asynchronous transfer mode (atm) and qos
DESCRIPTION
Asynchronous Transfer Mode (ATM) and QoS. ATM Era : Multiservice Networks Departure from Service Specialization. bulk data. video. Multiservice Network. voice. interactive data. Why ATM Did Not Make it the Way it was Initially Envisioned. header. payload. Fixed length packet = cell. - PowerPoint PPT PresentationTRANSCRIPT
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1COMP680E by M. Hamdi
Asynchronous Transfer Mode (ATM)
and QoS
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2COMP680E by M. Hamdi
ATM Era : Multiservice NetworksDeparture from Service Specialization
Multiservice Network
video
voice
bulkdata
interactivedata
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3COMP680E by M. Hamdi
Why ATM Did Not Make it the Way it was Initially Envisioned
Advantages of ATM
Disadvantages of ATM
Commercial Factors
• Single network optimized for everything (Data, phone, TV)
• Same technology for WAN, MAN, LAN (Seamless integration)
• QoS oriented and high-speed oriented
• Fast Hardware• Tremendous amount of research has been done
• Large overhead for packets
• QoS is a bit complicated from the applications point of view and network management point of view
• Not that great from web browsing (which is one killer application)
• Millions of networks already installed
• Lack of applications
• Expensive at the LAN (where it really matters)
• No strong business incentive for QoS (even up to now)
• Can achieve similar speed with an IP router as compared to an ATM switch (May be)
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4COMP680E by M. Hamdi
What is ATM?
ATM is packet switching!
• Switched or permanent connections
• Traffic type independent (voice, data, interactive video)
• Fixed length packet - 53 bytes (cell)
header payload
Fixed length packet = cell
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5COMP680E by M. Hamdi
ATM Cell Relay:The Underlying Technology
Cell Features Benefit
Small Low latency to support real-time services like audio and video (What is an appropriate size?)
Fixed Length Fast hardware switching and scalability
Standardized Usable in all networks (LAN and WAN)
Cells
Voice
Data
Video
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6COMP680E by M. Hamdi
Without Short Cells
Data packet(2000)
Voicepacket (50)
Router
Input
ports
Output
ports
A voice packet waits behind a large data packet
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7COMP680E by M. Hamdi
With Short Cells
Data #1(50)
Voice(50)
Data #40(50)
Router
Input
ports
Output
ports
Voice packet to be transmitted after Data #1
Data #2(50)
•Voice packet can go immediately after data packet #1
•Waiting for voice is reduced significantly
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8COMP680E by M. Hamdi
Virtual Paths & Virtual Channels
• Unique on a link-by-link basis• Virtual channels are contained within virtual paths• Interpreted at each switch to:
• determine output link• determine outgoing VPI/VCI
• Two-level structure:• allows “trunking” of virtual channels as one virtual path• virtual path can be switched• both used to route cells through network
PhysicalTransmission
LinkVCs VP
VCs VP
VCsVP
VCsVP
A Virtual Path (VP) describes the semi-permanent route between two end points. A Virtual Channel (VC) describes a cell transmission channel inside a virtual path
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9COMP680E by M. Hamdi
Connection Identifiers
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10COMP680E by M. Hamdi
ATM switch routing
ATMSwitch
ATMSwitch
ATMSwitch
ATMSwitch
ATMSwitch
VirtualPaths
VirtualCircuits
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11COMP680E by M. Hamdi
ATM Switches
• ATM switches translate VPI/VCI values
• VPI/VCI value unique only per interface—eg: locally significant and may be re-used elsewhere in network
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VPI/VCIPort VPI/VCIPort
Input Output
