Introduction to Network

Definition

A computing network is a computing environment with more than one independent processors
May be multiple users per system
Distance between computing systems is not considered (a communications media problem)
Size of computing systems is not relevant

Network resources

• Computers
• Operating system
• Programs
• Processes
• People

What is a network can provide?

• Logical interface function
• Sending messages
• Receiving messages
• Executing program
• Obtaining status information
• Obtaining status information on other network users and their status

Terminology

-Node
Single computing system in a network.
-Host
A single computing system's processor.
-Link
A connection between two hosts.
-Topology
The pattern of links in a network.

Bus Topology

To provide a single communication network on which any node can place information and from which any code can retrieve information
Attachments to the bus do not impact the other nodes on the bus

Star Topology

Has a central switch
All nodes wishing to communicate do so through the central host
The central host receives all messages, identifies the addresses, selects the link appropriate for that addresses and forwards the messages

Ring Topology

To connect a sequence of nodes in a loop or ring
Can be implemented with minimum cabling
Containing a token can control a “synchronous” loop

Mesh Topology
Each node can conceptually be connected directly to each other node
Has integrity and routing advantages
Not easily subject to destructive failures
Routing logic can be used to select the most efficient route through multiple nodes

ISO Reference Model

• Open Systems Interconnection (OSI)
• Describes computer network communications.
• Developed by the International Standards Organization (ISO).
• Consists of Seven Layers.
• Model describes peer-to-peer correspondence, relationship between corresponding layers of sender and receiver.
• Each layer represents a different activity performed in the actual transmission of a message.
• Each layer serves a separate function.
• Equivalent layers perform similar functions for sender and receiver.

Networks as Systems

• Single System
• Single set of security policies associated with each computing system.
• Each system concerned with:
• integrity of data
• secrecy of data
• availability of service
• Operating system enforces its owns security policies.

Advantages of Computing Networks

• Resource sharing
• Reduces maintenance and storage costs.
• Increased reliability (i.e. availability of service)
• If one system fails users can shift to another.
• Distributing the workload
• Workload can be shifted from a heavily loaded system to an underutilized one.
• Expandability
• System is easily expanded by adding new nodes

Who cause security problem

• Hacker
• Spy
• Student
• Businessman
• Ex-employee
• Stockbroker
• Terrorist
• etc

Network security problem area

+Authentication
Deals with determining whom you are talking to before entering into a business deal or before revealing sensitive information
+Secrecy
What usually comes to mind when people think about network security
+Non-repudiation
Deals with signature
+Integrity control
Keeping information is not modified, add or delete by unauthorized user