I'm trying to find out what AWDL is. On iOS, if you use Apple's peer-to-peer networking over BlueTooth, it seems Apple creates a new Network Interface "awdl0" to implement (I guess) IP-over-BT.
But I can't find any docs on this tech, or this interface, how it behaves, things we must / must not do with it, etc. Google comes up blank :(.
In particular, I believe it means "established a BT connection, and I'm running an IP bridge over the top, and you can use this to communicate peer-to-peer". Apple's own system libraries have bugs where this bridge isn't setup quickly enough, and if you send data too soon, it appears to get dropped by the OS. So ... if I can query this awdl0, I hope to check "are you ready yet?" and delay P2P messages until the OS is happy.
UPDATE
More info: I can get pairs of iOS devices to create awdl0 connections to each other - but they never get created to OS X machines, whether BT and Bonjour are on or not, whether the devices are paired or not.
Some background:
In iOS5, Apple permanently disabled the Bluetooth parts of Bonjour/Peer-to-peer networking, and published a technote instructing everyone to use DNS-SD if they wanted to keep using Bluetooth as a transport between iOS devices. This is fine, but it means you must use DNS-SD if you want high-performance BT, and you want it reliable.
(GameKit sometimes works fine, but we often see terrible performance in real-world scenarios, e.g. crowded public places - which goes away if you use DNS-SD)
DNS-SD protocol doesn't include info to tell you what the hardware is using. But it does tell you the Network Interfaces (which is how I know we're running on awdl0)
DNS-SD is awesome, and we have high-speed, low latency connections peer-to-peer between iOS devices - all the stuff that GameKit promises but often fails to deliver whenever there's more than a few wifi/BT devices in range.
AWDL recently caught a lot of attention when it caused Wi-Fi issues in iOS 8 and OS X Yosemite devices.
What is AWDL?
AWDL (Apple Wireless Direct Link) is a low latency/high speed WiFi peer-to peer-connection Apple uses for everywhere you’d expect: AirDrop, GameKit (which also uses Bluetooth), AirPlay, and perhaps elsewhere. It works using its own dedicated network interface, typically “awdl0".
While some services, like Instant HotSpot, Bluetooth Tethering (of course), and GameKit advertise their services over Bluetooth SDP, Apple decided to advertise AirDrop over WiFi and inadvertently destroyed WiFi performance for millions of Yosemite and iOS 8 users.
How does AWDL work?
Since the iPhone 4, the iOS kernels have had multiple WiFi interfaces to 1 WiFi Broadcom hardware chip.
en0 — primary WiFi interface
ap1 — access point interface used for WiFi tethering
awdl0 — Apple Wireless Direct Link interface (since iOS 7?)
By having multiple interfaces, Apple is able to have your standard WiFi connection on en0, while still broadcasting, browsing, and resolving peer to peer connections on awdl0 (just not well).
You can find more info here and here.
I'd like to provide a more precise answer as to how the protocol works internally. I quote part of the abstract of this paper.
In short, each AWDL node announces a sequence of Availability Windows
(AWs) indicating its readiness to communicate with other AWDL nodes.
An elected master node synchronizes these sequences. Outside the AWs,
nodes can tune their Wi-Fi radio to a different channel to communicate
with an access point, or could turn it off to save energy.
From a user perspective, AWDL allows a device remain connected to an infrastructure-based Wi-Fi network and communicate with AWDL peers "at the same time" by quickly hopping between the channels of the two networks (AWDL uses fixed social channels 6, 44, and 149). In contrast to the previous answer, we found that current versions of AWDL work fairly well and channel hopping only induces a small overhead.
Disclaimer: I'm co-author of this paper and we retrieved this information by means of reverse engineering. If you are interested in the details, please read the paper and have a look at the Wireshark dissector (published soon).
Related
We are developing a mobile application that tracks users while they are picking up and delivering commodities. We have overcome many issues, including poor connectivity in rural areas, the app going into the background, and so on.
