nwachi-ikpor, juliana o.€¦ · comparison of asynchronous transfer mode (atm) netw ork cell...

TRANSFER MODE (ATM) NETWORK CELL

Ebere Omeje

1

NWACHI- IKPOR, JULIANA O.

PG/M.ENG/10/57771

COMPARISON OF ASYNCHRONOUS


ROUTING ALGORITHMS

FACULTY OF ENGINEERING

DEPARTMENT OF ELECTRONIC

ENGINEERING

Ebere Omeje Digitally Signed by: Content manager’s Name

DN : CN = Webmaster’s name

O= University of Nigeria, Nsukka

OU = Innovation Centre

IKPOR, JULIANA O.

COMPARISON OF ASYNCHRONOUS



DEPARTMENT OF ELECTRONIC

Digitally Signed by: Content manager’s Name

Webmaster’s name

O= University of Nigeria, Nsukka

2

TITLE PAGE

COMPARISON OF ASYNCHRONOUS TRANSFER MODE (ATM)

NETWORK CELL ROUTING ALGORITHMS

BY

NWACHI-IKPOR, JULIANA O.

PG/M.ENG/10/57771

DEPARTMENT OF ELECTRONIC ENGINEERING


UNIVERSITY OF NIGERIA NSUKKA

DECEMBER, 2015.

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APPROVAL PAGE

COMPARISON OF ASYNCHRONOUS TRANSFER MODE (ATM) NETW ORK

CELL ROUTING ALGORITHMS

BY

NWACHI-IKPOR, JULIANA O.

(PG/M.ENG/10/57771)

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE

AWARD OF MASTER OF ELECTRONIC ENGINEERING (TELECOMMUNICATION

OPTION) IN THE DEPARTMENT OF ELECTRONIC ENGINEERING, UNIVERSITY OF

NIGERIA, NSUKKA.

____________________________ ______________________

NWACHI-IKPOR, JULIANA O . DATE

(STUDENT)

____________________________ ____________________ PROF. C.I.ANI DATE (SUPERVISOR)

__________________________ _____________________

EXTERNAL EXAMINER DATE

___________________________ _____________________

DR. M.A AHANEKU DATE

(HEAD OF DEPARTMENT)

___________________________ _____________________

4

PROF. E.S. OBE DATE

(CHAIRMAN, FACULTY POSTGRADUATE COMMITTEE)

CERTIFICATION

This is to certify that NWACHI-IKPOR, JULIANA O, a postgraduate student of the

department of electronic engineering with registration number PG/M.ENG/10/57771 has

satisfactorily completed the requirement for the award of Master of Engineering

(M.ENG) in Electronic Engineering.

____________________________ ____________________________

PROF. C.I.ANI DR. M.A AHANEKU (SUPERVISOR) (HEAD OF DEPARTMENT)

___________________________

PROF. E.S. OBE

(CHAIRMAN, FACULTY OF ENGINEERING POSTGRADUATE COMMITTEE)

5

DECLARATION

I, NWACHI-IKPOR, JULIANA O, a postgraduate student of the Department of

Electronic Engineering, University of Nigeria, Nsukka declare that the work embodied in

this thesis is original and has not been submitted by me in part or full for any other

diploma or degree of this or any other university.

____________________________ ______________________

NWACHI-IKPOR, JULIANA O DATE

6

DEDICATION

This work is dedicated to God Almighty for His infinite mercy and guidance towards me

throughout this program.

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ACKNOWLEDGEMENT

I am grateful to God Almighty for his sustenance, guidance and protection throughout the

period of my training.

I also wish to express my profound indebtedness to my supervisor, Prof. C.I. Ani, who

supervised me at all stages of the work. His achievement and attitude have inspired me in

many ways and have led me to new ideas for solving the problems I have faced. He never

denied me his fatherly advice and guidance which helped me to succeed in this work.

I will remain grateful to my lecturers and the entire staff of the Department of Electronic

Engineering, University of Nigeria, Nsukka, most especially, Prof. C. I. Ani, Prof. O.U

Okparaku, Prof. C.C. Osuwagu, Prof. A.N Nzeako, Dr. M.A.Ahaneku and Dr. I.Oge.

Their advice and constructive criticisms contributed in mo mean measure to the

successful completion of my programme.

There are many people who have made this dissertation possible; without them it would

have been impossible for me to finish it. Though it is difficult to name them without

omitting someone, I am happy to acknowledge them here, and I apologize if I have

omitted anyone. My endless thanks goes to my husband Sir Paul Ikpor Nwachi whose

constant love, care, encouragement and understanding guided me throughout the period

of my study and to my children and in-laws. I say thank you for all your love, financial

and moral support throughout this study was the engine that kept me going.

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I would also wish to express my sincere appreciation to all the members of my class,

victor, George, Iyke, Essein and my little friend and daughter Ify. To my Boss, Mr. E.U

Ezeorah and colleagues, a very big thanks to you all. Without your generous help,

continuous encouragement and moral support, this work could not have been complete.

9

ABSTRACT

The demand of telecommunication service is increasing rapidly. Asynchronous Transfer Mode

(ATM) network as a connection-oriented technology with fixed-size cell length reduce the

complexity of networks and improves the flexibility of traffic performance. ATM network

achieves this simplicity by the introduction of virtual path (VP) concept which helps to simplify

traffic control and resource management, by bundling several virtual channels (VCs) together

that have a common path, thus decreasing the amount of entities to be managed. This work

presents cell routing in VP-based ATM network. Network routing has to do with forwarding of

calls from one end to another while determining feasible paths from each source to destination.

The routing techniques can be implemented both in connection-oriented network and

connectionless networks. However, proper choice of routing algorithm is difficult because its

performance depends on the type of network. Two routing algorithms were investigated and

analyzed. These routing algorithms are: Deterministic Reservation Least Loaded Routing

Technique (LLR_D) and Deterministic Reservation Least Loaded Routing Algorithm with

Deterministic VP capacity sharing (LLR_VP). These algorithms were presented using flowcharts

and simulated in MATLAB environment. The quality of service (QoS) parameters such as delay,

utilization, and loss were compared with traffic intensity. A typical ATM model was developed

and these two algorithms were deployed and analyzed on this network. From the results

obtained, it is seen that the LLR_VP routing algorithms has the least delay, experiences the least

loss and better utilizes the network.

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TABLE OF CONTENT

Title Page…………………………………………………………………………………………..i

Approval Page………………………………………………………...…………………………..ii

Certification……………………………………………………………..………………………..iii

Dedication……………………………………………...…………………...………………...…..iv

Acknowledgement………………………………………………………..…………………….…v

Abstract………………………………………………………………..……………………….....vi

Table of Contents…………………………………………………...………………………...….vii

List of Figures……………………………………………………...…………………………....viii

List of Tables………………………………………………………….……………………….....ix

List of Abbreviations………………………………………………….………………………….x

CHAPTER ONE: INTRODUCTION

1.0 Background of Study -----------------------------------------------------------------------1

1.1 Problem statement --------------------------------------------------------------------------3

1.2 Objectives of the Research-----------------------------------------------------------------3

1.3 Scope of the Research----------------------------------------------------------------------4

1.4 Research Methodology --------------------------------------------------------------------4

1.5 Organization of the work ------------------------------------------------------------------4

CHAPTER TWO: LITRETURE REVIEW

2.0. Introduction ----------------------------------------------------------------------------------5

2.1 Brief overview on principles and operations of ATM Network----------------------5

2.2 Asynchronous Transfer Mode (ATM)----------------------------------------------------6

2.3 BISDN/ATM Protocol Architecture------------------------------------------------------9

2.3.1 ATM Adaptation Layer-------------------------------------------------------------------11

2.3.2 ATM Layer --------------------------------------------------------------------------------12

2.3.3 ATM Physical Layer----------------------------------------------------------------------12

2.4 Cell Network ------------------------------------------------------------------------------ 13

2.4.1 Structure of an ATM cell---------------------------------------------------------------- 14

11

2.5 ATM Network Traffic ------------------------------------------------------------------- 16

2.5.1 Network Traffic parameters -------------------------------------------------------------16

2.5.2 Traffic Flow Control ----------------------------------------------------------------------16

2.6 Quality of Service Parameters -----------------------------------------------------------17

2.7 ATM Connection Setup-------------------------------------------------------------------19

2.7.1 Virtual Connection ------------------------------------------------------------------------20

2.8 Statistical Multiplexing-------------------------------------------------------------------21

2.9 Connection Admission Control----------------------------------------------------------22

2.10 Traffic Model ------------------------------------------------------------------------------22

2.11 Fluid Flow Model ------------------------------------------------------------------------23

2.12 Virtual Path Concept ---------------------------------------------------------------------23

2.13 General Overview of Network Routing------------------------------------------------27

2.13.1 Routing Metrics --------------------------------------------------------------------------29

2.13.2 Types of Routing Schemes--------------------------------------------------------------30

2.13.2.1 Static Routing -----------------------------------------------------------------------------30

2.13.2.2 Dynamic Routing--------------------------------------------------------------------------30

2.13.2.2.1 Types of Dynamic Routing---------------------------------------------------------------32

2.14 Routine in ATM Network----------------------------------------------------------------35

2.15 Related Works------------------------------------------------------------------------------36

2.16 Conclusion ---------------------------------------------------------------------------------39

CHAPTER THREE: MODELING

3.0 Introduction --------------------------------------------------------------------------------40

3.1 The Network Architecture----------------------------------------------------------------41

3.2 The Network Model-----------------------------------------------------------------------42

3.3 Routing Algorithms for Comparison----------------------------------------------------43

3.3.1 Deterministic Reservation Least Loaded Routing Technique (LLR_D)-----------43

3.3.2 `Deterministic Reservation Least Loaded Routing Algorithm with Deterministic

Virtual Path Capacity Sharing (LLR_VP)----------------------------------------------46

3.4 Conclusion ---------------------------------------------------------------------------------46

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CHAPTER FOUR: RESULT AND ANALYSIS

4.0 Introduction --------------------------------------------------------------------------------47

4.1 Simulation Model Validation ------------------------------------------------------------51

4.2 Model Simulation -------------------------------------------------------------------------52

4.3 Simulation Result -------------------------------------------------------------------------53

4.3.1 Cell Loss Rate against Traffic Intensity For LLR_D And LLR_VP Algorithms for

the Entire Network -----------------------------------------------------------------------53

