What is Satellite Broadband?

The speed of using the satellite to access the Internet is dozens to hundreds of times faster than traditional modems, with a maximum transmission rate of 15 Mbps. Users can access the Internet through computer satellite modems, satellite antennas and satellites. It is an asymmetric access method with powerful business functions. It can provide users with Internet download speeds of 15 Mbps, and can also perform satellite broadcast services, such as large file delivery, multimedia broadcast, web page broadcast, etc. The service covers a wide range of areas in mainland China, Taiwan and Hong Kong and Macao. Very cost-effective, high-speed interaction can reduce repeated bandwidth consumption through a public proxy server, and one-to-many data broadcast downloads can greatly reduce Internet bandwidth and time waste. High-quality multimedia video and audio are conducive to the promotion of diversified value-added applications. The technology is mature and stable, and users access the Internet in the same way.

Satellite Internet

Keywords: Internet satellite communication access technology broadband technology

Introduction to Satellite Internet

After more than 20 years of tremendous development, the Internet has become the world's most extensive, largest, and most abundant computer information network. It is not only a special means of transmitting scientific research data between universities and scientific research departments, but also has become a daily work, Multimedia means for study, life, entertainment, etc. In China, the Internet business has developed more rapidly in recent years. According to the latest statistics from the China Internet Network Information Center, as of October 1999, domestic users have reached 4.5 million, and the total international line capacity has also reached 241M. But in contradiction to development, people who have used the Internet have a feeling that the speed of the network is too slow, especially when downloading materials, which makes people feel impatient and even give up access, so that many Internet users jokingly refer to the WWW as World Wide Wait. From the perspective of the entire network, the current low Internet backbone speed is one of the reasons for the slow network speed, but it is being gradually resolved with the expansion of the trunk line; the main reason is that the majority of Internet users still use the traditional Internet connection. Access mode, that is, using a pair of telephone lines plus an analog MODEM, even the latest MODEM based on the V.90 standard has only 56 kbit / s, and the access rate is low, which cannot meet the growing multimedia communication needs of users. The "bottleneck" effect of the network causes the network speed to be too low. Although fiber-to-the-home can solve the "bottleneck" effect of the access network and is the future development direction, it will be a huge investment to solve the "last mile" bottleneck, which is currently difficult to achieve. Therefore, finding a high-speed access method that can meet user needs at the current stage and is relatively easy to implement has become the focus of everyone's attention. Under this circumstance, satellite-based Internet emerged at the historic moment, and has increasingly shown its strong advantages and development prospects.

Internet Comparison of several high-speed Internet access methods for satellite Internet access

Judging from the current research results and applications, people are mainly optimistic about the three Internet broadband access methods: ADSL, Cable Modem and Satellite.

The ADSL broadband access method, that is, asymmetric digital subscriber line technology, has different uplink and downlink transmission rates. It can provide hundreds of kbit / s uplink rates and Up to 6Mbit / s downlink rate. Its advantages are high access rate, ready-made network, Internet access and phone call. The disadvantage is that the speed is limited by distance, it is not available everywhere, and the existing PSTN network needs to be modified. The Shenzhen Data Communication Bureau of China has opened ADSL broadband access service. The rate can reach 1.5Mbit / s when accessing the local network. The ADSL terminal equipment and commissioning costs are 3800 yuan and the monthly rent is 420 yuan.

The Cable Modem broadband access method is to use the existing HFC-based CATV network CATV to achieve high-speed Internet access. The advantage is that the access rate is high, there is an existing network, you can surf the Internet and watch TV, and the rate is basically not limited by distance. The disadvantage is that the channel bandwidth of the cable television network is shared, which means that the bandwidth of each user will become less and less as the number of users increases; the noise at the user end will be superimposed on the front end, forming the so-called "funnel effect" of noise interference. In addition, traditional cable TV is a broadcast service. Pay attention to security and reliability when performing interactive data communications. At the same time, the existing cable TV network needs to be transformed. The Guangdong Guangdong Video Broadband Network has launched the Cable Modem service. The current uplink / downlink rate is 10 Mbit / s, the equipment installation fee is 2500 yuan, and the monthly rental fee is 120 yuan / 40MB.

Satellite broadband access means that users access the Internet directly through satellites. At present, the satellite broadband access rate is generally 400 kbit / s, and the rate can be as high as 3 Mbit / s when downloading multimedia. The advantage is that the access rate is high; it is not restricted by the region, and it truly realizes seamless Internet access; it can also receive satellite TV. The disadvantage is that it is affected by climate, especially in rainy and snowy weather, and the reception will be affected; at the same time, the initial investment cost is high. China Telecom and Sunway Communication Network of Hong Kong will launch a broadband satellite Internet transmission service called TURBO 163 in China. It is estimated that the installation cost of the equipment on the client side is about 3,500 yuan and the monthly rental fee is about 300 yuan.

