Develop Reference

Websocket giving various numbers depending on OS

I'm doing a little test where I send out a short string(4-8 bytes) to a client every 0.5 seconds from a Node.js server using ws. The client is either using iOS/Android or a web browser. The client does not send anything back to the server, except for TCP-ACKS I suppose. The weird thing is, when I'm debugging the app in iOS using XCode network report, I can only see that the client sends out some bytes(approx 500) when the connections establishes, probably during the HTTP handshake. The remaining time ZERO data is going out from the device, there is only data coming in. The same results is achieved when receiving data in Chrome and tracking the data using Nettop.
The thing that makes so confused is that on the Android, almost the same amount of data that goes in to the device goes out when inspecting the network usage with Android profiler/Battery Historian/TrafficStats. I have tried using different libraries for the Websocket implementation and using different Android devices.
I have a hard time believing the ACKS sent out by the android is as big as the message received, even though it's just a small string of four characters.
So my questions are:
Could the case be that Nettop/XCode network report is simply ignoring all the ACKS, so in reality as much data is sent out in Chrome/iOS as in Android?
Is there something 'Wrong' with the libraries used in Android or could it be something with its operating system?
Could an ACK be as big as a simple TCP-package with 4 characters in it?
The result below when using Websocket
The data received/transmitted when using Android Battery Historian
The data received/transmitted on iOS using Network Report

Could an ACK be as big as a simple TCP-package with 4 characters in it?
An ACK consists of the IP and the TCP header and no payload. With IPv4 this means at least 20 bytes IP header and 20 bytes TCP header, i.e. 40 bytes. A packet with 4 bytes payload is only larger by 4 bytes, i.e. 44 bytes or just 10%.
The network report in Android shows 68350 in vs. 61370 in bytes, which is a difference of 11%. This matches the expected difference.
I'm not familiar with what iOS measure here, but it probably either measures only the application payload (i.e. the 4 bytes) or simply ignores packets with no payload, i.e. the ACK's.

unexpected ACKing behavoir in GCM XMPP Protocol

We are using GCM’s XMPP protocol to deliver push notifications to our customers, the problem we are facing is that when sending xmpp messages with high speeds, we don’t receive 'ack' or 'nack' messages from GCM anymore, These are the results of several tests we did for this matter :
500 XMPP messages - sent every 0.25 seconds:
all messages are acked
500 XMPP messages - sent every 0.1 seconds:
On average, ~4 messages remained un-acked
500 XMPP messages - sent every 0.01 seconds:
72 messages remained un-acked
500 XMPP messages - sent with no sleep time (As fast as possible)
reached the 100 unacked message limit set by GCM in less than 0.5 seconds !
The results are even worse when we go for more than 500 messages, E.g :
4000 XMPP messages - sent every 0.1 seconds:
On average, number of un-acked messages rose to about 16
4000 XMPP messages - sent every 0.01 seconds:
On average, reached the 100 unacked limit in the 800th xmpp message.
——————————————————————————————————
These results are from tests done on Google’s own cloud (Google cloud compute servers), while doing them in anyother place, would yield much worse results ( as we tested, no speed more than 1Msg/0.4S w
We are using GCM’s XMPP protocol to deliver push nould actually survive (!) the 100 unacked limit)
This is too bad for us, since there’s no optimal solution out, what should we do now?
Ignore the 100 unacked limit and continue sending, but that would mean we don’t know whether our messages are received by gcm or not.
We can resend any unacked message after several seconds, but duplicate messages (to same clients) are a result.
Wait to see if they maybe get acked in the near future, but that so far hasn’t worked. When we get to the unacked limit, pending messages are never acked (in our experience)
Limit the speed by which we send XMPP messages, but this solution greatly jeopardizes the main initiative we had to actually use XMPP !
Any help or guidance would be greatly appreciated.

I also had the same problem. I used to send ACKs for gcm's NACKs and when I stopped doing so, everything went perfectly fine. Check to see if you are sending unnecessary ACKs.

What's the quickest way to send lots of data over BLE?

If I want to transfer a lot of data (e.g. 1 MB file) over BLE, what's the best way to do it?
I control both sides of the connection, but the client side is iOS/Android so only has access to GATT. I can't do anything with L2CAP.
I also can't wait for Bluetooth 4.1, 6LoWPAN, Connection-Oriented-Channels or anything like that.
I would assume the answer is to have one "request" characteristic that you write a data request to ("Give me 3000 bytes starting at byte 0"), and a "data out" characteristic that sends lots of 20 byte notifications (the maximum characteristic size) containing the data.
Is there a better way?

Yes we are using the approach you have mentioned.
Request data with the last index number(First time the index is 0)
The server send you with data with index no.Store the index no for subsequent format
continue Step 1 and 2 till the time server sends end of data-probably with index -1 or something.
Make sure you transfer the data you required in the most space efficient format.See if you can zip the files and transfer it.

You can update connection interval to small value with smallest 6*1.25 ms in remote BLE device.
Actually, BLE is designed for Low energy, small packet, low data rate.
L2cap data will be transmitted in different data channel with frequency hop. Packets TX/RX happen within each connection interval and max number of packets TX/RX in an event is restricted by specification, finally implemented by manufacture. So we can change connection interval as small as possible to increase data rate.
Refer BT 4.0 spec Vol 2, 7.8.18 LE Connection Update Command.

Try to negotiate a larger MTU than the default.
Then each notification can be larger. Even though it will be fragmented by the L2CAP layer, you will get a slightly larger throughput since the packet header will be smaller.

