Q. To study communication guiding system Guidance system A guidance system is a device or group of devices used to navigate a ship, aircraft, missile, rocket, satellite, or other craft. Typically, this refers to a system that navigates without direct or continuous human control. Systems that are intended to have a high degree of human interaction are usually referred to as a navigation system. One of the earliest examples of a true guidance system is that used in the German V-1 during World War II. This system consisted of a simple gyroscope to maintain heading, an airspeed sensor to estimate flight time, an altimeter to maintain altitude, and other redundant systems. A guidance system has three major sub-sections: Inputs, Processing, and Outputs. The input section includes sensors, course data, radio and satellite links, and other information sources. The processing section, composed of one or more CPUs, integrates this data and determines what actions, if any, are necessary to maintain or achieve a proper heading. This is then fed to the outputs which can directly affect the system's course. The outputs may control speed by interacting with devices such as turbines, and fuel pumps, or they may more directly alter course by actuating ailerons, rudders, or other devices. Guidance systems Guidance systems consist of 3 essential parts: navigation which tracks current location, guidance which leverages navigation data and target information to direct flight control "where to go", and control which accepts guidance commands to effect change in aerodynamic and/or engine controls.
Transcript
Q. To study communication guiding system
Guidance system
A guidance system is a device or group of devices used to navigate a ship, aircraft, missile, rocket, satellite, or other craft. Typically, this refers to a system that navigates without direct or continuous human control. Systems that are intended to have a high degree of human interaction are usually referred to as a navigation system.
One of the earliest examples of a true guidance system is that used in the German V-1 during World War II. This system consisted of a simple gyroscope to maintain heading, an airspeed sensor to estimate flight time, an altimeter to maintain altitude, and other redundant systems.
A guidance system has three major sub-sections: Inputs, Processing, and Outputs. The input section includes sensors, course data, radio and satellite links, and other information sources. The processing section, composed of one or more CPUs, integrates this data and determines what actions, if any, are necessary to maintain or achieve a proper heading. This is then fed to the outputs which can directly affect the system's course. The outputs may control speed by interacting with devices such as turbines, and fuel pumps, or they may more directly alter course by actuating ailerons, rudders, or other devices.
Guidance systems
Guidance systems consist of 3 essential parts: navigation which tracks current location, guidance which leverages navigation data and target information to direct flight control "where to go", and control which accepts guidance commands to effect change in aerodynamic and/or engine controls.
Navigation is the art of determining where you are, a science that has seen tremendous focus in 1711 with the Longitude prize. Navigation aids either measure position from a fixed point of reference (ex. landmark, north star, LORAN Beacon), relative position to a target (ex. radar, infra-red, ...) or track movement from a known position/starting point (e.g. IMU). Today's complex systems use multiple approaches to determine current position. For example, today's most advanced navigation systems are embodied within the Anti-ballistic missile, the RIM-161 Standard Missile 3 leverages GPS, IMU and ground segment data in the boost phase and relative position data for intercept targeting. Complex systems typically have multiple redundancy to address drift, improve accuracy (ex. relative to a target) and address isolated system failure. Navigation systems therefore take multiple inputs from many different sensors, both internal to the system and/or external (ex. ground based update). Kalman filter provides the most common approach to combining navigation data (from multiple sensors) to resolve current position. Example navigation approaches:
Celestial navigation is a position fixing technique that was devised to help sailors cross the featureless oceans without having to rely on dead reckoning to enable them to strike land. Celestial navigation uses angular measurements (sights) between the horizon and a common celestial object. The Sun is most often measured. Skilled navigators can use the Moon, planets or one of 57 navigational stars whose coordinates are tabulated in nautical almanacs. Historical tools include a sextant, watch and ephemeris data. Today's space shuttle, and most interplanetary spacecraft, use optical systems to calibrate inertial navigation systems: Crewman Optical Alignment Sight (COAS),[9] Star Tracker.[10]
Long-range Navigation (LORAN) : This was the predecessor of GPS and was (and to an extent still is) used primarily in commercial sea transportation. The system works by triangulating the ship's position based on directional reference to known transmitters.
Global Positioning System (GPS) : GPS was designed by the US military with the primary purpose of addressing "drift" within the inertial navigation of Submarine-launched ballistic missile(SLBMs) prior to launch. GPS transmits 2 signal types: military and a commercial. The accuracy of the military signal is classified but can be assumed to be well under 0.5 meters. GPS is a system of 24 satellites orbiting in unique planes 10.9-14.4 Nautical miles above the earth. The Satellites are in well defined orbits and transmit highly accurate time information which can be used to triangulate position.
Inertial Measurement Units (IMUs) are the primary inertial system for maintaining current position (navigation) and orientation in missiles and aircraft. They are complex machines with one or more rotating Gyroscopes that can rotate freely in 3 degrees of motion within a complex gimbal system. IMUs are "spun up" and calibrated prior to launch. A minimum of 3 separate IMUs are in place within most complex systems. In addition to relative position, the IMUs contain accelerometers which can measure acceleration in all axis. The position data, combined with acceleration data provide the necessary inputs to "track" motion of a vehicle. IMUs have a tendency to "drift", due to friction and accuracy. Error correction to address this drift can be provided via ground link telemetry, GPS, radar, optical celestial navigation and other navigation aids. When targeting another (moving) vehicle, relative vectors become paramount. In this situation, navigation aids which provide updates of position relative to the target are more important. In addition to the current position, inertial navigation systems also typically estimate a predicted position for future computing cycles. See also Inertial navigation system.
