|Issue:||Asia-Pacific I 2002|
|Topic:||From Sky to Earth: Satellite Connectivity in Asia-Pacific|
Satellites are expensive and have less throughput than fiber, but they are invaluable in hard-to-reach areas, for rapid, private links and for multicasting. With ubiquitous coverage and instant availability, satellites provide a critical alternative to terrestrial IP connectivity. They have many specialized applications throughout Asia-Pacific. The recent availability of protocol gateways now allows satellites to be competitive with terrestrial options in performance and efficiency while multicast fan-out solutions can make satellites the ideal solution for distribution of content to multiple locations.
The use of satellites for IP connectivity is growing throughout Asia-Pacific despite highly competitive pricing of trans-Pacific fiber, and seems poised for broad penetration into a variety of specialized applications across the region. Satellite solutions are ideal for situations where terrestrial options are not readily available. While there is now no lack of fiber across the ocean and between many major cities in Asia-Pacific, the number and variety of specialized applications that rely on satellites is continuing to grow with the increasing dependency of corporations, governments, and the military on computer networking. The competitiveness of satellite options has been aided in recent years by the development of technology to enhance the performance and efficiency of IP over satellite and the availability of solutions for reliable multicast that can utilize the advantage of satellites for delivery of content to multiple receivers. Satellite Solutions Due to the high cost of building and launching communications satellites and the limited bandwidth per transponder compared to even a single strand of fiber, in nearly any situation where a fiber solution is available, it will be less expensive than satellite. However, satellites offer the advantage of ubiquitous, instantaneous coverage, making it possible to connect any locations in as little as minutes without the time and cost of building a terrestrial infrastructure. Because satellites broadcast the transmission across a wide area as opposed to fiber links which are fundamentally point-to-point, satellites are also ideal for multicasting video, data, and other content to large numbers of users. The highest profile examples of satellite usage in Asia-Pacific are intrepid explorers climbing the Himalayas, scientific expeditions exploring the jungles of Indonesia, and journalists in Afghanistan, Pakistan, and other hot spots throughout the region, all carrying a suitcase-sized Inmarsat terminal to communicate with the world. While still heavily based on traditional voice and video, these users are increasingly dependent on IP networking to exchange e-mail, relay video clips, and transfer data. Beyond these high profile examples are more typical users such as the oil and gas industry. In countries such as Vietnam and Thailand, offshore exploration and drilling depends on satellites for connectivity from the ships and drilling platforms to local corporate offices where geophysical data is processed and analyzed. Even much of the on-shore exploration and drilling in Asia-Pacific takes place in remote jungle or mountain locations with little existing infrastructure where satellites are the only feasible solution. Similarly, many industrial corporations based in Taiwan, Hong Kong, Singapore, and Japan use satellites to connect to their production facilities in China and other locations where labor costs are lower. The outsourcing industry also depends on satellite links to connect computer software developers in Bangalore, India and typists and call centers in India and the Philippines to their clients, primarily in the United States. In some countries, the entire banking system, with branch offices in every remote village, can only be supported by a satellite network. In addition to corporate applications, satellites are also used for some consumer Internet services. Taking advantage of abundant trans-Pacific fiber connectivity into Hong Kong and Singapore, teleports in those locations use satellites to provide Internet access, both direct to consumers and trunking lines to local points-of-presence, into less connected and rural communities throughout the region. Lastly, governments and military organizations are probably the largest users of satellite networking. For a country’s embassies and consulates throughout the world, satellites offer the flexibility of communicating directly to their ministry without depending on the host country for access that could be cut in times of conflict. Aid organizations working on local projects in remote villages connect to their headquarters in the donor countries over satellite link. And most critically, military and peacekeeping operations require immediate, mobile, high bandwidth connectivity for their operations in remote, hostile environments. Overcoming Performance Limitations Beyond cost issues, until recently satellites have been considered an inferior solution for data transmission due to performance and efficiency limitations when running IP over satellite. Fortunately, a new class of products called protocol gateways is now available which overcome these limitations, making the performance and efficiency of satellite links equivalent to terrestrial alternatives. Communications over geosynchronous satellites, orbiting at an altitude of 22,300 miles, have round trip times of approximately 540 ms, an order of magnitude greater than terrestrial networks. Wireless communication through the atmosphere can also introduce bit errors into the data stream, especially during periods of heavy rain common among equatorial countries. These factors, combined with back channel bandwidth typically much smaller than that available on the forward channel, reduce the effectiveness of the TCP protocol used to reliably transmit data and files over the IP infrastructure. These satellite conditions adversely interact with a number of elements of the TCP architecture to severely