| dc.description.abstract | In the present information society, Internet services have become a part of urban life due to the easy availability of dial-up/leased lines. Unfortunately, these services have not reached many rural/remote areas due to lack of terrestrial communication infrastructure. The cost involved in providing telephone lines in rural areas is high and it is difficult to cover the total rural areas of India. Making the Internet available as a knowledge resource to every Indian does not mean trying to provide broadband access to every village.
On the Internet, the maximum traffic is web-based, which involves a substantially larger flow of data towards the client (the forward direction) than from it (the reverse direction). This increased the interest in asymmetric networks, where bandwidth in the forward direction is often orders of magnitude larger than that in the reverse, motivated by technological and economic considerations as well. Such asymmetry is accentuated when the channel is unidirectional, necessitating the use of a different, often low-bandwidth channel (e.g., a dial-up line or a bandwidth-constrained channel for communication in the reverse direction). This once again puts a constraint on having telephone connectivity in rural areas. The line conditions should be good.
A satellite communication system distinguished by its global coverage is an excellent candidate to cater to rural/remote areas. The satellite communication system is particularly attractive for point-to-multipoint communications. The requirements discussed above for the rural people can be met through web-based Internet facilities. The work reported in this thesis deals with providing limited web-based facilities to the rural people in remote areas of India using the existing satellite resources where good telephone infrastructure is not available. To realize the above objective, we set up the following work:
Study the issues related to Internet access provided by dial-up Internet, Asynchronous Digital Subscriber Line, and cable modem.
Study the characteristics of the existing satellite-based networks.
Suggest an alternative approach to use the satellite channels in both ways, which combines wideband broadcasting with a narrowband return channel (an alternative to dial-up PSTN link) and realize a proof-of-concept model for satellite-based web services.
Study the system parameters viz. prefetch queue and cache size.
As per the objective set, the characteristics of Internet access provided by the dial-up line, Digital Subscriber Line, and Cable modem are studied and found to be unsuitable for remote rural places where a good telephone connection is not available. The characteristics of two satellite independent networks viz. INSAT reporting system (MSS) and Digital Sound and Data Broadcasting (DSDB) were studied. The INSAT reporting system is a low-bandwidth channel system used for sending short messages of length up to 40 characters from a remote place to the central hub and delivered to the user on a PC or a fax machine. This system uses random ALOHA mode and transmits the message twice with an interval of 5 seconds. The DSDB is a broadcast system having a large bandwidth channel supporting up to 2 Mbps and is used basically for MPEG-2 audio and data broadcasting.
Web traffic is based on the HTTP protocol, and the protocol presumes only a reliable transport; any protocol that provides such a guarantee can be used. This property of the HTTP protocol allowed us to implement our own packet formats as per the systems used, instead of using the standard TCP/IP protocol in the lower layers. For a URL having a length more than 40 characters, the limitation imposed by the characteristics of the INSAT reporting system is taken care of by introducing fragmentation of URLs at the remote end and defragmentation of URLs at the central hub end. This decreases the overall performance of the system.
In general, when a web page is requested, the browser will first fetch the HTML page and then fetch all the in-line objects referred to in the HTML page. This we refer to as the normal mode of fetching a web page. When the number of in-line objects to be fetched is large, the delay introduced by the INSAT reporting system will be significant. To overcome this, a new mode of fetching the web page is implemented and we refer to it as prefetch mode. In this mode, the in-line objects are prefetched at the central hub end and sent to the remote end along with a directory structure. The remote end services the request made by the browser for in-line objects without sending the request to the hub.
A study has been done on the overall performance of the system using prefetch mode and compared with that of the normal mode. The overall performance of the system using prefetch mode is also compared with that of an Internet leased line environment. The beta experiment was conducted to examine the robustness of the system in a controlled environment. To enhance the performance of the overall system, a First-in-First-Out (FIFO) based cache is implemented at the remote end and the performance characteristics of the cache for various sizes are carried out. Further, sending and receiving of e-mails from the central hub station is implemented using Common Gateway Interface (CGI) to show that the local information necessary for the remote people can be stored in a central place and can be retrieved or updated using the CGI. | |
