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  • How many bits for sequence number using Go-Back-N protocol.

    - by Mike
    Hi Everyone, I'm a regular over at Stack Overflow (Software developer) that is trying to get through a networking course. I got a homework problem I'd like to have a sanity check on. Here is what I got. Q: A 3000-km-long T1 trunk is used to transmit 64-byte frames using Go-Back-N protocol. If the propagation speed is 6 microseconds/km, how many bits should the sequence numbers be? My Answer: For this questions what we need to do is lay the base knowledge. What we are trying to find is the size of the largest sequence number we should us using Go-Back-N. To figure this out we need to figure out how many packets can fit into our link at a time and then subtract one from that number. This will ensure that we never have two packets with the same sequence number at the same time in the link. Length of link: 3,000km Speed: 6 microseconds / km Frame size: 64 bytes T1 transmission speed: 1544kb/s (http://ckp.made-it.com/t1234.html) Propagation time = 6 microseconds / km * 3000 km = 18,000 microseconds (18ms). Convert 1544kb to bytes = 1544 * 1024 = 1581056 bytes Transmission time = 64 bytes / 1581056bytes / second = 0.000040479 seconds (0.4ms) So then if we take the 18ms propagation time and divide it by the 0.4ms transmission time we will see that we are going to be able to stuff ( 18 / 0.4) 45 packets into the link at a time. That means that our sequence number should be 2 ^ 45 bits long! Am I going in the right direction with this? Thanks, Mike

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  • openSSL tutorial not fully working - Can sign but cannot restore original file

    - by djechelon
    I'm writing, and testing, a little tutorial for my groupmates involved in an openSSL homework. We have a bunch of PDF files, I'm the CA and each one should send me a signed PDF for me to be verified. I've told them to do the following (and tried to do it by myself) Request and obtain a certificate (I'll skip this part) Create a MIME message with the PDF file in it makemime -c "text/pdf" -a "Content-Disposition: attachment; filename=”Elaborato.pdf" Elaborato.pdf > Elaborato.pdf.msg Sign with openSSL openssl smime -sign -in Elaborato.pdf.msg -out Elaborato.pdf.p7m -certfile ca.pem -certfile nomegruppo.crt -inkey nomegruppo.key -signer nomegruppo.crt Verify with openssl smime -verify -in Elaborato.pdf.p7m -out Elaborato-verified.msg -CAfile ca.pem -signer nomegruppo.crt Extract attachment with munpack Elaborato-verified.msg View with Acrobat Reader The problem is that even if I get a file that (from its binary content) resembles a PDF file my current Ubuntu PDF viewer doesn't read it. The XXXElaborato.pdf extracted by munpack is a little bit smaller than the original. What's the problem with this procedure? In theory, they should send me the signed S/MIME message and I should be able to read the PDF within it. Why can't I restore the original content of the PDF file?

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  • Apache caching with mod_headers mod_expires

    - by Aaron Moodie
    Hi, I'm working on homework for uni and was hoping someone could clarify something for me. I need to set up the following: Configure the response header "Cache-Control" to have a "max-age" value of 7 days since access for all image files Configure the response header "Cache-Control" to have a "max-age" value of 5 days since modification for all static HTML files. Configure the response header "Cache-Control" to have a value of "public" for all static HTML and image files. Configure the response header "Cache-Control" to have a value of "private" for all PHP files. My question is whether it is better to use a FilesMatch, or the mod_expires ExpiresByType to best achieve this? I've so far used the following: <FilesMatch "\.(gif|jpe?g|png)$"> ExpiresDefault "access plus 7 days" Header set Cache-Control "public" </FilesMatch> <FilesMatch "\.(html)$"> ExpiresDefault "modification plus 5 days" Header set Cache-Control "public" </FilesMatch> <FilesMatch "\.(php)$"> Header set Cache-Control "private" </FilesMatch> Thanks.

