Computer Networks and Telecommunication

Prof. Rathnakar Acharya

a.rathnakar@gmail.com

91-9448871233

• Computer Network: It is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information.

• Data may be transmitted, via communications links, between remote locations and the computer.

• Collaboration of computer and telecommunication

• NEED AND SCOPE OF NETWORKS : – File Sharing

– Print Sharing

– E-Mail

– Fax Sharing

– Remote Access – VPN

– Shared Databases

– Fault Tolerance

– Internet Access and Security

– Communication and collaboration

• Benefits of using networks:

• improve communication• Staff, suppliers and customers are able to share information

and get in touch more easily

• More information sharing can make the business more efficient

• Organization can reduce costs and improve efficiency

• network administration can be centralized

• Organizations can reduce errors and improve consistency

• CLASSIFICATIONS OF NETWORKS

• Computer Networks can be classified in different ways like:

– Function Based,

– Area Coverage Based,

– Forwarding-based,

– Ownership-based and Media-based.

• Computer Networks Classification

• LAN

• MAN

• WAN

LAN

• Network that connects communication devices, or

computers within 2000 feet to share information.

• features of LAN: – Multiple user computers connected together

– Machines are spread over a small geographic region

– Communication channels between the machines are usually privately owned. Channels are relatively high capacity Mbps.

– Channels are relatively error free

Metropolitan Area Networks (MAN)

MANs are based on fiber optic transmission technology

• Provide high speed (10 Mbps )interconnection between sites.

• A MAN can support both data and voice.

Wide Area Networks (WAN):

• Features of WAN: – Multiple user computers connected together.

– Machines are spread over a wide geographical region

– Communications channels between the machines are usually furnished by a third party.

– Channels are of relatively low capacity

– Channels are relatively error-prone

Network Models• Client-Server – A form of distributed processing in

which several computers share the resources and are able to communicate with many other computers.

Peer-to-peer network

• Advantage: • Simplicity of design and maintenance. • No server, all nodes on the network are fully employed and

independent. • No single computer holds the control of entire networks.

• Limitations:• A failure of a node on a peer-to-peer network means that

the network can no longer access the applications or data on that node but other node can function properly.

• Lack of centralized control leads it is advisable to use less number of user system like 10 to 12 users.

• COMPONENTS OF A NETWORK:

• There are five basic components in any network :

1. The sender (Source Host)

2. The communications interface devices

3. The communications channel (Medium)

4. The receiver (Destination Host)

5. Communications software

Communication Interface Devices

• Network Interface Cards

• Characteristics of NICs include following:

• NIC construct, transmits, receives, and processes data to and from a host to network.

• Each NIC has a manufacturer provided 8 bytes permanent and unique MAC (media access control) address.

• This address is also known as physical address.

• The NIC requires drivers to operate

Switches and Routers

• Router: a communication processor that routs message through several connected LANs or to a WAN.

• Switch: is a computer networking device that that connects network segments or network devices.

• Hubs

• Bridges:

• The main task of a bridge computer is to receive and pass data from one LAN to another.

• In order to transmit this data successfully, the bridge magnifies the data transmission signal.

• Repeaters are devices that solve the snag of signal degradation which results as data is transmitted along the various cables.

• Repeater boosts or amplifies the signal before passing it through to the next section of cable.

• Gateways: Gateways are also similar to bridges in that they relay data from network to network.

• They translate data from one protocol to another.

• MODEM • MODEM stands for Modulator/Demodulator. In the simplest

form, it is an encoding as well as decoding device used in data transmission.

• It is a device that converts a digital signal into an analog telephone signal and converts an analog telephone signal into

a digital computer signal in a data communication system

• Communication channels

– Guided

– Unguided

Twisted pair cable (UTP)

• Communications Software: Communications software manages the flow of data across a network.

• Communications software is written to work with a wide variety of protocols, which are rules and procedures for exchanging data.– Access control

– Network management

– Data and file transmission

– Error detection and control

NETWORK STRUCTURE OR TOPOLOGY

• Star topology

• Advantages:– It is easy to add new and remove nodes.

– A node failure does not bring down the entire network

– It is easier to diagnose network problems through a central hub.

