What all would be the requirements for the following scenario:
A GSM modem connected to a PC running
a web based (ASP.NET) application. In
the application the user selects a
phone number from a list of phone nos.
When he clicks on a button named the
PC should call the selected phone
number. When the person on the phone
responds he should be able to have a
conversation with the PC user.
Similarly there should be a facility
to send SMS.
Now I don't want any code listings. I just need to know what would be the requirements besides asp.net, database for storing phone numbers, and GSM modem.
Any help in terms of reference websites would be highly appreciated.
I'll pick some points of your very broad question and answer them. Note that there are other points where others may be of more help...
First, a GSM modem is probably not the way you'd want to go as they usually don't allow for concurrency. So unless you just want one user at the time to use your service, you'd probably need another solution.
Also, think about cost issues - at least where I live, providing such a service would be prohibitively expensive using a normal GSM modem and a normal contract - but this is drifting into off-topicness.
The next issue will be to get voice data from the client to the server (which will relay it to the phone system - using whatever practical means). Pure browser based functionality won't be of much help, so you would absolutely need something plugin based.
Flash may work, seeing they provide access to the microphone, but please don't ask me about the details. I've never done anything like this.
Also, privacy would be a concern. While GSM data is encrypted, the path between client and server is not per default. And even if you use SSL, you'd have to convince your users trusting you that you don't record all the conversations going on, but this too is more of a political than a coding issue.
Finally, you'd have to think of bandwidth. Voice uses a lot of it and also it requires low latency. If you use a SIP trunk, you'll need the bandwidth twice per user: Once from and to your client and once from and to the SIP trunk. Calculate with 10-64 KBit/s per user and channel.
A feasible architecture would probably be to use a SIP trunk (they optimize on using VoIP as much as possible and thus can provide much lower rates than a GSM provider generally does. Also, they allow for concurrency), an Asterisk box (http://www.asterisk.org - a free PBX), some custom made flash client and a custom made SIP client on the server.
All in all, this is quite the undertaking :-)
You'll need a GSM library. There appear to be a few of these.
e.g. http://www.wirelessdevstudio.com/eng/
Have a look at the Ekiga project at http://www.Ekiga.org.
This provides audio and or video chat between users using the standard SIP (Session Initiation Protocol) over the Internet. Like most SIP clients, it can also be used to make calls to and receive calls from the telephone network, but this requires an account with a commercial service provider (there are many, and fees are quite reasonable compared to normal phone line accounts).
Ekiga uses the open source OPAL library to implement SIP communications (OPAL has support for several VoIP and video over IP standards - see www.opalvoip.org for more info).
Related
What I'm asking here may not be possible at all, due to my lack of knowledge with networks.
I want to start playing around with IOT objects in my house. I would love to be able to control various objects from the touch of a button on my phone.
I have bought a "smart" plug outlet which enables me to turn the power on or off via an app over my home WiFi, however I want to be able to build my own app and control the device exactly how I want to, just for fun.
This app I'm using at the moment comes with the outlet and as far as I can see, it was not meant to be customizable in any way.
My question is, is it possible to figure out the requests being made to and from the device, and create my own API to work with it?
I am a software developer day-to-day however my knowledge in networks is very basic. Any help is really appreciated!
If there is no documented API you can, in theory, to reverse engineer the API using sniffers. If you control the device from your phone you can install sniffers on the phone and see the incoming and outgoing requests. But the bigger problem for you is if there is some kind of security mechanism that the device and the app are implementing. The protocol can be encrypted so you wont be able to understand the network traffic or maybe some kind of key that will allow the device to get orders only from a specific app.
So my suggestion, if you are not experienced with this kind of work is to approach the device vendor and ask them for the API, some vendors would be happy to expose it if you would publish your code and let other customers to use it and expand their product.
My knowledge about network programming is limited, so, all the comments are more than welcome. Essentially my question boils down to the following question:
Q1. Is there really such a thing as decentralized asynchronous cross-platform peer-to-peer communication?