Comparing these three types of Internet broadband access methods, ADSL and Cable Modem have great advantages in metropolitan area networks, and in wide area networks, satellite systems have the most promising. It can not only achieve high-speed seamless access to the Internet, but also Can achieve satellite live broadcast to the home.

Internet Satellite Internet Internet Satellite Broadband Access Core Technology

In the asymmetric interaction model, we know that users' access to Internet data is asymmetric, requiring high downlink rates and low uplink rates. However, traditional communication equipment and networks are based on a symmetric model. In the case of asymmetric information, the utilization efficiency of communication resources is very low, which implicitly causes a waste of resources. The asymmetric interaction model of the communication channel is proposed to match the asymmetric model of the information flow. This model matching does not increase the capacity of the physical channel in essence, but the full use of the role of the communication system will help improve the system efficiency. The concept of asymmetric communication model matching will revolutionize the concepts in the traditional communication field.

Broadband technology, which can allocate bandwidth according to user needs and provide services at different speed levels. General personal users only provide network access services; for professional users, in addition to providing high-speed network access services, plus Services such as multimedia information transmission, webpage playback, and news broadcasting; for enterprises, they can connect to the intranet and provide multiple people with high-speed Internet access at the same time.

In point-to-multipoint broadcasting technology, the biggest advantage of satellite systems is the "broadcast mode", that is, the "point-to-face" method. This one-way, broadcast information exchange method is very effective for the high-speed transmission of a large number of common information. This will undoubtedly have economic benefits for those who need to multicast data such as distance education, and the use of ordinary networks will require additional Bandwidth and costs.

Cache technology. There is a cache area in the Satellite Network Operation Center (NOC), which stores the most popular URLs for quick access by users. The NOC here is the core of the Internet satellite broadband access system. It is a computer system with a high-performance server as its core. The NOC includes a cache area, an Internet access module, and a satellite data transfer module. It has the function of transmitting data to the satellite, and can access the Internet at high speed in real time.

In addition, there are technologies such as PUSH push, real-time transmission / control protocol, resource reservation protocol, and public key cryptosystem.

Internet Satellite Internet Internet Satellite Broadband Access System

At present, the common Internet satellite broadband access systems are mainly DirecPC and InSAT, among which there are many DirecPC users.

DirecPC is a combination of a satellite communication system and a terrestrial telephone network, that is, the telephone network is used as an uplink channel, and the satellite channel is used as a downlink of the Internet to achieve high-speed Internet access. The biggest difference from general telephone transmission is that DirecPC does not transmit completely in two directions via satellite. The user s receiving antenna can only download files and cannot issue instructions for the user. Therefore, satellite Internet users need to pass the local ISP to issue instructions, but All the instructions issued are attached to the satellite Internet IP address of the file download (the PC card on the user's computer has a dedicated IP address).

The working process of the DirecPC satellite direct dial network service is: When dialing up, the DirecPC software in the user's computer will also inform the service provider (ISP) and transfer the Internet access request to the DirecPC Network Operation Center (NOC). If the user wants to access the If the site is in the NOC cache area, the center will call out the web page content and immediately send it to the user via satellite; if the site the user wants to visit is not in the NOC cache area, the center immediately obtains the target host from the network host where the information is located. The information required by the user is then transmitted to the user through the satellite channel. It can be seen that the satellite channel replaces the transmission channel between the network where the target information is located and the local network and the telephone line between the local network and the user, and the transmission rate is greatly improved. Take a 2MB file, for example, it takes 9 minutes to download using a 33.6kit / s MODEM, and it takes only 40 seconds to download at 400kbit / s via satellite. For users, to access the Internet via satellite, in addition to a personal computer, a satellite adapter card, a pair of dish antennas, and a set of DirecPC software are required. Insert the adapter card into the computer, install DirecPC software, connect the antenna, and you can access the Internet. In Ku band, the antenna diameter is about 60cm.

There is no doubt that the above DirecPC satellite direct-dial network service is actually a one-way "effective broadband network". It mainly uses satellites to solve the problem of high-speed data download that cannot be solved by telephone lines. Users still need to rely on ground phones. The internet. For places where telephone line access is not yet available, satellite access systems can take full advantage of long communication distances, cost-independent distances, large coverage areas, and unrestricted geographical conditions. Two-way satellite transmission, namely InSAT, is used to access the Internet. To achieve ubiquitous Internet services.

Two-way satellite transmission can be achieved using VSAT. For example, the current TDM / TDMA data VSAT system can be considered to have been basically designed according to the client / server model, and the two-way communication volume differs by more than ten times. Of course, other VSAT standards such as TDMA or SCPC can be used. According to the needs of practical applications, it is best to improve the existing VSAT system to meet the needs of Internet communications.

