Internet Security Management Concepts / इंटरनेट सुरक्षा और साइबर क्राइम

Internet Security (इंटरनेट सुरक्षा) और  साइबर क्राइम  (Cyber Crime) 

Internet Security Management Concepts

यह ऐसा कार्य है जो गैर कानूनी है, तथा जिसमें सूचना तकनीक या कंप्यूटर/Internet का उपयोग किया जाता है| आधुनिक युग में बहुत से गैरकानूनी काम या अपराध करने के लिए कंप्यूटर का प्रयोग किया जाता है, जैसे data चोरी online धोखाधड़ी जालसाजी आदि| सूचना तकनीकी प्रगति ने अपराधिक गतिविधियों के लिए नई संभावनाएं भी बनाए हैं, इस प्रकार के अपराधों से निपटने के लिए साइबर लॉ बनाया गया है| साइबर क्राइम को दो तरीकों में बांटा जा सकता है।
साइबर क्राइम के अंतर्गत आते हैं:

• Unauthorized access of computer/network and Hacking
• Data data Theft (डाटा चोरी करना)
• Identity theft (पहचान चुराना)
• Virus Trojan or worms attack (कंप्यूटर वायरस)

Unauthorized access of computer/network and hacking

किसी भी कंप्यूटर या कंप्यूटर नेटवर्क में बिना अनुमति के प्रवेश करने को unauthorized access यह hacking कहा जाता है। अनाधिकृत व्यक्ति द्वारा कंप्यूटर नेटवर्क में किया गया कोई भी कार्य इस अपराध की श्रेणी में आता है। जो व्यक्ति किसी नेटवर्क में अनाधिकृत तरीके से प्रवेश करता है उसे हैकर कहा जाता है। हैकर ऐसे प्रोग्राम बनाते हैं जो वांछित नेटवर्क पर आक्रमण कर सकें। इस प्रकार की कार्य साधारणता वित्तीय अपराधों में बहुताय होते हैं। जैसे किसी बैंक के नेटवर्क में अनाधिकृत तरीके से प्रवेश कर उनके खाताधारकों के अकाउंट से दूसरे अकाउंट में पैसे स्थानांतरित करना।
किसी व्यक्ति के क्रेडिट कार्ड की जानकारी चुरा कर उसका दुरूपयोग करना आदि।
किसी वेबसाइट के घटक अनाधिकृत तरीके से बदलने की क्रिया को web हैकिंग कहा जाता है।
भारत देश में हैकिंग क्रिया को गैरकानूनी माना जाता है तथा इनफार्मेशन टेक्नोलॉजी एक्ट 2008 के अंतर्गत 3 साल तक सजा एवं जुर्माने का प्रावधान है।

Data data theft (डाटा चोरी करना)

किसी संस्था या व्यक्ति या कंप्यूटर नेटवर्क में अधिकृत व्यक्ति के अनुमति लिए बिना उसके कंप्यूटर के डाटा को कॉपी करना उसे शेयर करना डाटा चोरी के अपराध की श्रेणी में आता है। किसी अनाधिकृत व्यक्ति द्वारा किसी अन्य व्यक्ति या संस्था की अनुमति के बिना डेटा कॉपी करना गैरकानूनी माना जाता है। वर्तमान में बहुत से छोटे स्टोरेज डिवाइस जैसे पेन ड्राइव मेमोरी कार्ड आसानी से उपलब्ध है, इन डिवाइस की सहायता से डाटा चुराना बहुत आसान हो गया है| इसमें आईटी एक्ट 2008 के अंतर्गत सजा का प्रावधान है।

Identity theft (पहचान चुराना)

