If you were to implement a persistent tcp connection on android what port number would you choose?
This is the sort of connection used by Google's C2DM service.
Use any port really. It probably doesn't really matter so long as it's above 1024. Let's say you choose port 5000.
I'd recommend using a second ip address and forward all traffic on ip2:80 to ip1:5000. That way you can get around any firewall restrictions on your network.
If you want more details about adding a second ip address and adding a NAT to your iptables to forward traffic from port 80 on ip2 to port 5000 on ip1, I can share my notes with you.
How about 1764? (42*42). Or possibly 3141?
Technically it really doesn't matter what port you choose. You just can't use a port that is needed for another service if you also want to run this service. So if you want to run it on a mail server, port 25 is a bad choice.
But since there are sometimes firewalls in place that may filter traffic, I'd recommend port 443 (https) where you have a slightly higher chance of getting your traffic through.
Related
I want to connect 2 or more Android devices with p2p connection. As I understand I may use Wi-Fi Direct under one wifi network https://developer.android.com/guide/topics/connectivity/wifip2p.html
But I want to connect Android clients located in different places but possibly with the one IP (vpn or something). How can I do that?
Here is my algorithm
Client_1 register its name and current IP on Server
Client_2 register its name and current IP on Server
Client_1 request registred IP from Server by Client_2 name
Client_2 request registred IP from Server by Client_1 name
Client_1 send message directly to Client_2 IP
This algorithm will not work if Client_1 and Client_2 has the same IP. Or if client is behind NAT.
Is there a ready to use library to connect 2 or more Android devices in such way?
You can use Fixed Ip Simcards if you want to do a setup for your personal purpose. Another option is to convert your android phone local private ip into public ip , this can be done via Update No-IP app , this app will give you a direct link to communicate with public ip you have.
I hope my answer would be somewhat helpful to you.
Your best bet would be to look into NAT traversal on cellular connections. There are several threads on Stack Overflow that discuss this for example UPnP NAT Traversal for 3G/4G Wireless Data Connection on Android and Android: NAT Traversal?
To sum things up the easiest solution would be to look into using STUN to determine if your application/device is NATed and then using TURN or ICE to try to establish a (not necessarily direct) connection between your devices using NAT traversal. There exist multiple libraries that implement these protocols/methods for example http://www.pjsip.org/ which has Android support and has a pretty good documentation including sample applications for all mentioned techniques.
I worked on a simple app....which works by sending simple instructions to Arduino over my WiFi router, just like - 192.168.0.177/status or 192.168.0.177/currenttemp etc,while my phone is directly connected to the router.
What I am trying to achieve now,is to be able to send same instructions to Arduino(which is connected to router) over the 3G/2G data of my android(which is not directly connected to router).
I tried to research a bit,but its all is just fuzzing up things more & more....
(I m big nooooob).
So,what should I do to get that to happen?
is it--[PUBLIC IP of router]/status. I just cant understand.
Some port forwarding,router remote access,I do not know. Direction reqd.
++I dont know...how can i get this Public IP,,it quite keeps on changing & if so,,,how to set up.?.? :-(
So this seems like a question of 2 parts - but overall you're going to have to become familiar with your routers status page. It should allow you to do port forwarding (which you will have to do) and may help with your IP changing.
Finding your Router Status Page
Your router status page is usually available from one of these two urls:
http://192.168.0.1
http://192.168.1.1
Hopefully one of these will take you to a web page, where you can configure things- if neither do then you're going to have to find out what the right address is - this should be the same as your default gateway so you can follow these instructions: https://wiki.amahi.org/index.php/Find_Your_Gateway_IP
Port Forwarding
Simply put, for home internet connections you're probably going to use Port Forwarding whenever a device that's not on your network (in this case your phone) initiates a connection to a device that is on your network (your arduino).
This is because when your phone connects it will do so to an internet IP address rather than a local IP address and the internet IP can't specify which device within a local network you want to talk to. If your Arduino were to make the connection you wouldn't need to port forward on your home network.
Within your Router Status page you should find configuration options for port forwarding, without knowing your router I can't say much about where you'll find them but they're usually obvious - once there typically you can pick a port or range of ports you want to forward and which IP address you want to forward them too. Judging by your question the port you want is 80, the default one for web browsing - the IP address you want is the internal IP of the Arduino which seems to be 192.168.0.177.
Once you save that you should be able to make connections to your Arduino from off your network but you've still got your IP issue left.
