1. a type of circuit board inside all modems
   a specialized computer
2. a useful concept for understanding internet data flow

A router is a specialized computer that is programmed to interface between different networks. Some software programs can function as routers, but today, we'll just be quizzing you on the physical kind.

1. makes sure data sent over the Internet goes where it needs to go -- and not where it isn't needed
   acts like a traffic controller, working to cut down on congestion and keep everything flowing smoothly along the best possible path
2. both

Routers are programmed to perform both these critical functions, standing as gatekeepers between networks to control the flow of data over the Internet.

1. protocols routers follow to determine where information needs to go
   smaller packages of information routers shovel around the Internet
2. large bundles of data grouped into chunks for delivery

When you hit the send button on an email, place an online order, open a Web page or do any of the other myriad activities possible with the Internet, all that information is broken down into much smaller packets of data, sent individually and then reassembled at the intended destination.

1. every single packet of information that gets sent their way
   only packets with certain designations embedded in the coding
2. all packets that involve person-to-person correspondences

Routers are the only type of equipment twisted into the Internet's massive network of networks that look at every single packet passing by.

1. Packets can easily be routed around problems, and the overall load of information can be balanced across different Internet paths.
   Since packets are small, they don't get jammed up in the Internet's series of tubes.
2. Packet-switching decreases the memory needed on each individual computer.

All kinds of events can cause congestion along the different routes across the Internet. For example, a storm in one city could take out the power and all the routers located in range of the power failure with it. But don't worry, other routers looking to send packets in that direction can simply switch them along another more trouble-free route. Packet-switching networks offer this flexibility and redundancy.

1. Routers offer packets different route options, and the packets reject ones that aren't in the direction of their final destination.
   Routers can sense from the information contained within the packet where it ought to be going.
2. All devices connected to the Internet have unique addresses, and packets get labeled with delivery addresses and return addresses so the routers know where they're headed.

Packets, just like regular snail mail letters, are labeled with delivery addresses and return addresses. Using this information, routers can figure out what direction -- if not the exact location -- a packet needs to be headed.

1. They reroute traffic to less congested areas.
   They focus on speeding up areas experiencing high-volume traffic.
2. They delete unessential portions of data to ensure timely delivery despite congestion.

Routers are programmed to be capable of determining when certain segments of the Internet are busier than others. When one portion experiences some congestion, nearby routers simply send packets of information along another route.

1. Routers can be equipped with authentication and encryption features to monitor packets entering your network.
   Routers can have firewalls to block unwanted entry.
2. both

Routers can possess a number of features which fine-tune what the router will let pass and what it will flag as potentially dangerous or unnecessary.

1. Routers are tiny -- they fit in all types of computers.
   Routers are only placed at junction points between large networks.
2. Routers can come in all sizes.

Major routers handle vast amounts of data, but routers don't need to be that massive. They can be medium sized and even quite small -- it really just depends on the needs of the networks they are connecting.

1. tens of thousands of data packets per second
   hundreds of thousands of data packets per second
2. tens of millions of data packets per second

Large routers that operate at major Internet traffic points can handle tens of millions of data packets every second. For example, the Cisco 12016 GSR could handle a whopping 60 million packets a second.