Slow Links Research Articles

Thinternet: life at the end of a tether

Abstract As the Internet continues its exponential growth, the user profile is changing. Many of the newer Internet hosts are personal workstations, often connected by dial-up or other slow links. We examine some factors that motivate or mandate “thin” (low-bandwidth) connections to the Internet. We notice that the motivation for adopting thin links in the West can be different from those in developing countries. Using a profile of such typical users, we show how techniques exist that allow practical and adequately efficient use of the Internet even “at the end of a tether”. We are exploring the use of these methods in routine Internet use from a site in India (a software development laboratory, multi-user LAN, connected to an Internet service provider through an expensive dial-up link) and from mobile computers (e.g., HP100LX and Gateway Handbook) in the US. In each case the user's Internet access is through a thin link, with a bandwidth somewhere between 2400 bps and 28.8 kbps. Local caching and prefetching of resources naturally suggests itself as a useful candidate. It appears that transparent replay of application protocols is a practical way to retrofit resource caching into existing (shrinkwrapped) software. One promising method which works with most services of interest is Postel spoofing. Given the “browsing” mode of network usage, progressive encoding mechanisms are shown to effectively reduce the access time for particularly large Internet objects, such as Web pages. An ideal progressive encoding of a resource sends a gross quality rendering followed by successive refinements. Since only a fraction of the images retrieved in a session actually have long-term value, such techniques can reduce on-line bandwidth demands by an order of magnitude. Obviously, such encoding methods apply also to large archive and distribution files (such as from FTP archives). Filtering and relevance feedback have been recognised as effective tools in overcoming information overload. Many sophisticated general techniques are a subject of active research. However, we found that exploiting certain behaviour patterns typical in Internet usage permits particularly efficient filtering using surprisingly simple methods. We apply this to USENET communication, and extend this to other services (FTP, HTTP, Gopher, mail, etc.), and outline a method of filtering network hypermedia on the basis of relevance contours. Our method recognises the amount of selected information that can be digested by a user in a day, and maximises the value of the packet so selected. It also differs from others by integrating all network hypermedia and selecting and filtering items without regard to the service they were accessed from (USENET, Web, Gopher, FTP, etc.). It does not depend on a-priori categorisation such as news groups and the consequent need for explicit subscription and unsubscription.

Progressive refinement using local variance estimators

When transmitting an image over a slow communications link, it is desired to provide the best display possible in early stages of the transmission. Progressive refinement attempts to continuously minimize the deviation between the image and its displayed approximation. It is shown that this minimization is accomplished by transmitting average values of regions of the image at increasingly fine levels of resolution. The optimal refinement strategy is to subdivide the region which maximizes the product of area and pixel variance. Typically, the receiving process cannot determine the pixel variance. Estimators of the variance can be computed from information already received are developed. They are applied to refinement over the spatial distribution of values and simultaneously to refinement over their gray-scale quantization. The estimators are shown to apply equally well to monochrome and full-color image. These techniques are implemented with no transmission overhead and are shown to generate qualitatively and quantitatively superior displays. >

ASCII protocol conversion revisited

One of the first implementations of protocol conversion was the connection of 'dumb' ASCII (American Standard Code for Information Interchange) asynchronous terminals to IBM 370 hosts. A protocol converter box made the ASCII terminal appear to the host as a 3270 display and made the host appear to understand the escape sequences necessary to control the ASCII terminal. The author describes an approach to connecting 'smart' asynchronous ASCII devices to 370 hosts. By having a single screen at the microcomputer instead of two (one at the controller and one at the display) and by utilizing compression and asynchronous data links, the performance of remote workstations on slow links can be greatly improved. >

Bar code sample identification: the key to laboratory information management systems (LIMS) productivity

Abstract Laboratory information management systems (LIMS) are becoming increasingly sophisticated. The value of the LIMS is directly related to its accuracy (can these test results be trusted, verified, repeated?) and to its efficiency (how rapidly can the system operate?). LIMS is essentially a productivity tool that involves some of the most complex software in existence. While automated testing has been expanding in sophistication, the systems are often impeded by outmoded data collection techniques. Any system is only as good as its weakest link, and as fast as its slowest link. Increasing the speed of each testing step in the laboratory will produce only marginal productivity improvements. The key to increased LIMS productivity is the speed and accuracy of the data collection techniques. A fast and accurate method of automated data collection is bar coding scanning.

Diffusional processes in the welding of some refractory carbides to metals

1. A thermodynamic approach may be adopted for assessing the possibility of a chemical reaction occurring during the welding of unlike materials; in the case of refractory compounds with wide ranges of homogeneity it is necessary to take into account the effect of composition in the homogeneity range on their thermodynamic functions. 2. The extent of the third stage in the diffusion welding of carbides to carbides and carbides to metals is limited by the slowest link of the process, viz., self-diffusion of metal atoms in the crystal lattices of the carbides. 3. In the diffusion welding of refractory metals and carbides optimum welding temperatures monotonically rise with increasing degree of localization of valence electrons in the metallic lattices (metallic sublattices in the case of carbides).