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  • What is Slotted and pure aloha?

    - by caspert
    So I am having a really hard time understanding slotted and pure aloha. I have understood CSMA/CD fairly well, but that is it. I have the book: Computer networking - a top down approach, but I find the explanation very cryptic and hard to understand. Wikipedia did not help me. Does anyone have a brief "aloha for dummies" explanation? or perhaps a video tutorial? I think I need something visual. I don't need to be able to create the protocol, I just need a general understanding of it.

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  • Twisted pair cable twists and unwanted signals issue

    - by ziaharipur
    I am confused about one point I have read the following paragraph from the networking book. “the twists in the twisted pair cable are used to avoid the unwanted signals. For example one twist, one wire is closer to the noise source and the other is farther; in the next twist the reverse is true. Twisting makes its probable that both wires are equally affected by the unwanted signal. This means that the receiver which calculate the difference between the two receives no unwanted signal.” Now ok I understood the purpose of twists but I am confused about how receiver will calculate the difference when it will receive the signal?. How unwanted signal will be eliminated ? Another thing that I want to make clear is , I am beginner please provide such an answer that can be understood.

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  • parallel vms in VMWare Server - how to configure network so they can ping each other?

    - by IronGoofy
    I'm using VMWare Server (currently on Version 1.0.7) and have two VMs that I would like to run at the same time. However, I'm having problems in setting them up so they can ping each other. I've configured them to use 'Bridged' networking. They both obtain an IP address from the DHCP server on my network, but after that they can't ping each other. It seems that only the first one has a functioning network connection (I can ping it from the host machine and Internet connection works), but the other one does not. If it helps, both VMs are running XP SP 3. Any ideas? Thanks!

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  • Make my web-server traffic go through proxy?

    - by Eli
    I have a question that may or may not be possible. Basically Comcast isn't going to let me host a website on their ISP unless I have a business account. So, I spoke with my uncle who is big into networking and he told me to host my website through a proxy so Comcast cannot associate the website IP with my IP. I have purchases a proxy from proxy-hub.com, but I cannot seem to figure out what to do next. I may be approaching this totally wrong and I may need to create my own proxy server. Anybody have a clue? Thanks.

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  • Network flooded with seemingly empty packets

    - by Adam Particka
    Let me preface this with the fact that I'm just a web developer at my company with little networking knowledge. Earlier today there was a department that lost all of their network connections so I popped open Wireshark and observed the influx of packets to my machine. There was normal traffic (ARP requests, etc.) coming in at ~50 packets every second. Then all of a sudden the log was flooded with packets arriving ~5000 a second. It looks as though they all contain the same data, just a looped sequence. We have someone here looking at it but I thought I would ask if anyone had seen anything like this before. Here's a selection from one of the captures in Wireshark. http://www.cloudshark.org/captures/06f950725c74

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  • enable tcp_syncookies even after reboot

    - by Tim
    I'm running Scientific Linux 6.1 and would like to set net.ipv4.tcp_syncookies=1. I've set that in /etc/sysctl.conf and, if I do a sysctl -p then sysctl -q net.ipv4.tcp_syncookies it shows it's properly set. Sadly, if I reboot the machine, and sysctl -q again, it goes back to 0. I've tried to grep around and see if something else is resetting it to 0 during the boot process but haven't turned up anything. I've googled and everything points to sysctl.conf. The only thing I can think of is maybe networking isn't up by the time that file gets read but, honestly, I'm a developer and well beyond my natural skills here:) I'm tempted to just set it directly in /etc/init.d/network but then that feels hackish and so, I thought better of it and I'm here in search of the "right" way to do it. Any pointers?

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  • Why can a network address not be a valid host address?

