design of the autonomous satellite link 2004

8/4/2019 Design of the Autonomous Satellite Link 2004

1/59

2003 ( 15)

Design of the Autonomous Satellite LinkOperation Environment on the Internet


2/59

Abstract of Masters Thesis Academic Year 2003

Design of the Autonomous Satellite LinkOperation Environment on the Internet

The Internet has matured as a fundamental infrastructure on which a number of services areprovided and social communication is established. Now a days, connectivity to the Internetis a social requirement of where people exist. Satellite communication has wide coverage,broadcast capability, and flexibility in configuration as their characteristics, which othermedia does not have. Satellite links are expected to contribute to expanding the Internettoward everywhere on the earth.

However, operational scheme of satellite links is heterogeneous depending on their datalink scheme, such as multiplex modes, forms of earth stations, directions of connectivity, andso on. This heterogeneity makes the operational range closed in respective systems. Thus,from the view point of operating an IP network, satellite links are difficult to operate as anintegrated data link of the network. Therefore, a satellite network can not be easily extendedor interconnected with other satellite networks despite the distinguished characteristics ofsatellite communication.

This thesis designs the autonomous satellite link operation environment on the Internet.The essence of our operation environment is information exchange among earth stations andexternal nodes on the network. On our model, earth stations are abstracted as nodes whichcan be accessed from anywhere in the operational domain via the Internet. Satellite linkscan be operated in a unified scheme beyond the heterogeneity of operational schemes basedon the information exchange among those nodes. We described the essential functionaliries,the definition of operational domain, and the operational information of the proposed en-vironment. And then, we organized the required components to establish the environment.

On the implementation of our environment, we adopted SNMP as the protocol forexchanging operational information among nodes on the operational domain. Accordingto the focus on satellite modems as the core equipment of earth stations, we classified theoperational information and described it on a MIB by ASN.1.

We evaluated our operation model based on its design and achievement from the viewpoint of establishing the autonomous satellite link operation environment. We showed thatit is possible to shift the operation body from human operators to earth stations, andour model is superior to the existing operation scheme on granularity, cost, and flexibilityof satellite network operation. The evaluation also showed that our model removes theheterogeneity of operational environment, and provides the infrastructure technology forflexible satellite link operation.

Key Words1. Satellite Communication 2. Internet 3. Autonomous Operation

Keio University Graduate School of Media and GovernanceKotaro KATAOKA


3/59

2003 ( 15)

Design of the Autonomous Satellite Link

Operation Environment on the Internet

SNMP

ASN.1 SAT-MIB

Key Words

1. Satellite Communication 2. Internet 3. Autonomous Operation


4/59

Contents

1 Introduction 1

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Research Ob jective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Organization of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Existing Scheme of Satellite Link Operation 3

2.1 Earth Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.1.1 Classification by Communication Capability . . . . . . . . . . . . . . 32.1.2 Basic Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Forms of Earth Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2.1 HUB Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2.2 Terminal Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.3 Multiple Access Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3.1 Time Division Multiple Access (TDMA) . . . . . . . . . . . . . . . . 52.3.2 Frequency Division Multiple Access (FDMA) . . . . . . . . . . . . . 6

2.4 Data Link Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4.1 Point-to-Point Link . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4.2 Star-Shaped Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.4.3 Point-to-Multipoint Link . . . . . . . . . . . . . . . . . . . . . . . . 7

2.5 Basic Satellite Link Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 92.5.1 Satellite Link Configuration . . . . . . . . . . . . . . . . . . . . . . . 92.5.2 Data Link Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.6 Satellite Link Operation in the AI3 Project . . . . . . . . . . . . . . . . . . 112.6.1 Outline of Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.6.2 Satellite Link Configuration . . . . . . . . . . . . . . . . . . . . . . . 112.6.3 Satellite Link Monitoring . . . . . . . . . . . . . . . . . . . . . . . . 13

3 Operational Issues and Related Works 14

3.1 Heterogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.1.1 Functionality and Capability on Operational Environment . . . . . . 143.1.2 Operational Interfaces and Parameters . . . . . . . . . . . . . . . . . 15

3.2 Manual Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.3 Related Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.3.1 Dynamic Bandwidth Allocation (DBA) . . . . . . . . . . . . . . . . 173.3.2 Modem Watch Dog (MWD) . . . . . . . . . . . . . . . . . . . . . . . 19

i


5/59

4 Autonomous Satellite Link Operation Environment 22

4.1 Operation Model Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.2 Objective of Operation Model . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.2.1 Sustained connectivity of satellite links . . . . . . . . . . . . . . . . . 224.2.2 Routing Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . 244.2.3 Integrated Dynamic Bandwidth Allocation . . . . . . . . . . . . . . 254.2.4 Operation Cost Minimization . . . . . . . . . . . . . . . . . . . . . . 26

4.3 Functionalities of Autonomous Satellite Link Operation . . . . . . . . . . . 264.4 Communication Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . 264.5 Definition of Operational Domain . . . . . . . . . . . . . . . . . . . . . . . . 284.6 Definition of Operational Information . . . . . . . . . . . . . . . . . . . . . 284.7 Operational Information Focused on Satellite Modem . . . . . . . . . . . . . 304.8 External Information Available from the Internet . . . . . . . . . . . . . . . 314.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5 Requirements Organization 32

5.1 Unified Operation Interface and Functionalities . . . . . . . . . . . . . . . . 325.2 Redundant Connectivity to the Internet . . . . . . . . . . . . . . . . . . . . 345.3 Normalized Operational Information . . . . . . . . . . . . . . . . . . . . . . 345.4 Degree of Freedom on Notification Convention . . . . . . . . . . . . . . . . 34

5.4.1 Strict Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345.4.2 Free Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5.5 Coverage of Operational Information . . . . . . . . . . . . . . . . . . . . . . 355.6 Accesibility to Operational Information . . . . . . . . . . . . . . . . . . . . 36

6 Implementation of Autonomous Satellite Link Operation 37

6.1 Information Exchange on SNMP and MIB . . . . . . . . . . . . . . . . . . . 376.2 Definition of Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.3 Installation on Practical Satellite Link Operation . . . . . . . . . . . . . . . 39

6.3.1 Agent Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . 396.3.2 Modification of Modem Watch Dog . . . . . . . . . . . . . . . . . . . 40

6.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

7 Evaluation 43

7.1 Operational Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

7.2 Dissolution of Heterogeneity on Operational Environment . . . . . . . . . . 447.3 Sustainability of Satellite Links . . . . . . . . . . . . . . . . . . . . . . . . . 447.4 Operation Cost of Satellite Network . . . . . . . . . . . . . . . . . . . . . . 447.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

8 Conclusion 47

8.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478.2 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

8.2.1 Enhancement of the SAT-MIB . . . . . . . . . . . . . . . . . . . . . 488.2.2 Extension of Applicable Range of Our Model . . . . . . . . . . . . . 488.2.3 Security Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48


6/59

8.2.4 Standardization of Proposed Model . . . . . . . . . . . . . . . . . . . 49

Acknowledgement 50

Bibliography 51


7/59

List of Figures

2.1 Earth Station Components . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2 VSAT Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 Basic Concept of TDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.4 Basic Concept of FDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.5 Star-shaped Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.6 Broadcast Link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.7 Outline of Satellite Link Operation . . . . . . . . . . . . . . . . . . . . . . . 92.8 Overview of the AI3 Network . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1 System Dependent Environment . . . . . . . . . . . . . . . . . . . . . . . . 163.2 Overview of DBA System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.3 Overview of Modem Watch Dog . . . . . . . . . . . . . . . . . . . . . . . . . 193.4 Functionality of DCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.5 Functionality of MWD Server . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.1 Concept of Autonomous Satellite Link Operation . . . . . . . . . . . . . . . 234.2 Relationship between Eb/N0 and Coding Rate . . . . . . . . . . . . . . . . 244.3 Basic Concept of Rate Optimization . . . . . . . . . . . . . . . . . . . . . . 254.4 Cooperation between Earth Stations . . . . . . . . . . . . . . . . . . . . . . 274.5 Basic Concept of Operational Domains . . . . . . . . . . . . . . . . . . . . . 294.6 Structure of Operational Information . . . . . . . . . . . . . . . . . . . . . . 294.7 Structure of Operational Information on Satellite Modem . . . . . . . . . . 30