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  • Multiple possible jsp views for a request

    - by Karl Walsh
    I'm looking to offer the user some way of changing how a single page looks based on some pre-defined jsps. i.e. Two or more jsp's contain similar information, and would be backed by a single controller method. The controller would decide which view to return. Is there a common way of achieving this? At the moment I have some administration screens where I control a list of possible views. The user can then choose which one to see from a drop-down. My current issue is that I don't know how to confirm (at the admin screen) that the view is valid. Is there a way of asking spring for all possible views so I can filter them and resent a drop-down on the admin screen rather than a free text field? If not is there a way of asking spring if a single view is valid? All these views will reside under a common directory, so it would probably be possible to scan recursively from that point and build a list of possible views. This goes beyond simply changing the css, since the page content might be different despite being backed by the same model.

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  • Warnings When Undo Isn't Possible

    - by ultan o'broin
    Enjoyed this post Never Use a Warning When you Mean Undo by Aza Raskin. It makes sense never to warn users if an undo option is possible. The examples given are from the web space. Here's the conclusion: Warnings cause us to lose our work, to mistrust our computers, and to blame ourselves. A simple but foolproof design methodology solves the problem: "Never use a warning when you mean undo." And when a user is deleting their work, you always mean undo. However, in enterprise apps you may find that an undo option isn't technically possible or desirable. Objects may be shared, part of a flow elsewhere, or undoing something committed to the database (a rollback I guess) may not be feasible if it becomes locked by another process. Plus, what constitutes user ownership of objects isn't always clear to users. The implications of delete (and other) actions need to be clearly communicated out in advance. Really, warnings are important in the enterprise space. Data has a very high value, and users can perform a wide variety of actions that may risk that data, not always within the application itself (at browser level, for example). That said, throwing warnings all over the place when an undo option is possible is annoying. Instead, treat warnings with respect. When there is no undo option possible, use warning messages to communicate potentially dangerous or irrecoverable actions or the downstream consequences of user actions on the process or task flow. Force the user to respond to a warning message by using a modal dialog with clearly labeled action buttons. Here's a couple of examples. A great article that got me thinking. Let's see more like that. Let's not forget there's more types of messages than just error messages. User assistance and user experience professionals need to understand when best to use confirmation, information, and warning types too!

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  • Just quick: How do you call a mutator from within a constructor in the same class?

    - by Blockhead
    For a homework assignment the instructions state (within Undergrad class): You do NOT need to include a default constructor, but you must write a full parameterized constructor (it takes 4 arguments) -- this constructor calls the parent class parameterized constructor and the mutator for year level. Because Undergrad extends Student, then Student is my parent class, right? I just can't quite figure out how I'm to use my year level mutator (which is just the simplest of methods) to assign my "year" attribute. public void setYear(int inYear) { year = inYear; } public Student(String inName, String inID, int inCredits) { name = inName; id = inID; credits = inCredits; } public Undergrad(String inName, String inID, int inCredits,int inYear) { super(inName, inID, inCredits); year = inYear; } I keep missing assignments because I spend too much time on these small specific points of the homework so just asking for a little help. I swear it's the wording that throws me off on these assignments almost as often as just learning the material itself.

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  • sqrt(int_value + 0.0) ? The point?

    - by Earlz
    Hello, while doing some homework in my very strange C++ book, which I've been told before to throw away, had a very peculiar code segment. I know homework stuff always throws in extra "mystery" to try to confuse you like indenting 2 lines after a single-statement for-loop. But this one I'm confused on because it seems to serve some real-purpose. basically it is like this: int counter=10; ... if(pow(floor(sqrt(counter+0.0)),2) == counter) ... I'm interested in this part especially: sqrt(counter+0.0) Is there some purpose to the +0.0? Is this the poormans way of doing a static cast to a double? Does this avoid some compiler warning on some compiler I do not use? The entire program printed the exact same thing and compiled without warnings on g++ whenever I left out the +0.0 part. Maybe I'm not using a weird enough compiler?

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  • Any website with an api that serves mp3 songs(or just portions) for free?

    - by daniels
    As a homework i need to make a webapp that will play an mp3 file and the user has to guess the name of the song or the band in a certain time. My question is where can i get this songs? Is there any website that offers mp3's and an api from which i can get songs along with the band and the name? It doesn't have to be the whole song, in fact it will be better if it's just a part of it and also it should be free as it's just for a homework.

