Sunday, 26 June 2011

Web Terminologies Part 1

A global network connecting millions of computers.
World Wide Web (the Web)
An information sharing model that is built on top of the Internet,
utilizes HTTP protocol and browsers (such as Internet Explorer) to
access Web pages formatted in HTML that are linked via hyperlinks
and the Web is only a subset of the Internet (other uses of the
Internet include email (via SMTP), Usenet, instant messaging and
file transfer (via FTP)
URL (Uniform Resource Locator)
The address of documents and other content on the Web. It is
consisting of protocol, domain and the file. Protocol can be either
HTTP, FTP, Telnet, News etc., domain name is the DNS name of
the server and file can be Static HTML, DOC, Jpeg, etc., . In other
words URLs are strings that uniquely identify resources on internet.
TCP/IP protocol suite used to send data over the Internet. TCP/IP
consists of only 4 layers - Application layer, Transport layer,
Network layer & Link layer
Internet Protocols:
Application Layer - DNS, TLS/SSL, TFTP, FTP, HTTP, IMAP, IRC,
Transport Layer- TCP, UDP, DCCP, SCTP, IL, RUDP,
Network Layer - IP (IPv4, IPv6), ICMP, IGMP, ARP, RARP, …
Link Ethernet Layer- Wi-Fi, Token ring, PPP, SLIP, FDDI, ATM,
DTM, Frame Relay, SMDS,
TCP (Transmission Control Protocol)
Enables two devices to establish a connection and exchange data.
In the Internet protocol suite, TCP is the intermediate layer
between the Internet Protocol below it, and an application above it.
Applications often need reliable pipe-like connections to each other,
whereas the Internet Protocol does not provide such streams, but
rather only unreliable packets. TCP does the task of the transport
layer in the simplified OSI model of computer networks.
It is one of the core protocols of the Internet protocol suite. Using
TCP, applications on networked hosts can create connections to one
another, over which they can exchange data or packets. The
protocol guarantees reliable and in-order delivery of sender to
receiver data. TCP also distinguishes data for multiple, concurrent
applications (e.g. Web server and e-mail server) running on the
same host.
Specifies the format of data packets and the addressing protocol.
The Internet Protocol (IP) is a data-oriented protocol used for
communicating data across a packet-switched internet work. IP is a
network layer protocol in the internet protocol suite. Aspects of IP
are IP addressing and routing. Addressing refers to how end hosts
become assigned IP addresses. IP routing is performed by all hosts,
but most importantly by internetwork routers
IP Address
A unique number assigned to each connected device, often assigned
dynamically to users by an ISP on a session-by-session basis –
dynamic IP address. Increasingly becoming dedicated, particularly
with always-on broadband connections – static IP address.
A portion of a message sent over a TCP/IP Network. It contains
content and destination
HTTP (Hypertext Transfer Protocol)
Underlying protocol of the World Wide Web. Defines how messages
are formatted and transmitted over a TCP/IP network for Web
sites. Defines what actions Web servers and Web browsers take in
response to various commands.
HTTP is stateless. The advantage of a stateless protocol is that hosts
don't need to retain information about users between requests, but
this forces the use of alternative methods for maintaining users'
state, for example, when a host would like to customize content for
a user who has visited before. The common method for solving this
problem involves the use of sending and requesting cookies. Other
methods are session control, hidden variables, etc
example: when you enter a URL in your browser, an HTTP
command is sent to the Web server telling to fetch and transmit the
requested Web page
o HEAD: Asks for the response identical to the one that
would correspond to a GET request, but without the
response body. This is useful for retrieving metainformation
written in response headers, without
having to transport the entire content.
o GET : Requests a representation of the specified
resource. By far the most common method used on
the Web today.
o POST : Submits user data (e.g. from a HTML form) to
the identified resource. The data is included in the
body of the request.
o PUT: Uploads a representation of the specified
o DELETE: Deletes the specified resource (rarely
o TRACE: Echoes back the received request, so that a
client can see what intermediate servers are adding or
changing in the request.
o Returns the HTTP methods that the server supports.
This can be used to check the functionality of a web
o CONNECT: For use with a proxy that can change to
being an SSL tunnel.
HTTP pipelining
appeared in HTTP/1.1. It allows clients to send multiple requests at
once, without waiting for an answer. Servers can also send multiple
answers without closing their socket. This results in fewer
roundtrips and faster load times. This is particularly useful for
satellite Internet connections and other connections with high
latency as separate requests need not be made for each file. Since it
is possible to fit several HTTP requests in the same TCP packet,
HTTP pipelining allows fewer TCP packets to be sent over the
network, reducing network load. HTTP pipelining requires both the
client and the server to support it. Servers are required to support it
in order to be HTTP/1.1 compliant, although they are not required
to pipeline responses, just to accept pipelined requests.
technology allows users to perform various Internet tasks despite
the restrictions imposed by firewalls. This is made possible by
sending data through HTTP (port 80). Additionally, HTTP-Tunnel
technology is very secure, making it indispensable for both average
and business communications. The HTTP-Tunnel client is an
application that runs in your system tray acting as a SOCKS server,
managing all data transmissions between the computer and the
HTTP streaming
It is a mechanism for sending data from a Web server to a Web
browser in response to an event. HTTP Streaming is achieved
through several common mechanisms. In one such mechanism the
web server does not terminate the response to the client after data
has been served. This differs from the typical HTTP cycle in which
the response is closed immediately following data transmission.
The web server leaves the response open such that if an event is
received, it can immediately be sent to the client. Otherwise the
data would have to be queued until the client's next request is made
to the web server. The act of repeatedly queing and re-requesting
information is known as a Polling mechanism. Typical uses for
HTTP Streaming include market data distribution (stock tickers),
live chat/messaging systems, online betting and gaming, sport
results, monitoring consoles and Sensor network monitoring.
HTTP referrer
It signifies the webpage which linked to a new page on the Internet.
By checking the referer, the new page can see where the request
came from. Referer logging is used to allow websites and web
servers to identify where people are visiting them from, for
promotional or security purposes. Since the referer can easily be
spoofed (faked), however, it is of limited use in this regard except
on a casual basis. A dereferer is a means to strip the details of the
referring website from a link request so that the target website
cannot identify the page which was clicked on to originate a request.
Referer is a common misspelling of the word referrer. It is so
common, in fact that it made it into the official specification of
HTTP – the communication protocol of the World Wide Web – and
has therefore become the standard industry spelling when
discussing HTTP referers.

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