Month: January 2020
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4.4 Determining Your Route
There is no place in the Internet that knows in advance the route your packets will take from your computer to a particular destination. Even the routers that participate in forwarding your packets across the Internet do not know the entire route your packet will take. They only know which link to send your packets…
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4.3 When Things Get Worse and Better
Sometimes the network has problems and a router must find a way to route data around the problems. A common problem is that one of the outbound links fails. Perhaps someone tripped over a wire and unplugged a fiber optic cable. At this point, the router has a bunch of network numbers that it wants…
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4.2 How Routers Determine the Routes
While the idea of the collapsing many IP addresses into a single network number greatly reduces the number of individual endpoints that a router must track to properly route packets, each router still needs a way to learn the path from itself to each of the network numbers it might encounter. When a new core…
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4.1 Internet Protocol (IP) Addresses
In the previous section where we talked about Link layer addresses, we said that link addresses were assigned when the hardware was manufactured and stayed the same throughout the life of a computer. We cannot use link layer addresses to route packets across multiple networks because there is no relationship between a link layer address…
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4 Internetworking Layer (IP)
Now that we can move data across a single link, it’s time to figure out how to move it across the country or around the world. To send data from your computer to any of a billion destinations, the data needs to move across multiple hops and across multiple networks. When you travel from your…
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4.10 Questions-Chapter 4
You can take this quiz online at http://www.net-intro.com/quiz/4.10 What is the goal of the Internetworking layer? a) Move packets across multiple hops from a source to destina- tion computer b) Move packets across a single physical connection c) Deal with web server failover d) Deal with encryption of sensitive data How many different physical links…
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3.6 Questions-Chapter 3
You can take this quiz online at http://www.net-intro.com/quiz/ When using a WiFi network to talk to the Internet, where does your computer send its packets? a) A gateway b) A satellite c) A cell phone tower32 CHAPTER 3. LINK LAYER d) The Internet Central Office How is the link/physical address for a network device assigned?a)…
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3.5 Glossary-Chapter 3
base station: Another word for the first router that handles your packets as they are forwarded to the Internet.broadcast: Sending a packet in a way that all the stations connected to a local area network will receive the packet.gateway: A router that connects a local area network to a wider area network such as the…
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3.4 Summary-Chapter 3
So now we have looked at the “lowest” layer in our four-layer architecture. And we have only taken a simple look at how the Link layer works. There are many other details that must be designed into a link layer like connection distance, voltage, frequency, speed, and many others. A key benefit of the layered…
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3.3 Coordination in Other Link Layers
Sometimes when a link layer has many transmitting stations and needs to operate at near 100% efficiency for long periods of time, the design takes a different approach. In this approach, there is a “token” that indicates when each station is given the opportunity to transmit data. Stations cannot start a transmission unless they have…
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3.2 Courtesy and Coordination
Because many computers are sharing the same radio frequencies, it’s important to coordinate how they send data. When there’s a crowd of people in a room, they can’t all talk at the same time or everything will be garbled. The same thing happens when multiple WiFi radios transmit at the same time on the same…
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3.1 Sharing the Air
When your laptop or phone is using WiFi to connect to the Internet, it is sending and receiving data with a small, low-powered radio. The radio in your computer can only send data about 300 meters, so your computer sends your packets to the router in your home, which forwards the packets using a link…
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3 Link Layer
The lowest layer of our Internet Architecture is the Link layer. We call it the “lowest layer” because it is closest to the physical network media. Often the Link layer transmits data using a wire, a fiber optic cable, or a radio signal. A key element of the Link layer is that usually data can…
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2.5 Stacking the Layers
We usually show the four different layers (Link, Internetwork, Transport, and Application) stacked on top of each other with the Application layer at the top and the Link layer at the bottom. The reason we show them this way is because each layer makes use of the layers above and below it to achieve networked…
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2.4 The Application Layer
The Link, Internetwork, and Transport layers work together to quickly and reliably move data between two computers across a shared network of networks. With this capability to move data reliably, the next question is what networked applications will be built to make use of these network connections. When the first widely used Internet came into…