https://devzone.nordicsemi.com/f/nordic-q-a/42269/att-mtu-vs-data-lengthI am trying to support old phones without BLE 4.2 data length extension. I have read https://punchthrough.com/pt-blog-post/maximizing-ble-throughput-part-2-use-larger-att-mtu/ and am now confused. The article says that ATT MTU can be any value fromen-USTelligent Community 13Wed, 09 Jan 2019 12:16:09 GMThttps://devzone.nordicsemi.com/thread/164700?ContentTypeID=1Wed, 09 Jan 2019 12:16:09 GMT137ad170-7792-4731-bb38-c0d22fbe4515:42ca7b3e-bd5e-4624-a207-d76c767b1961haakonsh<p>We only support MTU sizes up to 251 bytes.&nbsp;<br /><br />&quot;<span>ATT MTU and &quot;data length&quot; are different right? Can I have a ATT MTU of 251 and a data length of 23? Does that mean I can place 251 bytes of data into my characteristic at a time and watch it go over the air in 23-byte chunks? &quot;<br /><br />Yes, as long as the peer also support an MTU size of 251.&nbsp;<br /><br />See&nbsp;<a class="activated" href="https://www.nordicsemi.com/DocLib/Content/SoftDevice_API_Doc/S132/v6-1-0/group_ble_gatts_mtu_exchange">GATTS ATT_MTU Exchange</a>&nbsp;and&nbsp;<a href="https://www.nordicsemi.com/DocLib/Content/SoftDevice_API_Doc/S132/v6-1-0/group_ble_gatts_functions?1396#gacb80e44fb1309fe388c6baf747f6f994">sd_ble_gatts_exchange_mtu_reply</a>.&nbsp;<br /><br />Btw, this question has been answered many times on this forum already.&nbsp;</span></p><div style="clear:both;"></div>