4.3.2 Server Utilization against Traffic Intensity for LLR_D and LLR_VP Algorithm

for the Entire Network.--------------------------------------------------------------------55

4.3.3 Cell delay against Traffic Intensity for LLR_D and LLR_VP Algorithms for the

Entire Network ---------------------------------------------------------------------------56

4.3.4 VP Utilization for LLR_D and LLR_VP Algorithms --------------------------------58

CHAPTER FIVE: SUMMARY, CONCLUSION AND RECOMMENDATIO N

5.0 Introduction---------------------------------------------------------------------------------60

5.1 Conclusion ---------------------------------------------------------------------------------60

5.2 Recommendation--------------------------------------------------------------------------60

5.3 Contributions to Knowledge ------------------------------------------------------------60

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REFERENCES

ACRONYMS

ACM Access Control Machine

ATM Asynchronous Transfer Mode

AVR Available Bit Rate

BISDN Broadband Integrated Digital Service

BRA Basic Rate Access

CAC Call Admission Control

CBR Constant Bit Rate

CCITT International Telegraph and Telephone Consultative Committee

CLP Cell Loss Priority

CMT Connection Management Mechanism

CP Complete Partitioning

C-PLAN Control Plane

CRC Cyclic Redundancy Check

CS Complete Sharing

CSMA/CD Carrier Sensing Multiple Access/ Collision Detection

DA Destination Address

FDDI Fiber Distributed Digital Interface

FDM Frequency Division Multiplexing

FXS Foreign Exchange Station

GFC Generic Flow Control

GFC Generic Flow Control

GM Guaranteed Minimum

HDLC High Level Data Link Control

IDN Integrated Digital Network

ISDN Integrated Digital Service Network

ISP Internet Service Provider

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LLR_D Deterministic Reservation Least Loaded Routing Technique

LLR_VP ` Deterministic Reservation Least Loaded Routing Algorithm

With Deterministic Virtual Path Capacity Sharing

PDU Protocol Data Unit

PHY Physical Layer Protocol

PLCP Physical Layer Convergence Protocol

PRA Primary Rate Access

PRM Protocol Reference Model

PVCS Permanent Virtual Channel

QOS Quality of Service

SDM Space Division Multiplexing

SMDS Switched Multimegabit Data Service

SMT Station Management

TDM Time Division Multiplexing

TDS Time Division Switching

TR Trunk Reservation

UBR Unspecified Bit Rate

UNI User Network Interface

UNT User to Network Interface

UP Upper Limit

U-PLAN User Plane

VBR Variable Bit Rate

VC Virtual Cell

VP Virtual Path

VPI Virtual Path Identifier

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LIST OF FIGURES

Figure 2.1: ATM Network Interface -------------------------------------------------------------------7

Figure 2.2: ATM Physical Architecture Interface --------------------------------------------------- 8

Figure 2.3: BISDN Reference Model ------------------------------------------------------------------9

Figure 2.4: ATM Protocol Architure ---------------------------------------------------------------10

Figure 2.5: ATM Cell Structure -----------------------------------------------------------------------14

Figure 2.6: ATM Connection --------------------------------------------------------------------------20

Figure 2.7: Virtual Path Network ---------------------------------------------------------------------24

Figure 2.8: VP Borrowing model ---------------------------------------------------------------------25

Figure 2.9: Flow chart of operation of an LLR -----------------------------------------------------36

Figure 3.1: An ATM network architecture ----------------------------------------------------------41

Figure 3.2: Network model ----------------------------------------------------------------------------42

Figure 3.3: Deterministic Reservation LLR Routing Technique (LLR_D) ---------------------44

Figure 3.4: Deterministic Reservation LLR Algorithm with Deterministic VP Capacity

Sharing --------------------------------------------------------------------------------------45

Figure 4.1: Block diagram of an ATM Based Network -------------------------------------------47

Figure 4.2: MATLAB Simulink Simevent Model for an ATM Based Network ---------------48

Figure 4.3: Heterogeneous Traffic source module -------------------------------------------------49

Figure 4.4: Traffic pattern from the different sources ----------------------------------------------49

Figure 4.5: Transmission Facility Module (VP&VC) ----------------------------------------------50

Figure 4.6: Cell loss computation module -----------------------------------------------------------50

Figure 4.7: Blocking probability against traffic intensity for video-related model and enterprise-wide

network traffic model for a trunk capacity of 15Mbps ----------------------------------------51

Figure 4.8: Cell Loss Rate against Traffic Intensity for LLR_D and LLR_VP algorithms for

the entire network. ------------------------------------------------------------------------53

Figure 4.9: Server Utilization against Traffic Intensity for LLR_D and LLR_VP Algorithms

for the Entire Network. ------------------------------------------------------------------54

16

Figure 4.10: Cell delay against Traffic Intensity for LLR_D and LLR_VP Algorithms for the

Entire Network. ---------------------------------------------------------------------------56

Figure 4.11: VP Utilization for LLR_D and LLR_VP Algorithms --------------------------------57

LIST OF TABLES

Table 1: ATM Architectural Diagram --------------- ---------------------------------------------

10

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CHAPTER ONE

INTRODUCTION

1.0 BACKGROUND OF STUDY

The rapid increase in the demand of telecommunication services has brought much technological

advancements. Several new high speed technologies are available today such as Fiber

Distributed Data Line (FDDI), Integrated Service Digital Network (ISDN) Asynchronous

Transfer Mode (ATM) and Digital Subscriber Line (DSL) [1, 2]. These networks have the

capability of transmitting information at high speed, and offer a wide range of Quality of

Service (QoS) properties. These advancements have spur the users of the network to demand for

remote data access, web services, great computing capabilities regardless of user location and

mobility in use [3, 1]. As a result, higher quality and versatile communication infrastructure with

more bandwidth capable of handling such demands are needed.

Broadband offers new brand of services where data, voice and video commonly known as

multimedia are delivered together as one packet. It is often referred to as “high speed” access to

the internet because of its high rate of data transmission [4]. Broadband Integrated Service

Digital Network (B-ISDN) is a standard network that provides wide range of services. ATM

being begotten from B-ISDN is appropriate network that are capable of offering such high

graded services. It plays an important role in the modern communication technology because of

its ability to handle high-bandwidth, low delay, packet-like switching and multiplexing

technique and also support quality of services (QoS) guarantees.

ATM is considered to reduce the complexity of the network and improve the flexibility of traffic

performance [4]. The data in ATM network is sent out in form of fixed-size length called cells,

each cell in ATM consists of 53 bytes. Out of these 53 bytes, 5 bytes are reserved for the header

field which contains information used to route cells from source to destination through the fixed

path set up during connection phase. 48 bytes are reserved for data field. ATM integrates the

multiplexing and switching functions and allows communication between devices that operate at

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different speeds to co-exist by allowing different traffic types with varied traffic characteristics

and different QoS requirements to co-exist with Virtual Path (VP) subnetworks within ATM

network [5].

ATM as a connection oriented technique with fixed-size cells specifically established a fixed

channel between source and destination nodes, and appropriate resources e.g bandwidth and

buffer are reserved whenever data transfer begins. This means that a virtual connection of virtual

path has to be setup between two end-points across the ATM network prior to transfer of any

data. It consist of nodes (switches) interconnected by point-to-point or point-to-multipoint links

and supports services with different traffic characteristic and quality of service (QoS)

requirements. Virtual circuit systems ensure that packets sent are received in their correct

chronological order but required a route to be established through the network before

transmission of data takes place. The virtual connection is identified by the combination of a

virtual path identifier (VPI) and a virtual channel identifier (VCI). The current values of

VPI/VCI have a local significance on a given link and these values are part of ATM cell header.

Based on this, ATM cells are switched from one link to another. A standard has been adopted by

the two unions that support ATM technology- ITU and ATM Forum which standardized the

routing and signaling protocols for establishing point – to – point connections. Routing is a

process of computing the route to be used for the connection. That is, selecting path in a network

along which to send network traffic [1]. To compute efficient routes, the routing protocol must

provide a method of gathering and maintaining the topology information. The topology

information comprises the state information concerning the links and nodes in the network and

this information is very important in the computation of efficient route. Efficient route leads to

better utilization of the network resources. The route selected for the new connection will remain

in use for a potentially long period of time, the consequences of inefficient routing decision

affects the connection for as long as that connection remain active. Therefore, it is imperative

that path selection should be done carefully.

The user of ATM network is allowed to specify when setting up a call, the quality of service

(QoS) and the bandwidth parameter values that can guarantee for that call. To setup a new

connection, the source end-system must send a connection request into the ATM network across

it User-to-network (UNI) interface. The request will include the destination address, traffic

19

parameter, QoS requirement and other essential information for the network to find the path from

source to destination. A request is propagated through the network, setting up the connection as

it moves, until it reaches the destination end system. Call establishment consist of two

operations, the selection of route (path), and the setup of the connection state at each point along

the route. In selecting the route, the chosen route must appear to support the QoS and bandwidth

request based on the current available information of the network. Routing protocols do not

specify any single required algorithm for route selection. The call processing at each node along

the route confirms that resources requested are available, if not, crankback will occur which

causes a new route if any to be computed. Therefore, the final outcome is either the

establishment of route satisfying the request or total denial of the call.

This work is mainly based on the route selection option. As stated earlier routing is a process of

selecting paths in a network to send network traffic and is performed for many networks such as

telephone network (circuit switching), electronic data network (internet), and transportation

networks [6].

1.1 PROBLEM STATEMENT

In ATM network, it is expected that information sent from source node to destination node

should follow any path of its choice. Path selection in network routing must be fully specified.

This does not usually work that way since in a dynamic environment, there are problems

encountered when routing due to fluctuations in traffic load, link failures and topology changes.

The Virtual Path (VP) concept is implemented to allow management of virtual circuits (VCs),

thereby reducing the control cost of connections sharing common paths through the network into

one (single) and also simplify network architecture.

1.2 OBJECTIVES OF THE RESEARCH

The aims of this study include:

1. To compare two cell routing algorithms in ATM network namely: Deterministic

Reservation Least Loaded Routing Technique (LLR_D) and Deterministic Reservation

20

Least Loaded Routing Algorithm with Deterministic Virtual Path Capacity Sharing

(LLR_VP)

2. To know whether the reserved bandwidth on VP will affect the QoS requirements namely

(cell delay, cell loss rate and network utilization)

3. How to minimize the Cell Loss rate and cell delay and still maintain high throughput in a

VP based ATM network

1.3 SCOPE OF THE RESEARCH

This study is limited to two cell routing algorithm in ATM network. These algorithms will be

investigated with the following set of Quality of Service (QoS) parameters in view: cell delay,

cell Loss/blocking rate and network utilization. A typical ATM network will be modeled using

MATLAB Simulink, and the two set of algorithms for investigation implemented on it.

