19-11-2012, 06:04 PM
Computer, Internet and Network Systems Security
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0Introduction
Basic Internet Technical Details
The Internet utilizes a set of networking protocols called TCP/IP. The applications
protocols that can be used with TCP/IP are described in a set of Internet
Engineering Task Force (IETF) RFCs (Request For Comment). These documents
describe the "standard" protocols and applications that have been developed to
support these protocols. Protocols provide a standard method for passing
messages. They define the message formats and how to handle error conditions.
Protocols are independent of vendor network hardware, this allows communication
between various networks with different hardware as long as they communicate
(understand) the same protocol. The following diagram provides a conceptual
layering diagram of the protocols.
IP : Transmission Control Protocol/Internet Protocol
TCP/IP is used to facilitate communication within a network of diverse hardware
technology. Information is broken into packets (usually in the range of 1-1500
characters long) to prevent monopolizing of the network. TCP is a transport level
protocol which allows a process on one computer to send data to a process on
another computer. It is a connection oriented
protocol which means that a path must be
established between the two computers. IP
defines the datagram, the format of the data
being transferred throughout the network and
performs connectionless delivery.
Connectionless delivery requires each
datagram to contain the source and destination
address and each datagram is processed
separately. TCP takes the information, and
breaks it into pieces called packets, numbers
the packets, and then sends them.
The receiving computer collects the packets,
takes out the data and puts them in the proper
order. If something is missing, the receiving
computer asks the sender to retransmit. The packet sent also contains a checksum
which is used to find errors that may have occurred during transmission. If the
receiving computer notices that an error has occurred when it computes and
compares the checksum, it throws that packet away and asks for a retransmission.
Once everything is received, the data is passed to the proper application (e.g. email).
User Datagram Protocol
The UDP has less overhead and is simpler than TCP. The concept is basically the
same except that UDP is not concerned about lost packets or keeping things in
order. It is used for short messages. If it does not receive a response, it just resends
the request. Thjs type of protocol transfer method is called a “connectionless
protocol.”
Types of Connections and Connectors
There are two types of computer hosts connected to the Internet: server hosts and
client hosts. The server host can be described as an “information provider”. This
type of host contains some type of resource or data which is available to other hosts
on the Internet. The second type of host connected to the Internet is the client host
which can be described as an “information retriever”. The client host will access
resources and data located on the server hosts, but usually will not provide any
resources back to the server host.
Both server and client host computers can be connected to the Internet by various
methods that offer different communication capabilities dependent on varied
communications surcharges.
Direct Internet Connections: A computer connected directly to the Internet via a
network interface will allow the user the highest internetwork functionality. Each
computer connected in this manner must also have a unique Internet (IP) address.
This type of connection is also the most expensive.
Serial Internet Connections: Another type of connection offering most
communications capabilities is a SLIP (Serial Line Internet Protocol) or PPP (Point
to Point Protocol) connection. These two connection schemes offer similar services:
full network and application capability over a serial (modem) line. Since this
connection offers full TCP/IP and ICMP functionality each computer configured in
this manner requires its own IP address. This type of connection is an on-demand
service, at slower speeds, that therefore reduces communications charges, however
all TCP/IP and Internet vulnerabilities remain when the connection is "live".