I am analyzing the traffic beacons generate using tshark and iptraf. I know they are mainly used to determine the proximity of a device and like any other network device the traffic generated by them must be having a header and payload information in it.
What is best way to find out the payload information though header info can be identified as to where packet is being sent etc , but how we can classify the payload and what information it contains in a beacon signal , is it the same like any other web traffic sent and receive on a network or is it different since they make use of Bluetooth ?
Any pointers regarding would be useful .
Bluetooth LE beacon transmissions are much simpler than the HTTP protocol. They are transmit only and have no real headers, although there are short segments within the transmissions called PDUs that have a similar purpose.
To see an example of a beacon transmission, see my answer here:
What is the iBeacon Bluetooth Profile
Related
first of all: What i am trying to do is only for private interest.
I'd like to connect a AT-09/HM-10 BLE-Module with Firmware 6.01 to another device which provides also a BLE Module, which it is not based on the CC254X-Chip,
I am able to communicate with this Device using my Laptop with integrated Bluetooth, Linux and the bluepy-helper. I am also able to make a connection using the HM10 through a USB-RS232-Module and "Hterm", but after that quite Stuck in my progress.
By "reverse-engineering" the Android-Application for controlling this particular device i found a set of Commands, stored as Strings in Hex-Format. The Java-Application itself sends out the particular Command combined with a CRC16-Modbus-Value in addition with a Request (whatever it is), to a particular Service and Characteristic UUID.
I also have a Wireshark-Protocol pulled from my Android-Phone while the application was connected to the particular device, but i am unable to find the commands extracted from the .apk in this protocol.
This is where i get stuck. After making a connection and sending out the Command+CRC16-Value i get no response at all, so i am thinking that my intentions are wrong. I am also not quite sure how the HM-10-Firmware handles / maps the Service and Char-UUIDs from the destination device.
Are there probably any special AT-Commands which would fit my need?
I am absolutely not into the technical depths of Bluetooth and its communication layer at all. The only thing i know is that the HM-10 connects to a selected BLE-Device and after that it provides a Serial I/O and data flows between the endpoints.
I have no clue how and if it can handle Data flow to certain Service/Char UUIDs from the destination endpoint, althrough it seems to have built-in the GATT , l2cap-Services and so on. Surely it handles all the neccessary communication by itself, but i don´t know where i get access to the "front-end" at all.
Best regards !
I'm working on a project that requires BLE Serial Profile.
I have successfully implemented it, but now I'm wondering what happens when server is sending data to the client, and client wants to send data back (while server is still sending). Is this handled on the low level with a queue or something similar?
Is there any risk that messages will get lost?
Thanks for any help.
Bluetooth provides the effect of full duplex transmission through the use of time division duplex (TDD). In principle transmission and reception do not happen at the same time. So in your case there is no risk of collision (loss) of data packets.
As you can see "Central" and "Peripheral" have a window of 625us during which they transmit.
For further details you can read "Timeslot" chapter of the base band specification in Core Bluetooth specification.
https://www.bluetooth.com/specifications/specs/core-specification-5-3/
I have an app that communicates with a bluetooth device, and I'm trying to replace that app with some code.
I tried using C# InTheHand nuget, Microsoft's Bluetooth LE Explorer, python's sockets and others to send data and see what happens.
But there's something I still don't understand - in each way using different libraries I saw in wireshark a different protocol: ATT, RFCOMM, L2CAP...
When I sniffed my bluetooth traffic from my phone using the app mentioned before, I saw mostly HCI_CMD protocol traffic.
How can I choose the protocol I want to send? Is there a simple package for that? something to read?
Do I need to build the packet myself? including headers and such?
Thank you!
Update:
Using Microsoft's Bluetooth LE Explorer I was able to send a packet that lit up my lamp, starting with 02010e10000c00040012(data)
Using bleak I was able to send a packet starting with 02010e10000c00040052(data)
the difference makes the lamp not ligh up and I'm not sure if I can change it via bleak as it's not part of the data I send
I think what you are showing is that bleak does a write without response while MS BLE Explorer does a write_with_response.
Looking at the Bleak documentation for write_gatt_char that seems to be consistent as response is False by default
write_gatt_char Parameters:
char_specifier (BleakGATTCharacteristic, int, str or UUID). The characteristic to write to, specified by either integer handle, UUID
or directly by the BleakGATTCharacteristic object representing it.
data (bytes or bytearray) – The data to send.
response (bool) – If write-with-response operation should be done. Defaults to False.
I would expect the following to have the desired effect:
await client.write_gatt_char(LIGHT_CHARACTERISTIC, b"\x55\xaa\x03\x08\x02\xff\x00\xff\xf5", True)
I recently aquired a Segway Ninebot ES2 electric scooter. I can connect to the scooter via Bluetooth LE and grab information such as battery status, current mileage, temperature, and so on. This is all done through an application.
On my Android device, I've successfully extraceted the HCI log file, which I imported into Wireshark. I can see all the requests and commands send back and forth between my phone and the scooter. However, the requests and responses are all garbage and I have no idea how to interpret them.
