Seminar Topic - Adding intelligence to internet using satellite

Satellites have been used for years to provide communication network links. Historically, the use of satellites in the Internet can be divided into two generations. In the first generation, satellites were simply used to provide commodity links (e.g., T1) between countries. Internet Protocol (IP) routers were attached to the link endpoints to use the links as single-hop alternatives to multiple terrestrial hops. Two characteristics marked these first-generation systems: they had limited bandwidth, and they had large latencies that were due to the propagation delay to the high orbit position of a geosynchronous satellite.

In the second generation of systems now appearing, intelligence is added at the satellite link endpoints to overcome these characteristics. This intelligence is used as the basis for a system for providing Internet access engineered using a collection or fleet of satellites, rather than operating single satellite channels in isolation. Examples of intelligent control of a fleet include monitoring which documents are delivered over the system to make decisions adaptively on how to schedule satellite time; dynamically creating multicast groups based on monitored data to conserve satellite bandwidth; caching documents at all satellite channel endpoints; and anticipating user demands to hide latency. 

 This paper examines several key questions arising in the design of a satellite-based system: 

• Can international Internet access using a geosynchronous satellite be competitive with today's terrestrial networks?
• What elements constitute an "intelligent control" for a satellite-based Internet link?
•  What are the design issues that are critical to the efficient use of satellite channels?

ISSUES IN SECOND-GENERATION SATELLITE LINK CONTROL

 We discuss in this section each of the questions raised in this paper's introduction.

Can international Internet access using a geosynchronous satellite be competitive with today's terrestrial networks?

 The first question is whether it makes sense today to use geosynchronous satellite links for Internet access. Alternatives include wired terrestrial connections, low earth orbiting (LEO) satellites, and wireless wide area network technologies (such as Local Multipoint Distribution Service or 2.4-GHz radio links in the U.S.). 

 We see three reasons why geosynchronous satellites will be used for some years to come for international Internet connections. The first reason is obvious: it will be years before terrestrial networks are able to provide adequate bandwidth uniformly around the world, given the explosive growth in Internet bandwidth demand and the amount of the world that is still unwired. Geosynchronous satellites can provide immediate relief. They can improve service to bandwidth-starved regions of the globe where terrestrial networks are insufficient and can supplement terrestrial networks elsewhere. 

 Second, geosynchronous satellites allow direct single-hop access to the Internet backbone, bypassing congestion points and providing faster access time and higher net throughputs. In theory, a bit can be sent the distance of an international connection over fiber in a time on the order of tens of microseconds. In practice today, however, international connections via terrestrial links are an order of magnitude larger. For example, in experiments we performed in December 1998, the mean round trip time between the U.S. and Brazil (vt.edu to embr.net.br) over terrestrial links were 562.9 msec (via teleglobe.net) and 220.7 (via gzip.net) [Habib]. In contrast, the mean latency between the two routers at the two endpoints of a satellite link between Bangledesh and Singapore measured in February 1999 was 348.5 msec. Therefore, a geosynchronous satellite has a sufficiently large footprint over the earth that it can be used to create wormholes in the Internet: constant-latency transit paths between distant points on the globe [Chen]. The mean latency of an international connection via satellite is competitive with today's terrestrial-based connections, but the variance in latency can be reduced. 

 As quality-of-service (QoS) guarantees are introduced by carriers, the mean and variance in latency should go down for international connections, reducing the appeal of geosychronous satellites. However, although QoS may soon be widely available within certain countries, it may be some time until it is available at low cost between most countries of the world. 

 A third reason for using geosynchronous satellites is that the Internet's traffic distribution is not uniform worldwide: clients in all countries of the world access content (e.g., Web pages, streaming media) that today is chiefly produced in a few regions of the world (e.g., North America). This implies that a worldwide multicast architecture that caches content on both edges of the satellite network (i.e., near the content providers as well as near the clients) could provide improved response time to clients worldwide. We use this traffic pattern in the system described in the case study (Section 3). 

 One final point of interest is to ask whether LEO satellites that are being deployed today will displace the need for geosynchronous satellites. The low orbital position makes the LEO footprint relatively small. Therefore, international connections through LEOs will require multiple hops in space, much as today's satellite-based wireless phone systems operate. The propagation delay will eliminate any advantage that LEOs have over geosynchronous satellites. On the other hand, LEOs have an advantage: they are not subject to the constraint in orbital positions facing geosynchronous satellite operators. So the total available LEO bandwidth could one day surpass that of geosynchronous satellites. 

