4-NetworkLayer-PartI routing optimization .ppt

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Part 4: Network Layer
Part A: Algorithms

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Summary
1) The Problem
2) The Dijkstra’s Shortest Path Algorithm
3) Distance Vector Routing
4) Link State Routing
5) Hierarchical Routing
6) Routing in Ad Hoc Networks

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1. The Problem (1)
•Store-and-Forward Packet Switching
•Services Provided to the Transport Layer
•Connectionless Service
•Connection-Oriented Service

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1. The Problem (2): Packet Switching
The environment of the network layer protocols.
fig 5-1

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1. The Problem (3): Connectionless
Service
Routing within a diagram subnet.

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1. The Problem (4): Connection-
Oriented Service
Routing within a virtual-circuit subnet.

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1. The Problem (5): Connectionless
VS. Connection-Oriented

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2 Shortest Path Algorithm
The first 5 steps used in computing the shortest path from A to D.
The arrows indicate the working node.

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3 Distance Vector Routing (1)
(a) A subnet. (b) Input from A, I, H, K, and the new
routing table for J.

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3 Distance Vector Routing (2)
The count-to-infinity problem.

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3 Distance Vector Routing (3): Loop-
Breaking Heuristics
Set infinity to a limited number, e.g. 16.
Split horizon
Split horizon with poison reverse

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Initialization
3 Example:

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Direct
Neighbours

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Neighbours
of neighbours

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Neighbours
of neighbours
of neighbours

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Stable
convergence

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Good news:
A new link!

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Direct
endpoints
know

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Neighbours
know

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Neighbours
of neighbours
know

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A happy and
stable network

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Bad news:
Link crash!!

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Direct
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Get help
from
neighbours

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Routing loop
(due to
inconsistent
state info)

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Counting
to infinity…

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Stability
again

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4 Link State Routing (1)
Each router must do the following:
• Discover its neighbors, learn their network
address.
• Measure the delay or cost to each of its
neighbors.
• Construct a packet telling all it has just learned.
• Send this packet to all other routers.
• Compute the shortest path to every other router.

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4 Link State Routing (2): Learning
about the Neighbors
(a) Nine routers and a LAN.
(b) A graph model of (a).

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4 Link State Routing (3): Measuring
Line Cost
A subnet in which the East and West parts are
connected by two lines.

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4 Link State Routing (4): Building
Link State Packets
(a) A subnet. (b) The link state packets for this
subnet.

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4 Link State Routing (5): Distributing
the Link State Packets
The packet buffer for router B in the previous slide (Fig.
5-13).

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5 Hierarchical Routing
Hierarchical routing.

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6. Routing in Ad Hoc Networks (1)
Possibilities when the routers are mobile:
Military vehicles on battlefield.
• No infrastructure.
A fleet of ships at sea.
• All moving all the time
Emergency works at earthquake .
• The infrastructure destroyed.
A gathering of people with notebook computers.
• In an area lacking 802.11.

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6. Routing in Ad Hoc Networks (2):
Route Discovery
(a) Range of A's broadcast.
(b) After B and D have received A's broadcast.
(c) After C, F, and G have received A's broadcast.
(d) After E, H, and I have received A's broadcast.
Shaded nodes are new recipients. Arrows show possible reverse routes.

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6. Routing in Ad Hoc Networks (3):
Route Discovery
Format of a ROUTE REQUEST packet.

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6. Routing in Ad Hoc Networks (4):
Route Discovery
Format of a ROUTE REPLY packet.

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6. Routing in Ad Hoc Networks (5):
Route Maintenance
(a) D's routing table before G goes down.
(b) The graph after G has gone down.