Networks, Computer network, data communication in computer Network, Network Criteria - Physical Structure Physical Topology Type of Connection , Mesh Topology

Networks, Computer network, data communication in computer Network, Network Criteria - Physical Structure  Physical Topology Type of Connection , Mesh Topology 

PART 1

Networks: 

Network Criteria - Physical Structure :

•  A network is the interconnection of a set of devices capable of communication. In this definition, a device can be a host (or an end system as it is sometimes called) such as a large computer, desktop, laptop, workstation, cellular phone, or security system. 
•   A device in this definition can also be a connecting device such as a router, which connects the network to other networks, a switch, which connects devices together, a modem (modulator demodulator), which changes the form of data, and so on. 
•   These devices in a network are connected using wired or wireless transmission media such as cable or air. When we connect two computers at home using a plug-and-play router, we have created a network, although very small.

Network Criteria :

 A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security. 

 Performance :

•  Performance can be measured in many ways, including transit time and response time. 
•  Transit time is the amount of time required for a message to travel from one device to another. 
•  Response time is the elapsed time between an inquiry and a response. 
•  The performance of a network depends on a number of factors, including 

1.  the number of users 
2.  the type of transmission medium 
3.  the capabilities of the connected hardware, and 
4.  The efficiency of the software. 

•  Performance is often evaluated by two networking metrics: throughput and delay. We often need more throughput and less delay. However, these two criteria are often contradictory. If we try to send more data to the network, we may increase throughput but we increase the delay because of traffic congestion in the network.  

Reliability :

In addition to accuracy of delivery, network reliability is measured by the frequency of failure, the time it takes a link to recover from a failure, and the network’s robustness in a catastrophe. 

 Security :

 Network security issues include protecting data from unauthorized access, protecting data from damage and development, and implementing policies and procedures for recovery from breaches and data losses. 

Physical Structures 

 Type of Connection - Physical Topology Type of Connection 

•   A network is two or more devices connected through links. 
• A link is a communications pathway that transfers data from one device to another. For visualization purposes, it is simplest to imagine any link as a line drawn between two points.
•  For communication to occur, the same time. There are two possible types of connections:

 point-to-point and 

 multipoint






 

Point-to-Point :

 A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. Most point -to-point  connections use an actual length of wire or cable to connect the two ends, but other options, such as microwave or satellite links, are also possible   .. When we change television channels by infrared remote control, we are establishing a point-to-point connection between the remote control and the television’s control system. 

Multipoint :

•  A multipoint (also called multidrop) connection is one in which more than two specific devices share a single link. 
•  In a multipoint environment ,the capacity of the channel is shared, either spatially or the capacity temporally. 
• If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshared connection
• The term physical topology refers to the way in which a network is laid out physically Two or more devices connect to a link; two or more links form a topology. The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another

There are four basic topologies possible: mesh, star, bus, and ring.

 Mesh Topology:

In a mesh topology, every device has a dedicated point -to-point link to every other device.  

• The term dedicated means that the link carries traffic only between the two devices it connects. To find the number of physical links in a fully connected mesh net work with n nodes, we first consider that each node must be connected to every other node.

• Node 1 must be connected  to n – 1 nodes, node 2 must be connected to n –1 nodes, and finally node n must be connected to n – 1 nodes. We need n (n-1)physical  links.

• If each physical link allows communication in both  If each physical link allows communication in both directions (duplex mode), we can divide the number of links by 2 [ we need n (n – 1) / 2 duplex-mode links]. 
• To accommodate that many links, every device on the network must have n-1input/output  (I/O) ports (see Figure ) to be connected to the other n  n – 1 stations.

  One practical example of a mesh topology is the connection of telephone regional offices in which each regional office needs to be connected to every other regional office.

 Advantages :

 1. The use of dedicated links guarantees that each connection can carry its own data load thus eliminating the traffic problems that can occur when links must be shared by multiple devices.

 2. A mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system.

 3. There is the advantage of privacy or security. When every  travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevent other users from gaining access to messages. 

 4. Point-to-point links make fault identification and fault isolation easy. Traffic can be routed to avoid links with suspected problems. This facility enables the network manager to discover the precise location of the fault and aids in finding its cause and solution.

Disadvantages :

 The main disadvantages of a mesh are related to the amount of cabling and the number of I/O  required. 

 1. Because every device must be connected to every other device, installation and reconnection are difficult. 

 2. The sheer bulk of the wiring can be greater than the available space (in walls, ceilings, or floors) can accommodate. 

 3. The hardware required to connect each link (I/O ports and cable) can be prohibitively expensive. For these reasons a mesh topology is usually implemented in a limited fashion.

you can learn here THANK YOU .........for visiting for more info  CONTECT

 Visit https://omnicen.blogspot.com/

 UNIX : UNIX notes  UNIX file system  naming file     Unix Directory     DIRECTORY COMMANDS

COMPUTER NETWORK : introduction    TOPOLOGIES 

PART 2  : part 2