Simulation results generated will be analyzed using Microsoft Excel. t.

1.4 RESEARCH METHODOLOGY

To realize the objectives of this work, the following methodology was adopted:

i. Review of The ATM network architecture and implementation,

ii. Review of some cell routing algorithm in ATM network.

iii. Compare three routing algorithms from the review

iv. Develop flowcharts and models for implementing the proposed schemes

v. Simulate the model and obtain data

vi. Analysis in terms of performance metrics

1.5 ORGANISATION OF THE WORK

This work is further organized as follows: Chapter Two present an overview of ATM network

and review of literature was carried out. Chapter Three, presents the models and simulations of

the Cell Routing Algorithm. Chapter Four show result. In Chapter Five, conclusions will be

drawn and recommendations made.

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CHAPTER TWO

LITERATURE REVIEW

2.0 INTRODUTION

In chapter one, an introduction of the research topic, aim of the research, scope of the work, its

significance and research method employed has been discussed. This chapter will explore the

ATM Principles and Operations, ATM basic principles, BISDN/ATM architecture, Structure of

An ATM Cell,

2.1 BRIEF OVERVIEW ON PRINCIPLES OF OPERATIONS OF A TM NETWORK

Several network applications require higher bandwidth and generation of heterogeneous mix of

network traffic. ATM network has the capability of supporting a diversity of traffic efficiently

with various service requirements such as voice, video and data in one transmission and

switching fabric technology. It promised to provide greater integration of capabilities and

services, more flexible access to the network, and more efficient and economical service.

ATM network employs small, fixed-length packets called cells to ensure that the switching and

multiplexing function could be carried out quickly, easily, and with least delay variation and also

to support delay-intolerant interactive voice service.

ATM is a connection-oriented technology in the sense that before two terminals on the network

can communicate, they should inform all intermediate switches about their service requirements

and traffic parameters. In ATM networks, each connection is called a virtual circuit or virtual

channel (VC), because it allows the capacity of each link to be shared by connections using that

link on a demand basis rather than by fixed allocations. The connections allow the network to

guarantee the quality of service (QoS) by limiting the number of VCs. Typically, a user declares

key service requirements at the time of connection setup, declares the traffic parameters, and

may agree to control these parameters dynamically as demanded by the network.

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ATM was intended to provide a single unified networking standard that could support both

synchronous and asynchronous technologies and services, while offering multiple levels of

quality of service for packet traffic [7].

ATM network use negotiated service connection and as a connection-oriented cell network, it

provides services based on connections negotiated contract, that will satisfied the QoS

requirement. It is, all in all, simpler to give QoS in ATM systems than in the connectionless IP

networks [8,]. Quality of Service (QoS) in ATM networks is provided by specifying the

performance requirements for the requested logical connections along with the amount of

bandwidth needed to meet the pre-specified execution level and directing a Connection

Admission Control (CAC) to verify that the performance of the current connections are not

degraded by adding new connections. Unlike the traditional LANs which broadcast data across

the network without the acknowledgment of how the path is established or where the end user is

physically connected, resulting in large overheads of network management. [9]

2.2. ASYNCHRONOUS TRANSFER MODE (ATM)

An overview of ATM network has been done in chapter one. This chapter will concentrate on the

network architecture and Management, routing protocol and Routing algorithms of the network.

ATM network is review as the technology that presently exists and according to the physical

architecture illustrated in figure 2.1 below.

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Figure 2.1: ATM Network Interface [6]

ATM architecture interface is a combination of hardware and software that can provide either an

end-to-end network or form a high-speed backbone. The structure of ATM and its software

components comprise the ATM architecture. ATM backbone is used as better option for services

that employed multimedia-type of transmission [10]. One of the merits of implementing ATM in

any network is its ability to provide a channel for time dependent transmission. Deploying ATM

may also result in a more future-proof network. ATM provides more flexibility when scaling up

from smaller to larger configurations. It also allows the creation of virtual LANs [11]. Virtual

networks provide ways of interconnection all systems at all sites of an organization [12]. Using

ATM as the backbone network simplifies network management by reducing some of the

problems encountered in a complex interworking environment, this backbone characteristic is

one of the reasons that makes ATM the most popular technology today. If the components are

not properly selected and configured correctly, it can create a more complex networking

environment. From figure 2.1, the ATM network architecture shows that some network

technologies connect directly to the ATM Central switch (backbone switch) while some connect

through the local switch (gateway switch). ATM network include two types of network

architecture: Private Network and Public Network. Private network is also known as Customer

Premise.

Figure 2.2: ATM Physical Architecture Interface [8]

The User-to-Network Interface (UNI):

network that the user subscribes to.

The Network-to-Network Interface (NNI):

another ATM switch within the same carrier’s ATM ne

The Broadband ISDN (BISDN) Inter Carrier Interface (B

public ATM carriers.

The ATM signaling protocol is private or public depending on the type of interface over which

the signaling is carried out. If the UNI is

network, the public UNI signaling protocol is used. If the UNI is between an end

and the end user’s private ATM network, the private UNI signaling protocol is used.

The ATM signaling protocol used

private NNI signaling protocol, which is referred to as the Private NNI or PNNI protocol.

24


Figure 2.2: ATM Physical Architecture Interface [8]

Network Interface (UNI): is the interface between the end user and the ATM

network that the user subscribes to.

Network Interface (NNI): is the interface between one ATM switch and

another ATM switch within the same carrier’s ATM network.

The Broadband ISDN (BISDN) Inter Carrier Interface (B-ICI): is the interface between two


the signaling is carried out. If the UNI is between an end-user terminal and a public ATM

network, the public UNI signaling protocol is used. If the UNI is between an end


The ATM signaling protocol used between the ATM nodes within the same ATM network is the



is the interface between the end user and the ATM

is the interface between one ATM switch and

is the interface between two


user terminal and a public ATM

network, the public UNI signaling protocol is used. If the UNI is between an end-user terminal


between the ATM nodes within the same ATM network is the


25

Between the ATM nodes in two different public ATM networks, the public NNI protocol is used.

This public NNI signaling protocol is referred to as the B-ICI protocol.

2.3 BISDN/ATM PROTOCOL ARCHITECTURE

This model contains three (3) planes: Control plane, Management plane and User plane. The

model is shown in figure 2.3.

Figure 2.3: BISDN Reference Model [8].

B-ISDN is the appropriate network that can be capable of giving such high graded services. The

three (3) planes have different functions, and are well discussed in detail as follows:

A. The Control Plane: This deals with call-establishment and call-release functions and other

connection-control functions necessary for providing switched services. The Control plane

structure shares the physical and ATM layers with the User plane. It also includes ATM

adaptation layer (AAL) procedures and higher-layer signaling protocols. [13]

B. The Management Plane: This plane provides management functions and has the ability

to exchange information between the User plane and the Control plane. The Management plane

contains two sections: layer management and plane management. The former performs

management functions relating to resources and parameters residing in its protocol entities. The

latter performs management functions related to a system as a whole and provides coordination

between all the planes.

26

C. User Plane: this is concerned with the transfer of user data including flow control and

error recovery. It has three basic layers that together provide support for user applications as

shown in figure 2.4: ATM adaptation layers, ATM layer and Physical layer [6].

Figure 2.4: ATM Protocol Architure [8]

Table 1: ATM Architectural Diagram

CS Sublayer

ATM Adaption Layer SAR Sublayer

ATM Layer

TC Sublayer

Physical Layer PM Sublayer

Each layer and sub-layer is described briefly below:

27

2.3.1 The ATM Adaptation Layer (AAL)

This layer has two (2) sublayers: Convergence sublayer and Segmentation and Reassembly

sublayer. This convert the higher layer service data unit (SDU) into 48 byte block used inside

ATM cells. The user information are converted into sequences of cells that can be transported by

the ATM Network. AAL entities on the receiver (destination) side reassemble and deliver the

information in a manner that is consistent with the requirement of a given application. AAL

entities reside in the terminal equipment and communicate on an end-to-end basis across the

ATM network. This layer enhances the services provided by the ATM Layer to a level required

by the next higher layer. It performs the functions for the user, control and management planes.

It supports the mapping between the ATM Layer and the next higher layer. It is the AAL

function to adapt all different services needed for higher layers to fit the ATM’s 48-byte payload.

There are different services offered by the AAL as follows:

AAL1: A connection–oriented service, it suitable for handling circuit-emulation applications,

such as voice and video conferencing. It requires timing synchronization between the source and

destination.

AAL2: It supports variable bit rate services with a timing relation between source and

destination. It is nearly identical to AAL1, except that it transfers service data units at a variable

bit rate, not a constant bit rate.

AAL3/4: It supports both connection-oriented and connectionless data. Compressed video and

frame relay use AAL3/4 to send data over ATM network.

AAL5: AAL5 provides a way for non-isochronous (time-dependent), variable bit rate,

connectionless applications to send and receive data. AAL5 was developed as a way to provide a

more efficient transfer of network traffic than AAL3/4. AAL5 merely adds a trailer to the

payload to indicate size and provide error detection. AAL5 is the preferred AAL when sending

connection-oriented or connectionless LAN protocol traffic over an ATM network.

Windows Server 2003 supports AAL5.

AAL5 provides a straightforward framing at the Common Part Convergence Sublayer (CPCS)

that behaves more like LAN technologies, such as Ethernet.

28

2.3.2 ATM Layers

This layer is solely concerned with the sequenced transfer of ATM cells in a connection setup

across the network. It accept a 48byte of user information from the AAL entities and add the

5byte header to form the ATM cell and the cell header use label to identifies connection used by

switch to determine the next hop in the path it follow and the type of priority scheduling a cell

will receive. It can also provide different QoS to different connections abiding with the service

contract negotiated between user and network during connection setup. Cell multiplexing/ DE

multiplexing: cells belonging to different virtual channels or virtual paths are

multiplexed/demultiplexed onto/from the same cell stream; the following functions are

performed by the ATM layer:

• Cell VPI/VCI Translation: the routing function is performed by mapping the virtual

path identifier/virtual channel identifier (VPI/VCI) of each cell received on an input link

onto a new VPI/VCI output link defining where to send the cell,

• Cell header Generation/Extraction: the header is generated (extracted) when a cell is

received from (delivered to) the AAL layer,

• Generic Flow Control: flow control information can be coded into the cell header at the

UNI [14].

