| description |
To avoid the well-known implosion problem, the majority of reliable
multicast protocols use hierarchical structures to pass
acknowledgment messages back to the sender. In most cases, a
technique called expanding ring search (ERS) is used to construct
the acknowledgment tree. In this paper we analyse ERS by simulation
studies. ERS is a simple and fault tolerant approach, but our
simulation results show that it has disadvantages like great
reliance on the multicast routing protocol and poor scalability. If
the background load exceeds a critical level, the message overhead
rises exponentially. In this paper, we will present an alternative
approach based on a so-called token repository service. The token
repository service stores a token for each successor, a node in an
ACK tree can accept. To find a node to connect to, the searching
node just retrieves a token from the token repository. We describe
how such a service can be implemented in a way that it can handle a
large number of multicast groups. Our simulation results show that
the token repository service is scalable, independent of the
multicast routing protocol and builds well-shaped ACK trees, causing
message delays that are comparable to ERS or even lower.
|