A T M (QoS ) A T M (QoS ). QoS (Quality of Service) ATM - Service Classes CBR - Constant Bit Rate Circuit emulation, e.g. T1 (1.5 Mbit/s) or E1 (2 Mbit/s)

A T M

(QoS)

A T M

(QoS)

QoS (Quality of Service)

ATM - Service Classes CBR - Constant Bit Rate Circuit emulation, e.g. T1 (1.5 Mbit/s) or E1 (2 Mbit/s) Real-time audio / video coded at a constant bit rate

rt-VBR - real time Variable Bit Rate Compressed video (MPEG-2) coded at a variable bit rate withstringent real- time requirements (video conference)

nrt-VBR - non real time Variable Bit Rate Frame Relay, data transfers for transaction-processingapplications (airline reservations, banking transactions, etc.)

UBR - Unspecified Bit Rate „Best effort“ without any guarantees (e-mail, file transfer, etc.)

ABR - Available Bit Rate Adaptive „best effort“ service with guaranteed minimum cellrate (LAN emulation)

ATM - Traffic Parameters

PCR - Peak Cell Rate Maximum rate at which cells will be sent

SCR - Sustainable Cell Rate Long-term average cell rate

MCR - Minimum Cell Rate Minimum acceptable cell rate

MBS - Maximum Burst Size Maximum number of consecutive cells in a burst

CDVT - Cell Delay Variation Tolerance Maximum acceptable cell jitter

The traffic parameters make up a traffic descriptor,describing the characteristics of the source.

QoS Parameters

CTD - Cell Transfer Delay Elapsed time between cell exit event at the source andcorresponding cell entry event at the destination. maxCTD - maximum Cell Transfer Delay

CDV - Cell Delay Variation Time difference between minimum and maximum cell transferdelay, i.e peak-to-peak cell delay variation.

CLR - Cell Loss Ratio Ratio of lost cells to total transmitted cells

The QoS parameters describe the desired performanceat the destination of the virtual channel.

LeastUnderstood

MostUnderstood

Traffic Characterization

LeastUnderstood

MostUnderstood

Voice


LeastUnderstood

MostUnderstood

VoiceCBRvideo


LeastUnderstood

MostUnderstood

VoiceCBRvideo

Packetdata


LeastUnderstood

MostUnderstood

VoiceCBRvideo

Packetdata


Image

LeastUnderstood

MostUnderstood

VoiceCBRvideo

Packetdata

Image

VBRvideo


Multiplexing

Two basic approaches Deterministic multiplexing Statistical multiplexing

Deterministic Multiplexing

The traditional means of bandwidth allocation in telecommunications networks

Each traffic type has an inherent bit rate (e.g., voice traffic = 64 kilobits per second)

Allocate precisely that bandwidth for each call, for the duration of the call

Deterministic Multiplexing (Cont’d)

Advantages: Simple Works great for CBR traffic (PCR =

SCR) Disadvantages:

Inefficient for VBR traffic (PCR !=SCR) Allocating PCR can waste lots of

capacity

A Statistical multiplexer (or stat-mux) is a device which allows broadcaster to change the bitrate of channels according to those channels' needs.

If, for example, a broadcaster is showing news on Channel 1 and football on Channel 2, with fixed multiplexing each channel has, say, 2 Mbps.

The news channel is fine — no movement requires very little bandwidth. The football channel however begins to suffer as fast movement and crowd shots require large bandwidth to produce a clear picture.

A statistical multiplexer allows the broadcaster to allocate bandwidth to wherever it is needed.

Thus 0.5 Mbps are allocated to the news and 3.5 Mbps to the football. This results in good a quality picture for both channels.

Deterministic versus Statistical Multiplexing

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rate

Source 1: peak 12 Mbps,mean 8 Mbps


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12 Mbps


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rate

Source 2:peak 10 Mbps,mean 6 Mbps


Bit

rate

22 Mbps(12 + 10)


Bit

rate

22 Mbps(12 + 10)

Average utilizationwill be 14/22 = 64%


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Bandwidth savingwith StatisticalMultiplexing

Traffic Contract

• User submits to network a request for a connection witha description of its traffic (traffic parameters) and the desired service (QoS parameters)

• Network performs admission control to determine if sufficient resources are available to(a) satisfy the desired QoS of new connection(b) without violating QoS of existing connections

If sufficient resources are available, it accepts the flow.Otherwise, it rejects the flow

• Network performs policing and shaping at the networkentrance to ensure that user’s adheres to its specification

THANK YOU!THANK YOU!

Documents

A T M (QoS ) A T M (QoS ). QoS (Quality of Service) ATM - Service Classes CBR - Constant Bit Rate Circuit emulation, e.g. T1 (1.5 Mbit/s) or E1 (2 Mbit/s)