    - by Goblinlord
    So... I have studied for CCNA and such and been working with IP networking at the least the past 8 years or so. I have always seen and been told that the network address for a subnet is not a valid host address. Now first I will start by saying I know this is true. My question is more... is there a technical reason it can not be used or was it just arbitrarily agreed upon when the specification was designed? I understand why a broadcast address can not be used (because it is ACTUALLY used). The thing is when I see a network address used it is normally only in routing which is specifically using NETWORK addresses. This being the case, (network addresses being used only when you are expecting a network address) is there some technical reason that they could not have the network address be an actual valid host address?

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  • Plagued by multithreaded bugs

    - by koncurrency
    On my new team that I manage, the majority of our code is platform, TCP socket, and http networking code. All C++. Most of it originated from other developers that have left the team. The current developers on the team are very smart, but mostly junior in terms of experience. Our biggest problem: multi-threaded concurrency bugs. Most of our class libraries are written to be asynchronous by use of some thread pool classes. Methods on the class libraries often enqueue long running taks onto the thread pool from one thread and then the callback methods of that class get invoked on a different thread. As a result, we have a lot of edge case bugs involving incorrect threading assumptions. This results in subtle bugs that go beyond just having critical sections and locks to guard against concurrency issues. What makes these problems even harder is that the attempts to fix are often incorrect. Some mistakes I've observed the team attempting (or within the legacy code itself) includes something like the following: Common mistake #1 - Fixing concurrency issue by just put a lock around the shared data, but forgetting about what happens when methods don't get called in an expected order. Here's a very simple example: void Foo::OnHttpRequestComplete(statuscode status) { m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } So now we have a bug in which Shutdown could get called while OnHttpNetworkRequestComplete is occuring on. A tester finds the bug, captures the crash dump, and assigns the bug to a developer. He in turn fixes the bug like this. void Foo::OnHttpRequestComplete(statuscode status) { AutoLock lock(m_cs); m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { AutoLock lock(m_cs); m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } The above fix looks good until you realize there's an even more subtle edge case. What happens if Shutdown gets called before OnHttpRequestComplete gets called back? The real world examples my team has are even more complex, and the edge cases are even harder to spot during the code review process. Common Mistake #2 - fixing deadlock issues by blindly exiting the lock, wait for the other thread to finish, then re-enter the lock - but without handling the case that the object just got updated by the other thread! Common Mistake #3 - Even though the objects are reference counted, the shutdown sequence "releases" it's pointer. But forgets to wait for the thread that is still running to release it's instance. As such, components are shutdown cleanly, then spurious or late callbacks are invoked on an object in an state not expecting any more calls. There are other edge cases, but the bottom line is this: Multithreaded programming is just plain hard, even for smart people. As I catch these mistakes, I spend time discussing the errors with each developer on developing a more appropriate fix. But I suspect they are often confused on how to solve each issue because of the enormous amount of legacy code that the "right" fix will involve touching. We're going to be shipping soon, and I'm sure the patches we're applying will hold for the upcoming release. Afterwards, we're going to have some time to improve the code base and refactor where needed. We won't have time to just re-write everything. And the majority of the code isn't all that bad. But I'm looking to refactor code such that threading issues can be avoided altogether. One approach I am considering is this. For each significant platform feature, have a dedicated single thread where all events and network callbacks get marshalled onto. Similar to COM apartment threading in Windows with use of a message loop. Long blocking operations could still get dispatched to a work pool thread, but the completion callback is invoked on on the component's thread. Components could possibly even share the same thread. Then all the class libraries running inside the thread can be written under the assumption of a single threaded world. Before I go down that path, I am also very interested if there are other standard techniques or design patterns for dealing with multithreaded issues. And I have to emphasize - something beyond a book that describes the basics of mutexes and semaphores. What do you think? I am also interested in any other approaches to take towards a refactoring process. Including any of the following: Literature or papers on design patterns around threads. Something beyond an introduction to mutexes and semaphores. We don't need massive parallelism either, just ways to design an object model so as to handle asynchronous events from other threads correctly. Ways to diagram the threading of various components, so that it will be easy to study and evolve solutions for. (That is, a UML equivalent for discussing threads across objects and classes) Educating your development team on the issues with multithreaded code. What would you do?