Satellite Internet Application Status and Development Prospects

Internet satellite broadband access can not only provide users with high-speed Internet access services, but also transmit information to every corner of the earth. Because of these advantages of satellite access, satellite communications are rapidly becoming an important way to access the Internet. Access to the Internet via satellite has been widely used in many countries and regions in North America, Europe, and Asia, and its application areas have been extended to distance courses, medical services, securities services, file transfers, multimedia services, and instant news alerts. With the introduction of the TURBO 163 service in China, it will solve the bandwidth bottleneck problem caused by the rapid growth of Internet users in China. At the same time, it is believed that with the introduction of Internet broadband satellite services in China, the development of the Internet in China will be promoted.

I. Development of VSAT

Driven by the Internet, like other communication technologies, satellite communications are turning to meet the full needs of data communications

. Specifically, on the one hand, the mature VSAT system based on C-band and Ku-band technology has continuously evolved to meet Int

ernet service requirements, and become an important part of the global Internet network, on the other hand, a higher K

a-band technology, a broadband satellite communication system that can truly realize personal communication, especially a low-orbit satellite group system is being developed

During development, testing, and construction, satellite communications have been selected by more and more telecommunications network operators, ISPs, and ICPs to provide Inte

Rnet service is an important means. At present, VSAT is the mainstream technology in satellite communication, and its application is quite successful and popular.

, But the service rate provided by traditional VSAT is not too high, the incoming link rate reaches 64kb / s, and the outgoing link rate is generally

It reaches 512kb / s. With the emergence of various new applications, high-speed requirements have been imposed. Some are competing in the VSAT market

Large companies invest a lot of money and manpower in a competition to increase network speed. Because the faster the VSAT network is,

The more competitive the company that sells and buys it. The VSAT network currently under construction can accommodate outbound link speeds of up to 2Mb / s

Rate, many VSAT companies plan to make the network speed reach 20Mb / s or higher by the turn of the century.

VSAT is very fast in increasing speed, and the VSAT products that are coming to the market are often named after turbo, cyber and surfer.

Such words are prefixed or suffixed. For example, the latest high-rate VSAT products introduced by the industry are: Link of Comsat Lab

way2000 system, GE Spacenet's high-speed Turbosat VSAT, Gilat's SkySurfer VSAT, New Medi

a CyberStream VSAT product.

Speed is not enough, VSAT system also continuously absorbs various latest information technologies such as IP Multicast, digital broadcasting technology

Technology, PUSH technology, support TCP / IP, UDP / IP and other protocols, extend the characteristics of satellite high-speed broadband broadcasting to the network

Applications, providing effective solutions for many new applications. In fact, VSAT has become a high-speed development in the world today.

Data services, especially part of the Internet.

The application of VSAT system in Internet access mainly has the following methods:

1. Provide remote Internet connection for large ISPs

According to statistics, currently about 80% of Internet information content is stored on computers in the United States. Many ISPs, content providers

Companies, communication service operators, and multinational companies want to efficiently access North American Internet backbone networks,

To establish a high-speed link with the US Internet. These links can be rate-symmetric or asymmetric.

Both directions have relatively stable data flow. Due to the asymmetry of Internet traffic, it is usually targeted at customers

The exact needs are to provide asymmetric satellite links. There are many companies providing such products and services, and the system generally uses

SCPC / DAMA system. For example, Loral Orion Corporation passed the China Telecom (Hong Kong) International Access Corporation (CTIA)

Support and provide satellite cross-border private network services to multinational companies in China.

2. Extend the Internet to remote areas and provide links between ISPs

Provide PPP (point-to-point) interconnection for areas with insufficient communication capabilities, and provide between large ISPs and small ISPs under it

High-speed connection, this connection is mainly within a country. The inbound rate means that the amount of information sent to the main ISP is relatively low.

For example, the connection between the China Science and Technology Network Network Center and its more than 50 entry points across the country, and the VSAT service network of Jinqiao Information

The high-speed satellite channel of China Education Network can be attributed to such applications.

3. Connect directly to the computer (including connecting to a LAN server)

For decades, only government agencies and large financially capable companies can enjoy the rapid, flexible and

Convenience. Nowadays, a series of new technological developments such as satellite communications and computers have enabled a new VSAT system to be implemented.

For reality, this new architecture is called Direct to PC or PCVSAT, and satellites connect ISPs through point-to-multipoint connections.

The server is directly connected to the user's computer, so that companies of all sizes, even individual users, can utilize spatial data communications.

Powerful features.

1) Working principle

In this way, the user accesses the database or network by dialing, and then through a satellite with a diameter of about tens of centimeters

Receiving antenna and special receiving equipment, receive, download database or download data at high rate of hundreds of Kbits or even megabits

Online information. This method makes full use of the existing telephone line access function and satellite communication broadcast function. It has

Easy to install, avoid network congestion, cheap, large download channel capacity, and services similar to fiber optics

Class and IP broadcast services have become the focus of recent developments.