किसी अन्य व्यक्ति की पहचान चुराकर कंप्यूटर नेटवर्क पर कार्य करना इस अपराध श्रेणी में आता है|
कंप्यूटर नेटवर्क पर स्वयं की पहचान बचा कर स्वयं को दूसरे के नाम से प्रस्तुत करना, उसके नाम पर कोई घपला कर ना, बेवकूफ बनाना आईटी एक्ट के अंतर्गत अपराध है|
इसके अतिरिक्त किसी अन्य व्यक्ति का पासवर्ड का प्रयोग करना,
डिजिटल सिग्नेचर की नकल करना भी इस अपराध की श्रेणी में आते हैं|
किसी अन्य के नाम का प्रयोग कर अवांछित लाभ लेना धोखाधड़ी करना भी इस प्रकार के अपराध में आते हैं|
जिस व्यक्ति की पहचान चुराई गई है उस से अनावश्यक रुप से कानूनी उलझनों का सामना करना पड़ता है, बहुत बड़ा नुकसान भी हो सकता है| उदाहरण के लिए आपके बैंक अकाउंट को कोई अन्य व्यक्ति आपकी पहचान चुराकर प्रयोग कर रहा है| आपकी पहचान चुरा कर दूसरी जगह धोखा धड़ी के लिए प्रयोग कर रहा है, इसलिए कंप्यूटर नेटवर्क पर अपने पासवर्ड व्यक्तिगत जानकारियां सार्वजनिक ना करें|आईटी एक्ट 2008 सेक्शन 66 सी के अंतर्गत सजा का प्रावधान है|

Virus Trojan or worms attack (कंप्यूटर वायरस)

जो प्रोग्राम किसी कंप्यूटर यह कंप्यूटर नेटवर्क की अनुमति के बिना कंप्यूटर में प्रवेश कर लेते हैं उन्हें कंप्यूटर वायरस की श्रेणी में डाला जाता है| साधारणता वायरस या वोर्म (Worm) प्रोग्राम का काम किसी अन्य के कंप्यूटर के डाटा को खराब /Delete/Edit करना है| इसीलिए कोई व्यक्ति या संस्था किसी ऐसे प्रोग्राम को अनावश्यक रुप से फैलाते हैं तो उन्हें इस अपराध की श्रेणी में रखा जाता है| बहुत से बड़े नेटवर्क को यदि वायरस प्रभावित करें तब बहुत बड़ा नुकसान हो सकता है| उदाहरण के लिए किसी विमान सेवा के कंप्यूटर में वायरस ने डाटा को बदल दिया है तब कोई प्लेन दुर्घटनाग्रस्त हो सकता है| यद्यपि सभी बड़े कंप्यूटर नेटवर्क में वायरस से कंप्यूटर को बचाने की प्रणाली होती है| भारतीय आईटी एक्ट 2008 के सेक्शन 43 (C) एवं 43 (e) के अंतर्गत वायरस फैलाने के कार्य के लिए सजा का प्रावधान है| Trojan उस प्रोग्राम को कहा जाता है जो दिखते तो उपयोगी हैं, लेकिन उनका कार्य कंप्यूटर कंप्यूटर नेटवर्क को नुकसान पहुंचाना होता है|

साइबर क्राइम के कुछ अन्य उदाहरण हैं –

• नेटवर्क का अनधिकृत तौर पर प्रयोग करना
• कंप्यूटर तथा नेटवर्क का प्रयोग कर व्यक्तिगत (Private) तथा गुप्त (Confidential) सूचना प्राप्त करना
• नेटवर्क तथा सूचना को नुकसान पहुंचाना
• बड़ी संख्या में ई – मेल भेजना (E – Mail Bombing)
• वायरस द्वारा कम्प्यूटर तथा डाटा को नुकसान पहुंचाना
• इंटरनेट का उपयोग कर आर्थिक अपराध (Financial Fraud) करना
• इंटरनेट पर गैरकानूनी तथा असामाजिक तथ्यों तथा चित्रों को प्रदर्शित करना

साइबर अपराध से बचने के उपाय (Ways To Prevent Cyber Crime)

• Login ID तथा पासवर्ड सुरक्षित रखना तथा समय – समय पर इसे परिवर्तित करते रहना
• Antivirus साफ्टवेयर का प्रयोग करना
• Fire wall का प्रयोग करना
• Data Backup रखना
• Proxy Server का प्रयोग करना
• Data को गुप्त कोड (Encrypted Form) में बदलकर भेजना व प्राप्त करना

Internet Security (इंटरनेट सुरक्षा)

