Original question:
The iOS Developer Library mentions in the Game Kit Programming Guide that
The maximum size of a client-server game is 16 players.
Does this limitation also apply to P2P GKsessions?
This was already kind-of asked here (but from a different angle).
Updated question:Is GKSession reliable when more than 4 peers are connected?
note:The question was updated based on the response by saulobrito below.
Reference: One example of an app that uses a large group of peers connected is Seedio. You will notie that they are not using GKSession as bluetooth is not an option for connectivity (with GKSession, you can't even chose bluetooth or wi-fi.. GKSession does that for you.) Check out their FAQ for some interesting information about why they chose Wi-fi rather than bluetooth.
What I can assure you is that GKSession is very unstable and you should not trust these docs. In fact, Apple recently decided to remove the documentation altogether.
I did a lot of testing and I would suggest that the practical limit is 4 connected devices (one acting as a server and 3 clients). Of course it's better that you do your own testing scenario.
I also couldn't find any game that allows more than 4 players. The only that I knew was Apple own Texas Hold'em - which allowed 8 players, but they decided to remove it.
And last, but not least, Game Center imposes a 4 player limit to peer-to-peer games.
Yes I'm developing a game that should support 10 players but, in our tests, it became unstable/unusable when there were more than 4 devices. By unstable I mean: sometimes you can't find a peer and connection drops in less than a minute. To make matters worse, updating to iOS 6 brought some strange behaviors like freezing (no error, no stack trace, no nothing) while trying to send a message. Other odd thing: when a player loses connection, all other players get disconnected.
EDIT: did a lot of testing since that response and have more information to share:
Using iOS 6 I was able to play reliably with 9 devices using either wi-fi or bluetooth. There's stil a huge issue although: You can't connect devices using iOS 6 with devices using iOS 5 cause you will face unexplainable freezing-with-no-stack-trace time to time if any of the devices is with its wi-fi enabled. You either set iOS 6 as the minimum supported version for your App or you will have to ask users to disable their wi-fi and use bluetooth.
On iOS 6.0 I can confirm that GKSession allows at least 6 players. I have found that you must make sure not to send messages to a peer until the state changes to connected though.
Overall, I think GKSession is a wonderful and simple API. It will use bluetooth or WiFi, meaning that you don't even have to think about whether the phone is connected to a WiFi network. The latency is nice and low ( I measured it at 4ms for unreliable and around 10ms for reliable networking ).
My main caveats are:
Use unreliable messaging if you can.
Make sure you set .available to NO on application exit ( if you're terminated while advertising, you may leave phantom sessions open ).
Do not try and send messages to a peer until the peer in question changes to the connected state.
Don't try to re-use a gksession once you've been disconnected.
You may need to retry a connection attempt ( I automatically retry 3 times if a connection attempt fails ). My timeout is 10 seconds.
Throttle your reliable messaging. I haven't quite figured out what the limit is, but eventually it seems like you will blow a transmission buffer and then your latency will balloon. Again, this just isn't a problem when you use unreliable messaging.
Related
I'm currently developing a react native app in combination with a device. The device and the app communicate via BLE. So far everything works as expected but I'm having issues with the connection stability of the iOS app and the device. What would happen is that the device would connect and I can update some characteristics but it would regularly either disconnect with a CBErrorDomain 7 or the response for a write would timeout. The implementation on the app or device side does not seem to be the problem as Android works stable and the device also disconnects when connecting with the LightBlue app.
I've already updated the BLE connection parameters as suggested here:
https://developer.apple.com/library/archive/qa/qa1931/_index.html.
This has increased the stability but did not resolve the problems completely. I've tried playing around with the values but so far no luck.
The current set of parameters we are using are:
conn_min_interval: 15
conn_max_interval: 15
conn_latency: 0
supervision_timeout: 2000
adv_min_interval: 1285
adv_max_interval: 1285
My question now would be if somebody has an idea what other things I could check or which parameter to tune?
Are you checking the maximumWriteValueLength and making sure your writes are smaller than this? A likely cause of your problems is overwhelming the device and it fails to keep up with sending ACKs. What version of Bluetooth does your device support, and does it implement DLE (Data Length Extension)?