Radar/Infrared/Laser : This form of navigation provides information to guidance relative to a known target, it has both civilian (ex rendezvous) and military applications.
o active (employs own radar to illuminate the target),o passive (detects target’s radar emissions),o semiactive radar homing,o Infrared homing : This form of guidance is used exclusively for military
munitions, specifically air-to-air and surface-to-air missiles. The missile’s seeker head homes in on the infrared (heat) signature from the target’s engines (hence the term “heat-seeking missile”),
o Ultraviolet homing, used in FIM-92 Stinger - more resistive to countermeasures, than IR homing system
o Laser designation : A laser designator device calculates relative position to a highlighted target. Most are familiar with the military uses of the technology on Laser-guided bomb. The space shuttle crew leverages a hand held device to feed information into rendezvous planning. The primary limitation on this device is that it requires a line of sight between the target and the designator.
o Terrain contour matching (TERCOM). Uses a ground scanning radar to "match" topography against digital map data to fix current position. Used by cruise missiles such as the BGM-109 Tomahawk.
Guidance is the "driver" of a vehicle. It takes input from the navigation system (where am I) and uses targeting information (where do I want to go) to send signals to the flight control system that will allow the vehicle to reach its destination (within the operating constraints of the vehicle). The "targets" for guidance systems are one or more state vectors (position and velocity) and can be inertial or relative. During powered flight, guidance is continually calculating steering directions for flight control. For example the space shuttle targets an altitude, velocity vector, and gamma to drive main engine cut off. Similarly, an Intercontinental ballistic missile also targets a vector. The target vectors are developed to fulfill the mission and can be preplanned or dynamically created.
Control. Flight control is accomplished either aerodynamically or through powered controls such as engines. Guidance sends signals to flight control. A Digital Autopilot (DAP) is the common term used to describe the interface between guidance and control. Guidance and the DAP are responsible for calculating the precise instruction for each flight control. The DAP provides feedback to guidance on the state of flight controls.
Q. Study and verification of standard network topologies.
Network topology
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Diagram of different network topologies.
Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer[1][2] or biological network.[3] Network topologies may be physical or logical. Physical topology refers to the physical design of a network including the devices, location and cable installation. Logical topology refers to how data is actually transferred in a network as opposed to its physical design. In general physical topology relates to a core network whereas logical topology relates to basic network.
Topology can be understood as the shape or structure of a network. This shape does not necessarily correspond to the actual physical design of the devices on the computer network. The computers on a home network can be arranged in a circle but it does not necessarily mean that it represents a ring topology.
Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. The study of network topology uses graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.
A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN has one or more links to one or more nodes in the network and the mapping of these links and nodes in a graph results in a geometric shape that may be used to describe the physical topology of the network. Likewise, the mapping of the data flow between the nodes in the network determines the logical topology of the network. The physical and logical topologies may or may not be identical in any particular
In local area networks where bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable is terminated on both ends and when without termination data transfer stop and when cable breaks, the entire network will be down.
Q.Study Various Type Of Correcting Technique.Community Language Learning
Community language learning (CLL) is an approach in which students work together to develop what aspects of a language they would like to learn. The teacher acts as a counsellor and a paraphraser, while the learner acts as a collaborator, although sometimes this role can be changed.
Examples of these types of communities have recently arisen with the explosion of educational resources for language learning on the Web.
Background
The CLL method was developed by Charles A. Curran, a professor of psychology at Loyola University in Chicago.[1] This method refers to two roles: that of the knower (teacher) and student (learner). Also the method draws on the counseling metaphor and refers to these respective roles as a counselor and a client. According to Curran, a counselor helps a client understand his or her own problems better by 'capturing the essence of the clients concern ...[and] relating [the client's] affect to cognition...;' in effect, understanding the client and responding in a detached yet considerate manner.
To restate, the counselor blends what the client feels and what he is learning in order to make the experience a meaningful one. Often, this supportive role requires greater energy expenditure than an 'average' teacher.[2]
Methods
Natural Approach
The foreign language learner's tasks, according to CLL are (1) to apprehend the sound system of the language (2) assign fundamental meanings to individual lexical units and (3) construct a basic grammar.
In these three steps, the CLL resembles the Natural Approach to language teaching in which a learner is not expected to speak until he has achieved some basic level of comprehension.[3]
There are 5 stages of development in this method.
1. “Birth” stage: feeling of security and belonging are established.2. As the learners' ability improve, they achieve a measure of independence from the parent.3. Learners can speak independently.4. The learners are secure enough to take criticism and being corrected.5. The child becomes an adult and becomes the knower.
A new wave of Community Learning Languages have come into place with the internet growth and the boom of social networking technologies. These online CLLs are social network services that take advantage of the Web 2.0 concept of information sharing and collaboration tools, for which users can help other users to learn languages by direct communication or mutual correction of proposed exercises.
Barriers in Community Language Learning
When learning a different language while in a multilingual community, there are certain barriers that one definitely will encounter. The reason for these barriers is that in language learning while in a multicultural community, native and nonnative groups will think, act, and write in different ways based on each of their own cultural norms. Research shows that students in multicultural environments communicate less with those not familiar with their culture. Long-term problems include that the foreign speakers will have their own terms of expression combined into the language native to the area, which oftentimes makes for awkward sentences to a native speaker. Native students tend to develop an exclusive attitude toward the nonnative speaker because they feel threatened when they do not understand the foreign language. Short-term problems include the fact that native students will usually lack in-depth knowledge of the nonnative cultures, which makes them more likely to be unwilling to communicate with the foreign speakers. Because these foreign students grew up and were educated in a totally different cultural environment, their ideologies, identities and logic that form in the early age cause different ways of expressing ideas both in written and spoken form. They will have to modify and redefine their original identities when they enter a multicultural environment (Shen, 459). This is no easy task. Consequentially, a low-level of social involvement and enculturation will occur for both native and nonnative speakers in the community.
