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Articles indexed in April 2012

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• Index Change event for Combobox of gridtemplateColumn in Telerik

  - by Ankur

  I can write a code. In this I can take a Template Column & in this I build a RadCombobox. When it's Index changed I want to affect the below text box. Link the selected value of the Combo box is set as Text on Below TextBox. Combo Box & Text Box are different Controls of Different Template Column. I can Write Control of Combo box like this : <telerik:RadComboBox ID="cmbGID" runat="server" DataSourceID="SqlDataSource8" DataTextField="Name" DataValueField="ID" AutoPostBack="True" OnSelectedIndexChanged="cmbGID_SelectedIndexChanged"> But I don't know the parameters of this event like this : protected void cmbGID_SelectedIndexChanged() { //code... } Any one plz tell me that parameters & tell me is that possible to set txtValue.Text = cmbGID.SelectedValue.ToString()...???

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• cannot set a variable to base on user input post method

  - by user1318960

  Hello i´m trying to set info from a post method into a variable that sets a session named name the value that the user input. I get the following error: Notice: Undefined index: name in F:\xampp\htdocs\Impossible game\index.php on line 18 This is line 18: $session = $_POST['name']; <form action="ms1.php" method="POST"> Name <input type="text" name="name"> <input type="Submit" value="Begin"> </form> <?php $session = $_POST['name']; session_start(); $_SESSION['name'] = $session;

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• go up to 3 level dephth in hibernate criterion

  - by Satyajitsinh Raijada

  i am using hibernate criterion for fetching results. Here with i provided demo design of my persistence class. Class A{ private B b; } Class B{ private C c; } Class C{ private Long val; } assume these are the hibernate persistence classes i am not writing all annotations of mapping with database. now my problem is i want to retrieve results of Class A according to the value of Class C's val property. i tried to fetch it using, Criteria c = Restrictions.eq("b.c.val", value); List l = c.list; it shows could not resolve property. i searched and came to know criteria wont work up to this much depth. i don't want shift to HQL. any idea??

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• implicit declaration of function usleep

  - by ant2009

  gcc (GCC) 4.6.3 c89 Hello, I am trying to use usleep. However, I keep getting the following warning: implicit declaration of function usleep I have included the unistd.h header file. The man pages mentions something about this. But I am not sure I understand by it: usleep(): Since glibc 2.12: _BSD_SOURCE || (_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) && !(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700) Before glibc 2.12: _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED But not sure what I a to do with the above? Many thanks for any suggestions,

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• How do I Benchmark RESTful Service with Variable Parameters?

  - by Eli

  I'm currently working on benchmarking a RESTful service I've made, and part of that is making sure it runs in a reasonable amount of times for a large array of parameters. For example, let's say I have RESTful API of the form some_site.com/item?item_id=y. In that case to be sure my service is working as fast as I'd like it to work, I'd want to try out many values for y one by one, preferably coming from some text file. I can't figure out any way of doing this in ab or httperf. I'm open to using a different benchmarking program if I have, but would prefer something simple and light. What I want to do seems like something pretty standard, so I'm guessing there must already be a program that let's me do it, but an hour or so of googling hasn't gotten me an answer. Ideas?

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• Python unicode search not giving correct answer

  - by user1318912

  I am trying to search hindi words contained one line per file in file-1 and find them in lines in file-2. I have to print the line numbers with the number of words found. This is the code: import codecs hypernyms = codecs.open("hindi_hypernym.txt", "r", "utf-8").readlines() words = codecs.open("hypernyms_en2hi.txt", "r", "utf-8").readlines() count_arr = [] for counter, line in enumerate(hypernyms): count_arr.append(0) for word in words: if line.find(word) >=0: count_arr[counter] +=1 for iterator, count in enumerate(count_arr): if count>0: print iterator, ' ', count This is finding some words, but ignoring some others The input files are: File-1: ???? ??????? File-2: ???????, ????-???? ?????-???, ?????-???, ?????_???, ?????_??? ????_????, ????-????, ???????_???? ????-???? This gives output: 0 1 3 1 Clearly, it is ignoring ??????? and searching for ???? only. I have tried with other inputs as well. It only searches for one word. Any idea how to correct this?