Dynamic IPs
You're quite right you'll need your public IP to connect, this can easily be found from within your network by going to a site like https://www.whatismyip.com
However as you've mentioned, your IP changes quite a lot, so if you don't want to keep looking it up you've only got a couple of choices:
Pay for a static IP from your internet service provider (if they offer this)
Use a dynamic DNS updating service
Probably the most well known amongst those services is DynDNS though there are free alternatives, it's worth remembering that you may be getting what you pay for and I'd perhaps look for recommendations from other StackOverflow users on which to use.
In terms of the actual updating you have two options, the easier one is to install a client on a supported computer which will periodically update your IP. Alternatively, some more sophisticated routers have Dynamic DNS updating built in and this would also be accessible by your router status page, which you're hopefully already a pro at rooting around in.
yes you need public ip of your router as your both device is not in the same network.
Here is my scenario.
I have my device (android phone).
And I know the IP address of another device (which is some remote device in the Internet)
So how do I send data to the other device?
Do I use protocols like Tcp or Udp?
EDIT : And I know there are public IP addresses and private IP addresses (like when a device connects via WiFi). In such a case is it even possible to use Tcp or Udp???
What you're looking to do is a common task with a common problem (but also with a common solution). You want to send data from one device (computer/phone/etc..) to another. Here's how it works behind the scenes:
There are a lot of computers in the world. Each computer is given an identity - a name, if you will, which is called the computer's IP address. There are many versions/standards of the IP address, and the current standard names an IP address as such: "111.222.333.444". There are only so many permutations with 12 digits of numbers - and entire ranges of IP addresses are reserved. In other words, there aren't enough IP addresses to go around for computers.
Now, routers were invented, among other reasons, to combat this problem. Routers give all computers within its local area network (LAN) one public (WAN) IP address. With an average of one router per household, this saves many IP addresses. Unfortunately, it also breaks direct communication between computers, because how does one communicate with three computers all using the same name? How does one identify computer A from computer B from computer C when they all share the same WAN IP address?
First, let's clarify that - just like there are a few versions and standards of IP addresses, so there are a few types of routers. By the way, it's not the router that is to blame for the problems of direct communication between computers - it's actually the router's underlying technology of network address translation (NAT). Anyways, there are a few types of NAT, and although information on the internet is relatively scarce on these types, you can still Wikipedia it and read a few university research papers. The types are Full Cone NAT, Restricted NAT, Port Restricted NAT, and Symmetric NAT.
So, computers in a LAN share the same WAN IP. This is a problem. What's one solution? What if we instructed the router to route all incoming traffic directed to a certain port, to a certain computer in our local area network? For example, if three LAN computers share the WAN IP of 1.1.1.1, we can setup a procedure called port forwarding to instruct the router to route all packets arriving on port 6000 to 192.168.1.101:3500.
uPnP is just a fancy technology (not always present in routers - or more importantly, hardly ever enabled by default) that allows you to port forward using code.
If we can't use uPnP to port forward because not all devices have it enabled, there must be another solution - and there is: hole punching.
Hole punching comes in two flavors: UDP and TCP, although TCP hole punching is a bit more complicated because TCP is inherently first a connection-oriented protocol. UDP hole punching is easier because you can send packets without a connection (in fact, is there really such a thing as a connection?)
You can read the procedure on UDP hole punching on Wikipedia and other sites. The concept works like this, though. Any computer sending an outbound packet will expect a reply, meaning the router will allow the inbound packet's reply. At first, two computers will not expect a reply from each other, so the first packet each computer sends will be rejected by the router. If we continue sending packets, however, the router will allow the rest of the packets to come through, because a reply is expected from each computer. As long as this hole-punched connection is maintained active by occasional keep-alive packets, it will stay alive. Unfortunately, this method of UDP hole punching is unsuccessful for Symmetric NATs (explained in the links below). That's why the end-all solution is to simply proxy the connection and traffic through your own server. This requires a farm of computers, so it's quite costly. But this end-all solution is called TURN. STUN is a web service you can query to determine your NAT type and public IP (as opposed to parsing cmyip.com). Just some terms you'll encounter along your personal research.
Playing around with these concepts help. Here are some resources to get your started:
Types of NATs: http://think-like-a-computer.com/2011/09/16/types-of-nat/
A Method for Symmetric NAT Traversal (basically by spamming a lot more packets to a lot more ports): http://www.goto.info.waseda.ac.jp/~wei/file/wei-apan-v10.pdf
Lidgren Networking Library (which has NAT traversal built-in, this is a C# library): http://code.google.com/p/lidgren-network-gen3/w/list
In most realistic cases, you send data to the other device by sending the data to an intermediate device from which the other phone picks it up. Can can use protocols like TCP or UDP directly between the two devices, and that may or may not work depending on the protocols and how the devices are getting Internet access.
