Can we choose a specific wifi channel in nearby connection api or not...?
If so how...?
Because we want to select specific channels in nearby connection for different purposes, as some channels are Congested and connection establishment between devices is slow, so, if possible we would like
A channel to Advertise/Discover
A channel to exchange the metadata files after the discovery/advertising
A channel to exchange files like images,videos etc
No, you do not get access to the underlying Wifi stack used by Nearby Connections. The goal is to be a simple abstraction layer, so we purposefully avoid exposing too many knobs to tweak and turn.
I can file a bug internally to more optimally choose the Wifi channel. If you have more specifics (eg. these channels are typically congested), I can attach that to the bug as well.
Related
I am investigating the SIP signaling and RTP media in VoLTE traffic. I can see RTP header but was told that the RTP payload and the SIP packets are all encrypted in IPsec. Is this true? If yes, at what interface I can see the decrypted packets?
Thanks.
LTE is based on IMS (IP Multimedia Subsystem) which is a very broad and encompassing set of specifications for an architectural framework that enables multimedia communication between IP connected end points.
Because it is so broad and all encompassing there are actually many different security points and interfaces - for example there are security specs for communication between an access network connected device (such as a mobile phone) and the core, for communication between different nodes within a single core network, for communication between different operator's or organisation's core networks etc.
3GPP and LTE build on the IMS specs and include specific security specs for the Mobile world also. There is a 3GPP spec which looks at access security for IMS (3GPP TS 33.203) and it includes the following diagram:
Each of the numbers in the diagram above is a different security 'association' and the above standard references one or more specifications for each one.
The result of all this security complexity and these many security layers is that the answer to your question depends on the point in the network you are looking at. For example, if you intercept the traffic between the phone and the base station you will not be able to see anything as it will all be encrypted at a lower layer (notwithstanding the latest GSM/3G security hacks etc). Similarly if you are looking at the traffic between the core network nodes or between different networks this may be over IPSEC tunnels etc and again you will not be able to see it.
If your aim is to intercept and eavesdrop on VoLTE voice calls then you are going to find this very hard as many of the above mechanisms are designed to prevent this - I won't say it is impossible as I'm sure someone will reference a hack or a 'government backdoor' example for similar technology etc.
If your interest is academic, or in profiling the performance of the network etc then you may be able to achieve what you want using one of the open source IMS solutions - e.g. http://www.openimscore.org.
Or, if you are working for, or with, one of the network equipment vendors then you may be in a position to insert or leverage network management and/or OSS 'hooks' or mechanisms which allow you gather info from some unencrypted data at certain points in the end to end flow.
We're writing a streaming service using wowza as our streaming server with a flash applet on the client. A recent concern we've had is a single client accessing the same stream from multiple tabs. In this scenario, we want to save bandwidth by sending the client only one copy of the stream.
How is this problem typically handled?
I think this is not possible for multiple technical reasons. This is my personal opinion, so experts can correct me if I am wrong)
The flash players on multiple tabs are not aware of each other and they can't be associated with each other on Wowza Streaming Engine side either. Wowza would see 2 different clients from the same IP, but that might be two different devices behind the same router.
The browser tabs are usually isolated from each other in the browser implementations for security and stability reasons, not allowing cross-browser data sharing
The 2 players are not in perfect sync, started at different points in time and lags, buffering might also introduce time shift
I haven't seen any attempt to reduce bandwidth in this scenario. There are solutions to prevent users from playing multiple streams in parallel though, which I would not like to link here, but do a search for "wowza forbidding concurrent stream" and you'll find it.
I think what you thought of is multicast streaming, where network packets are broadcast over the network and every player receives the same stream. This is used in IP TV systems, but that is not possible over internet, only on intranet.
I want to have two tcp connection in a single machine via socket programming, But this two connection should connect to two different network interfaces. One is say my 3g dongle and the other is wifi modem. But is it possible for a single machine(OS) to have two connection active at a time? If possible how to program the tcp connection via socket programming?
This can definitely be done, if you just create two programs and run each of them, they will both be able to communicate over their respective network. When you run a program, the operating system creates a process dedicated to running that program, which is assigned time on the CPU by the scheduling algorithm in the OS. So long as your CPU can keep up with any processing associated with the networks, they will both be able to run simultaneously.
You make no mention of your plans for this, but be aware that I/O times can also limit your speeds. If you're using an older computer, it may not be able to transmit a lot of data very quickly due to an out-dated (or just low powered) network card.
Next time try to research your question first, information about this can be found with relative ease using any popular search engine, including the search bar at the top of this page. Also read this, or one of the other several help articles about asking questions well, that are available from the page you had to go through before asking the question.
I am developing an iPhone application that allows to basically click through a series of actions. These series are predefined and synced with a common configuration server.
That app might be running on multiple devices at the same time. All devices are assumed to have the same series of actions defined on them. All devices are considered equal, there is not a server and multiple clients or something like that.
(Only) one of these devices is used by a person at any given time, it is however possible that the person switches to a different device at any given time. All "passive" devices need to be synchronized with the active one, so that they display the same action.
The whole thing should happen as automatically as possible. No selection of devices, configuration, all devices in the same network take part in the same series of actions.
One additional requirement is that a device could join during a presentation (a series of actions) and needs to jump to the currently active action.