5.1 System Integration in Operation Domain . . . . . . . . . . . . . . . . . . . 33

6.1 Interaction among Earth Stations and External Nodes using SNMP . . . . 38

6.2 Definition of Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.3 Conversion from Eb/N0 to C/N . . . . . . . . . . . . . . . . . . . . . . . . . 416.4 Satellite Modems and Abstracted Nodes on SNMP and MIB . . . . . . . . 42

iv


8/59

List of Tables

5.1 Required Parameters on Satellite Link Operation . . . . . . . . . . . . . . . 35

6.1 Units and Syntaxes for Common Parameters . . . . . . . . . . . . . . . . . 40

6.2 Availability of Data Link Status Parameters . . . . . . . . . . . . . . . . . . 40

7.1 Comparison of Operational Components . . . . . . . . . . . . . . . . . . . . 437.2 Comparison of Operational Items on the AI3 Network . . . . . . . . . . . . 46

v


9/59

Chapter 1

Introduction

1.1 Background

A satellite covers a wide area on the earth and can broadcast data beyond the limitationsof geographical boundaries. Satellite links are effective infrastructure to provide Internetconnectivity in the areas where terrestrial data links or additional bandwidth for an existingdata link is hardly available. Furthermore, satellite links have flexibility on their data linkconfiguration. Bandwidth for each link, data link topology, and even antenna location canbe easily changed. These are the distinguished features of satellite communication comparedto other data links used on the Internet.

In recent years, the environment for joining the satellite-based Internet is easily available

by using satellite links as unidirectional links. A unidirectional link can be shared by a hugenumber of receive-only stations, and the operation in a receive-only station is simplified withcheap and easy-to-use equipments compared to a send-capable station. Contents such asdistance education[9] can be shared on a satellite network as a broadcast capable shortcutto deliver data anywhere within the satellite footprints.

In order to use satellite links efficiently, satellite links should be operated more flex-ibly with maximizing the data link characteristics and satisfying requirements for trafficcapacity. Satellite links are sensitive to their environmental conditions such as weather orsun interference depending on their frequency bands. Thus, status of satellite links oftenfluctuate and the links can go down due to environmental changes. On the other hand, dueto the growth of traffic and variety of applications on the satellite-based Internet, various

requirements are raised from users and applications. The most likely requirements are theones for keeping connectivity as long as possible and maximize the utilization of bandwidthresource.

It is essential for satellite links to respond to sudden changes in the environmentalcondition, including weather conditions and amount of traffic on a network, or requirementsfrom applications as quickly and safely as possible. Because any data link can be used on theInternet, several operational schemes of satellite links can be mixed in a single network. Notall satellite links have the capability for flexible operation that satisfies every requirementtoward the data link and reflects it on the link operation. Thus, although satellite linkare effective as data link for the Internet, they are not utilized by taking the maximumadvantage of their data link characteristics from the view point of managing them as the

1


10/59

data link of an IP network.

1.2 Research Objective

The objective of this research is to realize a flexible satellite link operation environment thatmaximizes the data link characteristics and the utilization of satellite links on the Internet.This research contributes to build an infrastructure technology to realize a flexible satellitelink operation that is independent of the heterogeneity of operation environments.

1.3 Organization of Thesis

This thesis consists of 8 chapters. The next chapter describes an existing satellite link

operation scheme, explaining the AI3 project as an example. Chapter 3 states the issueson satellite link operation and related works regarding automation of the satellite linkoperation. Chapter 4 proposes a new operation model of satellite links using the Internetas its communication infrastructure. Chapter 5 discusses requirements to implement ourmodel, and then chapter 6 describes the implementation of the model on actual satellitenetwork. Chapter 7 evaluates the model presented in this thesis based on the design andachievement from the view point of establishing the autonomous operation environmentfor the satellite-based Internet. Chapter 8 concludes this thesis and describes the futureworks.


11/59

Chapter 2

Existing Scheme of Satellite LinkOperation

This chapter describes several typical topologies using satellite links as their data links,basic operation procedure of a satellite link, and an international satellite-based networkoperated by the AI3(Asian Internet Interconnection Initiatives) project[10].

A satellite link is established between at least two earth stations via a satellite transpon-der. In this thesis, we assume the satellite as a geostationary satellite which is on thegeosynchronous orbit about 36,000 kilometers above the equator.

2.1 Earth Station

2.1.1 Classification by Communication Capability

Earth stations can be classified into three types based on the feature of communicationtoward a satellite link:

Send-receive station: A send-receive station sends a carrier and receives a carrier from thesatellite. In this thesis, we call a send-receive station simply as an earth station.

Send-only station: A send-only station sends a carrier but cant receive any carrier.

Receive-only station: A receive-only station receives a carrier from the satellite but cantsend a carrier.

2.1.2 Basic Component

An earth station consists of several equipments. Each equipment has its own functionthat determines the communication characteristics of the link. Figure 2.1 shows the basiccomponents of an earth station.

2.2 Forms of Earth Stations

There are a variety of forms of earth stations depending on intended purpose and func-tionality of earth station. Normally, an earth station has several facilities which in total

3


12/59

High Power

Amplifier

Up Converter

Satellite Modem

Down Converter

Transmission

Reception

Antenna,Feed Horn,

Diplexer,

Low Noise Amplifier

Figure 2.1: Earth Station Components

determine the characteristics of the link, and the station is fixed in a same place. Forms ofearth stations can be classified into a HUB station and a terminal station.

2.2.1 HUB Station

A HUB station is an earth station which connects to many satellite links. In some cases, aHUB station administers the links and controls the terminals stations which are located onthe opposite end of those links. For example, if TDMA is employed to assign channels foreach link, the HUB station should synchronize terminal stations on the link. And then, aHUB station allocates the time slots and bandwidth for each channel.

A HUB station can be a single point of failure when it has a trouble. Therefore, some

facilities backups to provide redundancy for the HUB station. In general, a HUB stationis large in scale because it provides many functionalities and physical facilities to operatemany links.

2.2.2 Terminal Station

A terminal station connects to a HUB station or another terminal station. But, a terminalstation does not have the functionality of relaying received signals to another earth station.Some terminal stations are fully controlled by a HUB station after the terminals receive thesatellite signal. That is typical for TDMA systems, and users or operators in the terminalstations dont have to configure the frequency or information rate by themselves.

If an earth station is intended to be portable, the functionality of the earth stationis integrated in small number of facilities. A VSAT (Very Small Aperture Terminal) isa portable earth station. Using a VSAT, a satellite link can be established in almost allplaces, only if flat ground to put an antenna is available and a satellite is acquired withoutobstacles between the antenna and the satellite.

A VSAT is composed of an antenna, an IDU (Indoor Unit) and an ODU (Outdoor Unit).Generally, an IDU is a satellite modem. An ODU is an electric equipment that providesthe functionalities to communicate with a satellite: a feed horn, an up converter, a poweramplifier, and a combination of low noise amplifier and down converter (LNB: Low NoiseBlock converter). A coaxial cable is used to connect between the ODU and the IDU. Figure2.2 shows the basic topology of a VSAT earth station.


13/59

IDUSatellite Modem

Antenna,

ODUFeed Horn,Diplexer,Up Converter,

High Power Amplifier,

Low Noise Block Converter

Coaxial Cable

Figure 2.2: VSAT Components

2.3 Multiple Access Methods

A satellite link is established on a channel which is assigned to each link. In order to establishplural satellite links on a transponder, multiple access is applied. Multiple access dividesthe band of transponder into several channels on which multiple links are established. Thissection describes two major multiple access methods.

