The technical overview presented in this section details functional areas of the FCAPS management model addressed by DOCSIS for managing the CM.
5.2.1 Architectural Overview
This section defines the functional areas of network management in terms of FCAPS (Fault, Configuration, Accounting, Performance and Security) as applied to the management of a CM within a DOCSIS network. The requirements in the previous section were grouped both according to the management functional area and the relevant DOCSIS layer (using the OSI reference model) where they apply. This section provides an overview of the functions supported by each area. Even though specific functions are described for each area, there are
interdependencies amongst all these functions to achieve the overall objective of efficient and proactive management of a CM in the DOCSIS network.
Fault management seeks to identify, isolate, correct and record system faults. Configuration management modifies system configuration variables and collects configuration information. Accounting management collects usage statistics for subscribers, sets usage quotas and bills users according to their use of the system. Performance
Figure 5–1 illustrates the CM management architecture from the MSO back office interface perspective. The CM and CMTS reside within the Network Layer where services are provided to end Subscribers and various metrics are collected about network and service performance, among other things. Various management servers reside in the Network Management Layer within the MSO back office to provision, monitor and administer the Network Elements within the Network Layer (CM in this case). These management servers include, but are not limited to:
• The SNMP Manager performs SNMP configuration and queries against a CM's SNMP Agent.
• The Configuration File Server has the responsibility of transferring configuration files, via TFTP or optionally HTTP to the CM upon reinitialization.
• The Firmware File Server has the responsibility of transferring firmware images, according to the Secure Software Download mechanism, to a CM.
• The Notification Receiver receives autonomous SNMP notifications and Syslog messages from a CM.
• The DHCP Server has the responsibility of assigning a CM its IPv4 and/or IPv6 address as well as other DHCP
parameters in order for the CM to obtain its configuration file and register on the network.
• The Time Server provides a CM with current Time of Day (ToD).
• The IPDR Collector Servers do not communicate directly with the CM. Rather, the CMTS collects various CM-
related statistics and communicates this information to the IPDR Collector servers.
• The TR-069 Server does not communicate directly with the CM. Rather, if the CM is an eDOCSIS device and
includes an eSAFE which supports the TR-069 protocol, the eDOCSIS device will communicate with the TR- 069 server.
Figure 5–1 - CM Management Architecture
Finally, the Business and Service Management Layer is where higher level MSO business processes are implemented via BSS/OSS systems. These BSS/OSS systems utilize the data and information from the Network Management Layer which interrogated data from the Network Layer.
5.2.1.1 Fault Management
The goals of fault management are to provide failure detection, diagnosis, and perform or indicate necessary fault correction. Fault identification relies on the ability to monitor and detect problems, such as error-detection events. Fault resolution relies on the ability to diagnose and correct problems, such as executing a sequence of diagnostic test scripts, and correcting equipment or configuration faults. DOCSIS supports Event Reporting using Local Log, syslog and SNMP notifications.
5.2.1.2 Configuration Management
Configuration management is concerned with adding, initializing, maintaining and updating network elements. In a DOCSIS environment, network elements include CMs and CMTSs.
Configuration management is primarily concerned with network control via modifying operating parameters on network elements such as the CM and CMTS. Configuration parameters could include both physical resources (for example, an Ethernet interface) and logical objects (for example, QoS parameters for a given service flow). While the network is in operation, configuration management is responsible for monitoring the configuration state and making changes in response to commands by a management system or some other network management function.
For example, a performance management function may detect that response time is degrading due to a high number of uncorrected frames, and may issue a configuration management change to modify the modulation type from 16- QAM to QPSK. A fault management function may detect and isolate a fault and may issue a configuration change to mitigate or correct that fault.
5.2.1.3 Accounting Management
Accounting management, in general, includes collection of usage data and permits billing the customer based on the subscriber's use of network resources. The CMTS is the network element that is responsible for providing the usage statistics to support billing. Billing is outside the scope of this specification.
5.2.1.4 Performance Management
Performance management functions include collecting statistics of parameters such as number of frames lost at the MAC layer and number of codeword errors at the PHY layer. These monitoring functions are used to determine the health of the network and whether the offered Quality of Service (QoS) to the subscriber is met. The quality of signal at the PHY layer is an indication of plant conditions.
The previous versions of DOCSIS OSSI specification defines SNMP polling as the collection mechanism for CM and CMTS statistics for performance management. SNMP polling of CMs is scalable and widely deployed with specialized engines that minimize the upstream bandwidth allocated to management during the polling intervals.
5.2.1.5 Security Management
Security management is concerned with both security of management information to protect the MSOs operations systems as well as managing the security information. The latter is used to authenticate and secure the traffic on the HFC. Security of the management interface is required to prevent end users from accessing and initiating
configuration changes that may provide them with services for which they are not entitled or could result in the degradation or denial of services for other subscribers.
5.2.2 Management Protocols
As noted earlier in this section, the DOCSIS OSSI specification uses the Simple Network Management Protocol (SNMP) versions 1, 2c and 3 to define the management information for a CM DOCSIS network element in support of the functional areas mentioned in the previous section. SNMP is primarily a polling based protocol where the management system retrieves data such as counter values and state information. There are events defined as a notification that are used to inform the management systems of fault conditions and security violations. The support for SNMP versions is continued in DOCSIS 3.1.
5.2.3 Information Models
The approach is based on an object oriented modeling approach well known in the industry for capturing
requirements and analyzing the data in a protocol independent representation. This approach defines requirements with use cases to describe the interactions between the operations support systems and the network element. The management information is represented in terms of objects along with their attributes and the interactions between these encapsulated objects (or also referred to as entities in some representations). The diagrams developed to
UML Class Diagrams and Use Case Diagrams are referred to as the DOCSIS 3.1 Information Models. With the introduction of several new, complex features in DOCSIS 3.0 and DOCSIS 3.1 and the operator needs for a more proactive and efficient approach to management information, information modeling methodologies offer the ability to reuse the same definitions when new protocols are introduced in the future.
The managed objects are then represented in a protocol specific form referred to as a management data model. The management data models when using SNMP are described using the Structure of Management Information Version 2 (SMIv2) [RFC 2578] and the design of these models is determined by the capabilities of the protocol.