इंटरनेट सुरक्षा का अर्थ है – नेटवर्क तथा नेटवर्क पर उपलब्ध सूचना, डाटा या सॉफ्टवेयर को अनधिकृत व्यक्तियों (Unauthorized persons) की पहुंच से दूर रखना तथा केवल विश्वसनीय उपयोगकर्ताओं द्वारा ही इनका उपयोग सुनिश्चित करना।
इंटरनेट सुरक्षा के मुख्यत: तीन आधार हैं –
• Authentication
• Access Control
• Cryptography

उपयोगकर्ता के प्रामाणिकता की जांच करना (Authentication) 

उपयोगकर्ता के प्रामाणिकता की जांच Login ID, Password/fingerprint/iris, गुप्त कोड आदि द्वारा की जाती हैं।

एक्सेस कंट्रोल (Access Control) 

कुछ विशेष डाटा या सूचना की उपलब्धता, कुछ विशेष उपयोगकर्ताओं के लिए ही सुनिश्चित करना एक्सेस कंट्रोल कहलाता हैं। अंगुलियों के निशान (Finger Print) आवाज की पहचान (Voice Recognition) इलेक्ट्रानिक कार्ड आदि द्वारा ऐसा किया जाता हैं।

क्रिप्टोग्राफी (Cryptography)

सूचना या डाटा को इंटरनेट पर भेजने से पहले उसे गुप्त कोड में परिवर्तित करना तथा प्राप्तकर्ता द्वारा उसे प्रयोग से पूर्व पुन: सामान्य सूचना में परिवर्तित करना क्रिप्टोग्राफी कहलाता हैं। यह इंटरनेट पर डाटा सुरक्षा का एक महत्वपूर्ण आधार है। सूचना या डाटा को गुप्त संदेशों में बदलने की प्रक्रिया Encryption कहलाती हैं। जबकि इनक्रिप्ट किए गए डाटा या सूचना को पुन: सामान्य सूचना में बदलना Decryption कहलाता हैं। क्रिप्टोग्राफी से डाटा स्थानान्तरण के दौरान डाटा चोरी होने या लीक होने की संभावना नहीं रहती है।

इंटरनेट सुरक्षा में शामिल होता हैं –

• सूचना, डाटा तथा संसाधनों का उपयोग केवल अधिकृत व्यक्तियों द्वारा किया जाना।
• डाटा तथा संसाधन अधिकृत व्यक्तियों के लिए हमेशा उपलब्ध होना।
• नेटवर्क पर भेजे गए डाटा के Destination तक पहुंचने से पहले उसे रिकॉर्ड करने तथा छेड़छाड़ या परिवर्तन करने की संभावना न होना।

यूजर आइडेंटीफिकेशन(User Identification)

कम्प्यूटर तथा नेटवर्क पर अधिकृत उपयोगकर्ता की पहचान करना User Identification कहलाता हैं जबकि इस पहचान को सत्यापित करने की प्रक्रिया ऑथेनटिकेशन (Authentication) कहलाती हैं।
यूजर नेम तथा पासवर्ड (User Name and Password)
 उपयोगकर्ता की पहचान स्थापित करने (Identification) तथा उसे सत्यापित करने  (Authentication) की सर्वाधिक प्रचलित विधि यूजर नेम तथा पासवर्ड की हैं। इसके द्वारा केवल अधिकृत उपयोगकर्ता को ही कम्प्यूटर डाटा तथा नेटवर्क का उपयोग करने दिया जाता हैं। यूजर नेम तथा पासवर्ड उपयोगकर्ता द्वारा कम्प्यूटर सिस्टम में स्टोर किया जाता हैं। अगली बार कम्प्यूटर या नेटवर्क का उपयोग करने के लिए कम्प्यूटर सिस्टम यूजर नेम तथा पासवर्ड डालने का request करता हैं। कम्प्यूटर पहले से स्टोर किए गए यूजर नेम तथा पासवर्ड से दी गई सूचना का मिलान करता हैं, तथा सही पाए जाने पर ही कम्प्यूटर तथा नेटवर्क के प्रयोग की इजाजत देता हैं।

IP-Internet Protocol Address

Internet Addressing:

Physical-MAC

Logical-IP

Physical/MAC

A media access control address (MAC address) of a device is a unique identifier assigned to a network interface controller (NIC) for communications at the data link layer of a network segment.

