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  • Techniques for getting off the ground in any language

    - by AndyBursh
    When I start learning a new language, I have a couple of simple implementations that I like to complete to familiarise myself with the language. Currently, I write: Fibonacci and/or factorial to get the hang of writing and calling methods, and basic recursion Djikstras shortest path (with a node type) to get to grips with making classes (or whatever the language equivalent is) with methods and properties, and also using them in slightly more complex code. I was wondering: does anybody else have any techniques or tools they like to use when getting off the ground in a new language? I'm always looking for new things to add to my "start-up routine".

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  • Installing old Loki games on 12.04 64-bit results in no audio

    - by FlabbergastedPickle
    All, Here's an interesting problem. I followed instructions provided online for installing Loki Games' Heroes of Might and Magic 3 (see http://www.swanson.ukfsn.org/loki/ and http://wtanaka.com/node/7641) and got it installed and patched to the latest version. However, every time I start it regardless whether the pulseaudio is running, I get the following error: LD_LIBRARY_PATH=/usr/local/lib/Loki_Compat/ /usr/local/lib/Loki_Compat/ld-linux.so.2 /usr/local/games/Heroes3/heroes3.dynamic ALSA lib conf.c:3314:(snd_config_hooks_call) Cannot open shared library libasound_module_conf_pulse.so ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM default Couldn't open audio: My first soundcard is HDMI output and my second one is the actual soundcard (HP DM1 running 12.04 64-bit with latest updates). I did set up /etc/asound.conf as follows: asound.conf pcm.!default { type hw card 1 } ctl.!default { type hw card 1 } So, the default soundcard should work ok. Between Shadowgrounds that also stopped working and this it appears a there may be some unfinished business/regressions in 32-bit support on 64-bit systems in 12.04. Any thoughts?

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  • Humor in Documentation

    - by Lex Fridman
    Is a small amount of lighthearted wording or humor acceptable in source code documentation? For example, I have an algorithm that has a message hop around a graph (network) until its path forms a cycle. When this happens it is removed from the queue of the node it last resided on which removes it from memory. I write that in a comment, and finish the comment with "Rest in peace, little guy". That serves very little documenting purpose, but it cheers me up a bit, and I imagine it might cheer up other people I'm working with as they read through the code. Is this an acceptable practice, or should my in-code documentation resemble as much as possible the speeches of 2004 United States presidential candidate John Kerry? ;-)

