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

Network Typologies

The physical or logical layout of a network. It defines the way different nodes are placed and interconnected with each other. Alternately, network topology may describe how the data is transferred between these nodes.

Network topologies can be categorized into five basic models:

1. Star Topology

Star Topology: In a star network devices are connected to a central computer, called a hub. Nodes communicate across the network by passing data through the hub.

Main Advantage: In a star network, one malfunctioning node doesn't affect the rest of the network.
Main Disadvantage: If the central computer fails, the entire network becomes unusable.

2. Bus Topology

In networking a bus is the central cable -- the main wire - that connects all devices on a local-area network (LAN).

Advantage:  It's easy to connect a computer or device and typically it requires less cable than a star topology.
Main Disadvantage: The entire network shuts down if there is a break in the main wire and it can be difficult to identify the problem if the network shuts down.

3. Ring Topology

 A local-area network (LAN) whose topology is a ring. That is, all of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading those messages addressed to it.
Main Advantage: One main advantage to a ring network is that it can span larger distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it.

4. Tree Topology

This is a "hybrid" topology that combines characteristics of linear bus and star topologies. In a tree network, groups of star-configured networks are connected to a linear bus.

Main Advantage: Good choice for large computer networks as it "divides" the whole network into parts that are more easily manageable.
Main Disadvantage: The entire network depends on a central hub and a failure of the central hub can disturb whole network.

               5.  Mesh Topology

In a true mesh topology every node has a connection to every other node in the network. There are two types of mesh topologies:

Main Advantage : A broken node won't distract the transmission of data. Each node is connected to several other nodes which make it easier to relay data.

Main Disadvantage: Complex so maintenance is difficult and require expert net admin.

Hybrid Topology

It is two different types of topologies which is a mixture of two or more topologies. For example if in an office in one department ring topology is used and in another star topology is used, connecting these topologies will result in Hybrid Topology (ring topology and star topology).

Networking Type and Its Advantages

Networking and Its Advantages

A computer network refers two or more computer connected with each other through medias and share resources for communication purpose.

—Resource Sharing

—Reliability

—Financial Benefit

—Better Communication /work sharing medium

            Access to remote database.

Network Types

• WAN - Wide Area Network
• LAN - Local Area Network
• MAN - Metropolitan Area Network
• PAN-Personal Area Network
• CAN-Campus Area Network
• VAN-Value Added Network
• HAN-Home Area Network
• WLAN- Wireless Local Area Network

WAN: Wide Area Network

—As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

—A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

LAN: Local Area Network

—A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.

MAN: Metropolitan Area Network

—A network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned and operated by a single entity such as a government body or large corporation.

Open System Interconnection (OSI) Module

The seven Open Systems Interconnection layers are:

• Layer 7: The application layer. ...
• Layer 6: The presentation layer. ...
• Layer 5: The session layer. ...
• Layer 4: The transport layer. ...
• Layer 3: The network layer. ...
• Layer 2: The data-link layer. ...
• Layer 1: The physical layer.

The TCP/IP Model

Physical

What is Internet and how it works | इंटरनेट क्या है और इंटरनेट की कार्य प्रणाली

Internet | इंटरनेट 

दुनिया के लगभग सभी कंप्यूटर परस्पर जहाँ एक दूसरे से जुड़े हों और उनके बीच इनफार्मेशन व  कंटेंट का आदान प्रदान हो वही इंटरनेट कहलाता है | 

The Internet was created by the Advanced Research Projects Agency (ARPA 1969) and the U.S. Department of Defense for scientific and military communications. The Internet is a network of interconnected networks. The Internet uses high-speed data lines, called backbones, to carry data.  Smaller networks connect to the backbone, enabling any user on any network to exchange data with any other user.

इन्टरनेट कि सबसे अच्छी बात ये है कि इन्टरनेट  पर किसी भी एजेंसी / कंपनी का कोई Control नहीं है.

How Internet Works | इंटरनेट की कार्य प्रणाली 

ध्यान रहे पूरा internet हमारे द्वारा छोड़े गए उपग्रह से भी नहीं चलता है हाँ ! उपग्रह से पहले चलता था लेकिन ये तकनीक बहुत पुरानीं हो चूकी है और इसमें  डाटा ट्रांसमिशन भी धीरे  होता था. लेकिन वर्तमान में हम जो तेज गति के इंटरनेट का इस्तमाल कर रहे हैं ये तकनीक  Optical Fibers Cable है.

ये बात सच है कि  वर्तमान वर्ष 2018 में लगभग  448 submarine Optical Fiber Cable को समुद्र में है वही हमारे internet का 90% भाग है है. समुद्र में वही Optical Fiber Cable बिछाये जाते है जिनमे कम नुकसान और कम लागत आती है. एक फाइबर ऑप्टिक केबल की आयु लगभग 25 साल हो सकती है 

चूकी Cable को समुद्र में बिछाया जाता है जिसमे बड़े बड़े जहाज भी चलते है और कभी कभी जहाज के लंगर से भी Optical Fiber Cable को नुकसान हो जाता है ऐसा हि कुछ 13 जनवरी 2008 को Egypt में हुआ था l जिसके कारण Egypt का 70% Internet बंद हो गया था.

तब इस समस्या का भी समाधान किया गया था और  एसी कई टीम बनाई गयी है जो 24 घंटे समुद्र में Optical Fiber Cable कि निगरानी करती है. यदि कही किसी Optical Fiber Cable में नुकसान होता है तो ये टीमे उसको जल्दी से जल्दी ठीक कर देती है.

90% internet cable के जरिये चलता है लेकिन 10% कहा से चलता है. ये 10% internet ख़ुफ़िया एजेंसी के द्वारा एक्सेस किया जाता है जिनमें अभी भी  उपग्रह का इस्तमाल किया जाता है ! 

इस जानकारी की पुष्टि और वही केबल मैप देखने के लिए आप http://www.submarinecablemap.com विजिट कर सकते हैं यहाँ आपको TeleGeography केबल मैप के साथ ये भी जानकारी मिलेगी की ऐसी कोनसी कम्पनीज हैं जो इस टीयर 1 नेटवर्क केबल नेटवर्क मैप में इन्वेस्ट करती हैं ! 

Who manage internet? | इंटरनेट का प्रबंधन कौन करता है?

इंटरनेट कॉर्पोरेशन फॉर असाइंड  नेम्स एंड नंबर्स Internet Corporation for Assigned Names एंड and Numbers (ICANN) और  इंटरनेट असाइंड  नंबर्स अथॉरिटी (Internet Assigned Numbers Authority (IANA) यूनिक डोमेन नेम और आईपी एड्रेस का अलॉटमेंट करते हैं साथ ही ये  हर क्षेत्र  के लोकल रजिस्ट्रार जैसे GoDaddy and HostGator आदि के माद्यम से Domain or IP Address आवंटन और उसका रख रखाव करते हैं |