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  • Is it possible to test a theory?

    - by user363295
    We are a group of students who are working on a theory in software engineering (talking about the theory takes a lot of time so I just skip that). Implementing the theory is impossible, due to technical limitations, but it can be proven on a paper logically. We've been pushed to do a testing on it, so it can be proved that way too (although we bleieve that's not possible!), now: Basically, is it possible to test something like this? If it is, what type of testing should we use? I heard,its possible to handout a brief about it to some experts and asking about their opinion (not sure if that's true), is that a testing method? if it is, what does it called? and how exactly can be done?

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  • Is it possible to efficiently store all possible phone numbers in memory?

    - by Spencer K
    Given the standard North American phone number format: (Area Code) Exchange - Subscriber, the set of possible numbers is about 6 billion. However, efficiently breaking down the nodes into the sections listed above would yield less than 12000 distinct nodes that can be arranged in groupings to get all the possible numbers. This seems like a problem already solved. Would it done via a graph or tree?

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  • Java : Oracle recommande fortement d'appliquer un correctif qui colmate 21 vulnérabilités, et le plus rapidement possible

    Java : Oracle recommande fortement aux utilisateurs d'appliquer son correctif Qui colmate 21 vulnérabilités, et le plus rapidement possible « Suite à la menace provoquée par une attaque réussie, Oracle recommande fortement aux utilisateurs d'appliquer ce correctif le plus rapidement possible ». On ne pouvait être plus clair, d'autant plus que ce message, qui accompagne le CPU (Critical Patch Update) de février pour Java, a été mis en gras par les équipes d'Oracle. Ce correctif de sécurité apporte la correction de 21 failles. Il concerne Java SE et Java for Business.

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  • Double Linked List header node keeps returning first value as 0

    - by Craig
    I will preface to say that this is my first question. I am currently getting my Masters degree in Information Security and I had to take C++ programming this semester. So this is homework related. I am not looking for you to answer my homework but I am running into a peculiar situation. I have created the program to work with a doubly linked list and everything works fine. However when I have the user create a list of values the first node keeps returning 0. I have tried finding some reading on this and I cannot locate any reference to it. My question is then is the header node(first node) always going to be zero? Or am I doing something wrong. case: 'C': cout<<"Please enter a list:"<<endl; while(n!=-999){ myList.insert(n); cin>> n;} break; I now enter: 12321, 1234,64564,346346. The results in 0, 12321, 1234, 64564,346346. Is this what should happen or am I doing something wrong? Also as this is my first post please feel free to criticize or teach me how to color code the keywords. Anyway this is a homework assignment so I am only looking for guidance and constructive criticism. Thank you all in advance So I cannot figure out the comment sections on this forum so I will edit the original post The first section is the constructor code: template <class Type> doublyLinkedList<Type>::doublyLinkedList() { first= NULL; last = NULL; count = 0; } Then there is my insert function : template <class Type> void doublyLinkedList<Type>::insert(const Type& insertItem) { nodeType<Type> *current; //pointer to traverse the list nodeType<Type> *trailCurrent; //pointer just before current nodeType<Type> *newNode; //pointer to create a node bool found; newNode = new nodeType<Type>; //create the node newNode->info = insertItem; //store the new item in the node newNode->next = NULL; newNode->back = NULL; if(first == NULL) //if the list is empty, newNode is //the only node { first = newNode; last = newNode; count++; } else { found = false; current = first; while (current != NULL && !found) //search the list if (current->info >= insertItem) found = true; else { trailCurrent = current; current = current->next; } if (current == first) //insert newNode before first { first->back = newNode; newNode->next = first; first = newNode; count++; } else { //insert newNode between trailCurrent and current if (current != NULL) { trailCurrent->next = newNode; newNode->back = trailCurrent; newNode->next = current; current->back = newNode; } else { trailCurrent->next = newNode; newNode->back = trailCurrent; last = newNode; } count++; }//end else }//end else }//end Then I have an initialization function too: template <class Type> void doublyLinkedList<Type>::initializeList() { destroy(); } Did I miss anything?

