Friday, 25 November 2011

CABLING


COPPER-BASED CABLES
They are quite commonly used for connecting computers. They have two main types –
coaxial and twisted pair. In twisted pair there are two further options – unshielded twisted
pair (UTP) and Shielded Twisted Pair (STP).


FIBER-OPTIC CABLES

They are used on the internet. They deliver data at a very high speed. They use glass or
plastic filaments and the pulses of light as a data transfer method.



TELEPHONE AND ELECTRICAL WIRE NETWORKS





WIRELESS OPTIONS
Wireless options include radio connectivity (wi fi, bluetooth), infrared connectivity and
Satellite microwave transmissions.




ROUTERS


Routers use a combination of hardware and software to forward data packets to their
destination on the internet. They are more efficient and sophisticated than bridges and
switches. They can divide large networks into logical segments called Subnets on the basis of
IP addressing scheme. A router can communicate with another router on the internet with
the help of Routing Information Protocol, and thus it can build a routing table. This routing
table contains information about different network addresses and different routes for
delivery of data packets to a host machine on a network. A router is a decision making
device. When a data packet arrives at a router it reads the network addresses from the IP
address on the data packet and determines the shortest possible path through which this
packet can be delivered to its destination.

SWITCHES


A switch is also a combination of hardware and software having its own operating system.
Like bridges, the switches are also used to increase the bandwidth of a network. However, in
case of a switch, a network is virtually divided into small segments called Virtual LANs or
VLANs. Similar type of users can be grouped into a VLAN despite that they have no
physical proximity or closeness. A switch would read the MAC address on a data packet and

match it with the list of MAC addresses of the user machines contained in it. It then sends
data packets only to that machine on a VLAN to which these packets relate. Packets
belonging to other VLANs are not allowed to enter into a particular VLAN, hence
bandwidth increases.


BRIDGES


A Bridge is a combination of hardware and software. It has its own operating system. It
helps to conserve the bandwidth of a network. Bandwidth is the speed of a network. It
indicates how many bits can be transmitted across a network in a given time. In case of a
bridge, the larger network is physically chopped into smaller segments. A bridge can read the
MAC (Media Access Control) or physical address of a computer on data packets. MAC
address is printed on the Network Interface Card. A bridge matches this MAC address with
the one stored in its table and judges that which particular segment does a data packet
belong to and accordingly sends that packet to such a segment. It does not allow other
packets belonging to other segments to spread to a particular segment and hence conserves
the bandwidth.


INTERNET LAYERS TCP/IP STACK


Internet communication model (TCP/IP Stack) proposes a 4 layer architecture. Following
are the names of internet layers that map with the OSI model’s layers:


- Application layer is equivalent to OSI model’s Application, Presentation and Session layers
- Host-to-Host Layer is equivalent to OSI model’s Transport layer
- Internet layer is equivalent to OSI model’s Network layer
- Network Access layer is equivalent to OSI model’s data link layer





Thursday, 24 November 2011

Proxy Server


A proxy server sits between an internal trusted network and the untrusted network.



                                                                                                      
Mainly three thing to do by Proxy Server.                
(i)              An http request from the browser goes to proxy server.
(ii)            It can also act as a firewall filtering requests for certain web pages.
(iii)          An important job it can do is to speed up the processing of http requests by caching web pages.

Firewall


Firewall:-
          A firewall is a combination of hardware and software that sits between the internet and internal network of an organization to protect the network form outside attack.


Types of firewall:-
                      There are three main types of firewall.

(i)              Packet filter firewall
(ii)            Circuit level firewall
(iii)           Application gateway firewall.


(i)              Packet filter firewall:
It is set of rules to determine whether outgoing or incoming data packets are allowed to pass through the firewall.
(ii)            Circuit level firewall:
It is quite similar to the packet filter firewall. It also works on the basis of a set of rules for filtering packets but operates at the transport layer of the OSI Model so has greater functionality.
(iii)          Application gateway firewall:
It operates at application layer of OSI Model. It uses string user authentication to verify identity of a host attempting to connect to the network using application layer protocols such as FTP.