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• Last in First out UDP structure in MatLab.

  - by D Zondervan

  I am using MatLabs UDP function in their instrument control toolbox to send data packets from one computer to another. The first computer is constantly updating data values and sending them to the other computer, and I want that computer to be able to query the first one for the most recent values whenever it needs them. However, the default implementation of the UDP send and receive in MatLab is a FIFO structure- the first packet I send is the first the other computer receives when they execute the "fscanf" function. I want the last packet I sent to be the one the fscanf function returns. Is this possible or do I need to use a different protocol?

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• NDIS or TDI for packet redirection to a local proxy

  - by Enrico Detoma

  I need to develop a transparent filter to redirect outgoing HTTP packets to a local proxy, to do transparent content filtering. Which is the best technology to do it, TDI or NDIS IM? My main constraint is to avoid conflicts with antivirus software, which also do some kind of packet redirection to inspect HTTP content (I don't know whether antivirus programs use TDI, NDIS IM, or both). Rather than writing the driver myself, actually, I'm also considering two commercial SDKs for packet filtering/modification: one uses a TDI driver while the other uses a NDIS IM driver, so that's the origin of my question (I was only aware of NDIS IM, before looking at the two SDKs).

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• PCAP Web Service Usage Logging for Dummies

  - by nick

  I've been assigned the task (for work) of working with PCAP for the first time in my life. I've read through the tutorials and have hacked together a real simple capture program which, it turns out, isn't that hard. However, making use of the data is more difficult. My goal is to log incomming and outgoing web service requests. Are there libraries (C or C++) that stitch together the packets from PCAP that would make reporting on this simple? Baring that is there something short of reading all of the RFC's from soup to nuts that will allow me to have an "ah-ha!" moment (all of the tutorials seem to stop at the raw packet level which isn't useful for me)? It looks like PERL has a library that may do this and I may eventually attempt a reverse engineer from PERL. NOTE BENE: Web Server logs aren't acceptable here as I will be intercepting on a routing device. If I had access to those I'd be done and happy...I don't.

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• SYN flooding still a threat to servers?

  - by Rob

  Well recently I've been reading about different Denial of Service methods. One method that kind of stuck out was SYN flooding. I'm a member of some not-so-nice forums, and someone was selling a python script that would DoS a server using SYN packets with a spoofed IP address. However, if you sent a SYN packet to a server, with a spoofed IP address, the target server would return the SYN/ACK packet to the host that was spoofed. In which case, wouldn't the spoofed host return an RST packet, thus negating the 75 second long-wait, and ultimately failing in its attempt to DoS the server?

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• Server crash = How does a TCP/IP (and the browser-client) behave after this?

  - by jens

  Hello Experts, i would be thankfull for an explanation what happens with HTTP(TCP/IP) transmissions when the server crashes unexpectedly, how does the client Browser (Firefox / IE) handle this event. What happens in the following two standard cases: Clients-actively sends data: The TCP/IP Connection has been estableshed and the Client (Web-Browser) is Sending a POST Request with some data and in the middle of the process of sending the server crashes. What does this mean for the client? As far as I know TCP/IP does not "acknowledge" a send data-package so the client does not know that the server crashed. How will the client behave? (Firefox and Internet Explorer)? The Server is actively sending data: As above the tcp/ip connection has been established and the Server is sending a large website to the client (browser). In the middle of the sending-process the server crashes, so no futher packets are sent. How does the client browser react to this event (Firefox and Interne Expolrer) Thank you very much!! Jens

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• Download estimator control using JavaScript and Ajax

  - by Anil Namde

  I would like to implement the download estimator using the JavaScript and the Ajax. I have gone trough Google to find the existing implementations for the download estimator and i found most of the time asking user bandwidth and then calculating the number is strategy. It good approach and there is hardly anything on reliable to get the estimated time right. What i would like to try is use Ajax to request file size 100KB - 200 KB and do the maths get the number and update the display. Now this is surrounded with so many questions like network, number of packets formed, proxies etc ? These all factors are sufficient to turn down the approach. But THIS IS HOW I HAVE TO DO THIS ? Now i would like here inputs from you all to make it better (as good discussion)? what all can be added to this ? Can we get to know bandwidth user using without asking ?

