Person:
Ammar, Mostafa H.

Associated Organization(s)
Organizational Unit
ORCID
ArchiveSpace Name Record

Publication Search Results

Now showing 1 - 10 of 33
  • Item
    A Generic Framework for Parallelization of Network Simulations
    (Georgia Institute of Technology, 1999-10) Riley, George F. ; Fujimoto, Richard M. ; Ammar, Mostafa H.
    Discrete event simulation is widely used within the networking community for purposes such as demonstrating the validity of network protocols and architectures. Depending on the level of detail modeled within the simulation, the running time and memory requirements can be excessive. The goal of our research is to develop and demonstrate a practical, scalable approach to parallel and distributed simulation that will enable widespread reuse of sequential network simulation models and software. We focus on an approach to parallelization where an existing network simulator is used to build models of subnetworks that are composed to create simulations of larger networks. Changes to the original simulator care minimized, enabling the parallel simulator to easily track enhancements to the sequential version. We describe our lessons learned in applying this approach to the publicly available ns software package (McCanne and Floyd, 1997) and converting it to run in a parallel fashion on a network of workstations. This activity highlights a number of important problems, from the standpoint of how to parallelize an existing serial simulation model and achieving acceptable parallel performance
  • Item
    Providing Interactive Functions through Active Client Buffer Management in Partitioned Video Broadcast
    (Georgia Institute of Technology, 1999) Ammar, Mostafa H. ; Kamel, Ibrahim ; Mukherjee, Sarit ; Fei, Zongming
    Partitioned video broadcast divides a video into segments and sends each segment over one channel in cycles. In this paper, we propose an active buffer management scheme to provide interactive functions in partitioned video broadcast. The scheme uses client side buffering in a novel fashion that relies on the simultaneous availability of past, present and future parts of a video and lets the client selectively prefetch segments from broadcast channels based on the observation of the play point in its local buffer. The contents of the buffer are adjusted in such a way that the relative position of the play point is kept in the middle part of the buffer and a high probability of providing the interactive functions with the contents of the local buffer is achieved. Discontinuous interactive functions are used to deal with cases where the local buffering is not sufficient to provide some desired interaction. We design a new video partitioning that is more suitable for interactive behaviors of clients. We introduce the concept of feasible points which allows a client to move only to those points within the broadcast stream that can preserve the continuity of playback. Our simulations show that the active buffer management scheme can implement interactive actions through buffering with a very high probability in a wide range of user interaction levels.
  • Item
    Optimal Allocation of Clients to Replicated Multicast Servers
    (Georgia Institute of Technology, 1999) Ammar, Mostafa H. ; Zegura, Ellen W. ; Fei, Zongming
    Server replication is an approach that is often used to improve the scalability of a service. One of the important factors in the efficient utilization of replicated servers is the ability to direct client requests to the `best" server, according to some optimality criteria. Recently, there have been several proposals for multicast services in which a server delivers information to multiple clients simultaneously. Such proposals include multicasting of web content, multicast-based video services (on-demand and pay-per-view style services), multicasting of database content and broadcast disks. The goal of many of these proposals is to use multicast to enhance the ability of the service to handle a large number of clients economically. Multicast servers may be replicated for several reasons: to distribute the load among on-demand multicast servers, to balance the `feedback" load on the servers or on entities along the multicast tree from the servers, or to select the server that is at the root of the `best" multicast routing tree. In this paper we first give a definition of the static multicast server selection problem, in which we assume a set of static clients and multicast servers and consider how one might produce an optimalallocation of the clients to the servers. We propose a transformation method for deriving multicast server selection algorithms from the traditional multicast routing algorithms. To investigate the dynamic behavior of client join and leave and the cost incurred during the process, we next define the dynamic multicast server selection problem, in which the potential clients join and leave the multicast session dynamically, and the goal is to produce an optimal allocation of clients to servers with an emphasis on how this allocation behaves over time. We formulate the problem as a Markovian Decision Process (MDP) and analyze the tradeoff between the cost of the multicast tree(s) and the transition cost of establishing and removing links from the tree(s). We also explore the effect of join/leave frequency on optimal policy. Our analysis leads to two heuristics which we use to propose a selection algorithm. The algorithm uses a very simple join and leave strategy yet still can generate low cost trees. Our simulation compares the performance of our proposed algorithm with various other multicast server selection algorithms.
