Internet Technology
Even though the Internet
is still a young technology, it's hard to imagine life without it now. Every
year, engineers create more devices to integrate with the Internet. This
network of networks crisscrosses the globe and even extends into space. But
what makes it work?
To understand the Internet, it helps to
look at it as a system with two main components. The first of those components
is hardware. That
includes everything from the cables that carry terabits of information every
second to the computer sitting in front of you.
Other types of hardware that support the
Internet include routers, servers, cell
phone towers, satellites, radios,smartphones and other devices. All these devices
together create the network of networks. The Internet is a malleable system --
it changes in little ways as elements join and leave networks around the world.
Some of those elements may stay fairly static and make up the backbone of the
Internet. Others are more peripheral.
These elements are connections. Some are
end points -- the computer, smartphone or other device you're using to read
this may count as one. We call those end points clients.
Machines that store the information we seek on the Internet are servers.
Other elements are nodes which serve as a connecting point
along a route of traffic. And then there are the transmission lines which can
be physical, as in the case of cables and fiber optics, or they can be useless
signals from satellites, cell phone or 4G towers, or radios.
All of this hardware wouldn't create a
network without the second component of the Internet: the protocols. Protocols are sets of rules that machines follow
to complete tasks. Without a common set of protocols that all machines
connected to the Internet must follow, communication between devices couldn't
happen. The various machines would be unable to understand one another or even
send information in a meaningful way. The protocols provide both the method and
a common language for machines to use to transmit data.
We'll take a closer look at protocols and
how information travels across the Internet on the next page.
A Matter of Protocols
You've probably heard of several protocols
on the Internet. For example,hypertext
transfer protocol is
what we use to view Web sites through a browser -- that's what the http at the
front of any Web address stands for. If you've ever used an FTP server, you
relied on the file transfer protocol. Protocols like these and dozens more
create the framework within which all devices must operate to be part of theInternet.
Two of the most important protocols are the transmission
control protocol (TCP) and
the Internet protocol (IP).
We often group the two together -- in most discussions about Internet protocols
you'll see them listed as TCP/IP.
What do these protocols do? At their most
basic level, these protocols establish the rules for how information passes
through the Internet. Without these rules, you would need direct connections to
other computers to access the information they hold. You'd also need both your
computer and the target computer to understand a common language.
You've probably heard of IP addresses. These
addresses follow the Internet protocol. Each device connected to the Internet
has an IP address. This is
how one machine can find another through the massive network.
The version of IP most of us use today is
IPv4, which is based on a 32-bit address system. There's one big problem with
this system: We're running out of addresses. That's why the Internet
Engineering Task Force (IETF) decided back in 1991 that it was necessary to
develop a new version of IP to create enough addresses to meet demand. The
result was IPv6, a 128-bit address system. That's enough addresses to
accommodate the rising demand for Internet access for the foreseeable future
[source:Opus One].
When you want to send a message or retrieve
information from another computer, the TCP/IP protocols are what make the
transmission possible. Your request goes out over the network, hittingdomain name servers (DNS) along the way to find the target
server. The DNS points the request in the right direction. Once the target
server receives the request, it can send a response back to your computer. The
data might travel a completely different path to get back to you. This flexible
approach to data transfer is part of what makes the Internet such a powerful
tool.
Let's take a closer look at how information
travels across the Interne
Packet, Packet, Who's
Got the Packet?
In order to retrieve this article, your
computer had to connect with the Web
server containing
the article's file. We'll use that as an example of how data travels across the
Internet.
First, you open your Web browser and
connect to our Web site. When you do this, your computer sends an electronic
request over your Internet connection to your Internet service provider (ISP).
The ISP routes the request to a server further up the chain on the Internet.
Eventually, the request will hit a domain name server (DNS).
This server will look for a match for the
domain name you've typed in (such as www.howstuffworks.com). If it finds a
match, it will direct your request to the proper server's IP address. If it
doesn't find a match, it will send the request further up the chain to a server
that has more information.
The request will eventually come to our Web
server. Our server will respond by sending the requested file in a series of
packets. Packets are parts of a file that range between
1,000 and 1,500 bytes. Packets have headers and footers that tell computers
what's in the packet and how the information fits with other packets to create
an entire file. Each packet travels back up the network and down to your
computer. Packets don't necessarily all take the same path -- they'll generally
travel the path of least resistance.