Let me explain myself.
If we have two http servers running on computers with actual IP addresses, then clearly the answer is yes, assuming one writes a protocol for the interaction.
To go one step further, if one of them (or both) is (are) behind a router, then, with port forwarding the communication can still be established. However, here the problems start because if someone wants to run such a server on the background, say in a mobile phone, the app that is relying on this server really works when one is at home (we can not really expect to request port forwarding everywhere we go).
But even beyond that,
Q2. do mobile phones obtain an actual IP address from telecommunication companies when someone is not using a wi-fi?
If this is true, then clearly one can have cross-platform asynchronous peer-to-peer communication at the expense of not using wi-fi by running an http server on a smartphone. (I understand that this is not convenient, but it is certainly doable.)
Concluding, the two (perhaps there are more) relevant questions that I can think of are:
Q3. How does Skype really work?
Q4. How does Viber really work?
Based on the answer for Skype, it says: If one of the callee or both of them do not have a public IP, then they send voice traffic to another online Skype node over UDP or TCP.
So, it appears that there is no direct communication in Skype, because they have to use a man-in-the-middle for such a scenario.
Regarding Viber, I could not find a good-thorough answer to this particular question. Do people talk to each other through a Viber centralized server, or, do they establish a direct connection? Of course if they do establish a direct connection, then I really want to know how they manage such a thing since a mobile phone may or may not have a physical address. How is a Viber message routed to my cell phone from a friend of mine even when Viber is not running and I am behind a router?
I guess the answer to Viber is really push notifications, but as far as I can understand, all the variations of push notifications rely on open connections, and then the servers of the applications send the notifications to the clients through such connection(s). So, this approach gives us the feeling that it is asynchronous, but essentially it is not. We are cheating, in the sense that there is a constantly open connection to a server, and moreover, as far as I can understand, the application server has to push the notification through that server. Schematically:
A > Central App Server > Central Server w/ open connection to my cellphone > me
So, this seems to be once again a centralized approach.
Honestly, the only approach that I can think of that is both decentralized and asynchronous (on mobile phones as well) is to run an http server on every platform/device, but this comes at the expense of not using Wi-Fi and assuming that a telecommunication company really assigns a physical IP address to every mobile phone (which I do not know if it is true, do you?).
What about WASTE, darknets, F2Fs, etc? Do they offer advantages in the sense of a more direct asynchronous communication between some interested parties? Are there real-world applications (also including mobile phones) using such approaches for communication.
Really, this is not the actual problem that I would like to work on, but I would like to know what the state of the art is so that I can figure out how I can proceed from there. So, all comments are really more than welcome. If you have references for the state of the art I would like to know about them as well, but a brief description would also be nice.
I appreciate all your time and effort in advance.
You asked many questions, here is the beginning of the answers:
Q1: Yes. For example, take BitTorrent's very successful 10 million+ node network. Aside from the bootstrapping process, the protocol is entirely decentralized and asynchronous. See here for more info.
Q2: Yes! Go to www.whatismyip.com on your mobile telephone, and you will see your assigned IP. However, you are likely to be very filtered (e.g: incoming traffic on port 80 is likely to be blocked).
Q3: It has elements of P2P and clever tricks to get around NAT issues - see here for more info.
Q4: I don't know.
I want to write a program that programmatically sends faxes. Or receives faxes. But not with a modem. I guess I'm trying to write a fax simulator. Everything that the hardware does, I want to do using software.
There are a billion SO questions on the topic, but they either suggest an online service to use or they point me to a library, which talks to my computer's modem. So here are my specific questions:
When I send a fax, I can hear the warbling on the telephone line. This tells me that my fax machine is generating tones that are consumable by the recipient's. What is that protocol? Is there an RFC which specifies how a "pixel" is converted to a "frequency"? Do the machines communicate back and forth, or is it one-way?