2.3.3 The Physical Layer:

This layer is used for the transmission and reception of ATM cells across a physical medium

between two ATM devices. This can be transmission between an ATM endpoint and an ATM

switch, or it can be between two ATM switches. The physical layer is subdivided into a Physical

Medium Dependent (PMD) sublayer and Transmission Convergence (TC) sublayer. [6, 15]

physical layer has the following sub sections:

Physical Medium Dependent sublayer: This sublayer is responsible for transmission functions

and is highly dependent on the medium used. The principal function is the transmission and

reception of waveforms suitable for the medium, the insertion and extraction of bit timing

information and line coding (if required). The primitives identified at the border between the

PMD and TC sublayers are a continuous flow of logical bits or symbols with this associated

timing information [15]

29

Transmission convergence sublayer functions as:

• Transmission frame generation and recovery: This function performs the generation and

recovery of transmission frame.

• Transmission frame adaptation: This function performs the actions which are necessary

to structure the cell flow according to the payload structure of the transmission frame

(transmit direction) and to extract this cell flow out of the transmission frame (receive

direction).

• Cell delineation: Cell delineation prepares the cell flow in order to enable the receiving

side to recover cell boundaries according to the self-delineating mechanism. In the

transmit direction, the ATM cell stream is scrambled. In the receive direction, cell

boundaries are identified and confirmed (using the HEC mechanism) and the cell flow is

descrambled.

• HEC sequence generation and cell header verification: In transmit direction, the HEC

sequence is calculated and inserted in the header. In receive direction, cell headers are

checked for errors and, if possible, header errors are corrected. Cells whose headers are

determined to be errored and non-correctable are discarded.

• Cell rate decoupling: Cell rate decoupling includes insertion and suppression of idle cells,

in order to adapt the rate of valid ATM cells to the payload capacity of the transmission

system.

2.4 CELL NETWORKS

The adoption of cell network seems to solve many problems associated with frame

internetworking. A cell is a small data unit of fixed size. In a cell network, which uses the cell as

the basic unit of data exchange, all data are loaded into identical cells that can be transmitted

with complete predictability and uniformity. As frames of different sizes and formats reach the

cell network from a tributary network, they are split into multiple small data units of equal length

and are loaded into cells. The cells are then multiplexed with other cells and routed through the

cell network. Because each cell is the same size and all are small, the problems associated with

multiplexing different-sized frames are avoided [16].

2.4.1 Structure of an ATM Cell

The unit of transmission, multiplexing and switching in ATM is the fixed

[17]. Its fixed length is chosen to simplify the design of electronics in ATM switches and

multiplexers, because hardware manipulation of variable

processing a fixed length cell. ATM defines two different cell formats:

UNI (User-Network Interface) which interface the ATM endpoints and the ATM switches

NNI (Network-Network Interface) which interfaces two ATM sw

Figure 2.5: ATM Cell Structure [

GFC = Generic Flow Control (4 bits) (default: 4

VPI = Virtual Path Identifier (8 bits UNI) or (12 bits NNI)

VCI = Virtual Channel Identifier (16 bits)

PT = Payload Type (3 bits)

CLP = Cell Loss Priority (1 bit)

HEC = Header Error Control (8bits) (checksum of header only)

Generic Flow Control: This field consists of the first four bits of the first byte of the ATM

header. It is used to control the flow of traffic across the user

30

Structure of an ATM Cell

of transmission, multiplexing and switching in ATM is the fixed-length cell of 53 bytes

]. Its fixed length is chosen to simplify the design of electronics in ATM switches and

multiplexers, because hardware manipulation of variable-length packets is mor

processing a fixed length cell. ATM defines two different cell formats:

Network Interface) which interface the ATM endpoints and the ATM switches

Network Interface) which interfaces two ATM switches [13, 18].

Figure 2.5: ATM Cell Structure [6]

GFC = Generic Flow Control (4 bits) (default: 4-zero bits)

VPI = Virtual Path Identifier (8 bits UNI) or (12 bits NNI)

VCI = Virtual Channel Identifier (16 bits)

HEC = Header Error Control (8bits) (checksum of header only)

This field consists of the first four bits of the first byte of the ATM

header. It is used to control the flow of traffic across the user-to-network interface (UNI)

length cell of 53 bytes

]. Its fixed length is chosen to simplify the design of electronics in ATM switches and

length packets is more complex than

Network Interface) which interface the ATM endpoints and the ATM switches

].

This field consists of the first four bits of the first byte of the ATM

network interface (UNI) and is

31

only used at the UNI. When the GFC function is not in use, the value of this field is replaced

with zeros. This field has local significance only and can be used to provide standardized local

flow control functions of the end users. The value encoded in the GFC field is not carried end-to-

end and will be overwritten by the ATM switches [6].

Payload Type (PT): It is use to designate various special kinds of cells for Operation and

Management (OAM) purposes and to delineate packet boundaries in some AALs. It identifies

the cell content, if it is data cell, and idle, an OAM cell, VCC- level OAM information,

Explicitly Forward Congestion Indication (EFCI), AAL Information, Resources Management

Information

Cell Loss Priority (CLP): The CLP indicates the relative priority of cells. It acts as an indicator

as to whenever or not this cell is expendable, should the Network start becoming congested 1=

can discard the cell 0 = might not discard cell

Header Error Control (HEC): Several of ATM's link protocols use the HEC field to drive

algorithm which allows the position of the ATM cells to be found with no overhead required

beyond what is otherwise needed for header protection. It is an 8-bit field that allows an ATM

switch or ATM endpoint to correct a single-bit error or to detect multi-bit errors in the first 4

bytes of the ATM header. Multi-bit errored cells are silently discarded. The HEC only checks the

ATM header and not the ATM payload. The HEC needs to be recomputed at every switch since

the VPI/VCI value changes at every hop [15].

Virtual Path Identifier (VPI): VPI identifies path between two locations in an ATM network

that provides transportation for a group of virtual channels. It is an 8 bit field for UNI and 12 bit

that tells each switch along which virtual path the circuit will travel. In a UNI interface there is

maximum of 256 virtual paths and 4096 virtual paths in NNI [23]. When the end point has no

data to transmit, the VPI field is set to all zero to show idle condition. To permit a large VPI

value to be carried in the cell header, the four bits from GFC becomes an extension of the VPI

field.

32

Virtual Channel identifier VCI: VCI field is 16 bits long. The VPI/VCI is local identifier for a

given connection in a given link. Its values changes from one switch to another. The structure

supports a large number of connections and provides scalability to very large network [6]

2.5 ATM NETWORK TRAFFIC

The attributes of network traffic are made up of voice, video and data that provide network

administrators, the opportunity to manipulate freely the various services in terms of connection

acceptance, negotiation of the QoS, congestion control, and resource allocation. Therefore, the

feasibility and efficiency of the QoS management architecture are strongly dependent on the

nature of traffic to be accommodated.

2.5.1 Network Traffic Parameters

In [19], the following parameters may be used to describe network traffic characteristics.

� Cell peak arrival rate when the source is in the active state (peak rate);

� Average cell arrival rate;

� Burstiness. (i.e. the ratio between the peak rate and the average rate); and

� Average duration of the active state.

These traffic parameters are used for connection admission control (CAC), usage parameter

control (UPC) and resource allocation. The values of the traffic parameters are negotiated

between the user and the network during call set-up phase; combined with the traffic

characteristics of the aggregate cell arrival stream in the network, they are used for the operation

of the admission control for deciding whether or not a new connection is to be accepted.

In the usage parameter control, the algorithm monitors the user to know whether there is

violation of the traffic characteristic parameters negotiated during the connection establishment

phase. For the resource allocation purposes, the traffic parameters are used by network

administrators as the basis for allocating resources to user demands.

2.5.2 Traffic Flow Control

The network traffic flow has to be controlled in a predictable manner in order to agree with the

allocation of network resources. Flow control is a set of protocols that maintain the flow of

33

traffic within limits compatible with the amount of available resources. These limits may be

fixed or dynamically adjusted based on traffic status to ensure efficient network operations,

guarantee fairness to a certain degree in resource sharing, and protect the network from

congestion and deadlock [20]. It provides means for regulating the traffic inside the network so

that the behavior of internal traffic is more easily manageable. When user demands are allowed

to exceed network capacity it leads to congestion. The traffic is required to be kept within certain

bounds, such as peak bandwidth, maximal burst, and the network is committed to providing

certain service guarantees, such as maximal delay, loss rate etc [21]. Data flows between sources

and destination are disrupted if one or both resources are lacking anywhere along their network

paths. To ensure the integrity of the traffic, QoS parameters must be met at each point in the

entire network.

2.6 QUALITY OF SERVICE (QOS) PARAMETERS

According to [22], the performance of today’s networks is measured by QoS parameters, a

particular traffic and Quality of Service (QoS) parameters are requested in every ATM

application when establishing VCs to helps an end-user to send request to the network which will

in turn verify the set parameter and ensure that the services requested for are delivered by the

network with a certain quality. ITU - T defines QoS as a “Collective effect of service

performance which determines the degree of satisfaction of a user of the service” [23].

According to [23], the performance of today’s networks is measured by QoS parameters, such as,

This is the amount of time that elapse from the time a cell enter the source UNI to the time it

� Throughput: This is a technique used to describe the capacity a system to transfer data.

There are different ways to define and measure throughput, this includes: the cell rate across the

network; the cell rate of a specific application flow; the cell rate of end-to-end aggregated flows;

the cell rate of network-to- network aggregated flows. The amount of bandwidth allocated to

different types of cell affect throughput.

� Delay (or latency): exit at the destination UNI. There are a number of factors that

contribute to the amount of delay experienced by a cell as it traverses the network. They include;

propagation delay, processing delay, queuing delay,. The end-to-end delay can be calculated as

34

the sum of the individual propagation, processing and queuing, delays occurring at each

multiplexers and switches in the network.