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  • Easy Made Easier

    - by dragonfly
        How easy is it to deploy a 2 node, fully redundant Oracle RAC cluster? Not very. Unless you use an Oracle Database Appliance. The focus of this member of Oracle's Engineered Systems family is to simplify the configuration, management and maintenance throughout the life of the system, while offering pay-as-you-grow scaling. Getting a 2-node RAC cluster up and running in under 2 hours has been made possible by the Oracle Database Appliance. Don't take my word for it, just check out these blog posts from partners and end users. The Oracle Database Appliance Experience - Zip Zoom Zoom http://www.fuadarshad.com/2012/02/oracle-database-appliance-experience.html Off-the-shelf Oracle database servers http://normanweaver.wordpress.com/2011/10/10/off-the-shelf-oracle-database-servers/ Oracle Database Appliance – Deployment Steps http://marcel.vandewaters.nl/oracle/database-appliance/oracle-database-appliance-deployment-steps     See how easy it is to deploy an Oracle Database Appliance for high availability with RAC? Now for the meat of this post, which is the first in a series of posts describing tips for making the deployment of an ODA even easier. The key to the easy deployment of an Oracle Database Appliance is the Appliance Manager software, which does the actual software deployment and configuration, based on best practices. But in order for it to do that, it needs some basic information first, including system name, IP addresses, etc. That's where the Appliance Manager GUI comes in to play, taking a wizard approach to specifying the information needed.     Using the Appliance Manager GUI is pretty straight forward, stepping through several screens of information to enter data in typical wizard style. Like most configuration tasks, it helps to gather the required information before hand. But before you rush out to a committee meeting on what to use for host names, and rely on whatever IP addresses might be hanging around, make sure you are familiar with some of the auto-fill defaults for the Appliance Manager. I'll step through the key screens below to highlight the results of the auto-fill capability of the Appliance Manager GUI.     Depending on which of the 2 Configuration Types (Config Type screen) you choose, you will get a slightly different set of screens. The Typical configuration assumes certain default configuration choices and has the fewest screens, where as the Custom configuration gives you the most flexibility in what you configure from the start. In the examples below, I have used the Custom config type.     One of the first items you are asked for is the System Name (System Info screen). This is used to identify the system, but also as the base for the default hostnames on following screens. In this screen shot, the System Name is "oda".     When you get to the next screen (Generic Network screen), you enter your domain name, DNS IP address(es), and NTP IP address(es). Next up is the Public Network screen, seen below, where you will see the host name fields are automatically filled in with default host names based on the System Name, in this case "oda". The System Name is also the basis for default host names for the extra ethernet ports available for configuration as part of a Custom configuration, as seen in the 2nd screen shot below (Other Network). There is no requirement to use these host names, as you can easily edit any of the host names. This does make filling in the configuration details easier and less prone to "fat fingers" if you are OK with these host names. Here is a full list of the automatically filled in host names. 1 2 1-vip 2-vip -scan 1-ilom 2-ilom 1-net1 2-net1 1-net2 2-net2 1-net3 2-net3     Another auto-fill feature of the Appliance Manager GUI follows a common practice of deploying IP Addresses for a RAC cluster in sequential order. In the screen shot below, I entered the first IP address (Node1-IP), then hit Tab to move to the next field. As a result, the next 5 IP address fields were automatically filled in with the next 5 IP addresses sequentially from the first one I entered. As with the host names, these are not required, and can be changed to whatever your IP address values are. One note of caution though, if the first IP Address field (Node1-IP) is filled out and you click in that field and back out, the following 5 IP addresses will be set to the sequential default. If you don't use the sequential IP addresses, pay attention to where you click that mouse. :-)     In the screen shot below, by entering the netmask value in the Netmask field, in this case 255.255.255.0, the gateway value was auto-filled into the Gateway field, based on the IP addresses and netmask previously entered. As always, you can change this value.     My last 2 screen shots illustrate that the same sequential IP address autofill and netmask to gateway autofill works when entering the IP configuration details for the Integrated Lights Out Manager (ILOM) for both nodes. The time these auto-fill capabilities save in entering data is nice, but from my perspective not as important as the opportunity to avoid data entry errors. In my next post in this series, I will touch on the benefit of using the network validation capability of the Appliance Manager GUI prior to deploying an Oracle Database Appliance.

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  • Converting ANTLR AST to Java bytecode using ASM

    - by Nick
    I am currently trying to write my own compiler, targeting the JVM. I have completed the parsing step using Java classes generated by ANTLR, and have an AST of the source code to work from (An ANTLR "CommonTree", specifically). I am using ASM to simplify the generating of the bytecode. Could anyone give a broad overview of how to convert this AST to bytecode? My current strategy is to explore down the tree, generating different code depending on the current node (using "Tree.getType()"). The problem is that I can only recognise tokens from my lexer this way, rather than more complex patterns from the parser. Is there something I am missing, or am I simply approaching this wrong? Thanks in advance :)

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  • Synchronizing local and remote cache in distributed caching

    - by ltfishie
    With a distributed cache, a subset of the cache is kept locally while the rest is held remotely. In a get operation, if the entry is not available locally, the remote cache will be used and and the entry is added to local cache. In a put operation, both the local cache and remote cache are updated. Other nodes in the cluster also need to be notified to invalidate their local cache as well. What's a simplest way to achieve this if you implemented it yourself, assuming that nodes are not aware of each other. Edit My current implementation goes like this: Each cache entry contains a time stamp. Put operation will update local cache and remote cache Get operation will try local cache then remote cache A background thread on each node will check remote cache periodically for each entry in local cache. If the timestamp on remote is newer overwrite the local. If entry is not found in remote, delete it from local.

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  • 7-minute Community GlassFish Clustering Screencast

    - by alexismp
    Community member Faissal has recently put up a 7-minute screencast of an un-edited setup of a GlassFish cluster. His clustering setup spans across a mac and a virtualized Ubuntu host. It can probably be further simplified using the SSH provisioning feature (asadmin install-node) to avoid logging into remote machines. You may remember John's GlassFish clustering in under 10 minutes, a very successful video which was based on version 2. Since that we've put out a number of demos on YouTube for our 3.1.x versions including a full webinar replay.

