2 Functional division between Base Station System (BSS) and MSC

08.023GPPBase Station System - Mobile Services Switching Centre (BSS-MSC) Interface - Interface PrinciplesRelease 1999TS

Table 2.1: Functional split

Item/Task

BSS

MSC,VLR,HLR

Terrestrial Channel Management

channel allocation

X

X

blocking indication

X

X

Radio channel management

Radio channel configuration

management

X

frequency hopping management

X

idle channel observation

X

power control

X

TCH management

channel allocation (choice)

X

link supervision

X

channel release

X

X (Invoked by MSC)

BCCH/CCCH management

scheduling of messages

X

DCCH management

link supervision

X

channel release

X

X (Invoked

DCCH allocation

X

by MSC

Radio resource indication

report status of idle channels

X

Channel coding decoding

MSC defines

on the basis of call type

X

call type

Transcoding/rate adaptation

X

Interworking Function (data calls)

X

Measurements

reported from MS

X

uplink

X

traffic

X

Handover

internal (within one cell){if provided}

X

MSC informed

internal (between cells) {if provided}

X

MSC informed

external recognition radio reason

X

external recognition traffic reason

X

X

decision

X

X

execution

X

Mobility Management

authentication

X

location updating

X

paging

X

DRX paging (scheduling)

X

Call control

X

User data encryption

X

Key and permitted

algorithms from MSC

Signalling element encryption

X

Key and permitted

algorithms from MSC

2.1 Terrestrial channel management

2.1.1 Terrestrial channel allocation

Terrestrial channel allocation will be handled in the following manner.

The link between the MSC and the BSS will be considered by the BSS and the MSC as a route on "n" circuits. Within this route, certain of the circuits may not be able to support all types of traffic (e.g., data calls or half rate connections). This can be managed, according to the configuration, either by the MSC or by the BSS for a given route. The entity in charge of circuit allocation chooses the terrestrial circuit, whilst ensuring that the chosen circuit is able to support the type of connection needed.

2.1.2 Blocking of terrestrial channels

The entity not allocating the circuits shall be able to remotely block the terrestrial channel and remove it from service. This is signalled across the BSS/MSC interface using the appropriate signalling exchange as defined in 3GPP TS 08.08.

Local blocking of terrestrial channels on the side allocating the circuits may be supported and will result in the concerned channels not being chosen, no information need flow across the interface in these cases.

2.2 Radio channel management

2.2.1 Channel configuration management

The channel configuration management will be controlled between BSS and maintenance centre, the MSC holding no direct data concerning the allocation of radio timeslots etc.

2.2.2 Radio TCH management

2.2.2.1 Radio channel allocation

The BSS shall choose the radio channel to be used on the appropriate cell, based on information received from the MSC, which defines the channel type, channel coding and all other parameters relevant to defining channel type. The chosen radio channel shall be connected to the terrestrial channel in order to support the call. This connection mechanism is not further defined in these Technical Specifications.

2.2.2.2 TCH radio link supervision

Radio link supervision of dedicated radio resources shall be the responsibility of the BSS. If communication with the mobile is lost then the BSS can request that the call be cleared.

2.2.2.3 Frequency hopping management

Frequency hopping management shall be performed by the BSS. That is the BSS shall store and transmit all hopping parameters for the cell(s) that it controls, the hopping shall be performed such that it is not visible on the BSS/MSC interface.

2.2.2.4 Idle channel observation

The quality of idle radio channels shall be measured by the BSS and a condensed form of the information passed back to the MSC.

2.2.2.5 TCH power control

All power control functions shall be performed between MS and BSS. No real time power control commands shall be sent across the BSS/MSC interface.

2.2.2.6 TCH channel release

The release of a dedicated resource is primarily controlled by the MSC. However for radio propagation reasons the BSS can request of the MSC that a call be released. The necessary protocols are defined in 3GPP TS 08.08.

2.2.3 BCCH CCCH management

All BCCH data shall be either stored at or derived locally by the BSS.

CCCH random accesses shall be controlled autonomously by the BSS, paging messages shall be received from the MSC via the BSS/MSC interface.

2.2.3.1 Scheduling of BCCH and CCCH messages

The scheduling for all BCCH and CCCH messages shall be performed by the BSS.

2.2.4 DCCH Management

2.2.4.1 DCCH link supervision

Radio link supervision of dedicated radio resources shall be the responsibility of the BSS. If communication with the mobile is lost then the BSS can request that the call be cleared.

2.2.4.2 DCCH channel release

The release of a dedicated resource is primarily controlled by the MSC. However for radio propagation reasons the BSS can request of the MSC that a call be released. The necessary protocols are defined in 3GPP TS 08.08.