2.3.1 Time Division Multiple Access (TDMA)

TDMA divides the band of transponder into multiple channels by time. Sending earthstations burst signals during the assigned time slots in periodical time frames in order.Receiving earth stations discriminate the sender stations from the whole received signalsfrom the satellite by the time slots and frames. Those time slots and time frame have to

be synchronized among a sending station and a receiving station so that they can send orreceive the signals promptly. Figure 2.3 shows the basic concept of TDMA.

S2

S2

S2

S2

S1

S1

S1

S1

S3

S3

S3

S3

FrequencyBand

times

lot

frame

time(t)

(A)

(A)

(B)

(C)

(C)

(B)

Figure 2.3: Basic Concept of TDMA


14/59

If information speed of a certain link is to be modified, TDMA does not need to modifythe frequency assignment. This is because information speed of a link is determined bythe total size of time slots assigned for the link per unit of time. The functionality ofon-demand bandwidth allocation is introduced on the system which applies TDMA as itsmultiple access method.

2.3.2 Frequency Division Multiple Access (FDMA)

FDMA divides the band of transponder into multiple channels by frequency. Sending earthstations send signals on the frequency which is assigned for each station. Receiving earthstations discriminate the sending stations from the whole received signals from the satelliteby frequency which is assigned for each channel. Figure 2.4 shows the basic concept ofFDMA.

(A)

(A)

(B)

(C)

(C)

(B)

f1

FrequencyBand

f2

f3

Figure 2.4: Basic Concept of FDMA

FDMA is more popular than TDMA as a multiple access method. This is because, in

the case of FDMA, the procedure of multiple access is simple, and the equipment of earthstation is cheap compared with that of TDMA.

2.4 Data Link Topologies

In general, there are three types of data link topology by satellite link.

2.4.1 Point-to-Point Link

A point-to-point link directly connects two send-receive stations. These two earth stationstransmit radio wave to the satellite, and they have bidirectional communication with each


15/59

other. A point-to-point link is composed of two communication channels, one channel isused for one direction and the other channel is used for opposite direction.

2.4.2 Star-Shaped Links

Star-shaped links interconnects several terminal stations via a HUB station. Every terminalstation establishes a point-to-point link to the HUB station. To build a mesh topology bystar-shaped links, 2(n 1) channels are consumed on the mesh in total. On the otherhand, if every earth station establishes point-to-point links with the other earth stations,

n(n 1) channels are consumed on the mesh. Thus, to establish a network where manyearth stations are interconnected, star-shaped links are reasonable to apply, because theyconsume less channels than the point-to-point links in the data link mesh. Figure 2.5 showsthe basic concept of star-shaped links.

Send-ReceiveStation (HUB)

Send-Receive

Stations

Figure 2.5: Star-shaped Links

2.4.3 Point-to-Multipoint Link

A point-to-multipoint link broadcasts data from one send-only station to multiple receive-only stations at the same time. Figure 2.6 shows the outline of a point-to-multipoint link.A receive-only station is cheap in price and there is no limit on the number of receive-onlystations which listen to the link. Also, operation of a receive-only station is simple comparedwith earth stations which can transmit radio frequency, because a receive-only station haslimited functionalities and consists of equipments of small scale.

A point-to-multipoint link is used as a unidirectional link. However, because the Internetarchitecture assumes bidirectional connectivity of its data link, some functionalities of the


16/59

Send-OnlyStation (FEED)

Receive-OnlyStations (Receivers)

Figure 2.6: Broadcast Link


17/59

Internet, such as MAC address resolution and routing protocols, do not work correctly ona unidirectional link. UDLR (Unidirectional Link Routing)[4] was developed to utilize aunidirectional link on the Internet by layer 2 tunneling and broadcast emulation. Thistechnology makes it possible to use a satellite link as a broadcast link which is shared bymany earth stations like Ethernet.

2.5 Basic Satellite Link Operation

Operation of satellite links is divided into two phases. One is to configure and execute theparameter settings on each earth station. The other is to monitor the status of satellitelinks to be aware of the link status changes. Figure 2.7 shows the outline of basic satellitelink operation.

Configuration

Data Link Status

Configuration

Data Link Status

Manual Operation

Control Center

Figure 2.7: Outline of Satellite Link Operation

2.5.1 Satellite Link Configuration

Generally, the main component of satellite link operation is human operator at each earthstation. Operators configure the parameter setting of satellite links at each earth station,based on the topology plan and the assigned bandwidth usage of the network to be con-structed using these links. Parameters to establish a satellite link must be synchronized atevery earth station which is connect to the link. Operators have to use e-mail, telephoneor facsimile, etc. in order to share the parameter settings of satellite links. If parametersin each earth station are set differently, the link is not be established. In addition, if the


18/59

transmission frequency is accidently set to use other links frequency differently, communi-cation on those other links are disturbed. Typical parameters that must be synchronizedamong earth stations are as followed.

Transmission frequency

Reception frequency

Modulation type

Demodulation type

Coding information speed

In general, once the parameters of satellite links are set, these parameters are fixed for along period of time. However, when operators change the setting of the links, they need toconfirm the parameters to be changed and schedule the time and day of work. They haveto stay in close contact with operators in the other earth station all the time during thework.

2.5.2 Data Link Monitoring

Due to sensitivity of a satellite links, monitoring data link status is essential in the satellitelink operation. The definition of the data link status depends on the data link type. Inthe cases of the IEEE 802.3 wired data links or the ATM links, the status of its data linkis stable once the link is established. Thus, it is general that the status of those links issimply determined as UP or DOWN, though they have some operational parameters.On the other hand, in the cases of the IEEE 802.11 wireless data links, those data linkstatus fluctuates depending on their environmental conditoins such as composition of airstations, channel allocation and so on. And then, end users can easily check their datalink performance by estimated throughput, because the data link performance is monitoreddirectly on the users PCs.

The status of physical satellite link is determined by combination of several parametersthat shows the link status in different measures. Normally, those parameters are measured atthe input interface of a demodulator or calculated in the demodulator. Typical parametersthat show the data link status are as follows.

Received signal level (RSL): RSL is a measure of the received signal strength on the inputinterface of the demodulator.

Carrier to noise ratio (C/N or CNR): C/N is a measure of the received carrier strength tothe received noise strength.

Bit error rate (BER): BER is a ratio of the total numebr of transmitted bits to erroredbits. BER can be measured before or after error correction in the demodulator.

Energy per bit to spectral noise density (Eb/N0): Eb/N0 is a measure of the receivedsignal strength to noise in digital communication. Eb/N0 shows the data link qualitywhich is mapped to BER on a certain modulation type.


19/59

Because on a satellite-based network, the links are established by several earth stationslocated at different places, those links have different status depending on the environmentalconditions at the edges of the links. Thus, the total status of a satellite link has to bedetermined based on the collection of the monitoring result at all earth stations on thatlink.

Operators can not know the complete status of a satellite link by monitoring the linkstatus at a single earth station. It is difficult to know the link status based on the informationonly from the local earth station. Thus, to interpret the situation correctly, operators needexternal information on the status.

Regarding a single point-to-point link, the link status should be monitored at both edgeof the link. On the other hand, in order to monitor a broadcast link, the link status shouldbe monitored on the input interface of every receive-only station which listens to the link.In both cases, the monitoring result in each earth station should be shared to indicate thetotal status of satellite data link.

2.6 Satellite Link Operation in the AI3 Project

This section introduces the AI3 project as the instance on which several types of satellitelinks are operated in a single network. The AI3 project is an organization for research anddevelopment activities of the Internet technology. The AI3 project has established a widearea network that covers the Asian region utilizing satellite links as its data link. Severalresearch institutions and universities in the Asian region join the satellite-based network.We call an organization which joins the AI3 network as a site.

2.6.1 Outline of Network

The AI3 network is composed of three types of satellite links: Ku-band point-to-point links,C-band point-to-point links and C-band point-to-multipoint link. Figure 2.8 shows the basicdata link topology of the AI3 network.