� Jitter: Is the variation in delay over time experienced by consecutive cells that are part of

the same flow. It is measured by using mean, standard deviation, maximum or minimum of the

intercell arrival times for consecutive cells in a given flow. End-to-end jitter is never constant

because the level of network congestion always changes from time to time and from place to

place.

� Cell Loss: Is a situation where cells in a network fail to reach their destination due to

break in the link, corruption of cells or buffer overflow. The amount of cell loss in a network is

typically expressed in terms of the probability that the network will discard a given cell. The loss

is measured by rate – the number of cells lost, out of the total number transmitted

� Cell Blocking Probability: The chance or probability that all the buffers are full and any

subsequent cells are dropped (blocked).

� Cell Error rate: Sometimes cells are misdirected, or combined together, or corrupted,

while en route to its destination. The number of such cells from the total number transmitted

within a given period gives error rate. The receiver on detection of the erroneous cell would drop

the cell and either ask the source to repeat it or directly correct it. To ensure the integrity of

traffic, QoS parameters must be met over the entire network by the application of appropriate

resource allocation strategy.

ATM Forum defined the following traffic parameters for describing traffic that is injected into

the ATM network at the UNI [6, 24, 25].

• Peak Cell Rate (PCR): This refers to the maximum bit rate that may be transmitted from

the source.

• Cell Delay Variation Tolerance (CDVT): This refers to the level of cell delay variation

that must be tolerated in a give connection.

• Sustainable Cell Rate (SCR): This is Average traffic bandwidth the connection is

allowed to generate. That is the average cell rate that may be transmitted from the source.

• Maximum Burst Size (MBS): This is the maximum number of cells for which the

source may transmit at the PCR.

35

• Minimum Cell Rate (MCR): This is simply the minimum cell rate guaranteed by the

network.

• Maximum Cell Transfer Delay (maxCTD): Maximum allowed difference between

reception and transmission time for a cell between two end-user points.

• Peak-to-peak Cell Delay Variation (peak-to-peak CDV): Maximum allowed

difference between the maxCTD and minCTD for a cell between two end-user points. The

minCTD represents the minimum transfer time for a cell.

To help manage the growing complexity of specifying and routing on QoS, the ATM Forum’s

UNI 3.1 signaling specifies the following separate QoS classes that described general profile of

QoS parameters. These classes are:

� Constant Bit Rate (CBR) services include voice; circuit emulation with its traffic rate

specified by PCR while the QoS is specified by CTD, CDV as well as CLR. The cell

transmission rate is constant throughout the duration of the connection [6].

� Variable Bit Rate (VBR) that has real time and non real time. Real time VBR is also for

traffic with rigorous timing requirement such as video whose traffic is specified CR, SCR or

MBS and QoS specified by CLR, CTD or CDV, and also non-real-time variants and is used for

"bursty" traffic. Variable bit rate–real time is designed for applications that are sensitive to cell

delay variation. Examples for Variable bit rate–non real time allows users to send traffic at a rate

that varies with time depending on the availability of user information. Multimedia email is an

example of VBR–NRT.

� Available Bit Rate (ABR) is for source that can dynamically adapt the rate at which the

cells are transmitted in response to feedback from the network. It provides rate based flow

control and is aimed at data traffic such as file transfer and e-mail.

� Unspecified bit rate (UBR) is for ATM service category that does not provide and QoS

guarantee and appropriate for non critical application that can tolerate or readily adjust to the loss

of cell. This class is widely used today for TCP/IP.

36

2.7 ATM CONNECTIONS SETUP

ATM network as connection oriented network consists of endpoints and switches. It provides

different QoS to different connections and based on this a service contract is negotiated between

the user and the network when the connection is setup. The user will describe the traffic

requirement and the needed QoS when requesting for a connection. If the network accepts the

request, a contract is implemented to ensure traffic using the connection complies with the

stipulated traffic description or be discarded. �

ATM supports two types of connections in terms of users: point to point connection which can

be unidirectional or bidirectional and point to multipoint connection which are always

unidirectional. In term of duration, ATM provides permanent virtual connections (PVCs) and

switched virtual connections (SVCs). PVCs act as permanent leased lines between user sites, is a

connection that is setup and taken down manually by a network manager. A set of network

switches between the ATM source and destination are programmed with predefined values for

VCI/VPI. SVC is a connection that is setup automatically by a signalling protocol. It is widely

used because it does not require manual setup, but it is not reliable.

2.7.1 Virtual Connections

Connection across the network two endpoints is established through transmission paths (TPs),

virtual paths (VPs) and virtual circuits (VCs). These are the three major concepts in ATM:

Virtual channel

Virtual pathPhysical circuit

Figure 2.6: ATM Connection

Physical Transmission Circuit/ Path: A transmission path is a bundle of VPs. The VCs are

concatenated to create VPs, which, in turn, concatenate to create a transmission path. A physical

37

link can be shared by many VPs with different bandwidth allocation as far as it does not exceed

the link capacity and the peak bit rate transmitted on a VP shall never exceeds the VP bandwidth

allocation.

The virtual path (VP): This is a generic term for a bundle of virtual channel links; all the links

in a bundle have the same endpoints. A VPI identifies a group of VC links, at a given reference

point, that share the same VPC. A specific value of VPI is assigned each time a VP is switched

in the network. A VP link is a unidirectional capability for the transport of ATM cells between

two consecutive ATM entities where the VPI value is translated. VP connection provide several

benefit like efficient routing, in the sense that the intermediate nodes are not involves in call

setup when a VCC is assigned a preexisting VPC. Also traffic capacity and communication

resources can be reserved for VPCs so as to consolidate and manage traffic with similar

characteristics. VPC also allow fast recovery in link failure since alternative path can be set up

immediately [26].

Virtual channel (VC): A generic term used to describe a unidirectional communication

capability for the transport of ATM cells. Virtual channel link is a segment of virtual channel

connection between two adjacent nodes and are identifies by VCI for a given virtual path

connection (VPC). A specific value of VCI is assigned each time a VC is switched in the

network. A VC link is a unidirectional capability for the transport of ATM cells between two

consecutive ATM entities where the VCI value is translated. A VC link is originated or

terminated by the assignment or removal of the VCI value [26].

2.8 STATISTICAL MULTIPLEXING

Virtual Path concept inherently increases call blocking as a result of decreased capacity sharing,

it is important to consider the effect of statistical multiplexing especially, the bandwidth of VP

which can be shared between end-to-end connections through the establishment/release of end-

to-end connection and bandwidth management scheme, while considering the variability of

traffic on a connection. This technique concentrates traffic from multiple users or terminal onto a

shared communication link. This aggregation of cell flow into a single transmission line by the

multiplexer reduces the system cost, by reducing the number of transmission lines which leads to

38

improvement in system efficiency. Statistical multiplexing at the cell level during connection

lifetime is a powerful feature of ATM, inherited from packet switching network [6, 28, 29].

In this techniques, traffic of all cells are merged into queue and are transmitted on first-in-first-

out (FIFO) fashion, so that the entire bandwidth is allocated to the first cell out of the queue. The

result is a smaller average delay per cell. When several sources are active and are combined on a

single link at the same time, the required total bandwidth is less than the sum of the individual

connection. The statistical multiplexing gain is determined by the acceptable cell loss rates of the

connections [28, 30].

2.9 CONNECTION ADMISSION CONTROL

This scheme negotiates traffic description between user of the network and the network and

reserved bandwidth for virtual channel/ virtual path connection to guarantee the quality of

service (QoS). The number of VC to be carried on a link is the decision of the CAC while still

maintaining the required QoS. CAC in ATM network work like this, if a new call arrives at a

local switch, the total capacity of the new call and the existing VC will be calculated to know if it

can be accommodated by the VP and it will be compare to the unused bandwidth of that VP.

This calculation is based on a set of parameters established during call establishment which

represent the cell arrival process. The call is only accepted into the network when the required

bandwidth has been verified. The common CAC method can be taken as equivalent bandwidth

CAC which is a method used to convert traffic parameters and QoS into an equivalent bandwidth

for the connection and the value gotten is compared to the link unreserved bandwidth to see

whether the request can be supported. The function of CAC schemes depend on at least, the

following factors: the source traffic characteristics, the QoS and the free resources on the VP.

The concept of effective bandwidth help to reduce the complexity of CAC in ATM network, the

idea is to find the effective bandwidth that can support the needed QoS. There are two ways of

calculating the effective bandwidth: fluid-flow model and stationary bit rate model.

2.10 TRAFFIC MODEL

Each single connection in ATM network has a variable bit rate bounded by its peak rate. To

ascertain the effective bandwidth of a connection, an appropriate model has to be selected to

39

specify its characteristic with known parameters. In this work, the properties of individual

connections are of concern therefore the adoption of fluid flow model. The two state fluid flow

model that captures the basic feature (behavior) of traffic input source is adopted because a

traffic source can either be ON or OFF.

During ON state, cells are transmitted at the peak rate, r, and no cells are transmitted during OFF

state that is zero bit rate. The advantages of such traffic source are its simplicity and flexibility,

such as it can be used for connections ranging from burst to continuous bit streams.

Based on this, two state fluid flow model, the ON and OF state is the time when the source is at

active or idle state respectively. They are assumed to be exponentially distributed and therefore

the source is completely characterized by three parameters, namely peak rate r, utilization ρ, and

the mean ON period b, where ρ is the fraction of time the source is active and b is the mean of

the ON state period.

2.11 FLUID FLOW MODEL

The fluid flow model is adopted when focusing on individual connections which are statistically

independent. Each traffic source is assumed to be of two-state fluid flow type, i.e. it alternates

between ON and OFF states. During ON intervals, cells are transmitted at the peak rate, k, and

no cells are transmitted during OFF intervals that is zero bit rate. The duration of ON and OFF

intervals are exponentially distributed, therefore the traffic source is characterized by three

parameters: peak rate, r, utilization, p i.e the fraction of time the source is at ON state and mean

ON period b. More specifically, for sources with maximum cell loss probability ", peak bit rate r,

utilization, p, assume the buffer size of ATM multiplexer is B cells, then the required effective

bandwidth can be derived as follows [31]:

ê =αb�1 − � − B + α��1 − �r − �� + 4Bαb��1 − �I

2α��1 − p

where α = In�1/є)

For CBR cases r = 1, and b = ∞ then = Rpeak. This formular is used to calculate the effective

bandwidth.

