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Published byAsher Trivitt Modified over 9 years ago
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Computer Networking A Top-Down Approach Chapter 4.7
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When a packet is needed to be sent from a source node to ALL other nodes in the network. Example: A company needs to upgrade a program in all computers at the office building. The network admin can send an update to all computers on the network using broadcast routing.
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N-way-unicast Uncontrolled flooding Controlled flooding Spanning-tree broadcast
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The source node(R1) sends duplicates of a pkt to the N destinations (R3 & R4). The network nodes (R2) should instead create duplicates to the final destinations (R3 & R4). All destination addresses needs to be known: adds extra overhead and complexity.
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Flooding is the obvious technique of broadcast routing: 1. Source node sends copies of pkt to all its neighbours 2. Receiving node also sends copies to all neighbours(N) except its sender Can send a pkt into an endless cycle! Can create a broadcast storm if N>2
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Solution: Sending node should only flood neighbours that haven’t been flooded before. There are two ways of doing this: 1. Sequence-number-controlled flooding 2. Reverse Path Forwarding (RPF)
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1. Source node puts its address and broadcast sequence no. into a broadcast pkt 2. Sends this pkt to all its neighbors 3. Each node keeps a list with above info about each broadcast pkt already received 4. If pkt already received, drop pkt. Otherwise duplicate and forward to neighbors
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Router only transmits pkt if it arrived on shortest unicast path back to the source B, C, D, E and F receives one or two redundant packets!
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Every node only receives one copy of pkt Nodes only sends pkts to its neighbors in the spanning tree A node only need to know which neighbors are in spanning tree
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Example: Center-based approach 1. A center node is defined 2. Nodes unicast tree-join messages addressed to center node 3. Msg forwarded until hits the spanning tree
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Enables a single source node to send a copy of a packet to a subset of the other network nodes. Multiple receivers Problems: ◦ identify receiver ◦ address a packet
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Used in Internet architecture A multicast packet is addressed using this method. Single identifier Multicast group Still one difficulty…
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Operates between a host and its directly attached router. Provides operations for joining and leaving a group. IGMP messages
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Only a subset of routers that joined to the multicast group actually needs to receive the multicast traffic.
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Goal to find a tree of links that connects all of the routers that have attached hosts belonging to the multicast group. Two approaches: ◦ Multicast routing using a group-shaded tree. ◦ Multicast routing using a source-based tree.
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Constructs a single, shared routing tree to route packets from all senders.
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Constructs a multicast routing tree for each source in the multicast group. Reverse Path Forwarding is used to construct a multicast forwarding tree. Pruning to solve the problem with unwanted multicast packets.
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