Typical terminal products for direct satellite connection to the computer business include PCs equipped with a modem, satellite receiving adapter cards, and small satellites.

Antenna (caliber 60-90cm), system software. In enterprise applications, install a satellite receiving adapter card on the server.

Each PC sends files through the server.

The working process is as follows: the user clicks a web address on the browser software, and the URL request signal (URL) is sent by the modem

To the user's ISP, and before the request leaves the user's PC, the system software will append an IP address to the URL

Code, instructs the ISP to forward the user s URL request to the network operation center (NOC) of the satellite system.

After this request, delete the code, and then send the request signal to the corresponding website, and the website sends the requested information

Back to network operation center

The information is transmitted to the satellite, which is then sent to the user's satellite antenna at a high bandwidth rate and thus enters his PC or

Web server (for business users). This allows you to browse the web and download text at speeds up to 400kb / s.

3 times faster than standard ISDN.

2) Provision and use of services

Internationally, one-way satellite Internet access has been more successful in small and medium-sized enterprises and home applications. Direct PC in the United States

, Direct Internet in Japan, Telesat in Canada, Telstra in Australia, NIC India in India, etc.

The DirecPC system is used to provide this service in the country and surrounding countries. Germany has also launched a similar service called skyDSL

Business.

It is worth noting that last year, the world's largest PC manufacturer Compaq became a partner of DirecPC. Compaq released

A new plan to provide users with Internet access via satellite, starting in mid-April 1999 to custom PC users

Provides Internet access via the DirecPC satellite system. Users can use the navigation computer in the store or Compaq's

Order DirecPC satellite information service for self-assembled personal computers on the website.

In mid-1999, a strategic agreement between Hughes Networks and AOL attracted the attention of the industry.

Hughes Networks invested $ 1.5 billion in the development of new products and services for the Internet and live satellite television, and in the form of a tunnel. through

Through this partnership, Hughes Networks will provide AOL's interactive TV services to its 7 million DirecTV subscribers. AOL will

Provides Hughes' DirecTV and DirecPC services to its 16 million subscribers. Designed and manufactured by Hughes Networks

Set-top boxes for DirecTV and AOL TV.

With the vigorous promotion of these famous companies, satellite networking services have gradually begun to become a new choice for Internet access.

China currently plans to use Hughes' DirecPC system to provide users with high-speed Internet access and digital package delivery.

There are three companies of Broadband Satellite Communication Information Network for media information broadcasting. They are:

Guangzhou Post and Telecommunications Administration cooperates with Hughes Network and Dongfang Satellite Company to provide 400kb / s directly to the computer

Satellite Internet content download services and up to 3Mb / s digital package delivery and multimedia broadcasting. Plans will be in the near future

Put into operation, providing services to commercial and individual users across the country.

Beijing Tianguang Information and Communication Services Co., Ltd., a satellite network operation center contracted by Beijing Tianke Network Integration Company,

It has been debugged. The first phase of the project is mainly aimed at enterprise users. The user terminal is Hughes' PES terminal plus DirecPC.

The terminal, that is, dialed back through the PES satellite circuit, DirecPC downloads at high speed. Further development for individual users.

China Sunway Communication Network and China Cast Technology, which were participated in by China Telecom Data and Communications Bureau, last year

Just signed a $ 3 million contract with Hughes in August, Sunway Networks purchased DirecPC equipment and used their satellite technology

Technology, launched a satellite Internet plan called Turbo 163 in China early next year, targeting customers who are already online in China

1/4 customer. The company does not expect to charge more than double the current 163 network, but it can

20 times faster-the maximum Internet rate

From the current 38.8K to 400K. Sunway Network will be China's first to provide civilian Internet services using satellites combined with ground networks

Service company.

3) Representative products that provide satellite Internet access

There are many products and applications currently providing this service. Hughes Network Systems pioneered the revolutionary VSAT in 1994

Products-DirecPC receiving system that can be connected to personal computers, allowing PC users to use the small mouth of a live TV satellite

Diameter receiving antenna, which can download large-capacity information on the Internet at a speed of 400kb / s, making the Internet crowded

Ground line opens up a high-speed space download channel. Subsequently, many of the world's largest satellite companies, such as Gi

Lat, Science Atlantic, Comsat, GE Spacenet, etc. have launched for the Internet and value-added industries

VSAT systems (such as Skysurfer, PowerVu, CyberStream and Turbosat systems)

Some satellite companies are competing in this market. China's Beijing Saidekang and Shenzhen Jingtian Technology Co.

A similar product (SatcomLAN, PCVSAT) was issued and is already in use.