• Disadvantages:– If the central hub fails, the whole network ceases to

function.

– It costs more to cable a star configuration than other topologies.

• Bus topology

• Advantages: • Reliable in very small networks.

• Requires the least amount of cable to connect the computers together and therefore is less expensive.

• Is easy to extend.

• A repeater can also be used to extend a bus configuration.

• Disadvantages: – Heavy network traffic can slow a bus considerably.

– Individual user may use lot of bandwidth.

– Each connection between two cables weakens the electrical signal.

– Loss connection may disconnect the network

• Ring topology

• Advantages: • Ring networks offer high performance for a small number of

workstations or for larger networks where each station has a similar workload.

• Ring networks can span longer distances than other types of networks.

• Ring networks are easily extendable.

• Disadvantages: – Relatively expensive and difficult to install. – Failure of one computer on the network can affect the whole

network. – It is difficult to trouble shoot a ring network. – Adding or removing computers can disrupt the network

•

• Mesh Topology

• Advantages:

• Yields the greatest amount of redundancy in the event that one of the nodes fails where network traffic can be redirected to another node.

• Network problems are easier to diagnose.

• Disadvantages:

• The cost of installation and maintenance is high (more cable is required than any other configuration)

• Large number of network connections

TRANSMISSION TECHNOLOGIES

• Circuit Switching

– Network is one that establishes a fixed bandwidth circuit (or channel) between nodes and terminals before the users may communicate, as if the nodes were physically connected with an electrical circuit. In circuit-switching, this path is decided upon before the data transmission starts.

• Message Switching:

• The computer receives all transmitted data; stores it ; and, when an outgoing communication line is available, forwards it to the receiving point.

• Packet switching:

• Packet switching refers to protocols in which messages are broken up into small transmission units called packets

• TRANSMISSION PROTOCOLS

• Protocols are software that perform a variety of actions necessary for data transmission between computers.

• Protocols are a set of rules for inter-computer communication that have been agreed upon and implemented by many vendors, users and standards bodies.

• Network protocols which are essentially software are sets of rules for ;

• Communicating timings, sequencing, formatting, and error checking for data transmission.

• Providing standards for data communication

• A protocol defines the following three aspects of digital communication.

• (a) Syntax: The format of data being exchanged, character set used, type of error correction used, type of encoding scheme (e.g., signal levels ) being used.

• (b) Semantics: Type and order of messages used to ensure reliable and error free information transfer.

• (c) Timing: Defines data rate selection and correct timing for various events during data transfer. As stated earlier, communication protocols are rules established to govern the way the data are transmitted in a computer network.

• The Application Layer initiates or accepts a request from the user.

• The Presentation Layer adds formatting, displays and encrypts information to the packet.

• The Session Layer adds traffic flow information to determine when the packet gets sent or received. Transport Layer adds error handling information like CRC.

• The Network Layer does sequencing and adds address information in the packet.

• The data Link Layer adds error checking information and prepares the data for going on to the destination.

• Physical Layer

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• OSI Model

• It is an abstract description for layered communications and computer network protocol design.

• It was developed as part of the Open Systems Interconnection (OSI) initiative.

• It divides network architecture into seven layers; Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers.

• TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL;

• The protocols used on the Internet is called TCP/IP (transmission Control Protocol/Internet Protocol)

• A TCP/IP protocol which has two parts–

– TCP deals with exchange of sequential data

– IP handles packet forwarding and is used on the Internet

• TCI/IP has four layers• Application Layer which provides services directly the

users such as e-mail.

• Transport Layer which provides end-to-end communication between applications and verifies correct packet arrival.

• Internet Layer which provides packet routing for error checking and addressing and integrity.

• Network Interface Layer which provides an interface to the network hardware and device drivers. This can also be called the Data Link Layer.

• FTP is a file transfer protocol. It is a common mode of transferring between two internet sites. FTP is an application layer protocol

• Bandwidth

– Bandwidth is the difference between the highest and the lowest frequency that can be used to transmit data.