Your conn_min_interval and conn_max_interval are suspicious. Asking for 15ms with no leeway is likely to negotiate to 30ms instead. (See 41.6 Connection Parameters) Is your device comfortable with being re-negotiated to something other than 15ms? Can your device actually keep up with 15ms and no connection latency if it does get that? I'm betting it can't. Try setting your connection interval to 30ms (or even a bit slower), and you might even try setting your connection latency to 1 to make the connection a bit more forgiving (though I'd focus more on slowing the CI than increasing latency; increasing latency would be more of a hack in this case).
All my suspicions are around your peripheral not keeping up with its side of the connection. If you have any synchronous activities in response to the data, you need to make sure that it's not blocking your BLE stack from sending the required responses.
Finally, I've found the answer to my problem. The problem was that the pairing procedure of the BLE server was faulty and thus iOS was unable to have a stable connection. Now that this is fixed the connection is very stable.
I'm still unsure why iOS was able to have any communication at all without the pairing but I hope that this helps some people in the future.
I am using Multipeer Connectivity Framework in my APP and its working absolutely fine but when APP is invoking any API or downloading any file from server then its delaying the response. Sometimes its failed and sometimes I am getting Time out error.
I have also checked "Network" status on xCode debug navigator and found that speed is going up and down instantly and never going beyond 6kb/s and sometimes its showing as 0 kb/s but when I disable Multipeer Connectivity then it works fine and speed going at 70kb/s too.
I have also noticed that if bluetooth is ON then its happening not with the Wifi.
Any suggestion would be really appreciable.
This is happening because when advertising, Multipeer always advertises on the wifi (there's no way to say bluetooth only). The way it advertises is by switching the wifi access mode into adhoc multiple times per second to find other peers, then switching back to AP mode (ie. resuming its connection to your wifi router). Doing this is highly disruptive to large transfers.
You have two options to fix this:
1) as soon as you can, after getting connected, call stopAdvertising(). This will stop the wifi mode from being constantly changed, and your throughput will resume at its normal rate. Warning: you cannot micro-manage this, because it takes up to 30 seconds after calling stopAdvertising() until it takes effect
2) switch from Multipeer to an alternative framework that allows you to specify bluetooth-only, and only use bluetooth. I wrote one called BluePeer which I use in my apps. It is unicast (not multicast) and supports roles like Client/Server (as well as role-less like Multipeer)
I am developing a platform game trying to make it as well for multiplayer using the IOS Multipeer connectivity. I am stuck/confused/do not know what is the best way to send messages between peers (mostly like 4 peers in the game). The game style is like fun run and I have 4 hero running and firing each other and stuff like that. The thing is that keeping the positions of the other players is pushing me crazy!!
Sometimes other players are positioned in the wrong position (keeping in mind all devices are with the same screen size). Is that because of the lag of connectivity. How much information I can send per seconds and what is the best way to manage data transferring?
Any idea/thoughts are appreciated.
The throughput of MPC depends mostly upon the connection. What I've seen as the biggest performance problem is when one of the peers has WiFi disabled. This forces MPC to communicate over bluetooth which is incredibly slow. I've seen it run 20x slower than MPC over Wifi.
You don't need to be connected to a WiFi network. Just enable WiFi on all of the devices and iOS will leverage shared WiFi networks or create its own adhoc network.
The second thing you want to ensure is that your peers don't invite each other. You can only have one inviter in your network. When multiple peers invite and accept connections the MPC network become unstable.
Third thing is sendData:(NSData *)data toPeers:(NSArray *)peerIDs withMode:(MCSessionSendDataMode)mode error:(NSError **)error. If you are broadcasting your packets to all peers in the toPeers: array AND mode is MCSessionSendDataReliable then MPC waits until all of the connected peers ACK the message before moving on to the next packet.
UPDATE: I did some testing with my own app and over WiFi and two devices I can put about 100kbps. I'm using an iPhone 6 Plus and an iPhone 5S.
UPDATE 2: Thinking more about your question, there are a couple things to keep in mind with MPC communications:
Do all of your sendData and didReceiveData calls on a background thread and have that thread update your position data in your model. Tell your viewController that updates are available with a delegate method or notification.