Example of a sent command (info says Sent Write Command, Handle: 0x000e (Nordic UART Service: Nordic UART Tx))
Example of the received value I got right after (info says Rcvd Handle Value Notification, Handle: 0x000b (Nordic UART Service: Nordic UART Rx))
How am I supposed to interpret these responses? If the battery status was 59%, I would expect it to return something like 0x3b (0x3b hex is 59 decimal). But honestly, I have no idea how this works. Maybe they're returning a bunch of data in a data type only their app knows how to interpret? Like JSON for web.
Here's an example from the nRF Connect for Mobile application, where I hit the down arrow on all the characteristics: https://i.imgur.com/hREDomP.jpg (large image)
And probably more important: How do I replicate a request or command in nRF Connect? I've tried sending a byte array that looks like 0x {02410011000d.....} (from the Write Command) in the application, but I have no idea how to read the response.
If someone is still interested, I did the same research for this scooter.
That's standart BLE communacation, device offers BLE "services" and "characteristics". Service can contain one or more characteristics, by which you communicate with device. Each charateristic can allow different types of interaction with it: writing into it, reading from it, subscribing to notifications (so you dont have to to manually read, it kinda pushes data to your app), and more (read here, for example)
Take a look at your wireshark screenshot: you can see Service UUID, Handle UUID (the characteristic), and handle ID. You can communicate with device via uuid or id, depending on your programming language or library (more about uuids).
In this particular scooter there are two characteristics, one allows writing into it, another - allows subscribing to it. Together, they act like RX and TX wires in UART: you write data into one and read from another. So, to begin communication with scooter you must establish connection to it, subscribe for notifications from one ch, and write data to another.
As for protocol: look again at she screenshots, "UART Tx" is the actual payload that was sent to scooter and "UART Rx" was the response. Yes, it's binary data, that only app would understand. Luckily, protocol has been reverse engineered and is well documented. In your example app requests serial number, and it's returned in response - "N2GWX...". In order to request battery percentage you must build another payload according to protocol.
I'm not sure if it's still relevant, but at least for those, who will be interested in the topic.
You can try the following to understand how to interpret response from the device.
An option to consider is to fetch manufacturer's mobile app (apk) either by adb or from sites like apkmirror, etc.
Then apply some reverse-eng tool like JADX.
If you're lucky and the code is somewhat readable, then search for smth that has to do with response (like ResponseParser) and try to find algo that is used to interpret the response.
However, the very first attemp should always be to search on github/google if smb did it already for your device, unless it's very niche.
I'm new for this technology, can somebody help me to know about some doubt?
Q-1. What is the size of CoAP packet?
(I know there is 4 byte fixed header, but what is the maximum size limit including header, option and payload?)
Q-2. Is there any concept for Keep Alive like MQTT?
(It works on UDP for how much time it keeps open the connection, is there any default time or it keeps open every time when we send packet?)
Q-3. Can we use CoAP with TCP?
(Main problem with it CoAP is it works on UDP, is there any concept like MQTT QoS? Let's say a sensor publishes some data every one second, if subscriber goes offline, is there any surety in CoAP that subscriber will get all the data when it come online?)
Q-4. What is the duration of connection?
(CoAP supports publish/subscribe architecture, may be it needs connection open all the time, is it possible with CoAP whether it is based on UDP.)
Q-5. How does it discover the resources?
(I have one gateway and 5 sensors, how will these sensors connect to the gateway? Will the gateway find these sensors? Or will sensors find the gateway?)
Q-5. How does sensor register with gateway?
Please help me, I really need answer. I'm all new for these kind of things and suggest me something for implementation point of view.
Thanks.
It Depends:
Core CoAP messages must be small enough to fit into their link-layer packets (~ 64 KiB for UDP) but, in any case the RFC states that:
it SHOULD fit within a single IP packet to avoid IP fragmentation (MTU of 1280 for IPv6). If nothing is known about the size of the headers, good upper bounds are 1152 bytes for the message size and 1024 bytes for the payload size;
or less to avoid adaptation layer fragmentation (60-80 bytes for 6LoWPAN networks);
if you need to transfer larger payloads, this IETF draft extends core CoAP with new options for transferring multiple blocks of information from a resource representation in multiple request-response pair (so you can transfer more than 64KiB per message).
I never used MQTT, in any case CoAP is connectionless, requests and responses are exchanged asynchronously over UDP or DTLS. I suppose that you are looking for the observe functionality: it enables CoAP clients to "subscribe" to resources and servers to send updates to subscribed clients over a period of time.
There is an IETF draft describing CoAP over TCP, but I don't know how it interacts with the observe functionality: usually It follows a best-effort approach, it just happens that the client is considered no longer interested in the resource and is removed by the server from the list of observers.
The observe stops when the server thinks that the client is no longer interested in the resource or when the client ask to unsubscribe from the resource.
There is a well-known relative URI "/.well-known/core". It is defined as a default entry point for requesting the list of links about resources hosted by a server. Here for more infos.
Look at 5.