Element Managers or Agents are deployed with the Network Elements or are embedded with the Network Elements. Network Manager requests the information about the Network Elements from their respective Agents and these Agents interact with Network Elements and respond to Network Manager’s requests with requested information. Agents also monitor different parameters of Network Element and generate the Messages known as TRAPS or INFORMS for the Network Manager in case of some error, warning or to notify some event. The following diagram gives the overview architecture of the OAM&P solution.
Network Manager is responsible for the management of Network Elements by interacting with their respective Element Managers or Agents. Network Manager can manage multiple Agents in the network through SNMP protocol. The information or parameters of a Network Element that will be managed are defined in the form of MIB Variables using ASN notation.
Network Manager Components
The main components of Network Manager are:
- SNMP Manager
- MIB Module
- Database Module
- Data Model / Presentation Interface
- IRP Management
- Trap Service
The following diagram shows the logical placement of above mentioned components in the Network Manager:
Figure 3 – Network Manager Components
SNMP Manager handles all the SNMP protocol specific operations, and directly communicates with the Agents hiding the SNMP protocol level details from the upper layers. All the management requests made by Network Manager to the Agents are translated into SNMP PDUs at this layer are the responses from the Agents are translated to simple and understandable management information for the upper layers.
MIB Module holds the MIB related data for the Network Manager. It loads the management information from the MIB files and arranges them in high performance data structures for fast retrieval.
The Database Module provides the functionality for database interaction. Network Manager stores the management information in the database using the interfaces provided by Database Module.
Data Model / Presentation Interface
The Data Model / Presentation Interface is the layer that implements the Network Manager application logic. It holds the caches of the variable values fetched from the Agents and format the management information for presentation layer. This layer also implements the logic to communicate with the Agents.
IRP Management is a logical layer that logically separates the management information in Network Manager. There are three IRPs supported by OAM&P solution,
- Configuration Management
- Performance Management
- Fault Management
Trap Service is the component of Network Manager that listens for the TRAP or INFORM messages from the Agents. It is responsible for handling these messages and generating the response messages if necessary.
The Agent or Element Manager is implemented as Sub-Agent that connects with the Master Agent through AgentX protocol to provide the complete functionality. The Master Agent handles the entire SNMP related task and the management of Network Element is delegated to the Sub-Agent. The Sub-Agent communicates with the Network Element trough AMPS events.
Following are the main architectural components and their responsibility in Sub-Agent:
Implements the Callback functions against MIB OIDs that are called when Agent receives a request for that OID.
Monitor different parameters of Network Element when requested by Network Manager or configured otherwise. These parameters are analyzed by Network Manager and then performance reports are generated. All the SNMP GET requests are processed by this component.
It enforces the requested settings on the Network Element. All the SNMP SET requests are handled by Policy Enforcement component of Agent. So this component logically groups the Configuration Management functionality in Agent.
It generates Traps and Notifications for the Manager when some fault or reportable event occurs in Network Element. Trap Generation component groups the Fault Management related functionality of the Agent.
Interacts with the Network Element through AMPS events on behalf of other components of Agent i.e. Element Monitoring, Policy Enforcement, Trap Generation
Figure 5 – Agent Architecture and Components
The communication between Agent and Network Manager is done through the SNMP protocol. The SNMP session can be initiated by either Network Manager or the Agent. The Network Manager communicates with Agent using version 3 of SNMP, but for incoming messages (TRAPS or INFORMS) it also accept SNMP version 1 and SNMP version 2c along with SNMP version 3.
SNMP Request is generated by Network Manager and responded by the SNMP capable Agent. There are three different types of SNMP request that are generated by Network Manager i.e. GET, GETNEXT, SET. The agent generates GET-Response against all these requests; following is the sequence diagram of SNMP Request.
SNMP Trap or SNMP Inform is the message sent by the Agent to the Network Manager. These messages are generated asynchronously by the Agent triggered by different events that are defined in MIB files. These messages are used to notify some event to the Network Manager. Network doesn’t send any response against the SNMP Trap, but an acknowledgement is generated by Network Manager when it receives SNMP Inform.
Following is the sequence diagram of SNMP Traps or SNMP Informs.