BRIDGE
In telecommunication networks, a bridge is a product that  connects a local area network (LAN) to another local area network that  uses the same 
protocol (for example, 
Ethernet or 
token ring).   You can envision a bridge as being a device that decides whether a  message from you to someone else is going to the local area network in  your building or to someone on the local area network in the building  across the street.  A bridge examines each message on a LAN, "passing"  those known 
to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).  In bridging networks, computer or 
node  addresses have no specific relationship to location.  For this reason,  messages are sent out to every address on the network and accepted only  by the intended destination node.  Bridges learn which addresses are on  which network and develop a 
learning table so that subsequent messages can be forwarded to the right network. 
Bridging networks are generally always interconnected local area  networks since broadcasting every message to all possible destinations  would flood a larger network with unnecessary traffic.  For this reason,  
router  networks such as the Internet use a scheme that assigns addresses to  nodes so that a message or packet can be forwarded only in one general  direction rather than forwarded in all directions. 
A bridge works at the data-link (physical network) level of a network, copying a data 
frame from one network to the next network along the communications path.   
A bridge is sometimes combined with a router in a product called a 
brouter.
 
    
         
        
    
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