On Monday 10 June 2019 18:06:53 Frédéric Danis wrote: > Hi, > > Le 10/06/2019 à 12:51, Pali Rohár a écrit : > > On Friday 07 June 2019 18:23:41 Luiz Augusto von Dentz wrote: > > > Hi Pali, > > > > > > On Fri, Jun 7, 2019 at 4:00 PM Pali Rohár<pali.rohar@xxxxxxxxx> wrote: > > > > On Sunday 19 May 2019 14:22:23 Pali Rohár wrote: > > > > > On Sunday 19 May 2019 11:13:09 Luiz Augusto von Dentz wrote: > > > > > > Hi Pali, > > > > > > > > > > > > On Sat, May 18, 2019 at 11:12 PM Pali Rohár<pali.rohar@xxxxxxxxx> wrote: > > > > > > > Hello! How is L2CAP layer of bluetooth socket used for A2DP audio > > > > > > > transfer configured in bluez? It is reliable with big/infinite > > > > > > > retransmit count? Or in best-effort manner and some packets may be > > > > > > > dropped? And it is possible to change between these two modes for > > > > > > > application which uses bluez DBUS API? I'm asking because some A2DP > > > > > > > audio codecs are designed to deal with packet loss and for those codecs > > > > > > > it would be probably better to configure L2CAP socket to unreliable > > > > > > > mode. > > > > > > We don't use ERTM with AVDTP, both signaling and transport sockets are > > > > > > using basic mode which don't support retransmissions, there the > > > > > > concept of flush timeout which iirc we don't currently it. > > > > > On bluez.org site there is no information how to use bluez sockets and > > > > > the only documentation/tutorial which I found on internet was this: > > > > > > > > > > https://people.csail.mit.edu/albert/bluez-intro/x559.html > > > > > > > > > > I do not know how up-to-date it is, but seems that by default bluez > > > > > L2CAP sockets are reliable and to change them to unreliable mode it is > > > > > needed to issue OGF_HOST_CTL / OCF_WRITE_AUTOMATIC_FLUSH_TIMEOUT (0x28) > > > > > request. As default is zero = infinity = reliable connection. > > > > > > > > > > I do not understand low level bluetooth details, but is ERTM related to > > > > > OCF_WRITE_AUTOMATIC_FLUSH_TIMEOUT? > > > > > > > > > > So what are default settings for L2CAP socket used by AVDTP/A2DP > > > > > profiles which are transferred to user application via DBUS? > > > > Hi! Do you have any idea about OCF_WRITE_AUTOMATIC_FLUSH_TIMEOUT? It is > > > > related to ERTM or not? > > > The OCF usually describes an HCI command which may affect the entire > > > ACL connection, ERTM is a L2CAP channel mode that includes > > > retransmissions. The A2DP stream transport doesn't ERTM so no > > > retransmissions shall take place. > > Fine, no retransmission is good for A2DP. > > I am not sure there is no retransmission with current implementation. > AFAIU, ERTM and automatic flush timeout are not linked. ERTM operates at > L2CAP level while automatic flush timeout [1] operates at ACL level. > When I read the automatic flush timeout set for an A2DP SBC connection it > returns 0, which means that the connection uses an infinite timeout. So, > even if higher levels set packets as flushable, the ACL policy requests > baseband to indefinitely try to send data [3]: > "The default Flush Timeout shall be infinite, > i.e. re-transmissions are carried out until > physical link loss occurs. This is also > referred to as a 'reliable channel.'" > > [1] Bluetooth core Vol 2, Part E, 6.19 > [2] Bluetooth core Vol 2, Part E, 7.3.29 > [3] Bluetooth core Vol 2, Part B, 7.6.3 Mhm... I feeling quite lost. Is A2DP socket reliable with enabled retransmission or not? -- Pali Rohár pali.rohar@xxxxxxxxx