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  • Virtual IP, and Reverse Proxying Ports (Making up terms)

    - by macintosh264
    So here is the exact situation that I have I have 2 game servers in my house. One on port 25565, and the second on 25567. I have only one IP in my house I need to get a "virtual IP" for the second server. Some way of giving the computer that runs these game servers a second IP (linux) I need the Virtual IP to receive connections on 25565 and forward the data to 25567. Although if linux recognizes the second IP in networking I assume I can bind to the second IP on port 25565

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  • Sharp architecture; Accessing Validation Results

    - by nabeelfarid
    I am exploring Sharp Architecture and I would like to know how to access the validation results after calling Entity.IsValid(). I have two scenarios e.g. 1) If the entity.IsValid() return false, I would like to add the errors to ModelState.AddModelError() collection in my controller. E.g. in the Northwind sample we have an EmployeesController.Create() action when we do employee.IsValid(), how can I get access to the errors? public ActionResult Create(Employee employee) { if (ViewData.ModelState.IsValid && employee.IsValid()) { employeeRepository.SaveOrUpdate(employee); } // .... } [I already know that when an Action method is called, modelbinder enforces validation rules(nhibernate validator attributes) as it parses incoming values and tries to assign them to the model object and if it can't parse the incoming values  then it register those as errors in modelstate for each model object property. But what if i have some custom validation. Thats why we do ModelState.IsValid first.] 2) In my test methods I would like to test the nhibernate validation rules as well. I can do entity.IsValid() but that only returns true/ false. I would like to Assert against the actual error not just true/ false. In my previous projects, I normally use a wrapper Service Layer for Repositories, and instead of calling Repositories method directly from controller, controllers call service layer methods which in turn call repository methods. In my Service Layer all my custom validation rules resides and Service Layer methods throws a custom exception with a NameValueCollection of errors which I can easily add to ModelState in my controller. This way I can also easily implement sophisticated business rules in my service layer as well. I kow sharp architecture also provides a Service Layer project. But what I am interested in and my next question is: How I can use NHibernate Vaidators to implement sophisticated custom business rules (not just null,empty, range etc.) and make Entity.IsValid() to verify those rules too ?

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  • Resources related to data-mining and gaming on social networks

    - by darren
    Hi all I'm interested in the problem of patterning mining among players of social networking games. For example detecting cheaters of a game, given a company's user database. So far I have been following the usual recipe for a data mining project: construct a data warehouse that aggregates significant information select a classifier, and train it with a subsectio of records from the warehouse validate classifier with another test set lather, rinse, repeat Surprisingly, I've found very little in this area regarding literature, best practices, etc. I am hoping to crowdsource the information gathering problem here. Specifically what I'm looking for: What classifiers have worked will for this type of pattern mining (it seems highly temporal, users playing games, users receiving rewards, users transferring prizes etc). Are there any highly agreed upon attributes specific to social networking / gaming data? What is a practical amount of information that should be considered? One problem I've run into is data overload, where queries and data cleansing may take days to complete. Related to point above, what hardware resources are required to produce results? I've found it difficult to estimate the amount of computing power I will require for production use. It has become apparent that a white box in the corner does not have enough horse-power for such a project. Are companies generally resorting to cloud solutions? Are they buying clusters? Basically, any resources (theoretical, academic, or practical) about implementing a social networking / gaming pattern-mining program would be very much appreciated. Thanks.