For example, one device can send an email and the other device can retrieve that email. You can generalize that model to other types of communication.
All of the documentation, examples and questions I've seen so far on TCP connections with Android have been between an Android device and a computer. As unreliable as wireless can be, is it possible to make a client-server TCP connection between Android devices over WiFi, and if so, how?
Edit: I guess I should elaborate more on my situation.
My Droid does not respond to ping or accept incoming TCP requests from anything unless I first make the Droid a client and my laptop the server. After this initial connection is established I can then ping from my laptop, or make the Droid a server and my laptop the client. What I can't do is make one Droid the server and another a client, I always get a "No route to host" error.
It feels like there is something blocking incoming connections unless the device initiates a connection to something else, and even then the only request the device will accept is with this device. How can I make my Droid a server that accepts all incoming TCP requests from any device on my local intranet?
You should be able to. Just do like you would do with computer/device connections, except run the client and server code on the devices.
One of the neat things about the Internet is that the Internet doesn't care whether you are establishing a connection between two PC's, a PC and a phone, or two phones. I would look at the Socket documentation, that should be enough to get you rolling.
It's certainly possible. The only problem is figuring out the IP address. I don't expect a phone have a fixed IP... However, if there is a fixed "login" server somewhere in the Web which IP is known to both phones then they can do a handshake via that server and after that continue peer-to-peer.
re; The only problem is figuring out the IP address. I don't expect a phone have a fixed IP.
Try this;
Use the web browser on the phone to log into this website: It should provide you the IP address.
http://whatismyipaddress.com/
We want to establish TCP/IP connection between two android devices.
For now we thought that it would be simpler if we make the connection device to device. So there is no server that is between the two phones.
Most of the time (if not always) one has no real IP address (NAT and so on). Is this a problem for creating a TCP socket?
I didn't manage to find any exact information for this. Any advice and opinion will be highly appreciated.
Thanks
Is this a problem for creating a TCP
socket?
Answer is no, it does not make it impossible (unless NAT's have an unpredictable way of mapping IP addresses). However, it is not simple to accomplish.
The short answer is you'll always need a server-like peer with a public IP address to facilitate initial communication between peers located behind NATs. The peers connect to it. A tells server it wants to TCP connect with B. Server notifies B. NAT behavior analysis is performed and if possible, A and B attempt to open TCP communications with each other by predicting the next mapping of the other NAT. If all goes fine (and usually it does) A touches base with B or vice-versa. They close the other connection attempts and communicate with the operational TCP connection. This technique is called STUN for TCP.
Now, there are more complicated reason why things can go wrong. If you want to know more, I have written a book called Practical JXTA II which available for reading online at Scribd. There is a chapter dedicated to NAT traversal.
Hope this helps.
One device behind a NAT is not a problem. The requirement is: the server must be reachable by the client.
I'm using Apache Mina to handle TCP connections. It have really made my life easier. It can be used on both client and server. Give it a try...
Well to make a TCP socket one device must be listening and the other connecting. However in a real world scenario what you describe is sort of hard.
Like if you are going to communicate over a cell network between two phones, I wouldn't be surprised if the network did not allow inbound connections to a phone like that and just sandboxed each phone's IP. So while two phones might be on the same subnet IP range, they might not be on the same physical network which just makes the whole routing problem almost impossible.
If you are in control of the network and are using Wifi and natting the IPs yourself with both devices within your network, you should be able to do this just like any other client server TCP socket.
If both nodes does't have global IPs,, and are not physically in the same network,, then its impossible to communicate over TCP without a server, unless you created a controlling server that act as a relay to tell the nodes about any changes occurring on the other side
It is possible but you can experience some problems.
First of all you have to know the public address of the host you want to contact, and if your two host are in different NATTED networks you should do it using some server (like you do in SIP telephony).
Then you have to hope that the contacted host is behind a 'good' NAT like 'full cone' or similar and not behind a 'bad' NAT like 'symmetric' that not allow incoming connection. The fact you use a TCP connection instead of UDP datagram can help you because of the three-way-handshake. In fact most NAT routers accept incoming TCP connection, but not incoming UDP packets.