ACME a new Architecture for Content delivery in the Mobile - - PowerPoint PPT Presentation

ACME

a new Architecture for Content delivery in the Mobile Environment Oscar Santolalla Blerta Bishaj

Agenda

• Introduction
• ACME
• ACME in CDMA Networks
• ACME Director
• Conclusions

Introduction

• Increasing use of web access from mobile devices in

2.5G and 3G mobile networks

• Mobile networks are characterized by an error-prone

air interface, link-layer retransmissions, latency

Introduction

Content Delivery in wireline internet (1)

• Network scaling
• web caches
• Content Delivery Networks (CDNs)

It achieves:

• reduced load at the origin server
• distributed origin server
• reduced latency

Introduction

Content Delivery in wireline internet (2)

• End-system acceleration
• server farms and balance loader
• Content and protocol optimization
• eliminate redundancy
• content adaptation, like compression
• protocol optimization, like TCP connections in HTTP

Introduction

Content Delivery in wireless internet

Problem: the air interface is a bottleneck

• shields internet apps from wireless network specifics
• already used by WAP
• ACME is a flavour of this architecture

Solution: the split-proxy architecture

Agenda

• Introduction
• ACME
• ACME in CDMA Networks
• ACME Director
• Conclusions

ACME

Architecture for Content delivery in the Mobile Environment

• exploits user interest correlation – push content
• ther users request
• assumes unlimited-capacity cache
• trades local storage for latency reduction and

bandwidth efficiency

• each requested web object is broadcast to every

terminal

ACME

How it improves the performance

• increased hit ratio improves user experience

h – hit ratio N – terminals λ – Poisson rate of requests G – total load of the bandwidth qr – retransmission probability

E[TB] = 2 + eG -1 qr E[TB] = ( 2 + ) * (1 - h) exp(GM) -1 qr 1 – some requests are served immediately 2 – faster medium access due to reduced medium contention 3 – the higher the h, the better the performance

Baseline ACME

1 – at least 2 timeslots

Agenda

• Introduction
• ACME
• ACME in CDMA Networks
• ACME Director
• Conclusions

ACME in CDMA networks

Major benefit is reduced interference. Assuming A is an ACME-enabled terminal:

– Signals sent to B and C will reach A with very low Signal-to-interference ratio (SIR)

so its content can be decoded with low error rates

– Consequently the content is cached by A – A will improve its hit ratio and reduces bandwidth usage

Base station

A B C

• Near-far problem: Signals

for farther terminals are

• verwhelmed by other

nearby signals.

• Solution: Terminal power

control

Agenda

• Introduction
• ACME
• ACME in CDMA Networks
• ACME Director
• Conclusions

ACME Director

• ACME Director is a server that uses interest correlation information to

perform selective multicast for every content request.

• Director’s Objective: To achieve high hit ratio with a small multicast group

ACME Director

How does ACME Director work?

• On-demand broadcast is too power-consuming for mobile devices. ACME

rather uses selective multicast.

• Edge caching lies on the fact that different users have overlapping interest

in content.

• The algorithm the ACME director uses
• Matrix of P( j | i ) , where p(j|i) is the probability that user j will access a web
• bject previously accessed by user i.
• multicast factor ( α )

ACME Director

Director Effectiveness (1) Objective of simulations: evaluate caching performance and terminal

power consumption relation Director Parameters:

• Multicast factor α:
• α=0 is unicast (client caching)
• α=1 is broadcast (full edge caching), every terminal receives a copy of the

requested content

• Director effectiveness E( α ), measures ACME Director’s performance and is

dependent on both α and hit ratios.

• Relative push group size s( α ), normalized number of terminals receiving a

pushed object for a defined α. It is proportional to average terminal power consumption.

ACME Director

Director Effectiveness (2)

Results:

• s( α ) = 0.7 – 6 %

=> Efectiveness = 50%

• s( α ) near to 20 %

=> Efectiveness = 80%

• Relative push group size s(α)

does not increase proportionally to the general user group size, because it keeps only the users with the closest interest.

* UCB, BU, NLANR are web traces collected of users with wireline proxy connections

Relative push group size ( terminal power consumption) Effectiveness (caching performance)

• ACME also improves radio resource management. In case of increased

network utilization, the multicast can be spread more, to reduce the terminals’ need to use the network bandwidth in the future Conclusion: It balances bandwidth-delay-battery

• Examples:
• Director pushes more content if the phone is

connected to AC power

• Director stops pushing if terminal has fallen

certain threshold

ACME Director

Refinements to Director

Agenda

• Introduction
• ACME
• ACME in CDMA Networks
• ACME Director
• Conclusions

Contemplating ...

• In the web, we often follow link paths – false interest correlation
• Table Maintenance

huge tables to maintain according to ACME, little gain from increasing the group size

• Is user-to-user interest correlation a good guess?

ACME not clear about how to buid the table Maybe user-to-interest correlation? User-to-user is misleading and inaccurate

• Web browsing not yet very successful with the mobile hosts

Maybe notification nature in the future?

• Who pays for the pages ACME multicasts?

Possible solution?

• Wise cell projection, to discover profiles

stadiums theatres universities

• Maybe, notify the users about events

according to their profiles

Conclusions

About the content delivery scenario:

• Air interface is the bottleneck of mobile web user experience
• It is difficult to characterize and quantify correlation interest

because of many factors

About ACME itself:

• It adds a new dimension in radio resource management
• We think ACME makes false or too-good assumptions
• Not likely to be deployed any soon

Questions?