That's an important feature. Because
packets can travel multiple paths to get to their destination, it's possible
for information to route around congested areas on the Internet. In fact, as
long as some connections remain, entire sections of the Internet could go down
and information could still travel from one section to another -- though it
might take longer than normal.
When the packets get to you, your device
arranges them according to the rules of the protocols. It's kind of like
putting together a jigsaw puzzle. The end result is that you see this article.
This holds true for other kinds of files as
well. When you send an e-mail, it gets broken into packets before zooming
across the Internet. Phone calls over the Internet also convert conversations
into packets using the voice over Internet protocol (VoIP). We can thank network
pioneers like Vinton Cerf and Robert Kahn for these protocols -- their early
work helped build a system that's both scalable and robust.
That's how the Internet works in a
nutshell. As you look closer at the various devices and protocols, you'll
notice that the picture is far more complex than the overview w
One of the greatest
things about the Internet is that nobody really owns it. It is a global
collection of networks, both big and small. These networks connect together in
many different ways to form the single entity that we know as the Internet.
In fact, the very name comes from this idea of interconnected networks.
Since its beginning in 1969, the Internet
has grown from four host computer systems to tens of millions. However, just
because nobody owns the Internet, it doesn't mean it is not monitored and
maintained in different ways. The
Internet Society, a non-profit group established in 1992,
oversees the formation of the policies and protocols that define how we use and
interact with the Internet.
In this article, you will learn about the
basic underlying structure of the Internet. You will learn about domain name
servers, network access points and backbones. But first you will learn about
how your computer connects to others.
The Internet: Computer
Network Hierarchy
Every computer that is connected to the
Internet is part of a network, even the one in your home. For
example, you may use amodem and dial a local number to connect to anInternet Service Provider(ISP).
At work, you may be part of a local area network (LAN), but
you most likely still connect to the Internet using an ISP that your company
has contracted with. When you connect to your ISP, you become part of their
network. The ISP may then connect to a larger network and become part of their
network. The Internet is simply a network of networks.
Most large communications companies have
their own dedicated backbones connecting various regions. In each region, the
company has a Point of Presence (POP). The POP is a place for local
users to access the company's network, often through a local phone number or
dedicated line. The amazing thing here is that there is no overall controlling
network. Instead, there are several high-level networks connecting to each
other through Network Access Points or NAPs.
Internet Network Example
Here's an example. Imagine that Company A
is a large ISP. In each major city, Company A has a POP. The POP in each city
is a rack full of modems that the ISP's customers dial into. Company A leasesfiber optic lines from the phone company to connect the
POPs together (see, for example, this UUNET Data Center Connectivity Map).
Imagine that Company B is a corporate ISP.
Company B builds large buildings in major cities and corporations locate their
Internet server machines in these buildings. Company B is such a large company
that it runs its own fiber optic lines between its buildings so that they are
all interconnected.
In this arrangement, all of Company A's
customers can talk to each other, and all of Company B's customers can talk to
each other, but there is no way for Company A's customers and Company B's
customers to intercommunicate. Therefore, Company A and Company B both agree to
connect to NAPs in various cities, and traffic between the two companies flows
between the networks at the NAPs.
In the real Internet, dozens of large
Internet providers interconnect at NAPs in various cities, and trillions of
bytes of data flow between the individual networks at these points. The
Internet is a collection of huge corporate networks that agree to all
intercommunicate with each other at the NAPs. In this way, every computer on
the Internet connects to every other.
The Function of an
Internet Router
All of these networks rely on NAPs, backbones
and routers to talk to each other. What is
incredible about this process is that a message can leave one computer and
travel halfway across the world through several different networks and arrive
at another computer in a fraction of a second!
The routers determine where to send information from
one computer to another. Routers are specialized computers that send your
messages and those of every other Internet user speeding to their destinations
along thousands of pathways. A router has two separate, but related, jobs:
·
It ensures that information doesn't go where it's not needed.
This is crucial for keeping large volumes of data from clogging the connections
of "innocent bystanders."
·
It makes sure that information does make it to the intended
destination.
In performing these two jobs, a router is
extremely useful in dealing with two separate computer networks. It joins the
two networks, passing information from one to the other. It also protects the
networks from one another, preventing the traffic on one from unnecessarily
spilling over to the other. Regardless of how many networks are attached, the
basic operation and function of the router remains the same. Since the Internet
is one huge network made up of tens of thousands of smaller networks, its use
of routers is an absolute necessity. For more information, read How Routers Work.
