The MIB module allows a management application to select a set of MIB object instances whose values need to be collected on a periodic basis. The term 'data' in the context of this MIB is used to generically refer to the values of the selected set of object instances. Once the required setup is done, the MIB implementation carries out the following periodic tasks: - collects the required object values into local file-like entities called VFiles (virtual files). - transfers the VFiles to specified locations. - carries out VFile management operations. Some of the key features of this MIB are: a) Allows grouping of MIB objects into groups called data groups. The constraint is that the MIB objects grouped into a data group, need to have the same semantic MIB index. So it is possible to group MIB objects belonging to different MIB tables into a single data group as long as the above constraint is met. For e.g. it is possible to group ifInOctets from ifTable, ifHCInOctets from ifXTable, dot3StatsExcessiveCollisions from dot3StatsTable into a single data group. b) Allows the application to specify a set of instances (of the MIB objects in a data group) whose values need to be collected. c) The required data can be collected for each such data group on a periodic basis into a virtual file (VFile). A VFile is an abstraction of a file. d) The format of the contents of the VFile, can be specified by the application. e) An application can also specify a collection period. A collection period is an interval of time during which data is collected into a VFile. After the collection period ends, the VFile is frozen, and a new VFile is created for storing data. The frozen VFile is then transferred to a specified destination. An application can choose to retain such frozen VFiles on the device for a certain period of time, called the retention period. Data Collection MIB vs Bulkfile MIB *********************************** The data collection MIB can pretty much do what the CISCO-BULK-FILE-MIB (Bulkfile MIB) can do. The 'manual' mode of the Data collection MIB is similar to the way in which the Bulkfile MIB operates. However the data collection MIB is mainly targetted for medium to high-end platforms which have sufficient local storage (volatile or permanent) to store VFiles. Locally storing VFiles, helps minimize loss of data during temporary network outages. If the local store is permament, then the collected data is also available across agent restarts. The data collection MIB has more powerful data selection features than the Bulkfile MIB. It allows grouping of MIB objects from different tables into data groups. It also incorporates a more flexible instance selection mechanism, where the application is not restricted to fetching an entire MIB table. Definitions: ************ Base objects: ************* MIB objects whose values an application needs to collect. Data group: *********** A group of base objects. Can be of 2 types: 'object' and 'table'. An 'object' type data group can consist of only one fully instantiated base object. A 'table' type data group can consist of more than one base objects, each a columnar object in a conceptual table. In addition a 'table' type data group can specify the instances of the base objects whose values need to be collected. In the context of this MIB, collecting data for a data group means fetching the values of the associated base object instances and storing them into VFiles. Virtual File (VFile): ********************* A VFile is a file like entity used to collect data. An agent might choose to implement a VFile as a simple in-memory buffer, or it might choose to use a file in it's filesystem. An application does not really need to know the location of a VFile - the MIB provides mechanisms to transfer the VFile to application specified locations. However if the implementation supports it, the application can specify the location of the VFiles. Current VFile: ************** The VFile into which data is currently being collected. Frozen VFile: ************* A VFile which is no longer used for collecting data. Only frozen VFiles can be transferred to specified destinations. Collection interval: ******************** A collection interval is associated with a VFile. It is the interval of time over which a VFile is used to collect data. This interval of time can be specified by the application. However there are conditions under which a collection interval can be shorter than the specified time. For e.g. a collection interval is prematurely terminated when the maximum size of a VFile is exceeded, or when there is an error condition. Polling period: *************** A polling period is associated with a data group. It determines the frequency at which the base objects of a data group should be fetched and stored into a VFile. Data collection operations: ************************** A generic term used to refer to operations that are carried out while collecting data. These include: - Periodically creating new VFiles for collecting data. - Transferring frozen VFiles either automatically or on demand. - Fetching base object values and storing them into current VFiles, either periodically or on demand. - Deleting frozen VFiles, either periodically or on demand.