PAPER OVERVIEW:! Evaluation of two Multicasting protocols namely CBT and PIM.! Comparison of protocols in terms of End-to-end delay, Network resource usage, Join time, Size of the tables containing multicast routing information, and the impact of the timers introduced by the protocols.! Network Simulation tool OPNET is employed.! Suggestions given to Improve PIM Sparse Mode. MULTICASTING! Multicasting is a communication service that allows an application to efficiently transmit copies of a data packet to a set of receivers who are multicast group members.! Purpose of Multicasting Routing is to reduce cost for applications that send same data to Multiple recipients.! Performed by a multicast-capable virtual network called Multicast Backbone. 1
Uses of Multicasting.! Audio and Video Conferencing! Distributed Interactive Simulation! Exchanging experimental data and weather map MULTICAST ROUTING PROTOCOLS: Approaches: SOURCE BASED TREES! Uses a tree, specific to a particular sender and group.! Uses shortest path tree routed at a sender.! Ex: Core based Tree(CBT),PIM Sparse Mode Source Based Tree(PIM-SBT) SHARED TREES! Uses a single center-based tree or core based tree to route traffic from all senders to the group! Uses shortest path tree routed at one or more predefined nodes in the network called Core nodes! Ex: PIM Dense Mode, PIM Sparse Mode Shared Tree(PIM-ShT) 2
CORE BASE TREES(CBT)! CBT is based on single shared tree for every multicast group active in the network.! A join message is sent by a multicast router toward the Core node via the shortest path.! and a tree routed at the core is constructed as the acknowledgements of the join message are processed! When a node on the tree receives a packet addressed to the group it forwards copies of the packet on all branches of the group s tree except for the branch on which packet arrived. 3
PIM DENSE MULTICASTING ROUTING PROTOCOL! Floods the network with data packets to set up a source based tree for every sender to every group! Initially they send out packets to every potential receiver in the network! Any router which has no active members of the multicast group for which the data was sent out sends prune messages towards the senders to remove unwanted branches from trees for that particular multicast group! The data packets are again sent out to that router once the pruned interface times out 4
PIM SPARSE MULTICAST ROUTING PROTOCOL A node in the network called Rendezvous Point(RP) is assigned to the group RP is the center node of a directed shared tree for that group When a multicast router learns via IGMP that a local host has joined group G it sends a join message along the shortest path to the RP of that group A directed source based tree is built from the sender to the RP by the RP TWO TYPES OF PIM SPARSE TREES Shared tree case of PIM SPARSE(PIM ShT) Source Based Tree case of PIM SPARSE(PIM-SBT) 5
Shared Tree Case of PIM SPARSE(PIM-ShT) Any sender to a particular Multicast group sends the packet to the RP of that group The RP then sends the packets to all the members of the multicast group of which it s the RP A source based tree for sender S is built between the source S and the Rendezvous Point(RP) The shared tree is built which is directed away from the RP towards all the receivers of the group 6
SOURCE BASED TREE of PIM SPARSE (PIM SBT) A receiver learns of senders to a group when it receives data packets on the tree directed away from the RP The receiver then sends join messages towards specific senders to become part of a shortest path,source based trees routed at those senders The receiver also alerts routers on the shared tree such that no packets from these sources are forwarded to it 7
SIMULATION ENVIRONMENT The protocols(cbt,pim DENSE,Shared case of PIM Sparse and Source Based tree case of PIM Sparse) were simulated using the OPNET network simulation tool TOPOLOGIES CONSTUCTED USING OPNET: AAI/MAGIC/ATDnet HIGH BANDWIDTH MESH TOPOLOGY LOW BANDWIDTH MESH TOPOLOGY 8
SIMULATION PARAMETERS Experimental Results: 1.End to End Delay! PIM - SBT and PIM DENSE deliver packets faster than CBT. 9
NETWORK RESOURCES USAGE! Measure of the number of hops used to deliver the packets.! PIM DENSE uses network resource more than others. 10
OVERHEAD TRAFFIC PERCENTAGE! Percentage of Total Number of bits trasmitted.! CBT has the lowest overhead. 11
TRAFFIC CONCENTRATION! Measure of the distribution of the total n/w traffic on all links.! PIM Dense distributes traffic more evenly.! Helps to figure out locations of probable Cores and RP's. JOIN TIME! Time elapsed between, a host asking to join the group and the time it receives it'e first message.! PIM Dense join times are much higher than those of other protocols for every network 12
SUGGESTIONS FOR PIM SPARSE! Decision as to whether the Source-Based tree or Shared Tree mode be used should be made by the Initiator rather than individually by the receivers.! For Shared Tree group, There is no need for senders to register at the RP or to have source based routes from the sender to the RP. They can directly use the shared tree.! Operations of Source Based Tree could follow these steps: - A receiver sends a Join message to RP. - RP sends the current list of senders for a group back to the receiver. - New sources register with RP. - RP multicasts the arrival of new member. - RP periodically transmit a list of senders to the group. Thus Intricacy's of PIM protocol is greatly reduced. Number of Timers required are reduced. 13
CONCLUSIONS Experimental results are summarized. 14
LIMITATION! When using Source-based trees, the modifications done to PIM protocol, would make the Join Time Longer!!!!, as the receiver would not receive data from the sender until it joined the sender's source based tree.! The Simulation did not take into account the time to look up the routing table. IMPROVEMENT/SUGGESTION Comparing the performance of the Ordered CBT with the PIM, and tabulating the result would help to find ways to eliminate looping effects in a tree. As both CBT and PIM has it's own advantages and disadvantages, designing routers which could keep the traffic log and switch to the best multicasting method. 15