Our use-case is to use a Single TCP Connection (never close) and perform a request-reply model, while the next message waits until the reply is received for the current request (block mode). Should we consider 60 messages / min as Low-Volume or High-Volume, this will help us determine whether to use a Gateway or pair of Adaptors. Thanks
That would not generally be considered to be high volume, but only you can determine which architecture provides the performance you need.
e.g. the 60 messages come in 5 seconds and then no messages for 55.
Related
I want to make sure the latency between my app and the bluetooth headphones is accounted for, but I have absolutely no idea how I can get this value. The closest thing I found was:
BluetoothLEPreferredConnectionParameters.ConnectionLatency which is only available on Windows 11... Otherwise there isn't much to go on.
Any help would be appreciated.
Thanks,
Peter
It's very difficult to get the exact latency because it is affected by many parameters - but you're on the right track by guessing that the connection parameters are a factor of this equation. I don't have much knowledge on UWP, but I can give you the general parameters that affect the speed/latency, and then you can check their availability in the API or even contact Windows technical team to see if these are supported.
When you make a connection with a remote device, the following factors impact the speed/latency of the connection:-
Connection Interval: this specifies the interval at which the packets are sent during a connection. The lower the value, the higher the speed. The minimum value as per the Bluetooth spec is 7.5ms.
Slave Latency: this is the value you originally mentioned - it specifies the number of packets that can be missed before a connection is considered lost. A value of 0 means that you have the fastest most robust connection.
Connection PHY: this is the modulation on which the packets are sent. If both devices support 2MPHY, then the connection should be quicker.
Data Length/MTU Extension: these are two separate features but I am looping them together becuase the effect is the same - more bytes are sent per packet, which results in a higher throughput. The maximum value is 251 bytes per packet.
You can find more information about these parameters here:-
A Practical Guide to BLE Throughput
Maximizing BLE Throughput: Everything You Need to Know
Bluetooth 5 Speed - How to Achieve Maximum Throughput
And below are some other links that might help you understand what is supported on UWP:-
Bluetooth Developer FAQ
BluetoothLEConnectionParameters.OptimizedProperty
Bluetooth LE Preferred Connection Parameter Class
Bluetooth LE Connection PHY class
How to Change MTU Size and PHY on Windows UWP C++
While I was trying to compose test-suite using netperf I had to go through the manual where I came across the below line for option -D
If setting TCP_NODELAY with -D affects throughput and/or service demand for tests where the send size (-m) is larger than the MSS it suggests the TCP/IP stack’s implementation of the Nagle Algorithm may be broken, perhaps interpreting the Nagle Algorithm on a segment by segment basis rather than the proper user send by user send basis
My question is - how can setting TCP_DELAY and it's effect on throughput determines nagle implementation is broken? Can someone help me with a logical explanation on the same?
In broad terms Nagle goes something like:
Is the amount of data in this send, added to any data queued waiting
to be sent, larger than the Maximum Segment Size (MSS) of this
connection? If the answer is yes, then send the data now, so long
as there are no other constraints on sending such as the congestion
window or the receiver’s advertised window. If the answer is no,
then consider the next step:
Is the connection “idle?” In other
words, is there no un-ACKnowledged data out on the network. If so,
then send the data in the user’s send now. If the connection is not
idle, queue the data and wait. We know that one or more of three
things will happen to cause the data to be sent:
The application will continue making send calls and we get to an MSS-worth of data to send.
An ACKnowledgement will arrive from the remote for the currently un-ACKed data making the connection “idle” again.
The retransmission timer for the un-ACKed data will expire and we might piggy-back this data with the retransmission.
The main point being Nagle is supposed to be evaluated on a user-send by user-send basis. If disabling it results in higher throughput with a send size greater than the MSS, it implies the Nagle implementation of that stack is going TCP segment by TCP segment instead.
I'm new to BLE, and bluetooth in general, but I'm on a project that includes communication via BT 5.
As the BLE communication has to transmit around 2 bytes, to 1 MB at a time, I'm looking for a way to optimize the transmission time.
I know the pros n cons for the lower transmission freq (125 kbps), and for the highest transmission freq (2 Mbps), and for the DLE of 251 PDU bytes, but what I see from different forums and articles, the throughput mostly depend on the connection parameters as the connection interval and the packets per connection event. But where does the transmission frequency come in?
I've tried searching this forum for an answer, and several others, and even the BT core specification, but I haven't been able to find a solution for my problem.
If you read my answer at Why is BLE 4.2 faster than BLE 4.1, you can see that there are many components affecting the overall transfer speed.
You first have the radio transmission rate itself, which sets the upper limit.
You then have the overhead between all packets that becomes less apparant as longer packets you have.
The connection interval and length of each connection event can be important if you want the throughout to be high. If there is only one connection and the Bluetooth chip is not too stupid, the connection event length will fill the connection interval and therefore the connection interval doesn't really matter. However, if there are other conflicting radio events scheduled in a way that the connection event must be closed, the transmission cannot continue until the next connection event. So in this case, the throuhput will be higher if you lower the connection interval. So as a summary it highly depends on which Bluetooth stack the chip runs, how it's configured by the host and how many active connections you have.
