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Reliable Tree Multicast with a Server Set of Indeterminate Size

IP.com Disclosure Number: IPCOM000115241D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 154K

Publishing Venue

IBM

Related People

Dudley, JG: AUTHOR [+2]

Abstract

The receivers in a network that provide a given service can be grouped together with a common group identification. Network protocols can provide a valuable function by enabling senders to multicast messages to such a group.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 39% of the total text.

Reliable Tree Multicast with a Server Set of Indeterminate Size

      The receivers in a network that provide a given service can be
grouped together with a common group identification.  Network
protocols can provide a valuable function by enabling senders to
multicast messages to such a group.

      In some environments such as local area networks and one-way
satellite broadcast systems, support for multicast protocols is
easily provided.  However, more complex multicast mechanisms are
required for a network of nodes which may be interconnected in an
arbitrary manner.  In order to multicast a message to a group of
receivers in such a network, a tree (loopless graph) can be
constructed that connects the sender's node to all nodes of the
network containing a receiver in the group.  Use of such a tree
reduces the traffic in a network required to disseminate information
to all receivers in the group.

      No simple method exists for providing a reliable multicast
service over a tree when the number of receivers on the tree is
unknown.  Current methods require that the sender know the number of
receivers.  These methods require the sender to multicast the message
over the tree (i.e., send the message such that all receivers on the
tree can receive the message) and to store the message until an
acknowledgment is received from each receiver.  However, if the
number of receivers is not static (i.e., receivers may join or leave
the tree), the sender does not know how many receivers are on the
tree or how many acknowledgments to expect for the message.

      The algorithm herein disclosed is an improvement over previous
algorithms.  It allows reliable multicast over a tree with an unknown
number of receivers when the using application can define the number
of receivers it requires.  The multicast procedure terminates
successfully whenever acknowledgments are received from that
using-application-defined number of receivers.

The algorithm is as follows:
  1.  The using application passes to the sender a reliable message
       for a particular group of receivers, along with the number of
       acknowledgments required for successful completion and a
maximum
       retransmission count.
  2.  The sender sends the message on the multicast tree and starts a
       retransmission timer.
  3.  Each receiver in the specified group that receives the message
       sends an acknowledgment to the sender.
  4.  The sender stores the message until it has received an
       acknowledgment from the using-application-defined number of
       receivers or the protocol terminates unsuccessfully.
  5.  When the timer expires, if the sender has not received an
       acknowledgment from the using-application-defined number of
       receivers, the sender does the following:
      o  If the message has not been retransmitted the maximum number
          of times,...