Satellite Internet Technology Hotspots

1.Improve the performance of satellite link TCP / IP-satellite protocol gateway

The TCP / IP protocol used to transmit data on the Internet is a very flexible protocol that can be applied to include satellites

On any media including the system. However, satellite communications, especially geostationary satellite communications systems, have time delays.

Problems such as long length, high bit error rate, and asymmetric bandwidth have seriously affected the performance of TCP / IP.

Although it can directly access the Internet through satellites, its performance can only make users reluctantly accept it. Need to take optimization

Measures to improve satellite TCP / IP performance. Optimization measures include: adjusting the parameters of transmission control protocols in satellite link applications

Number: Reduce TCP load on satellite link: Use protocol conversion gateway.

Although the use of compression technology and cache can reduce the amount of data that needs to be transferred. But the remaining data is still affected by the above

Due to the limitation of factors, adjusting TCP parameters cannot fundamentally eliminate the impact of satellite links on the deterioration of TCP performance and improve the health

The most effective method of TCP / IP performance on the internet is to set up a protocol gateway.

The working principle of the protocol gateway is to replace the TCP on the satellite connection segment with a protocol that is most suitable for the satellite environment. Gateway

It can be a stand-alone device, or the function of the gateway can be installed in a satellite modem, VSAT, router,

Cache or other connected hardware.

The protocol gateway detects the TCP connection from the client computer and converts the data into a dedicated protocol suitable for satellite transmission.

The other side of the satellite link restores the data to TCP, which is used to communicate with the server. Protocol gateway connects end-to-end TCP

The connection is divided into the following three independent parts: the remote TCP connection between the client and the gateway, and the satellite protocol between the two gateways

Connection and the TCP connection between the server-side gateway and the server.

The main advantage of this structure is that by dividing the end-to-end connection, the most suitable satellite link can be used on the satellite link segment.

Protocol, while continuing to use TCP in the ground segment. This provides better results while remaining completely transparent to the end user

performance. No changes are required to the client or server, and all applications remain valid without modification. TCP avoids blocking

The congestion mechanism is still effective in the ground connection to protect the stability of the Internet. Users enjoy two technologies

All the benefits of combining, that is, existing transmission control protocol-based applications have not changed at all, and

At the same time, satellite-friendly protocols are used in the space link.

Therefore, almost all newly launched satellite communication products have built-in or external independent satellite protocol / TCP protocol conversion gateways.

To support Internet business.

2.External satellite communication technology

We know that the communication system is divided into two basic modes of one-way communication and two-way communication. The two-way communication generally has

Own transmit and receive channels. If the transmit and receive channels of a communication system are separated from each other, and a transmit channel can be implemented

For these two characteristics of one or more receiving channels, we can call it external interaction communication.

With the development of Internet technology, in the existing network communication, the phenomenon of unbalanced transmission is very serious. Take 3W as

For example, the difference in the amount of data between the uplink and downlink channels is generally 1: 5 to 1:10, depending on the text and picture occupancy in the homepage.

set. In FTP file downloading, this ratio can reach 1:20 to 1: 1100, but this imbalance is only preliminary.

. If network media is applied

System, then this ratio will reach 1: 1000 to 1: 100,000, any existing network, whether it is balanced transmission or

Unbalanced transmission can not adapt to such a wide range of transmission conditions, which will cause transmission channel

Waste or substantial increase in cost. How to find a better adaptation to this kind of non-flat transmission range

Balanced transmission method, which is a problem that must be seriously considered in the era of network multimedia, and also a part of future communication systems.

Development directions.

The external interaction technology has flexible networking and large system user capacity, and is easily adaptable to non-planar changes in a wide range of transmission ratios.

Balanced transmission. The downlink channel of the external interaction technology is changeable, including changes in the rate and changes in the number of channels.

Among them, the change in the rate is limited and not major, and the change in the number of channels (in principle) is infinite.

Main. This kind of change of the downlink channel can better adapt to the application situation that the transmission ratio changes in a wide range.

The flexible characteristics of the network, in the case of a large increase in the number of users, can appropriately increase the uplink channel, a large number of downlink channels,

To the purpose of accommodating a large number of users. These characteristics cannot be solved by current network transmission technologies or unbalanced transmission methods.

Problems, or difficult problems.

Adopting external interactive communication technology and using any ground return line to transform each satellite high-speed broadcasting system into a two-way network communication

The letter system is a very practical application at present, and the investment is very low. Therefore, it is also one of the current satellite communication fields.

hot spot.

As for wireless communication technology, external interactive communication technology realizes a low-cost unbalanced transmission method. Thanks Wei

The satellite two-way communication station has a high cost, which cannot be installed by ordinary units. But after using external interaction technology, the downlink channel

High-speed one-way satellite broadcasting and low-speed ground return line for the uplink channel can achieve two-way high-speed communication.