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  • Python libusb pyusb "mach-o, but wrong architecture"

    - by Jon
    I am having some trouble with the pyusb module. I have narrowed down the problem to a single line, and have created a small example script to replicate the error. #!/usr/bin/env python """ This module was created to isolate the problem in the pyusb package. Operating system: Mac OS 10.6.3 Python Version: 2.6.4 libusb 1.0.8 has been successfully installed using: sudo port install libusb I have also tried modifying /opt/local/etc/macports/macports.conf to force the i386 architecture instead of x86_64. """ from ctypes import * import ctypes.util libname = ctypes.util.find_library('usb-1.0') print 'libname: ', libname l = CDLL(libname, RTLD_GLOBAL) # RESULT: #libname: /usr/local/lib/libusb-1.0.dylib #Traceback (most recent call last): # File "./pyusb_problem.py", line 7, in <module> # l = CDLL(libname, RTLD_GLOBAL) # File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/ctypes/__init__.py", line 353, in __init__ # self._handle = _dlopen(self._name, mode) #OSError: dlopen(/usr/local/lib/libusb-1.0.dylib, 10): no suitable image found. Did find: # /usr/local/lib/libusb-1.0.dylib: mach-o, but wrong architecture # End of File This same script runs on Ubuntu 10.04 successfully. I have tried building the libusb module (directly from source AND through macports) for 32-bit (i386) instead of x86_64 (default for OS 10.6), but I receive the same error. Thank-you in advance for your help!

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  • sharp architecture question

    - by csetzkorn
    I am trying to get my head around the sharp architecture and follow the tutorial. I am using this code: using Bla.Core; using System.Collections.Generic; using Bla.Core.DataInterfaces; using System.Web.Mvc; using SharpArch.Core; using SharpArch.Web; using Bla.Web; namespace Bla.Web.Controllers { public class UsersController { public UsersController(IUserRepository userRepository) { Check.Require(userRepository != null,"userRepository may not be null"); this.userRepository = userRepository; } public ActionResult ListStaffMembersMatching(string filter) { List<User> matchingUsers = userRepository.FindAllMatching(filter); return View("ListUsersMatchingFilter", matchingUsers); } private readonly IUserRepository userRepository; } } I get this error: The name 'View' does not exist in the current context I have used all the correct using statements and referenced the assemblies as far as I can see. The views live in Bla.Web in this architecture. Can anyone see the problem? Thanks. Christian

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  • Web application architecture, and application servers?

    - by seanieb
    Hi, I'm building a web application, and I need to use an architecture that allows me to run it on two servers. The application scrapes information from other sites periodically, and on input from the end user. To do this I'm using Php+curl to scrape the information, Php or python to parse it and store the results in a MySQLDB. Then I will use Python to run some algorithms on the data, this will happen both periodically and on input from the end user. I'm going to cache some of the results in the MySQL DB and sometimes if it is specific to the user, skip storing the data and serve it to the user. I'm think of using Php for the website front end on a separate web server, running the Php spider, MySQL DB and python on another server. As you can see I'm fairly clueless. I'm familiar with using Php, MySQL and the basics of Python, but bringing this all together using something more complex than a cron job is new to me. How do go about implementing this? What frame work(s) should I use? Is MVC a good architecture for this? (I'm new to MVC, architectures etc.) Is Cakephp a good solution? If so will I be able to control and monitor the Python code using it?

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  • Architecture for data layer that uses both localStorage and a REST remote server

    - by Zack
    Anybody has any ideas or references on how to implement a data persistence layer that uses both a localStorage and a REST remote storage: The data of a certain client is stored with localStorage (using an ember-data indexedDB adapter). The locally stored data is synced with the remote server (using ember-data RESTadapter). The server gathers all data from clients. Using mathematical sets notation: Server = Client1 ? Client2 ? ... ? ClientN where, in general, a record may not be unique to a certain client. Here are some scenarios: A client creates a record. The id of the record can not set on the client, since it may conflict with a record stored on the server. Therefore a newly created record needs to be committed to the server - receive the id - create the record in localStorage. A record is updated on the server, and as a consequence the data in localStorage and in the server go out of sync. Only the server knows that, so the architecture needs to implement a push architecture (?) Would you use 2 stores (one for localStorage, one for REST) and sync between them, or use a hybrid indexedDB/REST adapter and write the sync code within the adapter? Can you see any way to avoid implementing push (Web Sockets, ...)?