What elements constitute an "intelligent control" for a satellite-based Internet link?

 The basic architecture behind intelligent control for a satellite fleet is to augment the routers at each end of a satellite link with a bank of network-attached servers that implement algorithms appropriate for the types of traffic carried over the links. We use certain terminology in our discussion. First, given the argument above for asymmetric traffic, our discussion is framed in terms of connecting content providers (in a few countries) to end users (in all countries). In some cases (e.g., two-way audio), however, the traffic may be symmetrical. Second, we refer to the content-provider endpoint of a satellite link as a warehouse, and the end-user endpoint as a kiosk. The architecture of warehouses and kiosks must be scalable: The number of servers, storage capacity, and throughput of warehouses and kiosks must scale as the number and bandwidth of satellite links, content providers, and end users grows

Content providers are connected via the terrestrial Internet to a router inside a warehouse. The router also connects to a local area network that interconnects various servers. The router also connects to the earth station for the satellite. Within the footprint of the satellite are many groundstations, each connected to a router within a kiosk. The kiosk is similar to the warehouse in that it connects to a local area network that interconnects servers, and optionally, to a terrestrial Internet connection. The kiosk also acts as the head end for Internet service providers (ISPs) that provide network connections to end users.

Intelligent controls reside in the warehouse and kiosk and are required to share limited satellite bandwidth among many users and to hide the quarter-second latency of a geosynchronous satellite. The controls are a distributed algorithm, in which part runs on warehouses and part runs on kiosks. All warehouses and kiosks must cooperate and must coordinate the use of satellite resources. Multicast groups are defined to allow communication between cooperating entities (e.g., between a warehouse and multiple kiosks). 

 To identify which controls make sense, it is useful to look at the characteristics of Internet traffic. Figure 2 is a taxonomy of traffic with six categories. Three of them represent Web pages: pages that are popular for months or longer (e.g., a news service such as cnn.com); pages that are popular for a short time (e.g., hours, days, or weeks, such as those resulting from Olympic games); and pages that are accessed only a few times. One of the facts known about this traffic is that most of the requests and most of the bytes transferred in client workloads come from a small number of servers. For example, in a study of proxy or client uniform resource locator (URL) reference traces from Digital Equipment Corporation (DEC), America Online, Boston University, Virginia Tech, a gateway to South Korea, and one high school, 80% to 95% of the total accesses went to 25% of the servers.

 The next category of traffic in Figure 2 is push channels. This consists of a collection of media that a content provider assembles and distributes, for example using the proposed World Wide Web Consortium (W3C) Information and Content Exchange (ICE) protocol. The remaining two categories are real-time traffic, such as streaming audio or video from a teleconference, and what we call timely but not real time. This last category includes information that is updated periodically and has a certain lifetime, such as financial quotes and Network News Transfer Protocol (NNTP). 

What are the design issues that are critical to using satellite channels efficiently?

 The overall system must achieve a balance between the throughput of the terrestrial Internet connection going into the warehouse, the throughput of the warehouse itself, the throughput of the satellite link, the throughput of each kiosk, and the throughput of the connection between a kiosk and its end users. In addition, a balance among the number of end users, the number of kiosks, and the number of warehouses is required. 

 Consider some examples. As the number of end users grows, so will the size of the set of popular Web pages that must be delivered, and the bandwidth required for push, real time, and timely traffic. Let's look at Web traffic in detail. Analysis of end-user traffic to proxy servers at America Online done at Virginia Tech shows that an average user requests one URL about every 50 seconds, which indicates a request rate of 0.02 URLs per second. (This does not mean that a person clicks on a link or types a new URL every 50 seconds; instead, each URL requested typically embeds other URLs, such as images. The average rate of the individual URLs requested either by a person or indirectly as an embedded object is one every 50 seconds.) Thus, a kiosk supporting 1,000 concurrent users must handle a request rate of 200 per second. The median file size from the set of traces cited above (DEC, America Online, etc.) is 2 kilobytes. Thus, the kiosk Hypertext Transfer Protocol (HTTP)-level throughput to end users must be 400 kilobytes per second.