MAC addresses are 6-byte (48-bits) in length.

eg. 00-14-22-01-23-45.

IP Address

Numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing.

1. Versions of IP Address

Internet Protocol Version 4 (IPv4)

• 32 bit number
• 4 octets
• Limitation : 4294967296 (2³²) addresses.
• e.g. 172.115.56.48

Internet Protocol Version 6 (IPv6)

• 128 bit number
• 16 octets
• Limitation : (2¹²⁸) 3.403×10³⁸ addresses
• It was developed in 1995 and standardized as rfc2460 in 1998.
• Not yet widely used.
• e.g. 2001:0:9d38:90d7:2c0f:19de:4b28:afba

2. Classes of IP Addresses

IPv4 Classes:

Class	A	B	C	D	E
1st Octet Range	1-126*	128-191	192-223	224-239	240-254
IP Addresses Range	1.0.0.1 to 126.255.255.254	128.1.0.1 to 191.255.255.254	192.0.1.1 to 223.255.254.254	224.0.0.0 to 239.255.255.255	240.0.0.0 to 254.255.255.254
Default Subnet Mask	255.0.0.0	255.255.0.0	255.255.255.0	NA	NA
Network / Host ID	N.H.H.H	N.N.H.H	N.N.N.H	NA	NA
Number of Networks configurable	126 (27 – 2)	16,382 (214 – 2)	2,097,150 (221 – 2)	NA	NA
Number of devices configurable per network	16,777,214 (224 – 2)	65,534 (216 – 2)	254 (28 – 2)	NA	NA
Purpose	Large networks	Medium sized networks	Small networks	Reserved for multi casting	For research and development

• Class A - range 127.0.0.1 to 127.255.255.255 - reserved for loop back and diagnostic purposes.
• Any server / system localhost ip address is 127.0.0.1

3. Types of IP Addresses

Public vs Private IP Addresses

Public IP address is assigned to a computer by the ISP when it is connected to the Internet.

Private IP addresses are used to configure the devices in a private network (LAN / MAN / WAN). 

Static vs Dynamic IP Addresses

Static

• ​Static IP address does not change once it is assigned to a device / computer in a network.
• Since, the IP is static and known there is more possibility for network attacks
• Used by Web Servers, E-mail Servers
• Number of allocatable IP addresses is limited in IPv4.Hence, nowadays it is not possible to connect all the devices that exists in world to Internet simultaneously by using IPv4. 

​​Dynamic

• Dynamic IP addresses are assigned by ISP using DHCP
• ​Available IP address is assigned to a device when it is connected to the network, after the session expiry the IP address released for other device's use.
• Effective use of IP addresses is an advantage of Dynamic IP address assigning.
• Since, the IP address changes frequently, it become not traceable. 

What is Subnetting:

A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting. Computers that belong to a subnet are addressed with an identical most-significant bit-group in their IP addresses

Why Sub netting Required ?

Subnetwork, or subnet, is a logically subdivision of

an IP network.

Method to divide network into two or more

networks.

Shortage of IP Address

Classless IP- No Network IP no Host ID.

Easy to manage smaller network then bigger

network.

Web Development and Web Hosting.

Web developers use the LAMP/WAMP stack to create feature-rich applications using programming languages and database storage to serve files through XHTML & DHTML. Web scripts like content management systems (CMS), blogging platforms, eCommerce stores, forums, wikis, and social networks all run on web servers through custom stack development. Web publishers have the option to program new websites using proprietary database frameworks, HTML authoring tools, or open source scripts based in shared development platforms. Web development requirements are one of the most determining factors in the choice of a web hosting platform. You may select windows and Linux web server to host your website.