Bandwidth
A DS1 circuit is made up of twenty-four 8-bit channels (also known as timeslots or DS0s), each channel being a 64 kbit/s DS0 multiplexed carrier circuit.[2] A DS1 is also a full-duplex circuit, which means the circuit transmits and receives 1.544 Mbit/s concurrently. A total of 1.536 Mbit/s of bandwidth is achieved by sampling each of the twenty-four 8-bit DS0s 8000 times per second. This sampling is referred to as 8-kHz sampling (See Pulse-code modulation). An additional 8 kbit/s of overhead is obtained from the placement of one framing bit, for a total of 1.544 Mbit/s, calculated as follows:
Frame synchronization is necessary to identify the timeslots within each 24-channel frame. Synchronization takes place by allocating a framing, or 193rd, bit. This results in 8 kbit/s of framing data, for each DS1. Because this 8-kbit/s channel is used by the transmitting equipment as overhead, only 1.536 Mbit/s is actually passed on to the user. Two types of framing schemes are Super Frame (SF) and Extended Super Frame (ESF). A Super Frame consists of twelve consecutive 193-bit frames, whereas an Extended Super Frame consists of twenty-four consecutive 193-bit frames of data. Due to the unique bit sequences exchanged, the framing schemes are not compatible with each other. These two types of framing (SF, and ESF) use their 8 kbit/s framing channel in different ways.
Routers, brouters, and gateways are inter-networking devices used for connecting different networks.
Repeaters
A repeater connects two segments of your network cable. It re times and regenerates the signals to proper amplitudes and sends them to the other segments. When talking about, ethernet topology, you are probably talking about using a hub as a repeater. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay which can affect network communication when there are several repeaters in a row. Many network architectures limit the number of repeaters that can be used in a row. Repeaters work only at the physical layer of the OSI network model.
Bridges
A bridge reads the outermost section of data on the data packet, to tell where the message is going. It reduces the traffic on other network segments, since it does not send all packets. Bridges can be programmed to reject packets from particular networks. Bridging occurs at the data link layer of the OSI model, which means the bridge cannot read IP addresses, but only the outermost hardware address of the packet. In our case the bridge can read the ethernet data which gives the hardware address of the destination address, not the IP address. Bridges forward all broadcast messages. Only a special bridge called a translation bridge will allow two networks of different architectures to be connected. Bridges do not normally allow connection of networks with different architectures. The hardware address is also called the MAC (media access control) address. To determine the network segment a MAC address belongs to, bridges use one of:
Transparent Bridging - They build a table of addresses (bridging table) as they receive packets. If the address is not in the bridging table, the packet is forwarded to all segments other than the one it came from. This type of bridge is used on ethernet networks.
Source route bridging - The source computer provides path information inside the packet. This is used on Token Ring networks.
Routers
A router is used to route data packets between two networks. It reads the information in each packet to tell where it is going. If it is destined for an immediate network it has access to, it will strip the outer packet (IP packet for example), readdress the packet to the proper ethernet address, and transmit it on that network. If it is destined for another network and must be sent to another router, it will re-package the outer packet to be received by the next router and
send it to the next router. Routing occurs at the network layer of the OSI model. They can connect networks with different architectures such as Token Ring and Ethernet. Although they can transform information at the data link level, routers cannot transform information from one data format such as TCP/IP to another such as IPX/SPX. Routers do not send broadcast packets or corrupted packets. If the routing table does not indicate the proper address of a packet, the packet is discarded. There are two types of routers:
1. Static routers - Are configured manually and route data packets based on information in a router table.
2. Dynamic routers - Use dynamic routing algorithms. There are two types of algorithms:o Distance vector - Based on hop count, and periodically broadcasts the routing
table to other routers which takes more network bandwidth especially with more routers. RIP uses distance vectoring. Does not work on WANs as well as it does on LANs.
o Link state - Routing tables are broadcast at startup and then only when they change. The open shortest path first (OSPF) protocol uses the link state routing method to configure routes or distance vector algorithm (DVA).
Common routing protocols include:
IS-IS -Intermediate system to intermediate system which is a routing protocol for the OSI suite of protocols.
IPX - Internet Packet Exchange. Used on Netware systems. NLSP - Netware Link Services protocol - Uses OSPF algorithm and is replacing IPX to
provide internet capability. RIP - Routing information protocol uses a distance vector algorithm.
There is a device called a brouter which will function similar to a bridge for network transport protocols that are not routable, and will function as a router for routable protocols. It functions at the network and data link layers of the OSI network model.
Gateways
A gateway can translate information between different network data formats or network architectures. It can translate TCP/IP to AppleTalk so computers supporting TCP/IP can communicate with Apple brand computers. Most gateways operate at the application layer, but can operate at the network or session layer of the OSI model. Gateways will start at the lower level and strip information until it gets to the required level and repackage the information and work its way back toward the hardware layer of the OSI model. To confuse issues, when talking about a router that is used to interface to another network, the word gateway is often used. This does not mean the routing machine is a gateway as defined here, although it could be.
Q.Case Study Of Voip Concept.
Internet
This article is about the public worldwide computer network system. For other uses, see Internet (disambiguation).
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (often called TCP/IP, although not all protocols use TCP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies. The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support email.
Most traditional communications media including telephone, music, film, and television are reshaped or redefined by the Internet, giving birth to new services such as Voice over Internet Protocol (VoIP) and Internet Protocol Television (IPTV). Newspaper, book and other print publishing are adapting to Web site technology, or are reshaped into blogging and web feeds. The Internet has enabled or accelerated new forms of human interactions through instant messaging, Internet forums, and social networking. Online shopping has boomed both for major retail outlets and small artisans and traders. Business-to-business and financial services on the Internet affect supply chains across entire industries.
The origins of the Internet reach back to research of the 1960s, commissioned by the United States government in collaboration with private commercial interests to build robust, fault-tolerant, and distributed computer networks. The funding of a new U.S. backbone by the National Science Foundation in the 1980s, as well as private funding for other commercial backbones, led to worldwide participation in the development of new networking technologies, and the merger of many networks. The commercialization of what was by the 1990s an international network resulted in its popularization and incorporation into virtually every aspect of modern human life. As of 2011, more than 2.2 billion people — nearly a third of Earth's population — use the services of the Internet.[1]
The Internet has no centralized governance in either technological implementation or policies for access and usage; each constituent network sets its own standards. Only the overreaching definitions of the two principal name spaces in the Internet, the Internet Protocol address space and the Domain Name System, are directed by a maintainer organization, the Internet Corporation for Assigned Names and Numbers (ICANN). The technical underpinning and standardization of the core protocols (IPv4 and IPv6) is an activity of the Internet Engineering Task Force (IETF), a non-profit organization of loosely affiliated international participants that anyone may associate with by contributing technical expertise
TerminologyComputer network types by geographical scope
Near field (NFC) Body (BAN) Personal (PAN) Near-me (NAN) Local (LAN)
o Home (HAN)o Storage (SAN)
Campus (CAN) Backbone Metropolitan (MAN) Wide (WAN) Internet Interplanetary Internet
This box:
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See also: Internet capitalization conventions
Internet is a short form of the technical term internetwork,[2] the result of interconnecting computer networks with special gateways or routers. The Internet is also often referred to as the Net.