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  • SQL SERVER – Not Possible – Delete From Multiple Table – Update Multiple Table in Single Statement

    - by pinaldave
    There are two questions which I get every single day multiple times. In my gmail, I have created standard canned reply for them. Let us see the questions here. I want to delete from multiple table in a single statement how will I do it? I want to update multiple table in a single statement how will I do it? The answer is – No, You cannot and you should not. SQL Server does not support deleting or updating from two tables in a single update. If you want to delete or update two different tables – you may want to write two different delete or update statements for it. This method has many issues – from the consistency of the data to SQL syntax. Now here is the real reason for this blog post – yesterday I was asked this question again and I replied my canned answer saying it is not possible and it should not be any way implemented that day. In the response to my reply I was pointed out to my own blog post where user suggested that I had previously mentioned this is possible and with demo example. Let us go over my conversation – you may find it interesting. Let us call the user DJ. DJ: Pinal, can we delete multiple table in a single statement or with single delete statement? Pinal: No, you cannot and you should not. DJ: Oh okey, if that is the case, why do you suggest to do that? Pinal: (baffled) I am not suggesting that. I am rather suggesting that it is not possible and it should not be possible. DJ: Hmm… but in that case why did you blog about it earlier? Pinal: (What?) No, I did not. I am pretty confident. DJ: Well, I am confident as well. You did. Pinal: In that case, it is my word against your word. Isn’t it? DJ: I have proof. Do you want to see it that you suggest it is possible? Pinal: Yes, I will be delighted too. (After 10 Minutes) DJ: Here are not one but two of your blog posts which talks about it - SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – Part 1 of 2 SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – T-SQL Example – Part 2 of 2 Pinal: Oh! DJ: I know I was correct. Pinal: Well, oh man, I did not mean there what you mean here. DJ: I did not understand can you explain it further. Pinal: Here we go. The example in the other blog is the example of the cascading delete or cascading update. I think you may want to understand the concept of the foreign keys and cascading update/delete. The concept of cascading exists to maintain data integrity. If there primary keys get deleted the update or delete reflects on the foreign key table to maintain the key integrity and data consistency. SQL Server follows ANSI Entry SQL with regard to referential integrity between PrimaryKey and ForeignKey columns which requires the inserting, updating, and deleting of data in related tables to be restricted to values that preserve the integrity. This is all together different concept than deleting multiple values in a single statement. When I hear that someone wants to delete or update multiple table in a single statement what I assume is something very similar to following. DELETE/UPDATE Table 1 (cols) Table 2 (cols) VALUES … which is not valid statement/syntax as well it is not ASNI standards as well. I guess, after this discussion with DJ, I realize I need to do a blog post so I can add the link to this blog post in my canned answer. Well, it was a fun conversation with DJ and I hope it the message is very clear now. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Joins, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • sqrt(int_value + 0.0) -- Does it have a purpose?

    - by Earlz
    Hello, while doing some homework in my very strange C++ book, which I've been told before to throw away, had a very peculiar code segment. I know homework stuff always throws in extra "mystery" to try to confuse you like indenting 2 lines after a single-statement for-loop. But this one I'm confused on because it seems to serve some real-purpose. basically it is like this: int counter=10; ... if(pow(floor(sqrt(counter+0.0)),2) == counter) ... I'm interested in this part especially: sqrt(counter+0.0) Is there some purpose to the +0.0? Is this the poormans way of doing a static cast to a double? Does this avoid some compiler warning on some compiler I do not use? The entire program printed the exact same thing and compiled without warnings on g++ whenever I left out the +0.0 part. Maybe I'm not using a weird enough compiler? Edit: Also, does gcc just break standard and not make an error for Ambiguous reference since sqrt can take 3 different types of parameters? [earlz@EarlzBeta-~/projects/homework1] $ cat calc.cpp #include <cmath> int main(){ int counter=0; sqrt(counter); } [earlz@EarlzBeta-~/projects/homework1] $ g++ calc.cpp /usr/lib/libstdc++.so.47.0: warning: strcpy() is almost always misused, please use strlcpy() /usr/lib/libstdc++.so.47.0: warning: strcat() is almost always misused, please use strlcat() [earlz@EarlzBeta-~/projects/homework1] $

