A FRAMEWORK FOR POLICY-BASED SLA MANAGEMENT

OVER WIRELESS LAN

Noh-sam Park, Gil-haeng Lee

Electronics and Telecommunications Research Institute

Keywords: Service Level Agreement, SLA, SLM, QoS.

Abstract: With the evolution of wireless networks, the wireless community

has been increasingly looking for a

framework that can provide policy-based SLA management. In this paper we first construct such a

framework and then describe how SLA-based control can be used to achieve QoS in wireless environment.

We provide a common generic framework capable of components to interwork via XML. The proposed

framework offers effective WLAN QoS control and management using client-side agent.

1 INTRODUCTION

In an environment of fast changing technologies and

uncertain business tendencies, network operators,

constructors, and organizations face new challenges

to keep up with the increasing needs of ubiquitous

network. This is a major driver for the technological

development of wireless networks.

A service level agreement (SLA) is a formal

cont

ract between a service provider and a subscriber

that contains detailed technical specifications called

service level specifications (SLSs). An SLS is a set

of parameters and their values that together define

the service offered to a traffic stream in a network(F.

De Turck, 2001).

An SLA can be defined and used in the context

f any industry and is used to specify what the

customer could expect from the provider, the

obligations of the customer as well as the provider,

performance, availability, and security objectives of

the service, as well as the procedures to be followed

to ensure compliance with the SLA.

Some work has been done in defining SLAs for

traditional IP

networks(Verma, 2004). Because

wireless LAN(WLAN) technologies belong to an

emerging domain, until now, no SLAs have been

defined that are adapted to the specific needs of

WLAN.

This work focuses on defining these SLAs

ecifically adapted to the relationship between W

LAN operators and their diverse clients. Moreover,

we propose a policy-based SLA management

framework that provides effective QoS control and

management.

The remainder of this paper is structured as

llows. Section 2 will discuss related works on SLA

management over other networks. After describing

the metrics related WLAN in section 3, we will

explain a framework of SLA Management system

for WLAN environment in section 4. Finally we’ll

summarize our work and sum up the conclusions

from this study

2 SLA MANGEMENT IN

NETWORK SERVICES

The importance of SLA has been recognized and

widely accepted by ASP’s, ISP’s, etc. In particular,

this section reviews features of various SLA

management systems for network services.

The work for service level agreement in optical

net

works has been done(Fawaz, W, 2004). It

proposes a service level agreement applied to the

optical domain (O-SLA), which is expected to be the

near- and long-term network technology thanks,

among other things, to the great bandwidth capacity

offered by optical devices. After an exposition of the

rationale behind an optical SLA, parameters that

could be included in this O-SLA, as well as their

values for four classes of services, are proposed.

173

Park N. and Lee G. (2005).

A FRAMEWORK FOR POLICY-BASED SLA MANAGEMENT OVER WIRELESS LAN.

In Proceedings of the Second International Conference on e-Business and Telecommunication Networks, pages 173-176

DOI: 10.5220/0001409401730176

 SciTePress

In traffic and performance parameters for O-SLS,

it describes the followings.

– Connection setup time

– Service availability and resilience

– Routing constraints(Stability, Route

Differentiation, Confidentiality, Distance,

Classes of Service)

– Service performance guarantees

– Traffic conformance and excess treatment

Furthermore, some values for O-SLS parameters

are proposed for four classes of service (from

platinum to bronze, excluding best effort traffic for

which no guarantee at all is provided).

Different client (wavelength or subwavelength)

and service types (from leased wavelength to

bandwidth on demand) are distinguished when

necessary.

In (Verma, 2004), it provides an overview of

service level agreements in IP networks. It looks at

the typical components of an SLA and identifies

three common approaches that are used to satisfy

SLAs in IP networks. It describes the components of

SLAs :

– A description of the nature of service to be

provided.

– The expected performance level of the service,

specifically its reliability and responsiveness.

– The procedure for reporting problems with the

service.

– The time frame for response and problem

resolution.

– The process for monitoring and reporting the

service.

– The consequences for the service provider not

meeting its obligations.

– Escape clauses and constraints.

Three common approaches are used to support

and manage SLAs. The first approach takes the

model of an insurance company toward monitoring

and supporting SLAs. The second approach uses

configuration and provisioning techniques to support

SLAs within the network. The third approach takes a

more dynamic and adaptive approach toward

supporting SLAs.

The implications of using the approaches in the

context of a network service provider, a hosting

service provider, and an enterprise are examined.

While most providers currently offer a static

insurance approach toward supporting SLAs, the

schemes that can lead to more dynamic approaches

are identified.

Core Network

Router

AAA Server

Switch

Figure 1: Wireless LAN

3 SLA ISSUES IN WIRELESS LAN

Access to data services via wireless LANs at private

and public hot spot sites is becoming

commonplace(Acharya, 2004). Wireless access

solutions based on the IEEE 802.11 family of

standards are mushrooming in many different places

where people congregate, like airports, hotels, cafés,

train stations, and parks. These public congregation

areas constitute connectivity islands, or hot spots,

where broadband access services can be provided

wirelessly to one’s personal devices, such as

notebook computers and PDAs.

