S
Joint Broadcast Scheduling and User’s Cache Management for Efficient Information Delivery Chi-Jiun SU* [email protected] Hughes Network Systems 11717 Exploration Lane Germantown MD 20876 Tel: (301) 601-7346 FAX: (301) 428-2750
Leandros T=siulas [email protected] Electrical Engineering Department University of Maryland College Park MD 20742 Tek (301) 405-6620 FAX (301) 3149920
user community without any feedback about the user’s needs due to the hmited upfink communication capability from the user to the server. Data broadcast by the server are organized into units called information items. When a user needs a certain information item, it monitors the broadcmt channel until the desired item is detected and captures it for use. There is some latency from the time the need of an information item arises until the time the item is actusdly broadcast by the server. This latency depends on the broadcast schedule of the server, as well as the user access pattern.
Abstract In information delivery through broadcasting, a server continuously pushes information in a broadcast channel and the users ZCCH it by tuning in and waiting until the information they are interwted in is transmitted. The server follows a schedule that attempts to match the user access statistics in order to reduce the ace= latency. In c=e of inhomog~ neous user populations with several ~erent ace= profila, the users have local cache to smooth out the mismatch= of their profle with the broadcast schedule statistics. In this work we propose a method for joint dwign of the server broadcast schedule and the user ctilng strate~ such that the zccw delay is minimized. We identify a fluid model of the joint problem on which the joint optimization is performed and subsequently the dynamic schedule is dmigned to match the optimal fluid model parameters. It turns out that with joint d=ign of the broadcast schedule and the user cache management policy significant performance improvement is tileved, particularly for inhomogeneous user populations. 1
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.. . . Uw Gmup I . ..-. .................
. ...Uxr Group ~....; . . . . . . . . . . ..-
Figure 1: A Broadcast Data Delivery System in a Wwel& Communication Environment There has been a lot of work in the past on the prob Iem of dwigning a broadcast schedule such that the average latency is minimized [5], [6], [18], [1], [9] and [15]. The approach is to determine the broadcast frequency of each information item in accordance with the user accfrequency of the item and then to distribute the broadc=t slots of each item as uniformly as posible. If there are more than one class of users with ~erent access distributions of information items, then it is unavoidable that some cl-es will suffer large latency. An approach to reduce the latency to a dwirable level for each user is to make use of local user storage. If a user has local storage, it can retrieve information items from the broadcast and store them in its memory prior to the items being requested. If the user makes a requwt for one of the “prefetched” stored items, the response time for this request will be instantaneous. By selectively prefetching information items from the broadcast, the user is able to effectively minimize the mismatch between its aceneeds and server’s broadcast schedule and the average latency of its information requmts is reduced. Therefore, user’s memory management becomes an important issue to consider in order to minimize the average response time of user’s r~ quests. As information items pass by in the broadcast, the
when the author
was with
Pemlission to make digital or hard copies of all or part of this }vork for personal or classroom use ia granted ~vhhout fee provided th3t copies are not made or distributed for prolit or commercial ad~antage and that copies bear this notice and the full citation on the first page. To copy othen~ise. to republish, to post on sen~ers or to redistribute to lists, requires prior specific permission antior a fee.
MOBICOM 9S Dallas Texas USA ACM 199S 1-5S1 13435-ti9S/10...
