Matakuliah : H0484/Jaringan Komputer
Tahun
: 2007
Teknik Routing
Pertemuan 20
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan teknik routing
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Outline Materi
• Routing table
• Routing Criteria
• Routing Strategies
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Routing
• Routing is the process of deciding what path to take from sender to
receiver (packet forwarding)
• Usually there is more than one route possible; devices that perform
routing must keep tables to make decisions about which path to send
packets on to reach a given destination (routing table)
• Routing decisions on the Internet are usually handled by special
purpose devices called Routers, that maintain their own routing tables
• End systems and routers maintain routing tables
• Routing table indicates next router to which datagram should be sent
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Routing
• Data delivery from one computer to another is accomplished through
store-and-forward technology
• Packet switch stores incoming packet and forwards the packet to
another switch or computer
• Packet switch has internal memory, can hold packet if outgoing
connection is busy (queued)
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Routing Techniques Criteria
Performance Criteria
Number of hops
Cost
Delay
Throughput
Decision Time
Packet (datagram)
Session (virtual circuit)
Decision Place
Each node (distributed)
Central node (centralized)
Originating node (source)
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Network Information Source
None
Local
Adjacent node
Nodes along route
All nodes
Network Information Update Timing
Continuous
Periodic
Major load change
Topology change
Routing Strategies
•
•
•
•
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Fixed
Flooding
Random
Adaptive
Types of Routing
–Static routing
Fixed routing tables which are developed by network
managers, typically used on simpler networks
–Dynamic routing:
Routing decisions are made dynamically, based on
routing condition information exchanged between
routing devices.
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Fixed Routing
• Single permanent route for each source to destination pair
• Determine routes using a least cost algorithm
• Route fixed, at least until a change in network topology
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Flooding
• No network info required
• Packet sent by node to every neighbor
• Incoming packets retransmitted on every link except incoming
link
• Eventually a number of copies will arrive at destination
• Each packet is uniquely numbered so duplicates can be
discarded
• Nodes can remember packets already forwarded to keep
network load in bounds
• Can include a hop count in packets
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Flooding Example
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Properties of Flooding
• All possible routes are tried
– Very robust
• At least one packet will have taken minimum hop count
route
– Can be used to set up virtual circuit
• All nodes are visited
– Useful to distribute information (e.g. routing)
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Random Routing
• Node selects one outgoing path for retransmission of
incoming packet
• Selection can be random or round robin
• Can select outgoing path based on probability
calculation
• No network info needed
• Route is typically not least cost nor minimum hop
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Adaptive Routing
• Used by almost all packet switching networks
• Routing decisions change as conditions on the network
change
– Failure
– Congestion
• Requires info about network
• Decisions more complex
• Tradeoff between quality of network info and overhead
• Reacting too quickly can cause oscillation
• Too slowly to be relevant
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Adaptive Routing - Advantages
• Improved performance
• Aid congestion control
• Complex system
– May not realize theoretical benefits
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