The Ku-band point-to-point links and the C-band point-to-point links form star topolo-gies, putting hub stations in Nara Institute of Science and Technology (NAIST) for Ku-bandand Keio University Shonan Fujisawa Campus (SFC) for C-band relatively. The C-bandpoint-to-multipoint link, whose hub station is SFC, is a shared by several recieve-only sta-tions and send-receive stations which connected to the point-to-point links. Because thebandwidth of the link is wider than other point-to-point links, some send-receive sites useit as their high speed down link. In the AI3 network, every site has a send-receive stationor a receive-only station, or both of them.

2.6.2 Satellite Link Configuration

The earth station in each site is operated by local operators. Configuration of satellite linksis done by manual operation in each site. When there is a major configuration renewalwhich involves all sites of the network, such as re-allocation of satellite link bandwidth, thework procedure and the schedule are fixed in advance and the related sites have to work atthe same time.


20/59

HUB

HUB

HUB

C-bandPoint-to-Point Links

C-bandPoint-to-Multipoint Link

Ku-bandPoint-to-PointLinks

Figure 2.8: Overview of the AI3 Network


21/59

In some sites, it is difficult for the local operators to configure the satellite link by themselves. Those site are very newbies in the network and the local operators dont have enoughskill to operate the earth station. In this case, operators from other site have to visit thesite and configure the link on behalf of the local operators.

2.6.3 Satellite Link Monitoring

On the AI3 network, the status of a satellite link is monitored at each earth station whichlistens to the link respectively. There are three types of satellite modems which are usedto monitor the status of each satellite data link. Although each satellite modem is capableof displaying the data link status, display style and access method of these modems aredifferent among them.

Currently, because each site is operated independently, the information captured in each

site is not shared on the whole network. In some cases, the lack of information makes itdifficult to detect the trouble or investigate the source of satellite link trouble.


22/59

Chapter 3

Operational Issues and RelatedWorks

This chapter elaborates problems on the existing operational cheme of satellite network ina widely spread area.

3.1 Heterogeneity

3.1.1 Functionality and Capability on Operational Environment

The Internet does not rely on a specific data link protocol or the data link itself. Therefore,

there are many forms of earth stations with different functionalities. And then, many kindsof satellite links can be introduced in a satellite network, only if those links are capable ofdelivering IP packets.

Operational environments that have their own charactristics can be mixed on a singlesatellite network. This factor makes the operation environment of satellite links hetero-geneous. For example, followings are the typical components that make operational envi-ronment of satellite network heterogeneous: data link topology and configuration schemes,controllable range of satellite link, availability of feedback from other earth statoins orexternal nodes, etc.

Depending on forms of earth stations, their basic compositoin may be different. Theirdetailed composition is also different according to their economic, operational or functional

constraint of equipment. The functionalities of earth stations can be different according tothe objectives to settle the earth stations. Also, major functionalities of an earth station areto send a carrir to a satellite, receive a carrier from a satellite, and both of them. Dependingon these functionalities, other functionalities are implemented on respective earth stations.

Heterogeneity of operational environment splits an operational domain into narrow subdomains. In those sub domains, operational functionalities are limited in their variety andapplicable range depending on forms and specification of earth stations. Thus, the operationof satellite links is not systemized from the view point of data link operation on the Internet.

Even though operation cost of a certain satellite link is low, the total cost of operationin the network may not be reduced radically. Furthermore, another cast can be created toachieve a operational balance among that link and the other links on that network. For

14


23/59

example, even though a HUB station is capable of on-demand bandwidth allocation toterminal stations on a satellite link, some other earth stations may need manual operationto configure the parameter settings of the remaining satellite links.

3.1.2 Operational Interfaces and Parameters

Equipments of an earth station have their vendors own operational interfaces, which arenot designed to be monitored and controlled via the Internet. In many cases, operators haveto handle those equipments directly or implement some agents to monitor and control themfrom remote based on the specification of each equipment. From the view point of datalink operation as a whole network, it costs much in time and human resources to operateequipments made by several vendors in different manners due to the difference of interfacespecification.

On the other hand, the operational parameters are defined differently depending onthe specification of vendors. It is often the case that different units are used on a singleparameter, some parameters are curtailed, and so on. For example, in the case of the AI3

network,

on an SNR-PS1000 satellite demodulator, demodulation information speed is set byonly symbol rate with the unit of sps

on a NEXTAR-CLVR VSAT IDU, radio frequency is set by only channel of 25KHzstep on its user interface.

Therefore, if several types of satellite link are operated in a single domain, operators have

to calculate the suitable parameter settings for each facility from the equipment-dependentconditions and the values of the target parameters. Additionally, in order to monitor thestatus of satellite links as correctly as possible, operators have to calculate the data linkstatus from limited values that are available on the equipments.

Figure 3.1 shows three applications that are separated into different applications becauseof the heterogeneity of operational environment. Each applicatoin in the figure providesthe same functionality. However, because the operational interfaces or parameters aredifferent between respective systems, the applicable range is limited to a single satellitelink, Therefore, three different applications are installed to provide the same service in asingle satellite network.

3.2 Manual Operation

In the operation of satellite links, operators have to coordinate among them in order to syn-chronize the parameter settings depending on the status of the data link and environmentalconditions. However, the cooperation among operators is often problematic.

One of typical problems in coordination among operators is a matter of language. In thewide area network operation that covers several countries and regions, it is often the casethat operators have trouble with communicating among them, because they are workingin different countries or regions. For instance, English is mostly spoken as the commonlanguage in the Asian region. However, not all of the operators can speak English well


24/59

BidirectionalLink(A)

Application (A)

BidirectionalLink(B)

Application (B)

UnidirectionalLink

Application (C)

Figure 3.1: System Dependent Environment


25/59

enough to understand the dialog to establish the link and to adjust operational parametersin detail.

Besides that, operators have to configure and check many parameters and status in theoperation. However, not all operators have enough knowledge and experience to operatea satellite link. In addition, because the earth station transmits amplified radio frequencywave in the air, operators are obligated by law to hold a license to operate a radio stationin some countries. Therefore in some cases, local staffs can not operate their earth stationby themselves.

It is hard for operators to continue to adjust the data link setting to its status orenvironmental conditions in a short period of time. This is because the operators have tosynchronize the operational schedule and stay at the earth station all the time. Thus, theoperation cost by human operators is very high to realize the flexible data link operationon the widely spread area. In an earth station whose operation relies on human operators,it costs very much in human resources and time. Thus, the various kinds of informationsuch as amount of traffic on network or data link status cant be reflected on the data linkoperation in real time. As a result, satellite links are operated without flexibility which thelinks have in nature.

3.3 Related Works

This section describes two systems are designed and implemented to minimize the opera-tional cost of satellite links: Dynamic Bandwidth Allocation and Modem Watch Dog.

3.3.1 Dynamic Bandwidth Allocation (DBA)DBA[5] describes a system which is designed to dynamically change the bandwidth of eachsatellite link based on the amount of traffic on the router of each link. DBA configuresthe parameter settings regarding modulation and demodulation frequency and informationspeed on the satellite modems from remote on the Internet.

Figure 3.2 shows the overview of DBA system. A HUB server calculates optimizedbandwidth allocation for each satellite link according to the notification of traffic from eachlink. And then, the server determines the parameter settings for each channel, such as infor-mation speed, frequency and so on. Those parameter setting are sent to the remote controlmodule which controls satellite modems to change the parameter settings of the links. Eachearth station has its own remote control module and the configuration is delivered on theInternet.

A remote control module works on a PC which is directly connected to a satellite modemwith a serial cable. The remote control module administrates the procedure of satellitemodem configuration that is executed by the modem control module that is running on thesame PC. If the configuration on the modem is failed on any earth station, the configurationof all the earth station is resumed to the previous one.

DBA system solved the problem that the bandwidth allocation was fixed for the longperiod of time and the bandwidth resource was utilized efficiently in the C-band networkof AI3 project.