One issue continues to befuddle us. When receiving calls some drivers lose connectivity, other drivers will gain connectivity, and others (most) have no change in connectivity.
I remember earlier that Verizon iPhone users couldn't access data while on a call. Naively I thought that this issue was completely overcome, but perhaps it is not.
My understanding is that a) there are still some cellular protocols that cannot handle voice and data and b) there are (or were) some settings in mobile phones that give the user a choice.
I have searched for some list of cellular protocols and iOS and Android settings but so far come up empty.
Any guidance would be greatly appreciated.
Hopefully this will provide some more clarity; it all depends on the Radio Access Network (RAN) technology they're using (2G/3G/4G) and the terminal itself's capabilities.
There's 3 umbrella terms of technologies, each with their own revisions and variants, but this should cover it:
LTE (4G) only supports voice calls via VoLTE (Voice over LTE). Calls made over VoLTE will allow the user to continue accessing data at the same time. Many devices & some networks don't yet have VoLTE capability, so they use Circuit Switched Fall Back (CSFB) to drop to a 2G/3G Radio Access Network for making voice calls. (If your terminal does this you then have that RAN's ability to allow simultaneous voice/data.)
3G - There's a few flavors of "3G", depending on the terminal and the RAN variant (UMTS / EDGE / CDMA / HSDPA / HSDPA+) you may be able to access data and be on a call at the same time.
GSM (2G) does not have this functionality, the handset is either in Circuit Switched (Voice) or Packet Switched (Data) mode but not both.
The decision of which RAN to use is based off the priorities stored in the SIM/USIM, the received signal strength of the available networks and the capabilities of the terminal.
This means for example your users who may gain connectivity may find themselves using a 3G access technology on a 4G enabled terminal, with VoLTE support, jumping up to VoLTE to make the call. (Some operators resell to MVNOs but default to slower / older RAN technology like the 3G family)
Others may loose connectivity as you've seen, if they're happily using LTE on a device with no VoLTE support and need to drop to 2G/3G for a call (CSFB) they may loose data services as they're back to the limitations of these older RAN technologies.
I’m not talking about Reachability.
What I’m talking about is figuring out how to create a network connection from an iOS device across the cellular interface.
Why? Because I have conditions where the device connects to a WiFi access point so it chooses WiFi… but that access point is not internet connected and goes nowhere. I have data which I must make every effort to deliver and it some cases it’s getting lost in the WiFi gateway to purgatory. In both cases of using Reachability and relying on MPTCP, Apple has already given priority to WiFi in the stack.
I know NSURLSessionConfiguration can set allowsCellularAccess to allow cellular access — I’m looking to require cellular for the routing.
Even at the CFNetwork level I’m looking at kCFStreamPropertyConnectionIsCellular for status, kCFStreamPropertyNoCellular to disable cellular.
I can’t find anyway to give preference to the cellular radio. I realize Apple has gone to great lengths to prefer WiFi and I’m going against that — which is why I’m having such difficulty finding an answer to this.
I'd like to keep this up in the Cocoa level, but not opposed to going into Foundation or deeper levels. I would like to avoid trying to parse an interface table (if it's even accessible) to figure out which is the cellular interface.
Has anyone successfully created a network connection across the cellular link despite WiFi appearing to be present?
Is some configuration of Multipath TCP the answer here?
To bind to a particular interface, as far as I'm aware, you'd have to drop all the way down to the raw socket level, and there's no way to provide a custom socket for NSURLSession purposes, so you'd basically be rewriting it from scratch. You should file a bug asking for support for binding an NSURLSession to a source IP.
The behavior you're experiencing is a known problem with iOS and disconnected networks. iOS 9 and later do a better job, but even then, they can be highly problematic; the devices sometimes refuse to talk to the Wi-Fi network, and sometimes refuse to talk to the cellular network. Specifically, it seems to fail spectacularly if either signal is weak. Just this morning, I actually had to force my iPhone (iOS 10) to talk to a disconnected Wi-Fi network by putting it in Airplane mode and enabling only Wi-Fi.