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  • Migrating from GlassFish 2.x to 3.1.x

    - by alexismp
    With clustering now available in GlassFish since version 3.1 (our Spring 2011 release), a good number of folks have been looking at migrating their existing GlassFish 2.x-based clustered environments to a more recent version to take advantage of Java EE 6, our modular design, improved SSH-based provisioning and enhanced HA performance. The GlassFish documentation set is quite extensive and has a dedicated Upgrade Guide. It obviously lists a number of small changes such as file layout on disk (mostly due to modularity), some option changes (grizzly, shoal), the removal of node agents (using SSH instead), new JPA default provider name, etc... There is even a migration tool (glassfish/bin/asupgrade) to upgrade existing domains. But really the only thing you need to know is that each module in GlassFish 3 and beyond is responsible for doing its part of the upgrade job which means that the migration is as simple as copying a 2.x domain directory to the domains/ directory and starting the server with asadmin start-domain --upgrade. Binary-compatible products eligible for such upgrades include Sun Java System Application Server 9.1 Update 2 as well as version 2.1 and 2.1.1 of Sun GlassFish Enterprise Server.

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  • Add SQL Azure database to Azure Web Role and persist data with entity framework code first.

    - by MagnusKarlsson
    In my last post I went for a warts n all approach to set up a web role on Azure. In this post I’ll describe how to add an SQL Azure database to the project. This will be described with an as minimal as possible amount of code and screen dumps. All questions are welcome in the comments area. Please don’t email since questions answered in the comments field is made available to other visitors. As an example we will add a comments section to the site we used in the previous post (Länk här). Steps: 1. Create a Comments entity and then use Scaffolding to set up controller and view, and add ConnectionString to web.config. 2. Create SQL Azure database in Management Portal and link the new database 3. Test it online!   1. Right click Models folder, choose add, choose “class…” . Name the Class Comment. 1.1 Replace the Code in the class with the following: using System.Data.Entity; namespace MvcWebRole1.Models { public class Comment {    public int CommentId { get; set; }    public string Name { get; set; }      public string Content { get; set; } } public class CommentsDb : DbContext { public DbSet<Comment> CommentEntries { get; set; } } } Now Entity Framework can create a database and a table named Comment. Build your project to assert there are no build errors.   1.2 Right click Controllers folder, choose add, choose “class…” . Name the Class CommentController and fill out the values as in the example below.     1.3 Click Add. Visual Studio now creates default View for CRUD operations and a Controller adhering to these and opens them. 1.3 Open Web.config and add the following connectionstring in <connectionStrings> node. <add name="CommentsDb” connectionString="data source=(LocalDB)\v11.0;Integrated Security=SSPI;AttachDbFileName=|DataDirectory|\CommentsDb.mdf;Initial Catalog=CommentsDb;MultipleActiveResultSets=True" providerName="System.Data.SqlClient" />   1.4 Save All and press F5 to start the application. 1.5 Go to http://127.0.0.1:81/Comments which will redirect you through CommentsController to the Index View which looks like this:     Click Create new. In the Create-view, add name and content and press Create.   1: // 2: // POST: /Comments/Create 3:  4: [HttpPost] 5: public ActionResult Create(Comment comment) 6: { 7: if (ModelState.IsValid) 8: { 9: db.CommentEntries.Add(comment); 10: db.SaveChanges(); 11: return RedirectToAction("Index"); 12: } 13:  14: return View(comment); 15: } 16:    The default View() is Index so that is the View you will come to. Looking like this: 1: // 2: // GET: /Comments/ 3: 4: public ActionResult Index() 5: { 6: return View(db.CommentEntries.ToList()); 7: } Resulting in the following screen dump(success!):   2. Now, go to the Management portal and Create a new db.   2.1 With the new database created. Click the DB icon in the left most menu. Then click the newly created database. Click DASHBOARD in the top menu. Finally click Connections strings in the right menu to get the connection string we need to add in our web.debug.config file.   2.2 Now, take a copy of the connection String earlier added to the web.config and paste in web.debug.conifg in the connectionstrings node. Replace everything within “ “ in the copied connectionstring with that you got from SQL Azure. You will have something like this:   2.3 Rebuild the application, right click the cloud project and choose “Package…” (if you haven’t set up publishing profile which we will do in our next blog post). Remember to choose the right config file, use debug for staging and release for production so your databases won’t collide. You should see something like this:   2.4 Go to Management Portal and click the Web Services menu, choose your service and click update in the bottom menu.   2.5 Link the newly created database to your application. Click the LINKED RESOURCES in the top menu and then click “Link” in the bottom menu. You should get something like this. 3. Alright then. Under the Dashboard you can find the link to your application. Click it to open it in a browser and then go to ~/Comments to try it out just the way we did locally. Success and end of this story!