The term the Internet, when referring to the entire global system of IP networks, has been treated as a proper noun and written with an initial capital letter. In the media and popular culture, a trend has also developed to regard it as a generic term or common noun and thus write it as "the internet", without capitalization. Some guides specify that the word should be capitalized as a noun but not capitalized as an adjective.[3][4]
The terms Internet and World Wide Web are often used in everyday speech without much distinction. However, the Internet and the World Wide Web are not one and the same. The Internet establishes a global data communications system between computers. In contrast, the Web is one of the services communicated via the Internet. It is a collection of interconnected documents and other resources, linked by hyperlinks and URLs.[5]
Internet packet routing is accomplished among various tiers of Internet Service Providers.
Internet Service Providers connect customers (thought of at the "bottom" of the routing hierarchy) to customers of other ISPs. At the "top" of the routing hierarchy are ten or so Tier 1 networks, large telecommunication companies which exchange traffic directly "across" to all other Tier 1 networks via unpaid peering agreements. Tier 2 networks buy Internet transit from other ISP to reach at least some parties on the global Internet, though they may also engage in unpaid peering (especially for local partners of a similar size). ISPs can use a single "upstream" provider for connectivity, or use multihoming to provide protection from problems with individual links. Internet exchange points create physical connections between multiple ISPs, often hosted in buildings owned by independent third parties.[citation needed]
Q. To study various types of errors correcting techniques
It is to S.P. Corder that Error Analysis owes its place as a scientific method in linguistics. As Rod Ellis cites (p. 48), "it was not until the 1970s that EA became a recognized part of applied linguistics, a development that owed much to the work of Corder". Before Corder, linguists observed learners' errors, divided them into categories, tried to see which ones were common and which were not, but not much attention was drawn to their role in second language acquisition. It was Corder who showed to whom information about errors would be helpful (teachers, researchers, and students) and how.
There are many major concepts introduced by S. P. Corder in his article "The significance of learners' errors", among which we encounter the following:
1) It is the learner who determines what the input is. The teacher can present a linguistic form, but this is not necessarily the input, but simply what is available to be learned.
2) Keeping the above point in mind, learners' needs should be considered when teachers/linguists plan their syllabuses. Before Corder's work, syllabuses were based on theories and not so much on learners’ needs.
3) Mager (1962) points out that the learners' built-in syllabus is more efficient than the teacher's syllabus. Corder adds that if such a built-in syllabus exists, then learners’ errors would confirm its existence and would be systematic.
4) Corder introduced the distinction between systematic and non-systematic errors. Unsystematic errors occur in one’s native language; Corder calls these "mistakes" and states that they are not significant to the process of language learning. He keeps the term "errors" for the systematic ones, which occur in a second language.
5) Errors are significant in three ways: - to the teacher: they show a student’s progress- to the researcher: they show how a language is acquired, what strategies the learner uses. - to the learner: he can learn from these errors.
6) When a learner has made an error, the most efficient way to teach him the correct form is not by simply giving it to him, but by letting him discover it and test different hypotheses. (This is derived from Carroll's proposal (Carroll 1955, cited in Corder), who suggested that the learner should find the correct linguistic form by searching for it.
7) Many errors are due to that the learner uses structures from his native language. Corder claims that possession of one’s native language is facilitative. Errors in this case are not inhibitory, but rather evidence of one’s learning strategies.
The above insights played a significant role in linguistic research, and in particular in the approach linguists took towards errors. Here are some of the areas that were influenced by Corder's work:
STUDIES OF LEARNER ERRORS
Corder introduced the distinction between errors (in competence) and mistakes (in performance). This distinction directed the attention of researchers of SLA to competence errors and provided for a more concentrated framework. Thus, in the 1970s researchers started examining learners’ competence errors and tried to explain them. We find studies such as Richards's "A non-contrastive approach to error analysis" (1971), where he identifies sources of competence errors; L1 transfer results in interference errors; incorrect (incomplete or over-generalized) application of language rules results in intralingual errors; construction of faulty hypotheses in L2 results in developmental errors.
Not all researchers have agreed with the above distinction, such as Dulay and Burt (1974) who proposed the following three categories of errors: developmental, interference and unique. Stenson (1974) proposed another category, that of induced errors, which result from incorrect instruction of the language. As most research methods, error analysis has weaknesses (such as in methodology), but these do not diminish its importance in SLA research; this is why linguists such as Taylor (1986) reminded researchers of its importance and suggested ways to overcome these weaknesses.
As mentioned previously, Corder noted to whom (or in which areas) the study of errors would be significant: to teachers, to researchers and to learners. In addition to studies concentrating on error categorization and analysis, various studies concentrated on these three different areas. In other words, research was conducted not only in order to understand errors per se, but also in order to use what is learned from error analysis and apply it to improve language competence.
Such studies include Kroll and Schafer's "Error-Analysis and the Teaching of Composition", where the authors demonstrate how error analysis can be used to improve writing skills. They analyze possible sources of error in non-native-English writers, and attempt to provide a process approach to writing where the error analysis can help achieve better writing skills.
These studies, among many others, show that thanks to Corder's work, researchers recognized
the importance of errors in SLA and started to examine them in order to achieve a better understanding of SLA processes, i.e. of how learners acquire an L2.