If we can agree that a fax machine translates sound frequencies to images, then one ought to be able to write a program which takes an MP3 of a fax transmission and outputs a graphic. What do I need to know in order to do this?
Are these questions based on any flawed assumptions? Where should I start so that I can accomplish goal #2 from above?
Actually in modem a chip called "DSP => Digital Signal Processing" is responsible to convert audio signals into digital DATA. and same can be done with a software library. there is already an open source DSP library called SpanDSP developed by "Steve Underwood" http://www.soft-switch.org/.
You can build your own application while using SpanDSP library, but it is wise to use some existing implementation of SpanDSP. Currently SpanDSP is implemented in open source FreeSwitch, CallWeaver and Asterisk PBX systems.
But if you only want to send and receive faxes without bothering low level development then try out ICTFAX Open Source FAX system.
The fax specifications you would need are ITU T4 and T30, which costs lots of money and are almost wilfully difficult to understand, and they'll refer you to the various modem standard for how the actual 'warbling' is done.
If you're hoping for something free/easy like an RFC, then you should probably give up now.
If you did want to decode an audio file, you would need to view that as two completely separate tasks - firstly decoding the tones to a data stream (build several soft-modems, for the various ways fax machines can agree to communicate), and then secondly decoding the data-stream to pixels (write a fax machine's software).
You are not fundamentally wrong that a fax machine converts light and dark into sound and then back again, or that it's possible to eavesdrop on a conversation between two fax machines and recover the image (either in real-time or via some kind of capture file, though I'm not sure that MP3 would work), but I suspect you've hugely, hugely underestimated the amount of work involved.
http://en.wikipedia.org/wiki/Fax
has plenty of background.
The ITU protocols are very involved, IIRC the exact specifications are not free.
I'm making a network game (1v1) where in-game its p2p - no need for a game server.
However, for players to be able to "find each other", without the need to coordinate in another medium and enter IP addresses (similar to the modem days of network games), I need to have a coordination/matching server.
I can't use regular web hosting because:
The clients will communicate in UDP.
Therefore I'll need to do UDP Hole Punching to be able to go through the NAT
That would require the server to talk in UDP and know the client's IP and port
afaik with regular web hosting (php/etc) I can only get the client's IP address and can only communicate in TCP (HTTP).
Options I am currently considering:
Use a hosting solution where my program can accept UDP connection. (any recommendations?)
UDPonNAT seems to do this but uses GTalk and requires each client to have a GTalk account for this (which probably makes it an unsuitable solution)
Any ideas? Thanks :)
First, let me say that this is well out of my realm of expertise, but I found myself very interested, so I've been doing some searching and reading.
It seems that the most commonly prescribed solution for UDP NAT traversal is to use a STUN server. I did some quick searches to see if there are any companies that will just straight-up provide you with a STUN hosting solution, but if there even were any, they were buried in piles of ads for simple web hosting.
Fortunately, it seems there are several STUN servers that are already up and running and free for public use. There is a list of public STUN servers at voip-info.org.
In addition, there is plenty more information to be had if you explore SO questions tagged "nat".
I don't see any other choice than to have a dedicated server running your code. The other solutions you propose are, shall we say, less than optimal.
If you start small, virtual hosting will be fine. Costs are pretty minimal.
Rather than a full-blown dedicated server, you could just get a cheap shared hosting service and have the application interface with a PHP page, which in turn interfaces with a MySQL database backend.
For example, Lunarpages has a $3/month starter package that includes 5gb of space and 50gb of bandwidth. For something this simple, that's all you should need.
Then you just have your application poll the web page for the list of games, and submit a POST request in order to add their own game to the list.
Of course, this method requires learning PHP and MySQL if you don't already know them. And if you do it right, you can have the PHP page enter a sort of infinite loop to keep the connection open and just feed updates to the client, rather than polling the page every few seconds and wasting a lot of bandwidth. That's way outside the scope of this answer though.