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  • io Exception error in wordcount example

    - by Anitha
    I have installed Hadoop 1.0.3 in Ubuntu 12.04 version (64bit) based on michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-single-node-cluster/ . I am trying to run a mapreduce job using the wordcount example. Running the command hduser@ubuntu: $/usr/local/hadoop/bin/hadoop jar hadoop-examples-1.0.3.jar wordcount /user/hduser/gutenberg /user/hduser/gutenberg-output gives the following error: Warning: $HADOOP_HOME is deprecated. Exception in thread "main" java.io.IOException: Error opening job jar: hadoop-examples-1.0.3.jar at org.apache.hadoop.util.RunJar.main(RunJar.java:90) Caused by: java.util.zip.ZipException: error in opening zip file at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.<init>(ZipFile.java:131) at java.util.jar.JarFile.<init>(JarFile.java:150) at java.util.jar.JarFile.<init>(JarFile.java:87) at org.apache.hadoop.util.RunJar.main(RunJar.java:88) Thanks in advance.

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  • MAAS/Juju architecture and issues

    - by Massimo
    I recently deployed a MAAS/Juju environment based on a six nodes cluster, using Ubuntu 12.04 LTS, to run a "proof of concept". I could appreciate how interesting the architecture is, and I'd like to understand if I can really base my future business on this technology. Therefore I'd like to understand more about any involved limitations, constraints and necessities. In particular I'd like to understand: 1) how can MAAS be made reliable, i.e. deployed over two or more physical nodes able to fail-over ? 2) can the same physical cluster host multiple juju environments, under the assumption openstack/virtualization is not used ? 3) can the same physical node host different charms of the same juju environment, deployed in a standard, reliable way by juju ?

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  • How important is using the same language for client and server?

    - by Makita
    I have been evaluating architecture solutions for a mobile project that will have a web-service/app in addition to native apps and have been looking at various libraries, frameworks, and stacks like Meteor, this being a sort of "open stack package framework", is tightly bound with Node.js. There is a lot of talk about the benefits of using the same language both client and server side, and I'm not getting it. I could understand if you want to mirror the entire state of a web application on both client and server but struggling to find other wins... Workflow efficiency? I'm trying to understand why client/server language parity is considered to be a holy grail. Why does client/server language parity matter in software development?

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  • Moving DataSets through BizTalk