Internet Backbone
The National Science Foundation (NSF) created the first high-speed
backbone in 1987. CalledNSFNET,
it was a T1 line that connected 170 smaller networks
together and operated at 1.544 Mbps (million bits per second). IBM, MCI and Merit worked with
NSF to create the backbone and developed a T3 (45 Mbps) backbone the following
year.
Backbones are typically fiber optic trunk
lines. The trunk line has multiple fiber optic cables combined together to
increase the capacity. Fiber optic cables are designated OC for optical
carrier, such as OC-3, OC-12 or OC-48. An OC-3 line is capable of transmitting
155 Mbps while an OC-48 can transmit 2,488 Mbps (2.488 Gbps). Compare that to a
typical 56K modem transmitting 56,000 bps and you see just how fast a modern
backbone is.
Today there are many companies that operate
their own high-capacity backbones, and all of them interconnect at various NAPs
around the world. In this way, everyone on the Internet, no matter where they
are and what company they use, is able to talk to everyone else on the planet.
The entire Internet is a gigantic, sprawling agreement between companies to
intercommunicate freely.
Internet Protocol: IP
Addresses
Every machine on the Internet has a unique
identifying number, called an IP Address. The IP
stands for Internet Protocol,
which is the language that computers use to communicate over the Internet. A
protocol is the pre-defined way that someone who wants to use a service talks
with that service. The "someone" could be a person, but more often it
is a computer program like a Web browser.
A typical IP address looks like this:
To make it easier for us humans to
remember, IP addresses are normally expressed in decimal format as a dotted
decimal number like
the one above. But computers communicate in binary form. Look at the same IP address in
binary:
The four numbers in an IP address are
called octets, because they
each have eight positions when viewed in binary form. If you add all the
positions together, you get 32, which is why IP addresses are considered 32-bit
numbers. Since each of the eight positions can have two different states (1 or
zero), the total number of possible combinations per octet is 28 or 256. So each octet can contain any
value between zero and 255. Combine the four octets and you get 232 or a possible 4,294,967,296 unique
values!
Out of the almost 4.3 billion possible
combinations, certain values are restricted from use as typical IP addresses.
For example, the IP address 0.0.0.0 is reserved for the default network and the
address 255.255.255.255 is used for broadcasts.
The octets serve a purpose other than
simply separating the numbers. They are used to createclasses of IP addresses that can be assigned
to a particular business, government or other entity based on size and need.
The octets are split into two sections: Net and Host. The Net section
always contains the first octet. It is used to identify the network that a
computer belongs to. Host (sometimes referred to as Node)
identifies the actual computer on the network. The Host section always contains
the last octet. There are five IP classes plus certain special addresses. You
can learn more about IP classes at What is an IP address?.
Internet Protocol:
Domain Name System
When the Internet was in its infancy, it
consisted of a small number of computers hooked together with modems and
telephone lines. You could only make connections by providing the IP address of
the computer you wanted to establish a link with. For example, a typical IP
address might be 216.27.22.162. This was fine when there were only a few hosts
out there, but it became unwieldy as more and more systems came online.
The first solution to the problem was a
simple text file maintained by the Network Information Center that mapped names
to IP addresses. Soon this text file became so large it was too cumbersome to manage.
In 1983, the University of Wisconsin created the Domain
Name System (DNS),
which maps text names to IP addresses automatically. This way you only need to
rememberwww.howstuffworks.com, for example, instead
of HowStuffWorks.com's IP address.
URL: Uniform Resource
Locator
When you use the Web or send an e-mail
message, you use a domain name to do it. For example, theUniform Resource Locator (URL) "http://www.howstuffworks.com"
contains the domain name howstuffworks.com. So does this e-mail address:
example@howstuffworks.com. Every time you use a domain name, you use the
Internet's DNS servers to translate the human-readable domain name into the
machine-readable IP address. Check out How Domain Name Servers
Work for
more in-depth information on DNS.
Top-level domain names, also called
first-level domain names, include .COM, .ORG, .NET, .EDU and .GOV. Within every
top-level domain there is a huge list of second-level domains. For example, in
the .COM first-level domain there is:
Yahoo
Microsoft
Every name in the .COM top-level domain
must be unique. The left-most word, like www, is the host name. It specifies
the name of a specific machine (with a specific IP address) in a domain. A
given domain can, potentially, contain millions of host names as long as they
are all unique within that domain.
