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Editorial Team
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Asked: 2026-06-10T08:11:27+00:00

This is a bit long so I’ll start with the question: how do I

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This is a bit long so I’ll start with the question: how do I get the ip to link up sockets (not on a private network) on Android phone?

And how can I check if a port is being blocked by the phones ISP?

A bit more info:

I have a program that show users locations on a map and you can click on them and start a chat. I’ve tested the socket conntion and it was working fine on 2 emulators, but when I tried it on a phone it failed to link up the socket.

Out of time exception on the:

NotificationChat.ChatSocket = new Socket(serverAddr, 5000);

And my best guess is the IP of the server (aka phone 1) is not right, or maybe the port is blocked or in use.

I tried 2 ways to get the phone IP:

public static String getLocalIpAddress() {      
    try {
        Socket socket = new Socket("www.google.com", 80);
        Log.i("iptest", socket.getLocalAddress().toString().substring(1));
        String ip=socket.getLocalAddress().toString().substring(1);
        socket.close();
        return ip;

    } catch (Exception e) {
        Log.i("", e.getMessage());
        return "exception in get ip";
    }

    /*
    try {
        for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();) {
            NetworkInterface intf = en.nextElement();
            for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements();) {
                InetAddress inetAddress = enumIpAddr.nextElement();
                if (!inetAddress.isLoopbackAddress()) {
                    return inetAddress.getHostAddress().toString();
                }
            }
        }
    } catch (SocketException ex) {
        Log.e("b2264", ex.toString());
    }
    return null;  */
}

IP I got was: 10.227.130.191
Which if i remember right is a class A local IP.

The server side:

while(flag==1)
    {   
        if(ss==null)
        {
            try {
                    ss = new ServerSocket(SERVERPORT);

                } catch (IOException e) {
                    e.printStackTrace();
                }                     
        }
            try {
                    Log.d("thread","chatnotifiction befor ss accpect");
                    Socket NotAvilabale=null;
                     NotAvilabale = ss.accept();
                    if(ChatSocket!=null)
                    {
                        Log.d("test55","not avilable");
                        PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(NotAvilabale.getOutputStream())),true);
                        out.println("notav");
                        NotAvilabale.close();
                        continue;
                    }
                    ChatSocket=NotAvilabale;
                    Log.d("thread","chatnotifiction after ss accpect");
                    CharSequence contentText = "someone wants to talk to you";

                    PendingIntent contentIntent = PendingIntent.getActivity(this, 1, notificationIntent, 2);

                    notification.setLatestEventInfo(context, contentTitle, contentText, contentIntent);         

                    mNotificationManager.notify(NOTIFI_ID, notification);
            } catch (IOException e) {
                Log.d("chat notifi io exception","chat notifi io exception ");
                    e.printStackTrace();
            }catch (Exception e) {
                Log.d("chat notifi Exception 2","chat notifi Exception 2 ");
                // TODO: handle exception
            }


    }

I do not have much experience with sockets. This is the first time I am using them. I hope one of you has a bit more experience and can help me out.

Thanks in advance (sorry for the crape english).

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1 Answer

  1. Editorial Team

    So while I don’t know much about how the cell infrastructures work, I can only imagine that it is similar to any ISP.

    So imagine you are a large carrier with millions of clients. You can’t give them all each their own reserved public IPs, that would be costly and inefficient. But you do have to give them IPs in order to send data to them. So you basically carve up your network into multiple segments. Each segment has complete network of private ips. Since most connections on phones are not peer to peer it would be safe to assume that all outbound traffic goes through a gateway or a set of gateways until it reaches a public gateway that will relay the message out to which ever public host is beng request. Whatever that gateway’s IP is though, is probably what your server (and any server on the internet) would see as the client ip (which is probably not the same as the reported IP by the client). With all the devices acting this way, it would also be safe to assume that you can’t just make a connection to 10.227.130.191 from a routable IP within the same network unless it has a port open, which in this case would probably mean running your software. I think physical proximity of phones may come into play on some level deciding as to which private segments two different phones get put it. However in most cases, it is not predictable enough to be able to say that Phone A at Lat1,Lng1 IP 10.127.x.x can talk to Phone B at Lat1,Lng1 IP 10.127.x.y simply because they do not have enough information to know if they are on the same physical segment of the network.

    So unless you are on a wifi AP, it would be really really hard to allow a direct connections between the phones simply because the probability of them being on the same routable network would be very low.

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