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• WCF: What is the practical difference between transport and message reliability?

  - by mrlane

  Hello I am looking at differences between using WPF in .NET or using Silverlight 4 for the GUI front end of an app that connects to WCF services. I have read that net.tcp binding in Silverlight 4 only supports transport level reliability. With a WPF desktop app we can use message level reliability. What is the actual difference? If transport level reliability ensures that all TCP packets get through, doesnt that also mean that all WCF SOAP messages will also get through? I am also concerned that Silverlight only supports async message but thats a different issue. Thanks

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• Pushing a variable onto a vector, value at that point in vector changes when the variable does.

  - by David Andrews

  I have a programming problem =) std::vector<char*> Names; if(MyPacket.ID == 3) {Names.push_back(MyPacket.Buffer);} I push the recieved buffer onto a vector like so, but when the buffer changes so does the value of the variable at that point in the vector. So say I sent and pushed a buffer containing 'Simon' onto the vector that would be fine so at point [0] on the vector would be the word Simon. but then when I recieve a new buffer it overwrites position [0] even though the packets ID is different, a breakpoint within the if statement is not reached with this new buffer. I really hope i'm explaining this well enough, I tried asking a friends advice and he pointed me towards this site. Any help appreciated David Andrews

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• my realtime network receiving time differs a lot, anyone can help?

  - by sguox002

  I wrote a program using tcpip sockets to send commands to a device and receive the data from the device. The data size would be around 200kB to 600KB. The computer is directly connected to the device using a 100MB network. I found that the sending packets always arrive at the computer at 100MB/s speed (I have debugging information on the unit and I also verified this using some network monitoring software), but the receiving time differs a lot from 40ms to 250ms, even if the size is the same (I have a receiving buffer about 700K and the receiving window of 8092 bytes and changing the window size does not change anything). The phenomena differs also on different computers, but on the same computer the problem is very stable. For example, receiving 300k bytes on computer a would be 40ms, but it may cost 200ms on another computer. I have disabled firewall, antivirus, all other network protocol except the TCP/IP. Any experts on this can give me some hints?

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• What does "infinity" really mean on a connection timeout? Does it retry the connection?

  - by corgrath

  The difference between connection and read timeout, is that read specifies how long the data connection can be open until it automatically closesc, correct? A connection timeout specifies how long the socket should wait until a connection is established, correct? So if a connection timeout is set to "infinity" what does that really mean? Will it try to establish a connection and if no response is given (as on packets are lost? or port is down?) it will just idle? or will Could someone please explain the basics of network/socket timeouts? and in what situation can a client socket wait infinity?

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• tracing a linux kernel, function-by function (biggest only) with us timer

  - by osgx

  Hello I want to know, how does the linux kernel do some stuff (receiving a tcp packet). In what order main tcp functions are called. I want to see both interrupt handler (top half), bottom half and even work done by kernel after user calls "read()". How can I get a function trace from kernel with some linear time scale? I want to get a trace from single packet, not the profile of kernel when receiving 1000th of packets. Kernel is 2.6.18 or 2.6.23 (supported in my debian). I can add some patches to it.

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• C# Proxy, what is the best way to do this?

  - by Kin

  I'm writing a proxy using .NET and C#. It has a couple of functions that it needs to fulfill. I haven't done much Socket programming, and I am not sure the best way to go about it. Should I use Synchronous Sockets, Asynchronous sockets? Please help! It must... Accept Connections from the client on two different ports, and be able to receive data on both ports at the same time. When a connection is made on a port, it must immediately connect to the server, and start sending data as it receives it from the client to the server. Packets must be forwarded in the order they are received, exactly as they were received. It needs to be as low latency as possible. I don't need the ability for multiple clients to use the proxy, but it would be a nice feature if its easy to implement.