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• Python Importing object that originates in one module from a different module into a third module

  - by adewinter

  I was reading the sourcode for a python project and came across the following line: from couchexport.export import Format (source: https://github.com/wbnigeria/couchexport/blob/master/couchexport/views.py#L1 ) I went over to couchexport/export.py to see what Format was (Class? Dict? something else?). Unfortunately Format isn't in that file. export.py does however import a Format from couchexport.models where there is a Format class (source: https://github.com/wbnigeria/couchexport/blob/master/couchexport/models.py#L11). When I open up the original file in my IDE and have it look up the declaration, in line I mentioned at the start of this question, it leads directly to models.py. What's going on? How can an import from one file (export.py) actually be an import from another file (models.py) without being explicitly stated?

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• MySQL storage engine dilemma

  - by burntblark

  There are two MySQL database features that I want to use in my application. The first is FULL-TEXT-SEARCH and TRANSACTIONS. Now, the dilemma here is that I cannot get this feature in one storage engine. It's either I use MyIsam (which has the FULL-TEXT-SEARCH feature) or I use InnoDB (which supports the TRANSACTION feature). I can't have both. My question is, is there anyway I can have both features in my application before I am forced to make a choice between the two storage engines.

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• How to make margin be relative to the center of the UIElement and not its top-left corner in a Grid?

  - by Nockawa

  I'd like the Margin property to reference the center of the UIElement and not the top-left corner. That way when I change the width/height of the UIElement it stays in the same spot. Is there a way to configure this behavior or I'll have to rely on Binding to make the adjustment ? Thanks. For instance if I change the Width/Height of the following rectangle, its center will move. <Grid> <Rectangle Fill="#FF991C1C" Width="10" Height="40" HorizontalAlignment="Left" Margin="90,161,0,0" VerticalAlignment="Top"/> </Grid>

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• Android Google Analytics

  - by ibenot

  I'm trying to use Google Analytics in my Android application with Google Configuration Add .jar in my project Insert this in AndroidManifest Add this in my java file public class MainActivity extends Activity { GoogleAnalyticsTracker tracker; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); tracker = GoogleAnalyticsTracker.getInstance(); tracker.startNewSession("My-UA–XXXXXXXX", this); setContentView(R.layout.main); Button createEventButton = (Button)findViewById(R.id.NewEventButton); createEventButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { tracker.trackEvent( "Clicks", // Category "Button", // Action "clicked", // Label 77); // Value } }); setContentView(R.layout.main); Button createPageButton = (Button)findViewById(R.id.NewPageButton); createPageButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // Add a Custom Variable to this pageview, with name of "Medium" and value "MobileApp" and // scope of session-level. tracker.setCustomVar(1, "Navigation Type", "Button click", 2); // Track a page view. This is probably the best way to track which parts of your application // are being used. // E.g. // tracker.trackPageView("/help"); to track someone looking at the help screen. // tracker.trackPageView("/level2"); to track someone reaching level 2 in a game. // tracker.trackPageView("/uploadScreen"); to track someone using an upload screen. tracker.trackPageView("/testApplicationHomeScreen"); } }); Button quitButton = (Button)findViewById(R.id.QuitButton); quitButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { finish(); } }); Button dispatchButton = (Button)findViewById(R.id.DispatchButton); dispatchButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // Manually start a dispatch, not needed if the tracker was started with a dispatch // interval. tracker.dispatch(); } }); } @Override protected void onDestroy() { super.onDestroy(); // Stop the tracker when it is no longer needed. tracker.stopSession(); } } == And it's ok, no error, compiling and executing but i have created my ua account yesterday (more 24h) and i have nothing in my google analytics panel. My Question : is there an error in my code or i want to wait again ? Live trafic works for Android application (like tradicional website) ??? I have no information about Live trafic (when i play my app, i would like to show the number of person using my application) and Saved trafic (with viewed pages, time) Thank you for your replies and excuse my poor english :) bye

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• Rails - Format number as currency format in the Getter

  - by daemonsy

  I am making a simple retail commerce solution, where there are prices in a few different models. These prices contribute to a total price. Imagine paying $0.30 more for selecting a topping for your yogurt. When I set the price field to t.decimal :price, precision:8, scale:2 The database stores 6.50 as 6.5. I know in the standard rails way, you call number_to_currency(price) to get the formatted value in the Views. I need to programmatically call the price field as well formatted string, i.e. $6.50 a few places that are not directly part of the View. Also, my needs are simple (no currency conversion etc), I prefer to have the price formatted universally in the model without repeated calling number_to_currency in views. Is there a good way I can modify my getter for price such that it always returns two decimal place with a dollar sign, i.e. $6.50 when it's called? Thanks in advance.

