Internet Architecture
and Packet Switching
03
Embedded Files
As we've learned in previous lessons, the Internet is network of disparate networks that is managed by a collection of protocols. We've already seen the role that the HTTP protocol plays in supporting the World Wide Web application. In this lesson we delve more deeply into the basic architecture and infrastructure of the Internet. We'll learn that the main Internet protocols are organized into a hierarchy of abstraction layers (the application, transport, internet, and link layers) each of which manages certain specific tasks required to route messages between hosts on the Internet. We'll learn about:
Internet architecture and abstraction layers
The packet switching routing scheme
The TCP/IP protocol
After this lesson you should have a pretty good understanding of how some of your familiar applications (web browsing, email, smartphone apps) are supported by the underlying Internet hardware and software.
Here is a short video called A Packet's Tale to get us started on our journey.
Technical Terminology
Technical Terminology
ping - Ping is a networking utility used by network administrators to test the reachability of a host on the Internet
traceroute - Traceroute is a networking utility used to trace the route and measure delays of packets moving through the Internet
packet switching - Packet switching is the method by which information is transmitted through the Internet. Information is broken into packets and each packet is routed independently from source to destination
packet - A packet is a collection of data used by the TCP/IP protocol to transmit data across the Internet. Each packet contains routing data as well as the content of the message
packet sniffer - A packet sniffer is software used by network administrators to monitor data being transmitted over a network. In the wrong hands, it can be used to steal email messages and other information
abstraction layer - The Internet is organized into several abstraction layers that are controlled by various protocols. From the bottom up, we have the link layer (Ethernet protocol), the Internet layer (IP), transport layer (TCP), and application layer (HTTP)
Internet Architecture and Packet Switching
Internet Architecture and Packet Switching
This first video focuses on basic architecture and packet switching. It illustrates how the ping utility can be used to test whether certain hosts are reachable on the network. And it introduces a new tool, traceroute, that can be used to trace the routes that packets take from one computer to another on the Internet.
Activity - Using Ping to Test the Reachability of Internet Hosts
Activity - Using Ping to Test the Reachability of Internet Hosts
In this activity, you will use the ping and traceroute utilities at network-tools.com to measure the latency and observe trace routes to answer the question: Does geographical distance between the source and the destination on the network affect latency?
On Windows, search for the command prompt application (cmd), then type in the commands shown in red. Calculate the average ping and the average number of hops for each server, then answer the following questions.
mit.edu
stanford.edu
ox.ac.uk
kyoto-u.ac.jp
usp.br
Did any of the servers lose packets or time out? Some servers will block ping and trace for security reasons which are seen as time outs. Were there any surprising locations in the hops that the packet went through?
Did different trials have different results for the same destination? Do packets always get routed in the same way?
Can you guess where the network-tools server is located based on the latency data you collected? Can you confirm your guess using trace or whois (which gives you information about who owns a server)?
How does the number of hops in the trace affect latency (the round trip time seen in ping)?
How does geographical distance affect latency? What are some other factors that may be affecting latency?
Network Redundancy
Network Redundancy
Given the enormous number of devices on the Internet and the reality that pieces of a complex system fail at unexpected times (and often in groups of neighbors such as a whole city), the Internet had to be designed to be reliable. This is achieved by building many redundant connections into the physical systems of the Internet. That way, if part of the Internet fails, data can be re-routed via a different path. And such changes to the path can happen in transit because routing on the Internet is dynamic; it is not specified in advance. Creating such redundancy can require additional resources (such as additional computers and cables) but it also increases the Internet's fault tolerance (ability to work around problems) and helps the Internet scale (expand) to more devices and people.
Internet Abstraction Layers
Internet Abstraction Layers
This video focuses on the main protocols that manage the routing of messages on the Internet. It introduces the concept of a hierarchy of abstraction layers and shows how the various control protocols, such as TCP, IP, SMTP, work together in the hierarchy to support applications such as email and web browsing.
Packet Sniffers & Public Networks
Packet Sniffers & Public Networks
Packet Order. Does it matter whether the packets of a message arrive in order? Explain how this set of protocols handles that.
Missing Packets. What should happen if a packet goes missing? Which layer would handle this? What action would it have to take? And what additional information would be needed in the packet in order to handle it?
Corrupted Packets. Suppose there’s some kind hardware glitch that corrupts one or more bits in a packet? Can this be detected? What action should be taken in this case? What additional information would be needed to handle this issue?
Security/Privacy. As the packets are being transmitted through the network, can people other than the sender and receiver read the messages? What methods can we use to protect the message?
Still Curious?
Still Curious?
There is a wealth of good introductory and comprehensive information about the Internet and the WWW.
As always, Wikipedia is an excellent resource as a first stop. Its pages on Internet protocol, Ping, Traceroute, and the other topics in this lesson are all accurate and accessible. Wikipedia's entry on the Internet.
The How Stuff Works site has a nice animated description of how routers work to direct traffic on the Internet.
Warriors of the Net is a classic 12 minute animated video about packets traveling through the Internet.
For a very detailed and comprehensive discussion of networking, sort of like reading a short book, see the CTDP's Networking Tutorial, which covers the topic in much more detail than we have done here.
Explore this map of the underwater cables that carry 99% of international data. (2016 interactive version of map)
Watch this video that describes how a hacker could view your data on a public network using a packet sniffer.
Report abuse