Network diagnosis refers to the process of identifying the cause of faults in the network. A cause

Diagnostics
Self-Diagnosis
Network diagnosis refers to the process of identifying the cause of faults in the network. A cause could be a hardware failure such as a broken baseband card in a base station or a bad parameter value, that is, transmission power, antenna tilt, or a control parameter such as a RRM parameter. A fault in the network can generate multiple alarms that make it hard to identify its cause. In this case the alarm correlation process may be required to access the root source. A fault may trigger no alarms but result in low performance, poor QoS, and failure of RRM procedures. Often the diagnosis of fault cause requires processing information comprising both alarms and performance indicators. The OMC gathers alarms, counters, and more evolved indicators from the network. A self-diagnosis function can be implemented as an entity within the OMC that can access and process information and perform statistical inference [25]

(a) Passive hubs

A passive hub simply receives data on input ports and broadcasts it on the output ports without even rectifying it. As the name suggests, passive hubs work simply as an interface between the networking topologies. They do not rectify or enhance the data or signals they pass on in the network, thus they do not enhance network performance. It is very hard to get any help from passive hubs while troubleshooting if there is any fault in the hardware or the network.

(b) Active hubs

An active hub participates in data communication within the enterprise or local area networks. Active hubs come with various features, such as the ability to receive the data or signal from the input port and store it before forwarding it, which allows the hub to monitor the data it is forwarding; some have a feature that helps in preferentially transmitting data of high priority; some can synchronize data communication by retransmitting the data packets that are not properly received at the receiving computer or by adjusting re-transmission of the data packets to compensate timing; some active hubs come with a feature that rectifies the data or signal before forwarding them. Active hubs also help in troubleshooting at a certain level by identifying bottlenecks within the network.