists of two different information elements coded as follows:

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Bit 8

7

6

5

4

3

2

1 Octect 1

ESTABLISHMENT

RANDOM

CAUSE

REFERENCE

Figure 2.

CHANNEL_REQUEST message, only one octet long

The ESTABLISHMENT CAUSE information field indicates the reason for requesting the establishment 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 NECI parameter is set to OFF. The following estbalishment causes are supported: (RANDOM REFERENCE field is filled with 'x'). .

.

NECI parameter is set to OFF: MESSAGE 8 .... 1 000xxxxx

Other procedures (SDCCH).

100xxxxx

Answer to paging. (SDCCH or TCH/F)

101xxxxx

Emergency call. (SDCCH or TCH/F)

110xxxxx

Call re-establishment. (SDCCH or TCH/F)

111xxxxx

Originating call. (SDCCH or TCH/F)

NECI parameter is set to ON: MESSAGE 8 .... 1 0000xxxx

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MEANING OF ESTABLISHMENT CAUSE

MEANING OF ESTABLISHMENT CAUSE Location updating (SDCCH needed).

0001xxxx

Other procedures which can be completed with an SDCCH.

100xxxxx

Answer to paging. (SDCCH or TCH/F)

101xxxxx

Emergency call. (SDCCH or TCH/F)

110xxxxx

Call re-establishment (SDCCH or TCH/F)

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Channel required procedure of FACCH Call Set-up

111xxxxx

Originating call (SDCCH or TCH/F)

0010xxxx

Answer to paging. Dual rate MS and TCH/F is requested. (TCH/F or SDCCH)

0011xxxx

Answer to paging. Dual rate MS and TCH/H or TCH/F is requested. (TCH/H, TCH/F or SDCCH)

0100xxxx

Originating speech call from dual rate MS when TCH/H is sufficient. (TCH/H, TCH/F or

SDCCH) 0101xxxx

Originating data call from dual rate MS when TCH/H is sufficient. (TCH/H, TCH/F or

SDCCH) 011010xx

Call re-establishment; TCH/H was in use and the network sets NECI bit to 1. (TCH/H, TCH /F or SDCCH)

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 access is not granted within the time limit defined by the T3120, the MS makes a second attempt, sending 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. CHANNEL_REQUIRED message

After receiving the CHANNEL_REQUIRED message (b), the BSC starts to allocate a relevant channel. The CHANNEL_REQUIRED message from the BTS includes the following data:

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message discriminator: common channel management

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message type: channel required

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channel number: uplink CCCH (RACH)

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request reference: establishment cause, random reference received in the channel request and the frame number on which it was received

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

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Channel reservation procedure of FACCH Call Set-up

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Channel reservation procedure of FACCH Call Set-up After receiving the CHANNEL_REQUIRED message, the BSC starts to search for a SDCCH channel. If there are no SDCCHs available the BSC starts to search for a TCH channel. If a TCH channel is available in the cell from which the original access was granted, the BSC reserves it and the IMMEDIATE ASSIGNMENT procedure starts. The BSC can allocate TCH or SDCCH channels as follows: .

TCH/F or TCH/H channel due to the CHANNEL_REQUIRED message, if there are no SDCCHs available and the FACCH set-up is allowed

.

SDCCH channel due to the CHANNEL_REQUIRED message, if there are SDCCHs available and the FACCH set-up is allowed

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SDCCH channel due to the CHANNEL_REQUIRED message, if the FACCH set-up is not allowed.

The number of TCH and SDCCH channels depends on the radio configuration. If all the SDCCH and TCH channels are reserved in the cell, the BSC sends an IMMEDIATE_ASSIGNMENT_REJECT message to the MS.

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Channel activation procedure of FACCH Call Set-up

5

Channel activation procedure of FACCH Call Set-up After a new TCH has been successfully reserved, the BSC activates the channel by sending the CHANNEL_ACTIVATION message to the BTS. The GSM timer T9103 supervises the channel activation procedure. The channel mode for the TCH channel is signalling . If the BTS refuses to activate the new channel, it sends the CHANNEL_ACTIVATION_NACK message that includes the reason for the failure to the BSC. Figure 3 shows the CHANNEL ACTIVATION procedure.

MS

BTS

BSC

MSC

a) CHANNEL ACTIVATION b) CHANNEL ACTIVATION ACK

Figure 3.

5.1

CHANNEL ACTIVATION procedure

CHANNEL_ACTIVATION message The BSC sends the CHANNEL_ACTIVATION message to the BTS in order to activate the new TCH channel. The CHANNEL_ACTIVATION message includes the following data:

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message discriminator: dedicated channel management

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message type: channel activation

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channel number

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activation type

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

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channel identification: channel description and mobile allocation

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encryption information

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BS power: maximum BS power level authorised in the cell

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MS power: maximum MS power level authorised in the cell

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timing advance to be used by the MS in subsequent communications

.

SACCH_INFORMATION .

When the Abis interface is on the GSM phase 2 level, channel identification is not used. Encryption information is present if needed. SACCH information is used in dual band cell (see Basic Call ). Other optional elements are always present.