2.12 VIRTUAL PATH CONCEPT

Routing in ATM networks is based on Virtual Path Connections (VPCs); a route is defined as a

concatenation of VPCs. ATM standards specify two types of

connections and Virtual Channel (VC) connections. While VCs are used as the virtual circuits on

which data is transferred, VPs are used to bundle several VCs together, thus decreasing the

amount of entities to be managed. Vi

effective, flexible network when network architecture and node processing are simplified [

Figure 2.7: Virtual Path Network [

Virtual path concept is used for segregating different types

resource is assigned to each type of traffic between a source and destination pair. As a result of

this, more than one VP may be established between the same Source and Destination pair with

each carrying different types of traffic. In the case of this work, it is assumed that traffic of the

same type requires identical end-

The introduction of this concept according to [

VCs to be groups in bundles, processed and t

advantages like reduction in node cost and the simplification of the network architecture thereby

promoting the required operation, administration and management functions. The fundamental

40

VIRTUAL PATH CONCEPT


concatenation of VPCs. ATM standards specify two types of connections - Virtual Path (VP)



amount of entities to be managed. Virtual path concept is the key to the development of a cost

effective, flexible network when network architecture and node processing are simplified [

Figure 2.7: Virtual Path Network [28]

Virtual path concept is used for segregating different types of traffics i.e. a VP with dedicated



s of traffic. In the case of this work, it is assumed that traffic of the

-to-end QoS.

The introduction of this concept according to [6, 28, 32] in ATM network allow management of

VCs to be groups in bundles, processed and transmitted. To manage in bundles, allow significant




Virtual Path (VP)



rtual path concept is the key to the development of a cost-

effective, flexible network when network architecture and node processing are simplified [28].

of traffics i.e. a VP with dedicated



s of traffic. In the case of this work, it is assumed that traffic of the

] in ATM network allow management of

ransmitted. To manage in bundles, allow significant



importance of VP concept is that individual connections are grouped together so that they share a

common path through the network as a single unit.

The action of management is applied to a small number of groups of the connections instead of

the large number of individual connections. This results to a lesser total processing requirement

per VC and a better use of network resources.

Figure 2.8: VP Borrowing model

Another advantage of VP Concept is that it allowed borrowing from one VP to another if they

share the same source node and the set of links in the former VP is subset of that of the latter.

Deterministic reservation Least Loaded Routing algorithm with dynamic VP capacity sharing

help to achieve this if the call is blocked on the direct path, it check if there

free capacity that can be shared by the direct VP as illustrated in figure 2.8

The implementation of VPs reduces the processing and delay associated with call acceptance

control (CAC) function, therefore plays an important role in cal

[33]. This concept reserved capacity on a VP connection in anticipation of later call arrivals, new

VC connection can be established by executing simple control functions at the endpoint of the

VP connection (terminator). No ca

as a result, cost effective network with enhanced performance is realized [

ATM network is constructed with nodes and links and VC is defined by creating a connection

between two endpoints which exchange information. A route is assigned to each VC in the

network; cells are transported along the assigned route to the VC to which it belongs. In this

ways several node functions are performed by each node recognizing the outgoing link to whic

incoming cells should be sent [41

P concept is that individual connections are grouped together so that they share a

common path through the network as a single unit.


al connections. This results to a lesser total processing requirement

per VC and a better use of network resources.

Figure 2.8: VP Borrowing model


source node and the set of links in the former VP is subset of that of the latter.


help to achieve this if the call is blocked on the direct path, it check if there is another VP with

free capacity that can be shared by the direct VP as illustrated in figure 2.8


control (CAC) function, therefore plays an important role in call admission control in BISDN

]. This concept reserved capacity on a VP connection in anticipation of later call arrivals, new


VP connection (terminator). No call processing is carried out at the transit nodes in VP network,

as a result, cost effective network with enhanced performance is realized [28].


ts which exchange information. A route is assigned to each VC in the


ways several node functions are performed by each node recognizing the outgoing link to whic

incoming cells should be sent [28]. But one thing is common in transfer network like ATM

P concept is that individual connections are grouped together so that they share a


al connections. This results to a lesser total processing requirement


source node and the set of links in the former VP is subset of that of the latter.


is another VP with


l admission control in BISDN

]. This concept reserved capacity on a VP connection in anticipation of later call arrivals, new


ll processing is carried out at the transit nodes in VP network,


ts which exchange information. A route is assigned to each VC in the


ways several node functions are performed by each node recognizing the outgoing link to which

]. But one thing is common in transfer network like ATM

42

technology, queuing delay and cell loss always occur whenever statistical cell multiplexing is

performed at nodes. This delay and cell loss probability depends on the maximum queuing buffer

size at the node and the link capacity between nodes. A traffic network is accommodated within

a large capacity transmission facilities network therefore in designing ATM networks the

minimum capacity of a virtual path between switches must be devised so as to provide the

required service quality such as cell blocking probability and cell transfer quality for each virtual

circuit. The designing algorithm to determine the VP capacity of the nodes and link capacity s

must be developed to realize an ATM network [34].

VPs play an important role in traffic control and resource management in ATM networks, as it is

defined as a logical direct link between two nodes in the network that are connected through two

or more sequential physical links. A VP is identified with the Virtual Path Identifier (VPI) and

each VP has its own bandwidth, limiting the number of VCs that it can accommodate. The

number of VPs in each link is not limited. The only limit is that the sum of bandwidth of the

VPs, does not exceed the capacity of the link. Setting up of a path in the network is done once for

all VCs using the same path and the required node function are effectively simplified, rewriting

of routing table of the transit node is not necessary at call setup because an area known as virtual

path identifier (VPI) is reserved at the cell header which can be compared at the arrival of cell

through the transit node with their VPI in the routing table. Routing table is only concerned with

the VP so the routing procedure at call setup is also eliminated at the transit not because this is

done by selecting an appropriate VP from end nodes terminating the VP [28]. Transit nodes are

free of bandwidth allocation process at call setup by comparing the bandwidth of the requested

connection to the unused bandwidth of the VP at the end nodes.

Reserving bandwidth for VPs makes VC connection to be established quickly and simply

because bandwidth along their path are guaranteed because the function is performed only at the

beginning of a VP. The action of eliminating node processing at the transit node has lead to low

cost of node construction which is a valuable issue in the construction of economical ATM

network since transmission cost has been reduced because of the development of high capacity

transmission system. Also it provide a logical service separation on network service access and

adaptability to varying traffic and network failure through dynamic resource management [28].

Implementation of priority control is possible by segregating traffic with different Quality of

43

Service (QoS), where each VP is considered as a logical link for a certain services. This leads to

building a VP subnetwork with different service with the network. Each VP has a number of

physical links assigned and effective bandwidth to assured QoS requirements. Several VPs can

be multiplexed on the same physical link, and varying traffic conditions and network failures can

also be tuned to accommodate the changing network condition and still maintain network

performance.

In all these mention merits of VP, there are still some demerit like the reservation of capacity in

anticipation of new traffic which decreases the capacity sharing leading to under utilization of

available bandwidth. It also do not exploit redundant bandwidth in another VP, so the network

throughput decreases as the total call blocking rate increase and network transmission cost also

increases. This work looks into how to use this redundant bandwidth in another VP when there

are VPs that need the bandwidth, thereby increasing the throughput and decreasing the call

blocking rate.

Dynamic bandwidth control method helps to flexibly reassign the individual VP bandwidth when

the connection on one VP increases, the remaining link bandwidth can be assigned to the busy

VP by statistically sharing of transmission facilities among VPs. With this, no link will be

redundant therefore the transmission efficiency will be improved as each VP in the link is well

utilized, although this control may increase the processing load, but the advantage in reduce node

processing is expected to maintained by changing the bandwidth less frequently than call setup

and clearance. Since VP bandwidth can be varied by merely modifying the bandwidth data

stored in the processor of the end nodes and not by accessing the switches, the transit nodes and

all the switches do not need to be accessed for bandwidth changes.

2.13 GENERAL OVERVIEW OF NETWORK ROUTING

The task of routing data from source to a destination is an important procedure for any network.

An efficient routing protocol, in conjunction with efficient connection admission control, allows

for correct operation of the network by ensuring that cells are delivered to their destination in a

correct chronological order. The overall objective of a routing policy is to increase the network

throughput in terms of call admissions, while guaranteeing the performance of the network

within specified levels. The design of an efficient routing policy is of enormous complexity,

44

since it depends on a number of variable and sometimes uncertain parameter. This complexity is

increased by the diversity of bandwidth and performance requirements of different connection

types in a multi-class network environment. Furthermore, the routing policy should be adaptive

to cater for changes in the network: topological changes due to faults or equipment being taken

in and out of service; and changing traffic conditions.

Various types of traffic like CBR for voice, VBR for video, and ABR for data or best effort

traffic, are moved across the network using different types of routing techniques. Diverse

requirements for Quality of Service (QoS) from different users must be satisfied. In order to

guarantee the QoS, some connections may have to be blocked by the connection admission

control (CAC) mechanism during the connection setup, and traditional routing meets a new

challenge to avoid network congestion and be able to route around congested regions when there

is congestion in the network. Routing over ATM networks should be connection oriented and

dynamic, not only to the physical connectivity topology of the network, but also according to the

congestion status of each link and node in the network and be able to scale to the network with

large size while reasonably limiting the overhead for memory, bandwidth and processing time

required for storing and exchanging routing information. The connection blocking probability as

well as the rerouting probability should be low.

Many existing routing algorithms have serious problems of lack of cooperation between

congestion control and routing. Routing having a very close relationship with congestion control,

especially with CAC affect the selection of paths. Path selected by the routing algorithm may be

rejected by CAC if the new connection request will seriously degrade the QoS of other existing

connections. Another problem is that a conventional routing algorithm will cause a significant

overhead when the network size gets very large or rerouting occurs frequently due to the varying

link state. In an ATM network the number of switch node may be very large, so reducing routing

overhead must be taken into account in the design of a routing algorithm [35].

To obtain high utilization under the QoS requirement in ATM, CAC must decide whether to

accept a new connection, based on not only the new connection’s anticipated traffic

characteristics and the QoS requirement of connected calls including the new call, but also the

bandwidth capacity of the links along the path which is selected by the routing algorithm. A

45

good routing algorithm should select the path with very low rejecting probability by the CAC,

besides the lowest cost criteria.

