D-Link DWS-3227P - xStack Switch - Stackable Manuel d'utilisateur Page 3

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Semaphore Technologies Pvt. Ltd. – (technolo[email protected]om)
Semaphore Technologies Pvt. Ltd. – (technolo[email protected]om)
A modular network switch with 3 network modules (a total of 24 Ethernet and 14
Fast Ethernet ports) and one power supply.
While switches may learn about topologies at many layers, and forward at one or
more layers, they do tend to have common features. Other than for computer-room
very high performance applications, modern commercial switches use primarily
Ethernet interfaces, which can have different input and output speeds of 10, 100,
1000 or 10000 megabits per second. Switch ports almost always default to full-
duplex operation, unless there is a requirement for interoperability with devices that
are strictly half duplex. Half-duplex means that the device can only send or receive
at any given time, whereas full-duplex can send and receive at the same time.
At any layer, a modern switch may implement power over Ethernet (PoE), which
avoids the need for attached devices, such as an IP telephone or wireless access
point, to have a separate power supply. Since switches can have redundant power
circuits connected to uninterruptible power supplies, the connected device can
continue operating even when regular office power fails.
Layer-1 hubs versus higher-layer switches
An Ethernet hub, or repeater, is a fairly unsophisticated broadcast device, and
rapidly becoming obsolete. Hubs do not manage any of the traffic that comes
through them. Any packet entering a port is broadcast out or "repeated" on every
other port, save the port of entry. Since every packet is repeated on every other
port, packet collisions result, which slows down the network.
Hubs have actually become hard to find, due to the widespread use of switches.
There are specialized applications where a hub can be useful, such as copying traffic
to multiple network sensors. There is no longer any significant price difference
between a hub and a low-end switch.
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