5 Information Model
3GPP52.021Network Management (NM) procedures and messages on the A-bis interfaceRelease 17TS
5.1 Managed Objects
The BCF mentioned in 3GPP TS 48.052 and 3GPP TS 48.056 is the agent at the BTS end of the A-bis O&M interface. It has four different descriptions depending on the object that is managed: Site Manager, BTS, Radio Carrier and Baseband Transceiver.
This model describes how objects are managed across A-bis interface, but it doesn’t specify how information is transferred inside the site. That is, the manner of communication between an object and objects under it is not specified in the present document.
As shown in Figure 1, the Object Classes used on the A-bis interface are a subset of those found under Site Manager on the OMC-BSC interface. The Object Classes are listed below and the functionalities that describe them are found in table 2.
Site Manager: manages common control functions of several BTSs and transceivers on one site. These can include managing external alarms, front-end switch, etc. This model describes logical sites. There can be multiple logical sites in one physical site. Communication between entities within a logical site is manufacturer dependent.
BTS: is associated with one cell. BTSs are typically created at installation phase by connecting transceivers to antennas thus forming cells from the air interface point of view. The BTS can also contain control functions common to various transceivers. The way BTSs are formed from transceivers and how corresponding BTS numbers are determined is configuration dependent information, which is stored during installation.
Radio Carrier: represents manageable properties pertaining to radio transmission and reception of one carrier.
Baseband Transceiver: represents functions common to eight radio time slots.
Channel: is a physical channel in air interface, which can contain several logical channels depending on channel combination. A Channel is described with radio time slot and frequency hopping attributes (see 3GPP TS 45.002).
NOTE: Site Manager and BTS don’t necessarily require separate equipment. For example, the Site Manager and a Baseband Transceiver can be associated with the same physical equipment.
Figure 1/GSM 12.21: Object model seen across A-bis interface
Table 2/GSM 12.21: Objects, attributes and procedures seen across A-bis interface
|
Object class |
Attributes |
Procedures |
|---|---|---|
|
Site Manager |
Abis Channel Availability Status HW Configuration Manufacturer Dependent State Manufacturer Id Operational State Site Inputs Site Outputs SW Configuration |
Equipment Management Establish TEI Get Attributes Measurement Management Set Site Outputs State Management and Event Report SW Download Management Test Management |
|
BTS |
Administrative State Availability Status BCCH ARFCN BSIC BTS Air Timer CCCH Load Ind. Period CCCH Load Threshold Connection Failure Criterion GSM Time HW Configuration Intave Parameter Interterference Level Boundaries Manufacturer Dependent State Max Timing Advance Ny1 Operational State Overload Period RACH Busy Threshold RACH Load Averaging Slots SW Configuration T200 |
Equipment Management Get Attributes Measurement Management Report Procedures Set BTS Attributes State Management and Event Report SW Download Management Test Management |
|
Radio Carrier |
Administrative State ARFCN List Availability Status HW Configuration Manufacturer Dependent State Manufacturer Id Operational State Power Class RF Max Power Reduction SW Configuration |
Equipment Management Get Attributes Measurement Management Set RadioCarrier Attributes State Management and Event Report SW Download Management Test Management |
|
Baseband Transceiver |
Abis Channel* Administrative State Availability Status HW Configuration Manufacturer Dependent State Manufacturer Id Operational State SW Configuration |
Connect Terrestrial Signalling Disconnect Terrestrial Signalling Equipment Management Get Attributes Measurement Management State Management and Event Report SW Download Management Test Management |
|
Channel |
Abis Channel* Administrative State ARFCN List* Availability Status Channel Combination HW Configuration HSN* MAIO* Operational State SW Configuration TSC |
Connect Terrestrial Traffic Disconnect Terrestrial Traffic Equipment Management Get Attributes Measurement Management Set Channel Attributes State Management and Event Report SW Download Management Test Management |
NOTE: If more than one layer 2 link is defined to handle this information model, the actual implementation may affect on which layer 2 link attributes concerning frequency hopping and front-end switch are sent. Equipment used to implement frequency hopping can be common to several radio carriers or located inside one radio carrier. Front-end switch is handled by Site Manager, therefore all ‘Abis Channel’ attributes must be sent to it. Those attributes that need a link identifier in BSC data structures are marked with an asterisk (*).
5.2 Addressing of Objects
It is a GSM requirement that the BSC is capable of operating with BTSs from different manufacturers. So, it is necessary that the differences between BTSs, as seen by the BSC, are minimised as much as possible. This is achieved by addressing NM messages by the Managed Object Class and Managed Object Instance. There must be in the BSC an object model with a complete layer 2 link description for each object instance in the BTS (e.g., Baseband Transceiver 1, Baseband Transceiver 2, Baseband Transceiver 3,…). When a message has to be sent to an object instance this mapping is used to find the correct link.
