“Adapting to Network and Client Variation Using Infrastructural

Proxies :Lessons and Perspectives”

University of California Berkeley

Armando Fox , Steven D. Griddle, Yatin Chawathe,

Eric A. Brewer

Presented by :Presented by : Shruthi R BompelliShruthi R Bompelli..

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INTRODUCTION :: why..

• The current Internet infrastructure includes an extensive range and number of clients and servers.

• These variations in clients make it difficult for servers to provide a level of service that is appropriate for every client.

• An Application-Level Adaptation is required to provide meaningful Internet experience.

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Approach to ADAPTATION :: where..

Server-Based Approach • Attempts to insert adaptation machinery at each end server.

Client-Based Approach • Attempts to bring all clients up to a least-common denominator level

of functionality.

Proxy-Based Approach • Proxy agents placed between clients and servers perform

aggressive computation and storage on behalf of clients.

Advantages of Proxy-Based Approach -• Leveraging the installed infrastructure through incremental

deployment.• Rapid prototyping during turbulent standardization cycles.

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Adaptation via Datatype - Specific Distillation :: what..

Lossy Compression Mechanism or Distillation –

• Lossy compression that preserves most of the semantic content of a document.

• makes intelligent decision of what information to throw away based on semantics type of data (shrinking the image, quantizing the color map).

Example -

• A PostScript text document, can be distilled by extracting the text.

• Adobe Systems' Distiller Pro package constructs a PDF file from a PostScript file.

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Adaptation …what..

Refinement - Is a process of fetching some part (possibly all) of a source

object at increased quality.

Distilled Image of Soda Hall (a) occupies 17KB at 320x200 pixels (b) refinement occupies 12 KB of the original with 492KB 889x600 pixel.Distillation took 6 seconds on a SPARCstation & Refinement took less than a Second.

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Perform Adaptation on the fly :: what..

• End – to – End Latency is reduced.

The delivery latency -- about 2 seconds to get from the local server, about 8 seconds to distill it, & about 32 seconds to send the distilled version to the client on a lightly-loaded SPARCstation-20.

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On-Demand Distillation ::

(a) Image Distiller - GIFMUNCH (b) Rich Text Distiller

Distills & Refines Gif Images.

Transformation Axis -

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On-Demand Distillation …

Image and Video Transformation ::

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Design Principles ::

• When bandwidth of P-C in smaller than P-S then on-demand

D & R reduces End-End latency perceived by the client.• Improves Performances when D & R is in network infrastructure

rather than End Points.• D&R achieves better compression than Lossless compression.

SPAND – Shared Passive Network Performance Discovery.

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Advantages of Cluster –Based Network ::

Scalability when the load offered to the service increases, an incremental and

linear increase in hardware can maintain the same per-user level of service.

Availability the service must be available 24x7 despite the inevitable reality of

faults.

Cost Effective service must be economical to administer and expand.

(cost, service and support, delivery time, alternate suppliers, trained employees).

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Challenges of Cluster Computing ::

Administration serious concern for systems of many nodes.

Component vs. System Replicationeach PC in a cluster is not usually powerful enough to support entire service but at least can for a component.

Partial Failures has ability to survive and adapt to failures of subsets of the system.

Shared State Clusters have no shared state.

If shared state is avoided across the Cluster, Performance can be increased and Reduce Complexity.

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Shared Semantics required by Network Services ::

ACID (Atomicity, Consistency, Isolation, Durability)• Used in Traditional Database.• Provides strong Consistency and Durability but not high Availability.• Suited for internet commerce transactions.

BASE (Basically Available, Soft State Eventual Consistency)• That are not strictly ACID.• Allows to handle partial failures in clusters with less complexity & cost.• Allows to avoid communication and disk activity or to postpone it until a

convenient time.• Greatly simplifies the implementation of fault-tolerance and availability.

Transformational Proxies –• Is placed between the Client & Server that transforms Internet Content

on-the-fly.• The transformed Content is Base Data.• If any data from database i.e. Acid Data.

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TACC : Programming Model for Internet Services how..

T – Transformation Includes Filtering, Transcoding, Re-rendering, encryption & compression.

i.e. format changes , resolution, size, quality, color map, language, etc.

A – Aggregation Collects data from various sources as search engines & collates it in a pre-specified way.

