I have a certain application running on my computer. The same application can run on many computers on a LAN or different places in the world. I want to communicate between them. So I basically want a p2p system. But I will always know which computers(specific IP address) will be peers. I just want peers to have join and leave functionality. The single most important aim will be communication speed and time required. I assume simple UDP multicast (if anything like that exists) between peers will be fastest possible solution. I dont want to retransmit messages even if lost. Should I use an existing p2p library e.g. libjingle,etc. or just create some basic framework from scratch as my needs are pretty basic?
I think you're missing the point of UDP. It's not saving any time in a sense that a message gets faster to the destination, it's just you're posting the message and don't care if it arrives safely to the other side. On WAN - it will probably not arrive on the other side. UDP accross networks is problematic, as it can be thrown out by any router on the way which is tight on bandwidth - there's no guarantee of delivery for it.
I wouldn't suggest using UDP out of the topology under your control.
As to P2P vs directed sockets - the question is what it is that you need to move around. Do you need bi/multidirectional communication between all the peers, or you're talking to a single server from all the nodes?
You mentioned multicast - that would mean that you have some centralized source of data that transmits information and all the rest listen - in this case there's no benefit for P2P, and multicast, as a UDP protocol, may not work well accross multiple networks. But you can use TCP connections to each of the nodes, and "multicast" on your own, and not through IGMP. You can (and should) use threading and non-blocking sockets if you're concerned about sending blocking you, and of course you can use the QoS settings to "ask" routers to rush your sockets through.
You can use zeromq for support all network communication:
zeromq is a simple library encapsulate TCP and UDP for high level communication.
For P2P you can use the different mode of 0mq :
mode PGM/EPGM for discover member of P2P on your LAN (it use multicast)
mode REQ/REP for ask a question to one member
mode PULL/PUSH for duplicate one resource on the net
mode Publish/subscribe for transmission a file to all requester
Warning, zeromq is hard to install on windows...
And for HMI, use green-shoes ?
i think you should succeed using multicast,
unfortunately i do not know any library,
but still in case you have to do it from scratch
take a look at this:
http://www.tldp.org/HOWTO/Multicast-HOWTO.html
good luck :-)
Related
There are 10 processes in my machine and each should have the capability to communicate with each other.
Now the scenario is all the 10 processes should be in the listening state so that any process can communicate with it at any time. Again when required it should be able to pass a message to any of the processes.
I am trying to code it with C++ and unix tcp/udp sockets. However I don't understand how to structure it. Shall I use UDP or TCP, which would be better? How can a process listen and send data simultaneously.
I need help.
The decision of UDP vs TCP depends on your messages, whether or not they need to be reliably delivered, etc.
For pure TCP, each peer would have a TCP socket on which each process accepts connections from other peers (and each accept would result in a new socket). This new socket is bi directional and can be used for sending / recieving from one peer to another. With this solution, you would need some sort of discovery mechanism.
For UDP, it's much the same except you don't need the accept socket. You still need some form of discovery mechanism.
The discovery mechanism could either be another peer with a well known (via configuration, etc) address, or possibly you could use UDP broadcast for the discovery mechanism.
In terms of zeroMQ, which is a slightly higher level than raw sockets, you would have a single ROUTER socket on which you're listening and recieving data, and one DEALER socket per peer on which you're sending data.
No matter the solution, you would likely need a thread for handling the network connections using poll() or something like that, and as messages are received you need another thread (or thread pool) for handling the messages.
you can run each process as severer & span 9 more thread to connect other processes as client.
This question applies to any language, so the answer is not C++ related.
When given a choice, look for a library to have an easier communication (e.g. apache-thrift).
About TCP/UDP: TCP is typically slower but more reliable, so by default, go for TCP, but there might be reasons for choosing UDP, like streaming, multicast/broadcast,... Reliability might not be an issue when all processes are on the same board, but you might want to communicate with external processes later on.
A threaded process can use the same socket for sending and receiving without locks.