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• Unreasonable errors in merge sort

  - by Alexxx

  i have the following errors - please help me to find the error: 9 IntelliSense: expected a '}' 70 4 it points on the end of the code - but there are no open { anywhere!! so why?? 8 IntelliSense: expected a ';' 57 1 it points on the { after the void main but why to put ; after the { of the void main?? Error 7 error C1075: end of file found before the left brace '{' at 70 1 points to the beginig of the code - why??? #include <stdio.h> #include <stdlib.h> void merge(int *a,int p,int q,int r) { int i=p,j=q+1,k=0; int* temp=(int*)calloc(r-p+1, sizeof(int)); while ((i<=q)&& (j<=r)) if(a[i]<a[j]) temp[k++]=a[i++]; else temp[k++]=a[j++]; while(j<=r) // if( i>q ) temp[k++]=a[j++]; while(i<=q) // j>r temp[k++]=a[i++]; for(i=p,k=0;i<=r;i++,k++) // copy temp[] to a[] a[i]=temp[k]; free(temp); } void merge_sort(int *a,int first, int last) { int middle; if(first < last) { middle=(first+last)/2; merge_sort(a,first,middle); merge_sort(a,middle+1,last); merge(a,first,middle,last); { } void main() { int a[] = {9, 7, 2, 3, 5, 4, 1, 8, 6, 10}; int i; merge_sort(a, 0, 9); for (i = 0; i < 10; i++) printf ("%d ", a[i]);

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• How can I show print statements in debug mode of OPNET Modeler?

  - by Here now

  I'm writing C++ code in OPNET Modeler. I try to simulate my scenario in debugger mode & I need to trace the function that I wrote it. I need to show print statements which I put it in my code. I used in debugger mode: ***ltr function_name()*** then ***c*** But the result looks like: Type 'help' for Command Summary ODB> ltr enqueue_packet() Added trace #0: trace on label (enqueue_packet()) ODB> c |-----------------------------------------------------------------------------| | Progress: Time (1 min. 52 sec.); Events (500,002) | | Speed: Average (82,575 events/sec.); Current (82,575 events/sec.) | | Time : Elapsed (6.1 sec.) | | DES Log: 28 entries | |-----------------------------------------------------------------------------| |-----------------------------------------------------------------------------| | Progress: Time (1 min. 55 sec.); Events (1,000,002) | | Speed: Average (69,027 events/sec.); Current (59,298 events/sec.) | | Time : Elapsed (14 sec.) | | DES Log: 28 entries | |-----------------------------------------------------------------------------| |-----------------------------------------------------------------------------| | Progress: Time (1 min. 59 sec.); Events (1,500,002) | | Speed: Average (51,464 events/sec.); Current (34,108 events/sec.) | | Time : Elapsed (29 sec.) | | DES Log: 28 entries | |-----------------------------------------------------------------------------| |-----------------------------------------------------------------------------| | Simulation Completed - Collating Results. | | Events: Total (1,591,301); Average Speed (48,803 events/sec.) | | Time : Elapsed (33 sec.); Simulated (2 min. 0 sec.) | | DES Log: 29 entries | |-----------------------------------------------------------------------------| |-----------------------------------------------------------------------------| | Reading network model. | |-----------------------------------------------------------------------------| I need to show the print statements in my code. Where it has to be appeared? Is there any step before run the simulation to insure that OPNET debugger using Visual Studio & go through my code??

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• getline won't let me type, c++