C – Customization Per-user preference database that allows workers to tailor their output. Key strength – app preferences are automatically delivered to the users.

C – Caching Caches both transformed data and original content. i.e. post-transform, post-aggregation, and WAN content.

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Cluster-Based TACC Scalable Service Architecture ::

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TACC Applications :: TranSend • A scalable Transformation & caching proxy.

• Performs lossy Web Image compression on the fly.

• Accepts servers' existing pages and allows each user to select how much quality he is willing to sacrifice to improve loading speed.

• Runs on a cluster if SPARCstation 19 & 20 machines, interconnected by switched 10 Mb/s segment.

• Extensibility – adds support for new datatypes.

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Test of Scalability & Load Balance :: TranSend…

• Fig 8 – cluster figs• Table 2 – cluster figs

Worker queue lengths observed overtime as the load presented to the system fluctuates.

Measured by 15 SunSPARC Ultra-1 workstations connected by 100Mb/s Ethernet Card & a HTTP trace back used by 25,000 UC Berkley dialup IP users.

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Fault Tolerance & Crash Recovery :: TranSend…

• Resilience against crashes is via process-peer fault tolerance. (The Manager , Distiller & Front Ends)

• Crash Recovery is seamless.

• Secondary Manager takes over the Primary Manager. ( Manager Stub)

• Broken Connections, Timeouts or loss of Beacon are used to infer component failures.

– The manager reports the distiller failures to the manager stubs, they update their caches of where distillers are running.

– The manager detects & restarts a crashed front end.– The Front End detects & restarts a crashed Manager.

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Cache Partition Performance :: TranSend…

• Collection of Harvest caches considered as siblings.• All cache nodes are seen as one Virtual Cache, (Uses hashing key space to separate each cache, rehashes when added or deleted.)

to improve scalability and fault tolerance.• All siblings are requested on each request.• Nodes manage BASE data.

Statistics ::• A small cache of 400Mb can reduce the load on the network infrastructure by 40%.• The Average Cache Hit takes 27ms to service.• An Average of serviced Hits are 37 requests per Second.• A Miss Penalty varies from 100ms to 100 seconds.• 95% of all cache Hits take 100ms to service. (includes Network & OS Overhead).

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TranSend & HotBot :: Differences

HotBot HotBot -- Search Engine. -- Search Engine.

• An Aggregation server.An Aggregation server.• Performs millions of Performs millions of queries. queries. • Runs on single ,multiple-Runs on single ,multiple-CPU SPARCstation server CPU SPARCstation server nodesnodes• Front Ends runs 50-80 Front Ends runs 50-80 threads per node.threads per node.• workers partition the workers partition the database for Load Balance.database for Load Balance.

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Other TACC Applications…

Top Gun Wingman ::

• A Graphical Web Browser for 3com Palm Pilot.

• Image worker delivers 2-bit-per-pixel images.

• Html Parser ensures that not more than 32KB data is delivered.

• TACC workers transform data given the knowledge of the clients dimensions, image format, font metrics.

• Special Worker, that delivers data in AportisDoc format (e-book format).

• Replaced HTTP with simpler datagram oriented protocol based on Application level Framing.

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Other TACC Applications…

Top Gun Mediaboard ::

• Electronic shared whiteboard application for Palm Pilot.

• Remote collaboration and for enhancing meetings and presentations

• Is an IP Multicast group which sends messages to itself.• SRM is the reliable communication protocol.• RMX has complete knowledge of the clients hence makes the needed transformation.• RMX coverts the entire SRM data into unicast TCP stream that the client can handle.

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Network of MBone :: Mbone screen for a Palm Pilot ::

Wayne State University’s MediaBoard is at -- http://elearning.wayne.edu

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Mediaboard screen on a regular PC ::

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Conclusion ::

• End – End latency is reduced.• The average cache Hit takes 27ms for 37 requests & a Miss takes

100ms – 100 sec for 1 request.• Is Extensible – creates workers and chains them easily.• Faster communication and better modem access even at low

bandwidth by distilling image files.

References :: • Cluster Based Scalable Network.• A Network Architecture for Heterogeneous Mobile Computing.• Top Gun MediaBoard -- A Shared Whiteboard for PDA's.• Reducing WWW Latency and Bandwidth Requirements .

Questions Please !!!

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Thank You.