L2CAP Group Transmission
Original Post: Questions - Groups at L2CAP (eGroups Msg. 158 )
Date: 2000-01-08
The L2CAP supports grouping, (note: however a group
is not the same as a piconet, a device can be a member of a piconet but not of a
group).
Question
However a problem can arise :If some data is to
transferred to all the members of the group, how will L2CAP inform HCI about the
broadcast? There is no primitive in HCI Specs that will set a broadcast
connection. Will L2CAP transmit the data differently to all the devices in the
group?
Answer
Note:Broadcast transmission is different from group
data transmission. There are 2 ways in which packets could be guaranteed to be
sent to all packets in a group:
- L2CAP group data(marked as active broadcast) could be transmitted by the
baseband with AM_ADDR of zero. This will mark the baseband packets as broadcast
packets & hence will be picked up by all the members of the piconet (and
consequently the group).
- Or else the L2CAP will use the connectionless (group) CID of 0x002, which
uniquely identifies the group channel. The baseband layer will then send these
packets to each AM_ADDR (in the group) individually
Method 1 would be used to guarantee speed, and ease of use
it would send the group data to all the group members in a single ACL slot
& saving b/w in the process by avoiding duplication of the data in multiple
ACL slots{corresponding to each member).
Method 2 would be used to guarantee security and
regularity.
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