  - by Stijn

  I try to get the name of a game the users chooses and store it in a vector. I use getline so the user can use a space. When I try to type a new game to add it won't let me. It automaticly displays me games library. Please tell me what I do wrong. Problem is at if(action == "add") Here's my code: #include <iostream> #include <string> #include <vector> #include <algorithm> #include <ctime> #include <cstdlib> using namespace std; int main() { vector<string>::const_iterator myIterator; vector<string>::const_iterator iter; vector<string> games; games.push_back("Crysis 2"); games.push_back("GodOfWar 3"); games.push_back("FIFA 12"); cout <<"Welcome to your Games Library.\n"; cout <<"\nThese are your games:\n"; for (iter = games.begin(); iter != games.end(); ++iter) { cout <<*iter <<endl; } //the loop! string action; string newGame; cout <<"\n-Type 'exit' if you want to quit.\n-Type 'add' if you want to add a game.\n-Type 'delete' if you want to delete a game.\n-Type 'find' if you want to search a game.\n-Type 'game' if you don't know what game to play.\n-Type 'show' if you want to view your library."; while (action != "exit") { cout <<"\n\nWhat do you want to do: "; cin >> action; //problem is here if (action == "add") { cout <<"\nType the name of the game you want to add: "; getline (cin, newGame); games.push_back(newGame); for (iter = games.begin(); iter != games.end(); ++iter) { cout <<*iter <<endl; } continue; } else if (action == "show") { cout <<"\nThese are your games:\n"; for (iter = games.begin(); iter != games.end(); ++iter) { cout <<*iter <<endl; } } else if (action == "delete") { cout <<"Type the name of the game you want to delete: "; cin >> newGame; getline (cin, newGame); iter = find(games.begin(), games.end(), newGame); if(iter != games.end()) { games.erase(iter); cout <<"\nGame deleted!"; } else { cout<<"\nGame not found."; } continue; } else if (action == "find") { cout <<"Which game you want to look for in your library: "; cin >> newGame; getline (cin, newGame); iter = find(games.begin(), games.end(), newGame); if (iter != games.end()) { cout << "Game found.\n"; } else { cout << "Game not found.\n"; } continue; } else if (action == "game") { srand(static_cast<unsigned int>(time(0))); random_shuffle(games.begin(), games.end()); cout << "\nWhy don't you play " << games[0]; continue; } else if (action == "quit") { cout <<"\nRemember to have fun while gaming!!\n"; break; } else { cout <<"\nCommand not found"; } } return 0; }

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• PHP getting full server name including port number and protocol

  - by vivid-colours

  In PHP, is there a reliable and good way of getting these things: Protocol: i.e. http or https Servername: e.g. localhost Portnumber: e.g. 8080 I can get the server name using $_SERVER['SERVER_NAME']. I can kind of get the protocol but I don't think it's perfect: if(strtolower(substr($_SERVER["SERVER_PROTOCOL"],0,5))=='https') { return "https"; } else { return "http"; } I don't know how to get the port number though. The port numbers I am using are not 80.. they are 8080 and 8888. Thank you.

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• Cheapest way of binding local variable to closure

  - by mmotorny

  I believe following to be a cheapest way of binding local variable to closure: void ByRValueReference(A&& a) { } std::function<void ()> CreateClosureByRValueReference() { A a; std::function<void ()> f = std::bind(&ByRValueReference, std::move(a)); // !!! return f; } However, it does not compile under Clang 3.1: error: no viable conversion from '__bind<void (*)(A &&), A>' to 'std::function<void ()>' and gcc 4.6.1: /usr/include/c++/4.6/functional:1778:2: error: no match for call to ‘(std::_Bind<void (*(A))(A&&)>) ()’ Am I violating the standard or it's just broken standard libraries?

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• ASP.NET MVC: Is it good to access HttpContext in a controller?

  - by Zach

  I've been working with ASP.NET(WebForm) for a while, but new to ASP.NET MVC. From many articles I've read, in most cases the reason that the controllers are hard to test is because they are accessing the runtime components: HttpContext (including Request, Response ...). Accessing HttpContext in a controller seems bad. However, I must access these components somewhere, reading input from Request, sending results back via Response, and using Session to hold a few state variables. So where is the best place to access these runtime components if we don't access them in a controller? Best regards, Zach@Shine

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• Recording audio from many source/microphones

  - by user657429

  I'm curious if it's possible to record audio from many sources and if not, what's the limitation. Many current devices have two internal microphones (basically for noise reduction). On top of that it's possible to plug additional external one using audiojack. You can as well have another audio stream via bluetooth headset. You are allowed to specify AudioSource in android but is it possible to do recording from many sources at the same time? I'm also interested how the situation look like on the iOS devices.

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• Oracle Enterprise Linux or Red Hat Enterprise Linux?