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  • Validating User Input? C#

    - by Alex
    Hi, in an assignment, I have designed a input validation loop in C#, and I would like it to be able to check for the correct input format. I'm not for sure, but I think my designed loop is not checking the type of input, just what char is entered. I know I could use a try-catch block, but shouldn't you only use exceptions for exceptional situations? This is not an exceptional situation, because I expect that the user would enter an incorrect value. Input validation is not part of my assignment, so the loop is in a homework assignment, but is not part of the homework assignment. Question: Is there a way I could redesign this loop so that it checks for valid input type as well? Code: do { Console.Write("Do you wish to enter another complex number?: (Y or N)"); response = char.Parse(Console.ReadLine()); response = char.ToUpper(response); if (response != 'Y' && response != 'N') Console.WriteLine("You must respond Y or N!"); } while (response != 'Y' && response != 'N'); Thanks!!

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  • How to create extensible dynamic array in Java without using pre-made classes?

    - by AndrejaKo
    Yeah, it's a homework question, so givemetehkodezplsthx! :) Anyway, here's what I need to do: I need to have a class which will have among its attributes array of objects of another class. The proper way to do this in my opinion would be to use something like LinkedList, Vector or similar. Unfortunately, last time I did that, I got fire and brimstone from my professor, because according to his belief I was using advanced stuff without understanding basics. Now next obvious solution would be to create array with fixed number of elements and add checks to get and set which will see if the array is full. If it is full, they'd create new bigger array, copy older array's data to the new array and return the new array to the caller. If it's mostly empty, they'd create new smaller array and move data from old array to new. To me this looks a bit stupid. For my homework, there probably won't be more that 3 elements in an array, but I'd like to make a scalable solution without manually calculating statistics about how often is array filled, what is the average number of new elements added, then using results of calculation to calculate number of elements in new array and so on. By the way, there is no need to remove elements from the middle of the array. Any tips?

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  • Find the order among tasks in a company by using prolog?

    - by Cem
    First of all,I wish a happy new year for everyone.I searched more and worked a lot but I could not solve this question.I am quite a new in prolog and I must do this homework. In my homework,the question is like this: Write a prolog program that determines a valid order for the tasks to be carried out in a company. The prolog program will consist of a set of "before" predicates which denotes the order between task pairs. Here is an example; before(a,b). before(a,e). before(d,c). before(b,c). before(c,e). Here, task a should be carried before tasks b and e, d before c and so on. Hence a valid ordering of the tasks would be [a, b, d, c, e]. The order predicate in your program will be queried as follows. ?- order([a,b,c,d,e],X). X = [a, b, d, c, e] ; X = [a, d, b, c, e] ; X = [d, a, b, c, e] ; false. Hint: Try to generate different orders for the tasks (permutation) and then check if the order is consistent with the "before" relationships given. Even if you can generate a single valid order, you will get reasonable partial credits.

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  • Javascript mouseover image failure

    - by CaptainTeancum
    This is what I have so far, I have been watching a ton of Javascript videos and I feel I mimicked them solid but this is still not functioning as I want. Than being, it changes from logo1 to logo2 on mousover. This is homework. However homework that is important to me so any help or guidance would be appreciated. </head> <body> <p> <div> <script type="text/javascript"> // Pre load images for rollover function imgOver(id) { document.getElementById(id).src="logo1.jpg"; } function imgOut(id) { document.getElementById(id).src="logo2.jpg"; } </script> <a href="#" onmouseover="imgOver('logo1');" onmouseout="imgOut('logo2')"> <img alt="logo" height="150" src="images/Logo1.jpeg" width="110" /> </a> </div> </body> </html>

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  • Which subnet masks are valid for a subnetted Class B address?