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  • make arm architecture c library in mac

    - by gamegamelife
    I'm trying to make my own c library in Mac and include it to my iphone program. The c code is simple , like this: math.h: int myPow2(int); math.c: #include "math.h" int myPow2(int num) { return num*num; } I search how to make the c library file ( .a or .lib ..etc) seems need to use gcc compiler (Is there other methods?) so I use this command: gcc -c math.c -o math.o ar rcs libmath.a math.o And include it in iPhone Project. Now it has the problem when build xcode iphone project. "file was built for unsupported file format which is not the architecture being linked" I found some pages discuss about the problem, but no detail how to make the i386/arm architecture library. And I finally use this command to do it: gcc -arch i386 -c math.c -o math.o /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/arm-apple-darwin10-gcc-4.2.1 -c math.c -o math.o I dont know if this method is correct? Or there has another method to do it?

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  • Declarative Architectures in Infrastructure as a Service (IaaS)

    - by BuckWoody
    I deal with computing architectures by first laying out requirements, and then laying in any constraints for it's success. Only then do I bring in computing elements to apply to the system. As an example, a requirement might be "world-side availability" and a constraint might be "with less than 80ms response time and full HA" or something similar. Then I can choose from the best fit of technologies which range from full-up on-premises computing to IaaS, PaaS or SaaS. I also deal in abstraction layers - on-premises systems are fully under your control, in IaaS the hardware is abstracted (but not the OS, scale, runtimes and so on), in PaaS the hardware and the OS is abstracted and you focus on code and data only, and in SaaS everything is abstracted - you merely purchase the function you want (like an e-mail server or some such) and simply use it. When you think about solutions this way, the architecture moves to the primary factor in your decision. It's problem-first architecting, and then laying in whatever technology or vendor best fixes the problem. To that end, most architects design a solution using a graphical tool (I use Visio) and then creating documents that  let the rest of the team (and business) know what is required. It's the template, or recipe, for the solution. This is extremely easy to do for SaaS - you merely point out what the needs are, research the vendor and present the findings (and bill) to the business. IT might not even be involved there. In PaaS it's not much more complicated - you use the same Application Lifecycle Management and design tools you always have for code, such as Visual Studio or some other process and toolset, and you can "stamp out" the application in multiple locations, update it and so on. IaaS is another story. Here you have multiple machines, operating systems, patches, virus scanning, run-times, scale-patterns and tools and much more that you have to deal with, since essentially it's just an in-house system being hosted by someone else. You can certainly automate builds of servers - we do this as technical professionals every day. From Windows to Linux, it's simple enough to create a "build script" that makes a system just like the one we made yesterday. What is more problematic is being able to tie those systems together in a coherent way (as a solution) and then stamp that out repeatedly, especially when you might want to deploy that solution on-premises, or in one cloud vendor or another. Lately I've been working with a company called RightScale that does exactly this. I'll point you to their site for more info, but the general idea is that you document out your intent for a set of servers, and it will deploy them to on-premises clouds, Windows Azure, and other cloud providers all from the same script. In other words, it doesn't contain the images or anything like that - it contains the scripts to build them on-premises or on a cloud vendor like Microsoft. Using a tool like this, you combine the steps of designing a system (all the way down to passwords and accounts if you wish) and then the document drives the distribution and implementation of that intent. As time goes on and more and more companies implement solutions on various providers (perhaps for HA and DR) then this becomes a compelling investigation. The RightScale information is here, if you want to investigate it further. Yes, there are other methods I've found, but most are tied to a single kind of cloud, and I'm not into vendor lock-in. Poppa Bear Level - Hands-on EvaluateRightScale at no cost.  Just bring your Windows Azurecredentials and follow the these tutorials: Sign Up for Windows Azure Add     Windows Azure to a RightScale Account Windows Azure Virtual Machines     3-tier Deployment Momma Bear Level - Just the Right level... ;0)  WindowsAzure Evaluation Guide - if you are new toWindows Azure Virtual Machines and new to RightScale, we recommend that youread the entire evaluation guide to gain a more complete understanding of theWindows Azure + RightScale solution.    WindowsAzure Support Page @ support.rightscale.com - FAQ's, tutorials,etc. for  Windows Azure Virtual Machines (Work in Progress) Baby Bear Level - Marketing WindowsAzure Page @ www.rightscale.com - find overview informationincluding solution briefs and presentation & demonstration videos   Scale     and Automate Applications on Windows Azure  Solution Brief     - how RightScale makes Windows Azure Virtual Machine even better SQL     Server on Windows Azure  Solution Brief   -       Run Highly Available SQL Server on Windows Azure Virtual Machines