How to start a method in the same time on 2 devices

I have 2 android phones phones, both connected to the same wifi, both with bluetooth.
I want some method that syncs somehow the phones and starts a function on the same time on both phones.
For example playing a song at the same time.
I already tried with bluetooth but its with lag, sometimes 0.5 secs. I want something in +- 0.01sec if possible.
Someone suggesting playing it in the future with 2-3 seconds, sending the time-stamp, but how do you sync the internal clocks of the devices then ?

Before calling that particular method, try to measure the latency between the two devices:
1.First device says Hi(store the current time)
2.Second device receives the Hi.
3.Second device says back Hi !!
4.First device receives the Hi.((storedTime - currentTime) / 2 )
Now you have the latency, send your request to second device to start your particular method and start it on first one after the latency.
Try to measure the latency 5 to 10 times to be more accurate.

you have a way to transfer data between the devices right ?
if so you can send a time-stamp which is in the future,
ex: if the present time stamp is 1421242326 you send 1421242329 or something and start the function at that time on both devices.

Basically use #Dula's suggestion (device 1 sends command to device 2 and gives a "start time" which lies in the future). Both devices then start the action at the same time (in the future).
To make sure that the devices are synchronized, you can use a server-based time sync (assuming that both devices have Internet access). To do this, each device contacts the same server (using NTP, or HTTP-based NTP, or contacts a known HTTP server, like www.google.com and uses the value in the "Date" header of the HTTP response). The "server-date" is compared to the system clock on the device, and the difference is the "time-offset from server-time". The time-offsets can be used to synchronize on the "server-time", which is then used as the time base for the actual action (playing the media, etc.).

If your WiFi router allows clients to talk to each other (many public hotspots disable this), you could implement a simple socket listener on one (or each) device and have the initiating device broadcast a message.
For more complicated things and network flexibility, I've had good success with connected sessions using AllJoin. There is a bit of a learning curve to do interesting things, but the simple stuff is pretty easy once you understand the architecture.

Use a server to provide a synchronous event to just the two clients who have decclared their mutual affinity (random as a parm and pair serializer Partner-1 or Partner-2 which they share prior to their respectve calls for the sync event).
Assume both clients on same subnet (packets from 2 events serialized on the server , arrive across the network at the 2 clients simultaneously client-side) This provides synchronous PLays by 2 , bound clients.
The event delivered by server is either a confirm to play queued selected track OR a broadcast( decoupled, more formal)
The only tricky thing is the server side algorythm implementing this:
Queue a pair of requests or error
Part1, part2 with same Random value constitute valid pair if both received before either times out.
On a valid pair schedule both to the same future event in their respective , committed responses.
OnSchedule do the actual IO for 2 paired requests. Respective packets will arrive back at respective clients at same time, each response having been subject to equal network latency
Ng if two diff carrier 4G or lte networks involved. (Oops)

This thing is possible via socket, you will send a event via socket then the other device receive that event. For learn socket io chat

maybe it's not the answer you are looking for but i think that due to the high precision you are wanting , you should look for a push technology, i advice you to take look at SignalR. It's real time technology which gives you abstraction of sending methods , it have a built-in methods like Clients.All.Broadcast that fit your needs.

You can try to use some MQTT framework to send message between two device, or into a set with more number of devices.

Sending long sms messages

I've got an app that lets users send sms messages. Works great when the message < 160 characters. After that, things work less-perfectly. Seems like there are a few options here:
Manually break the message up into multiple SMSs, send each part as a separate SMS.
Use the multi-part send SMS function (sendMultipartTextMessage()).
Send the message as an MMS message (sendDataMessage()?).
Here's my novice take on it:
1)
most well supported across carriers. Users may get mad that you just cost them N separate messages though, instead of converting to MMS or something.
2)
not sure if this is supported by different carriers, and read that once the message is greater than 3 * 160 chars in length, gets converted to MMS anyway by different SMS apps - maybe stay away from this altogether.
3)
not sure how to do this, and older phones might not support MMS. To send an MMS using the android SDK, do we just use the SmsManager.sendDataMessage() method?
Thanks

This is quite an old post but it's high up on Google when searching for Android multipart sms, so maybe it helps someone.
Regarding part 1 and 2, it's pretty much the same thing. To use sendMultipartTextMessage, you need to break up the long message into an ArrayList of Strings. It then sends as many SMS as needed. In short:
SmsManager sms = SmsManager.getDefault();
ArrayList<String> parts = sms.divideMessage(longMessage);
sms.sendMultipartTextMessage(phoneNumber, null, parts, null, null);
Part 3: MMS is not an option, as it has been pointed out. The charges and all.

seems to me that the first option is what most mobile phones do by default. sms messages by design can only send a certain amount of characters (160 probbaly), just inform the user that the message is too big and if he still wants to send it anyway (informing also how many sms would the total be).
as for MMS and multipart as you said not every carrier supports it, so they dont seem to be the best option.
EDIT: as for how does MMS work on android-sdk check this thread out: Android SDK MMS

I would suggest the usage of option 2 when you are working on Androids GSM based handsets.
GSM based Mobile device takes care of segmentation in which breaking the messages to multiparts for sending in performed and also assembling of the multipart messages in to one message on receipt.
If you have a method which takes care of sending text messages, than by default use the options of manager.divideMessage as it will work even if the message segments required are only 1 in number.
I dont think you should have any problem sending messages using option 2 and it will also ensure that the receiver receives the message as a single message.
Else we need to write your our own protocol stack where in you write reference number and number of messages for the receipient to understand and recreate the complete message; which is not very tough. We can use byte arrays with headers and the messages can be sent as base64 encoded.
Also I dont know much about the limits the carriers enforce on the number of segments in multipart message; based on my test I was able to send and receive 160*8 segments properly. Based on the GSM standards the segments can be upto 255 but that count might depend on the service provider implementation.