Different Types of Web Hosting

Web hosting accounts can be subdivided into different categories based on the way that server resources are allocated and shared on the hardware that is used in a data center. Other ways to classify web hosting depend on the way the accounts are billed or the market sector to which the services are targeted. Accordingly, the most common forms of web hosting available are:

• Free Web Hosting
• Shared Web Hosting
• VPS Web Hosting
• Dedicated Web Hosting
• Cloud Web Hosting

Each type of hosting has value for a certain segment of the web development community, as well as unique advantages and disadvantages which make it most suitable for a particular domain application. Understanding the differences between the types of web hosting available is important for site owners and businesses to make the right purchasing decision to support the development requirements of various scripts under a wide variety of user traffic conditions.

Free Web Hosting

Free web hosting is offered by various companies primarily in order to up-sell other domain services or to publish advertising on pages that are hosted under the account. Free web hosts usually offer only subdomain support for user web pages, for example: user.geocities.com. Many popular CMS platforms like WordPress and Joomla offer free web hosting for web publishers to get started blogging or building a website. Free web hosting is not considered a viable solution for business owners or websites that require custom content development, eCommerce facilities, and domain name support. Free web hosting is mostly popular with bloggers and can be viewed as another form of social networking, i.e. Tumblr, Facebook, Instagram, MySpace, Blogger, Ning, WordPress, and other brand name sites.

Shared Web Hosting

Shared web hosting provides for the management of a large number of domain names on a single server using IP addressing, where all of the registered websites will simultaneously use the same CPU, RAM, hard drive, and bandwidth resources to serve files or run scripts according to temporary commands. With shared web hosting, there may be thousands of different businesses, individuals, and organizations all serving their website files to the public from the same computer. A single data center is able to host millions of domains on this model, allowing web hosting companies to scale at volume and offer the lowest pricing to consumers for web file management and database storage tools.

How Does Shared Web Hosting Work?

With shared web hosting, each user account is provided with a unique login to the server which is registered to a root domain name and identified through a public IP address. Additional domain names are added to the account through the use of a control panel by administrators. The web hosting company employs systems administrators to manage the server software installation and security updates. The hosting clients use file transfer management tools to host web pages in HTML or other programming languages which serve the files to the public through the browser. The hard disk space on the remote server can be used for other purposes than web hosting, for example remote file storage, email accounts, sandbox web development, mobile app support, or running software scripts online.

Advantages of Shared Web Hosting

The number one benefit of shared web hosting traditionally is that it is an extremely cheap way to publish information online. Shared web hosting accounts can cost as little as $1 – $3 dollars per month and rarely cost more than $20. It is estimated that over 90% of the websites on the internet use shared web hosting to keep their information online 24 hours a day. Shared web hosts never turn off their services and offer seamless hardware upgrades in the data center that can keep a website online for years. Most of the available web development tools will integrate easily with a shared hosting account.

These services allow the internet to function as a vast library of self-published information in a non-hierarchical, distributed network system. Because web hosting companies hire experts to manage the data centers and typically keep up-to-date with the latest security releases on server software installs, the end users receive a simple to use platform to manage file transfers, databases, email accounts, and web publishing that is generally secure. There is a huge amount of flexibility in what can be done creatively with the remote data processing and storage facilities on a shared web hosting account.

Disadvantages of Shared Web Hosting

The main disadvantage of shared web hosting is that it is not able to scale effectively to support the traffic of large websites and usually includes strict limitations on the use of CPU processing power because of the pooled resources.

There is still no opportunity for advanced systems administration and custom server configurations on most shared hosting plans. Security on shared web hosting frameworks is not considered robust enough for sensitive corporate information and government accounts. There can also be performance issues.

Who is Shared Web Hosting Best For?

Shared web hosting is recommended for self-published websites and small business networks. Web designers can host unlimited domains on a shared account for development, and then transfer them to cloud or dedicated servers if the traffic develops more than the web hosting company will permit. One of the most popular uses for shared web hosting is single and multi-user blog sites built on WordPress. 

VPS Web Hosting

Virtual Private Servers (VPS) are a web hosting solution designed to give more power and flexibility to website owners for custom developed software requirements and complex applications. Technically, a VPS will operate in the same manner as a dedicated server while operating on a partitioned hardware framework that allows for the use of only a fraction of the resources of the host machine. VPS accounts are based on the amount of RAM, hard drive storage, and CPU processing power allocated to the virtual machine.