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  • High Availability for IaaS, PaaS and SaaS in the Cloud

    - by BuckWoody
    Outages, natural disasters and unforeseen events have proved that even in a distributed architecture, you need to plan for High Availability (HA). In this entry I'll explain a few considerations for HA within Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). In a separate post I'll talk more about Disaster Recovery (DR), since each paradigm has a different way to handle that. Planning for HA in IaaS IaaS involves Virtual Machines - so in effect, an HA strategy here takes on many of the same characteristics as it would on-premises. The primary difference is that the vendor controls the hardware, so you need to verify what they do for things like local redundancy and so on from the hardware perspective. As far as what you can control and plan for, the primary factors fall into three areas: multiple instances, geographical dispersion and task-switching. In almost every cloud vendor I've studied, to ensure your application will be protected by any level of HA, you need to have at least two of the Instances (VM's) running. This makes sense, but you might assume that the vendor just takes care of that for you - they don't. If a single VM goes down (for whatever reason) then the access to it is lost. Depending on multiple factors, you might be able to recover the data, but you should assume that you can't. You should keep a sync to another location (perhaps the vendor's storage system in another geographic datacenter or to a local location) to ensure you can continue to serve your clients. You'll also need to host the same VM's in another geographical location. Everything from a vendor outage to a network path problem could prevent your users from reaching the system, so you need to have multiple locations to handle this. This means that you'll have to figure out how to manage state between the geo's. If the system goes down in the middle of a transaction, you need to figure out what part of the process the system was in, and then re-create or transfer that state to the second set of systems. If you didn't write the software yourself, this is non-trivial. You'll also need a manual or automatic process to detect the failure and re-route the traffic to your secondary location. You could flip a DNS entry (if your application can tolerate that) or invoke another process to alias the first system to the second, such as load-balancing and so on. There are many options, but all of them involve coding the state into the application layer. If you've simply moved a state-ful application to VM's, you may not be able to easily implement an HA solution. Planning for HA in PaaS Implementing HA in PaaS is a bit simpler, since it's built on the concept of stateless applications deployment. Once again, you need at least two copies of each element in the solution (web roles, worker roles, etc.) to remain available in a single datacenter. Also, you need to deploy the application again in a separate geo, but the advantage here is that you could work out a "shared storage" model such that state is auto-balanced across the world. In fact, you don't have to maintain a "DR" site, the alternate location can be live and serving clients, and only take on extra load if the other site is not available. In Windows Azure, you can use the Traffic Manager service top route the requests as a type of auto balancer. Even with these benefits, I recommend a second backup of storage in another geographic location. Storage is inexpensive; and that second copy can be used for not only HA but DR. Planning for HA in SaaS In Software-as-a-Service (such as Office 365, or Hadoop in Windows Azure) You have far less control over the HA solution, although you still maintain the responsibility to ensure you have it. Since each SaaS is different, check with the vendor on the solution for HA - and make sure you understand what they do and what you are responsible for. They may have no HA for that solution, or pin it to a particular geo, or perhaps they have a massive HA built in with automatic load balancing (which is often the case).   All of these options (with the exception of SaaS) involve higher costs for the design. Do not sacrifice reliability for cost - that will always cost you more in the end. Build in the redundancy and HA at the very outset of the project - if you try to tack it on later in the process the business will push back and potentially not implement HA. References: http://www.bing.com/search?q=windows+azure+High+Availability  (each type of implementation is different, so I'm routing you to a search on the topic - look for the "Patterns and Practices" results for the area in Azure you're interested in)

