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The history of the Internet began with the ARPANET _Advanced

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The history of the Internet began with the ARPANET _Advanced Powered By Docstoc
					                      INTERNET SERVICES

INTERNET DEVELOPMENT
The history of the Internet began with the ARPANET (Advanced
Research Projects Agency Network) and connected mainframe
computers on dedicated connections. The second stage involved
adding desktop PCs which connected through telephone wires. The
third stage was adding wireless connections to laptop computers.
And currently the Internet is evolving to allow mobile phone
Internet connectivity ubiquitously using cellular networks.
An Internet service provider (ISP, also called Internet access
provider or IAP) is a company that offers its customers access to
the Internet. The ISP connects to its customers using a data
transmission technology appropriate for delivering Internet Protocol
datagrams, such as dial-up, DSL, cable modem or dedicated high-
speed interconnects.
ISPs may provide Internet e-mail accounts to users which allow
them to communicate with one another by sending and receiving
electronic messages through their ISPs' servers. (As part of their e-
mail service, ISPs usually offer the user an e-mail client software
package, developed either internally or through an outside contract
arrangement.) ISPs may provide other services such as remotely
storing data files on behalf of their customers, as well as other
services unique to each particular ISP.
THE DOMAIN NAME SYSTEM (DNS) is a hierarchical naming
system for computers, services, or any resource participating in the
Internet. It associates various information with domain names
assigned to such participants. Most importantly, it translates
domain names meaningful to humans into the numerical (binary)
identifiers associated with networking equipment for the purpose of
locating and addressing these devices world-wide. An often used
analogy to explain the Domain Name System is that it serves as the
"phone book" for the Internet by translating human-friendly
computer      hostnames     into  IP    addresses.    For   example,
http://en.wikipedia.org/wiki/Example.com           translates      to
208.77.188.166.
The Domain Name System makes it possible to assign domain
names to groups of Internet users in a meaningful way,
independent of each user's physical location. Because of this,
World-Wide Web (WWW) hyperlinks and Internet contact
information can remain consistent and constant even if the current
Internet routing arrangements change or the participant uses a
mobile device. Internet domain names are easier to remember than
IP     addresses        such      as       208.77.188.166(IPv4)      or
2001:db8:1f70::999:de8:7648:6e8 (IPv6). People take advantage of
this when they recite meaningful URLs and e-mail addresses
without having to know how the machine will actually locate them.
The Domain Name System distributes the responsibility of
assigning domain names and mapping those names to IP addresses
by designating authoritative name servers for each domain.
Authoritative name servers are assigned to be responsible for their
particular domains, and in turn can assign other authoritative
name servers for their sub-domains. This mechanism has made the
DNS distributed, fault tolerant, and helped avoid the need for a
single central register to be continually consulted and updated.
In general, the Domain Name System also stores other types of
information, such as the list of mail servers that accept email for a
given Internet domain. By providing a world-wide, distributed
keyword-based redirection service, the Domain Name System is an
essential component of the functionality of the Internet.
Other identifiers such as RFID tags, UPC codes, International
characters in email addresses and host names, and a variety of
other identifiers could all potentially utilize DNS [1].
The Domain Name System also defines the technical underpinnings
of the functionality of this database service. For this purpose it
defines the DNS protocol, a detailed specification of the data
structures and communication exchanges used in DNS, as part of
the Internet Protocol Suite (TCP/IP). The context of the DNS within
the Internet protocols may be seen in the following diagram. The
DNS protocol was developed and defined in the early 1980s and
published by the Internet Engineering Task Force (cf. History)
LEVELS OF CONNECTIVITY
There are several levels of Internet connectivity. For our purposes, I
am just going to call these levels "Level One," through "Level Six."
Before I talk about the six levels of connectivity, experience shows
that I have to say the following to keep myself from being overrun
with e-mail: the "six level approach" to Internet connectivity is a
very simplified view of the different ways that you can access the
Internet. This is just my way of describing the levels, you will not
hear anyone else describing connectivity with these levels. This
oversimplification is on purpose. Please recognize that I have taken
some editorial liberties in this lesson to make the lesson easier to
understand for the new users (a.k.a. "newbies").
