Android How do bluetooth UUIDs work

Question

I don t understand what a bluetooth UUID denotes  Do UUIDs denote protocols  e g  RFCOMM   If so  why do the createRfcommSocketToServiceRecord   methods require UUIDs  when they specify rfcomm right in their names  Why does the BluetoothChat sample code have a seemingly arbitrary  hardcoded UUID   My question arises because  as per this question  I m getting a null pointer exception when devices running 4 0 4 try to connect  to an external  non-android device  using reflection  However  the solution to that question doesn t work for me  UUID muuid   device getUuids   0  getUuid    raises an exception    Edit  I ve solved that problem by hardcoding the UUID for Serial port service as per this answer  using UUID fromString  00001101-0000-1000-8000-00805f9b34fb       I m further puzzled by why I need to supply a UUID to create an unsecured rfcomm socket using createInsecureRfcommSocketToServiceRecord    but not using the reflection method    Can anyone straighten me out

User · Answer

The UUID stands for Universally Unique Identifier. UUID is an simple 128 bit digit which uniquely distributed across the world.

Bluetooth sends data over air and all nearby device can receive it. Let's suppose, sometimes you have to send some important files via Bluetooth and all near by devices can access it in range. So when you pair with the other devices, they simply share the UUID number and match before sharing the files. When you send any file then your device encrypt that file with appropriate device UUID and share over the network. Now all Bluetooth devices in the range can access the encrypt file but they required right UUID number. So Only right UUID devices have access to encrypt the file and others will reject cause of wrong UUID.

In short, you can use UUID as a secret password for sharing files between any two Bluetooth devices.

User · Answer

UUID is similar in notion to port numbers in Internet  However  the difference between Bluetooth and the Internet is that  in Bluetooth  port numbers are assigned dynamically by the SDP  service discovery protocol  server during runtime where each UUID is given a port number  Other devices will ask the SDP server  who is registered under a reserved port number  about the available services on the device and it will reply with different services distinguishable from  each other by being registered under different UUIDs

User · Answer

In Bluetooth  all objects are identified by UUIDs   These include services  characteristics and many other things   Bluetooth maintains a database of assigned numbers for standard objects  and assigns sub-ranges for vendors  that have paid enough for a reservation    You can view this list here   https   www bluetooth com specifications assigned-numbers   If you are implementing a standard service  e g  a serial port  keyboard  headset  etc   then you should use that service s standard UUID - that will allow you to be interoperable with devices that you didn t develop   If you are implementing a custom service  then you should generate unique UUIDs  in order to make sure incompatible third-party devices don t try to use your service thinking it is something else   The easiest way is to generate random ones and then hard-code the result in your application  and use the same UUIDs in the devices that will connect to your service  of course

User · Answer

To sum up  UUid is used to uniquely identify applications  Each application has a unique UUid   So  use the same UUid for each device

User · Answer

UUID is just a number   It has no meaning except you create on the server side of an Android app   Then the client connects using that same UUID    For example  on the server side you can first run  uuid   UUID randomUUID   to generate a random number like fb36491d-7c21-40ef-9f67-a63237b5bbea   Then save that and then hard code that into your listener program like this    UUID uuid   UUID fromString  fb36491d-7c21-40ef-9f67-a63237b5bbea       Your Android server program will listen for incoming requests with that UUID like this       BluetoothServerSocket server   mBluetoothAdapter listenUsingRfcommWithServiceRecord  anyName   uuid     BluetoothSocket socket    server accept

User · Answer

It usually represents some common service  protocol  that bluetooth device supports   When creating your own rfcomm server  with listenUsingRfcommWithServiceRecord   you should specify your own UUID so that the clients connecting to it could identify it  it is one of the reasons why createRfcommSocketToServiceRecord requires an UUID parameter    Otherwise  some common services have the same UUID  just find one you need and use it    See here

User · Answer

The UUID is used for uniquely identifying information   It identifies a particular service provided by a Bluetooth device  The standard defines a basic BASE UUID  00000000-0000-1000-8000-00805F9B34FB    Devices such as healthcare sensors can provide a service  substituting the first eight digits with a predefined code   For example  a device that offers an RFCOMM connection uses the short code  0x0003  So  an Android phone can connect to a device and then use the Service Discovery Protocol  SDP  to find out what services it provides  UUID    In many cases  you don t need to use these fixed UUIDs   In the case your are creating a chat application  for example  one Android phone interacts with another Android phone that uses the same application and hence the same UUID   So  you can set an arbitrary UUID for your application using  for example  one of the many random UUID generators on the web  for example

[android] Android: How do bluetooth UUIDs work?

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