Also, you need some kind of scheme to find out to what port to send to reach a process and with TCP, you need to decide whether to use static connections or connect every time you want to send.
what you want to do seems to be message passing.
before trying to build it yourself, take a look at boost mpi
Let's say I have a server, and two clients connected to it. (via TCP, but it doesn't matter)
My goal is to allow a direct connection between those two clients. This is to allow direct voice contact between two players, for example, or any other client plugin they may have installed which don't need server interaction (like playing some kind of random game between the two). The server can be there to help setting up the connection.
From duskwuff's answer, I got several leads:
http://en.wikipedia.org/wiki/STUN which describes an algorithm to do that, and
http://en.wikipedia.org/wiki/UDP_hole_punching
From those, I got more leads:
http://www.h-online.com/security/features/How-Skype-Co-get-round-firewalls-747197.html
http://nutss.gforge.cis.cornell.edu/stunt.php -- A possible STUN implementation with TCP
With time, I could surely work out something for my program. For now I'm using C++ and TCP (Qt Sockets or Boost sockets), but if needed I don't mind doing UDP in C and wrapping it.
The bounty is there for any programmer having experience with those in C and C++ that may give tips to make this easier, by linking to example programs, updated libraries, or any other useful information. A documented, flexible & working C++ TCP implementation would be the best but I'll take what I get!
Punching TCP holes in NAT is sometimes/often possible (it depends of the NAT behavior). This is not a simple subject to learn, but read the corresponding chapter about NAT traversal from Practical JXTA II (available online on Scribd) to understand the nature of the issues to solve.
Then, read this. It comes from the guy who wrote that: http://nutss.gforge.cis.cornell.edu/stunt.php (one of the links in your question).
I am not a C/C++ specialist, but the issues to solve are not language specific. As long as you have access to TCP from your code base, that's enough. Keep in mind that implementing UDP traversal is easier than TCP.
Hope these tips help.
P.S.: I am not aware of a C/C++ implementation of the solution. The code mentioned in Cornell's link is NOT operational as confirmed by the author. I tried to resuscitate it myself, but he let me know it was completely tweaked for research purposes and far from production ready.
I'm not aware of any way to reliably punch through firewalls for TCP, but there's a similar method for UDP traffic that's pretty well documented:
http://en.wikipedia.org/wiki/STUN
http://en.wikipedia.org/wiki/UDP_hole_punching
A few links to projects that might be of interest or helpful:
http://sourceforge.net/projects/stun/
http://udt.sourceforge.net/
http://www.telehash.org/
You're looking for rendezvous server for NAT hole punching: the server that is publicly accessible (not behind NAT/firewall or they are properly configured) to help computers behind NAT/firewall to establish peer-to-peer connection.
UDP is more popular in NAT punching because provides much better results than TCP. Clear and informative description of UDP NAT hole punching can be found here.
If you need reliable communication, you can use reliable protocols over UDP:
SCTP (libraries) - standardized one, or
one of many custom protocols, e.g. RakNet (I used this library, it's quite mature and feature-rich and has NAT punching implementation), Enet or many others (Q8)
Ephemeral ports won't magically eliminate the need to relay through the server, because they are only valid during the life of the session opened through a well known service port. Basically ephemeral ports depend on a server session.
You will need to use the server to relay communications between both clients, that is act as a proxy server. One option would be to setup a SSH tunnel through a SSH proxy server, with the added benefit of security.
Still this doesn't guarantee that the firewall won't block the connection. That depends on the firewall type and configuration. Most residential routers that act as firewalls, by default block all incoming connections. This is normally fine because most of the time the computers behind the firewall act only as clients, which initiate the connections to the outside. And this setup varies, because some restrict initiating connections only to well known service ports like HTTP, HTTPS, FTP, SFTP, SSH, etc., and if your proxy server uses a non-well-known-service port then the connection will be blocked.
