2 Replies Latest reply on Jul 2, 2017 11:35 PM by anpm

    Effect of value change in Attribute MTU Size

    alper.koybasi_1600091

      Hi everyone.

         

      I'm working on communication client-server.

         

      I have some questions

         

       - Attribute MTU Size in BLE datasheet
      Maximum Transmission Unit size (bytes) of an attribute to be used in the design. Valid range is
      from 23 to 512 bytes. This value is used to respond to an Exchange MTU request from the GATT
      Client.

         

      I don't understand exactly.

         

      If MTU size increase 512 from 23 bytes. What effects are observed ?

         

      In which situations should I increase or decrease mtu size?

         

      Thanks,

        • 1. Re: Effect of value change in Attribute MTU Size
          e.pratt_1639216

          Changing the size would normally increase the number of bits being physically transmitted over the air for each packet; However, I don't know the behavior for BLE (I think it is limited to 23?)

             

          I would adjust the MTU size to match the expected data characteristic packet sizes that you plan to exchange over the BLE connections. That way, the module knows that it is okay to send more data at a time if the situation occurs.

          • 2. Re: Effect of value change in Attribute MTU Size
            anpm

            Hi Alper,

               

            E.pratt is correct that changing the would normally increase the number of bits being physically transmitted over the air for each packet.

               

            Thus if you want to send a data in one particular normal read / write, then MTU should be greater than or equal to the data size. Else you might have to use read/write long.

               

            In effect, if you want to send a large packet, the speed of transmission increase as the MTU using in the connection increases.

               

            But in general,  default MTU will be 23. If you want to use an MTU > 23, you have to make sure the Client can support the same. Then Client have to send a MTU exchange request. For some Clients like mobile phones, MTU size may limited to some particular values.

               

            You can also have a look at the following KBA :http://www.cypress.com/knowledge-base-article/maximum-packet-size-according-mtu-kba203312

               

            Thanks,
            Anjana