  - by peturgretars

  I would highly appreciate hearing some opinions regarding the choice of Linux distribution when it comes to setting up an Oracle 11.2.0.3 RAC. We are about to install 2 node Oracle 11.2.0.3 RAC's in data centers A and B. Then we are going to have a standby in B for A and a standby in A for B using Data Guard in ASYNC transmit (long distance). Personally I have more experience with OEL and I know that for example Oracle Smart Flash Cache and zero patching downtime were only supported in OEL 5. I am not sure about OEL 6 vs RHEL 6 though. My question is, which Operating System should we go for and why, Oracle Enterprise Linux 5/6 or Red Hat Enterprise Linux 5/6? The hosting company is unfortunately not supporting OEL at the moment so if OEL is the choice then how would convince the hosting company to start using OEL and supporting it? Thanks so much!

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• Multiple instances of this carousel on a single page - can't get it to work

  - by Andy

  This code comes from a tutorial so it's not originally my own work. What I am trying to do is implement this several times on a single page. I have tried and so far failed - by numbering the id "carousel" and so forth. Any help would be seriously appreciated. I'm tearing my hair out. http://jsfiddle.net/AndyMP/zcKDV/5/ For completeness.. this is the carousel JQuery as it stands. //rotation speed and timer var speed = 5000; var run = setInterval('rotate()', speed); //grab the width and calculate left value var item_width = $('#slides li').outerWidth(); var left_value = item_width * (-1); //move the last item before first item, just in case user click prev button $('#slides li:first').before($('#slides li:last')); //set the default item to the correct position $('#slides ul').css({'left' : left_value}); //if user clicked on prev button $('#prev').click(function() { //get the right position var left_indent = parseInt($('#slides ul').css('left')) + item_width; //slide the item $('#slides ul').animate({'left' : left_indent}, 200,function(){ //move the last item and put it as first item $('#slides li:first').before($('#slides li:last')); //set the default item to correct position $('#slides ul').css({'left' : left_value}); }); //cancel the link behavior return false; }); //if user clicked on next button $('#next').click(function() { //get the right position var left_indent = parseInt($('#slides ul').css('left')) - item_width; //slide the item $('#slides ul').animate({'left' : left_indent}, 200, function () { //move the first item and put it as last item $('#slides li:last').after($('#slides li:first')); //set the default item to correct position $('#slides ul').css({'left' : left_value}); }); //cancel the link behavior return false; }); //if mouse hover, pause the auto rotation, otherwise rotate it $('#slides').hover( function() { clearInterval(run); }, function() { run = setInterval('rotate()', speed); } ); //a simple function to click next link //a timer will call this function, and the rotation will begin :) function rotate() { $('#next').click(); }

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• Execute TSQL statement with ExecuteStoreQuery in entity framework 4.0

  - by Jalpesh P. Vadgama

  I was playing with entity framework in recent days and I was searching something that how we can execute TSQL statement in entity framework. And I have found one great way to do that with entity framework ‘ExecuteStoreQuery’ method. It’s executes a TSQL statement against data source given enity framework context and returns strongly typed result. You can find more information about ExcuteStoreQuery from following link. http://msdn.microsoft.com/en-us/library/dd487208.aspx So let’s examine how it works. So Let’s first create a table against which we are going to execute TSQL statement. So I have added a SQL Express database as following. Now once we are done with adding a database let’s add a table called Client like following. Here you can see above Client table is very simple. There are only two fields ClientId and ClientName where ClientId is primary key and ClientName is field where we are going to store client name. Now it’s time to add some data to the table. So I have added some test data like following. Now it’s time to add entity framework model class. So right click project->Add new item and select ADO.NET entity model as following. After clicking on add button a wizard will start it will ask whether we need to create model classes from database or not but we already have our client table ready so I have selected generate from database as following. Once you process further in wizard it will be presented a screen where we can select the our table like following. Now once you click finish it will create model classes with for us. Now we need a gridview control where we need to display those data. So in Default.aspx page I have added a grid control like following. <%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="EntityFramework._Default" %> <asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent"> </asp:Content> <asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"> <h2> Welcome to ASP.NET! </h2> <p> To learn more about ASP.NET visit <a href="http://www.asp.net" title="ASP.NET Website">www.asp.net</a>. </p> <p> You can also find <a href="http://go.microsoft.com/fwlink/?LinkID=152368&amp;clcid=0x409" title="MSDN ASP.NET Docs">documentation on ASP.NET at MSDN</a>. <asp:GridView ID="grdClient" runat="server"> </asp:GridView> </p> </asp:Content> Now once we are done with adding Gridview its time to write code for server side. So I have written following code in Page_load event of default.aspx page. protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack) { using (var context = new EntityFramework.TestEntities()) { ObjectResult<Client> result = context.ExecuteStoreQuery<Client>("Select * from Client"); grdClient.DataSource = result; grdClient.DataBind(); } } } Here in the above code you can see that I have written create a object of our entity model and then with the help of the ExecuteStoreQuery method I have execute a simple select TSQL statement which will return a object result. I have bind that object result with gridview to display data. So now we are done with coding.So let’s run application in browser. Following is output as expected. That’s it. Hope you like it. Stay tuned for more..Till then happy programming.