I'm told that you can fix this by configuring the network's DHCP server to not provide a router advertisement; that said, every time I've tried that, the iOS device would just keep asking for an offer repeatedly. Maybe that bug got fixed at some point. If so, it might be worth a shot, but don't expect it to work in older versions of iOS.
Failing that, assuming you don't need to support web browsers in iOS 3 and earlier, you might try eliminating the DHCP server on that Wi-Fi network entirely, and just rely on DNS service discovery with zero-conf IPs. That way, the device won't see a router, and it won't try to send data out that interface except to those link-local IPs.
If that isn't possible for some reason, ordinarily I would suggest using a customized copy of libcurl, except that I doubt this will work in your case, because POSIX networking doesn't wake the cellular hardware.
In iOS 12 and later you can use the Network Framework. Sample code is here.
I have two entities which I would like to be able to start a communication:
Hardware Device Using Atmel ATSAMS70 and WINC1500 Wifi Module
HTML 5 App
The idea to have a HTML 5 app is to be able to communicate easily with most of the commercial devices like: Windows computers, Android Phones, Mac OSX computer and iOS devices. Apart from that, I would avoid working with native code at all.
Currently, they can talk with each other using WebSockets but somehow the IP address of the custom board has to be known from HTML 5 to initiate the communication.
In order to do this, I can think of 3 options:
Using WebRTC I can get the local IP address of the browser and then I could do a scan of the local devices considering a 255.255.255.0 network mask.
Have an external server that the hardware device can send its local address which will be later retrieved by HTML 5.
Using Bonjour or some sort of device discovery service between the board and HTML5.
I could not find a way to achieve #3 but #2 seems feasible to me. #1 is what I am doing now, but WebRTC is currently not supported on iOS.
So, is there any other better possibility to achieve this communication?
You don't mention how the WINC1500 unit is being connected to the network but presumably this is in STA mode (acting as a wifi station rather than becoming a software access point or part of an ad-hoc network) and is being provided with its IP details through an existing access point?
Ordinarily I'd suggest that once connected, the device ought to start indicating its availability on the network via a regular UDP broadcast on a specific port but my (admittedly limited) understanding of WebSockets it is that it creates TCP connections. The only implementation of Bonjour that I've seen uses UDP messaging too, that may be why you've had trouble with your third approach.
Your second approach seems more likely to work well. A server at a known (or discoverable) IP on the local network which allows the Atmel device to register itself (and its IP address) and also allows other applications (your HTML 5 WebSockets applications) to request that connection information to allow them to create the WebSocket TCP connections they need.
I suppose that doesn't really answer your question as to "Is there a better way?", other than to say "Not that I can think of, your second approach looks good to me...". Sorry! Sounds like a very interesting project, overall,
I would like to do data sharing(Maybe xml or json file) between 2 iOS devices (iPhone or iPad) and communication would be like "one to many bidirectional" bases at a time.
With some experience and from articles , I have found below ways to do it.
Wi-Fi Direct
AirDrop
Bluetooth(By creating Master and Slaves)
Bonjour SDK.
Bump API(Which is already closed from january 2014)
Could anybody please suggest the best way to fulfill my requirement, which is a good way to do it?
Since IOS 7 Multipeer Connectivity could also be quite interesting.
The Multipeer Connectivity framework provides support for discovering services provided by nearby iOS devices using infrastructure Wi-Fi networks, peer-to-peer Wi-Fi, and Bluetooth personal area networks and subsequently communicating with those services by sending message-based data, streaming data, and resources (such as files).
Here is a nice tutorial about implementing a file sharing system using multipeer connectivity:
http://www.appcoda.com/intro-ios-multipeer-connectivity-programming/
Wi-Fi
Connecting to your Personal Hotspot via Wi-Fi is the default option provided by Apple, since you have to specifically accept if you also want to enable the Bluetooth connection. A Wi-Fi connection provides:
Pros
High throughput: Throughput via Wi-Fi Personal Hotspot can be of around 30 Mbps between two devices and even more.