2.2.4.3 DCCH power control

All power control functions shall be performed between MS and BSS. No real time power control commands shall be sent across the BSS/MSC interface.

2.2.4.4 Radio Channel Allocation

The BSS shall choose the DCCH to be used on the appropriate cell. This shall be performed initially after the random access to the CCCH has been made by the MS. The chosen DCCH may at a later stage in the call be connected to the terrestrial channel in order to support the service, this is controlled by the appropriate indications in an assignment message from the MSC.

2.3 Resource indication

The status of idle radio channels is reported to the MSC using the protocol described in 3GPP TS 08.08.

2.4 Channel coding decoding

The encoding decoding and interleaving shall be performed by the BSS. The type of channel coding and interleaving is derived from the information in the assignment message from the MSC.

2.5 Transcoding/rate adaptation

Rate adaptation or transcoding shall be performed by the BSS. The selection of the appropriate function shall be based on information received from the MSC.

2.6 Interworking function (data calls)

The interworking function required for data calls to other networks shall be performed on the MSC side of the MSC/BSS interface.

2.7 Measurement information

2.7.1 Measurement information reported from the MS

Measurement information reported from MSs with dedicated radio resources shall be processed by the BSS.

2.7.2 Uplink measurement information

The BSS shall process uplink information.

The results of the processing of the "Measurement information reported from the MS" and the "Uplink measurement information" may be transmitted to the MSC as described in 3GPP TS 08.08.

2.7.3 Traffic information

Traffic information concerning the traffic environment outside a BSS is not passed from MSC to BSS.

2.8 Handover

Handovers (both internal and external) can occur for one of several reasons e.g. radio propagation, traffic distribution, O and M activity, equipment failure.

2.8.1 Internal handover within one cell

Internal handover within one cell can be supported within a BSS. It is optional for an BSS to be able to perform autonomous internal handover.

The MSC will be informed when an autonomous internal handover has been completed (see 3GPP TS 08.08).

2.8.2 Internal handover between cells

Internal Handover between cells on the same BSS can be supported within an BSS. Multi cell BSSs would normally be expected to support internal inter cell handover, however it is optional that they do so.

The MSC will be informed when an autonomous internal handover has been completed (see 3GPP TS 08.08).

2.8.3 External handover

This type of handover includes inter MSC handover as discussed in 3GPP TS 03.09.

2.8.3.1 Recognition that a handover is required for a radio reason

The BSS shall be able to generate an indication that a handover is required to the MSC using the protocols defined in 3GPP TS 08.08.

No additional guidance is given in the 3GPP TS 08.0X series concerning the algorithm within the BSS that generates either an internal handover, or an indication to the MSC that an external handover is required.

2.8.3.2 Recognition that a handover is required for a traffic reason

The BSS shall be able to generate an indication to the MSC that a handover is required for traffic reason (e.g. directed retry) using the protocols defined in 3GPP TS 08.08.

Within a multi BSS area only the MSC has a perspective of the overall traffic loading. The MSC may therefore originate inter BSS traffic handovers due to traffic reasons.

2.8.3.3 Decision of Target Cell

The choice of the target cell in an external traffic handover shall be made by the MSC, based on information received from the BSS.

2.8.3.4 Execution

Having received an indication from an BSS that an external handover is required, the decision of when and whether an external handover should take place shall be made by the MSC.

2.9 Mobility management

All transactions concerning mobility management (as specified in 3GPP TS 04.08) shall take place transparently between the MS and MSC/VLR/HLR, using the protocols described in Technical Specifications 3GPP TS 08.08 and 3GPP TS 08.06. The only exception to this rule is that of paging which is scheduled by the BSS on the appropriate cell.

2.10 Call control

Call control will be the responsibility of the MSC/HLR/VLR.

2.11 Security features

Information on security aspects are found in 3GPP TS 03.20. The BSS/MSC interface supports all of the required interchange of encryption keys.

2.11.1 User data confidentiality

Encryption and decryption of user data (e.g. speech) takes place within the mobile station and within the BSS. In order to decrypt/encrypt user data the encryption device used for the call must be loaded with the relevant key and algorithm. The key and the permitted algorithms are supplied by the MSC.

2.11.2 User identity confidentiality

This feature is supported by using a TMSI rather than an IMSI, over the radio path. The translation between TMSI and IMSI is performed at the MSC and within the mobile. Both TMSI and IMSI are carried transparently by the BSS-MSC interface as far as possible.

2.11.3 Signalling information confidentiality

As for user data.

2.11.4 Authentication of users

Authentication is carried out at the mobile and at the MSC/VLR/HLR. The MSC to BSS interface is required to transport the necessary challenge and response messages.