list (Li) which contains a list of nodes reaccepted also needs to forward the data to the nodes
in this list in addition to whom it is already forwarded. A Dd block has a list (Ld) which
informs the node received router to stop forwarding data packets to the nodes included in the
list.
Each node for each active multicast session maintains a Forwarding Set (FS), where this set
is a set of destinations that this node should forward the multicast data packet to. The FS at
the source node is ML itself.
3.3.2 A Scalable Multicast protocol for MANETs
A Scalable Multicast protocol for MANETs (E2M) [38] is an explicit multicast protocol built
on the top of Xcast. It overcomes some of the limitations found in Xcast schemes, which
introduces a level of scalability. By dynamic selection of a node to be an Xcast Forwarder
(XF), the XF selection is made according to the number of group members and the traffic
load in the network. This protocol is designed to take into consideration the mobility feature
for MANETs.
3.3.2.1 Membership management
The membership management in this protocol is similar to the one used in [10] with an
addition of two new messages, XF_JOIN and XF_ACK. The Designated Router (DR) which
is eligible to become an XF sends an XF_JOIN towards the source with the list of
destinations served by this XF. The source upon receiving this message sends back an
XF_ACK to the XF router. Each member which wants to join the multicast group G sends a
MEMBER_JOIN directly towards the source S. Each multicast session is uniquely identified
by a pair of (S,G). The source upon receiving the MEMBER_JOIN message from the
members, it adds this node to its Session Membership Table (SMT). The E2M protocol
initially put all destinations in its SMT table in the Xcast header of the packet and forwards
it. This initial packet forwarding is similar to the Xcast scheme for packet forwarding.
3.3.2.2 XF Selection
An intermediate node may decide to become an XF. In [30] the authors mentioned that the
traffic load and the number of downstream group members are considered the criteria for
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