Computer Networking A Top-Down Approach Chapter 4.7.
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Transcript of Computer Networking A Top-Down Approach Chapter 4.7.
![Page 1: Computer Networking A Top-Down Approach Chapter 4.7.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649c785503460f9492d15d/html5/thumbnails/1.jpg)
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 Freceives one or tworedundant 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 tothe 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 fromall senders.
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Constructs a multicast routing tree for eachsource in the multicast group.
Reverse Path Forwarding is used to construct amulticast forwarding tree.
Pruning to solve the problem with unwanted multicast packets.