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  • SOA, Governance, and Drugs

    Why is IT governance important in service oriented architecture (SOA)? IT Governance provides a framework for making appropriate decisions based on company guidelines and accepted standards. This framework also outlines each stakeholder’s responsibilities and authority when making important architectural or design decisions. Furthermore, this framework of governance defines parameters and constraints that are used to give context and perspective when making decisions. The use of governance as it applies to SOA ensures that specific design principles and patterns are used when developing and maintaining services. When governance is consistently applied systems the following benefits are achieved according to Anne Thomas Manes in 2010. Governance makes sure that services conform to standard interface patterns, common data modeling practices, and promotes the incorporation of existing system functionality by building on top of other available services across a system. Governance defines development standards based on proven design principles and patterns that promote reuse and composition. Governance provides developers a set of proven design principles, standards and practices that promote the reduction in system based component dependencies.  By following these guidelines, individual components will be easier to maintain. For me personally, I am a fan of IT governance, and feel that it valuable part of any corporate IT department. However, depending on how it is implemented can really affect the value of using IT governance.  Companies need to find a way to ensure that governance does not become extreme in its policies and procedures. I know for me personally, I would really dislike working under a completely totalitarian or laissez-faire version of governance. Developers need to be able to be creative in their designs and too much governance can really impede the design process and prevent the most optimal design from being developed. On the other hand, with no governance enforced, no standards will be followed and accepted design patterns will be ignored. I have personally had to spend a lot of time working on this particular scenario and I have found that the concept of code reuse and composition is almost nonexistent.  Based on this, too much time and money is wasted on redeveloping existing aspects of an application that already exist within the system as a whole. I think moving forward we will see a staggered form of IT governance, regardless if it is for SOA or IT in general.  Depending on the size of a company and the size of its IT department,  I can see IT governance as a layered approach in that the top layer will be defined by enterprise architects that focus on abstract concepts pertaining to high level design, general  guidelines, acceptable best practices, and recommended design patterns.  The next layer will be defined by solution architects or department managers that further expand on abstracted guidelines defined by the enterprise architects. This layer will contain further definitions as to when various design patterns, coding standards, and best practices are to be applied based on the context of the solutions that are being developed by the department. The final layer will be defined by the system designer or a solutions architect assed to a project in that they will define what design patterns will be used in a solution, naming conventions, as well as outline how a system will function based on the best practices defined by the previous layers. This layered approach allows for IT departments to be flexible in that system designers have creative leeway in designing solutions to meet the needs of the business, but they must operate within the confines of the abstracted IT governance guidelines.  A real world example of this can be seen in the United States as it pertains to governance of the people in that the US government defines rules and regulations in the abstract and then the state governments take these guidelines and applies them based on the will of the people in each individual state. Furthermore, the county or city governments are the ones that actually enforce these rules based on how they are interpreted by local community.  To further define my example, the United States government defines that marijuana is illegal. Each individual state has the option to determine this regulation as it wishes in that the state of Florida determines that all uses of the drug are illegal, but the state of California legally allows the use of marijuana for medicinal purposes only. Based on these accepted practices each local government enforces these rules in that a police officer will arrest anyone in the state of Florida for having this drug on them if they walk down the street, but in California if a person has a medical prescription for the drug they will not get arrested.  REFERENCESThomas Manes, Anne. (2010). Understanding SOA Governance: http://www.soamag.com/I40/0610-2.php