Level One Internet access ("remote modem access") is access
through a dial-up terminal connection. Through the use of a
modem, you access a "host" computer, usually a UNIX-based
computer that displays text and operates with commands you type
in on individual lines. Your your home computer acts like it is a
terminal on a 'mainframe'. You may type the commands on your
own computer, but it is the host that carries out your commands.
Level One connectivity once was the most "popular" (in the sense
that more people had Level One connectivity than any other level)
and the most misunderstood level of connectivity. To begin with,
Level One connectivity limits you to using the programs (also
known as "clients") that are running on the host. If, for example,
you hear of this hot new client called "Mosaic" and you want to try
it out, if your host does not have a Mosaic client on it you are out of
luck! Putting a copy of the Mosaic client software on your own
computer won't do ANYTHING for you -- remember that the only
programs that you can use when you have Level One connectivity
are the programs that the host has!
Also, with Level One connectivity you must always remember that
everything you are doing is through the host, NOT through your
own computer. If you download a file from somewhere (like we did
last Friday with the GET command) that file will go to the host,
NOT to your own personal computer. You'll need to download the
file one more time -- this time from the host to your computer -- if
you want the file to be on YOUR computer
Level Two connectivity ("access through a gateway") is access to
the Internet from a network that really isn't "on" the Internet. This
is becoming less and less common as network providers are
adopting the Internet standard. Services that used this model have
been 'Compuserve', 'Prodigy', and 'AOL'. Picture two circles that
touch each other at only one point. One of the circles is the
Internet, the other circle is a non-Internet network, and the point
where the two networks touch is called a gateway. The gateway
allows the two networks to "talk" to each other, but users of the
non-Internet network are limited in their ability to fully access all of
the tools of the Internet. For example, AOL is, in effect, its own
network. It has a great number of different programs that its
subscribers can use, but ALL of these programs only run on the
AOL network. Gradually, AOL has been shifting to adopt the
Internet standard, and has essentially become an Internet Service
Provider in addition to its own services, providing you with many of
the features of the Internet.
Both Level One and Two are older means of connecting. They are
still in use, but the primary means of connecting for home and
small business users is Level Three.
Level Three connectivity can also be called "On-Demand Direct
Connectivity." Since you probably aren't going to spend twenty-four
hours a day on the Internet, there are many service providers that
will let you connect to the Internet whenever you want using a high
speed modem and something called "Point to Point Protocol (PPP)"
or "Serial Line Internet Protocol (SLIP)" connection. Nearly all
Internet service providers such as Sovernet or Togethernet, or I-
100, or ...... use this type of service, and I suspect most of you do
too.
There are two cool things about PPP and SLIP connections. First,
because you aren't connected to the Internet all day long, (using up
your phone line) it doesn't cost as much as regular Level Three
connectivity (you can find sites that will only charge you about $15
or $20 US per month for a PPP or SLIP connection). The second
cool thing about PPP and SLIP connections is that the client
software is stored on YOUR computer. Want to play with Netscape
or Explorer? Load it onto your computer and play with it.
The majority of local Vermont Internet service providers provide
PPP or SLIP Services. These providers include SoVerNet and
Together Networks; I-100, Plainfield By Pass, Kingdom.Com and
PowerShift. These companies allow users to dial into their systems
and then provide access to the Internet network.
The first three levels mentioned above all use conventional modems
to access the network. We discussed how these worked in the last
lesson. Modems have speeds up to 56K or kilobits per second, or
56 thousand bits (Os and 1s) passing through the line per second.
But this is a big limitation for some users who need or want a lot of
data transferred quickly. Another limitation - one usually doesn't
receive full 56K access due to line 'noise' - static or other
interruptions that limit the data through-put. This is particularly
common in rural areas. Digital switches and fiber transmission
improves line quality, but this requires the replacement of all the
wire to your building, and that won't happen overnight. Better
performance is possible through higher levels of service and digital
transfers.
Level Four connectivity is in a way a hybrid of Level Three and
Level Four. Three major types of high speed connectivity have
emerged in the last few years and are increasingly available across
the country. ISDN (Integrated Services Digital Network), DSL
(Digital Subscriber Line) and Cable.
ISDN is like a modem service that involves dial up, but it uses a
high quality line capable of higher performance data transfer up to
256KB/second and higher. Generally this service is offered by the
local phone company. It is falling out of favor due to cost and being
replaced by digital services described below.