Achieved low cost requirements. Costs can be reduced very low. Such as the price of a satellite receiving station (including antenna, tuner

) Available at 5000-6000 RMB, antenna size can be reduced to 45 cm, and it has the conditions for digital home. No ground

No matter what kind of digital communication technology, it is difficult to cover the vast urban fringe areas, rural areas and mountain areas. And this satellite communication

The information system, especially for a vast developing country like China, is very suitable and practical.

Although there are currently some users using external interaction technology to implement satellite communications, there are also many problems. Sum up

The main performance is:

1) System compatibility issues. After using external interaction technology, the system cannot be 100% compatible with the terrestrial Internet.

The amount of network software cannot run on external interaction systems, or the security of the original Internet is lost.

2) The system user capacity is low. Opening an external interaction channel can only increase the capacity of 100 to 200 users

Large capacity of interactive system users.

3) The rate is low. Especially in satellite communication systems, the downlink channel rate is not high, and it cannot take advantage of the advantages of high-speed downlink channels.

Potential.

The earliest domestic company that studies foreign interaction technologies, such as Beijing Saidecom Communication Technology Co., Ltd., has completed the third

Productization of intergenerational interaction technology. In terms of system openness and compatibility, they have reached a very high level

, And has been applied in many systems. External interactive satellite data communication system and external interactive cable television

The data communication system, combined with multimedia on-demand technology and multimedia courseware production system, has developed an application on the Internet

The application prospects will play a huge role in Internet education and entertainment and browsing.

The future of broadband satellite communications

Current satellite communications usually belong to C-band and Ku-band systems, modern broadband satellite systems, except for INTELSAT and Cyber

Star intends to consider the Ku / Ka progressive transition, and the Skybridge system uses the Ku frequency band, mostly using the Ka frequency band (20 / 30G

Hz), even higher frequency bands of EHF or Q / F (40/50 / 60GHz). These systems are mainly used for multi-channel broadcasting,

The remote transmission of the Internet and intranet and the access means of terrestrial multimedia communication systems, they can develop

Become an important part of the global information superhighway, become a global seamless personal communication, Internet high-altitude

An essential means of fast track.

Industry experts predict that not only C-band and Ku-band VSAT will continue to thrive, but also a new generation of VSAT systems will be born.

Just as the ability of two-way communication to drive VSAT penetration into the global telecommunications market, Teledesic, Spaceway and Sky are expected to

Ka-band systems such as bridges will also push VSAT into more data business areas, and eventually into homes.

Second, the development of the Internet is entering a mature period, but it is necessary to overcome the trouble caused by the rapid growth. The three major dilemmas of the Internet mainly come from the three major bottlenecks of the backbone network, access network, and server. There are many solutions to solve these three major bottlenecks. This article discusses the existing mature technologies-the combination of satellite communications and the Internet, and the combination of CATV and the Internet.

The combination of the Internet and satellite communication networks

Dilemma of the Internet

The Internet is a network of computer networks (Network of Networks), the Internet. It is a complex network system composed of many IP autonomous domain systems interconnected by routers. This Internet is bound to have an imbalance in the distribution of the network and content. On the one hand, the network facilities in developed areas are relatively sound, but in remote areas, network facilities are scarce; on the other hand, the information content is mainly concentrated in a few developed areas. For example, the United States is the birthplace of the Internet. Many information content comes from the United States. Therefore, the bandwidth from the United States is much wider than the bandwidth to the United States. The large-scale construction of IDC will exacerbate this imbalance. Although a series of measures such as increasing bandwidth, increasing exchange speed, and multicast technology have been adopted, the working mode of multi-hop, store-and-forward, and point-to-point transmission in the process of transmitting information has not been fundamentally changed. In addition, the large-scale commercialization of the Internet and the explosive growth of online content, especially the popularity of streaming media, have caused problems such as blocked backbone networks, difficult remote access, and slow content distribution and delivery to the Internet.

2. Satellite communication network and Internet complement each other

The structure of the Internet determines its asymmetry, while the satellite communication network has broadcast characteristics, the uplink and downlink are asymmetric, and it has the advantages of large space span, large coverage area, remote connection, direct one-time delivery to households, and real-time transmission. , And this is exactly what the current Internet network needs.

As can be seen from Table 1, satellite communication is an important supplement to the Internet. The combination of the two is an inevitable trend in technology. We call this combination the satellite Internet network. It is based on the VSAT system, with a broadcast function, IP as the network service platform, and Internet applications as the service object.

3. Introduction to Satellite Internet

a. The composition of satellite Internet

The typical structure of the satellite Internet consists of a dedicated data center and a star-shaped VSAT satellite network, as shown in Figure 1.

The functions of the data center are: information processing, that is, obtaining, receiving, packaging, and publishing information content; system management, including user management, user authentication, network management, and billing.