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  • VPN Network intermittantly fails to provide internet: What could be possible causes

    - by Jake M
    We have a small office with our own VPN setup. We occasionally experience failures in our internet connection where we cannot access the internet. Most of the time the internet connection will resume by itself(without me doing anything) after a period of time(10 mins). Would you be able to suggest possible causes of the connection failure so I can then go and run some tests? Our network architecture is like so: A 'Billion' brand router that is connected to the internet via phone cable and then connected to our Cisco Switch A Cisco Switch/Bus which is connected to all our office nodes, our external harddrive and also to our router as stated above. All connections are via ethernet cable A series of work computers(nodes) connected via ethernet cable to the Cisco switch. Our ISP is TPG Australia We have a Virtual Private Network All the ethernet cables are about 3 years old Do you think that the causes of our intermittant connection problems could be due to the following: Data collisions in the ethernet cables Old/Faulty ethernet cables Our ISP has bad service Can you think of any other causes of the problem?

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  • Which equipments should I buy for a laboratory?

    - by Hossein Margani
    Hi every body! I want to create a network of computers for a network laboratory in a university. I want to install windows on them. What is the fastest way for doing this and also which equipments I should buy for this laboratory. I also want to use this network as a computer laboratory, operating system laboratory, programming laboratory, microprocessor laboratory, computer architecture laboratory and software engineering laboratory. I should emphasis that this is a scholastic laboratory. Thanks.

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  • Working WCF WebServices with NLB server

    - by gguth
    Im starting the architecture of a new project using WCF, but im not the right person to make some network considerations, so im doing some research but cannot find the answers to these questions: We´ll host the WCF service in a common Windows Service app in 2 servers and we´ll have another server to make the Load-Balancing job using the WNLB. The fact that we are hosting the WCF in a Windows Service app can disturb the NLB job? Before my research i thought the load balancing was tought to configure, but with NLB it seems to be very simple, its really that simple? Note: The binding will be basicHttpBinding

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  • How to connect a wifi router to a cable modem router?

    - by DavidD
    Here's the thing: I have a cable modem router (Thomson TCW710) with wifi-g that I rent from my cable company. I would like to use a wireless-n router (D-Link DIR-655, that I received for free) with it in order to take advantage of the faster wifi. I basically need advice on how to architecture my home network with these two beasts. What configuration should I need to apply on my old and new router to make it all work? The two routers will of course be connected together with a RJ-45 cable.

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  • Connecting office to data center via Metro-ethernet

    - by Eric
    I am installing a metro ethernet link from my office to my data center. The office will have a cisco 3750 with several vlans. The data center end will have a more complicated set up. The metro e from the office will connect to a 2960, which will have two other 2960s with a few vlans and a 2811 router connected to it for connectivity to our other environments and the internet. I am looking at implementing this by connecting the office 3750 and the data center 2960 with a dot1q trunk and doing all routing at the 2811. I will configure subinterfaces for gateways for each of the vlans on the 2811. I work for a small company and don't have much of a budget for an ideal architecture. I can post a simple diagram if needed for clarification. Is there anything I am missing here? I feel like I am forgetting something very basic and want to make sure I eliminate any boneheaded mistakes.

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  • Central Storage for windows user accounts homedirs .. hardware/software needed?

    - by mtkoan
    We have ~120+ users in our network, and are endeavoring to centralize logon authentication and home directory storage server-side. Most of the users are Windows 2000/XP machines, and a few running Mac OS X. Ideally the solution will be open-source-- can this all be managed from a Linux server running LDAP and Samba? Or would a hacked-NAS Box with a FreeNAS or similar suffice? Or is Micro$oft's Active Directory really the preference here. Is it viable to store PST files on this server for users to read from and write to? They are very large ~1.5gb. We have no mail server (or money) capable of Exchange or IMAP, only an old POP3. What kind of hardware horsepower and network architecture should we have for this kind of thing?

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