At the other end, the warehouse has a connection to the Internet. The bandwidth of this connection must exceed that of the satellite connection, because the warehouse generates cache consistency traffic. The servers within the warehouse and kiosk have limited throughput, for example, the throughput at which the cache engines can serve Web pages. To do multicast transmission, a collection of content (Web pages, pushed documents) must be bundled up at the application layer at the warehouse into a unit for transmission to a multicast group, then broken down into individual objects at the kiosk. This assembly and disassembly process also limits throughput. 

 A second issue is how to handle Web page misses as kiosks. If the kiosk has no terrestrial Internet connection, then these situations obviously must be satisfied over the satellite channel. This reduces the number of kiosks that a satellite link can handle. On the other hand, if the kiosk does have a terrestrial connection, an adaptive decision might be to choose the satellite over the terrestrial link if there is unused satellite capacity and if the performance of the territorial link is erratic. 

 A third issue is how to handle Domain Name System (DNS) lookups. A DNS server is necessary at kiosks to avoid the delay of sending lookups over a satellite. However, how should misses or lookups of invalidated entries in the kiosk's DNS server be handled? One option is for the DNS traffic to go over a terrestrial link at the kiosk, if one is available. An alternative is for the warehouse to multicast DNS entries to the kiosks, based on host names encountered in the logs transmitted from the kiosks to the warehouse. 

 A fourth issue is fault tolerance. If a kiosk goes down and reboots, or a new kiosk is brought up, there must be a mechanism for that kiosk to obtain information missed during the failure

ROADMAP FOR THE FUTURE

 Although the concept of "shortcuts" from the content providers to service providers is not new, this idea has been harnessed only recently. This recent development has resulted from the availability of enabling technologies such as IP multicast/broadcast over satellite, Web caches that accept push, and transparent redirection of layer-4 traffic. While the planet becomes wired through terrestrial and undersea high-bandwidth fiber links, geostationary satellites offer an ideal platform for offering an intelligent and high-performance infrastructure for Internet delivery. The first generation of such intelligent products will be available this year. These products and services will also serve as the proving grounds for several next-generation internet services, such as virtual private networks (VPNs), which offer security as well as guaranteed quality of service from the content providers to the end users. 

 At the writing of this document the IDS prototype has been tested at INTELSAT labs and is poised for deployment in international trials. The trials will comprise ten signatories of INTELSAT, including Teleglobe International (Canada), Telia (Sweden), British Telecom (UK), French Telecom (France), and Embratel (Brazil). The international trials will have a single warehouse located near Montreal, Canada, and operated by Teleglobe, and 10 kiosks located at participating signatory sites in North America, Europe, and Africa. The trials will last for three months. 

Commercial releases of IDS will add functionality to provide the following:

• Content-provider-based push of Web content into the warehouse Web cache. IDS modules within the warehouse as well as the content provider will be developed to implement this feature. 
• A transport and proxy for real-time streaming traffic within IDS. 
• Security and QoS for all traffic flowing through IDS. 
• Billing components for warehouses and kiosks. 
• Information mined from warehouse and kiosk databases to content providers and service providers.

 The first commercial version of IDS is scheduled for release in May 1999. Two subsequent commercial releases are planned in 1999. 

 

CONCLUSION

 A new generation of Internet access built around geosynchronous satellites can provide immediate relief. They can improve service to bandwidth-starved regions of the globe where terrestrial networks are insufficient and supplement terrestrial networks elsewhere. This new generation of satellite system manages a set of satellite links using intelligent controls at the link endpoints. Mechanisms controlled include caching, dynamic construction of push channels, use of multicast. and scheduling of satellite bandwidth

REFERENCES

1. [Abdulla] Ghaleb Abdulla, Edward A. Fox, Marc Abrams, "Shared User Behavior on the World Wide Web," WebNet97, Toronto, October 1997, http://www.cs.vt.edu/~nrg/docs/97webnet/ 
2. [Chen] Chen et. al, "Wormhole Caching with HTTP Push Method for a Satellite-Based Global Multicast Replication System," submitted to the International Cache Conference, San Diego, June 1999. 
3. [Danzig] Peter Danzig, "NetCache Architecture and Deployment," February 2, 1997. 
4. [Gwertzman] James Gwertzman and Margo Seltzer, "World-Wide Web Cache Consistency," http://www.eecs.harvard.edu/vino/usenix.196/ 

Department, Computer Science and Engineering, MESCE