Q.Case study of various routing algorithm
a router is used to manage network traffic and find the best route for sending packets. But have you ever thought about how routers do this? Routers need to have some information about network status in order to make decisions regarding how and where to send packets. But how do they gather this information?
Routers use routing algorithms to find the best route to a destination. When we say "best route," we consider parameters like the number of hops (the trip a packet takes from one router or intermediate point to another in the network), time delay and communication cost of packet transmission.
Based on how routers gather information about the structure of a network and their analysis of information to specify the best route, we have two major routing algorithms: global routing algorithms and decentralized routing algorithms. In decentralized routing algorithms, each router has information about the routers it is directly connected to -- it doesn't know about every router in the network. These algorithms are also known as DV (distance vector) algorithms
Dijkstra's algorithm
Dijkstra's algorithm runtime
Dijkstra's algorithm, conceived by Dutch computer scientist Edsger Dijkstra in 1959,[1] is a graph search algorithm that solves the single-source shortest path problem for a graph with nonnegative edge path costs, producing a shortest path tree. This algorithm is often used in routing. An equivalent algorithm was developed by Edward F. Moore in 1957.[2]
For a given source vertex (node) in the graph, the algorithm finds the path with lowest cost (i.e. the shortest path) between that vertex and every other vertex. It can also be used for finding costs of shortest paths from a single vertex to a single destination vertex by stopping the algorithm once the shortest path to the destination vertex has been determined. For example, if the vertices of the graph represent cities and edge path costs represent driving distances between pairs of cities connected by a direct road, Dijkstra's algorithm can be used to find the shortest route between one city and all other cities. As a result, the shortest path first is widely used in network routing protocols, most notably IS-IS and OSPF (Open Shortest Path First).
Algorithm
Let the node we are starting be called an initial node. Let a distance of a node Y be the distance from the initial node to it. Dijkstra's algorithm will assign some initial distance values and will try to improve them step-by-step.
1. Assign to every node a distance value. Set it to zero for our initial node and to infinity for all other nodes.
2. Mark all nodes as unvisited. Set initial node as current.3. For current node, consider all its unvisited neighbours and calculate their distance (from
the initial node). For example, if current node (A) has distance of 6, and an edge connecting it with another node (B) is 2, the distance to B through A will be 6+2=8. If this distance is less than the previously recorded distance (infinity in the beginning, zero for the initial node), overwrite the distance.
4. When we are done considering all neighbours of the current node, mark it as visited. A visited node will not be checked ever again; its distance recorded now is final and minimal.
5. Set the unvisited node with the smallest distance (from the initial node) as the next "current node" and continue from step 3.
Description of the algorithm
Suppose you're marking over the streets on a street map (tracing the street with a marker) in a certain order, until you have a route marked in from the starting point to the destination. The order is conceptually simple: from all the street intersections of the already marked routes, find the closest unmarked intersection - closest to the starting point (the "greedy" part). It's the whole marked route to the intersection, plus the street to the new, unmarked intersection. Mark that street to that intersection, draw an arrow with the direction, then repeat. Never mark any two intersections twice. When you get to the destination, follow the arrows backwards. There will be only one path back against the arrows, the shortest one.
BELLman ford AlgorithmsDV algorithms are also known as Bellman-Ford routing algorithms and Ford-Fulkerson
routing algorithms. In these algorithms, every router has a routing table that shows it the best route for any destination. A typical graph and routing table for router J is shown below.
Destination Weight Line
A 8 A
B 20 A
C 28 I
D 20 H
E 17 I
F 30 I
G 18 H
H 12 H
I 10 I
J 0 ---
K 6 K
L 15 K
A typical network graph and routing table for router J
As the table shows, if router J wants to get packets to router D, it should send them to router H. When packets arrive at router H, it checks its own table and decides how to send the packets to D.
In DV algorithms, each router has to follow these steps:
1. It counts the weight of the links directly connected to it and saves the information to its table. 2. In a specific period of time, it send its table to its neighbor routers (not to all routers) and receive
the routing table of each of its neighbors. 3. Based on the information in its neighbors' routing tables, it updates its own.
One of the most important problems with DV algorithms is called "count to infinity." Let's examine this problem with an example:
Imagine a network with a graph as shown below. As you see in this graph, there is only one link between A and the other parts of the network. Here you can see the graph and routing table of all nodes:
A B C D
A 0,- 1,A 2,B 3,C
B 1,B 0,- 2,C 3,D
C 2,B 1,C 0,- 1,C
D 3,B 2,C 1,D 0,-
Network graph and routing tables
Now imagine that the link between A and B is cut. At this time, B corrects its table. After a specific amount of time, routers exchange their tables, and so B receives C's routing table. Since C doesn't know what has happened to the link between A and B, it says that it has a link to A with the weight of 2 (1 for C to B, and 1 for B to A -- it doesn't know B has no link to A). B receives this table and thinks there is a separate link between C and A, so it corrects its table and changes infinity to 3 (1 for B to C, and 2 for C to A, as C said). Once again, routers exchange their tables. When C receives B's routing table, it sees that B has changed the weight of its link to A from 1 to 3, so C updates its table and changes the weight of the link to A to 4 (1 for C to B, and 3 for B to A, as B said).
This process loops until all nodes find out that the weight of link to A is infinity. This situation is shown in the table below. In this way, experts say DV algorithms have a slow convergence rate.
B C D
Sum of weight to A after link cut ,A 2,B 3,C
Sum of weight to B after 1st updating 3,C 2,B 3,C
Sum of weight to A after 2nd updating 3,C 4,B 3,C
Sum of weight to A after 3rd updating 5,C 4,B 5,C
Sum of weight to A after 4th updating 5,C 6,B 5,C
Sum of weight to A after 5th updating 7,C 6,B 7,C
Sum of weight to A after nth updating ... ... ...
The "count to infinity" problem
One way to solve this problem is for routers to send information only to the neighbors that are not exclusive links to the destination. For example, in this case, C shouldn't send any information to B about A, because B is the only way to A.
