Thursday, April 15, 2010
Network analysis
A network, in the context of electronics, is a collection of interconnected components. Network analysis is the process of finding the voltages across, and the currents through, every component in the network. There are a number of different techniques for achieving this. However, for the most part, they assume that the components of the network are all linear. The methods described in this article are only applicable to linear network analysis except where explicitly stated.
Yahoo
Yahoo! Inc. (NASDAQ: YHOO) is an American public corporation headquartered in Sunnyvale, California, (in Silicon Valley), that provides Internet services worldwide. The company is perhaps best known for its web portal, search engine (Yahoo! Search), Yahoo! Directory, Yahoo! Mail, Yahoo! News, advertising, online mapping (Yahoo! Maps), video sharing (Yahoo! Video), and social media websites and services. As of January, 2010, Yahoo held the world's largest market share in online display advertising. JP Morgan put the company’s US market share for display ads at 17%, well ahead of No. 2 Microsoft at 11% and AOL at 7%.[3]
Yahoo! was founded by Jerry Yang and David Filo in January 1994 and was incorporated on March 1, 1995. On January 13, 2009, Yahoo! appointed Carol Bartz, former executive chairperson of Autodesk, as its new chief executive officer and a member of the board of directors.[4]
According to Web traffic analysis companies (including Compete.com, comScore,[5] Alexa Internet,[6] Netcraft,[7] and Nielsen ratings[8]), the domain yahoo.com attracted at least 1.575 billion visitors annually by 2008.[9] The global network of Yahoo! websites receives 3.4 billion page views per day on average as of October 2007[update].
Yahoo! was founded by Jerry Yang and David Filo in January 1994 and was incorporated on March 1, 1995. On January 13, 2009, Yahoo! appointed Carol Bartz, former executive chairperson of Autodesk, as its new chief executive officer and a member of the board of directors.[4]
According to Web traffic analysis companies (including Compete.com, comScore,[5] Alexa Internet,[6] Netcraft,[7] and Nielsen ratings[8]), the domain yahoo.com attracted at least 1.575 billion visitors annually by 2008.[9] The global network of Yahoo! websites receives 3.4 billion page views per day on average as of October 2007[update].
Router
A router, pronounced /ˈraʊtər/ in the United States and Canada, and /ˈruːtər/ in the UK and Ireland (to differentiate it from the tool used to rout wood), is a purposely customized computer used to forward data among computer networks beyond directly connected devices. (The directly connected devices are said to be in a LAN, where data are forwarded using Network switches.)
More technically, a router is a networking device whose software and hardware [in combination] are customized to the tasks of routing and forwarding information. A router differs from an ordinary computer in that it needs special hardware, called interface cards, to connect to remote devices through either copper cables or Optical fiber cable. These interface cards are in fact small computers that are specialized to convert electric signals from one form to another, with embedded CPU or ASIC, or both. In the case of optical fiber, the interface cards (also called ports) convert between optical signals and electrical signals.
Routers connect two or more logical subnets, which do not share a common network address. The subnets in the router do not necessarily map one-to-one to the physical interfaces of the router.[1] The term "layer 3 switching" is used often interchangeably with the term "routing". The term switching is generally used to refer to data forwarding between two network devices that share a common network address. This is also called layer 2 switching or LAN switching.
Conceptually, a router operates in two operational planes (or sub-systems):[2]
* Control plane: where a router builds a table (called routing table) as how a packet should be forwarded through which interface, by using either statically configured statements (called statical routes) or by exchanging information with other routers in the network through a dynamical routing protocol;
* Forwarding plane: where the router actually forwards the traffic (or called packets in IP protocol) from ingress (incoming) interfaces to an egress (outgoing) interface that is appropriate for the destination address that the packet carries with it, by following rules derived from the routing table that has been built in the control plane.
More technically, a router is a networking device whose software and hardware [in combination] are customized to the tasks of routing and forwarding information. A router differs from an ordinary computer in that it needs special hardware, called interface cards, to connect to remote devices through either copper cables or Optical fiber cable. These interface cards are in fact small computers that are specialized to convert electric signals from one form to another, with embedded CPU or ASIC, or both. In the case of optical fiber, the interface cards (also called ports) convert between optical signals and electrical signals.
Routers connect two or more logical subnets, which do not share a common network address. The subnets in the router do not necessarily map one-to-one to the physical interfaces of the router.[1] The term "layer 3 switching" is used often interchangeably with the term "routing". The term switching is generally used to refer to data forwarding between two network devices that share a common network address. This is also called layer 2 switching or LAN switching.
Conceptually, a router operates in two operational planes (or sub-systems):[2]
* Control plane: where a router builds a table (called routing table) as how a packet should be forwarded through which interface, by using either statically configured statements (called statical routes) or by exchanging information with other routers in the network through a dynamical routing protocol;
* Forwarding plane: where the router actually forwards the traffic (or called packets in IP protocol) from ingress (incoming) interfaces to an egress (outgoing) interface that is appropriate for the destination address that the packet carries with it, by following rules derived from the routing table that has been built in the control plane.
Code division multiple access
Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne and CDMA2000 (which are often referred to as simply "CDMA"), which use CDMA as an underlying channel access method.
One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of different frequencies. This concept is called multiplexing. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.
One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of different frequencies. This concept is called multiplexing. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.
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