Dedicated Web Hosting

Dedicated web hosting is the most expensive and flexible of all of the service plans offered by companies in the industry, as site owners are able to directly rent or lease a complete rack-mount server in a data center. The advantage of dedicated hosting is that the client has complete control over the software configuration of the server, which can be used to harness the full processing power of the CPU, all of the allocated hard drive space, and available RAM memory. Dedicated servers are required to host the largest sites by traffic on the web, as well as by mobile apps which require elite performance.

Cloud Web Hosting

Cloud web hosting provides solutions for websites that need more processing power and require more than a single server instance because the amount of online traffic, including the number of queries to the database and resource files, is too high in volume for a single machine to effectively manage for all simultaneous users. Website users now frequently require access to remote processing power from data centers (cloud computing) in order to do complex work in the browser rather than on the desktop with software downloads.

Which Features Should You Look For in a Web Hosting Plan?

After understanding the different types of web hosting accounts available from data center companies, it is important to closely review the total package of features that each plan offers in order to determine which provide the best value for the money invested. Some of the main features to look for in any web hosting account are:

• Server Architecture
• Operating System Version
• Domain Management Tools
• Systems Administration Tools
• Bandwidth & CPU Limitations
• Free Offers & Promotions
• Data Security
• Technical Support

These factors can be found across all web hosting accounts including shared, VPS, dedicated, managed, and cloud hosting. Because most web hosting companies offer the lowest pricing on long-term plans, it is easy to get “locked in” to an account on sign-up, only to find out later that it is lacking in major required aspects or underperforms other services in significant ways. To avoid this problem, which can lead to having to transfer a website repeatedly between web servers, confirm the account under review for these factors in advance of any long-term commitment to the company platform.

Communication Media

Communication Media:

Guided Media

1. Twisted Pair Cable
2. Co-Axial Cable
3. Optical Fiber Cable

Unguided Media

1. Radio Wave
2. Micro Wave
3. Infrared

Twisted Pair Cable

Advantages : 

      1. Cheaper and far easier for installation
2. Less susceptible to electrical interference caused by nearby equipment or wires.
3. Flexible.
4. STP wire can carry data at a faster speed just because extra shielding.

Disadvantages : 

       1. Noise
 2. Slow Bandwidth than Co-Axial and Fiber  

Co-Axial Cable

Advantages 

• Better Transmission then Twisted pair cable.
• Less attenuation and less noise then Twisted Pair
• Mostly used in Broadband Transmission
• Thick coaxial cable has an extra protective plastic cover that help keep moisture away.

Disadvantages 

• Expensive then Twisted pair
• Cannot mixed with TP cable.
• Thick coaxial is that it does not bend easily and is difficult to install.

Optical Fiber Cable

Advantages:

• Total internal reflection 
• One single mode fiber can replace a metal of time larger and heavier.
• Very High data transmission rate
• Suitable for every environment.

Disadvantages 

• Difficult to install
• Connecting two fiber
• Very expensive  as compared TP and Coaxial.
•  Fiber optic versus metal cable is that it is difficult to make connections to with another Fiber Optic.

Guided Media Connectors:

Fiber Optical Cable Connector

Co-Axial Cable Connector

Twisted Pair Cable Connector

Unguided Media

Infrared

Low frequency infrared waves are used for very short distance communication like TV remote, wireless speakers, automatic doors, hand held devices etc. Infrared signals can propagate within a room but cannot penetrate walls. However, due to such short range, it is considered to be one of the most secure transmission modes.

Advantages :

➨Infrared motion sensors detect motion in daytime and nighttime reliably. 
➨The sensor does not require any contact with the product to be sensed. 
➨It provides good stability over time. 
➨It delivers high reputability. 