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• Intercept windows open file

  - by HyLian

  Hello, I'm trying to make a small program that could intercept the open process of a file. The purpose is when an user double-click on a file in a given folder, windows would inform to the software, then it process that petition and return windows the data of the file. Maybe there would be another solution like monitoring Open messages and force Windows to wait while the program prepare the contents of the file. One application of this concept, could be to manage desencryption of a file in a transparent way to the user. In this context, the encrypted file would be on the disk and when the user open it ( with double-click on it or with some application such as notepad ), the background process would intercept that open event, desencrypt the file and give the contents of that file to the asking application. It's a little bit strange concept, it could be like "Man In The Middle" network concept, but with files instead of network packets. Thanks for reading.

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• Threading and pcap issues.

  - by cftmon

  I have a GUI program that allows a user a scan a network, the issue is that when the pcap_loop function is called, my GUI program becomes unresponsive.(the pcap_loop blocks the current thread). When i try to use pthreads, i got a SIGSEGV fault at the pcap_loop function.Why?It's as if the thread can't see the procPacket function itself. void procPacket(u_char *arg, const struct pcap_pkthdr *pkthdr, const u_char *packet) { //show packets here } void* pcapLooper(void* param) { pcap_t* handler = (pcap_t*) param; pcap_loop(handler, 900 ,procPacket, NULL ); } //some function that runs when a button is pressed //handler has been opened through pcap_open_live pthread_t scanner; int t = pthread_create(&scanner,NULL,&pcapLooper, &handler ); if(t) { std::cout << "failed" << std::endl; } pthread_join(scanner,NULL); //do other stuff.

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• Why are nanosleep() and usleep() too slow?

  - by user351990

  I have a program that generates packets to send to a receiver. I need an efficient method of introducing a small delay between the sending of each packet so as not to overrun the receiver. I've tried usleep() and nanosleep() but they seem to be too slow. I've implemented a busy wait loop and had more success, but it's not the most efficient method, I know. I'm interested in anyone's experiences in trying to do what I'm doing. Do others find usleep() and nanosleep() to function well for this type of application? Thanks, Danny Llewallyn

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• Good XMPP Java Libraries for server side?

  - by Taylor Gautier

  I was hoping to implement a simple XMPP server in Java. What I need is a library which can parse and understand xmpp requests from a client. I have looked at Smack (mentioned below) and JSO. Smack appears to be client only so while it might help parsing packets it doesn't know how to respond to clients. Is JSO maintained it looks very old. The only promising avenue is to pull apart Openfire which is an entire commercial (OSS) XMPP server. I was just hoping for a few lines of code on top of Netty or Mina, so I could get started processing some messages off the wire.

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• Sending file over socket

  - by johannix

  I'm have a problem sending data as a file from one end of a socket to the other. What's happening is that both the server and client are trying to read the file so the file never gets sent. I was wondering how to have the client block until the server's completed reading the file sent from the client. I have this working with raw packets using send and recv, but figured this was a cleaner solution... Client: connects to server creating socket connection creates a file on socket and sends data waits for file from server Server: waits for file from client Complete interraction: client sends data to server server sends data to client

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• ASF duration is 29 secs, WMP plays 25 secs. How come?