The first connection shall be established from the BTS site by using a (semi‑) permanently programmed default TEI. Subsequent to the establishment of the default connection to the site, further initial connections to other objects shall be established using TEIs provided by procedures in subclause 6.3.1.
Possible additional TEIs to an object already having an initial TEI are assigned with a GSM 12.21 message found in subclause 6.3.1 through an already assigned signalling link.
Object instances also have a layer 3 address. The instance number is used to address the object instance. Regardless of whether the layer 2 address uniquely identifies the object instance or not, the layer 3 address must also be provided so that it can be used by management agent to determine which object instance is being addressed. This combination of layer 2 and layer 3 addressing accommodates BTS sites with either single or multiple physical links.
Specific equipment configuration information is manufacturer dependent. However, for interoperability, link configuration, default TEI assignment and instance numbering must be known by both manager and agent. This, as well as supported functions, is considered as Shared Management Knowledge.
5.3 State Management of Objects
State management in the present document is generally in line with ITU-T Recommendation X.731. How state values are applied is explained below.
ITU-T Recommendation X.731 states that "the management state of a managed object represents the instantaneous condition of availability and operability of the associated resources from the point of view of management".
In the present document there are two different factors (ITU-T Recommendation X.731 defines usage state in addition to these two) that are considered to affect the management state of a managed object. They are:
– administration: permission to use or prohibition against using the resource, imposed through the management services;
– operability: whether or not the resource is physically installed and working.
The present document defines the following three state management attributes to represent the management state of a managed object:
– administrative state;
– operational state;
– availability status (this elaborates the operational state).
5.3.1 Administrative State
Administrative states of the managed objects can be controlled only by the BSC. In fact, the control of resource usage comes from the MSC).
Setting the administrative state of a Channel to locked means that it has to discontinue all transmission and reception of information on Air interface and all telecommunication (traffic and signalling) information transmission on A-bis interface.
Setting the administrative state of a Radio Carrier to locked means that it has to discontinue all RF emission on Air interface for the frequencies it is responsible.
Setting the administrative state of a Baseband Transceiver to locked means that it has to discontinue all telecommunication tramissions and the Channels which are affected should indicate that they are Disabled or Degraded.
Setting the administrative state of a BTS to locked means it has to discontinue all RF emission on all Radio Carriers and all telecommunication transmissions on all Channels of all Baseband Transceivers, i.e., Radio Carriers, Channels and Baseband Transceivers are in Disabled, Dependency state.
The administrative state at the BTS site is also used to provide information e.g., for a local MMI user at a BTS site.
The locked state of a 12.21 managed object means that BSC has disconnected all the calls that go through the resource that is represented by the managed object. No new traffic is connected through this resource any more.
The shutting down state means that no new traffic is connected through this resource any more. The on‑going calls remain.
The unlocked state means that new traffic is allowed through the resource represented by the managed object.
5.3.2 Operational State and Availability Status
ITU-T Recommendation X.731 gives the following definitions for the values of the operational state attribute:
– disabled: the resource is totally inoperable and unable to provide service to the user(s);
– enabled: the resource is partially or fully operable and available for use.
In the present document the value Disabled represents the following conditions that the resources could have:
– hardware or software is not installed;
– power is turned off;
– failure has occurred;
– radio parameters has not yet been set by elementary procedures, therefore, the resource is off line.
The availability status elaborates the operational state attribute. In the present document the following values are used (availability status is a set value):
In test: the resource is undergoing a test procedure.
Failed: the resource has an internal fault that prevents it from operating. The operational state is disabled.
Power off: the resource requires power to be applied and is not powered on. The operational state is disabled.
Off line: the resource requires some manual and/or automatic operation(s) to be performed to make it available for the use.
Dependency: the resource cannot operate because some other resource on which it depends is unavailable. The operational state is disabled.
Degraded: the service available from the resource is degraded in some respect, such as in speed or operating capacity. The operational state is enabled.
Not installed: the hardware or the software associated with the managed object has not been installed at the site. Operational state is disabled.
Figure 2 illustrates the operational state and availability status behaviour of GSM 12.21 objects (i.e., Site Manager, BTS, Radio Carrier, and Baseband Transceiver) during initialization. The initial value of the administrative state is locked.
Figure 2/GSM 12.21: GSM 12.21 Objects’ Operational state
and availability status behaviour during initialization