The functions of the satellite network are: two-way communication, that is, providing Internet access services to remote users; one-way broadcast, data broadcast, multicast, and delivery; interaction, generally through the ground network to achieve interaction.

b. Application of Satellite Internet

It can be seen from Figure 1 that the information on the Internet is processed by the data center and then enters the satellite ground station, which is sent from the ground master station to the satellite. Remote users, whether collective users or individual users, can be obtained through satellite channels. The required information content; on the other hand, the satellite can also push the user's required content to the user's hard disk, all of which can also be completed by the satellite Internet operator. According to the needs of users and services, satellite Internet can ensure the scalability of the network by increasing the number of uplink carriers, satellites, and uplink stations. Satellite Internet at this time can be used as an open, broadband, and real-time broadcast network platform, which can provide a wider range of services.

Satellite Internet is an IP network system with satellite lines as the physical transmission medium. The link layer protocol between the IP layer and the physical layer is DVB / MPEG-2. DVB provides the integrated transmission mechanism of video, audio, and data multiplexing by expanding the multiplexing part of MPEG-2 and service information description, making the DVB system a multimedia system that integrates video, audio, and data. For IP applications, the original IP data is converted to a DVB / MPEG-2 transport stream through data encapsulation / multiplexing, making DVB an important carrier for supporting Internet applications. The packager has become the "matchmaker" in the IP world and DVB world. The formulation of the DVB standard has greatly promoted the integration of the Internet and radio and television networks, especially the development of satellite Internet.

Based on the DVB / MPEG-2 satellite Internet, a data transmission rate of about 45Mb / s can be obtained through a 54MHz transponder. In addition to its broadcasting and multiplexing functions, the Internet is even more powerful. With the help of satellite functions, it can fly to space and make satellite Internet a A brand new network system and information service system. Satellite In-ternet has various attributes such as VSAT, ISP, audio, video broadcasting, etc. It spans the three major industries of telecommunications, the Internet and radio and television, and can be interactively applied through the terrestrial network. The external interaction and internal interaction of satellite lines are applied interactively, which overcomes the bottleneck of the Internet.

4. Several methods of VSAT system and Internet access

VSAT is the mainstream technology in satellite communications, extending the characteristics of satellite high-speed broadband broadcasting to Internet applications, providing effective solutions for many new applications. In fact, VSAT has long been part of the Internet. The application of VSAT system in Internet access has the following methods.

a. VSAT provides remote Internet connectivity for large ISPs

Satellite asymmetrical line schemes are popular with ISPs. For asymmetric satellite connections in the satellite Internet market, the ratio of downlink and uplink traffic is approximately 8: 1. Since the United States is the birthplace of the Internet, according to statistics, about 80% of Internet information content is currently stored on computers in the United States. Generally, packet data services sent from the United States are about 4 to 8 times as received. Therefore, ISPs around the world need more bandwidth from the United States, while there are relatively fewer routes to the United States. Obviously, satellite VSAT meets this asymmetric demand and can provide remote Internet connections for large ISPs.

b. VSAT extends the Internet to remote areas

It is almost impossible to extend the Internet's optical fiber to remote areas or mountains in a short time, and VSAT can do it. A geostationary satellite can cover one-third of the world's range, provide point-to-point interconnections for special environments such as insufficient communication capabilities, and provide connections between large ISPs and their small ISPs. This connection is mainly within a country. For example, the China Science and Technology Network Network Center is the connection of more than 50 entry points in the country, the VSAT service network of Jinqiao Information Network, and the high-speed satellite channel network of China Education Network. application.

c. VSAT is directly connected to the computer

Due to the development of a series of new technologies such as satellite communications and computers, a new architecture based on the VSAT system is called Direct to PC or PC-VSAT. The satellite connects the ISP server directly to the user's computer through a point-to-multipoint connection Allows companies, large or small, and even individual users, to take advantage of the power of spatial data communications.

Its working process is: the user accesses the database or network through dial-up mode, and then receives and downloads information from the database or the Internet at a high rate of hundreds of kb / s or even Mb / s through satellite receiving antennas and special receiving equipment. This method makes full use of the existing telephone line access function and satellite communication broadcast function. It has the advantages of easy installation, avoiding network congestion, cheap price, large download channel capacity, and similar service level and IP broadcast service as optical fiber, so it has become the focus of development.

The terminal products that connect the satellite to the computer business include: a PC equipped with a modem, a satellite receiving adapter card, a small satellite receiving antenna (the diameter is only 60-90cm, and can be installed on the drying platform of an individual user), and system software.