– It also represent the channel information carrying capacity

– It is mentioned in terms of bits per second (bps)

TCP/IP vs OSI

• Wireless LAN (WLAN)

• How wireless LANs Work?

• Wireless LANs use electromagnetic waves (radio or infrared) to communicate information from one point to another without relying on any physical connection.

• In a typical wireless LAN configuration, a transmitter/receiver (transceiver) device, called an access point.

• Connects to the wired network from a fixed location using standard cabling.

• CLIENT / SERVER TECHNOLOGY • The client/server model is a computing model that acts as

distributed application which partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients.

• Often clients and servers communicate over a computer network.

• A server machine is a host that is running one or more server programs which share their resources with clients.

• A client does not share any of its resources, but requests a server's content or service function.

• Clients therefore initiate communication sessions with servers which await incoming requests.

• Implementation examples of client / server technology:

• Online banking application

• Internal call centre application

• Applications for end-users that are stored in the server

• E-commerce online shopping page

• Intranet applications

• Financial, Inventory applications based on the client Server technology.

• Tele communication based on Internet technologies

• Benefits of the Client /Server Technology– Reduce the total cost of ownership. – Increased Productivity – End user productivity – Developer productivity – Reduces the hardware cost– It make the organization effectively and efficiently – Management control over the organization– Long term cost benefit– Can use multiple vendors software

• Client/Server Components • Client

• Server

• Middleware

• Fat-client or Fat-server

• Network:

• VIRTUAL PRIVATE NETWORK( VPN)

– A VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together.

– Instead of using a dedicated, real-world connection such as leased line, a VPN uses "virtual" connections routed through the Internet from the company's private network to the remote site or employee.

• Intranet-based - Company has one or more remote locations that they wish to join in a single private network, they can create an intranet VPN to connect LAN to LAN.

• Extranet-based - When a company has a close

relationship with another company (partner, supplier or customer), they can build an extranet VPN that connects LAN to LAN, and that allows all of the various companies to work in a shared environment. It is an extended Intranet.

• TYPES OF SERVERS

• Database servers

• Application Servers :

• An application server is a server program that resides in the server and provides the business logic for the application program.

• The server can be a part of the network, more precisely the part of the distributed network. – First Tier: Front End - Browser (Thin Client) - a GUI

interface lying at the client/workstation.

– Second Tier: Middle Tier - Application Server - set of application programs

– Third Tier: Back End - Database Server.

• Features of the Application Servers– Component Management: session management, and

synchronous/asynchronous client notifications, as well as executing server business logic

– Fault Tolerance

– Load Balancing

– Transaction Management. Management Console

– Security

• Categories of Application Server – Web Information Servers – to generate web pages

– Component Servers - database access and transaction processing services

– Active Application Server - server-side logic

– Print Servers

– Transaction Servers - MTS is all about managing the way applications use components, and not just about managing transactions

Explain caching server and proxy server 2009 5mk

• Types of Internet Servers File server• Mail server

• DNS server

• Gopher server

• Web server

• FTP server

• News server

• Chat server

• Caching server

• Proxy server

• DIFFERENT TIER ARCHITECTURES

• The Tier -A tier is a distinct part of hardware or software.

– Single Tier: A single computer that contains a database and a front end to access the database.

– Generally, this type of system is used in small businesses.

• Advantages:

• A single-tier system requires only one stand-alone computer. It also requires only one installation of proprietary software which makes it the most cost-effective system available.

• Disadvantages: • Can be used by only one user at a time. A single tier

system is impractical for an organization which requires two pr more users to interact with the organizational data stores at the same time.

• Two Tier systems: A two-tier system consists of a client an a server.

• The database is stored on the server, and the interface used to access the database is installed on the client.

• Two-tier architecture : A two tier application or architecture is a client server application where the processing load can fall either on the server or on the client.

• When the processing load falls on the client then the server simply acts as a controller between the data and the client.

• Such a client is called as a fat client and imposes a lot of memory and bandwidth on the client’s machine.

• The three components are

• 1. User system interface (such as session, text input, dialog, and display management services)

• 2. Processing Management (such as process development, process enactment, process monitoring, and process resource services)

• 3. Database /Management (such as data and file services)

• Advantages: • Since processing was shared between the client and

server, more users could interact with system.

