Wireless networking has become one of the fastest growing trends in the home computer market. The latest complete standard, 802.11n (or “wireless-N”), is capable of speeds faster than many wired networks and has better range and reliability than its predecessors. However, a replacement standard called 802.11ac (or “wireless-AC”) is already on the drawing board and some manufacturers have even released products using the incomplete standard.
802.11ac, expected to have final approval in 2013, improves upon many of the new technologies that debuted in the 802.11n standard. Wireless-N typically connects at speeds up to 150Mbps, with some higher end devices capable of an impressive 300Mbps or even 450Mbps. However, wireless-AC promises to triple those speeds so the lower end devices using wireless-AC will be as fast as the highest-end devices using the current 802.11n standard and the higher end devices will be able to outperform today’s fastest wired connections. While wireless-N is already fast enough for most current network needs, including streaming HD video, the 802.11ac standard promises to allow even higher quality media to be streamed to multiple devices at the same time.
In addition to huge speed increases, the new standard also promises better range and reliability. Although the overall technology behind it is complex, there are two features of 802.11ac that make the biggest difference. Firstly, wireless-AC will use the 5GHz wireless spectrum, which helps to avoid interference with wireless phones and many other devices (including older wireless-G and wireless-B networks) that use the 2.4GHz frequency.
let’s know about fiber optics
Fiber optics is a type of transmission line or cable is made of glass or plastic is very smooth and smaller than a hair, and can be used to transmit light signals from one place to another. The light source used is usually a laser or LED. This cable is approximately 120 micrometers in diameter. Light that is in the optical fiber does not come out because the refractive index of glass is greater than the refractive index of air, because the laser has a very narrow spectrum. Speed optical fiber transmission is very high so it is great to use as a communication channel. The efficiency of the optical fiber is determined by the purity of the building blocks of glass / glass. The more pure glass material, the less light is absorbed by the fiber optics.
Structure of Fiber Optics
Broadly speaking, the structure of the optical fiber is divided into two parts, namely core and cladding (wrapping of the core). Caldiing have a function to protect the light that bounces off the core leads out to be reflected back into the core. Cladding can reflects the light from the core that leads out because the cladding have a lower refractive index.
In fact the optical fiber is also wrapped in a layer called resin-called jacket. This resin layer can absorb the light so as to prevent leakage that leads out of the core.
Types of Optical Fiber
Broadly speaking, the distribution of types of optical fibers can be seen from two aspects, namely based on the propagated mode and based on the core refractive index.
a. Based on the propagated mode optical fiber can be divided into two general categories:
Google’s secure data centers are some of the most energy efficient in the world. Each year we save millions of dollars on energy costs, and we use renewable energy whenever we can.
Lets see the from original page : http://www.google.com/about/datacenters/
Cloud computing is the delivery of computing and storage capacity as a service to a community of end-recipients. The name comes from the use of a cloud-shaped symbol as an abstraction for the complex infrastructure it contains in system diagrams. Cloud computing entrusts services with a user’s data, software and computation over a network.
There are three types of cloud computing:
- Infrastructure as a Service (IaaS),
- Platform as a Service (PaaS),
- Software as a Service (SaaS).
Using Software as a Service, users also rent application software and databases. The cloud providers manage the infrastructure and platforms on which the applications run.
End users access cloud-based applications through a web browser or a light-weight desktop or mobile app while the business software and user’s data are stored on servers at a remote location. Proponents claim that cloud computing allows enterprises to get their applications up and running faster, with improved manageability and less maintenance, and enables IT to more rapidly adjust resources to meet fluctuating and unpredictable business demand.
Cloud computing relies on sharing of resources to achieve coherence and economies of scale similar to a utility (like the electricity grid) over a network (typically the Internet).At the foundation of cloud computing is the broader concept of converged infrastructure and shared services.
article source: wikipedia
Sliding Window is the method of flow control TCP uses. The algorithm basically places a buffer between the application and the network data flow. The purpose of sliding window is to prevent from the sender to send too many packets to over flow the network resource or the receiver’s buffer. The “sliding window size” is the maximum amount of data we can send without having to wait for ACK. TCP achieve the flow control by using the sliding Window algorithm which takes into consideration 2 important parameters. The first one is the receiver advertised window size which basically tells the sender what is the current buffer of TCP receiver, the second parameter is congestion window which control the number of packets a TCP flow may have in the network in any given time.
Receiver Advertised Window
The Receiver Advertised Window (adwn) is the buffer size sent in each ACK from TCP receiver to TCP sender. The TCP header uses a 16 bit field to report the receive window size to the sender. Therefore, the largest window that can be used is 2^16=65k bytes..
Congestion Window (cwnd) controls the number of packets a TCP flow may have in the network in any given time. cwnd is dynamically adapting to changing network condition Slow-start is one of the algorithms that TCP uses in its quest to control congestion inside the network and it is also known as the exponential growth phase. Slow-start works by increasing the TCP congestion window each time the ACK is received. it increases the window size by the number segments acknowledged. If a loss event occurs, TCP assume this is due to network congestion and takes step to reduce the offered load on the network.