Improvements in electronic hardware have allowed conventional
phone lines to accept data transfers at high rates using new
technology called "DSL" or Digital Subscriber Line.            At 1.5
megabytes per second, the data transfer rates are almost fifty times
faster than the fastest modems. All this for about $50.00 per
month. Two 'flavors' of DSL are available, ADSL and SDSL. Of the
two, SDSL is the more powerful performer and businesses generally
choose it over ADSL. However, any DSL service is only available in
larger metropolitan areas so far, as it requires that the phone
company or other ISPs to have installed special hardware in their
switch offices.
Cable companies are offering high performance services through
'modems' that link through the conventional cable lines.        These
services require that you have cable service, and many parts of
Vermont do not have this service. Data transfer rates and costs
are similar to DSL services.
Level Five connectivity ("Direct Internet Access") is the highest,
and most expensive, level of connectivity there is. With Level Five
connectivity, you are directly wired into the Internet using high-
speed lines, and you are "on-line" twenty-four hours a day, seven
days a week.
Level Five connectivity is great if you are a mainframe, or a
business with a number of users, but is not too advantageous if
you are a sole user with a beat-up PC. Besides, Level Five Internet
access is so incredibly expensive (1) (the University of Alabama
pays $29,000.00 (US) each and every year as of 1995) just to
connect to the Internet, and that doesn't include the software,
hardware, facility, and staff expenses. Until recently, Level Five
connectivity was limited to large corporations and Universities.
Now, even small businesses are using Level Five services.
Finally, there is another category of connectivity that uses satellites
and wireless methods, and these provide the most promise for
those in rural areas that need higher capacity. No land
infrastructure is needed except the receiver. Wireless connections
are like cell phones. You have to have a wireless modem and a
laptop, or a hand-held computer that is wireless-capable, and you
need a subscription to a service. This provides mobility, and for
those folks really out of distance from a phone line, connection
possibilities. Data transmission rates are not particularly high
performance - the benefits are in the mobility. However, satellites
offer high-speed data transmission. Today, services such as Web
PC offer performance of up to 400kb/sec download via a dish like
the small satellite TV dishes. The downside is that there has to be
a land line or conventional phone line to send data requests to the
Internet. So, there's some extra cost. Soon there will be full two
way satellite service, which will really assist users in remote areas,
with poor quality phone lines and no high speed services. This will
initially be offered by Hughes Network Systems and Pegasus
through the Direc PC service.

LEVEL DESCRIPTION    COMMENTS
                     Commands executed by host
                     All programs on host
                     Can only run client software already on
                     the host
                     All files on host unless you download to
                     your computer
      Remote modem
One                  Example: Dial into a host computer
      access
                     directly. (Dial in to UVM - Vermont
                     Automated Libraries (VALS) has this kind
                     of service)
                     Speed: Access speed is determined by
                     modem speed, quality of phone line.Up to
                     56K/second.
                     Mix of Internet access and access to a
                     private network.
      Access through Speed: Access speed is determined by
Two
      a Gateway      modem speed, quality of phone line. Up
                     to 56K/second.
                     Examples: AOL, Prodigy, CompuServe
                     Most popular today.
                     Connect when you want through a
                     modem to an Internet Service Provider.
Three PPP/SLIP
                     (ISP) Client software runs on YOUR
                     computer! Use Internet Explorer,
                     Netscape Navigator, etc.
                      Speed: Access speed is determined by
                      modem speed, quality of phone line. Up
                      to 56K/second.
                      24 hour connection. ISDN is like dial up
                      services with better performance. DSL
       ISDN, DSL,     and Cable are always available.
Four
       Cable,         Speed: High data transfer capablilities.
                      Ranges from 56KB/second to
                      300KB/second depending.
                      24 hour connection.
                      Speed: Very high data transfer
       Leased Line
Five                  capablilities. Ranges from 56KB/second
       (56K to T-3)
                      to 44 MB/second (T-3) Possible to buy
                      fractions of a line.
                      Wireless access through wireless modems
       Wireless and   and cell phone-like towers.
Six    Satellite      Satellite through 400kbps download and
       Services       land line upload. Full two way satellite
                      services will be offered soon.

				
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