The transmission rate controls your underlying bitrate but on top of that sits different layers of the BLE protocol which slow down the realizable throughput. This article has general derivation of how the different layers impact throughput in case that's useful!
Is there a limit on maximum number of packets (LE_DATA) that could be send by either slave or master during one connection interval?
If this limit exists, are there any specific conditions for this limit (e.g. only x number of ATT data packets)?
Are master/slave required or allowed to impose such a limit by specification?
(I hope I'm not reviving a dead post. But I think the section 4.5.1 is better suited to answer this than 4.5.6.)
The spec doesn't define a limit of packets. It just states the following:
4.5.1 Connection Events - BLUETOOTH SPECIFICATION Version 4.2 [Vol 6, Part B]
(...)
The start of a connection event is called an anchor point. At the anchor point, a master shall start to transmit a Data Channel PDU to the slave. The start of connection events are spaced regularly with an interval of connInterval and shall not overlap. The master shall ensure that a connection event closes at least T_IFS before the anchor point of the next connection event. The slave listens for the packet sent by its master at the anchor point.
T_IFS is the "Inter Frame Space" time and shall be 150 μs. Simply put it's the job of the master to solve this problem. As far as I know iOS limits the packet number to 4 per connection event for instance. Android may have other hard coded limits depending on the OS version.
There is max data rate that can be achieved both on BT and BLE. You can tweak this data rate by changing MTU (maximum transmission unit - packet size) up to max MTU both ends of transmission can handle. But AFAIK there is no straight constraint on number of packets, besides physical ones imposed by the data rate.
You can find more in the spec
I could find the following in Bluetooth Spec v4.2:
4.5.6 Closing Connection Events
The MD bit of the Header of the Data Channel PDU is used to indicate
that the device has more data to send. If neither device has set the
MD bit in their packets, the packet from the slave closes the
connection event. If either or both of the devices have set the MD
bit, the master may continue the connection event by sending another
packet, and the slave should listen after sending its packet. If a
packet is not received from the slave by the master, the master will
close the connection event. If a packet is not received from the
master by the slave, the slave will close the connection event.
Two consecutive packets received with an invalid CRC match within a
connection event shall close the event.
This means both slave and masters have self-imposed limit on number of packets they want to transmit during a CI. When either party doesn't wish to send more data, they just set this bit to 0 and other one understands. This should usually be driven by number of pending packets on either side.
Since I was looking for logical limits due to spec or protocol, this probably answers my question.
Physical limits to number packets per CI would be governed by data rate, and as #morynicz mentioned, on MTU etc.
From my understanding, the limit is: min{max master event length, max slave event length, connection interval}.
To clarify, both the master and slave devices (specifically, the BLE stack thereof) typically have event length or "GAP event length" times. This time limit may be used to allow a central and/or advertiser and/or broadcaster to schedule the "phase offset" of more than one BLE radio activity, and/or limit the CPU usage of the BLE stack for application processing needs. E.g. a Nordic SoftDevice stack may have a default event length of 3.75ms that is indefinitely extendable (up to the connection interval) based on other demands on the SoftDevice's scheduler. In Android and iOS BLE implementations, this value may be opaque or not specified (e.g. Android may set this value to "0", which leaves the decision up to the controller implementation associated with the BLE chip of that device).
Note also that either the master or the slave may effectively "drop out" of a connection event earlier than these times if their TX/RX buffers are filled (e.g. Nordic SoftDevice stack may have a buffer size of 6 packets/frames). This may be implemented by not setting the MD bit (if TX buffer is exhausted) and/or "nacking" with the NESN bit (if RX buffer is full). However, while the master device can actually "drop out" by ending the connection event (not sending any more packets), the slave device must listen for master packets as long as at least one of master and slave have the MD bit set and the master continues to transmit packets (e.g. the slave could keep telling the master that it has no more data and also keep NACKing master packets because it has no more buffer space for the current connection event, but the master may keep trying to send for as long as it wants during the connection interval; not sure how/if the controller stack implements any "smarts" regarding this).
If there are no limits from either device in terms of stack-specified event length or buffer size, then presumably packets could be transmitted back and forth the entire connection interval (assuming at least one side had data to send and therefore set the MD bit). Just note for throughput calculation purposes that there is a T_IFS spacing (currently specified at 150us) between each packet and before the end of the connection interval.
I would like to track a large number of beacons (~500) at once within a 50-100 m radius via an app on an iPhone (5s). I've had a look at the spec and online and I can't see if there is any limit on the number of beacons you can track at once using BLE. Does anyone know if there is limitation on the number of beacons you can track exists or if an iPhone 5s would be up to the task of tracking that many beacons?
You used the word track, but iOS has two different methods: monitoring and ranging.