    - by Daddy Warbox
    Yes, this is a school question, and yes I already know the correct possible answers (supposedly), so I'm not going to bother posting them. Instead, I just want to understand the meaning of this question. I know what class B addresses are, and what valid class B subnet addresses are. I guess one way to define my question is to ask why the answer "255.255.0.0" is wrong, necessarily? That seems to defy my understanding, or else some part of my brain is just not registering the question correctly. Thanks in advance.

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  • SQL SERVER – SELECT INTO with FileGroup or Partitionis Not Possible

    - by Pinal Dave
    The other day, I received an email from user and after a long time before I answer the question, I had to check the answer online. Here is the question - I want to create a new table based from old table, but when I execute following script it gives me an error. Is there anything I am missing in my syntax? SELECT *  INTO NewTableName ON MyFileGroup FROM MyOldTableName I faintly remember that this was not possible in earlier version of SQL Server but I was not sure if this feature was added in the recent versions or not. I quickly tried few syntaxes and referred online documentation and learned that it is still not possible in the latest version of SQL Server. The alternative is to just go ahead and change the default filegroup of any new table with following script. Though, I do not like change the default filegroup for new tables. It is possible that when I have changed the default filegroup some other code executes behind the scene by automated system or my colleague, it will be also created on new filegroup. ALTER DATABASE DatabaseName MODIFY FILEGROUP NameofFileGroup DEFAULT The reason this feature is not supported is that SELCT INTO is minimally logged operation. I seriously hope that some day in the future this feature get added in. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL Tagged: Filegroup

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  • maximum size filesystem on my test .... approach?

    - by jocco
    Hello all I'm new at the site, and I have a question. I got this question at a test and really like to know the correct approach to solving this problem? Here is the question. In an indexed filesystem the first indexblock (inode) has 12 direct pointers and 1 pointer to an indirect indexblock. The filesystem is implemented on a disk with a diskblock-size of 1024 bytes. All pointers are 32 bit. Question: what is the maximum filesize (Kilobytes) of this filesystem? If it's possible not an just an answer but an explanation. edit: It was a multiple choice btw with 4 answers a. 13 K b. 268 K c. 524 K d. 1036 K As for my approach I only got as far as to know that 1 pointer is 32 bit Also I found something else here on the site which seems very usefull. http://stackoverflow.com/questions/2755006/understanding-the-concept-of-inodes Ok i got this far There are 12 blocks and each block is 1024 bytes. 1024 * 12 = 12288 bytes or 12 KB directly accessible. Please correct me if I'm wrong. Each pointer is 32 Bit = 4Byte And to be honest at this point I'm starting to get confused especially since my answer is way over any of my multiple choice answers.

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  • xna networking, dedicated server possible?

    - by Jake
    Hi I want to release my xna game to the XBOX platform, but I'm worried about the networking limitations. Basically, I want to have a dedicated (authoritative) server, but it sounds like that is not possible. Which is why I'm wondering about: a.) Using port 80 web calls to php-driven database b.) Using an xbox as a master-server (is that possible?) I like the sound of [b] , because I could write my own application to run on the xbox, and I would assume other users could connect to it similar to the p2p architecture. Anyone able to expand on theory [b] above? or [a] as worst-case scenario?

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  • Bluetooth broadcasting realtime - is it possible

    - by user69961
    Is it possible to broadcast data via bluetooth to one ore more connected devices? I mean that each phone will be master and slave at the same time and each phone will broadcast data that should be received by all other phones. Or is the only possibility to use a "client-server"-like topology; one phone acts as a server and listens to all clients and then sends data from each client to the rest of clients in the network? Which variant should be more effective? If broadcasting is possible then the same implementation can be used for all devices and if one device will die communication between rest of network can continue. And also will there be enough to send one message per device - not message from each device to server and then back to all devices. Am I right?

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  • it means quick-select algorithm?

    - by matin1234
    Hi, I have a question from my homework. I think my teacher needs an algorithm like quick select for this question is this correct? The question: Following a program (Subroutine) as a "black box" is given (for example, inside it is not clear and we do not even inside it) with the worst case linear time, can find the middle of n elements. Using this black box, get a simple linear algorithm that takes input i and find the element which its rank is equal to i (among the n elements) Thanks.

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