Placeshifting systems stream videos from the home to a single remote user using the limited upstream capacity of the home broadband link. We analyze the behavior of two placeshifting systems each using two types of broadband networks. We show that the duration between packets did not depend on the way that the servers were sending the packets through the bottleneck link. Even though both of these systems used TCP, the duration between packets did not follow the round trip times either. Instead, it depended on the particular broadband network. Our analysis shows how the bottlenecked first mile network leads to predictable packet delivery at the remote client. Paradoxically, it also leads to shorter periods and a single packet within each data burst. We discuss the limitations imposed by this behavior on a client side energy saving mechanism. We also describe techniques that allow the placeshifting servers to better operate with client side WNIC energy saving mechanisms.
Transcoding is a technique employed by network proxies to dynamically customize multimedia objects for prevailing network conditions and individual client characteristics. Transcoding can be performed along a number of different axes and the specific transcoding technique used depends on the type of multimedia object. Our goal in this paper is to understand the nature of typical Internet images and their transcoding characteristics. We focus our attention on transcodings intended to customize an image for file size savings. Our results allow the developers of a transcoding proxy server to choose the appropriate transcoding techniques for the important classes of Internet images.We analyze the characteristics of images available on the Web through a representative trace. We show that most GIF images accessed on the Internet are small; about 80% of the GIF images are smaller than 6 KBs. JPEG images are larger than GIF images; about 40% of the JPEG images are larger than 6 KBs. We also establish the characteristics of popular image transcoding operations. We show that for JPEG images, the JPEG compression metric and a transcoding that reduces the spatial geometry are productive transcoding operations (saves at least 50% of the file size for 50% of the images). Our systematic study of image characteristics leads to some surprising results. For example, a naive spatial geometry reduction of GIF images by a factor of 2 along each axis actually causes to an increase in the file size compared to the original image for 40% of the images. Thus it is important to understand the characteristics of individual images before choosing the proper transcoding operation.
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