Right now, I see two options to implement the networking/communication part of that:
Bonjour. I have implemented a working prototype that can automatically connect with one (1) other device in the network and communicate with that. I am not sure at this point how much additional work the "multiple devices" requirement is. Would I have to open a set of connections for every device and manually send the sync events to all of them? Is there a better way or does bonjour provide anything to help me with that? What does Bonjour provide given that I want to communicate with every device in the network anyway?
Multicast with AsyncUdpSocket. Simply define a port and send multicast sync events out to that port. I guess the main issue compared to using bonjour with tcp would be that the connection is not safe and packets could be lost. This is however in a private, protected wlan network with low traffic if that would really be an issue. Are there other disadvantages that I'm not seeing? Because that sounds like a relatively easy option at this point...
Which one would you suggest? Or is there another, better alternative that I'm not thinking of?
You should check out GameKit (built in to iOS)--they have a lot of the machinery you need in a convenient package. You can easily discover peers on the network and easily send data back for forth between clients (broadcast or peer to peer)
In my experience Bonjour is perfect for what you want. There's an excellent tutorial with associated source code: Chatty that can be easily modified to suit your purposes.
I hobbled together a distributed message bus for the iphone (no centralized server) that would work great for this. It should be noted that the UI guy made a mess of the code, so thar' be dragons there: https://code.google.com/p/iphonebusmiddleware/
The basic idea is to use bonjour to form a network with leader election. The leader becomes the hub through which all the slaves subscribe to topics of interest. Then any message sent to a given topic is delivered to every node subscribed to said topic. A master disconnection simple means restarting the leader election process.
Is it possible to multiplex sa ocket connection?
I need to establish multiple connections to yahoo messenger and i am looking for a way to do this efficiently without having to hold a socket open for each client connection.
so far i have to use one socket for each client and this does not scale well above 50,000 connections.
oh, my solution is for a TELCO, so i need to at least hit 250,000 to 500,000 connections
i'm planing to bind multiple IP addresses to a single NIC to beat the 65k port restriction per IP address.
Please i would any help, insight i can get.
**most of my other questions on this site have gone un-answered :) **
Thanks
This is an interesting question about scaling in a serious situation.
You are essentially asking, "How do I establish N connections to an internet service, where N is >= 250,000".
The only way to do this effectively and efficiently is to cluster. You cannot do this on a single host, so you will need to be able to fragment and partition your client base into a number of different servers, so that each is only handling a subset.
The idea would be for a single server to hold open as few connections as possible (spreading out the connectivity evenly) while holding enough connections to make whatever service you're hosting viable by keeping inter-server communication to a minimum level. This will mean that any two connections that are related (such as two accounts that talk to each other a lot) will have to be on the same host.
You will need servers and network infrastructure that can handle this. You will need a subnet of ip addresses, each server will have to have stateless communication with the internet (i.e. your router will not be doing any NAT in order to not have to track 250,000+ connections).
You will have to talk to AOL. There is no way that AOL will be able to handle this level of connectivity without considering cutting your connection off. Any service of this scale would have to be negotiated with AOL so both you and they would be able to handle the connectivity.
There are i/o multiplexing technologies that you should investigate. Kqueue and epoll come to mind.
In order to write this massively concurrent and teleco grade solution, I would recommend investigating erlang. Erlang is designed for situations such as these (multi-server, massively-multi-client, massively-multithreaded telecommunications grade software). It is currently used for running Ericsson telephone exchanges.
While you can listen on a socket for multiple incoming connection requests, when the connection is established, it connects a unique port on the server to a unique port on the client. In order to multiplex a connection, you need to control both ends of the pipe and have a protocol that allows you to switch contexts from one virtual connection to another or use a stateless protocol that doesn't care about the client's identity. In the former case you'd need to implement it in the application layer so that you could reuse existing connections. In the latter case you could get by using a proxy that keeps track of which server response goes to which client. Since you're connecting to Yahoo Messenger, I don't think you'll be able to do this since it requires an authenticated connection and it assumes that each connection corresponds to a single user.
You can only multiplex multiple connections over a single socket if the other end supports such an operation.
In other words it's a function protocol - sockets don't have any native support for it.
I doubt yahoo messenger protocol has any support for it.
An alternative (to multiple IPs on a single NIC) is to design your own multiplexing protocol and have satellite servers that convert from the multiplex protocol to the yahoo protocol.
I'll trow in another approach you could consider (depending on how desperate you are).
Note that operating system TCP/IP implementations need to be general purpose, but you are only interested in a very specific use-case. So it might make sense to implement a cut-down version of TCP/IP (which only handles your use-case, but does that very well) in your application code.
For example, if you are using Linux, you could route a couple of IP addresses to a tun interface and have your application handle the IP packets for that tun interface. That way you can implement TCP/IP (optimised for your use-case) entirely in your application and avoid any operating system restriction on the number of open connections.
Of course, it's quite a bit of work doing the TCP/IP yourself, but it really depends on how desperate you are - i.e. how much hardware can you afford to throw at the problem.
500,000 arbitrary yahoo messenger connections - is your telco doing this on behalf of Yahoo? It seems like whatever solution has been in place for many years now should be scalable with the help of Moore's Law - and as far as I know all the IM clients have been pretty effective for a long time, and there's no pressing increase in demand that I can think of.
Why isn't this a reasonable problem to address with hardware plus traditional solutions?