The problem of DBA system is taht the applicable range of the system is restricted.This is because the system is designed exclusively for the AI3 C-band network, and highly


26/59

Control Line

Data Line

Spectrum

Analyzer

Data Line

Control Line

Data Line

Control Line

Data Line

Control Line

HUB Server

Bandwidth Allocation Module

Remote Control Module

Radio Frequency Monitor Module

HUB Server

Send Command of Control Information

Request for Radio Frequency Status

Traffic Monitor Module

Remote Control Module

Modem Control Module

Terminal PC

NotificationofTraffic

ExchangeofControl

Information

Satellite Modem

Control

InformationExchange

Figure 3.2: Overview of DBA System


27/59

depends on the specification of satellite modem. Therefore, to deploy this system on othertypes of satellite links, the developers have to make many modules to suit the equipmentof the earth stations to the system.

3.3.2 Modem Watch Dog (MWD)

MWD[6] is a system that automatically collects status of satellite links and summarizes itin a graph that shows continuous status of satellite data link. Operators can monitor thedata link status from anywhere via the Internet. Figure 3.3 shows the overview of MWD.

INTERNETINTERNET

MWDS

DCMSDM-300A

WWW Client

Request for

Link Status

Response

Figure 3.3: Overview of Modem Watch Dog

MWD is composed of the data collect module (DCM) and the MWD server. DCM works

on a PC that is connected to a satellite modem with a serial cable. Because the satellitemodems that are dealt with on this system do not have accessibility on the TCP/IP suite.Thus, DCM connect to control port of the satellite modem and sends several commands torequest the necessary status information: Eb/N0, BER, and RSL. DCM, which is connectedto the Internet, makes it possible for other nodes to access those parameters on the Internet.Figure 3.4 shows the functionality of DCM.

MWD server requests a DCM for the data link status of each satellite link. The serverhas a database and stores the status information in it. MWD server also visualizes thestored data link status in graphs whish different time scale: three hours, one day and oneweek. The graphs are uploaded onto the web page and operator can check them on theInternet. Figure 3.5 shows the functionality of MWD server.


28/59

Multi-portSerial Card SDM-300A

Satellite Modems

RS-232

Commands forGet Status

StatusResponse

DCM

Figure 3.4: Functionality of DCM

Graph

Generator

HTTP Server

Database

MWD Server

Raw Data from DCM

Summarization

Web Page

DBDB

Figure 3.5: Functionality of MWD Server


29/59

MWD reduced the operational cost of satellite link regarding monitoring those datalink status. However, as is the case with DBA system, MWD focuses on specific satellitemodems in the AI3 network. Therefore, it takes cost to extend the system to different typesof satellite modems.


30/59

Chapter 4

Autonomous Satellite LinkOperation Environment

This chapter proposes a new operation model of satellite networks that is called au-tonomous satellite link operation environment.

4.1 Operation Model Outline

The new operation model abstracts earth stations as nodes which are accessible from any-where on the Internet. Figure 4.1 shows the basic concept of the proposed operationenvironment. In the real space, a satellite network is composed of several satellite link

topologies, and earth station have different forms and accessibility from the links. However,when those earth stations are projected onto the proposed operation environment, theycan be controlled from remote on the unified operation scheme beyond the heterogeneity ofoperational environment.

4.2 Objective of Operation Model

The objective of this operation model is to realize a flexible satellite network operationthat provides following features to construct the operational infrastructure for generalizedsatellite link operation.

Sustained connectivity of satellite links

Routing Optimization

Integrated Dynamic Bandwidth Allocation

Operation Cost Minimization

4.2.1 Sustained connectivity of satellite links

A satellite link can go up and down intermittently when the data link status fluctuates.However, if the total data link status gets improved by some ways, the link can be keptestablished or the connectivity can be resumed.

22


31/59

Accessible via the Internet

Projection from the Real Space

to the New Operation Model

Figure 4.1: Concept of Autonomous Satellite Link Operation


32/59

There is a relationship between required Eb/N0, information speed and coding rateon desired BER. Figure 4.2[1] shows the shifting of BER that is calculated from severalcombinations of Eb/N0 and coding rate. A satellite modem has its own communicablerange on every coding rate selectable on the modem. The communicable range is differentbetween the coding rate settings. In general, if a coding rate employs the combination ofhigh information speed and low FEC rate, a satellite link requires high Eb/N0 level acquirethe desired BER and to keep the link established. On the other hand, if the coding rateis set with slow information speed and high FEC rate, even though the Eb/N0 is low on asatellite link, the link can be kept established.

Figure 4.2: Relationship between Eb/N0 and Coding Rate

The coding optimization controls the information speed and the coding rate to acquirethe coding gain of the link when the status of receiving carrier changes for worse.On the other hand, based on the data link status, the information speed can be always

maximized upon best effort. Figure 4.3 shows the basic concept of the rate optimization.

4.2.2 Routing Optimization

In order to build a routing table based on dynamic routing protocols, routers on the linkperiodically exchanges available paths with their neighbors. However, those routing pro-tocols do not hold the detailed data link status of each satellite link as their operationalinformation. Thus, the routers can not correctly determine whether the link is available ornot, if the data link connectivity fluctuates.


33/59

2048

1536

1024

512InformationSpeed(Kbps)

Time (t)

Data Link Status

Optimized

Information Rate

Figure 4.3: Basic Concept of Rate Optimization

When a satellite link fluctuates a little, the route that uses the link as the path to thenext hop may not be advertized to the other neighbors, even though the link has goodenough data link quality to establish it. On the other hand, the route may be treated asan available path all the time, even though the satellite link is down almost all the time.Route flaps[2] or mis-selection of path occur because of divergence between the actual datalink status and the link status that is recognized by the routing protocols. As a result, theperformance of a satellite network will be depressed.

Connectivity of a satellite link may continue to go up and down in a short period of time,or the link may keep to be barely up. Thus, routing optimization that ensures routers knowthe satellite link status is considered as a solution for stabilize dynamic routing on a satellitenetwork. The routers can determine the link availability based on not the simple packetexchange among routers but the continuous status of the link status and advertisementpolicy of the link.

If the status of satellite data link is available on the network, the router can flexibly de-termine the availability of the link based on the link status. As a result, mis-advertisementsof dead path or route flaps can be reduced, and the stability on the satellite network willbe improved.

4.2.3 Integrated Dynamic Bandwidth AllocationDBA system creates a high cost in deploying among new equipments, because developerhas to write the control module which is suitable for the new equipment. Therefore, therange of deployment is limited and the link utilization or performance can not be improvedon the whole network. However, if uniformed accessibility to the operational informationand interface are consolidated on every earth station, the cost for installing DBA systemwill be minimized.

In the network where the multiple satellite link utilized toward the single destination,load balancing in the data link layer beyond the difference of specification of equipmentsor the frequency bands is realized. If the load balancing in the upper layers is failed, the


34/59

bandwidth of satellite data link is reconfigured and overflow of the link can be avoided.

4.2.4 Operation Cost Minimization

The autonomous satellite link operation allows human operators to be free from manualoperation in the earth station unless mechanical failure occurs in the earth station. Manualoperation by human is the bottle neck of the flexible satellite link operation which can berealized in real time from the view point of potential of satellite date link itself.

The role of human operators will be decreased to check the visualized result of systemadministration or monitored data link status from remote. Human operators do not have toknow all values of each parameter that is continuously acquired in the earth station. Whenany failure is detected by a system, human operators take some actions to fix it. This isthe same with the general operation scheme of the Internet.

4.3 Functionalities of Autonomous Satellite Link Operation

The elements of this operation model are as follows.

Dynamic configuration of satellite link

Automatic monitoring of satellite data link status

Operational Information exchange among earth stations

Reflection of information from external environments

Each earth station dynamically changes the parameter settings based on the opera-tional information from other earth stations and external nodes on the Internet. Therefore,this operation model attaches importance to interaction among earth stations and nodeswhich have requirements or information to the link. Figure 4.4 shows the basic concept ofcooperation between earth stations in this operation model.