• Disadvantages: • Performance deteriorates if number of users is

greater than 100. • Restricted flexibility and choice of DBMS, since data

language used in server is proprietary to each vendor.

• Limited functionality in moving program functionality across servers

• Three Tier The three-tier architecture overcome the limitations of the two-tier architecture.

• The third tier architecture (middle tier server) is between the user interface (client) and the data management (server) components.

• This middle tier provides process management where business logic and rules are executed and can accommodate hundreds of users by providing functions such as queuing, application execution, and database staging.

• Client-tier

• Application-server-tier

• Data-server-tier

• The advantages• 3-tier architecture solves a number of problems that

are inherent to 2-tier architectures.• Clear separation of user-interface-control and data

presentation from application-logic:• Client-applications are clear: quicker development

through the reuse of pre-built business-logic components and a shorter test phase, because the server-components have already been tested.

• Dynamic load balancing: If bottlenecks in terms of performance occur, the server process can be moved to other servers at runtime.

• Multi-tier

•

• Multi-tier architecture (often referred to as n-tier architecture) is a client-server architecture in which an application is executed by more than one distinct software agent.

• The most widespread use of "multi-tier architecture" refers to three-tier architecture

• The advantages of a multi-tier architecture are:

• Forced separation of UI and business logic.

• Low bandwidth network.

• Business logic sits on a small number (maybe just one) of centralized machines.

• Enforced separation of UI and business logic.

• WHAT IS A DATA CENTRE ?

• A data center is a centralized repository for the storage, management and dissemination of data and information.

• Data centers can be defined as highly secure, fault-resistant facilities, hosting customer equipment that connects to telecommunications networks.

• Often referred to as an Internet hotel/ server farm, data farm, data warehouse, corporate data center, Internet service provider (ISP) or wireless application service provider (WASP), the purpose of a data center is to provide space and bandwidth connectivity for servers in a reliable, secure and saleable environment.

• These data centers are also referred to as public data centers because they are open to customers.

• Captive, or enterprise data centers, are usually reserved for the sole and exclusive use of the parent company, but essentially serve the same purpose.

• These facilities can accommodate thousands of servers, switches, routers and racks, storage arrays and other associated telecom equipment.

• Facilities provided by data centers;

– housing websites,

– providing data serving and other services for companies.

Data center may contain a network operations center (NOC), which is a restricted access area containing automated systems that constantly monitor server activity, Web traffic, network performance and report even slight irregularities to engineers, so that they can spot potential problems before they happen.

• Types of data centers

• Public

• Private, Enterprise data center, or Captive

• Private Data Centre:

• A private data center (also called enterprise data centers) is managed by the organization’s own IT department.

• It provides the applications, storage, web-hosting, and e-business functions needed to maintain full operations.

• Public data centers:

• A public data center (also called internet data centers) provide services ranging from equipment collocation to managed web-hosting.

• Clients typically access their data and applications via the internet.

• Data centers can be classified in tiers,

• Tier 1 being the most basic and inexpensive,

– Does not necessarily need to have redundant power and cooling infrastructures.

– It only needs a lock for security and can tolerate upto 28.8 hours of downtime per year.

• Tier 4 being the most robust and costly. The more ‘mission critical’ an application is, the more redundancy, robustness and security are required for the data center.

• Redundant power and cooling, with multiple distribution paths that are active and fault tolerant.

• the facility must permit no more than 0.4 hours of downtime per year.

• Access should be controlled with biometric reader and single person entryways

• Which sectors use them? :

• Any large volume of data that needs to be centralized, monitored and managed centrally needs a data center.

• The need of data center depends on the size and criticality of data.

• Data centers are extremely capital-intensive facilities.

• What can they do? : Some of the value added services that a data center provides are:

• Database monitoring

• Web monitoring

• Backup and restore

• Intrusion detection system (IDS)

• Storage on demand

• Features of Data Centers:

– Size

– Data Security

– Availability of Data

– Electrical and power systems

• Security

• Physical security:

• ♦ Security guards

• ♦ Proximity card and PIN for door access

• ♦ Biometrics access and PIN for door access

• ♦ 24 x 365 CCTV surveillance and recording

• Data security:

• Perimeter security: This is to manage both internal and external threats. This consists of firewalls, intrusion detection and content inspections; host security; anti-virus and access control and administrative tools.

