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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B6. Istanbul 2004
are servers. And the machines that are used to connect to those
services are clients. When a html page is requested to a server,
the browser forms a connection to a Web server, requests a
page and receives it. In detail (Figure 3), the browser breaks the
URL into 3 parts: the protocol ("http"), the server name
(^vww.isprs.org") and the file name ("isprs.html"). The
browser communicated with a domain name server (DNS) to
translate the server name "www.isprs.org" into an IP numerical
address, which it uses to connect to the server machine. The
browser then forms a connection to the server at that IP address
on port 80 and following the HTTP protocol, it sends a GET
request. lo | ihe. server, — asking ^ for the. file
"http://www.isprs.org/isprs.html". The ISPRS server then sends
the HTML text to the browser, which formats the page onto
your screen.
URL
| http J] WWNW.ISprs.org/ spe .html |
Path or
file name
Host or
server name
Protocol
Figure 3: An Internet address (or URL) subdivided in its main
parts.
This big network is design in a way that each information can
reach its destination using many different paths. When the
information is sent through the network, it is split into tiny
packets and each packet use a different path to reach its
destination. When all the packets reach the destination, they are
regrouped to form the original information. If one packet does
not reach the destination, the receiving site asks for another
copy of this packet. The routes covered by the Internet
information are not always the shortest ones, but usually the
fastest one (Figure 4).
Figure 4: A graphical trace-route of a Internet path covered
between a server in Switzerland and the server hosting ISPRS
Commission 7 in India. The request passes through US as faster
route compared to a Middle East route. Source: [VisualRoute].
2.3 Internet Domain
A domain is a name which identify a web site on the Internet.
Domain names have always two or more parts, separated by
dots, e.g. 'www.commissionS.isprs.org'. The part on the left is
the most specific ('commission5'), the part on the right the more
general ('isprs'. The extension .org identifies the kind of
domain and together with the previous generic part, they are
often called Top-Level Domains (TLD). There are two types of
top-level domains:
* Generic Top-Level Domains (gTLDs), created for use by the
Internet public. The most common generic TLD, available
since „1984; «are: COM: (Commercial), ....EDU
(Educational), .GOV (US Government), .INT (International
113
Organisations), .MIL (US Dept. of Defence), .NET
(Networks), .ORG (Organisations). On November 2000,
ICANN passed a resolution to add seven new generic top-
level domains. These new generic Top-Level Domains
(gTLDs) are: .BIZ (Business Organisations), .MUSEUM
(Museum Organisations), NAME (Personal), INFO (Open
TLD), .PRO (Professionals as Accountants, lawyers, and
physicians), .AERO (Air-transport industry), .COOP
(Cooperatives). These were activated in 2001 and 2002.
Four of them (.biz, .info, .name, and .pro) are unsponsored
while the other three (.aero, .coop, and .museum) are
sponsored.
* Country Code Top-Level Domains (ccTLDs), created to be
used by each individual country. The Country Code TLD
are designed to be assigned to each individual country:
it, .fr, .uk, jp, .ch, .co, .er, They almost follow the ISO
3166 standard that provides codes for the names of
countries and dependent areas, even if there are some
exceptions. The ISO codes EH (Western Sahara), KP
(North Korea), TL (East Timor), CS (Serbia and
Montenegro) and AX (Aland Islands), although
theoretically available as ccTLDs have never been assigned
and do not exist in DNS. On the other hand, eight ccTLDs
are currently in use despite not being ISO two-letter codes,
namely AC (Ascension Island), GG (Guernsey), IM (Isle of
Man), JE (Jersey), SU (Soviet Union), TP (East Timor),
UK (United Kingdom) and YU (Serbia and Montenegro).
As April 2004, there are 243 country code domains (see
[IANA] for an updated list). CcTLD managers, who are
also responsible for the operation of the domain, develop
the rules regarding who is entitled to domains the ccTLD.
But in some cases, anyone in the world can acquire a
domain in the ccTLD list, like in the case of Armenia
(AM), Austria (.AT) Cocos Islands (.CC), Germany (.DE),
Niue (.NU), Samoa (. WS), Tonga (.TO), Tuvalu (.TV) and
Turkmenistan (. TM). This allows domains names like I.am,
start.at and go.to.
In addition to gTLDs and ccTLDs, there is a special
TLD, .ARPA, which is used for technical infrastructure
purposes. ICANN administers this domain name in cooperation
with the Internet technical community under the guidance of
the Internet Architecture Board.
According to some Internet statistics, the maximum number of
characters in one component of a domain name is 63 while the
average number of characters in a domain name is 11.
2.4 Wired Internet Connection
The network allows all the computers to communicate with one
another and to send and receive data through a network of
transmission lines Tae 5).
Users + dish;
Figure 5: The Internet connection from a home or office