Disadvantages:

➨Infrared frequencies are affected by hard objects (e.g. walls, doors) , smoke, dust, fog, sunlight etc. Hence it does not work through walls or doors. 
➨Infrared waves at high power can damage eyes. 
➨In monitor & control application, it can control only one device at one time. Moreover it is difficult to control things which are not in LOS (Line of Sight). It requires line of sight between transmitter and receiver to communicate. 

Radio Wave

Transmission of data using radio frequencies is called radio-wave transmission. We all are familiar with radio channels that broadcast entertainment programs. Radio stations transmit radio waves using transmitters, which are received by the receiver installed in our devices.

Both transmitters and receivers use antennas to radiate or capture radio signals. These radio frequencies can also be used for direct voice communication within the allocated range. This range is usually 10 miles.

Advantages of Radio Wave

• Inexpensive mode of information exchange
• No land needs to be acquired for laying cables
• Installation and maintenance of devices is cheap

Disadvantages of Radio Wave

• Insecure communication medium
• Prone to weather changes like rain, thunderstorms, etc.

Micro Wave

Disadvantages:

1. Line-of-sight will be disrupted if any obstacle, such as new buildings, are in the way.
2. Signal absorption by the atmosphere. Microwaves suffer from attenuation due to atmospheric conditions.
3. Towers are expensive to build.

Advantages: 

• No cables needed
• Multiple channels available
• Wide bandwidth

Networking Devices

• Repeaters
• Hubs
• Bridge
• Switches
• Router
• Gateway

Repeater

 —  A repeater regenerates the signal it receives. In other terms, you can think of repeater as a device which receives a signal and retransmits it at a higher level or higher power so that the signal can cover longer distances.

—  No Filtering

—   Operates at the Physical Layer of OSI

Attenuation

Attenuation is a natural consequence of signal transmission over long distances.

Collision:

In a half duplex Ethernet network, a collision is the result of two devices on the same Ethernet network attempting to transmit data at exactly the same time. The network detects the "collision" of the two transmitted packets and discards them both.

Hubs

—   A hub is basically a multiport repeater. A hub connects multiple wires coming from different branches.

—  Hubs cannot filter data, so data packets are sent to all connected devices. It Depends on receiving computer that the packet is useful or not.

—  Shared Traffic

—  No addressing

—  Mostly used in LAN for Star topology

—  Operates at the Physical Layer of OSI

Bridge

—  Used for interconnecting two LANs working on the same protocol.. It has a single input and single output port, thus making it a 2 port device.

—  It can remove collision domain.

—  As compared Switches it use Software so it is slower then Switch and only 2 ports available so broadcasting not possible.

—  Functionality of filtering content by reading the MAC addresses of source and destination.

—  Data Transmission as Frame therefore, it operates at the Data Link Layer of OSI

Switch

—  Switch is more intelligent than a hub. While hub just does the work of data forwarding, a switch does ‘filter and forwarding’ which is a more intelligent way of dealing with the data packets.

—  It maintains a CAM (Content Addressable Memory) table that reads frame’s MAC destination address and forward to the destination. (If destination available)

—  It is faster than bridge because it has built in hardware chips for switching.

—  Reduces the Traffic just because multiport.

—  Data Transmission as Frame therefore, it operates at the Data Link Layer of OSI.

Router

—  A router is a network device which is responsible for routing traffic from one to another network. 

—  Connects deferent network LAN and WAN (eg. Internet)

—  Work with different protocols as well.

—  Router uses IP Address to forward packets.

—  Collision can be controlled by Router.

—  It creates Route Table using IP add and filter, forward packets to destination with best path.

Gateway

—  Gateway is very intelligent device from Router and it is combination of H/W and S/W.

—  It can operate with Network Layer and all above layers but mostly it operates with Application Layer of OSI.

—  It is very complex then Router.

—  It can handle different type of Protocols and network architecture.(it can connect and Translate)

  

 Conclusion:  

Repeater	Regenerate the signals
Hub	Forward all data to all ports
Bridge	Only 2 port (incoming and outgoing)
Switch	Frames forwarded to destination Unit-Frames (Data Link)
Router	Work with different  protocols (eg. Internet ) and provide routing facility.
Gateway	Handle different Protocols and Architecture . H/w and S/w