Welcome to ENTC 415

Welcome to ENTC 415

Asynchronous Transfer Mode (ATM) and QoS COMP680E by M. Hamdi 1 ATM Era : Multiservice Networks Departure from Service Specialization bulk data video Multiservice Network voice interactive data COMP680E by M. Hamdi 2

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 highspeed oriented 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) Fast Hardware Tremendous amount of research has been done COMP680E by M. Hamdi 3 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 COMP680E by M. Hamdi 4 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) Voice Data Video Cells COMP680E by M. Hamdi 5 Without Short Cells Router I n p u t p o r t s

O u t p u t Voice packet (50) Data packet (2000) p o r t s A voice packet waits behind a large data packet COMP680E by M. Hamdi 6 With Short Cells Router

I n p u t p o r t s O u t p u t Data #40 (50) Data #2 (50) Voice (50) Data #1

(50) p o r t s Voice packet to be transmitted after Data #1 Voice packet can go immediately after data packet #1 Waiting for voice is reduced significantly COMP680E by M. Hamdi 7 Virtual Paths & Virtual Channels 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 VCs

VP VCs VP Physical Transmission Link VP VCs VP VCs 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 COMP680E by M. Hamdi 8 Connection Identifiers COMP680E by M. Hamdi 9 ATM switch routing Virtual Paths ATM Switch ATM Switch ATM Switch ATM Switch

ATM Switch Virtual Circuits COMP680E by M. Hamdi 10 ATM Switches Input Output Port VPI/VCI Port 45 VPI/VCI 1 29 2 45

2 45 1 29 1 64 3 29 3 29 1 64 29

64 2 1 3 29 ATM switches translate VPI/VCI values VPI/VCI value unique only per interface eg: locally significant and may be re-used elsewhere in network COMP680E by M. Hamdi 11 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

COMP680E by M. Hamdi 12 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 COMP680E by M. Hamdi 13 Routing with a VP Switch COMP680E by M. Hamdi 14 A Conceptual View of a VP Switch COMP680E by M. Hamdi

15 Routing with a VC Switch COMP680E by M. Hamdi 16 A Conceptual View of a VC Switch COMP680E by M. Hamdi 17 ATM Protocol Stack Upper Layers ATM Adaptation Layer ATM Layer Physical Layer COMP680E by M. Hamdi 18 ATM Architecture Application Upper Layer Protocols

Presentation Session ATM Adaptation Layer Transport Network ATM Layer Data Link Transmission-convergence physical medium dependent Physical COMP680E by M. Hamdi 19 Adaptation Layers: Service Classes COMP680E by M. Hamdi 20

Service Classes and Capacity of Network COMP680E by M. Hamdi 21 QUEUES and PRIORITY CBR Traffic Priority 2 Priority 3 Output ABR Traffic Classifier VBR Traffic Priority 1 Priority 4 UBR Traffic COMP680E by M. Hamdi

22 ATM Adaptation Layer: Summary Class ATM Adaptation Layer (AAL) A Service Categories AAL1 AAL2 ATM Layer Connection Timing Mode Concern Yes Bandwidth and throughput guaranteed

Good for voice and video Connection(Variable) Oriented Yes Best effort bandwidth and throughput Good for live video, multimedia, LAN-to-LAN Connection(Available) Oriented No Best effort with congestion feedback Reliable delivery of bursty traffic if latency okay No

No guarantee For SMDS/LAN VBR VBR-RT and VBR-NRT C AAL5 D AAL3/4 Application Examples ConnectionOriented CBR (Constant) B

Physical Layer Bit Rate ABR UBR (Unspecified) Connectionless COMP680E by M. Hamdi 23 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 COMP680E by M. Hamdi 24 Application Requirements Bandwidth Peak Cell Rate (PCR) Sustained Cell Rate (SCR) Minimum Cell Rate (MCR)

Cell Transfer Delay (CTD) Cell Delay Variation (CDV) Delay Cell Loss Ratio (CLR) Reliability Cost ($ or Admin) Link Weighting COMP680E by M. Hamdi 25

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