An network hub or concentrator is a device for connecting multiple twisted pair
or fiber optic thernet devices together, making them act as a single network segment.
Hubs work at the physical layer (layer 1) of the OSI model, and the term layer 1 switch
is often used interchangeably with hub. The device is thus a form of multiport repeater.
Network hubs are also responsible for forwarding a jam signal to all ports if it detects a
collision.
Hubs also often come with a BNC and/or AUI connector to allow connection to legacy 10BASE2
or 10BASE5 network segments. The availability of low-priced network switches has largely
rendered hubs obsolete but they are still seen in older installations and more specialized
applications.
A network switch is a computer networking device that connects network segments.
Low-end network switches appear nearly identical to network hubs, but a switch contains more
"intelligence" (and comes with a correspondingly slightly higher price tag) than a network hub.
Network switches are capable of inspecting data packets as they are received, determining
the source and destination device of that packet, and forwarding it appropriately. By delivering
each message only to the connected device it was intended for, a network switch conserves network
bandwidth and offers generally better performance than a hub.
In the past, it was faster to use Layer 2 techniques to switch, when only MAC addresses could be
looked up in content addressable memory (CAM). With the advent of ternary CAM (TCAM), it was equally
fast to look up an IP address or a MAC address. TCAM is expensive, but very appropriate for
enterprise switches that use default routes plus a moderate number of other routes. For routers
that need a full Internet routing table, TCAM may not be cost-effective.
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