• Access management: This is for both applications and operating systems that host these critical applications.

• System monitoring and support

• Storage: Data centers offer more than just network storage solutions.

• ♦ Primary storage (SAN, NAS, DAS)

• ♦ Secondary storage (tape libraries)

• ♦ Tertiary storage (offline tape storage, such as DAT drives, and magneto-optical drives)

• Constituents of a Data Centre• ♦ Network connectivity with various levels of physical (optical fibre

and copper) and service• ♦ Dual DG sets and dual UPS • ♦ HVAC systems for temperature control • ♦ Fire extinguishing systems • ♦ Physical security systems: swipe card/ biometric entry systems,

CCTV, guards and so on. • ♦ Raised flooring • ♦ Network equipment • ♦ Network management software • ♦ ♦ Network security: segregating the public and private network,

installing firewalls and intrusion detection systems (IDS)

• Leveraging the best :

• Using both enterprise/captive and public data centers cost savings

• Provide value-added services

• One-stop solution provider and give them an end-to-end outsourcing experience.

• Challenges faced by the management

– Maintaining a skilled staff and the high infrastructure needed for daily data center operations

– Maximizing uptime and performance

– Technology selection

– Resource balancing

• Disaster recovery sites • Data centers need to be equipped with the

appropriate disaster recovery systems that minimize downtime for its customers.

• Downtime can be eliminated by having proper disaster recovery (DR) plans for mission-critical types of organizations.

• Cold site:• Warm site:• Hot site

• Business Continuity Planning (BCP)

• It is a documented description of action, resources, and procedures to be followed before, during and after an event, functions vital to continue business operations are recovered, operational in an acceptable time frame.

• Disaster events: -• There is a potential for significantly interrupt

normal business processing, • Business is associated with natural disasters like

earthquake, flood, tornadoes, thunderstorms, fire, etc.

• Disasters are disruptions causing the entire facility to be inoperative for a lengthy period of time

• Catastrophes are disruptions resulting from disruption of processing facility.

• Components of BCP

• (i) Define requirements based on business needs,

• (ii) Statements of critical resources needed,

• (iii) Detailed planning on use of critical resources,

• (iv) Defined responsibilities of trained personnel,

• (v) Written documentations and procedures cove all operations,

• (vi) Commitment to maintain plan to keep up with changes.

• Life Cycle of BCP: The development of a BCP manual can have five main phases.

• 1. Analysis • 2. Solution design • 3. Implementation • 4. Testing and

organization acceptance

• 5. Maintenance

• ANALYSIS: The analysis phase in the development of a BCP manual consists of an impact analysis, threat analysis, and impact scenarios with the resulting BCP plan requirement documentation.

• Impact analysis (Business Impact Analysis, BIA) • An impact analysis results in the differentiation between critical

(urgent) and non-critical (non-urgent) organization functions/ activities.

• For each critical (in scope) function, two values are then assigned: • • Recovery Point Objective (RPO)- the acceptable latency of data

that will be recovered • • Recovery Time Objective (RTO) - the acceptable amount of time

to restore the function

• The Recovery Point Objective must ensure that the Maximum Tolerable Data Loss for each activity is not exceeded.

• The Recovery Time Objective must ensure that the Maximum Tolerable Period of Disruption (MTPD) for each activity is not exceeded.

• The impact analysis results in the recovery requirements for each critical function. Recovery requirements consist of the following information:

• • The business requirements for recovery of the critical function, and/or

• • The technical requirements for recovery of the critical function

• Threat analysis

• Documenting potential threats is recommended to detail a specific disaster’s unique recovery steps.

• Some common threats include disease, earthquake, fire , flood, Cyber attack , bribery, hurricane , utility outage, terrorism .

• Recovery requirement documentation

• After the completion of the analysis phase, the business and technical plan requirements are documented in order to commence the implementation phase.