As usual, during the communication session at a

hot spot area, the following phases are experienced:

– Personal device configuration : During this

phase, user devices are properly configured and

permitted access to the hot spot site’s intranet.

– User Authentication : During this phase, users

provide identification credentials to the system.

These could be provided explicitly, where a user

explicitly provides personal information, or

implicitly, where a pointer to a stored log-on

profile is provided by the users or their devices.

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Network

Provider

Client

r-SLA

- Order Manage

- XML Conversion

- Data Manage

- Daemon Job

- Metrics Manage

- Monitoring

- Messaging

- Presentation

- Policy Manage

Agent

Figure 2: Framework of SLMS

– Service access control : During this phase, the

intelligence configures the hot spot site’s intranet

to allow users to access only services within the

service tier they have selected.

– Session management : This is a supervisory

activity that keeps track of user sessions

including their service tier selections, the

duration of accessing services at a selected tier,

or traffic statistics.

We derive the SLA metrics related WLAN from

its inherent properties. In this environment, typical

clauses related to performance and availability may

look like the following.

– The average delay measured monthly between

the hot spot and router in core network should be

less than 200 ms.

– The customer will not have unscheduled

connectivity disruption within hot spots

exceeding 5 min.

– The connection setup time, representing the time

between service ordering and service availability,

should be less than 30 seconds.

4 FRAMEWORK FOR SLM

OVER WLAN

The framework for policy-based SLA

management(SLMS) supports the QoS control in

WLAN environment. The framework incorporates

two key ideas: a generalized monitoring concept,

and a contract negotiation and translation feature for

all the components. It includes automation of r-

SLAs(retail SLAs), not w-SLAs(wholesale SLAs).

4.1 Components

SLMS framework proposes the architecture that

partitions system functionalities into five major

components : an access manager, a data manager, a

monitoring manager, a user interface manager, and a

Agent(Fig. 2).

Access Manager (AM) : The AM is the entity

that receives the information related service opening,

trouble and performance. It is responsible for

translating the information into XML format,

pushing the translated XML document into the

message queue.

Data Manager (DM) : The DM reads the XML

data from the message queue, classifies the data

according to the SLA metrics. As the DM manages

the information in the database, it can response to

the UM the retrieve and save the SLA related data.

Monitoring Manager (MM): The MM plays

the important role of monitoring the violation of

SLA metrics. Periodically it monitors whether QoS

violates the SLAs. If the MM detects the violation, it

sends the violation information through the message

queue.

User interface Manager (UM): The UM

interacts with the operators, and provides the variety

of data including the alert messages. Operators can

configure the policy of SLM such as the execution

of monitoring or not.

Agent: The client-side agent collects the

performance data by polling the access router at the

core network periodically. And it records the

connection setup time per session. The agent sends

those information to the AM.

The combined role of these components is to

efficiently manage SLA of the service, present the

QoS information, and appropriately refund if the

violation of SLA happens.

4.2 Prevention of the SLA Violation

Monitoring is the core function of our framework to

prevent the violation of SLA. We developed the

monitoring function reacting not only when an SLA

is violated, but also before imminent SLA violations.

Our system has the monitoring component which

A FRAMEWORK FOR POLICY-BASED SLA MANAGEMENT OVER WIRELESS LAN

175

checks the threshold at first, and compares the

metrics value secondly. The threshold is the value

which can be alerted to the operator by sending the

‘warning’. If the operator receives the warning

message from the system, he/she reviews the details,

and can take an action to prevent the violation of

SLA.

The MM has the following monitoring

functions : service opening, trouble, and

performance monitoring. At the system initiation

stage, the MM creates three threads in order to

monitor the categorized metrics.

At the defined thread invoke time, the MM

periodically creates threads. Threads retrieve the

monitored data, threshold and metric. Firstly, the

MM thread compares the data with the threshold. If

the current value is greater than the threshold, the

‘warning’ message is sent to the AM via XML

format. The MM thread will detect the violation of

SLA by comparing the issued time with metric value.

If the violation event occurs, the ‘violation’ message

will be sent, and the violation details is recorded in

the database through the DM. Finally, the threads

are disposed after execution.

Policy-based monitoring can be accomplished by

configuring the various preferences. The interval of

monitoring can be changed by using the UM. If the

operator changes the monitoring interval, the UM

sends the message to the MM. The MM receives the

event, and changes the thread invoke time.

Furthermore, the operator can have the metrics

monitored or not. Using the UM, the operator can

configure whether the metrics are monitored or not.

If the metric is set not to be monitored, the MM will

not execute the monitoring function. But if the

history of warning and violation is recorded in the

database, and can be retrieved via the UM.

5 CONCLUSIONS

We propose a form of architecture for an SLA

Management System using web service. We first

explore the SLA-related works in various network

environments. As describing the characteristics of

WLAN, we issued the metrics related WLAN. A

framework for SLM over WLAN are introduced

with detailed description of its components. Our

system has the capability to manage the SLA from

the service opening to the service termination. By

using the client-side agent which collects the

network performance information, we can easily

manage the SLA, and control the QoS.

According to the implications of the research,

future work has been conducted to interwork

Operation Supporting Systems (OSSs) such as the

refund system and NMS.

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