You can set a maximum of 20 regions to monitor. (Found in documentation for the startMonitoringForRegion: method.) Region limits mostly come into play if your app is in the background. The OS will alert your app when you enter or leave a region that you're monitoring (give or take a few minutes). The OS will even launch your app just to let it know what happened (although only for a short time).
The other method is ranging, which is to find all the beacons within the Bluetooth range of the device (typically around 100 feet give or take). If your beacons are spread out over 100 miles, then you probably won't run into any practical limit here. I have not found any documentation for this, and I have only four beacons that I'm testing with, and four at a time works.
Here's one way to handle your situation. Make all your 500 beacons use the same UUID, and make a beacon region using initWithProximityUUID:identifier: method. (Identifier is just for you -- it doesn't affect anything). Starting monitoring for that beacon region. That way, your app will be notified whenever one of your 500 beacons are found (give or take a few minutes). Once notified, you can use startRangingBeaconsInRegion: to find all the beacons around that area, then use the major and minor values to figure out which beacons the user is near.
I'll add to Tim Tisdall's answer, which sets out the right framework. I can't speak to the specific capabilities of the iPhone 5s, or iOS in general, but I don't see any reason why it wouldn't return every ADV_IND packet (i.e. beacon transmission) that it receives.
The question is, will the 500 beacons be able to transmit their ADV_IND packets without collisions?
It takes about 0.128ms to transmit an ADV_IND packet. The time between advertising transmissions is configurable between 20ms and 10240ms (at intervals of 0.625ms), so the probability of collisions depends on the configuration of the beacons.
Based on the Poisson distribution, the probability of a collision for any given ADV_IND packet is 1-exp(-2*N*(0.128/AI)), where N is the number of beacons within range, AI is the time in milliseconds of the advertising interval (assuming all the beacons are configured the same), and the 0.128 is the time in milliseconds it takes to send the ADV_IND packet. (See http://www3.cs.stonybrook.edu/~jgao/CSE590-fall09/aloha-analysis.pdf if you want an explanation.)
For 500 beacons with the maximum advertising interval of about 10 seconds, there will be a collision about once every 81 packets (or about 6 out of 500). If you're willing to wait for a couple intervals (i.e. 30 seconds), there's a good chance you'll be able to receive all 500 ADV_IND packets.
On the other hand, if the advertising interval is smaller, say 500ms, you'll have a collision about 23% of the time (or 113 out of 500). You'd have to wait for several more intervals to improve the probability that you'd see the broadcasts from all the beacons.
The other way to look at it is that the more beacons you have, the longer you have to wait to make sure you receive all their packets. (The math to calculate the delay to receive the packets with a certain probability from the number of beacons and the advertising interval is too much for me today.)
One caveat: if you want to connect to these beacons, as opposed to just receiving the ADV_IND packet, that requires an exchange of two more packets on the advertising channels, and the probability of a collision in the advertising channels goes up a bit.
If I am reading your question right, you want to put all 500 iBeacons within 100 meters of each other, meaning their transmissions will overlap. You will probably run into radio congestion problems long before you run into any limitations of iOS7 or your phone.
I have successfully tested 20 iBeacons in close proximity without problems, but 500 iBeacons is an extreme density. this discussion on the hardware issue suggests you may run into trouble.
At a minimum, the collisions of the transmissions of 500 iBEacons will make it take longer for your iOS device to see each iBeacon. Normally, iOS7 provides a ranging update once per second for each iOS device, but you may find that you get updates much less often. It all depends on your application whether or not less frequent updates are acceptable.
Even if delays are acceptable, I would absolutely test this before counting on it working at all. Unfortunately, that means getting your hands on lots of iBeacons.
I don't agree. It is true that ble beacons only transmit advertising data, but the transmission of such data last about 3ms (considering three advertising channels).
Having 500 beacons, WITHOUT considering any collision, the scanner will takes 1.5s to see them all.
But, if all beacons are configured in same way (same advertising interval) it is inevitable to have collisions which lead to have undiscovered beacons. Even if the advertising interval is different between beacons collisions occur. To avoid collision probability one should use longer advertising interval, but this lead to longer discovery latency.
This reasoning is very raw, it doesn't take care of many effects, but is just an order of magnitude calculation.
By the way, the question is not easy, there are many parameters which play role, some are known some are unknown. But I'm working with ble since one year about and, to me, 500 is a huge number and there is the possibility that you don't see the majority of nodes because of collisions.
I was doing some research into iBeacon's because of this question (I had no idea what it was about).
It seems that on the "beacon" side of things all that happens is general advertising packets are sent out. It's similar to how a device advertises that you can connect to it. However, you don't actually connect to iBeacon's, it just reads those advertising packets. There's no built-in limitation on how many advertising packets a device can receive.
So, it wouldn't surprise me if 500 iBeacon's would run with no issues. The advertising packets are small and are spaced out (time wise, they are repeated every X ms). There's no communication going from the phone to the iBeacon, the phone is simply receiving the packets it hears. If there's interference on one packet it'll likely manage to get the next one.