DNS servers accept requests from programs
and other name servers to convert domain names into IP addresses. When a
request comes in, the DNS server can do one of four things with it:
1. It can answer the
request with an IP address because it already knows the IP address for the
requested domain.
2. It can contact another
DNS server and try to find the IP address for the name requested. It may have
to do this multiple times.
3. It can say, "I
don't know the IP address for the domain you requested, but here's the IP
address for a DNS server that knows more than I do."
4. It can return an error
message because the requested domain name is invalid or does not exist.
DNS Example
Let's say that you type the URL www.howstuffworks.com into your browser. The browser contacts a
DNS server to get the IP address. A DNS server would start its search for an IP
address by contacting one of the root DNS servers. The
root servers know the IP addresses for all of the DNS servers that handle the
top-level domains (.COM, .NET, .ORG, etc.). Your DNS server would ask the root
for www.howstuffworks.com, and the root would say, "I don't know the IP
address for www.howstuffworks.com, but here's the IP address for the .COM DNS
server."
Your name server then sends a query to the
.COM DNS server asking it if it knows the IP address for www.howstuffworks.com.
The DNS server for the COM domain knows the IP addresses for the name servers
handling the www.howstuffworks.com domain, so it returns those.
Your name server then contacts the DNS
server for www.howstuffworks.com and asks if it knows the IP address for www.howstuffworks.com. It
actually does, so it returns the IP address to your DNS server, which returns
it to the browser, which can then contact the server for www.howstuffworks.comto get
a Web page.
One of the keys to making this work is
redundancy. There are multiple DNS servers at every level, so that if one
fails, there are others to handle the requests. The other key is caching. Once
a DNS server resolves a request, it caches the IP address it receives. Once it
has made a request to a root DNS server for any .COM domain, it knows the IP
address for a DNS server handling the .COM domain, so it doesn't have to bug
the root DNS servers again for that information. DNS servers can do this for
every request, and this caching helps to keep things from bogging down.
Even though it is totally invisible, DNS
servers handle billions of requests every day and they are essential to the
Internet's smooth functioning. The fact that this distributed database works so
well and so invisibly day in and day out is a testimony to the design. Be sure
to read How Domain Name Servers Work for more information on DNS.
Internet Servers and
Clients
Internet servers make the Internet possible. All of the
machines on the Internet are either servers orclients. The machines that provide
services to other machines are servers. And the machines that are used to
connect to those services are clients. There are Web servers, e-mail servers,
FTP servers and so on serving the needs of Internet users all over the world.
When you connect to www.howstuffworks.com to read a page, you are a user sitting at a
client's machine. You are accessing the HowStuffWorks Web server. The server
machine finds the page you requested and sends it to you. Clients that come to
a server machine do so with a specific intent, so clients direct their requests
to a specific software server running on the server machine. For example, if
you are running a Web browser on your machine, it will want to talk to the Web
server on the server machine, not the e-mail server.
A server has a static IP address that does
not change very often. A home machine that is dialing up through a modem, on
the other hand, typically has an IP address assigned by the ISP every time you
dial in. That IP address is unique for your session -- it may be different the
next time you dial in. This way, an ISP only needs one IP address for each
modem it supports, rather than one for each customer.
Ports and HTTP
Any server machine makes its services
available using numbered ports -- one for each service that is available on the
server. For example, if a server machine is running a Web server and a file
transfer protocol (FTP) server, the Web server would typically be available on
port 80, and the FTP server would be available on port 21. Clients connect to a
service at a specific IP address and on a specific port number.
Once a client has connected to a service on
a particular port, it accesses the service using a specific protocol. Protocols
are often text and simply describe how the client and server will have their
conversation. Every Web server on the Internet conforms to the hypertext
transfer protocol (HTTP). You can learn more about Internet
servers, ports and protocols by reading How Web Servers Work.
Networks, routers, NAPs, ISPs, DNS and
powerful servers all make the Internet possible. It is truly amazing when you
realize that all this information is sent around the world in a matter of
milliseconds! The components are extremely important in modern life -- without
them, there would be no Internet. And without the Internet, life would be very
different indeed for many of us.
For more information on the structure of the Internet and related
topics, check out the links on the next page.
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