What are the Hub, Switch Routerand Bridges?
HUB
Hub also called a repeater hub is the basic networkingcomponent used in traditional 10-Mbps Ethernet networks to connect networkcomputers to form a local area network (LAN).
SWITCH
A switch is a networking component used to connect workgrouphubs to form a larger network or to connect computers that have highbandwidth needs. The switches provide superior performance to hubs but aremore expensive.
When a signal enters a port of the switch, the switch looksat the destination address of the frame and internally establishes alogical connection with the port connected to the destination node. Otherports on the switch have no part in the connection. The result is thateach port on the switch corresponds to an individual collision domain, andnetwork congestion is avoided. Thus, if a 10-Mbps Ethernet switch has 10ports, each port effectively gets the entire bandwidth of 10 Mbps-to theframe, the switch's port appears to provide a dedicated connection to thedestination node. Ethernet switches are capable of establishing multipleinternal logical connections simultaneously, while routers generallyprocess packets on a first-come, first-served.
There are two main types of switches. Layer-2 switchesoperate at the data-link layer of the OSI model and are based on bridgingtechnologies. They establish logical connections between ports based onMAC addresses. Use layer-2 switches for segmenting your existing networkinto smaller collision domains to improve performance. Layer-3 switchesoperate at the layer 3 of the OSI model and are based on routingtechnologies. They establish logical connections between ports based onnetwork addresses. Use these for connecting different networks into aninternetwork. Layer-3 switches are sometimes called routing switches ormultilayer switches.
The actual mechanism by which switching occurs dividesEthernet switches into two general device classes. Store-and-forwardswitches buffer whole incoming frames, perform error checking, and switchthe packet to the correct port according to the internal address table ofthe switch. This is similar to how bridges work, but this mechanismsuffers from high latency (delay) as the frame is processed. Cut-throughswitches read only the source and destination addresses of an incomingpacket, check the address table, and switch the packet to the correctport. Error checking is not performed. This kind of switching hasextremely low latency but can cause problems by forwarding jabbersthroughout the network.
ROUTER
Router is a networking device that is used to extend orsegment networks by forwarding packets from one logical network toanother. Routers are most often used in large internetworks that use theTCP/IP protocol suite and for connecting TCP/IP hosts and local areanetworks (LANs) to the Internet using dedicated leased lines.
Routers work at the network layer (layer 3) of the OpenSystems Interconnection (OSI) reference model for networking to movepackets between networks using their logical addresses. Routers containinternal tables of information called routing tables that keep track ofall known network addresses and possible paths throughout theinternetwork, along with the cost of reaching each network. Routers routepackets based on the available paths and their costs, thus takingadvantage of redundant paths that can exist in a mesh topologynetwork. Because routers use destination network addresses of packets,they work only if the configured network protocol is a routable protocolsuch as TCP/IP or IPX/SPX. This is different from bridges, which areprotocol independent.
There are two kinds of router. Static routers must havetheir routing tables configured manually with all network addresses andpaths in the internetwork. Dynamic routers automatically create theirrouting tables by listening to network traffic. (The first route must beconfigured manually, however.)
BRIDGE
Bridge is a networking component used either to extend or tosegment networks. Bridges work at the OSI data-link layer. They can beused both to join dissimilar media such as unshielded twisted-pair(UTP) cabling and fiber-optic cabling, and to join different networkarchitectures such as Token Ring and Ethernet. Bridges regenerate signalsbut do not perform any protocol conversion, so the same networkingprotocol (such as TCP/IP) must be running on both network segmentsconnected to the bridge. Bridges can also support Simple NetworkManagement Protocol (SNMP), and they can have other diagnostic features.
Bridges come in three basic types. Local bridges directlyconnect local area networks. Remote bridges can be used to create a widearea network (WAN) link between LANs. Wireless bridges can be used to joinLANs or connect remote stations to LANs.Bridges operate by sensing the source MAC addresses of the transmittingnodes on the network and automatically building an internal routingtable. This table is used to determine which connected segment to routepackets to, and it provides the filtering capability. If the bridge knowswhich segment a packet is intended for, it forwards the packet directly tothat segment. If the bridge doesn't recognize the packet's destinationaddress, it forwards the packet to all connected segments except the oneit originated on. And if the destination address is in the same segment asthe source address, the bridge drops the packet. Bridges also forwardbroadcast packets to all segments except the originating one.
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