(a) Fire Wall

It is the first line of defense for any computer system or network. All packets that enter the network should come though this point. A modern firewall is a system of applications and hardware working together. A sophisticated firewall performs a combination of packet filtering  network address translation and proxy services. FIrewalls have two general methods of implementing security for a network .Firewall have two general methods of implementing security for a network and are explained below

1 Packet filtering:

Packet filering were designed to look at header information of the packet. packet filtering, the first type of firewall used by many organizatin to protect their network. The general method of implementing a packet filter was to use a router

2 proxy servers: 

Proxy servers use software to imtercept network traffic that is destined for  a given application. The proxy server, recognizes the request and behalf of the client makes the request to external server. Instead, the proxy functions as middleman and speaks to both the client and server

(B) packet Switching:

·           Packet switching combines the advantages of message and circuit switching.

·         Packet switching is functionally similar to message switching, in which data is transmitted in block, stored by the first switching node it meets in the network and is forwarded to the next and subsequent downstream nodes until it reaches the destination.

·         The message is fragmented in small fixed size packets in packet switching network. Typical lengh of packets is between 1 kilobyers to 4 kilobytes

·         In virtual circuit approach, a fixed logical path though the network from the sender to the receiver is established befor any packets are sent. This path remains unchanged for the duration of the sesseion.

(c) Unguided  Transmission media

which does not guide along a physical path e.g. propagation through air, water or vacuum.

Twisted pair cable

Physical description:

·         consist of two insulated copper wires arranged in a regular spiral pattern, acts as a single communication link

·         bundled together into a cable by wrapping them in tough protective sheath.

·         The twisting tends to decrease the cross- talk interfarenes between adjacent pair in a cable. the twist lengh varies from 2 to6 per inch.

·         Thickness is 0.016 inch to 0.036 inch.

Application

·         Used for both analog and digital signals.

·         Used in telephone network.

·         Used in local area networks.

·         It is widely used due to easy handling and teast expensive.

(d) Multi threading

Multitherading is a popular technology that is used to improve application performace throgh parallel execution of multiple threads. A thread is alight weight process

(1) repeater

 Repeaters: repeters also called regenerator, are physical hardware device. They connet two network segments and broadcast packets between them they have the primary function to regenerate the electrical signal:

·         Reshaping the wavefrom

·         Amplifying the waveform

·         Retiming the singnal, to avoid collision on the network

As signal travels along a cable, its strength or amplitude decreases. This is called attenuation. In other words, the signal attenuates as it travels along  a cable. This limits the length of a cable used to connect the computers together. Since singnal is a factor in the maximum length of a segment, repeater can cable length. A repeater has intelligence so that it takes a weak signal from one cable segment, regenerates it and passes it on to the next segment. The repeater does not amplift the original signal, it regenrates the original bit pattern.

(2) Hub

Hubs can also be called either MUlti port Tepeaters or concentrators. They are physical hardware devices. A hub is similar to a repeater, except that it broadcasts data received by any port to all other ports on the hub. Intelligent Hubs can perform basic diagnostics, and test the nodes to see if they are operating correctly. If they are not, the samrt hubs(or Intelligents Hubs) will remove the node form the network. Hubs are used to provide a physical star Topology the logical Topology is dependent on the medium Access control Protocol.

(3) Bridge

A bridge sends the data frames only to the concerned segment, thus preventing excess traffic. A bridge can split an overloaded network into two separate network, reducing the amount to traffic on each segment and thus making each network more efficient. Bridges can also be used to connect dissimilar networks like Ethernet system to a Token Ring system. Bridges are both hardware and software devices.

(4) Router

A router can connect network that use different technologies, addressing methods, media type, frame formats and speeds. A router keeps track of the address of all the segment of a network and can even determine the best path for sending data. Routers do not pass broadcast traffic.

(5) Gateway

A gateway is the Hardware software that is used to interconnect LANs and WANs. Gateway are much more complex and powerful than a router. They are slower than a router and are expensive. A grateway incorporates the functions of routers and bridges, but it can translate instruction set on sending network into corresponding instruction set of the receiving network.

(1)cAT[OPTIONS] FILE  -  concatenate (list) a file

(2) diff [option] file1 file2  - compare the two files and display the differnces (text files only)

(3) sort [option] file  -  read commands form the file and execute them in the current shell. source: C shell, :Bpurne charc

(4)cmp[option] file1 file2  -  compress file and save it as file.Z

(1) DNS architecture

Name SERVERS are server programs, which hold information about the domain tree's structure and set information. A name server may cache structure or set information about any part of the domain tree, but in general a particular name name server has complete information about a subset of the domain space and pointers to other name servers that can be used to lead to information from any part of the domain tree

(2) DNS Zones

The zone, as indicated in the figure on the next page, is a subtree of the DNS that is administered separately. A name server can support multiple zones. Zones are contiguous regions of the name space, where each can be forked into sub zones. Each of these sub zones can have its independent management.

