CGI scripts, for example web applications, operate on the CGI interface of the webserver.
Do I have access to details of the TCP/IP packets associated with a certain connection? For example, I can get "request" details, like the environment, remote host details, etc. But can I also read out, for example, the 16-bit id field of the TCP/IP packets associated with this connect?
No, you're several layers of abstraction above the raw TCP packets. You can't access their content directly.
And there is no "TCP packet associated with this connection". A connection is a stream of packets that run both ways. Packets contents are also not necessarily delivered to user as-is - they can be aggregated or split to fit the receiving buffer.
Related
Is the signaling server used only the first time to establish a connection between 2 peers or is it also used to send and receive data-streams between the peers?
According to the w3c proposal:
An RTCPeerConnection allows two users to communicate directly, browser to browser. Communications are coordinated via a signaling channel which is provided by unspecified means, but generally by a script in the page via the server, e.g. using XMLHttpRequest.
So the Server is only used for signalig not for data transmission. But signaling is not limited to establishing the first connection. The signaling channel is also used for transmitting error messages, metadata such as codecs, codec settings, networkdata and keys for secure transmission.
This depends on the network configuration.
If at least one of the peers is not behind a NAT firewall, the peer that is directly on the internet acts as server, and the signalling server is no longer used after the connection is established.
If both peers are behind a NAT appliance, under certain circumstances it might be possible to negociate a client server connection between the peers, and the data is again sent directly between the two peers.
If both peers are behind a NAT firewall that is locked down, all the traffic between the peers passes through the signalling server.
Notice also that in the first two cases, a STUN server is used to establish the connection. If the full data is relayed through the server, a TURN server is used.
Look at a good explanation in the article an video on html5rocks. They claim only about 14% of all connexions need TURN, which seems a really low number to me (This corresponds to only 37% of all clients are behind a locked down NAT router).
What I want is, basically, to create a connection between two different computers on same local network. But i want to do this by computers' local IP's. (like 192.168.2.23 etc)
This must be a totally local connection. no TURN or STUN Servers. I am not sure if this is possible. Because there are not much documentation/example/information about WebRTC.
So, how can I create a connection from my computer to another one just passing its local IP as parameter?
Update: To be more clear; imagine there is an html page contains some code that activates my camera and audio services. and another -almost same- page is open in other computer. Waiting a connection request... And there is a textbox in my page to type an IP belongs to other computer on my local network. type 192.168.2.xx and bingo! i have connection between me and other computer.
I want this process as IP based, because there may be more than 2 devices on the network. And all of them are possible devices to create connection. So i need to reach them by their IP's.
Any example code or explanation would be great! even if it tells that this is not possible.
Thanks
Peer discovery is a vital part in any WebRTC application. It's an expensive term for saying: "Hi, I'm computer 4 and I want to talk to you!".
See it as calling a friend over the phone. You need to dial his number first.
This part is not defined in the WebRTC standards. You need to implement this logic in your application. Once you know who you want to call, you need a way of exchanging vital information. This is called signaling, like flo850 put in his answer.
Signaling is needed before any peer-to-peer connection can be set up.
To come up with an idea for your use case of 7 devices in a LAN.
If you have these devices connected to for example a WebSockets server and are in the same channel.
The WebSockets server can be written to route messages to specific receivers.
Devices connected to the channel often are identified with some kind of ID, imagine you use the device's IP.
When you want to talk to computer 4 with IP 192.168.0.4 you send the exchange messages (signaling) on the channel to the receiver with ID, the IP of the device you want to connect with.
How to send the signaling (offer, answer) is described here with example code.
Hope this helps
Users usually sit behind NATs; that's why ICE concept implemented in WebRTC.
If both users are sitting behind same NAT; you can skip ICE servers by passing "NULL" parameter value over "RTCPeerConnection" constructor:
var peer = new [webkit|moz]RTCPeerConnection ( null );
Now, browser will use "host" candidates, also known as "local" candidates.
you still need a signaling server. During the ICE candidate search, your clients will exchange their local ip through this signaling server
For an iOS app I am developing, I want multiple phone to connect to each other and be able to voice chat between those devices.
I have it working when both devices are on the same network. This was quite simple and most of the stuff I want to do, is possible.
But now I am adding internet support, which is quite a hassle. I'll first try to explain how I want to match the devices, using a small webservice I set up.
Server
Start a new GameKit session, with session-mode GKSessionModePeer
Find the "Peer ID" of the server on the session I just created
Create a new CFSocketRef on an free port and keep it ready to accept connections
Send Peer ID and Port number to my webservice, running on an external server.
WebService
Webservice receives the information and stores it together with an ID and the IP address of the client in a database.
Send ID back to Server, which displays the ID
Client
When the user chooses to use the "Online" feature of GameKit to search for games, I ask the user for an ID (where the user should input the ID the server receives).
Client connects to the webservice supplying the ID. The webservice returns the information about the session (IP, PORT, Peer ID) of the server.
The user tries to connect to the IP address, with the port information and set up an input and output stream with the server.