5. Unique advantages of satellite-Internet

There are currently two satellite solutions for accelerating Internet transmission. One is to use a two-way transmission of broadband satellites to provide users with a transmission rate of 16kb / s to 2.048Mb / s; the other is to use satellite high-speed download and ground feedback. The external interaction method is proposed based on the current asymmetry of Internet information traffic. For currently commonly used Internet services, the amount of data received is far greater than the amount of data sent. In this traditional interactive satellite communication technology, the round-trip transmission of information is achieved on the same physical link, while interactive satellite communications are performed outside In the technology, satellite links are used as downlink data links, and other communication networks, such as telephone dial-ups, local area networks, etc. are used as uplinks, which greatly alleviates the congestion of the Internet network and reduces the cost of the entire system.

Satellite Internet broadband applications have two key technologies, multicast technology and push technology, which are different from other terrestrial networks. Multicast technology can reduce network traffic and reduce the possibility of network congestion. Push technology, one is to provide information according to user requirements and send it to users; the other is to automatically collect the information that users are most likely to be interested in and send it to users.

Satellite Internet bypasses terrestrial circuits when transmitting information, which can avoid crowded public telecommunication networks or download files through the air satellite link to the Internet without using busy submarine cables, thereby opening up an air channel for the development of the Internet .

The satellite Internet asymmetric line solution allows ISPs to flexibly lease the capacity of the required transponders according to their business needs, becoming the best way for ISPs to seek access to Web "content" in the United States.

The construction of satellites is much faster and more economical than fiber optic cables. Using satellite links to access the Internet is much more economical than fiber-optic leased lines. For asymmetric services of point-to-multipoint ISPs, satellites are the most economical and efficient solution and can quickly expand services. For point-to-point services Satellites are also more cost effective than fiber optics.

Due to the development of global economic integration, the number of multinational companies is increasing, the demand for short-range Internet is increasing, and the number of LANs connected to the backbone network via satellites is increasing. Through satellite Internet, the offices of multinational companies can be connected for file transfer, distance learning, and training applications.

When the Internet gradually evolves into broadcast media, satellite Internet will be of great use, because satellites themselves are an effective broadcast media, with unique functions of "broadcasting" from a single orbit to one-third of the world. Information transmission on the Internet takes an average of 15 hops, and the packet loss rate sometimes reaches as high as 20%. The root cause is that the Internet is composed of many independent subnets. Information needs to be multi-hop during transmission. Each node is stored and forwarded. Rather than straight through. The combination of satellite and Internet is a "sky-ground" combination. Content is delivered to the edge of the Internet through a satellite system. Content providers (ICP) can send any updated audio or video programs to users, or direct remote users directly. Access to the backbone network to solve the problems of backbone network blocking and content distribution.

Combination of two satellites-CATV-Internet

1. Novel marriage of satellite-CATV-Internet

At present, the connection method with the Internet is mainly a telephone line connection and a dedicated line connection. The telephone line connection method is limited by the line speed, up to 56kb / s. And the cost of surfing the Internet is still high for ordinary people. The connection method of the dedicated line refers to the use of optical cables, cables, or wireless channels such as satellites and microwaves, or the lease of a DDN leased line to connect the personal user or unit's local area network to the Internet. The advantage of the dedicated line connection is that a site can be established with fast transmission speed, but networking Expensive, only suitable for large business units and institutional users, not for individual users.

In order to find a fast way to access the Internet, low cost, low investment and quick results, we have discovered a new way to connect the Internet by combining satellite and cable television networks.

The HFC network of the cable television network is a hybrid fiber-optic and coaxial cable, which has the characteristics of low cost, good signal quality, and frequency bandwidth. It opens a new way for home users to access the Internet at high speed and speed.

To access the Internet through a cable TV network, the cable station must first access the Internet, that is, the cable station establishes a gateway from the Internet to the wired network. Which method the cable station uses to access will affect the Internet quality of the entire network user. Obviously, the use of ordinary telephone lines to access the cable station will not work. You can only choose a dedicated line to access. The DDN dedicated line is connected to the Internet gateway of the local telecommunications department. , And will be limited by the rate of the domestic Internet backbone line, so when users go to other places or foreign sites, the speed is still slow. Furthermore, many small and medium cities in China have not yet opened Internet access services and cannot apply for DDN dedicated lines. The use of satellite dedicated lines can solve this problem.

This new method of accessing the Internet makes full use of the current status of the CATV network and the characteristics of satellite asymmetric one-way broadcasting. Specifically: CATV still uses the current one-way transmission, and the satellite also uses one-way broadcast transmission, and the user's return information is transmitted to the information source through the ground Internet. In this way, the cable station does not need to establish a satellite uplink station, and the cable television network does not need to perform a two-way transformation, which greatly reduces the capital investment and greatly shortens the network construction time.

2. Satellite and CATV combined system

As the most commonly used operation by Internet users is to browse the www site, it has the characteristic that the amount of downlink data is much larger than the amount of uplink data. This type of satellite channel and cable network are used to transmit downlink data in one direction. Meet this characteristic. Its system block diagram is shown as in Fig. 2.