5.2

CHANNEL_ACTIVATION_ACKNOWLEDGE message A successful activation is acknowledged by the BTS with the CHANNEL_ACTIVATION_ACK message. 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. The BTS acknowledges a failure with the CHANNEL_ACTIVATION_NACK message. The following failure cases are possible (see ETS 300 596 (GSM 08.58)):

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radio resource not available

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radio channel already activated or allocated

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protocol error and subclause, such as mandatory information error

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

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encryption algorithm not implemented

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equipment failure

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Channel activation procedure of FACCH Call Set-up

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service or option not available

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not implemented unspecified

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mandatory IE error

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general IE error.

If the BSC does not receive the CHANNEL_ACTIVATION_ACK or CHANNEL_ACTIVATION_NACK message within the time limit of the GSM timer T9103, or if it has received the CHANNEL_ACTIVATION_NACK message, it releases the allocated channel and sends an IMMEDIATE_ASSIGNMENT_REJECT message to the MS.

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Immediate assignment procedure of FACCH Call Set-up

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Immediate assignment procedure of FACCH Call Set-up The IMMEDIATE_ASSIGN message enables the MS to assign onto a TCH channel, whereas the IMMEDIATE_ASSIGN_REJECT message refuses to grant the MS access. The GSM timer T3101 supervises the immediate assignment procedure. If the TCH channel reservation or activation has failed, the BSC sends the IMMEDIATE_ASSIGN_REJECT message to the MS. Figure 4 shows the IMMEDIATE ASSIGNMENT procedure.

MS

BTS

BSC

MSC

a) IMMEDIATE ASSIGN COMMAND b) IMMEDIATE ASSIGN SABM c) d) ESTABLISH INDICATION e) UA

Figure 4.

6.1

IMMEDIATE ASSIGNMENT procedure

IMMEDIATE_ASSIGN_COMMAND message After a successful TCH channel activation, the BSC sends the IMMEDIATE_ASSIGN_COMMAND message (a) to the BTS. This message contains the IMMEDIATE_ASSIGN message, which the BTS sends to the MS. The IMMEDIATE_ASSIGN_COMMAND message includes the following data:

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message header

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message type

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channel number

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immediate assignment information.

IMMEDIATE ASSIGNMENT information contains the complete IMMEDIATE_ASSIGNMENT message:

6.2

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message header

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page mode: normal paging

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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

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initial timing advance

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mobile allocation if frequency hopping is used

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rest octet only for phase 2.

IMMEDIATE_ASSIGNMENT, SABM, UA messages 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 the service type required to the network through the service request message. The service request message is as follows: 1.

CM (Connection Management) Service Request - for mobile originating calls and for a mobile originating SMS (Short Message Service) - contains: . . . . .

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header CM service types ciphering key sequence number MS classmark 2 mobile identity.

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2.

Paging Response contains: . . . .

3.

header ciphering key sequence number MS classmark 2 mobile identity.

CM_Re-establishment

The BTS acknowledges the SABM by sending the UA (e) frame to the MS. The MS expects this acknowledgement within the time T; otherwise it acts as described in I-ETS 300 022-1 (GSM 04.08).

6.3

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

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message type: establishment indication

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channel number: TCH + SACCH

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link identifier: main signalling channel TCH

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

Having received the ESTABLISH_INDICATION message, the mobile measurement (power control and handover) algorithm starts.

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Mode modify procedure of FACCH Call Set-up

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Mode modify procedure of FACCH Call Set-up The MODE MODIFY procedure changes the channel mode from signalling to speech. The ASSIGNMENT_REQUEST message from the MSC starts the procedure. Figure 5 shows the MODE MODIFY procedure.

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)

Figure 5.

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MODE MODIFY procedure

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7.1

ASSIGNMENT_REQUEST message The ASSIGNMENT_REQUEST message (a) from the MSC involves the following actions: The MSC sends an ASSIGNMENT_REQUEST message to the BSC for the assignment of channels on the A interface and the Radio interface. Furthermore, it runs a supervisory timer. If the MSC fails to receive any response, that is, the ASSIGNMENT_COMPLETE or ASSIGNMENT_FAILURE message, from the BSS within the defined time, the MSC is expected to clear the call with a CLEAR_COMMAND message. The BSS releases the MS connection with the CHANNEL RELEASE procedure. 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

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

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downlink DTX flag

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radio channel identity

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interference band to be used .

If any of the situations listed below is identified without taking any action towards the BTS, the BSC will reject the request with the ASSIGNMENT_FAILURE message on analysing the ASSIGNMENT_REQUEST message. On receiving the ASSIGNMENT_FAILURE message, the MSC can either issue a CLEAR COMMAND or retry.

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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 message with the cause requested terrestrial circuit already allocated .

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 message with the cause request terrestrial resource unavailable .

3.

If the CIC is blocked, the BSC rejects the request with the ASSIGNMENT_FAILURE message (the cause requested terrestrial resource unavailable ) and sends a BLOCK message to the MSC. For reasons which cause a circuit to be blocked by the BSC, see ETS 300 590 (GSM 08.08).