Q.. To study and configure various type of routers and bridge?Ans: A router is a device that forwards data packets across computer networks. Routers perform the data "traffic directing" functions on the Internet. A router is a microprocessor-controlled device that is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table, it directs the packet to the next network on its journey. A data packet is typically passed from router to router through the networks of the Internet until it gets to its destination computer. Routers also perform other tasks such as translating the data transmission protocol of the packet to the appropriate protocol of the next network, and preventing unauthorized access to a network by the use of a firewall.[1]
Types of Routers
There are several types of routers that you will want to understand. You need to know the difference so that you can set up your network or at least so that you can understand what the local computer guy tells you to do.
1.Broadband Routers
Broadband routers can be used to do several different types of things. They can be used to connect two different computers or to connect two computers to the Internet. They can also be used to create a phone connection.
If you are using Voice over IP (VoIP) technology, then you will need a broadband router to connect your Internet to your phone. These are often a special type of modem that will have both Ethernet and phone jacks. Although this may seem a little confusing, simply follow the instructions that your VoIP provider sends with your broadband router - usually you must purchase the router from the company in order to obtain the service.
2.Wireless Routers
Wireless routers connect to your modem and create a wireless signal in your home or office. So, any computer within range can connect to your wireless router and use your broadband Internet for free. The only way to keep anyone from connecting to your system is to secure your router.
A word of warning about wireless routers: Be sure your secure them, or you will be susceptible to hackers and identity thieves. In order to secure your router, you simply need to come to WhatIsMyIPAddress.com, and get your IP address. Then, you'll type that into your web browser and log into your router (the user ID and password will come with your router).
There are six main types of bridges: beam bridges, cantilever bridges, arch bridges, suspension bridges, cable-stayed bridges.
1.Beam bridges
Beam bridges are horizontal beams supported at each end by abutments, hence their structural name of simply supported. When there is more than one span the intermediate supports are known as piers. The earliest beam bridges were simple logs that sat across streams and similar simple structures. In modern times, beam bridges are large box steel girder bridges. Weight on top of the beam pushes straight down on the abutments at either end of the bridge. [11] They are made up mostly of wood or metal. Beam bridges typically do not exceed 250 feet (76 m) long. The longer the bridge, the weaker. The world's longest beam bridge is Lake Pontchartrain Causeway in southern Louisiana in the United States, at 23.83 miles (38.35 km), with individual spans of 56 feet (17 m).[12]
2.Cantilever bridges
Cantilever bridges are built using cantilevers—horizontal beams that are supported on only one end. Most cantilever bridges use a pair ofcontinuous spans extending from opposite sides of the supporting piers, meeting at the center of the obstacle to be crossed. Cantilever bridges are constructed using much the same materials & techniques as beam bridges. The difference comes in the action of the forces through the bridge. The largest cantilever bridge is the 549-metre (1,801 ft) Quebec Bridge in Quebec, Canada.
Arch bridges have abutments at each end. The earliest known arch bridges were built by the Greeks and include the Arkadiko Bridge. The weight of the bridge is thrust into the abutments at either side. Dubai in the United Arab Emirates is currently building the Sheikh Rashid bin Saeed Crossing which is scheduled for completion in 2012. When completed, it will be the largest arch bridge in the world.[13]
4.Suspension bridges
Suspension bridges are suspended from cables. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo. In modern bridges, the cables hang from towers that are attached to caissons or cofferdams. The caissons or cofferdams are implanted deep into the floor of a lake or river. The longest suspension bridge in the world is the 12,826 feet (3,909 m) Akashi Kaikyo Bridge in Japan.[14] Seesimple suspension bridge, stressed ribbon bridge, underspanned suspension bridge, suspended-deck suspension bridge, and self-anchored suspension bridge.
5.Cable-stayed bridges
Cable-stayed bridges, like suspension bridges, are held up by cables. However, in a cable-stayed bridge, less cable is required and the towers holding the cables are proportionately shorter. [15] The first known cable-stayed bridge was designed in 1784 by C.T. Loescher. [16] The longest cable-stayed bridge is the Sutong Bridge over the Yangtze River in China.
Easily extendable script language which became most famous for the "TcTk GuiToolkit" and "TclExpect", as well as for easy embeddability, but it is increasingly used in other spheres. Some of its most unique features:
Everything is a string (native representation is used behind the scenes). All values can be used inter-changeably and anywhere where a string can be used for natural serialization.
Extremely minimalistic syntax: cmd arg arg arg ... No reserved keywords No static language constructs (for, while etc. are just commands like any
which greatly reduces the need for threads Has a threading system, too. Everything can be dynamically changed and replaced (remember: language
constructs are also just commands too!) The Virtual Filesystem mechanism Doesn't force any particular programming paradigm. For instance, a wide
range of OO extensions exist from the more traditional [incr Tcl] to the more dynamic ExtendedObjectTcl and delegation -style Snit.
Cons of the TCL Language:
Not terribly fast, perl and python are generally faster. Usually fast enough though.
o As usual, it depends on exactly what you are doing, with common benchmarks often being written to make other languages look good. The old quote about "lies, damned lies and benchmarks" does apply.
Events in Tk are evaluated at the top level scope. No closure tricks for you. Lots of "gotchas" with respect to quoting
o This is a bit inbetween really; the quoting rules are actually very simple, but beginners do sometimes have problems, as they infer extra semantics which aren't really there (typically by assuming {} marks blocks of code like in C).
o I find it's difficult to x-ray or study all the potential levels of quoting and escape indirection unwinding. It's sort of the quote-level version ofThickBreadSmell. I'd rather break things up a bit, DivideAndConquer and have a language that facilitates such.
No anonymous functions - packages that do appear to provide them create global objects that are not garbage collected among other problems.
o However anonymous code fragments are available, and version 8.5 allows these fragments to have scopes.
o Doesn't the "apply" command in Tcl 8.5 provide anonymous functions? Suffered under a disgustingly hype-laden regime under scriptics. ("Leverage
your cross-functional b2b synergies with scripting!") Thankfully no longer a problem after the dot com crash.