Oh, and if you're looking for something absolutely free, search for a free PHP host. Those exist too! Even with an ad-supported host, your app could just grab the page and ignore the ads when you parse the list of games. I know that T35 used to be one of my favorites because their free plan doesn't track space or bandwidth (it limits the per-file size, to eliminate their service being used as a media share, but it shouldn't be a problem for PHP files). But of course, I think in the long run you'll be better off going with a paid host.
Edit: T35 also says "Free hosting allows 1 domain to be hosted, while paid offers unlimited domain hosting." So you can even just pay for a domain name and link it to them! I think in the short term, that's your best (cheapest) bet. Of course, this is all assuming you either know or are willing to learn PHP in order to make this happen. :)
There's nothing that every net connection will support. STUN is probably good, UPnP can work for this.
However, it's rumored that most firewalls can be enticed to pass almost anything through UDP port 53 (DNS). You might have to argue with the OS about your access to that port though.
Also, check out SIP, it's another protocol designed for this sort of thing. With the popularity of VOIP, there may be decent built-in support for this in more firewalls.
If you're really committed to UDP, you might also consider tunneling it over HTTP.
how about you break the problem into two parts - make a game matcher client (that is distinct from the game), which can communicate via http to your cheap/shared webhost. All gamers who wants to use the game matching function use this. THe game matcher client then launches the actual game with the correct parameters (IP, etc etc) after obtaining the info from your server.
The game will then use the standard way to UDP punch thru NAT, etc etc, as per your network code. The game dont actually need to know anything about the matcher client or matcher server - in the true sense of p2p (like torrents, once you can obtain your peer's IPs, you can even disconnect from the tracker).
That way, your problems become smaller.
An intermediate solution between hosting your own dedicated server and a strictly P2P networking environment is the gnutella model. In that model, there are superpeers that act like local servers, having known IP addresses and being connected to (and thus having knowledge of) more clients than a typical peer. This still requires you to run at least one superpeer yourself, but it gives you the option to let other people run their own superpeers.
I'm developing a multi-player game and I know nothing about how to connect from one client to another via a server. Where do I start? Are there any whizzy open source projects which provide the communication framework into which I can drop my message data or do I have to write a load of complicated multi-threaded sockety code? Does the picture change at all if teh clients are running on phones?
I am language agnostic, although ideally I would have a Flash or Qt front end and a Java server, but that may be being a bit greedy.
I have spent a few hours googling, but the whole topic is new to me and I'm a bit lost. I'd appreciate help of any kind - including how to tag this question.
If latency isn't a huge issue, you could just implement a few web services to do message passing. This would not be a slow as you might think, and is easy to implement across languages. The downside is the client has to poll the server to get updates. so you could be looking at a few hundred ms to get from one client to another.
You can also use the built in flex messaging interface. There are provisions there to allow client to client interactions.
Typically game engines send UDP packets because of latency. The fact is that TCP is just not fast enough and reliability is less of a concern than speed is.
Web services would compound the latency issues inherent in TCP due to additional overhead. Further, they would eat up memory depending on number of expected players. Finally, they have a large amount of payload overhead that you just don't need (xml anyone?).
There are several ways to go about this. One way is centralized messaging (client/server). This means that you would have a java server listening for udp packets from the clients. It would then rebroadcast them to any of the relevant users.
A second way is decentralized (peer to peer). A client registers with the server to state what game / world it's in. From that it gets a list of other clients in that world. The server maintains that list and notifies the other clients of people who join / drop out.
From that point forward clients broadcast udp packets directly to the other users.
If you look for communication framework with high performance try look at ACE C++ framework (it has Java bindings).
Official web-site is: http://www.cs.wustl.edu/~schmidt/ACE-overview.html
You could also look into Flash Media Interactive Server, or if you want a Java implementation, Wowsa or Red5. Those use AMF and provide native functionality for ShareObjects including synching of the ShareObjects among connected clients.
Those aren't peer to peer though (yet, it's coming soon I hear). They use centralized messaging managed by the server.
Good luck