    - by EltonStoneman
    [Source: http://geekswithblogs.net/EltonStoneman] Yuck. But sometimes you have to, so here are a couple of things to bear in mind: Schemas Point a codegen tool at a WCF endpoint which exposes a DataSet and it will generate an XSD which describes the DataSet like this: <xs:elementminOccurs="0"name="GetDataSetResult"nillable="true">  <xs:complexType>     <xs:annotation>       <xs:appinfo>         <ActualTypeName="DataSet"                     Namespace="http://schemas.datacontract.org/2004/07/System.Data"                     xmlns="http://schemas.microsoft.com/2003/10/Serialization/" />       </xs:appinfo>     </xs:annotation>     <xs:sequence>       <xs:elementref="xs:schema" />       <xs:any />     </xs:sequence>  </xs:complexType> </xs:element>  In a serialized instance, the element of type xs:schema contains a full schema which describes the structure of the DataSet – tables, columns etc. The second element, of type xs:any, contains the actual content of the DataSet, expressed as DiffGrams: <GetDataSetResult>  <xs:schemaid="NewDataSet"xmlns:xs="http://www.w3.org/2001/XMLSchema"xmlns=""xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">     <xs:elementname="NewDataSet"msdata:IsDataSet="true"msdata:UseCurrentLocale="true">       <xs:complexType>         <xs:choiceminOccurs="0"maxOccurs="unbounded">           <xs:elementname="Table1">             <xs:complexType>               <xs:sequence>                 <xs:elementname="Id"type="xs:string"minOccurs="0" />                 <xs:elementname="Name"type="xs:string"minOccurs="0" />                 <xs:elementname="Date"type="xs:string"minOccurs="0" />               </xs:sequence>             </xs:complexType>           </xs:element>         </xs:choice>       </xs:complexType>     </xs:element>  </xs:schema>  <diffgr:diffgramxmlns:diffgr="urn:schemas-microsoft-com:xml-diffgram-v1"xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">     <NewDataSetxmlns="">       <Table1diffgr:id="Table11"msdata:rowOrder="0"diffgr:hasChanges="inserted">         <Id>377fdf8d-cfd1-4975-a167-2ddb41265def</Id>         <Name>157bc287-f09b-435f-a81f-2a3b23aff8c4</Name>         <Date>a5d78d83-6c9a-46ca-8277-f2be8d4658bf</Date>       </Table1>     </NewDataSet>  </diffgr:diffgram> </GetDataSetResult> Put the XSD into a BizTalk schema and it will fail to compile, giving you error: The 'http://www.w3.org/2001/XMLSchema:schema' element is not declared. You should be able to work around that, but I've had no luck in BizTalk Server 2006 R2 – instead you can safely change that xs:schema element to be another xs:any type: <xs:elementminOccurs="0"name="GetDataSetResult"nillable="true">  <xs:complexType>     <xs:sequence>       <xs:any />       <xs:any />     </xs:sequence>  </xs:complexType> </xs:element>  (This snippet omits the annotation, but you can leave it in the schema). For an XML instance to pass validation through the schema, you'll also need to flag the any attributes so they can contain any namespace and skip validation:  <xs:elementminOccurs="0"name="GetDataSetResult"nillable="true">  <xs:complexType>     <xs:sequence>       <xs:anynamespace="##any"processContents="skip" />       <xs:anynamespace="##any"processContents="skip" />     </xs:sequence>  </xs:complexType> </xs:element>  You should now have a compiling schema which can be successfully tested against a serialised DataSet. Transforms If you're mapping a DataSet element between schemas, you'll need to use the Mass Copy Functoid to populate the target node from the contents of both the xs:any type elements on the source node: This should give you a compiled map which you can test against a serialized instance. And if you have a .NET consumer on the other side of the mapped BizTalk output, it will correctly deserialize the response into a DataSet.

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  • How does session middleware generally verify browser sessions?

    - by BBnyc
    I've been using session middleware to build web apps for years: from PHP's built-in session handling layer to node's connect session middleware. However, I've never tried (or needed) to roll my own session handling layer. How would one go about it? What sort of checks are necessary to provide at least some modicum of security against HTTP session highjacking? I figure setting a cookie with a token to keep track of the session, and then perhaps some check to see that the originating IP address of the session doesn't change and that the client browser software remains consistent. Hoping to hear about current best-practices...

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  • GTK applications do not start

    - by Greg
    Hello, I have a fresh install of Ubuntu 10.04 Server on nodes of a computational cluster, and I access the nodes via ssh. I configured a X server, which I start with the command startx -- -ac. The server is running fine on port :0. Then, I set the environment variable DISPLAY to :0. Now, when I run a GTK application on the node, it fails with the following error: Error: Unable to initialize gtk, is DISPLAY set properly? Now, my question is, is there any runtime library that I need for running GTK applications on top of a X server? I'm probably missing something obvious here, but I can't tell what :P

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  • Order independent transparency in particle system

    - by Stepan Zastupov
    I'm writing a particle system and would like to find a trick to achieve proper alpha blending without sorting particles because: Each particle is a point sprite in a single mesh and I can't use scene graph ability to sort transparent nodes. The system node should be properly sorted, though. Particle position is computed on shader from initial velocity, acceleration and time. In order to sort the system I would have to perform all this computations on CPU, which is something I want to avoid. Sorting hundreds of particles against camera position and uploading it on GPU each frame seams to be quiet heavy operation. Alpha testing seems to be fast enough on GLES 2.0 and works fine for non-transparent but "masked" textures. Still, it's not enough for semi-transparent particles. How would you handle this?