More on TCL
It is untyped and uncompiled [-- It does, however, utilize a bytecode compiler for efficiency now, making it about as slow as other scripting languages]. Tcl is much more a dynamic language than comparable scripting languages, and makes use of data as code model to great advantage.
TCL's main attraction is its small footprint, ease of network and GUI programming, event model, write-once-run-many (programmers usually have to go out of their way to make Tcl programs platform specific.)
It has a C API which makes embedding an interpreter easy (making it an EmbeddedLanguage). Passing data back and forth is easy, as is writing extension commands to the interpreter.
See http://wiki.tcl.tk/4364 (a two-player car racing game in 127 LOC) or http://wiki.tcl.tk/4448 (pages on TheTclersWiki) for examples of why some people like Tcl so much - brevity and automation of complex tasks.
Tcl was invented by JohnOusterhout while he was a professor at CalBerkeley.
Tcl has several implementations and is widely available on many platforms: Unix, MacOs9/ MacOsx, Windows, Palm OS, Windows CE, MSDOS, several realtime OS's, and as a browser plugin for Mozilla, Netscape, Windows IE. Tcl is also available
as Jacl, a Tcl port to Java, thus it also runs anywhere Java runs. See: http://tcljava.sf.net
Hiring Tclers
You will find a list of Tclers interested in doing contract work or working full time here: http://wiki.tcl.tk/1588
Comments
Indeed, Tk is popular; it can even be accessed from Python and Perl (and Erlang). -- FalkBruegmann
Tk is a common reason Tcl is widely used. It is a very good GUI toolkit: lightweight, easy to use, simple to extend. It had a Motif look and feel,but was far simpler to use than Motif. It now uses the local look-and-feel of the platform on which it is running [- which is Motif on UNIX]. It is quite common that programs written on Unix/X11 runs unchanged on Windows and Mac (the same is true for Windows to Unix.)
Tcl as a language is highly dynamic and provides useful introspection facilities. If one writes idiomatic Tcl, using MetaProgramming techniques, rather than using it in the way one writes C or Pascal, one can write efficient and elegant programs. -- NatPryce
Nat, how are those techniques when used for Tcl? I've written quite a lot of Tcl/Tk code but I am not sure of what you are talking about. A friend and I were thinking about writing a Tcl module so we could make an abstraction layer for access to databases. The idea was creating something similar to DBI in Perl or JDBC in Java, but for Tcl (starting with postgresql). I got a nice design and when I sent it to my friend, he had already written a prototype, which created a 'database widget', similar to a Tk widget, indeed virtually indistinguishable. I found the idea fascinating and so we took that approach. Is this that metaprogramming you're talking about? -- DavidDeLis
Q. study and installation steps of standard network simulator n.s-2.
ns (from network simulator) is a name for series of discrete event network simulators, specifically ns-1, ns-2 and ns-3. All of them are discrete-event network simulator, primarily used in research[4] and teaching. ns-3 is free software, publicly available under the GNU GPLv2 license for research, development, and use.
The goal of the ns-3 project is to create an open simulation environment for networking research that will be preferred inside the research community:[citation needed]
It should be aligned with the simulation needs of modern networking research.
It should encourage community contribution, peer review, and validation of the software.
Since the process of creation of a network simulator that contains a sufficient number of high-quality validated, tested and actively maintained models requires a lot of work, ns-3 project spreads this workload over a large community of users and developers
ns-1
The first version of ns, known as ns-1, was developed at Lawrence Berkeley National Laboratory (LBNL) in the 1995-97 timeframe by Steve McCanne, Sally Floyd, Kevin Fall, and other contributors. This was known as the LBNL Network Simulator, and derived from an earlier simulator known as REAL by S. Keshav. The core of the simulator was written in C++, with Tcl-based scripting of simulation scenarios.[5] Long-running contributions have also come from Sun Microsystems, the UC Berkeley Daedelus, and Carnegie Mellon Monarch projects.
ns-2
In 1996-97, ns version 2 (ns-2) was initiated based on a refactoring by Steve McCanne. Use of Tcl was replaced by MIT'sObject Tcl (OTcl), an object-oriented dialect of Tcl. The core of ns-2 is also written in C++, but the C++ simulation objects are linked to shadow objects in OTcl and variables can be linked between both language realms. Simulation scripts are written in the OTcl language, an extension of the Tcl scripting language.
Presently, ns-2 consists of over 300,000 lines of source code, and there is probably a comparable amount of contributed code that is not integrated directly into the main distribution (many forks of ns-2 exist, both maintained and unmaintained). It runs on GNU/Linux, FreeBSD, Solaris, Mac OS X and Windows versions that support Cygwin. It is licensed for use underversion 2 of the GNU General Public License.
ns-3
A team led by Tom Henderson (University of Washington), George Riley (Georgia Institute of Technology), Sally Floyd, and Sumit Roy (University of Washington), applied for and received funding from the U.S. National Science Foundation (NSF) to build a replacement for ns-2, called
ns-3. This team collaborated with the Planete project of INRIA at Sophia Antipolis, with Mathieu Lacage as the software lead, and formed a new open source project joined by other developers worldwide.
In the process of developing ns-3, it was decided to completely abandon backward-compatibility with ns-2. The new simulator would be written from scratch, using the C++ programming language. Development of ns-3 began in July 2006. A framework for generating Python bindings (pybindgen) and use of the Waf build system were contributed by Gustavo Carneiro.
The first release, ns-3.1 was made in June 2008, and afterwards the project continued making quarterly software releases, and more recently has moved to three releases per year. ns-3 made its eighteenth release (ns-3.18) in the third quarter of 2013.
Current status of the three versions is:
ns-1 is no longer developed nor maintained, ns-2 build of 2009 is not actively maintained (and is not being accepted for journal
publications[citation needed]) ns-3 is actively developed (but not compatible for work done on ns-2)
Design
ns-3 is built using C++ and Python with scripting capability. The ns-3 library is wrapped to python thanks to the pybindgen library which delegates the parsing of the ns-3 C++ headers to gccxml and pygccxml to generate automatically the corresponding C++ binding glue. These automatically-generated C++ files are finally compiled into the ns-3 python module to allow users to interact with the C++ ns-3 models and core through python scripts. The ns-3 simulator features an integrated attribute-based system to manage default and per-instance values for simulation parameters. All of the configurable default values for parameters are managed by this system, integrated with command-line argument processing, Doxygen documentation, and an XML-based and optional GTK-based configuration subsystem.