constrict the data throughput rate that can be achieved over satellite links. The overall effect of satellite conditions on TCP is that data is frequently held in buffers or transmitted at a low speed, even when bandwidth is available, and expensive bandwidth is further wasted with unnecessary acknowledgements and retransmissions. Protocol gateways, also referred to as TCP Performance Enhancing Proxies (TCP-PEP), overcome these performance limitations by converting TCP traffic to a transport protocol especially optimized for satellite conditions. A protocol gateway situated on one side of the satellite link intercepts each TCP connection and establishes a new connection over the satellite link using the satellite-optimized protocol. The protocol gateway on the opposite side of the satellite link translates the data back to TCP for communication with the end device. This process offers vastly improved performance while remaining transparent to end users and compatible with the Internet infrastructure. (See Figures 1 and 2.) By designing a protocol which is especially adapted to high latency conditions and taking advantage of optimizations specific to satellite network architectures, the protocol gateway can provide performance and efficiency dramatically greater than is possible with TCP. As an example, on a 2 Mbps E1 link, an unenhanced TCP connection is limited to a throughput of 100 Kbps or less, an efficiency of only 5%. Unless there are other connections running in parallel, the remainder of the bandwidth will simply remain wasted. Using a protocol gateway, the same TCP connection can achieve a throughput of 1.9 Mbps, an efficiency of 95%. By taking advantage of a satellite optimized transport protocol, the protocol gateway is fully capable of utilizing essentially all of the available bandwidth. In addition to the protocol translation process, protocol gateways are well situated to provide additional performance and efficiency optimizations to take best advantage of the expensive satellite bandwidth. Data compression functionality is frequently combined into protocol gateway products, increasing download speeds while conserving bandwidth. Integrated rate control and QoS mechanisms can also help maximize performance while fairly dividing the bandwidth resources between users. Multicast Fan-Out In addition to the use of protocol gateways to optimize performance and efficiency, satellite operators strive to use multicast technology to take best advantage of the broadcast nature of satellite communications. Multicast technology allows a single transmission to reach multiple users, effectively dividing the cost of bandwidth among all users. For applications where data needs to be transmitted to multiple receivers, multicast can render satellite communications more cost effective than terrestrial options. Almost all computer networking applications are based on unicast transfers, where data is sent point-to-point between two devices. Even when the sender is transmitting the same data to multiple recipients, a separate copy of the data is delivered to each one. In contrast, multicast technology allows the sender to transmit a single copy to multiple receivers. Although IP includes multicast functionality, the usage of IP Multicast is currently limited to a few experimental applications. Management and billing of Internet traffic assumes unicast traffic patterns and does not apply well to multicast traffic. Although this could be fixed, most terrestrial ISPs avoid the problem by simply blocking multicast traffic from their networks. In addition, IP Multicast utilizes the UDP protocol. UDP has no mechanisms for retransmitting any data that is lost or corrupted on the network, it can only be used for streaming applications and other best-effort services. IP Multicast is therefore not suitable for file transfers and similar data applications. Fortunately, reliable Multicast Fan-Out (MFO) overcomes both of these problems. MFO transparently converts unicast TCP connections into reliable multicast transfers over the satellite network. This provides a convenient solution for reliable multicast that works with standard data applications including FTP. The Multicast Fan-Out process uses a MFO Transmitter at the hub of the satellite network that converts the unicast data transfer from the content server into a specialized multicast protocol. This provides a reliable multicast transfer over the satellite portion of the link. At each remote site, a MFO Receiver re-transmits the data to a local client using a standard TCP unicast connection. This allows the end nodes to communicate using standard TCP-based applications over any type of network, while transparently taking advantage of reliable multicast over the satellite link. MFO saves time while reducing bandwidth costs. As an example, consider the distribution of a 100 MB file to twenty-five remote offices over a 2 Mbps link. Using twenty-five separate unicast connections would require a minimum of three hours to complete the transfer to all sites. With MFO, the transaction would only need to take place once and could be completed in less than seven minutes. Now imagine a 100 GB movie delivered simultaneously, direct to hundreds of theaters throughout the region. Although an ideal tool for the satellite industry, Multicast Fan-Out can also be used with any multicast-enabled wide area network to distribute all types of data files to multiple sites. ISPs can replicate hub caches to a local cache at each point of presence. For corporate usage, MFO makes it easy to efficiently distribute database, inventory, and pricing files from headquarters to local offices. Summary With ubiquitous coverage and instant availability, satellites provide a critical alternative to terrestrial options for IP connectivity and have many specialized applications throughout Asia-Pacific. The recent availability of protocol gateways now allows satellites to be competitive with terrestrial options in performance and efficiency while multicast fan-out solutions can make satellites the ideal solution for distribution of content to multiple locations.