  - by Roey

  Hi All. I've created a custom ASF file containing compressed voice + screen streams. The total duration of the file according to the header is 29 secs. When opening it in WMP (using custom DMOs to play the streams), the file plays 25 seconds, and then the seek bar snaps to the beginning, but oddly, WMP continues to play 4 more seconds before stopping. Looking at the ASF with ASF Viewer - there are 29 seconds of packets , and both "play duration" and "send duration" are 29 seconds. Why would WMP only see 25 seconds?? Thanks

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• Need direction in creating a voice chat application

  - by WarDoGG

  I want to create a voice chat application as a part of a project. However, i am totally lacking direction regarding the programming language to use, the technologies involved. Can somebody please guide me as to how i should proceed ? Here are the features that i require : user to user voice chat ability to chat in conference (more than 2 users) How do i connect one user to another ? How to handle voice transmission ? How to effectively route packets in a conference ? I'm thinking the most probably langauge to develop this in would be Flash. Any suggestions are welcome.

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• How can I log into gmail in a script/program using HTTPS?

  - by master chief

  My teacher has given me as an assignment to log into gmail and then send one e-mail or read the list of unread e-mails, but I can't use IMAP/POP3/SMTP or anything that isn't HTTP or HTTPS. I've tried looking for libraries in Ruby/Java to do it but nothing really worked for me. I tried looking at the gmail source code page but I couldn't really understand what was going on. The page seems to call a post method on a link, but sniffing the packets what I saw was a GET apparently using a session generated using the info I send. So sending it "raw" didn't work either. I've no idea what to do now.

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• Deciphering Encoding: Packet Analyzation Tools

  - by Zombies

  I am looking for better tools than wireshark for this. The problem with wireshark is that it does not format the data layer (which is the only part I am looking at) cleanly for me to compare the different packets and attempt to understand the third party encoding (which is closed source). Specifically, what are some good tools for viewing data, and not tcp/udp header information? Particularly, a tool that formats the data for comparison. To be very specific: I would like a program that compares multiple (not just 2) files in hex.

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• Object to Network serialization - with an existing protocol

  - by cpf

  I'm writing a client for a server program written in C++. As is not unusual, all the networking protocol is in a format where packets can be easily memcopied into/out of a C++ structure (1 byte packet code, then different arrangements per packet type). I could do the same thing in C#, but is there an easier way, especially considering lots of the data is fixed-length char arrays that I want to play with as strings? Or should I just suck it up and convert types as needed? I've looked at using the ISerializable interface, but it doesnt look as low level as is required.

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• Giving Users an Option Between UDP & TCP?

  - by cam

  After studying TCP/UDP difference all week, I just can't decide which to use. I have to send a large amount of constant sensor data, while at the same time sending important data that can't be lost. This made a perfect split for me to use both, then I read a paper (http://www.isoc.org/INET97/proceedings/F3/F3_1.HTM) that says using both causes packet/performance loss in the other. Is there any issue presented if I allow the user to choose which protocol to use (if I program both server side) instead of choosing myself? Are there any disadvantages to this? The only other solution I came up with is to use UDP, and if there seems to be too great of loss of packets, switch to TCP (client-side).

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• Verify p2p node

  - by mazzzzz

  Hey guys, I have been working on a p2p namespace for some of my programs. I created a system to encrypt/decrypt the packets send/received with the class. I was using the basic public private key system: 1) encrypt the data with Symmetric encryption 2) encrypt the symmetric key with RSA. Then do the opposite when you decrypted.. I was wondering though, how would you verify if the packet was coming from where it said it was. I was going to use a basic certificate system (where you encrypt with your private RSA key, then they decrypt it with your public key), but I don't know how to do this with C#. I am using the RSACryptoServiceProvider class. Does anyone know how do this? Thanks, Max

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• C++ networking simple send and receive

  - by Wallter

  I'm trying to link 10 computers together, the program i would like to write would have one 'control' computer. From what I've looked up this computer would take all the packets sent over the network and do a echo with them... right? The other computers would need to be able to send information (then echoed to the others) to the 'control' ... is there a easy! or simple way to do this? From what I've seen i want a non-blocking socket? I have looked into sockets and such but for an armature programmer like me, this seems like a daunting task :) I'm kind-of looking for an easy class implication that has a send() and an event driven recv(). I'm not going to be sending that much information over the network.

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