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12COMP680E by M. Hamdi
ATM Switching
Connections (routes) set up by software• Routing (path through multiple-switch network)
and resource allocation is performed once per connection by switch control CPU
Cells are switched by hardware• Hardware (table lookup + switching fabric)
switches each incoming cell to appropriate output port
• Once a connection is established, cells are not touched by software
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13COMP680E by M. Hamdi
VP and VC Switch
• Two types of ATM switch• VP switch does not look at VCIs, switching is based
on VPIs only• VCI does not change when passing through a VP
switch; VPI may change• VC switch looks at both VPI and VCI• VCI (as well as VPI) may change when passing
through a VC switch
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14COMP680E by M. Hamdi
Routing with a VP Switch
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15COMP680E by M. Hamdi
A Conceptual View of a VP Switch
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16COMP680E by M. Hamdi
Routing with a VC Switch
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17COMP680E by M. Hamdi
A Conceptual View of a VC Switch
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18COMP680E by M. Hamdi
ATM Protocol Stack
Upper LayersUpper Layers
ATM Adaptation LayerATM Adaptation Layer
ATM LayerATM Layer
Physical LayerPhysical Layer
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19COMP680E by M. Hamdi
ATM Architecture
Presentation
Session
Network
Data Link
PhysicalTransmission-convergencephysical medium dependent
Transport
Application
ATM Layer
ATM Adaptation Layer
Upper Layer Protocols
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20COMP680E by M. Hamdi
Adaptation Layers: Service Classes
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21COMP680E by M. Hamdi
Service Classes and Capacity of Network
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22COMP680E by M. Hamdi
QUEUES and PRIORITY
Classifier
CBR TrafficCBR Traffic
VBR TrafficVBR Traffic
UBR TrafficUBR Traffic
ABR TrafficABR Traffic
Ou
tpu
t
Priority 1
Priority 2
Priority 3
Priority 4
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23COMP680E by M. Hamdi
ATM Adaptation Layer: Summary
ServiceCategories
Class
ATM ATM Adaptation LayerAdaptation Layer
(AAL)(AAL)
ATM LayerATM Layer
Physical LayerPhysical Layer
Bit Rate ConnectionMode
TimingConcern
ApplicationExamples
• Bandwidth andBandwidth andthroughput guaranteedthroughput guaranteed
• Good for voice Good for voice and videoand video
AAL1A CBR(Constant)
Connection-Oriented
Yes
• Best effort bandwidth Best effort bandwidth and throughputand throughput
• Good for live video,Good for live video,multimedia, multimedia, LAN-to-LANLAN-to-LAN
AAL2B VBR(Variable)VBR-RT
andVBR-NRT
Connection-Oriented
Yes
• Best effort withBest effort withcongestion feedbackcongestion feedback
• Reliable delivery Reliable delivery of bursty traffic ifof bursty traffic iflatency okaylatency okay
AAL5C ABR(Available)
Connection-Oriented
No
• No guaranteeNo guarantee• For SMDS/LANFor SMDS/LAN
AAL3/4D UBR(Un-
specified)
Connection-less
No
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24COMP680E by M. Hamdi
QUALITY OF SERVICE
– Max CDT, Mean CTD, CDV, CLR, CER, SECBR, CMR
CBR rt-VBR nrt-VBR ABR UBR
PCR Yes Yes Yes Yes Yes
SCR N/A Yes Yes N/A N/A
MBS N/A Yes Yes N/A N/A
MCR No No No Yes No
CDVT(PCR) Yes Yes Yes Yes Yes
CDVT(SCR) N/A Yes Yes N/A N/A
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25COMP680E by M. Hamdi
Application Requirements
BandwidthBandwidth
DelayDelay
ReliabilityReliability
Cost ($ or Admin)Cost ($ or Admin)
• Peak Cell Rate (PCR)• Sustained Cell Rate (SCR)• Minimum Cell Rate (MCR)
• Peak Cell Rate (PCR)• Sustained Cell Rate (SCR)• Minimum Cell Rate (MCR)
• Cell Transfer Delay (CTD)• Cell Delay Variation (CDV)• Cell Transfer Delay (CTD)• Cell Delay Variation (CDV)
• Cell Loss Ratio (CLR)• Cell Loss Ratio (CLR)
• Link Weighting• Link Weighting