Matakuliah : H0524/Jaringan Komputer
Tahun
: 2009
Teknik Routing
Pertemuan 10
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan teknik routing
Bina Nusantara
Outline Materi
•
•
•
•
•
Bina Nusantara
Routing table
Routing Criteria
Routing Strategies
Interior Routing Protocol
External Routing Protocol
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
Bina Nusantara
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)
Bina Nusantara
Routing Techniques Criteria
Performance Criteria
Number of hops
Cost
Delay
Throughput
Decision Time
Packet (datagram)
Session (virtual circuit)
Network Information Source
None
Local
Adjacent node
Nodes along route
All nodes
Network Information Update
Timing
Continuous
Decision Place
Periodic
Each node (distributed)
Major load change
Central node (centralized)
Topology change
Originating node (source)
Bina Nusantara
Routing Strategies
•
•
•
•
Bina Nusantara
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.
Bina Nusantara
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
Bina Nusantara
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
Bina Nusantara
Flooding Example
Bina Nusantara
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)
Bina Nusantara
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
Bina Nusantara
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
Bina Nusantara
Routing Protocols
• Routing Information
– About topology and delays in the
internet
• Routing Algorithm
– Used to make routing decisions
based on information
• Routing algorithms are implemented
using routing protocols
Bina Nusantara
Interior Routing Protocol
• Routing protocols that operate within a
network (called an autonomous system) are
called interior routing protocols.
• Passes routing information between
routers within AS
• Routing algorithms and tables may differ
between different AS
• IRP needs detailed model
Bina Nusantara
Exterior Routing Protocol
• Exterior router protocol (ERP) is used for
operating outside of or between networks.
• As there are many more possible routes it is far
more complex than interior routing.
• It cannot maintain tables of every single route
and have to concentrate instead on the main
routes only.
• Routing algorithms and tables may differ
between different Autonomous System (AS).
• ERP supports summary information on
reachability
Bina Nusantara
RIP
Routing Information Protocol (RIP)
• Routing protocol commonly used on the
Internet.
• Computers using RIP broadcast routing
tables every minute or so.
• Now used on simpler networks
• The original dynamic distance vector
protocol
Bina Nusantara
OSPF
•
•
•
•
•
•
Open Shortest Path First (OSPF)
Has overtaken RIP as the most popular interior routing
protocol on the Internet.
Has the ability to incorporate traffic and error rate
measures in its routing decisions.
Sends updates state info, not entire routing tables, and
only to other routers (not broadcasting them).
Each router keeps list of state of local links to network.
Little traffic (less burdensome to the network since) as
messages are small and not sent often.
Route computed on least cost based on user cost
metric using Link State Routing Algorithm - RFC 2328.
Bina Nusantara
IRP and ERP
Bina Nusantara