Compared with the existing operation model mentioned formerly, the operation pro-cedure is simplified and the operation cost is drastically reduced in this operation model.This is because the proposed model doesnt need human operators as the main componentand a human friendly schedule can be eliminated from satellite link operation, becauseearth stations cooperate by themselves. Thus, interval of configuration modification can be

shortened and the data link can be optimized according to the data link status in real time.

4.4 Communication Infrastructure

In the proposed model, connectivity among earth stations is necessary as well as that tothe external nodes. We adopt the Internet as the communication infrastructure in theoperational domain. Therefore, even if direct connection via a satellite link is down, anearth station can communicate with other earth stations. Even though an earth stationonly has receive-only connectivity to the satellite link, it can communicate with other earthstations by the UDLR technology. On the other hand, earth stations can easily communicatewith external nodes, such as routers or any other nodes which may hold the information


35/59

Configuration

Data Link Status

INTERNETINTERNET

Configuration

Data Link Status

Autonomous Cooperation

Figure 4.4: Cooperation between Earth Stations


36/59

regarding bandwidth consumption, time schedule or any other requirements toward thesatellite data link.

4.5 Definition of Operational Domain

An operational domain is an administrative range of satellite links that can be autonomouslyoperated. The operational domain does not depend on a specific system or the types of theearth stations. The operational domain administrates the frequency bands allocated by thesatellite communication carrier based on its own operational policy. In this domain, theoperational information is shared among earth stations and external nodes on the domain.And then, ach earth station condigures the parameters to connect to the link. Also, a nodescan request an earth station to change the configuration of satellite link.

Figure 4.5 shows the basic concept of the operational domain. A circle and a box in thefigure indicate an earth station and an external nodes respectively. Also, a croud, a dashedoval and a dashed arrow indicate a network, a range of operational domain and informationexchange. The case A, C, and D show that satellite links are established by several earthstations with communicating with external nodes. In the case A, an operational domaincovers earth stations and external nodes across two netwroks. In the case C, an operationaldomain covers earth stations and an external node in a same network. In the case D, anoperational domain covers 3 types of earth stations and an external node in a same network.Lastly, in the case B, an operational domain covers only earth stations in a same network,and the earth stations exchanges the operational information between them.

On the other hand, if an earth station is accessible without security consideration,

satellite links can be configured illegally and impact other satellite links which share thesame transponder. Therefore, this is desirable that the access to the operational domainis limited by some authentication methods. In this thesis, we focus on systemizing theinformation of satellite link operation based on the assumption that, because earth stationsare treated as nodes on network, they are taken care of in the same way with other nodesaccording to the security policy of each network.

4.6 Definition of Operational Information

Operational information is hold by earth stations in an operational domain. The opera-tional information is exchanged by the earth stations in the operational domain and the

information consists of three components. Figure 4.6 shows the main components of theoperational information.

Earth Station Information: In an operational domain, an earth station is an administrativeunit. Earth station information is the aggregation of parameters that identify eachearth station by station ID or code name, location, responsible organization and soon.

Satellite Link Information: Generic link information is the aggregation of representativeparameters which describe each satellite links operated in the earth stations. Thegeneric link information includes the name of target satellite and transponder, andcarrier frequency, information speed and so on.


37/59

Case A Case B

Case D Case C

Figure 4.5: Basic Concept of Operational Domains

Earth StationIdentification

Satellite LinkInformation

Facility Information

OperationalInformation

Figure 4.6: Structure of Operational Information


38/59

Facility Information: Facility information is the aggregation of the parameters which eachfacility in the earth station have. The entries of facility information can differ accord-ing to composition of the earth station. If the earth stations is an VSAT, the entriesshould be the antenna, the IDU, the ODU and the Inter-Facility Lines (IFL) such asthe coaxial cable. In the case of a HUB station, the many facilities are listed as entriesin the facility information as described in the section 2.2.1.

In the generic information, the satellite link information and the facility informationis cross-referred with each other so that the facility can be referred easily. If a trouble isoccurring on a satellite link, all facilities which establish the link can be referred one afteranother. Assuming that every facility has its own status information, the referrence to thosefacilities provides quick investigation of trouble source in the earth station.

4.7 Operational Information Focused on Satellite Modem

As mentioned in the section 2.1.2, an earth station is composed of several equipments.However, in satellite link operation, it is general that most of parameter settings for asatellite link are configured on a satellite modem.

In this thesis, we focus on a satellite modem and define the operational information tobe shared among earth stations via the Internet. We define the operational informationbased on functionalities which are necessary to establish a satellite link. Figure 4.7 showsthe structure of the operational information on a satellite modem.

System Information

Modulation (TX)Configuration

Demodulation (RX)Configuration

Data Link Status

Alerts

Satellite Modem

Figure 4.7: Structure of Operational Information on Satellite Modem

System Information: System information signifies the parameters which are related to iden-tification of the satellite modem and the system specific information such as systemtime or network configuration to connect to the Internet.

Modulation Configuration: Modulation configuration the aggregation of parameters whichare related to transmitting carrier to a satellite.


39/59

Demodulation Configuration: Demodulation configuration the aggregation of parameterswhich are related to receiving carrier from a satellite.

Data Link Status: Data link status the aggregation of parameters which are related tothe status of satellite data link. Because the data link status is no determined by asingle parameter, several parameters are required to show the link status from differentaspects.

Alerts: Alerts are the aggregation of parameters which are related to the alerts which asatellite modem issues to notify a mechanical fault or any other incident occurring onthe modem.

4.8 External Information Available from the Internet

In this thesis, we avoid to define external information strictly. This is because the informa-tion from the external environment is boundless and the necessary information varies fromobjective that is intended to be achieved in each application or system. Thus, this operationmodel should provide an access interface that enables interaction with other applicationsor systems. This access interface increases the extensibility of this operation model.

The external information can contain any semantic data: operational command fromhuman operator, real time status of weather condition or network, prediction of sun inter-ference, or any other data. This operation model provides any other nodes with the accessinterface to give feedback or reflect such information to the satellite link operation.

4.9 Summary

In a satellite network, frequency band is essential resources, and it is shared by severalsatellite links. Thus, no matter what functionality is available on a satellite link, every linkshould be operated based on the cooperation with the other satellite links. However, inthe existing operational scheme, the heterogeneity of operational environment depress theefficiency of satellite link operation. This is because heterogeneous operational methodsand components coexist in a single satellite network.

This chapter proposed a new operation model for satellite networks: Autonomous Satel-lite Link Operation. The objective of our model is to realize the flexible satellite link oper-ation by cooperation among earth stations and exteral nodes on the Internet. Our modelprovides a unified platform for earth stations, human operators and any other nodes whichwant to access to the satellite link operation environment. As the main components of thenew operation model, we described the functionality, communication infrastructure and theinformation to be exchanged among the earth stations. We focused on a satellite modemas the main facility of satellite link operation and classified the operational information byfunctionality of them.


40/59

Chapter 5

Requirements Organization

This chapter describes the requirements organization on the implementation of the au-tonomous satellite link operation model, In the proposed operation model, the applicablerange of an operational functionality is extended from a specific satellite link to the datalink network.

Figure 5.1 shows basic concept of applicable range which should be commonly keptin design of each application in the satellite network. Compared with the figure 3.1 in thesection 3.1.2, a single application covers the whole satellite network beyond the heterogeneityof each satellite link.

Information exchange is the essential component on the autonomous satellite link op-eration. This is because integration of an operational functionality is achieved based on

exchange of the operational information. Following sections describes the requirements inorder to cover up the heterogeneity of the operational environment of satellite network.