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  • Why does sound stop working after a while?

    - by badp
    I don't know how to reproduce this problem, because I don't regularly play music or sound. All I know is that, sometimes, I'll load a video (from youtube or from a local file) and there will be no sound. Everything looks fine software wise: Rebooting always fixes. aplay, paplay and pals give no error message I'm not in the audio group, as advised The device exists and appears in use: $ lsof /dev/snd/by-path/pci-0000\:00\:1b.0 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME pulseaudi 17313 badp 23u CHR 116,10 0t0 7628 /dev/snd/by-path/../controlC0 pulseaudi 17313 badp 30u CHR 116,10 0t0 7628 /dev/snd/by-path/../controlC0 Restarting pulseaudio or alsa seems to do no good. What is wrong here?

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  • Basic game architechture best practices in Cocos2D on iOS

    - by MrDatabase
    Consider the following simple game: 20 squares floating around an iPhone's screen. Tapping a square causes that square to disappear. What's the "best practices" way to set this up in Cocos2D? Here's my plan so far: One Objective-c GameState singleton class (maintains list of active squares) One CCScene (since there's no menus etc) One CCLayer (child node of the scene) Many CCSprite nodes (one for each square, all child nodes of the layer) Each sprite listens for a tap on itself. Receive tap = remove from GameState Since I'm relatively new to Cocos2D I'd like some feedback on this design. For example I'm unsure of the GameState singleton. Perhaps it's unnecessary.

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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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  • Getting into C# and MVC4 coming from Javascript

    - by Stefan V.
    Let me know if this is the wrong place to ask this but, I am trying to get into a backend/server language coming from a front-end javascript background (vanilla, angular, jQuery and a bit of node and mongodb, also some experience with PHP and MySQL). Why C#? My company's entire server-side is MVC4. Occasionally, I am going through commits of the backend guys and have asked them all sorts of questions. A lot of what I have heard and seen just seems appealing. Anyway, I'd rather start with C# first and gradually adopt .NET MVC. Does anybody advice, tips, recommended books, etc for somebody trying to learn C# coming from a JS background?

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  • Stumbling Through: Visual Studio 2010 (Part II)

    I would now like to expand a little on what I stumbled through in part I of my Visual Studio 2010 post and touch on a few other features of VS 2010.  Specifically, I want to generate some code based off of an Entity Framework model and tie it up to an actual data source.  Im not going to take the easy way and tie to a SQL Server data source, though, I will tie it to an XML data file instead.  Why?  Well, why not?  This is purely for learning, there are probably much better ways to get strongly-typed classes around XML but it will force us to go down a path less travelled and maybe learn a few things along the way.  Once we get this XML data and the means to interact with it, I will revisit data binding to this data in a WPF form and see if I cant get reading, adding, deleting, and updating working smoothly with minimal code.  To begin, I will use what was learned in the first part of this blog topic and draw out a data model for the MFL (My Football League) - I dont want the NFL to come down and sue me for using their name in this totally football-related article.  The data model looks as follows, with Teams having Players, and Players having a position and statistics for each season they played: Note that when making the associations between these entities, I was given the option to create the foreign key but I only chose to select this option for the association between Player and Position.  The reason for this is that I am picturing the XML that will contain this data to look somewhat like this: <MFL> <Position/> <Position/> <Position/> <Team>     <Player>         <Statistic/>     </Player> </Team> </MFL> Statistic will be under its associated Player node, and Player will be under its associated Team node no need to have an Id to reference it if we know it will always fall under its parent.  Position, however, is more of a lookup value that will not have any hierarchical relationship to the player.  In fact, the Position data itself may be in a completely different xml file (something Id like to play around with), so in any case, a player will need to reference the position by its Id. So now that we have a simple data model laid out, I would like to generate two things based on it:  A class for each entity with properties corresponding to each entity property An IO class with methods to get data for each entity, either all instances, by Id or by parent. Now my experience with code generation in the past has consisted of writing up little apps that use the code dom directly to regenerate code on demand (or using tools like CodeSmith).  Surely, there has got to be a more fun way to do this given that we are using the Entity Framework which already has built-in code generation for SQL Server support.  Lets start with that built-in stuff to give us a base to work off of.  Right click anywhere in the canvas of our model and select Add Code Generation Item: So just adding that code item seemed to do quite a bit towards what I was intending: It apparently generated a class for each entity, but also a whole ton more.  I mean a TON more.  Way too much complicated code was generated now that code is likely to be a black box anyway so it shouldnt matter, but we need to understand how to make this work the way we want it to work, so lets get ready to do some stumbling through that text template (tt) file. When I open the .tt file that was generated, right off the bat I realize there is going to be trouble there is no color coding, no intellisense no nothing!  That is going to make stumbling through more like groping blindly in the dark while handcuffed and hopping on one foot, which was one of the alternate titles I was considering for this blog.  Thankfully, the community comes to my rescue and I wont have to cast my mind back to the glory days of coding in VI (look it up, kids).  Using the Extension Manager (Available under the Tools menu), I did a quick search for tt editor in the Online Gallery and quickly found the Tangible T4 Editor: Downloading and installing this was a breeze, and after doing so I got some color coding and intellisense while editing the tt files.  If you will be doing any customizing of tt files, I highly recommend installing this extension.  Next, well see if that is enough help for us to tweak that tt file to do the kind of code generation that we wantDid you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Why should I use Bower? [closed]

