4.6.1 Comparison and Cost analysis
A. Comparison between SReM , Xcast, Xcast+ and SEM
Xcast encodes the list of the addresses of all receivers in each packet, while Xcast+ encodes
the list of designated routers in each packet. However, both SReM and SEM use this
mechanism only in the branching message. In Xcast and Xcast+, the packet will follow the
unicast path between the source and the destination, but in SEM and SReM the packet will
follow a unicast path among branching nodes. Furthermore, there are two major differences
between SEM and SReM as follows.
In SEM, all of the destinations of a multicast session are encoded in branching messages to
build a multicast tree in advance and the source or sender is always responsible of the set-up
and maintenance of the whole multicast tree, and the multicast tree needs to be rebuilt
whenever the joining or leaving of one of destinations is happened. This leads to two
disadvantages.
-I- First, SEM has the scalability problem, like the Xcast and Xcast+. This is due to the
fact that as the size of a multicast group increases, both the size of delivering packets
in Xcast and Xcast+ and the size of BNMs in SEM will increase correspondingly.
I Secondly, SEM has the problem of a big join/leave latency, which is occurred by the
set-up of the whole multicast tree in advance or rebuilt the whole multicast tree
whenever a new member is joining or an old member is leaving.
B. Comparison between SReM, HBH and REUNITE
The main similarity between our proposed SReM, HBH and REUNITE is that all of them use
unicast infrastructure to perform packet forwarding, and only the branching node
routers(BNRs) are required to maintain a multicast forward tables (MFTs). This feature of
our proposed SReM, like HBH and REUNITE, enable it to be deployed under existing
Internet which is based on unicast infrastructure.
The main difference between SReM and HBH and REUNITE is that SReM uses the so-
called DBT mechanism to maintain and update the multicast tree, while HBH and REUNITE
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