• A good asset management program can be of great assistance here and allow for quick identification of available and re-allocateableresources.

• For an office-based, IT intensive business, the plan requirements may cover the following elements: – The numbers of recovery methods and secondary location.

– The individuals involved in the recovery effort along with their contact and technical details.

– The applications and application data required from the secondary location desks for critical business functions.

– The manual and solutions

– The maximum outage allowed for the applications

– The peripheral requirements like printers, copier, fax machine, calculators, paper, pens etc.

SOLUTION DESIGN • The goal of the solution design phase is to

identify the most cost effective disaster recovery solutions.

• For IT applications, this is commonly expressed as:

• 1. The minimum application and application data requirements

• 2. The time frame in which the minimum application and application data must be available

• The solution phase determines: • The crisis management command structure • The location of a secondary work site (where necessary) • Telecommunication architecture between primary and

secondary work sites • Data replication methodology between primary and

secondary work sites • The application and software required at the secondary

work site, and • The type of physical data requirements at the secondary

work site.

• IMPLEMENTATION

• It is the execution of the design elements identified in the solution design phase.

• Work package testing may take place during the implementation of the solution, however; work package testing does not take the place of organizational testing.

• TESTING AND ORGANIZATIONAL ACCEPTANCE The purpose of testing is to achieve organizational acceptance.

• Testing may include:• Crisis command team call-out testing • Technical swing test from primary to secondary work

locations • Technical swing test from secondary to primary work

locations • Application test • Business process test • At minimum, testing is conducted on a biannual or annual

schedule.

• MAINTENANCE • Maintenance of a BCP manual is broken down into

three periodic activities. • The first activity is the confirmation of information in

the manual, roll out to ALL staff for awareness and specific training for individuals whose roles are identified as critical in response and recovery.

• The second activity is the testing and verification of technical solutions established for recovery operations.

• The third activity is the testing and verification of documented organization recovery procedures. A biannual or annual maintenance cycle is typical.

• Information update and testing • Some types of changes that should be identified and

updated in the manual include: • Staffing changes • Changes to important clients and their contact details • Changes to important vendors/suppliers and their contact

details • Departmental changes like new, closed or fundamentally

changed departments. • Changes in company investment portfolio and mission

statement • Changes in upstream/downstream supplier routes

• Testing and verification of technical solutions • As a part of ongoing maintenance, any specialized

technical deployments must be checked for functionality.

• Virus definition distribution • Application security and service patch

distribution • Hardware operability check • Application operability check • Data verification

• Testing and verification of organization recovery procedures

• As work processes change over time, the previously documented organizational recovery procedures may no longer be suitable. Some checks include:

• Are all work processes for critical functions documented? • Have the systems used in the execution of critical functions

changed? • Are the documented work checklists meaningful and

accurate for staff? • Do the documented work process recovery tasks and

supporting disaster recovery infrastructure allow staff to recover within the predetermined recovery time objective

• NETWORK SECURITY • Need for security: The basic objective for providing network

security is twofold: • To safeguard assets • To ensure and maintain the data integrity. • To establish the system resources that the users desire to employ • There are two types of systems security.

– Physical security is implemented to protect the physical systems assets of an organization like the personnel, hardware, facilities, supplies and documentation.

– Logical security is intended to control -(i) malicious and non-malicious threats to physical security and (ii) malicious threats to logical security itself.

• Level of Security: The task of a Security Administration in an organization is to conduct a security program which is a series of ongoing, regular and periodic review of

• controls exercised to ensure safeguarding of assets and maintenance of data integrity. Security programs involve following eight steps –

• Preparing project plan for enforcing security, • Assets identification, • Assets valuation, • Threats identification, • Threats probability of occurrence assessment,• Exposure analysis, • Controls adjustment, • Report generation outlining the levels of security to be

provided for individual systems, end user, etc.

• First outlining the objectives

• Second prepare an action plan

• Third step of valuation of Assets can pose a difficulty

• The fourth step in a security review is Threats Identification

• The fifth step in a security review is assessment or the probability of occurrence of threats over a given time period.