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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• Computer Networks UNISA - Chap 10 &ndash; In Depth TCP/IP Networking

  - by MarkPearl

  After reading this section you should be able to Understand methods of network design unique to TCP/IP networks, including subnetting, CIDR, and address translation Explain the differences between public and private TCP/IP networks Describe protocols used between mail clients and mail servers, including SMTP, POP3, and IMAP4 Employ multiple TCP/IP utilities for network discovery and troubleshooting Designing TCP/IP-Based Networks The following sections explain how network and host information in an IPv4 address can be manipulated to subdivide networks into smaller segments. Subnetting Subnetting separates a network into multiple logically defined segments, or subnets. Networks are commonly subnetted according to geographic locations, departmental boundaries, or technology types. A network administrator might separate traffic to accomplish the following… Enhance security Improve performance Simplify troubleshooting The challenges of Classful Addressing in IPv4 (No subnetting) The simplest type of IPv4 is known as classful addressing (which was the Class A, Class B & Class C network addresses). Classful addressing has the following limitations. Restriction in the number of usable IPv4 addresses (class C would be limited to 254 addresses) Difficult to separate traffic from various parts of a network Because of the above reasons, subnetting was introduced. IPv4 Subnet Masks Subnetting depends on the use of subnet masks to identify how a network is subdivided. A subnet mask indicates where network information is located in an IPv4 address. The 1 in a subnet mask indicates that corresponding bits in the IPv4 address contain network information (likewise 0 indicates the opposite) Each network class is associated with a default subnet mask… Class A = 255.0.0.0 Class B = 255.255.0.0 Class C = 255.255.255.0 An example of calculating  the network ID for a particular device with a subnet mask is shown below.. IP Address = 199.34.89.127 Subnet Mask = 255.255.255.0 Resultant Network ID = 199.34.89.0 IPv4 Subnetting Techniques Subnetting breaks the rules of classful IPv4 addressing. Read page 490 for a detailed explanation Calculating IPv4 Subnets Read page 491 – 494 for an explanation Important… Subnetting only applies to the devices internal to your network. Everything external looks at the class of the IP address instead of the subnet network ID. This way, traffic directed to your network externally still knows where to go, and once it has entered your internal network it can then be prioritized and segmented. CIDR (classless Interdomain Routing) CIDR is also known as classless routing or supernetting. In CIDR conventional network class distinctions do not exist, a subnet boundary can move to the left, therefore generating more usable IP addresses on your network. A subnet created by moving the subnet boundary to the left is known as a supernet. With CIDR also came new shorthand for denoting the position of subnet boundaries known as CIDR notation or slash notation. CIDR notation takes the form of the network ID followed by a forward slash (/) followed by the number of bits that are used for the extended network prefix. To take advantage of classless routing, your networks routers must be able to interpret IP addresses that don;t adhere to conventional network class parameters. Routers that rely on older routing protocols (i.e. RIP) are not capable of interpreting classless IP addresses. Internet Gateways Gateways are a combination of software and hardware that enable two different network segments to exchange data. A gateway facilitates communication between different networks or subnets. Because on device cannot send data directly to a device on another subnet, a gateway must intercede and hand off the information. Every device on a TCP/IP based network has a default gateway (a gateway that first interprets its outbound requests to other subnets, and then interprets its inbound requests from other subnets). The internet contains a vast number of routers and gateways. If each gateway had to track addressing information for every other gateway on the Internet, it would be overtaxed. Instead, each handles only a relatively small amount of addressing information, which it uses to forward data to another gateway that knows more about the data’s destination. The gateways that make up the internet backbone are called core gateways. Address Translation An organizations default gateway can also be used to “hide” the organizations internal IP addresses and keep them from being recognized on a public network. A public network is one that any user may access with little or no restrictions. On private networks, hiding IP addresses allows network managers more flexibility in assigning addresses. Clients behind a gateway may use any IP addressing scheme, regardless of whether it is recognized as legitimate by the Internet authorities but as soon as those devices need to go on the internet, they must have legitimate IP addresses to exchange data. When a clients transmission reaches the default gateway, the gateway opens the IP datagram and replaces the client’s private IP address with an Internet recognized IP address. This process is known as NAT (Network Address Translation). TCP/IP Mail Services All Internet mail services rely on the same principles of mail delivery, storage, and pickup, though they may use different types of software to accomplish these functions. Email servers and clients communicate through special TCP/IP application layer protocols. These protocols, all of which operate on a variety of operating systems are discussed below… SMTP (Simple Mail transfer Protocol) The protocol responsible for moving messages from one mail server to another over TCP/IP based networks. SMTP belongs to the application layer of the ODI model and relies on TCP as its transport protocol. Operates from port 25 on the SMTP server Simple sub-protocol, incapable of doing anything more than transporting mail or holding it in a queue MIME (Multipurpose Internet Mail Extensions) The standard message format specified by SMTP allows for lines that contain no more than 1000 ascii characters meaning if you relied solely on SMTP you would have very short messages and nothing like pictures included in an email. MIME us a standard for encoding and interpreting binary files, images, video, and non-ascii character sets within an email message. MIME identifies each element of a mail message according to content type. MIME does not replace SMTP but works in conjunction with it. Most modern email clients and servers support MIME POP (Post Office Protocol) POP is an application layer protocol used to retrieve messages from a mail server POP3 relies on TCP and operates over port 110 With POP3 mail is delivered and stored on a mail server until it is downloaded by a user Disadvantage of POP3 is that it typically does not allow users to save their messages on the server because of this IMAP is sometimes used IMAP (Internet Message Access Protocol) IMAP is a retrieval protocol that was developed as a more sophisticated alternative to POP3 The single biggest advantage IMAP4 has over POP3 is that users can store messages on the mail server, rather than having to continually download them Users can retrieve all or only a portion of any mail message Users can review their messages and delete them while the messages remain on the server Users can create sophisticated methods of organizing messages on the server Users can share a mailbox in a central location Disadvantages of IMAP are typically related to the fact that it requires more storage space on the server. Additional TCP/IP Utilities Nearly all TCP/IP utilities can be accessed from the command prompt on any type of server or client running TCP/IP. The syntaxt may differ depending on the OS of the client. Below is a list of additional TCP/IP utilities – research their use on your own! Ipconfig (Windows) & Ifconfig (Linux) Netstat Nbtstat Hostname, Host & Nslookup Dig (Linux) Whois (Linux) Traceroute (Tracert) Mtr (my traceroute) Route