This does not work ofcourse, because my network does not allow incoming connections and a random port (from an external network).
But now the question is, how do I solve this? I want to be able to set up a peer to peer connection between 2 devices, those devices could be on the same network, but also on separate networks.
Is there a framework, example or anything showing how to do this? I want to be able to send data from device to device, without sending it to a server first.
I'm not aware of any frameworks that do this. I do however have a lot of experience with p2p networking across multiple networks.
One important rule I learned: when communicating between networks, don't create a direct connection unless necessary. There are just too many factors that can (will?) cause issues, such as firewalls, NATs, etc.
Sure, you can let the connection try first. You can try to connect to the given IP addresses*, but in most cases it will fail. Even when using UPnP and NAT-PMP, you'll find that in a lot of cases (more than half?) you won't be able to accept incoming connections at all.
So make sure to have a backup plan. Make a network layer abstraction that doesn't only listen(), but also connects to a server. That way, when you can't connect to the IPs* of the client, you simply setup a connection via the server and the network abstraction takes care of it all.
Let me reiterate the above: don't rely on incoming connections only, always have a backup plan.
* I write IPs because clients can have multiple local/remote IPs. Always iterate over all these IPs when connecting. Example: my phone has 2 local IPv4 addresses (10.0.0.172 and 10.8.0.2), and an IPv6 address ([2001:x:x::6]). Of these three addresses, only the IPv6 address is publicly reachable, and the two IPv4 addresses are on different subnets so whether you can connect to them depends on the subnet that the other client is on. Always try to connect to both, and fall back to a server-proxied connection when it fails.
** I mentioned IPv6, yes. Let's not forget that IPv6 is not limited by NATs, unlike IPv4, and this means that you're far more likely to get a good connection via IPv6 than IPv4, if supported.
I'm developing a filetransfer app in VB.Net
The sizes of the files vary, but can get up to 10+ GB.
I already create a chat app as a test.
On the clientside I run this code to connect to the server.
Dim clientSocket As New System.Net.Sockets.TcpClient()
Dim serverStream As NetworkStream
clientSocket.Connect("127.0.0.1", 80)
Can I also use this to transfer files?
I want the app to work through a firewall and stuff.
So I think I need the outgoing data on the client to go through port 80. On the server I want to be able to receive the data on another port (E.g. 8888). Is this possible?
And final question is. What protocol should I use for this purpose TCP or UDP.
Sorry for the three-in-one question :)
Thanks for helping me out.
Transfer Files: Yes you can very well use a reliable network stream to transfer files. Well at least the data of those files. You have to do the file system management (creating the destination file in the right folder, etc.) yourself.
TCP/UDP: As you need reliability and flow control to transfer big chunks of data over the internet, you might want to go for TCP. Also the other features of TCP like in-order delivery and error detection won't hurt. You would probably end up implementing all those yourself if using UDP, wasting a lot of your time.
Firewall: There shouldn't be a problem with firewalls on the client side of your application, unless they are really very strict and only allow outgoing HTTP connections. But the server port has to be accessible from the internet, that is you want your server side network configured such that incoming connection requests to your public IP and your chosen port are forwarded to the chosen port on your server. Look up "port forwarding" or "port NAT" for more information. Bypassing firewalls and NATs on both sides is really much more difficult if not impossible. Don't try.
In order to transfer extremely large files like you have, you are going to need to break them up into small chunks. This will help you set up an application that can resume after a network error. It is for this reason, as well as many others, that you also want to choose TCP for your transport protocol. UDP might be faster than TCP, but it doesn't have the error detection and correction you are going to need in order to have a safe transfer of data.
Here is a C# article on how to transfer large files from both the client and server perspective. If this is what you are looking for, you will just need to translate the code to VB.NET (which a translator can do automatically for your).
http://codetechnic.blogspot.com/2009/02/sending-large-files-over-tcpip.html
Basically, the code converts the file over to a byte array and then sends it across the network/Internet. Since you can choose the port you use, you won't have an issue with firewalls when you host this. On the client end, when the client initializes the connection, it will be an outbound initialization so it will go out of the network without any issue.
I assume you are on Windows, so just use BITS
There is a nice .net wrapper available sharpbits
Is it possible to use WCF discovery to access services that reside outside your local network ?
The short answer is no.
Discovery uses a UDP broadcast packet. You can discover anything that your UDP broadcast packet is allowed to reach. There is the catch, most routers, firewalls, and commercial switches block udp broadcast packets. You may be able to change the settings on your router where you connect to the next larger network (or internet), and you 'might' extend your discovery slightly. Again though, the very next switch or router you hit will most likely be set to block udp.
In this situation, most people design a "report in" server. This is one static place to which all other hosts and clients and pre-programmed to "report in" on startup. This one server keeps a table of where all hosts and clients are, and if one client wants to find a certain host, it asks this main server for the uri of the host its looking for.
EDIT:
Robin mentioned increasing the TTL (Time To Live) from the default of 1 to a higher number. Maybe this will help someone.
https://serverfault.com/a/619825/146341