INTERNET
INFRASTRUCTURE
INTERNET PROTOCOL (IP)
Unlike
TCP, IP is an unreliable, connectionless protocol. IP doesn't care whether a
packet gets to it's destination or not. Nor does IP know about connections and
port numbers. IP's job is too send and route packets to other computers. IP packets
are independent entities and may arrive out of order or not at all. It is TCP's
job to make sure packets arrive and are in the correct order. About the only
thing IP has in common with TCP is the way it receives data and adds it's own
IP header information to the TCP data. The Internet Protocol (IP) is the
method or protocol by which data is sent from one computer to another on the internet.
Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other
computers on the Internet.
When you send or receive data (for example, an
e-mail note or a Web page), the message gets divided into little chunks called
packets. Each of these packets contains both the sender's Internet address and
the receiver's address. Any packet is
sent first to a gateway computer that understands a small part of the Internet.
The gateway computer reads the destination address and forwards the packet to
an adjacent gateway that in turn reads the destination address and so forth
across the Internet until one gateway recognizes the packet as belonging to a
computer within its immediate neighbourhood or domain. That gateway then
forwards the packet directly to the computer whose address is specified.
IP
add consists of 2 part:
1. Identifying the
network
2. Identifying the
node/host
Class of addresses determines which part belongs to
the network add & which part belongs to node. All nodes on a given network share the same network
prefix but must have a unique host number
Class A network
Binary add start with 0
therefore decimal number can be anywhere from 1 to 126. The first 8 bits (the
first octet) identify the network and the remaining 24 bits indicate the host
within the network. For example 102.168.212.226
Class B network
Binary add start with 10 =
decimal number can be anywhere from 128 to 191 . The number 127 is reserved for
loopback and is used for internal testing on the local machine). The first 16
bits (first 2 octet) = identify the network & the remaining 16 bit indicate
the host for example 168.212.226.204
Class C network
Binary add start with 110 =
decimal number can be anywhere from 192 to 223. The first 24 bits (first 3
octets) = identify the network for example 200.168.212.226
Class D network
Binary add start with 1110 =
decimal number can be anywhere from 224 to 239. Used to support multicasting.
Class
E network
Binary add start with 1111 = decimal number can
be anywhere from 240 to 225. Used for experimentation, never been documented or
utilized in a standard way.
Definition:
The DNS translates Internet domain and host names to IP addresses. DNS
automatically converts the names we type in our Web browser address bar to the
IP addresses of Web servers hosting those sites. DNS implements a distributed
database to store this name and address information for all public hosts on the
Internet. DNS assumes IP addresses do not change (are statically assigned
rather than dynamically assigned).
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 and
fault tolerant and has helped avoid the need for a single central register to
be continually consulted and updated. Additionally, the responsibility for
maintaining and updating the master record for the domains is spread among many
domain name registrars, who compete for the end-user's, domain-owner's,
business. Domains can be moved from registrar to registrar at any time.
INTERNET SERVICE PROVIDER
An Internet service provider (ISP) is an organization that
provides access to the internet. Short for Internet
Service Provider,
it refers to a company that provides Internet services, including personal and
business access to the internet. For a monthly fee, the service provider
usually provides a software package, username, password and access phone
number. Equipped with a modem, you can then log on to the Internet and browse the
World Wide Web and and USENET ,send and receive e-mail. For broadband access
you typically receive the broadband modem hardware or pay a monthly fee for
this equipment that is added to your ISP account billing.
Just as their customers pay them for Internet access, ISPs themselves pay
upstream ISPs for Internet access. An upstream ISP usually has a larger network
than the contracting ISP and/or is able to provide the contracting ISP with
access to parts of the Internet the contracting ISP by itself has no access to
One
of the most commonly used services on the Internet is the World Wide Web (WWW).
The application protocol that makes the web work is Hypertext Transfer Protocol
or HTTP. Do not confuse this with the Hypertext Markup Language (HTML). HTML is
the language used to write web pages. HTTP is the protocol that web browsers
and web servers use to communicate with each other over the Internet. It is an
application level protocol because it sits on top of the TCP layer in the
protocol stack and is used by specific applications to talk to one another. In
this case the applications are web browsers and web servers.
HTTP
is a connectionless text based protocol. Clients (web browsers) send requests
to web servers for web elements such as web pages and images. After the request
is serviced by a server, the connection between client and server across the
Internet is disconnected. A new connection must be made for each request. Most
protocols are connection oriented. This means that the two computers
communicating with each other keep the connection open over the Internet.
Application
Protocols: SMTP and Electronic Mail
Another commonly used Internet service is electronic
mail. E-mail uses an application level protocol called Simple Mail Transfer
Protocol or SMTP. SMTP is also a text based protocol, but unlike HTTP, SMTP is
connection oriented. SMTP is also more complicated than HTTP. There are many
more commands and considerations in SMTP than there are in HTTP.
Transmission Control Protocol
Under the application layer in the protocol stack
is the TCP layer. When applications open a connection to another computer on
the Internet, the messages they send (using a specific application layer
protocol) get passed down the stack to the TCP layer. TCP is responsible for
routing application protocols to the correct application on the destination
computer. To accomplish this, port numbers are used. Ports can be thought
of as separate channels on each computer. For example, you can surf the web
while reading e-mail. This is because these two applications (the web browser
and the mail client) used different port numbers. When a packet arrives at a
computer and makes its way up the protocol stack, the TCP layer decides which
application receives the packet based on a port number.
TCP works like this:
- When the TCP layer receives the application layer protocol data
from above, it segments it into manageable 'chunks' and then adds a TCP
header with specific TCP information to each 'chunk'. The information contained
in the TCP header includes the port number of the application the data
needs to be sent to.
- When the TCP layer receives a packet from the IP layer below it,
the TCP layer strips the TCP header data from the packet, does some data
reconstruction if necessary, and then sends the data to the correct
application using the port number taken from the TCP header.