Routing has a strong relationship with CAC in ATM networks. Routing plays an important role

in ATM congestion control; because it can prevent congestion by dynamically selecting paths

according to the traffic load and link bandwidth conditions [35]. It can also mitigate congestion

occurrence by routing around the congested region. To do this, we extract a sub topology from

the entire network topology, by checking all the links and including only the links that have high

probability to accommodate the new connection before the path selection. Routing on this

abstracted effective topology will lead to low call blocking probability and rerouting probability,

thus improving the network performance and reducing the routing overhead

In order to let the routing overhead processing time be as low as possible, a few link metrics and

QoS metrics should be used to consume less bandwidth, memory and processing time while

providing enough information for routing.

Routing as stated is an act of moving network traffic along the selected path in the network

towards the destination and is performed for many kind of networks. The path selection in

network routing is typically formulated as a shortest path problem. There is also a problem of

routing in a dynamic environment due to fluctuations in traffic load, link failures and topology

changes [36].

2.13.1 Routing Metrics

Metrics are a way to measure or compare. Routing protocols use metrics to determine which

route is the best path. There are cases when a routing protocol learns of more than one route to

the same destination. To select the best path, the routing protocol must be able to evaluate and

differentiate among the available paths. For this purpose, a metric is used. A metric is a value

used by routing protocols to assign costs to reach remote networks. The metric is used to

determine which path is most preferable when there are multiple paths to the same remote

network. Metrics used in routing protocols include the following:

• Hop count: A simple metric that counts the number of routers a packet must traverse.

• Bandwidth: Influences path selection by preferring the path with the highest bandwidth.

• Load: Considers the traffic utilization of a certain link.

46

• Delay: Considers the time a packet takes to traverse a path.

• Reliability: Assesses the probability of a link failure, calculated from the interface error

count or previous link failures.

• Cost: A value determined by the network administrator to indicate preference for a route.

Cost can represent a metric, a combination of metrics, or a policy.

2.13.2 Types of Routing Schemes

Various routing schemes proposed and implemented in current public and commercial networks

from an ATM network perspective are discussed. This can be classified in many ways based on

their responsiveness. It can be Static or dynamic routing schemes [6, 33, 37].

2.13.2.1 Static Routing:

This approach is simply the process of manually entering routes into a device's routing table via

a configuration file that is loaded when the routing device starts up. As an alternative, these

routes can be entered by a network administrator who configures the routes manually. Since

these manually configured routes don't change after they are configured (unless a human changes

them) they are called 'static' routes. Static routing is the simplest form of routing, but it is a

manual process.

It is used when you have very few devices to configure and when you know the routes will

probably never change. Static routing also does not handle failures in external networks well

because any route that is configured manually must be updated or reconfigured manually to fix

or repair any lost connectivity. The static routing is the simplest way of routing the data packets

from a source to a destination in a network. Static routing has metric of zero.

2.13.2.2 Dynamic Routing:

Dynamic routing is an efficient method of traffic control where cell routing is frequently altered

due to the status of the network or anticipated demand shifts, so that the network can respond

quickly and properly to the changes in traffic and facility conditions. The routing decisions are

influenced by the current traffic conditions. Dynamic routing gives a better chance of success to

an individual cell by increasing the number of ways the cell can traverse the network. When

47

there is a new connection requests between a pair of switches, it is possible that the call is

established along the direct route or along an alternative allowable route. Normally routing

schemes attempt the direct route first and if it is unavailable then the alternative routes are

considered. The dynamic routing scheme increases network efficiency by routing calls away

from busy area through lightly loaded portion s of the network. The routing algorithms differ

mainly in how they choose the one route from the set of allowable routes.

Dynamic routing is complementary to alternative and adaptive routing, their time scale over

which traffic condition are assessed are different. This can exploit the non-coincidence of busy

hours across a large network and if the VP concept is used to the full, it can effectively mean

reconfiguration of the VPN layer [38]

Usually two-link alternative routes are considered. Removing the restriction of two VPs allows a

wider choice of alternative routes and as such tends to reduce the blocking probability. On the

other hand, it also tends to reduce the effective capacities of the physical links [39]. In general

the use of multiple VPs for a single call means inefficient use of network resources, because the

same resources could be used to complete the several separate calls [39]. The dynamic routing

method has two parts: The routing protocol that is used between neighboring routers to convey

information about their network environment. Routing algorithm is used to determine paths

through that network.

• Routing Protocol: The protocol defines the method used to share the information

externally, Routing protocol s capture the state information (e.g available resources) and

disseminate it throughout the network,. A routing protocol is the language a router speaks with

other routers in order to share information about the reachability and status of networks.

• Routing Algorithm: Routing algorithms use this information to compute appropriate

paths that is processing the information internally. Several routing algorithm can be defined by

changing factors such as: the metric parameter of the VP cost function, the composite rule of the

alternative route cost, the route selection scheme and the determination of available alternate

route. The cost parameter associates VP with a certain value that is adjusted dynamically

according to the varying load of the VP. The calculation is done based on the knowledge of the

current network load, on the traffic descriptors and on the QoS requirements.

48

Dynamic routing protocols not only perform these path determination and route table update

functions but also determine the next-best path if the best path to a destination becomes

unusable. The capability to compensate for topology changes is the most important advantage

dynamic routing offers over static routing.

2.13.2.2.1 Types of Dynamic routing protocols

� Distance-Vector: A distance-vector routing protocol sends a full copy of its routing table

to its directly attached neighbours. This is a periodic advertisement, meaning that even if there

have been no topological changes, a distance-vector routing protocol will, at regular intervals, re-

advertise its full routing table to its neighbors[40]. Obviously, this periodic advertisement of

redundant information is inefficient. Ideally, you want a full exchange of route information to

occur only once and subsequent updates to be triggered by topological changes. Another

drawback to distance-vector routing protocols is the time they take to converge, which is the time

required for all routers to update their routing table in response to a topological change in a

network. Hold-down timers can speed the convergence process. After a router makes a change to

a route entry, a hold-down timer prevents any subsequent updates for a specified period of time.

This approach helps stop flapping routes (which are routes that oscillate between being available

and unavailable) from preventing convergence. Yet another issue with distance-vector routing

protocols is the potential of a routing loop.

� Routing Information Protocol (RIP): A distance-vector routing protocol that uses a

metric of hop count. The maximum number of hops between two routers in an RIP-based

network is 15. Therefore, a hop count of 16 is considered to be infinite. Also, RIP is an IGP.

Three primary versions of RIP exist. RIPv1 periodically broadcasts its entire IP routing table,

and it supports only fixed-length subnet masks. RIPv2 supports variable-length subnet masks,

and it uses multicasts (to a multicast address of 224.0.0.9) to advertise its IP routing table, as

opposed to broadcasts. RIP next generation (RIPng) supports the routing of IPv6 networks, while

RIPv1and RIPv2 support the routing of IPv4 networks. The Routing Information Protocol (RIP)

was the first dynamic routing protocol to be used in an internetwork, so it was created and used

49

primarily with UNIX hosts for the purpose of sharing routing information [41]. RIP uses Hop

count metric that is the best path is chosen by the route with the lowest hop count.

� Interior Gateway Routing Protocol (IGRP): An IGRP exchanges routes between

routers in a single Autonomous System (AS). Common IGRPs include OSPF and EIGRP.

Although less popular, RIP and IS-IS are also considered IGRPs. Also, BGP is used as an EGP;

however, you can use interior BGP (IBGP) within an AS [42]. IGRP uses Bandwidth, delay,

reliability, and load metrics. Best path is chosen by the route with the smallest composite metric

value calculated from these multiple parameters. But by default, only bandwidth and delay are

used.

� Enhanced Interior Gateway Routing Protocol (EIGRP): EIGRP is classified as an

advanced distance-vector routing protocol, because it improves on the fundamental

characteristics of a distance-vector routing protocol. For example, EIGRP does not periodically

send out its entire IP routing table to its neighbors. Instead it uses triggered updates, and it

converges quickly. Also, EIGRP can support multiple routed protocols (for example, IPv4 and

IPv6). EIGRP can even advertise network services (for example, route plan information for a

unified communications network) using the Cisco Service Advertisement Framework (SAF).

By default, EIGRP uses bandwidth and delay in its metric calculation; however, other parameters

can be considered. These optional parameters include reliability, load, and maximum

transmission unit (MTU) size. EGRP also uses Bandwidth, delay, reliability, and load metrics.

Best path is chosen by the route with the smallest composite metric value calculated from these

multiple parameters and only bandwidth and delay are used by default.

� Link State: A link-state routing protocol allows routers to build a topological map of a

network. Then, similar to a global positioning system (GPS) in a car, a router can execute an

algorithm to calculate an optimal path (or paths) to a destination network. Routers send link-state

advertisements (LSA) to advertise the networks they know how to reach. Routers use those

LSAs to construct the topological map of a network. The algorithm run against this topological

map is Dijkstra’s Shortest Path First algorithm. Unlike distance-vector routing protocols, link-

50

state routing protocols exchange full routing information only when two routers initially form

their adjacency. Then, routing updates are sent in response to changes in the network, as opposed

to being sent periodically. Also, link-state routing protocols benefit from shorter convergence

times, as compared to distance-vector routing protocols

� Open Shortest Path First (OSPF): A more powerful routing protocol developed

subsequent to RIP, defined originally as RFC 1131 and more recently as RFC 2178, is called

Open Shortest Path First (OSPF). It is the preferred routing protocol for medium or large

networks which, in OSPF, are referred to as autonomous systems (ASs) [42].A link-state routing

protocol that uses a metric of cost, which is based on the link speed between two routers. OSPF

is a popular IGRP, because of its scalability, fast convergence, and vendor interoperability. SPF

uses cost metric

� Intermediate System to Intermediate System(ISIS): This link-state routing protocol

has similar operation as OSPF, It uses a configurable, yet dimensionless, metric associated with

an interface and runs Dijkstra’s Shortest Path First algorithm. Although using IS-IS as an IGP

offers the scalability, fast convergence, and vendor interoperability benefits of OSPF, it has not

been as widely deployed as OSPF.

� Path Vector: A path-vector routing protocol includes information about the exact path

packets take to reach a specific destination network. This path information typically consists of a

series of autonomous systems through which packets travel to reach their destination.