• The sixth step is the Exposures Analysis by first identifying the controls in the place, secondly assessing the reliability of the existing controls, thirdly evaluating the probability that a threat can be successful and lastly assessing the resulting loss if the threat is successful.

• The seventh step is the adjustment of controls which means whether over some time period any control can be designed, implemented and operated such that the cost of control is lower than the reduction in the expected losses.

• The reduction in the expected losses is the difference between expected losses with the (i) existing set of controls and (ii) improved set of controls.

• The last step is report generation documenting, the findings of the review and specially recommending new assets safeguarding techniques that should be implemented.

• IDS Components : The goal of intrusion detection is to monitor network assets to detect anomalous behavior and misuse.

• Network Intrusion Detection (NID) : Network intrusion detection deals with information passing on the wire between hosts. Typically referred to as "packet-sniffers," network intrusion detection devices intercept packets traveling along various communication mediums and protocols, usually TCP/IP.

• Host-based Intrusion Detection (HID): Host-based intrusion detection systems are designed to monitor, detect, and respond to user and system activity and attacks on a given host.

• Hybrid Intrusion Detection: Hybrid intrusion detection systems offer management of and alert notification from both network and host-based intrusion detection devices. Hybrid solutions provide the logical complement to NID and HID - central intrusion detection management.

• Network-Node Intrusion Detection (NNID) : Network-node intrusion detection was developed to work around the inherent flaws in traditional NID. Network-node pulls the packet-intercepting technology off of the wire and puts it on the host.

• With NNID, the "packet-sniffer" is positioned in such a way that it captures packets after they reach their final target, the destination host.

• The packet is then analyzed.

• Threats and Vulnerabilities The threats to the security of systems assets can be broadly divided into nine categories:

• (i) Fire • (ii) Water • (iii) Energy variations like voltage fluctuations, circuit

breakage, etc. • (iv) Structural damages • (v) Pollution • (vi) Intrusion like physical intrusion and eavesdropping

which can be eliminated / minimized by physical access controls, prevention of electromagnetic emission and providing the facilities with their proper locations / sites

• (vii) Viruses and Worms (being discussed in detail later on)

• (viii) Misuse of software, data and services which can be avoided by preparing an employees’ code of conduct and

• (ix) Hackers, the expected loss from whose activities can be mitigated only by robust logical access controls.

• The controls to guard against the virus are threefold –• Preventive controls like using only clean and licensed copies of

software files, cutting the use of pubic domain software / shareware, downloading files or software only from a reliable websites, implementing read-only access to software.

• Detective controls like regularly running antivirus software, undertaking file size comparison to observe whether the size of programs has changed, undertaking date / time comparisons to detect any unauthorized modifications.

• Corrective controls like maintaining a clean backup, having a recovery plan from virus infections, regularly running antivirus software (which is useful for both detection and removal of virus) Worms, unlike virus, exist as separate and independent programs and like virus, propagate their copies with benign or malignant intention using operating system as their medium of replication.

• Abuse of software, Data and Services can arise in the following ways:

• (i) Generalized software and proprietary databases of the organization are often copied and taken away without an authority, by the employees who may keep it for their own purposes or for handing it over to competitors,

• (ii) Organization fails to protect the privacy of the individuals who data are stored in it databases,

• (iii) Employees use system services for their own personal gains and activities,

• Techniques of Network security Firewalls : Access controls are common form of controls encountered in the boundary subsystem by restricting the use of system resources to authorize users, limiting the actions authorized users can take with these resources and ensuring that the users obtain only authentic system resources.

• Current systems are designed to allow users to share their resources. This is done by having a single system simulate the operations of several systems, where each of the simulated system works as virtual machine allowing more efficient use of resources by lowering the idle capacity of the real system.

• Firewall is a device that forms a barrier between a secure and an open environment when the latter environment is usually considered hostile, for example the Internet. It acts as a system or combination of systems that enforces a boundary between more that one networks.

SAN vs NAS

• Storage area network is a dedicated centrally managed secure information infrastructure

• Resource management is centralized and simplified

• It increases the overall efficiency

• Network attached storage is dedicated server for file sharing

• It is a single purpose stand alone high performance computer

• Its failure will hall the entire work