5.1 Unified Operation Interface and Functionalities

Actual equipments in each earth station have physically different access lines or controlinterfaces respectively. In the operation model provides an operation interface by whichany nodes or human operators can access earth stations in the same way. And then, onthe Internet, those equipments are abstracted as nodes which are accessible from remoteindependently of difference of the physical specification of equipment. Basically, followingtwo functionalities must be provided on the unified interface.

Get function: Get function retrieves and displays a requested parameter on equipment inan earth station.

Set function: Set function sets a parameter on equipment in an earth station. Set functionshould respond with some return values no matter whether the function is succeed inexecuting the function or not.

Considering the cost on adopting this unified interface on existing equipment and earthstations, it is desirable that there is no modification on them. Also, not all earth stationsare capable of IP-based communication. It is practical that agents that is capable of bothconnecting to the Internet and communicating with earth stations on their own access lines.

32


41/59

BidirectionalLink(A)

BidirectionalLink(B)

UnidirectionalLink

Integrated Application (A+B+C)

Figure 5.1: System Integration in Operation Domain


42/59

5.2 Redundant Connectivity to the Internet

If an earth station connects to the Internet only by a satellite link, the earth station canbe isolated from the operation domain when the IP connectivity via the satellite link islost. And then, the earth stations can not communicate with other earth stations, and thesatellite network may loss the total balance as an operation domain. Therefore, redundantconnectivity to the Internet should be guaranteed in each earth station by some ways. It isdesirable that another satellite link is excluded as the external link for the Internet. Thisis because both of those satellite links can get down at the same time because of weatherconditions.

5.3 Normalized Operational Information

The operational information should be defined clearly enough so that any satellite modemcan recognize each parameter. Thus, every parameter should be defined with its suitablemeasure and granularity relatively. In order to normalize the operational information, someparameters have different units. For example, in general, the frequency of radio wave isdescribed in Hz, KHz or MHz. However, some satellite modems specify the frequency aschannel with interval scales in several KHz. And then, KHz is chosen as the unified measureof frequency.

5.4 Degree of Freedom on Notification Convention

5.4.1 Strict ValuesOn the other hand, some parameters such as Forward Error Correction rate or Reed Solomonrate which are ratio of the redundant data in the total amount of data. In order to describerates of those parameters, several types of values are used on satellite modems. FECrate (ex. 3/4) can be described as follows. Both notifications have their advantage anddisadvantage.

String in a single value: FEC Rate (Data Bits/Total Bits) = 3/4

Integer in plural values: Data Bits = 3, Total Bits = 4

The notification by string is human operators friendly. However, when the string value isspecified wrongly, for example, 3/4 is written as 3:4 or 4/3, which cant be recognizedby a satellite modem. Thus, string notification costs in verification of the specified value andprocess after inconsistency is detected. On the other hand, the notification by two integersis not so human friendly. But, the meaning of each value is clear and the inconsistency ofnotification will be less than the case of the notification by string.

Assuming that any application can access to the values and human operators dont haveto directly configure those values, the two integers are used for the notification of FEC andReed Solomon rate.


43/59

5.4.2 Free Description

It is impossible to strictly classify the status of trouble which is occurring inside the satellitemodem, because the granularity of error state can differ among satellite modems. It has anegative aspect of decreasing the degree of accuracy of information to unify the error statestrictly. Thus, regarding the error status, the degree of freedom on notification conventionshould be high.

5.5 Coverage of Operational Information

The parameters which are available on an earth station are different depending of thespecification of each earth station. It is probable that not all parameters are availabledirectly on it. However, because some of those parameters are critical for the satellite link

operation, we should acquire such parameters by means of calculation from other relatedparameters or other ways.

Table 5.1 shows the parameters which should be available on each earth station. Weclassified them by functionality of earth stations. If an earth station is a send-receive station,all of listed parameters are required. The parameters of the field (A) and (B) should beavailable on a send-only station, and those of the field (A) and (C) should be available ona receive-only station.

Table 5.1: Required Parameters on Satellite Link OperationEarth Station ID

Identification of Satellite Link IDSatellite Link (A) Target SatelliteTarget Transponder

Modulation Radio FrequecyModulation Intermediate FrequecyModulation TypeModulation Information Speed

Sending Carrier (B) Modulation Coding TypeModulation Coding RateModulation Reed-Solomon Conding RateCarrier Transmission Power

Carrier Transmission StatusDemodulation Radio FrequecyDemodulation TypeDemodulation Information SpeedDemodulation Decoding Type

Receiving Carrier (C) Demodulation Decoding RateDemodulation Reed-Solomon Deconding RateCarrier DetectionC/NEb/N0


44/59

5.6 Accesibility to Operational Information

Assuming the interaction between earth stations and external nodes or application on theInternet, the operational information should be easily accessed on the earth stations bythe external environment. Therefore, this operation model should be implemented on theprotocol which both earth stations and external nodes can cover.


45/59

Chapter 6

Implementation of AutonomousSatellite Link Operation

There are some network management protocols and description languages that are generallyused on the Internet, such as CMOT[11], SNMP[3], and so on. The shape of implementationvaries according to the objectives or the situation of normalization of information. Ingeneral, compared with CMOT, SNMP is light-weight[8] as an application to carry thenetwork management information. Considering propagation and install cost of our modelin other satellite-based networks, we choose the combination of SNMP and MIB as theimplementation platform of the autonomous satellite link operation.

6.1 Information Exchange on SNMP and MIB

We implemented the information exchange infrastructure on SNMP and MIB. SNMP (Sim-ple Network Management Protocol) is a protocol that is widely employed for the networkmanagement on the UDP/IP suite. Earth stations in a operational domain exchange theiroperational information using SNMP. On SNMP, every earth station is treated as an SNMPagent whish holds a MIB (Managed Information Base). MIB is an aggregation of opera-tional parameters of satellite network, that is described by ASN.1. An external node worksas an SNMP manager that exchanges the operational information with earth stations toprovide the functionality of the autonomous satellite link operation. Figure 6.1 shows theinteraction among nodes using SNMP and MIB via the Internet.

If an earth station can not deal with SNMP and MIB, a proxy agent exchange theoperational information with other nodes by communicating with an earth station on thelocal protocol.

This thesis defines the SAT-MIB that describes the parameters regarding satellite linkoperation. On the SAT-MIB, we defined the parameters for earth station identification,satellite link information, and satellite modem as the main facility in the earth station.

The SAT-MIB functions as an interface to set or acquire the operational parameters onthe earth station. Therefore, the SAT-MIB does not archive values, and the MIB holds thesingle field for each parameter so that earth station return only latest values.

37


46/59

Vender PrivateSpecification

Unified Information ExchangeRemote Control and Monitoring

Satellite Modems with Unified Operational Interface

Node

Agent

Applications /Protocols

Interaction with external nodes

NodeRemote

Interface

Figure 6.1: Interaction among Earth Stations and External Nodes using SNMP


47/59

However, some variable parameters may not make sense as instantaneous values. Be-cause they need to be archived for a certain period of time to be summarized as the con-tinuous status. Otherwise, the transition of status information can not be achieved andsome functionalities of the proposed model may not work correctly. We assume that anexternal storage retrieves status information from the earth station by the SAT-MIB, andthen, applications access to the storage to utilize the status information.

6.2 Definition of Parameters

In order to describe parameters appropriately, we defined a data type FloatGauge andAlternatives in the SAT-MIB using TEXTUAL-CONVENTION[7]. The FloatGauge typeis defined to use floating point values in the SAT-MIB, such as C/N, Eb/N0, Transmission

Power and so on. The Alternatives type is defined to use alternatives, such as FEC types,coding types, interface types of equipments and so on. Figure 6.2 shows the definition ofthe two data types. TEXTUAL-CONVENTION is one of the ASN.1 macros to conciselyconvey the syntax and semantics of a textual convention.