� Border Gateway Protocol (BGP): Border Gateway Protocol (BGP) is the only path-

vector protocol you are likely to encounter in a modern network. Also, BGP is the only EGP in

widespread use today. In fact, BGP is considered to be the routing protocol that runs the Internet,

which is an interconnection of multiple autonomous systems. BGP’s path selection is not solely

based on AS hops, however. BGP has a variety of other parameters that it can consider.

Interestingly, none of those parameters are based on link speed. Also, although BGP is incredibly

scalable, it does not quickly converge in the event of a topological change. The current version of

BGP is BGP version 4 (BGP-4). However, an enhancement to BGP-4, called Multiprotocol BGP

(MP-BGP), supports the routing of multiple routed protocols, such as IPv4 and IPv6.

51

2.14 Routing In Atm Network

The standard Cell routing techniques in ATM network is simply based on the utilization of VP

concept. This concept plays an important role in traffic control and resources management [43].

Dynamic routing gives a better chance of success to an individual cell by increasing the number

of ways the cell can traverse the network. When there is a new connection requests between a

pair of switches, it is possible that the call is established along the direct route or along an

alternative allowable route. Normally routing schemes attempt the direct route first and if it is

unavailable then the alternative routes are considered. The dynamic routing scheme increases

network efficiency by routing calls away from congestion area through lightly loaded portion of

the network. The routing algorithms differ mainly in how they choose the one route from the set

of allowable routes.

Dynamic routing algorithms in ATM network can be classified into two categories: Least

Loaded Routing –based (LLR-based) and Markov Decision Process-based (MDP-based). In the

course of this work, the least loaded routing algorithm is chosen to check the traffic load in the

network by comparing three routing algorithms based on LLR. The LLR approach tries to route a

call to the direct link first, if the call is blocked because of no free circuit, the least busy with the

maximum number of free circuit is then tried. The MDP approach can result in optimal or least

cost route, but are reported to be more computationally intensive [44, 45]. As a result of this,

knowing the computational complexity of each algorithm can be helpful. The effectiveness of

most of them depends on the loading conditions of the networks, while some other have

increased hardware requirements or require considerable execution time which render them

unsuitable for real-time applications [43]. Most dynamic routing schemes implemented in real

world are variations of LLR and each of them has its merits and demerits.

52

Figure 2.9: Flow chart of operation of an LLR

2.16 Related Works

Shun-Ping and Chi-Ming [31] in their study proposed a novel routing scheme, Random early

blocking (REBR) based on least loaded routing in Virtual Path-based ATM networks and

derive efficient approximation method to find call-level performance measures such as call

blocking and cell delay. The result shows that REBR performs much better than LLR when the

traffic load is light, but REBR approaches LLR when the traffic load becomes heavier. REBR is

a modification of least loaded routing. It first considers the direct link/route from the source to

Drop call

N

Y

N

Y

START

Scanning/Waiting

for Arrival

Any Arrival

Check least loaded

path

Any paths

available

Direct call to the least

loaded path

Initialization

53

destination. If the direct link/route is not available or not sufficient for the transmission, it then

finds a pair of alternate routes. If the alternate routes are occupied, it then looks for another pair

of alternate route for each pair of free alternate, the one with highest bandwidth is chosen for

transmission. In a situation where the bandwidths are equal, it chooses one at random.

Hon-Wai and Tsang [44], in their study proposed a Dynamic Routing Algorithm based on LLR

with packing and compared its performance with other routing algorithms. While considering

difference bandwidth requirement by direct and alternate route. It stated that all dynamic routing

scheme outperform the direct routing though the difference is very small as it shows

approximately the same performance.

Ren-Hung [45], in his work on routing problem in homogeneous VP-based ATM networks

stated that network blocking probability can be significantly reduced by LLR routing.

He further described the LLR routing algorithms; the free capacity of a VP is measured by the

maximum number of direct calls that can be added to the VP. As shown in Figure 2.7, when an

alternate call is added to a VP, the maximum number of direct calls that can be added to this VP

may decrease by more than one

Two algorithms based on Deterministic strategy were studied namely: deterministic reservation

LLR algorithm (LLR-D) and Deterministic Reservation LLR algorithm with dynamic VP

Capacity Sharing (LLR_DS). In LLR-_D, when a call arrives at the source node, the call is first

offered to the direct VP. If the direct VP does not have enough capacity available to carry the

call, the call is offered to the alternate path with the maximum free capacity where the free

capacity of an alternate path is defined as the minimum free capacity over the path’s VP’s. If the

call still cannot be carried by the alternate path with the maximum free capacity, then the call is

blocked.

Antonios, et al [43], in their study presented a simple heuristic routing algorithm suitable for real

time application, which, achieves an increased in the network throughput irrespective of the

network traffic load. Although, it is enhanced with the trunk reservation concept, which is

applied according to a probability that is increased linearly as the network load increases; this

54

policy aims at a better overall performance of the algorithm irrespective of the traffic load. The

effectiveness of this algorithm is based on the cost metric, that achieves a successful trade-off

between the use of the minimum-hop routes and the load balancing. Aimed at this target, an

efficient cost metric for the route selection was designed. Therefore the cost of a link is defined

as:

= ( - ) ……………………….………………………….(1)[43]

Let = already used equivalent bandwidth link i

Let = expected link utilization for the new call

Let = expected equivalent bandwidth for the new call

Let = equivalent bandwidth that correspond to the new call

Adding the costs of each link that belong to the candidate route, while considering the resources

that are required in terms of the number of the hops of this route. Hence, the cost of the route j

is defined as:

= ( ) be the cost of route j ……………………………. (2)[43]

The difference between is the additional equivalent bandwidth needed to establish the

new call, but are not necessarily equal with the equivalent bandwidth that corresponds to the

new call, if the last call was considered independence of the already established calls. In fact, due

to statistical multiplexing it generally holds that:

+

From equation (2)[43], it can be noticed that the cost of the route j increases as:

• The required additional bandwidth for establishing the new call increases.

• The congestion level of the links (expressed by their utilization factor) that comprise a

specific route increases.

• The number of the hops of the particular route increases

55

From the above statements, it show that the proposed cost function combines the number of the

hops the required, equivalent bandwidth and the congestion level of the routes.

In order to minimize the processing required at the intermediate nodes, satisfying one of the main

targets of the ATM networks, a call-level execution of the routing algorithm at the source nodes

is proposed (source-routing). In summary, the following on-line algorithm is defined:

When a new call request occurs:

1. For each candidate route estimate = ( - ) of each link according to the CAC

algorithm that is used.

2. Compute the cost of each route j using equation (2)[49].

3. Select the route with the minimum cost.

4. Apply the trunk reservation concept to the selected route with probability:

Pr =

4.1. IF trunk reservation concept is applied.

IF the route is accepted by the CAC

AND

the route is a minimum-hop one establish the call.

ELSE

select the route with the next minimum cost and run again step 4.

4.2. IF the trunk reservation concept is not applied.

IF the route is accepted by the CAC, establish the call

ELSE

select the route with the next minimum cost and run step 4 again.

5. IF all the routes have been rejected, the incoming call is blocked.

Siebenhar [46] in his paper carried out Simulative comparison of call routing algorithms in VP-

based ATM network. He proposed a dynamic algorithm known as Minimum Free Capacity

Routing (MFCR) for VP-based ATM networks with several direct paths connecting a pair of

56

nodes. The algorithm selects the direct path with the smallest residual capacity among those

paths having enough residual capacity. Because of this, the MFCR tries to aggregate the unused

bandwidth on one path. From the VC routing task, many routing algorithms such as fixed

alternate routing, Least Loaded Routing (LLR) or MFCR can be used. These algorithms were

compared andassumed to be more favorable for VP-based ATM network.

2.16 CONCLUSION

Having discussed different types of routing techniques, it is observed that the dynamic routing

algorithm better utilizes network resource while admitting traffic into the network. It also

noticed that most dynamic routing schemes implemented in real world are variations of LLR.

The next chapter will talk about two routing techniques out of the ones earlier discussed. These

routing algorithms are Deterministic Reservation LLR Routing Technique (LLR_D) and

Deterministic Reservation LLR Algorithm with Deterministic VP Capacity Sharing (LLR_VP).

These algorithms will be investigated to determine their performance with respect to server

utilization, cell loss rate in the network and cell delay.

57

CHAPTER THREE

MODELING

3.0 INTRODUCTION

From the literature reviewed, it is observed that many types of models exist, from mathematical

models, analytical, flowchart, computer program models to graphical models. For the purpose of

this work, graphical and flowchart models will be used to compare three routing algorithms as

shown in the previous chapter.

In this study, the model design of Cell routing is therefore designed and implemented using

MATLAB Simulink Simevent package. The simulation model was chosen due to the fact that

there is no single analytical model that can be traceable and still handle all the QoS parameters as

seen from all the models touched therefore, the advantage of computer simulation technique.

The two dynamic routing algorithms mentioned earlier were considered as basis for the analysis

of its variants: Deterministic Reservation LLR Routing Technique (LLR_D) and Deterministic

Reservation LLR Algorithm with Deterministic VP Capacity Sharing (LLR_VP). The network

architecture and model that were used for simulation and analysis are presented with simplified

flowcharts showing the stages involved in selecting route in ATM Network.

3.1 NETWORK ARCHITECTURE

The network architecture diagram shown in figure 3.1 supports: data, voice, and video traffic that

are based on virtual path technique. Each node realized the usual functions of traffic switching,

processing and transmission. The input traffics are from varied sources comprising of data,

voice, and video, which are bundled into virtual path.

Figure 3.1: An ATM network architecture

The virtual path concept is introduced to simplify

ATM networks consist of several VP subnetwork for which nodes are interconnected by VP.

The network topology is modeled by a directed graph G(V,E), where V is a set of nodes and E

represented the link. The physical network topology, with its nodes, links and links capacity

make up the first set of input parameter for the cell routing problem. Another input parameter is

the traffic demand matrix in term

The input parameters proposed in the designed model provides a set of cell with their route; that

is start, intermediate, end nodes and the allocated capacities. The model also determined the

combination of VPs to be assigned in order to route the VCs (cells).

No restrictions are imposed on the topology of the network

All nodes can be the source or destination of the network traffic. The virtual paths ( network

links) are assumed to be unidirectional logical links which can be established between

nodes in the network. There cannot be more than one VP with the same endpoints and are also

assumed to have determinstic bandwidth that are not subjected to statistical multiplexing with

cells from different VP. All VCs (cells) are routed entirely

VC carrying traffic without being assigned to a VP.

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