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• Partial sync of Mysql databases on two remote computers

  - by Beck

  Does mysql replication supports delayed sync if remote slave server is OFF? For example I want to make my developing server have a fresh copy of databases each morning. It should be partial sync, not full copy of databases each morning. And synchronization should be only ONE way, not duplex, to avoid deleting something of master server. What utilities are out there or native functionality of mysql itself? Thanks!

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• lots of dns requests from China, should I worry?

  - by nn4l

  I have turned on dns query logs, and when running "tail -f /var/log/syslog" I see that I get hundreds of identical requests from a single ip address: Apr 7 12:36:13 server17 named[26294]: client 121.12.173.191#10856: query: mydomain.de IN ANY + Apr 7 12:36:13 server17 named[26294]: client 121.12.173.191#44334: query: mydomain.de IN ANY + Apr 7 12:36:13 server17 named[26294]: client 121.12.173.191#15268: query: mydomain.de IN ANY + Apr 7 12:36:13 server17 named[26294]: client 121.12.173.191#59597: query: mydomain.de IN ANY + The frequency is about 5 - 10 requests per second, going on for about a minute. After that the same effect repeats from a different IP address. I have now logged about 10000 requests from about 25 ip addresses within just a couple of hours, all of them come from China according to "whois [ipaddr]". What is going on here? Is my name server under attack? Can I do something about this?

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