Switching ดร. อนันต์ ผลเพิ่ม Anan Phonphoem, Ph.D. anan@cpe.ku.ac.th...

Switching

ดร . อนั�นัต์� ผลเพิ่ �มAnan Phonphoem, Ph.D.

anan@cpe.ku.ac.thhttp://www.cpe.ku.ac.th/~anan

Computer Engineering DepartmentKasetsart University, Bangkok, Thailand

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Switching Point-to-point connection (Mesh)

wasteful Multipoint connection (Bus)

Distance (collision Domain) Number of devices

Switch

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Switched Network

Switching Methods

Circuit switching Message switchingPacket switching

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Circuit switched network

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Switch

Creates a temporary connection between input/output

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A folded switch

Switching Methods

Circuit switching Message switchingPacket switching

Space-division Time-division

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Space-Division Switches:Crossbar Switches

•Using electronic micro-switches (transistors)•Low efficiency (<25% use)

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Multistage Switch

• More efficiency• Blocking

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Switching path

• Also provide multiple paths

Switching Methods

Circuit switching Message switchingPacket switching

Space-division Time-division

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TDMTime-slot interchange (TSI)

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Time-slot interchange

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Space VS. Time-Division Space-division switching

+ Instantaneous- # of cross points

Time-division switching + No cross point

- Create delay

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Time-space-time (TST) switch

Other combinations: TSST, STTS, etc.

Switching Methods

Circuit switching Message switchingPacket switching

Datagram Virtual circuit

SVC PVC

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Circuit switching weakness Design for voice (telephone)

Non-voice transmission is bursty Data rate

Assume a single data rate for both ends

Inflexibility Same path (no adaptation)

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Datagram approach

Each packet is treated independentlyPacket is called Datagram

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Multiple channels in datagram approach

A XB Y

B

Switching Methods

Circuit switching Message switchingPacket switching

Datagram Virtual circuit

SVC PVC

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Virtual Circuit Same route – choose at start PVC (Permanent VC)

Leased Line SVC (Switched VC)

Dial-up

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Switched virtual circuit (SVC)

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Switched virtual circuit (SVC)

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Switched virtual circuit (SVC)

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Circuit-switched VS. Virtual-circuit connection

Path VS. route Dedicated VS. sharing

Circuit-switched connection Virtual-circuit connection

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Virtual Circuit in WAN

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VCI

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VCI Phases

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Switching

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Source-to-destination data transfer

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SVC setup request

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SVC setup acknowledgment

Switching Methods

Circuit switching Message switchingPacket switching

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Message switching