    - by Wil
    I can fully appreciate the benefits of a package manager like Python PIP, Node npm, or Ruby Gems since they're doing much more than adding files to your applications path. Maybe I'm missing the point, or I'm being obtuse, but here are the negatives I can see: Separate step when building a project Separate dependency to install via another package manager (yo dawg) More clutter in the projects root with bower.json and / or .bowerrc Reliance on the registry being up to date, correct, and available Some imports / references to things like images won't work The positives I can see are these: I don't have to download the dependencies manually Optionally install packages as part of scaffolding based on user prompts or the like I'd really like to know of any benefits I'm unaware of, and I should say I'm not trying to be provocative I genuinely want to know.

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  • How should I interpret these DirectX Caps Viewer values?

    - by tobi
    Briefly asking - what do the nodes mean and what the difference is between them in DirectX Caps Viewer? DXGI Devices Direct3D9 Devices DirectDraw Devices The most interesting for me is 1 vs 2. In the Direct3D9 Devices under HAL node I can see that my GeForce 8800GT supports PixelShaderVersion 3.0. However, under DXGI Devices I have DX 10, DX 10.1 and DX 11 having Shader model 4.0 (actually why DX 11? My card is not compatible with DX 11). I am implementing a DX 11 application (including d3d11.h) with shaders compiled in 4.0 version, so I can clearly see that 4.0 is supported. What is the difference between 1 and 2? Could you give me some theory behind the nodes?

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  • Custom graph comparison?

    - by user57828
    I'm trying to compare two graphs using hash value ( i.e, at the time of comparison, try to avoid traversing the graph ) Is there a way to make a function such that the hash values compared can also lead to determining at which height the graphs differ? The comparisons between two graphs are to be made by comparing children at a certain level. One way to compare the graphs is have a final hash value for the root node and compare them, but that wouldn't directly reflect at which level the graphs differ, since their immediate children might be the same ( or any other case ).

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  • MAAS fails to Commission nodes

    - by user3644848
    I'm evaluating MaaS/Juju. I followed instructions in this link http://maas.ubuntu.com/docs1.5/install.html to setup MaaS. I'm running this in Oracle VirtualBox environment so Power options are not configured for the VMs. PXE booting VM works fine. The node shuts down itself and registers with MaaS in Declared state. Issues: a) When I Commission the VM (which is in the Declared state), first it gets IP-Config: no response after 60 secs - giving up errors. (See link below for a screenshot). b) Fails to mount the boot device and drops into initramfs prompt. I've copied logs here: https://www.dropbox.com/sh/5gy9nnonbnccufo/AAD9o4awSOtyaCCmRe5q7rBva Any help to get past this is greatly appreciated. Thanks!

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