·         To provide an enviroment for a computer user to execute programs on computer hardware in a convenient and efficient manner.

·         To allocate the separate resources of the computer as needed to solve the problem given. The allocation process should be as fair and efficient as prossible

Following are the characteristics:

Open graphics library(Open GL):  Cross-platform standard specification for multimedia graphics.

Direct X:  collection of APIs related to multimedia tasks for microsoft Windows.

Command Line Interface(CLI):  The user types commands at a prompt.

Graphical User Interface (GUI):  The user interacts with menus and icons.

Control Hardware Access:  The operating system manages the interaction between application and the hardware. To access and communicate with the hardware, the operating system intalls a device driver for each hardware component.

Trusted computer system evaluation criteria is a united states government Department of Defense standard that sets basic requirement for assessing the effectiveness of computer security controls built into a computer system. The TCSEC was used to evalute, classify and select computer system being considered for the processing, storage and retrieval or classified information.

Divisions and classes:

The TCSEC defines four divisions: D,C,B and A where division A has the highest security. Each division represents a significant difference in the trust an individual or organization can place on the evaluated system. Additionally divisions C, B and A are broken into a series of hierarchical subdivisions called classes: C1, C2, B1,B2, B3 and A1.

Each division and class expands or modifies as indicated the requirements of the immediately prior higher division.

The memory management subsystem is one of the most important parts of the operating system. The memory management subsystem includes:

Protection: Each process in th system has its own virtual address space. These virtual address space are compeletly separate from each other and so a process running one application cannot affect another.

large address space:  The operating system makes the system appear as  if it has a larger amount of memory than it actually has. The virtual memory can be many times larger than the physical memory the physical memory in the system.

Memory mapping: Memory mapping is used to map image and data files into a processes address space. In memory mapping, the contents of a file are linked directly into the virtual address space of a process.

Fair Physical memory allocation:  The memory management subsystem allows each running process in the system a fair share of the physical memory of the system.

Shared virtual memory:  There could be several processes in the system running concurrently and simultaneously depending upon the number of processors residing in the system but might be using the common file.

(1) Trust Relationships and Work Groups

Trust Relationships: Trust relationship refers to a line between two domains, where one domain is referred to as the trusting domain and other the trusted domain. Trusting domain lets the trusted domain logon. User accounts and groups that are defined for a trusted domain can access trusting domain resource even though those accounts are not present in trusting domain directory database.
Work Group: A distinctive name network resource can be referred to as an object. Similar objects can be grouped into workgroup e.g. printer, scanner etc.

2) Remote Access

Windows 2000 support two kinds of remote access connection metthod:

1. VPN (virtual private network) remote access
2. Dial up remote access

with dial up remote access: A remote access client uses telecommunication infrastructure to crate a temporary physical structure to create a temporary network or a virtual network.

A dial up Remote Access Connection consist of:

1.  Remote access server
2.  WAN infrastructure
3.  Remote access server

with VPN remote access: VPNprovides a secure network connection between two remote machines. remote access of a VPN client uses an IP network to create virtual point-to point connection with a RAS server acting as a VPN server.

(3) ip sec 276

Ip sec is a framework for ensuring secure private coomunication over Ip network. Ip sec provides security for transmission of critical and sensitive information over unprotected security for transmission of critical and sensitive information over unprotected network such as the Internet. IPSec VPNs use the services defined within IPSec to ensure confidentiality, Integrity and authenticty of data communications over the public network, like internet. IPSec operates at the network layer protecting and authenticating IP packets between participating IPSec devices.

Anti Reply: The IPSec receive can detect and reject replayed packet.

Data Origin Authentication: The IPSec receiver can authenticate the source of the IPSec packets sent. This service is dependent upon the data integrity service.

Data confidentiality: The IPSec sender can encrypt packets before transmitting them across a network.

Data integrity: The receiver can authenticate packets sent by the IPSec sender to ensure that the data has not been altered during transmission.

(4) user mode:

User Mode is responsible for providing insulation of end users from kernel mode. Windows 2000 user mode API subsystems are responsible for execution for different supporting system applications like win32 and POSIX. These subsystems have their own API’s (Application Programming Interface) System data and hardware is accessible to kernel mode layer of Windows2000. Operating system itself runs in the kernel mode. Environment subsystems run in user mode. The lowest two layers nearest to the hardware use the kernel and Hardware Abstraction Layer (HAL) that is written in C and assembly language. Upper layers are written in C and are machine independent layers. Most of the drivers in Windows2000 are written in C or C++.