INFORMATION AND COMMUNICATION SYSTEMSMERIT 2008 Research SymposiumMelbourne Engineering Graduates Look to the Future

System Architecture

An internetworking of CDNs is formed by a set of autonomous CDNs, which cooperate through a mechanism that provides facilities and infrastructure for cooperation in order to virtualize multiple providers.

Architecture of a system to assist the creation of peering CDNs is shown in Figure 1.

Such a constellation permits flexible resource sharing and dynamic collaboration between autonomous CDNs in the form of a peering arrangement.

The ‘resource sharing’ approach in the peering CDNs model endeavours to balance a CDN’s service requirements against the high costs of deploying customer-dedicated and therefore over-provisioned resources.

It is anticipated that proper management and cooperation will enable a CDN to avoid violating SLAs even when the service demands could not have been predicted ahead of time.

Mukaddim Pathan and Rajkumar BuyyaGRIDS Laboratory, Department of Computer Science and Software EngineeringEmail: raj@csse.unimelb.edu.au; Website: http://www.gridbus.org/cdn

iCDN – Internetworking of Content Delivery Networks

Figure 1: Abstract architecture for the creation of peering CDNs.

Results

Key Reference

Pathan, M., Vecchiola, C., and Buyya, R. Load and proximity aware request-redirection for dynamic load distribution in peering CDNs. In Proc. of CoopIS’08, Monterrey, Mexico, 2008.

Peering CDNs Formation

The process of peering negotiation is triggered on traffic surges under degenerated load conditions (e.g. flash crowds).

Figure 2 illustrates the typical steps to create a peering arrangement between CDNs.

Load and Proximity Aware Request-Redirection

A dominant factor for the success of peering between CDNs is to perform load distribution to handle highly skewed loads. Our approach for dynamic load distribution adopts a request-redirection mechanism by taking traffic load and network proximity into account.

In our approach, load indices are obtained through an asynchronous feedback mechanism and network proximity is measured using a pinger logic with low messaging overhead.

Overview

Content Delivery Networks (CDNs) emerged to provide fast and reliable Web access services by distributing content to edge servers located close to end-users. To operate effectively a CDN is required to either over-provision its capacity or to harness external resources on demand.

Cooperation between CDNs can reduce costs with over-provisioning and provide users with high quality services in a global scale. This collaboration, termed as peering between CDNs, can be short-term wherein CDNs operate to handle flash crowds, or long-term in which they explore the delivery of specialized services.

Aim

The proprietary nature of existing CDNs means that they are closed and do not naturally cooperate. Finding ways for distinct CDNs to coordinate and cooperate with other CDNs is necessary to achieve better overall service, as perceived by end-users, at lower cost.

This research aims to provide a means for distinct CDNs to coordinate and cooperate with other CDNs, by investigating and developing

an architecture for an open and decentralized system to support effective internetworking between CDNs, which is achieved through a peering arrangement;

protocols for service delivery in a cooperative environment of CDNs;

economic models for an effective content replication policy; and

policies for autonomic management of service level through resource negotiation in an on-demand basis.

Web User2

Request is served by local surrogate server or origin server (on cache miss)

User request of CDN 2 is served by external surrogate server from

CDN N

`

`

Web User1

`

Web Users

User request of CDN 1 is served by external surrogate server from

CDN 2

CDN N

Request Routing System

Web Server

PA

Request Routing System

CDN 2

SR

PR

Mediator

RRS

Origin Server

Web Server

PA

Peering CDNsOverlay

Web Server

Web Server

Web Server

Web Server

Global SR

PR

Mediator

RRS

Web Server

CDN 1

Web Server

Peering Agent (PA)

Origin Server

Hotspot generated

(3) Determine service requirements and policies for resource negotiation(5) Acquire

resources from peered CDNs

(4) Contact PAs of other CDNs

(5) Store negotiated

policies

(4) Request to create a peering of CDNs

Client requests

WS

WS

WS

(1) Initialization request

(2) Obtain service and

policy information

PA

PRPA

PA

PA

SR instance

Mediator instance

(5) A peering arrangement

formed

Figure 2: Typical steps for creating a peering arrangement.

Properties Parameters Description

Activation Activation trigger (when)

Asynchronous (on CDN server request)

Activation decision (where)

Distributed (Gateway redirection upon requests from distributed servers)

Implementation Status information Traffic load (correlated with server response load = utilization * capacity)

Alarm (Asynchronous feedback)

Redirection policy

Server selection (how)

Minimize redirection cost from available server list (mapping of overloaded and underloaded server lists)

Redirected entities (what)

User requests

Table 1: Significant properties of the request-redirection scheme

0

0.2

0.4

0.6

0.8

1

Server 1 Server 2 Server 3 Server 7 Server 4 Server 5 Server 6 Server 8 Server 9 Server10

CDN 1 CDN 2 CDN 3 CDN 4

CDN Servers

Uti

liza

tio

n

No redirection

LD_RR

LD_PRR

LD_LL

LD_minCost

Figure 4: Average utilization of the primary CDN in each scheme.

Figure 5: Comparison of the request-redirection schemes.

Figure 3: Server utilization in different request-redirection schemes.