Teknik Routing Pertemuan 10

Matakuliah : H0524/Jaringan KomputerTahun : 2009

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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• Interior Routing Protocol• External Routing Protocol

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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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• 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)

Routing

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Routing Techniques Criteria

Performance CriteriaNumber of hopsCostDelayThroughput

Decision TimePacket (datagram)Session (virtual circuit)

Decision PlaceEach node (distributed)Central node (centralized)Originating node (source)

Network Information SourceNoneLocalAdjacent nodeNodes along routeAll nodes

Network Information Update Timing

ContinuousPeriodicMajor load changeTopology change

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Routing Strategies

• Fixed• Flooding• Random• Adaptive

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–Static routingFixed 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.

Types of Routing

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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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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

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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

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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

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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

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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.

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IRP and ERP