FloatGauge ::= TEXTUAL-CONVENTION

STATUS currentDESCRIPTION

"A syntax for displaying gauge in the floating point value"SYNTAX DisplayString

Alternatives ::= TEXTUAL-CONVENTIONSTATUS currentDESCRIPTION

"A syntax for displaying alternatives to choice"SYNTAX Integer32

Figure 6.2: Definition of Data Types

By fixing the appropriate units, those parameters can be considered precisely by externalnodes, human operators, and the earth stations themselves. Figure 6.1 shows the units andthe syntaxes of the common parameters defined in the SAT-MIB.

6.3 Installation on Practical Satellite Link Operation

6.3.1 Agent Implementation

In order to install the Autonomous Satellite Link Operation on the real operational envi-ronment, we implemented an SNMP agent for the satellite modems operated in the AI3

project. We implemented the part of managing the operational parameters for satellite linkstatus on the satellite modems that are operated in the AI3 network: SDM-300A modemsand SNR-PS1000 demodulators. Following table 6.2 shows the availability of data link sta-tus on the both types of satellite modems. A circle, a triangle and a cross in the table


48/59

Table 6.1: Units and Syntaxes for Common Parameters

Parameter Unit Granularity SyntaxFrequency KHz 1 KHz step Integer32

Information Speed bps 1 bps step Integer32

Coding Type Alternatives

Symbol Rate sps 1 sps step Integer32

FEC Data Bit bit 1 bit step Integer32

FEC Block Bit bit 1 bit step Integer32

FEC Type Alternatives

Transmission Power dBm 0.1 dBm step FloatGauge

Noise Ratio dB 0.1 dB step FloatGauge

Impedance ohm 1 ohm step Integer32

indicate that a parameter is available by specification, available by calculation from otherparameters, and no available respectively.

Table 6.2: Availability of Data Link Status ParametersSDM-300A SNR-PS1000

RSL

C/N

Eb/N0

BER AGC

Carrier Detection

We converted C/N and Eb/N0 on the both types of modems according to the followingexpression. Bw indicates the receiver noise bandwidth, and fb is the information speed.

C

N=

Eb

Nofb

Bw

Then Bw is calculated by the following expression. The indicates the number of

phases of PSK modulation.

Bw = symbolrate 1.0

synbolrate =fb

FECRate log2()

Figure 6.3 shows for the parameter conversion from Eb/N0 to C/N on the SNMP agent.

6.3.2 Modification of Modem Watch Dog

In this research, we modified MWD to adapt it to the proposed operation model. In theautonomous satellite link operation, MWD is considered as one of the core application


49/59

float

ebno2cn(float ebno, float fec_rate, int phi){

float bw;

float cn;

bw = fec_rate * log2f(phi);

cn = ebno + nlog10f(10, bw);

return(cn);

}

Figure 6.3: Conversion from Eb/N0 to C/N

to provide the functionality of automatic monitoring of satellite data link status. Everyapplication that requires the data link status can retrieve the status information by MWD.

MWD stores every value of administrative satellite link status in a database on thenetwork. The stored data can be retrieved by any nodes that requires the monitoring resultof satellite links on the operational domain. Figure 6.4 shows the concept of this systemwhich is implemented using on the unified interface.

6.4 SummaryThis chapter described the implementation of the autonomous satellite link operation inthe practical operational environment. The implementation mentioned here is to build theoperational infrastructure to realize the functionalities of the autonomous satellite link oper-ation. Those functionalities are implemented based on exchange of operational informationamong earth stations. We adopted SNMP as the protocol for exchanging the operationalinformation in the operational domain. And then, we defined the operational informationin the SAT-MIB.

We adapted the parameters regarding satellite link status of the SAT-MIB to the twotypes satellite modems that are operated in the AI3 project. And then, we modified the

MWD to retrieve the data link status from both types of satellite modem with the sameoperational interface. Regarding the automatic monitoring of satellite link status in theAI3 network, it was achieved beyond the heterogeneity operational environment of thosesatellite modems.


50/59

Data Collect Module(SNMP Agent of Satellite Modems)

Abstracted Satellite Modemon SNMP+MIB

SNR-PS1000Receive-Only Satellite Modems

SDM-300A

Send-Receive Satellite Modems

Figure 6.4: Satellite Modems and Abstracted Nodes on SNMP and MIB


51/59

Chapter 7

Evaluation

This chapter evaluates the autonomous satellite link operation environment based on themode design and the comparison between the existing operation model and our model.

7.1 Operational Components

Table 7.1 compares the operational components between our model and the existing oper-ational scheme.

Table 7.1: Comparison of Operational ComponentsExisting Scheme Our Model

Operation Fea-ture

Manual Autonomous

OperationBody

Human Operator Earth Station

InformationExchange

E-mail, Telephone or Facsimile Applications on the Internet

OperationTiming

Schedule Base Real Time

OperationCost

High Low

Operational

Interface

Many Single

Extensibilityof OperationalDomain

Low High

Application System Specific System Independent

43


52/59

7.2 Dissolution of Heterogeneity on Operational Environ-

mentIn general, an earth station is designed and composed to be suitable of the characteris-tics of the satellite link. Operational scheme, facility composition, available operationalinformation and feedbacks, and many other aspects are different among earth stations andsatellite links. Therefore, it is very difficult to completely get rid of the heterogeneity fromoperational environment of satellite networks. It is not realistic to integrate the physical oroperational specification on every earth stations and all facilities among related venders.

Our model was designed to remove the heterogeneity of operational environment ofsatellite network. We organized the required components of the model to remove theheterogeneity: unified operational interface, redundant connectivity to the Internet, and

normalized operational information. We implemented a unified operational interface usingSNMP which is a popular protocol for network management on the Internet. On the otherhand, the operational information is defined in the SAT- MIB. We considered the degreeof freedom on the notification convention to keep accuracy and semantic volume of definedparameters in the SAT-MIB. Because our model normalizes the essential parameters amongdifferent types of satellite links and different forms of earth stations, the heterogeneity ofsatellite link operation environment can be covered up.

7.3 Sustainability of Satellite Links

In the existing operation scheme, configuration of satellite links is apt to be fixed for the long

period of time. Even if dynamic configuration systems are available for some satellite links,those systems are designed for the specific data links, and they can not cover other typesof satellite links. Therefore, once satellite link go down because of change of environmentalconditoins, the links are not recovered until those conditions are dissolved.

On the other hand, our model is designed to provide the functionality of automaic mon-itoring and the dynamic configuration of satellite links based on the assumption that thelinks can be recovered if their configuration is tuned according to their status. This func-tionality can be achieved by the information exchange and the unified operational interfacewhich allows any node to set or retrieve the configuration and the status of satellite links onearth stations. As a result, our model provides the technical platform to keep all satellitelinks sustained by best efforts.

7.4 Operation Cost of Satellite Network

Monitor the status of satellite links all the time and modifying the parameter setting ofthe links on demand are requirement to operate the satellite network. In the existingoperation scheme, a satellite network is not operated efficiently because of heterogeneity ofoperational environment or dependency on manual operation. Our model does not rely onhuman operators to operate satellite links, and earth stations are abstracted as nodes whichare accessible on the Internet. Those nodes provide the normalized operational informationvia the unified interface regardless of the forms earth station and the type or directionssatellite links.


53/59

On the other hand, a single application can be adapted to the all earth stations onthe unified platform. Thus functionalities of satellite link operation can be available as awhole network, and the operational cost of those links is reduced compared with manualoperations. Even if the operational domain gets larger, increment of operational cost will besuppressed. Following table 7.2 estimates the cost of operating the satellite links on the AI3

network between the existing operation the and our operation environment. Currently, theAI3 project administrates 2 Ku-band point-to-point links, 5 C-band point-to-point links,and 1 C-band Unidirectional link with more than 10 receive-only stations.

From the view point of operationg the whole AI3 network, our model can provide thesame functionalites throughout the network. And then, our model reduces the total op-erational cost of the AI3 network. Based on the out design that gets rid of heterogeneityof satellite link operation environment, our model is expected to contribute to achieve thesame performance and reduce

design of the autonomous satellite link 2004

Documents