4.

If there is no circuit pool on the A interface which is able to support the requested type of TCH, the BSC sends an ASSIGNMENT_FAILURE message with cause requested transcoding/rate adaption not available to the MSC.

5.

If there is a circuit pool on the A interface which is able to support the requested type of TCH but the pool implied by the CIC is totally contradictory with the TCH type requirement, the BSC sends an ASSIGNMENT_FAILURE message with the cause circuit pool mismatch to the MSC.

6.

If the circuit pool implied by the CIC is at least partially compliant with the requested TCH type the change of the circuit pool may be required. Reasons for the change are the actual traffic channel resource situation of the cell and the attempt to allocate the resources in the most optimized way. In this case the BSC can send the ASSIGNMENT_FAILURE message with the cause switch circuit pool .

7.

If requested speech coder versions are not supported, the BSC sends an ASSIGNMENT_FAILURE message with the cause requested speech version unavailable to the MSC.

8

If the radio interface data rate requirement is totally contradictory with the requested TCH channel rate, the BSC sends an ASSIGNMENT_FAILURE message with the cause invalid message contents to the MSC.

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.

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7.2

MODE_MODIFY in the BSS If the ASSIGNMENT_REQUEST 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. 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 ETS 300 597 (GSM 08.60). The MODE_MODIFY message includes the following data: .

message discriminator: dedicated channel management

.

message type: mode modify

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channel number

.

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

.

multirate configuration .

Multirate configuration element is present in calls using multirate speech codec (see Enhanced Speech Codecs ). On receiving the MODE_MODIFY_ACK message (c), the BSC starts to change the MS channel mode. If the BSC fails to receive the MODE_MODIFY_ACK message (c) within the defined time, 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_NACK message, the BSC returns 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 from the MODE_MODIFY_NACK message. The MSC either aborts with a CLEAR_COMMAND message or retries.

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7.3

CHANNEL_MODE_MODIFY in the BSS After receiving the MODE_MODIFY_ACK, the BSC sends the CHANNEL_MODE_MODIFY message (d,e) to the MS and starts a timer. This command is transparent to the BTS and is transferred as the DATA_REQUEST message over the Abis interface. The CHANNEL_MODE_MODIFY gives the MS all the information necessary to change the channel mode to speech. The message consists of the following: .

header

.

channel description

.

channel mode: speech full rate or speech half rate.

.

multirate configuration .

Multirate configuration element is present in calls using multirate speech codec (see Enhanced Speech Codecs ). On receiving the CHANNEL_MODE_MODIFY over the Radio interface, the MS changes the channel mode from signalling to speech and acknowledges it to the BSC by sending the CHANNEL_MODE_MODIFY_ACK message to it. 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 IE of the CHANNEL_MODE_MODIFY_ACK message. If - instead of the one that was ordered - the old mode is returned, the procedure has failed (see ETS 300 597 (GSM 08.60)). If the ordered mode is returned, the BSC sends the ASSIGNMENT_COMPLETE message (h) to inform the MSC of the successful channel MODE MODIFY procedure. If the timer for waiting for the CHANNEL_MODE_MODIFY_ACK message expires, the BSC returns an ASSIGNMENT_FAILURE message to the MSC with the cause radio interface message failure . The MSC either aborts or retries.

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Glossary

Glossary AGCH

Access Grant Channel

BCCH

The Broadcast Control Channel is a unidirectional channel from a network to an MS.

BSC

Base Station Controller

BSS

Base Station Subsystem

BTS

Base Transceiver Station

CCCH

The Common Control Channel covers the logical channels of the type RACH, PCH and AGCH.

FACCH

The Fast Associated Control Channel is always associated with a traffic channel.

GSM phase

There are two possibilities for the GSM phase: GSM phase 1 and GSM phase 2. On the GSM phase 1 level, the network element is compliant with the protocols defined by the GSM phase 1 specifications. Respectively, on the GSM phase 2 level, the network element is compliant with the protocols defined by the GSM phase 2 specifications.

IMSI

International Mobile Subscriber Identity

MMI

Man-Machine Interface

MS

Mobile Station

MSC

Mobile Services Switching Centre

NECI

New establishment causes support.

NMS

Network Management System

NSS

Network Switching Subsystem

Ordinary call

Refers to both MS originated and terminated calls.

Phase 1 MS

An MS that complies with the protocols defined in Phase 1 GSM specifications.

Phase 2 MS

An MS that complies with the protocols defined in Phase 2 GSM specifications.

PLMN

Public Land Mobile Network

PSTN

Public Switched Telephone Network

RACH

Random Access Channel

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SACCH

The Slow Associated Control Channel is always associated with a traffic channel or an SDCCH.

SDCCH

Stand alone Dedicated Control Channel

TCH

Traffic Channel

TMSI

The Temporary Mobile Subscriber Identity field is included in the cell selection parameter IE. The information in this field is broadcast in the frames of System Information 3 and 4 to the mobile stations.

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