Faster: Connecting via Wi-Fi tends to be quite faster than connecting via Bluetooth.
Cons
Might need you to reconnect every time: Wi-Fi tends to be unstable and to turn itself off every time you put your iPhone to sleep. This means that you have to take out your iPhone and re-enable the Personal Hotspot if you want to connect.
Time limit: Perhaps the biggest drawback of using a Wi-Fi Personal Hotspot with your iPhone is that in order to minimize power consumption, your iPhone only gives you a short while (90 seconds reportedly) to connect a device to it after you enable Wi-Fi Personal Hotspot. If you take longer than that, you are forced to enable the option again.
More power consumption: The Wi-Fi Personal Hotspot consumes more power than its Bluetooth counterpart, which is also part of the reason it only gives you a short while to connect a device.
A bit more complex: The iPhone’s Wi-Fi Personal Hotspot requires you to enter a password and to configure your own security options.
Bluetooth
Contrary to the Wi-Fi connection, using your Personal Hotspot via Bluetooth offers some key advantages and one huge drawback:
Pros
No time limit: Once you enable Bluetooth Personal Hotspot, there is no time limit for you to connect your device to your iPhone.
Automatic pairing: Bluetooth remains dormant and ready to connect to your devices the moment you wake them up. Additionally, Bluetooth is more power-efficient than Wi-Fi.
Security handled automatically: The security level of a Bluetooth Personal Hotspot is equivalent to Wi-Fi’s WPA2, and it is all handled transparently from the moment you connect to it.
Cons
Very limited throughput: Without a doubt the biggest drawback of using a Bluetooth Personal Hotspot is its limited throughput, which can be of just 3 Mbps at the most, making it 10 times less than what your Wi-Fi Personal Hotspot can offer.
Please tell me in detail why it is impossible to send the data between two phones over GSM? I can find almost no information about this problem.
There are 2 points here.
Firstly, GSM is a mobile voice telephony system - plain GSM doesn't do data connections.
GPRS and EDGE are add-ons to the GSM network that allow data to be sent.
There are other kinds of wireless phone networks that also use a SIM and allow data to be sent (UMTS, LTE).
Secondly, when you establish a data connection with a mobile phone and a phone network, you are establishing an IP connection between your phone/modem and a gateway server in the operator's network. The gateway server allows you access to the internet (together with the DNS server etc, obviously).
This is similar to a computer plugging in a LAN cable and connecting to their ISP. But you can also connect 2 computers with a crossover cable, and configure them to have an IP connection directly. So what you are asking is, why can't I do the same with 2 GSM phones? what is the equivalent of a wireless crossover cable?
The reason is because GSM has no protocol to connect phones to each other. It only defines a protocol for phones to connect to a network base station.
To transfer data between 2 phones, therefore, you need a different protocol, one which will work between 2 peers. Bluetooth is a common such protocol, but it only works over short distances.
If you want to connect 2 distant phones, you can do this via a third party, like a website, to which data can be uploaded into the cloud by the first phone and downloaded by the second phone.
Or, you could establish a connection at the IP level via the internet, e.g. if one mobile device was a web server (the last sentence is only theorising).
See also this related question
EDIT: 3GPP Release 12 includes direct Device to Device communications. At the time of writing, it's still very new, and not yet commercially available, so the answer above still holds. D2D is designed for emergency services, eg if the network is damaged by a disaster, they can still communicate directly. But 3GPP suggests that it will be commercially available as well. From 3GPP news
There are also commercial benefits of D2D, with new applications building on the physical proximity of users being trialed by operators.
2nd EDIT: Apple has created a feature called Multipeer Connectivity Framework, which uses a mixture of WiFi networks, peer-to-peer WiFi and Bluetooth to enable short distance connectivity between iPhones when there is no GSM network.
NFC is another peer-to-peer technology for communicating between 2 devices, that is supported by some phones. More information here.