The large majority of its users focuses on wireless simulations which involve models for Wi-Fi, WiMAX, or LTE for layers 1 and 2 and routing protocols such as OLSR and AODV.
Components
ns-3 is split over couple dozen modules containing one or more models for real-world network devices and protocols.
ns-3 has more recently integrated with related projects: the Direct Code Execution extensions allowing the use of C or C++-based applications and Linux kernel code in the simulations, and the NetAnim offline animator based on the Qttoolkit.
Q.Case Study Of Various Type Of Cryptographic Algorithm ( Diffie Hellman Rsa EtcIn an asymmetric key encryption scheme, anyone can encrypt messages using the public key, but only the holder of
the paired private key can decrypt. Security depends on the secrecy of the private key.
In the Diffie–Hellman key exchangescheme, each party generates a public/private key pair and distributes the public
key. After obtaining an authentic copy of each other's public keys, Alice and Bobcan compute a shared secret offline.
The shared secret can be used, for instance, as the key for a symmetric cipher.
Public-key cryptography, also known as asymmetric cryptography, is a class
of cryptographic algorithms which require two separate keys, one of which is secret (or private) and
one of which is public. Although different, the two parts of this key pair are mathematically linked.
The public key is used toencrypt plaintext or to verify a digital signature; whereas the private key is
used to decrypt ciphertext or to create a digital signature. The term "asymmetric" stems from the use
of different keys to perform these opposite functions, each the inverse of the other – as contrasted
with conventional ("symmetric") cryptography which relies on the same key to perform both.
Public-key algorithms are based on mathematical problems which currently admit no efficient
solution that are inherent in certain integer factorization,discrete logarithm, and elliptic
curve relationships. It is computationally easy for a user to generate their own public and private key-
pair and to use them for encryption and decryption. The strength lies in the fact that it is "impossible"
(computationally unfeasible) for a properly generated private key to be determined from its
corresponding public key. Thus the public key may be published without compromising security,
whereas the private key must not be revealed to anyone not authorized to read messages or
perform digital signatures. Public key algorithms, unlike symmetric key algorithms, do notrequire
a secure initial exchange of one (or more) secret keys between the parties.
Message authentication involves processing a message with a private key to produce a digital
signature. Thereafter anyone can verify this signature by processing the signature value with the
signer's corresponding public key and comparing that result with the message. Success confirms the
message is unmodified since it was signed, and – presuming the signer's private key has remained
secret to the signer – that the signer, and no one else, intentionally performed the signature
operation. In practice, typically only a hash or digestof the message, and not the message itself, is
encrypted as the signature.
Public-key algorithms are fundamental security ingredients in cryptosystems, applications and
protocols. They underpin such Internet standards asTransport Layer Security (TLS), PGP, and GPG.
Some public key algorithms provide key distribution and secrecy (e.g., Diffie–Hellman key
exchange), some provide digital signatures (e.g., Digital Signature Algorithm), and some provide
both (e.g., RSA).
How it works[edit]
The distinguishing technique used in public-key cryptography is the use of asymmetric key
algorithms, where the key used to encrypt a message is not the same as the key used to decrypt it.
Each user has a pair of cryptographic keys – a public encryption key and a private decryption key. Similarly, a key pair used for digital signatures consists of a private signing key and a public verification key. The public key is widely distributed, while the private key is known only to its
proprietor. The keys are related mathematically, but the parameters are chosen so that calculating
the private key from the public key is either impossible or prohibitively expensive.
In contrast, symmetric-key algorithms – variations of which have been used for thousands of years – use a single secret key, which must be shared and kept private by both the sender and the receiver, for both encryption and decryption. To use a symmetric encryption scheme, the sender and receiver must securely share a key in advance.
Because symmetric key algorithms are nearly always much less computationally intensive than asymmetric ones, it is common to exchange a key using a key-exchange algorithm, then transmit data using that key and a symmetric key algorithm. PGP and the SSL/TLS family of schemes use this procedure, and are thus called hybrid cryptosystems.
There are two main uses for public-key cryptography:
Public-key encryption, in which a message is encrypted with a recipient's public key. The message cannot be decrypted by anyone who does not possess the matching private key, who is thus presumed to be the owner of that key and the person associated with the public key. This is used in an attempt to ensure confidentiality.
Digital signatures , in which a message is signed with the sender's private key and can be verified by anyone who has access to the sender's public key. This verification proves that the sender had access to the private key, and therefore is likely to be the person associated with the public key. This also ensures that the message has not been tampered, as any manipulation of the message will result in changes to the encoded message digest, which otherwise remains unchanged between the sender and receiver.
An analogy to public-key encryption is that of a locked mail box with a mail slot. The mail slot is exposed and accessible to the public – its location (the street address) is, in essence, the public key. Anyone knowing the street address can go to the door and drop a written message through the slot. However, only the person who possesses the key can open the mailbox and read the message.
An analogy for digital signatures is the sealing of an envelope with a personal wax seal. The message can be opened by anyone, but the presence of the unique seal authenticates the sender.
A central problem with the use of public-key cryptography is confidence/proof that a particular public key is authentic, in that it is correct and belongs to the person or entity claimed, and has not been tampered with or replaced by a malicious third party. The usual approach to this problem is to use a public-key infrastructure (PKI), in which one or more third parties – known as certificate authorities – certify ownership of key pairs. PGP, in addition to being a certificate authority structure, has used a scheme generally called the "web of trust", which decentralizes such authentication of public keys by a central mechanism, and substitutes individual endorsements of the link between user and public key. To date, no fully satisfactory solution to the "public key authentication problem" has been found.
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