But firewalls can be setup to block outgoing traffic also, this is most common in corporate networks, which don't even allow direct connections to web servers and route everything through proxy servers, in order to control resource usage.
You can also research on the use of UPnP to open ports dynamically.
I have written a server and a client both as separate apps. They communicate through UDP Multicast (becouse I need that everyone who joins the group can read & write messages). Now I have two windows, but my aim is to create one simple chat program, but I don't know how to listen and send at the same time. Do I need to create 2 sockets? Or can I use just one? I've even tried to merge both apps in one, but I didn't succeeded (I know, I know.. but I was kinda desperate).
I've searched google for a tut, but didn't succeeded.
I'm using c++.
You can use one or two sockets, it all depends on whether you wish to bind to a particular network adapter and whether you wish to use unicast & broadcast packets. It is often easier to manage one for sending and one for receiving.
To listen to sent multicast packets on the same host check the IP_MULTICAST_LOOP socket option, noting it applies differently on Windows to Unix.
I want to play that Qbasic Gorillas game with someone that lives in Florida.
Here's the flash version online
Gorillas
This link is to someone's post about the remake he programmed - there is a link to the game above in there and also his source code for it
playerio.com
If possible, how can I modify the code so that I can play against them over the innernet?
Should the game be public, private, or some combination of both?
It would also be cool if you could replay tosses or entire rounds with their respective angle/velocity inputs.
Take a look at sockets. Sockets are how you can connect two computers over the internet. In most implementations of sockets, you have a server socket and a client socket. The server socket listens for connections, and the client socket tries to connect to a server socket. In your case with just you and your friend, it doesn't matter much which of you is the server or client, but you will have to program for both. You also have to choose a protocol to use. The two protocols for online gaming are TCP and UDP. TCP is the most common and it is a reliable "guaranteed" connection (TCP would send data that is important). UDP is a connectionless protocol where the client just sends data with no guarantee that the data will actually get there. UDP is mostly used for very frequent updates in online games (UDP would most likely be used to send positional data in a first person shooter for example). So with your protocol in mind, I would start by adding a simple chat feature to the game. That way, you can see something working and start to understand what is happening better.
Just to suggest an alternative approach, if you want to play a game that is local multiplayer, you could set up DosBox or a Virtual Machine and then install a VNC server that both of you can log into. This would give you both KVM control.
Since it is a take-your-turn game. you could even use a chat application that has the ability to share keyboard and mouse input.
I would like to create a connection between two applications. Should I be using Client-Server or is there another way of efficiently communicating between one another? Is there any premade C++ networking client server libraries which are easy to use/reuse and implement?
Application #1 <---> (Client) <---> (Server) <---> Application #2
Thanks!
Client / server is a generic architecture pattern (much like factory, delegation, inheritance, bridge are design patterns). What you probably want is a library to eliminate the tedium of packing and unpacking your data in a format that can be sent over the wire. I strongly recommend you take a look at the protocol buffers library, which is used extensively at Google and released as open source. It will automatically encode / decode data, and it makes it possible for programs written in different languages to send and receive messages of the same type with all the dirty work done for you automatically. Protobuf only deals with encoding, not actually sending and receiving. For that, you can use primitive sockets (strongly recommend against that) or the Boost.Asio asynchronous I/O library.
I should add that you seem to be confused about the meaning of client and server, since in your diagram you have the application talking to a client which talks to a server which talks to another application. This is wrong. Your application is the client (or the server). Client / server is simply a role that your application takes on during the communication. An application is considered to be a client when it initiates a connection or a request, while an application is considered to be a server when it waits for and processes incoming requests. Client / server are simply terms to describe application behavior.
If you know the applications will be running on the same machine, you can use sockets, message queues, pipes, or shared memory. Which option you choose depends on a lot of factors.
There is a ton of example code for any of these strategies as well as libraries that will abstract away a lot of the details.
If they are running on different machines, you will want to communicate through sockets.
There's a tutorial here, with decent code samples.