Keep your data packets small, but design them so an update received represents the current state of your player. This allows you to miss an update and not be completely out of sync -- "send player 1 moved to (10, 10)" instead of "player 1 moved by (1, -1)"
Number your packets and use MCSessionSendDataUnreliable. If you get a packet with an earlier number than the last one you processed, throw it away. If you follow the second guideline above, you won't need this packet.
If you follow Dan Loughney's suggestions, I think your best bet in debugging is to log the received coordinates from the other players. That should help you identify whether the problem is due to timing issues, misinterpreted data or something else.
I'm developing an iOS app that connects to a certain type of BLE device, but I'm writing the code in a room that has 20+ such devices sitting around, powered up. I consistently find that in the morning, I can connect to my personal device just fine, but as the day wears on, it becomes impossible to connect to my device, as if the 20+ other devices have woken up somehow and are blocking my signal. No one is using most of these devices; they're just sitting on tables. Is this a known bug? Is Apple working on it?
Are all the devices Advertising?
If they are advertising with say 20ms then it could be difficult to hear all. There are "only" 3 advertising channels to share between all devices. The connection happens on the same channels (the peripheral listens after it's own advertising to hear if someone want to connect).
It has nothing to do with Apple CoreBluetooth. In my experience CoreBluetooth can handle around 20 devices after connection has succeeded and the activity has moved to the traffic channels.
1) Try using a slower advertising interval. This should work okay if your app is in the foreground.
2) Use a BLE sniffer (TI USB dongle is fine) and see if connections fail on protocol level, then it is not CoreBluetooth's fault.
3) Only advertise with fast interval when needed or you really really need a fast discovery.
As a rule of thumb apple needs up to 55 advertisements in background mode to see a device when it's the only one visible. So if you really need around 1.1second discovery then you might need 20ms advertisement interval, else use 100ms or even more (see Apple advertising interval guidelines for the exact number that will optimise discovery)
100ms gives so much more capacity and not too bad discovery.
1-2s gives a much longer battery lifetime and will be found in 1-2 minutes if your app is in the background. This would be quite fine for eyeBeacons in malls or the like while you might want 100-200ms in smaller areas.
I've encountered a pretty large issue and have been trying to find a solution for 2 months now with no luck. I've submitted it as a bug, ( https://bugzilla.xamarin.com/show_bug.cgi?id=4910 ) but was hoping maybe someone here could shed some light on the cause of the problem, or suggest a work-around.
In a nutshell, to encounter the error:
Create a basic .Net socket connection between two devices
Create and initialize a GameKit.GKSession object on a least one device.
What occurs is the transfer of the data on the .NET socket becomes erratic and too slow to be usable. I've performed many tests across different devices (see link below) and it affects all of them (iPad 3 affected the least). I've tested it between an iPhone and a Windows PC and it still occurs. MonoTouch's GameKit code is somehow affecting the Socket code.
As you can see from the spreadsheet, speed drop from a few milliseconds to send 1 MB to several minutes to forever.
As soon as the GameKit.GKSession is set to null, any backedlogged data on the socket flows freely again and the sockets act normally once more.
Sample Windows and iOS/MonoTouch Apps demonstrating problem: https://dl.dropbox.com/u/8617393/SocketBug/SocketBug.zip
Test results across different devices (PDF Spreadsheet):
https://dl.dropbox.com/u/8617393/SocketBug/SocketBugTestResults.pdf
This issue seems so hard even Apple decided to circumvent it: http://developer.apple.com/library/ios/#qa/qa1753/_index.html#//apple_ref/doc/uid/DTS40011315
The revealing sentence is this: "This change was made to reduce interference with Wi-Fi."
To assist with anyone that comes across this problem, the issue only manifests itself when the GKSession.Available is set to true. This is required for the device to be discoverable, but not to maintain a connection. With this in mind, a temporary work-around can be used where the GKSession.Available is only set to true when required, and set to false as soon as the connection has been made.
In my scenario, I have a socket connection to the server on both devices. I use this connection to send a message from device A to device B, asking it to become discoverable via bluetooth for the next 10 seconds. As soon as the message is sent, device A begins looking for device B and connects as soon as it finds it. Once the connection is established (or 10 seconds elapses without a connection), device B turns off discoverability and the socket behaves as normal.
In my circumstances, this is an acceptable (pending no real fix) workaround to the problem.