Blog 2 Computer Networking Continued

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The objective of this blog is to:

- get an idea about the various Central devices used for establishing Computer Network

- configure that which type of device or network will be best suited for a particular organization

- what is Internet

Computer Networking Devices (Continued)

** Data Packet – When data is transmitted over a network,  it is broken into similar structures of data before transmission, called packets. Each packet has three parts of information -- 

A header which holds the sender’s IP address and the destination’s IP address and the sequence number of all the packets.

A payload that holds the broken piece of data.

A trailer that holds a signature which indicates the end of the packet and also holds the number sequence of data packets in order such that they are reassembled in a way to get the original data back exactly as it was prior to transmission. The packets are reassembled to the original data chunk once they reach the destination.

Bandwidth - is the range or amount of data in bits or bytes being carried in a bus in a fixed amount of time and is expressed in bits or bytes per second for digital devices and cycles per second or Hertz in analog devices.

A Router is a device which does not only carry data from a network to another but it has the logical   calculation inbuilt capability which helps to decide the best suited possible paths (minimising the     travel distance, eliminating the chances of collision). Is also said that a router bridges its own path       when connection different networks/ types of networks.

This is a wireless Router 

This is a wired Router

A Router has the Capability to read the IP address of nodes on a network.

Now these are the three major Central Devices used to establish network specially LAN.

Click on the link  -->  Working Method of Hub Switch and Router  and watch this video to understand the differences among these three central devices with respect to their working phenomenon.

A Gateway is a node on a network that serves as an entrance to another network. (the two networks can be completely different in their structure). A network gateway can be implemented completely in software, completely in hardware, or as a combination of both. As the name suggests, is a passage to connect two networks together that may work upon different networking models. 

Here gateway is a program over the internet for a dedicated network.

Here the hardware central device is Switch which is connected to a program where it can convert protocols ( set of rules that system follows while exchanging information) of one network to another.

Examples - The computers that control traffic at your local Internet Service Provider (ISP) are gateway nodes.

A computer server in a company acting as a gateway node is often also acting as a proxy server.  Here the proxy server is a node that is not actually a server but just appears to be so to prevent from unauthorised access to or from a private network.

A Bridge is also known as an Ethernet bridge, connects two segments of a network together or divides a network into manageable sections. A bridge can be used in computer networks to interconnect two LANs together and separate network segments.

4. Network Topologies

Topology – is the pattern in which nodes (devices on an active network) are connected to each other physically and logically over a network or the arrangement of a network which comprises of nodes and connecting lines via sender and receiver is referred as network topology.

Why do we need these patterns? Why can’t we just connect the nodes the way we want?

·      The Cost of connecting the nodes matter
·      The type of cables we use to connect matters
·      Some access methods work with only specific pattern
·      Speed also matters

Types of Network Topologies

Bus Topology – is a type of network in which nodes are connected to a single cable(bus) called backbone. This backbone has two ends called terminals which is a device attached to the end-points of a bus network or daisy-chain. The purpose of the terminator is to absorb signals so that they do not reflect back down the line. It has multiple nodes connected to it called multipoint.

** The bus can only transmit data in one direction, and if any one node network is damaged all the rest ceases.

 ** A host on a bus network is called workstation / station

** The network traffic and transmission priority is equal for each station.

Advantages of Bus Topology

i)  Since there is a single common data path connecting all the nodes, the bus topology uses a very short cable length which considerably reduces the installation cost.

ii)  The linear architecture is very simple and reliable.

iii) Additional nodes can be easily connected to the existing bus network at any point along the length of the transmission medium.

Disadvantages of Bus topology

i)  Fault detection and isolation is difficult. This is because control of the network is not centralized in any particular node. If a node is faulty on the bus, detection of fault may have to be performed at many points on the network. The faulty node has then to be rectified at that connection point.

ii)  If the central bus length becomes too long, then repeaters might have to be used to amplify the signal. The use of repeaters makes reconfiguration necessary.

iii) Since each node is directly connected to the central bus, so there has to be some way of deciding who can use the network at any given time.

Nutshell of Bus Topology - Advantages – easy to connect, works good (speed) for small network, less cable length.

Disadvantages – terminators at both end required, backbone breaks entire network shuts, any cable breaks network splits, more devices added network becomes slow

Applications – Message broadcasting, Computer Motherboards connectivity, Lan Setup

Ring Topology – is a bus topology with no end which means the end or terminator are joined in a loop.

