Switches

A network switch (or just switch) is a networking device that performs transparent bridging (connection of multiple network segments with forwarding based on MAC addresses) at up to the speed of the hardware. more...

Home
Cables, Connectors
Filers, Load Balancers
Home Networking, Cable & DSL
Hubs
KVM Switch Boxes, Cables
Mainframe, DEC, VAX, AS/400
Network Interface Cards,...
Networking, Telecom Tools
Other Networking Equipment
Print Servers, Wired
Racks, Mounts & Patch Panels
Router Components, Memory
Routers, Wired
Security, Firewall, VPN
Server Components, Memory
Servers
Software
Software, Operating Systems
Storage Equipment, NAS, SAN
Switch Components, Memory
Switches
3Com
Adtran
Alcatel
Cisco
D-Link Professional Switches
Dell
Extreme Networks
Foundry
HP, Compaq
Intel
Linksys Professional...
Lucent, Avaya Cajun
Marconi, Fore Systems
Netgear
Nortel, Bay Networks
Other Switches
Telephone Systems, Telecom
UPS, Power Protection, APC
Wholesale Lots
Wireless Networking, WiFi
Workstation Components,...
Workstations, Terminals

Common hardware includes switches, which can connect at 10,100, or 1000 megabits per second, at half or full duplex. Half duplex means that the device can only send or receive any given time, whereas full duplex can send and receive, at the same time. The use of specially designed expansion also makes it possible to have large numbers of connections utilizing different mediums of networking, including Ethernet, Fibre Channel, ATM, 802.11, to name frequently used technologies.

A switch can connect Ethernet, token ring, Fibre Channel or other types of packet switched network segments together to form a Internetwork.

If a network has only switches and no hubs then the collision domains are either reduced to a single link or, if both ends support full duplex, eliminated altogether. The principle of a fast hardware forwarding device with many ports can be extended to higher layers giving the multilayer switch.

A repeater is the simplest multi-port device in use. However, its technology has been considered outdated since a hub is a "dumb device", as it resends every datagram it receives to every port except the original incoming. With multiple computers, the speed quickly slows down, and collisions start occurring, making the connection even slower. However, with the advent of the network switch, this problem has been solved.

Forwarding methods

There are four forwarding methods a switch can use:

Store and forward - The switch buffers and, typically, performs a checksum on each frame before forwarding it on.; Cut through - The switch only reads up to the frame's hardware address before starting to forward it. There is no error checking with this method.; Fragment free - A method which attempts to retain the benefits of both "Store and Forward" and "Cut-through". Fragment Free checks the first 64 bytes of the frame, where addressing information is stored. This way the frame will always reach its intended destination. Error checking of the actual data in the packet is left for the end device in Layer 3 or Layer 4 (OSI), typically a router.; Adaptive switching - A method automatically switching between the other three modes.;

Note that "cut through" switches have to fall back to "store and forward" if the outgoing port is busy at the time the packet arrives.

Note that these forwarding methods are not controlled by the user and are configured only by the switch itself.

Types of switches

Form factor

Rack mounted; Non rack mounted;

Read more at Wikipedia.org