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

(c) Intelligent hubs

In addition to having all the features of passive and active hubs, an intelligent hub also provides some features to help in managing data communication within the network. An intelligent hub can decide which data packet goes in which output line, which helps in controlling and minimizing data traffic in the network. An intelligent hub recognizes the slower devices automatically and helps them to transmit the data at their own speed. This feature also improves the performance of the network manifolds. An intelligent hub also adapts to changes in the network very easily and it also supports different technologies without the need to change anything in the configuration. As an active hub helps in finding out where problems are, but an intelligent hub locates the problem in the network, diagnoses it and tries to rectify it without letting the problem hamper the performance of the network. Intelligent hubs provide features that help in determining the exact cause and location of the fault, which saves a lot of time and energy.

(d) USB hubs

A universal serial bus (USB) hub is used in a network for connecting a set of computer peripheral apparatus to a host computer. All USB devices attach to the USB via a port on specialized USB devices known as hubs. A USB hub is an intelligent wiring connector coupled to a networking device to allow attachment of peripheral devices. USB hubs are also wiring concentrators that enable multiple attachment characteristics – converting a single attachment point into multiple attachment points. The USB hub is connected to the computer via a single upstream connector. The upstream port of a hub connects the hub to the host. The USB hub also includes a plurality of downstream ports for connecting the peripheral devices to the hub. Each of the other downstream ports of a hub allows connection to another hub or function. The USB hub uses a standardized connector at the downstream ports to provide universal connectivity between peripheral devices and the computer. USB hubs can detect attaching and detaching at each downstream port and enable the distribution of power to the downstream devices. Each downstream port can be individually enabled and configured as either full or low speed. The hub also isolates low-speed ports from full-speed signalling ports. The hub relays data from the computer to all enabled devices coupled to the data hub, and relays data from the enabled devices to the computer without any data storage or significant delay. A USB hub typically includes a hub controller, a hub repeater, and a transaction translator. The hub repeater provides a USB protocol-controlled switch between the upstream port and downstream ports as well as support for reset and suspend/resume signaling. The host controller facilitates communication to and from the host. The USB hub carries out its internal functions and distributes power supplied to other hubs and functions connected further down.
Protocol, port, and features are the most important specifications to consider for network hubs. Protocol is the fundamental mechanism for network communications; they specify the software attributes of data communications including the structure of a packet and the information contained in it. They may also prescribe all or some of the operational characteristics of the hardware on which they will run. UDP and TCP/IP are the most popular, but ATM, CANbus, ControlNet, DeviceNet, 10 Base-2 Ethernet, 10/100 Ethernet, 10Base-T Ethernet, Fast Ethernet, Gigabit, Ethernet, Fiber Channel, FDDI, Fieldbus, Frame Relay, Interbus, ISDN, Profibus, SONET, Token Ring, and xDSL are also available.
The number of ports and port type need to be specified. The number of ports determines the total number of ports available on the networking device. Port types can be IEEE 1394, ISDN, or USB. Common features for network hubs include stackability, rack mounting, and LED indicators. Network hubs that are stackable conserve space. Rack mount hubs are designed to be mounted into a rack. LED indicators are used to indicate the status of the hub.