Each data packet is send around the ring until reaches its destination (node to node). All the traffic flow moves only in one direction at a high speed.

Ring Topology with a Token – is a network in which

• A token continually circulates inside the ring network
• To transmit a message, a node inserts a message and destination address inside an empty token.
• The token is examined by each successive node.
• The destination node copies the message data and returns the token to the source with the source address and a data receipt message.
• The source receives the returned token, verifies copied and received data and empties the token.
• The empty token now changes to circulation mode, and the process continues.

Watch to know how does this token ring work - Working of a token ring   https://www.youtube.com/watch?v=p72R2uGglnU

Advantages – Organized, Each node has equal access to resources, Additional components do not effect the performance of network,

Disadvantages –Moving and Changing the devices may affect the network, Bandwidth is shared with all devices.

Applications – In smaller network areas like schools, offices.

Star Topology –  in which all nodes are individually connected to a central connection point, like a hub or a switch or a router. The hub can be passive ​in nature i.e. not intelligent hub such as broadcasting devices, at the same time the hub can be intelligent known as active ​hubs. Active hubs have repeaters in them.

A star may take more cable than e.g. a bus. No direct traffic between devices.

Advantages of Star Topology

i)  Failure of a single connection does not affect the entire network. It just involves disconnecting one node from an otherwise fully functional network. This also helps in easy reconfiguration of the network.

ii)  Fault detection is easier.

iii) Access protocol being used in a Star network are very simple since the central node has the control of the transmission medium for data transmission

Disadvantages of Star Topology

i)  Since every node is directly connected to the centre, so large amount of cable is needed which increases the installation cost of the network.

ii)  The entire network is dependent on the central node. If the central node fails the entire network goes down.

Nutshell of Star Topology

Advantages - 

Easy to install and wire, no disruptions to the network when connecting or removing devices, easy to detect faults and to remove parts, performance depends on the capacity of central device.

Disadvantages - 

Requires more cable length (Bus). If the connecting network device (network switch/hub/router) fails, entire network fails. More expensive than linear bus topology (network switches). Performance and Number of nodes which can be added depends on capacity of central devices.

Applications – to establish LAN.

Mesh Topology –  A mesh network is a local network topology in which the infrastructure nodes connect directly, dynamically and non-hierarchically, to as many other nodes as possible and cooperate with one another to efficiently route data from/to clients.

                          

The main advantage of Mesh topology is multiple paths to the destination computer. If one link is down, we have another path to reach the destination.

Nutshell of Mesh Topology

Advantages – can withstand high traffic(alternative paths), Data transfer simultaneously, expansion and modification is easy (other nodes not affected)

Disadvantages – Cost ineffective (set-up, maintenance, high chances of redundancy)

Applications – Telephone Regional offices, WAN

Tree Topology - is a combination of bus and star topology. The network looks like a tree (can be inverted) with the central root branching and sub-branching sideways/down to the nodes. It integrates multiple star topologies together onto a bus.

The above image is of a Tree Topology where the backbone is upright rooted and the star topologies are branched.

The above image is of a Tree Topology where the parent central device(backbone) is at first level branched towards the central devices of second level and then these central devices are further branched towards workstations/nodes/servers at the third level which are configured in star topology.

Nutshell of Tree topology 

Suitable for larger networks, spread into many branches. 

Main disadvantage of tree topology is that the connectivity between tree branches are dependent on main backbone switches. If there is no redundancy solution applied at backbone switches, connectivity between branches will fail.

Applications - Tree topology based networks are not suitable for small networks because of the requirement for additional devices and cables. Example: Big university campuses, hospitals etc.

5. Internet –  (Inter + net = Interconnected + Network )

                                                   

In the above image there are three different types of net and when we connect these nets with each other it is called interconnected network. 

The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups. 

The Internet is made up of many networks each run by a different companies and are interconnected at peering points. It is really a network of networks spread across the globe, all of which are connected to each other.

While exchanging info over a network these nodes have to follow a set of rules called – protocols, the internet uses Transmission Control Protocol/Internet Protocol (TCP/IP - TCP part has to do with the verifying delivery of the packets and IP has to do the moving of data packets between nodes.)

Programs such as web browsers, File Transfer Protocol (FTP) clients, and email clients are some of the most common ways through which the users work on the Internet.

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