Schedule
se..r;..~:~::~~:J””j”j &
With recent advancw in information technology, on-way push-b=ed broadcast defivery is becoming a method of main interest for the d=tribution of information to a large user population. Apphcations that employ broadcast delivery are Boston Community Information System [8], Datacycle project at Bellcore [7], Hughw’ DirectPC multimedia and package defivery system [10], PointCast’s webcasting [14], Marimba’s Castanet [13], AirMedia Live Internet Broadcast Network [3] and Intel’s intercast [11] among others. Data to be disseminated in the applications includes news and weather information, trfic information, schedule information in airports and train stations, stock quots and so on. Under the broadcasting approach as shown in figure 1, a server continuously and repeatedly broadcasts data to a
Cop~ght
Breadcmt
“-;:S
Leandros T=siulas [email protected] Electrical Engineering Department University of Maryland College Park MD 20742 Tek (301) 405-6620 FAX (301) 3149920
user community without any feedback about the user’s needs due to the hmited upfink communication capability from the user to the server. Data broadcast by the server are organized into units called information items. When a user needs a certain information item, it monitors the broadcmt channel until the desired item is detected and captures it for use. There is some latency from the time the need of an information item arises until the time the item is actusdly broadcast by the server. This latency depends on the broadcast schedule of the server, as well as the user access pattern.
Abstract In information delivery through broadcasting, a server continuously pushes information in a broadcast channel and the users ZCCH it by tuning in and waiting until the information they are interwted in is transmitted. The server follows a schedule that attempts to match the user access statistics in order to reduce the ace= latency. In c=e of inhomog~ neous user populations with several ~erent ace= profila, the users have local cache to smooth out the mismatch= of their profle with the broadcast schedule statistics. In this work we propose a method for joint dwign of the server broadcast schedule and the user ctilng strate~ such that the zccw delay is minimized. We identify a fluid model of the joint problem on which the joint optimization is performed and subsequently the dynamic schedule is dmigned to match the optimal fluid model parameters. It turns out that with joint d=ign of the broadcast schedule and the user cache management policy significant performance improvement is tileved, particularly for inhomogeneous user populations. 1
.l@
.. . . Uw Gmup I . ..-. .................
. ...Uxr Group ~....; . . . . . . . . . . ..-
Figure 1: A Broadcast Data Delivery System in a Wwel& Communication Environment There has been a lot of work in the past on the prob Iem of dwigning a broadcast schedule such that the average latency is minimized [5], [6], [18], [1], [9] and [15]. The approach is to determine the broadcast frequency of each information item in accordance with the user accfrequency of the item and then to distribute the broadc=t slots of each item as uniformly as posible. If there are more than one class of users with ~erent access distributions of information items, then it is unavoidable that some cl-es will suffer large latency. An approach to reduce the latency to a dwirable level for each user is to make use of local user storage. If a user has local storage, it can retrieve information items from the broadcast and store them in its memory prior to the items being requested. If the user makes a requwt for one of the “prefetched” stored items, the response time for this request will be instantaneous. By selectively prefetching information items from the broadcast, the user is able to effectively minimize the mismatch between its aceneeds and server’s broadcast schedule and the average latency of its information requmts is reduced. Therefore, user’s memory management becomes an important issue to consider in order to minimize the average response time of user’s r~ quests. As information items pass by in the broadcast, the
when the author
was with
Pemlission to make digital or hard copies of all or part of this }vork for personal or classroom use ia granted ~vhhout fee provided th3t copies are not made or distributed for prolit or commercial ad~antage and that copies bear this notice and the full citation on the first page. To copy othen~ise. to republish, to post on sen~ers or to redistribute to lists, requires prior specific permission antior a fee.
MOBICOM 9S Dallas Texas USA ACM 199S 1-5S1 13435-ti9S/10...
Schedule
se..r;..~:~::~~:J””j”j &
With recent advancw in information technology, on-way push-b=ed broadcast defivery is becoming a method of main interest for the d=tribution of information to a large user population. Apphcations that employ broadcast delivery are Boston Community Information System [8], Datacycle project at Bellcore [7], Hughw’ DirectPC multimedia and package defivery system [10], PointCast’s webcasting [14], Marimba’s Castanet [13], AirMedia Live Internet Broadcast Network [3] and Intel’s intercast [11] among others. Data to be disseminated in the applications includes news and weather information, trfic information, schedule information in airports and train stations, stock quots and so on. Under the broadcasting approach as shown in figure 1, a server continuously and repeatedly broadcasts data to a
Cop~ght
Breadcmt
“-;:S