  • Item
    Design and Evaluation of Router-Supported and End-to-End Multicast Receiver-Based Scoping Protocols
    (Georgia Institute of Technology, 1999) Ammar, Mostafa H. ; Clay, Lenitra M.
    IP multicasting allows a source to define a multicast group address and receivers can dynamically join and leave this group. Currently the propagation of multicast packets is controlled by two scoping methods: TTL scoping and administrative scoping. Both of these approaches require the source to control the scope of the multicast. In this paper we explore two receiver-based scoping protocols. Receiver-based scoping allows a receiver to place conditions on its multicast join that must be met in order to join successfully and remain a member of the multicast group. Such a scoping mechanism would be useful in environments where the receiver incurs a cost for its membership of the multicast group. In this paper we discuss receiver-based scoping and its design goals. In order to perform receiver-based scoping a receiver needs information about the shape of the multicast tree. We describe two receiver-based scoping approaches to obtaining this information: router-supported and end-to-end. The router-supported approaches requires state to be maintained in routers while the end-to-end approach uses the multicast traceroute tool and does not require state maintenance by the routers. We evaluate the performance of these approaches in terms of their accuracy, bandwidth overhead and state requirements.
  • Item
    Inter-Receiver Fair Multicast Communication over the Internet
    (Georgia Institute of Technology, 1999) Zegura, Ellen W. ; Ammar, Mostafa H. ; Jiang, Tianji
    Multicast protocols target applications involving a large number of receivers with heterogeneous data reception capabilities.To accommodate heterogeneity, the sender may transmit at multiple rates, requiring mechanisms to determine the rates and allocate receivers. In this paper, we develop a protocol to control the rate of a multicast session, with the goal of maximizing the inter-receiver fairness, an intra-session measure that captures the collective "satisfaction" of the session receivers. Our target environment is the Internet, where fair sharing of bandwidth must be achieved via end-system mechanisms and fairness to TCP is important. We develop and evaluate protocols to maximize this measure by maintaining a fixed-rate base group and a variable-rate group. We show that our schemes offer improvement over single-rate sessions, while maintaining TCP-friendliness.
  • Item
    A Greedy Approach For Improving Update Processing In Intermittently Synchronized Databases
    (Georgia Institute of Technology, 1999) Omiecinski, Edward ; Navathe, Shamkant B. ; Ammar, Mostafa H. ; Donahoo, Michael J. ; Malik, Sanjoy ; Yee, Wai Gen
    Replication of data on portable computers is a new DBMS technology aimed at catering to a growing population of mobile database users. Clients can download data items such as email, or sales data from a server onto these machines, per use it during commutes, and return any modifications to the server at the end of the day. In this paper, we describe how the servers in these systems generally process update information for clients and reveal a scalability problem--server processing increases quadratically with respect to increasing numbers of clients. We develop a cost model, and propose a solution based on heuristics. By aggregating client interests into datagroups, based on notions such as interest overlap, we can reduce server cost. These techniques are attractive because they are simple and computationally cheap. Simulations show that even simple techniques may yield significant performance improvements.
  • Item
    Multiple-Channel Multicast Scheduling for Scalable Bulk-data Transport
    (Georgia Institute of Technology, 1998) Ammar, Mostafa H. ; Zegura, Ellen W. ; Donahoo, Michael J.
    A key technique for allowing a server to handle a large volume of requests for file transfers is to multicast the data to the set of requesting clients. Typically, the paths from the server to the clients will be heterogeneous in bandwidth availability. Multiple-Channel Multicast (MCM) is an approach that can be used to handle this heterogeneity. In this approach the data is multicast over multiple channels, each addressed as a separate multicast group. Each receiver subscribes to a set of channels (i.e., joins the corresponding multicast groups) commensurate with its own rate capabilities. Of particular interest in the design of MCM schemes is the scheduling of data transmission across the multiple channels to accomodate asynchronous requests from clients. In this paper, we present and analyze a new multiple-channel multicast approach called Partition Organization (PO) scheduling. The scheme is designed to result in good reception efficiency when compared to existing proposals while improving on their performance when other measures of interest (which we introduce) are considered.
  • Item
    Improving the scalability and cost-effectiveness of database access for
    (Georgia Institute of Technology, 1998) Ammar, Mostafa H.
  • Item
    Evaluating the scalability of aggregation techniques for database replication
    (Georgia Institute of Technology, 1998) Ammar, Mostafa H.
  • Item
    Scalable Delivery of Web Pages Using Cyclic Best-Effort (UDP) Multicast
    (Georgia Institute of Technology, 1997) Ammar, Mostafa H. ; Fei, Zongming ; Almeroth, Kevin C.
    The World Wide Web (WWW) has gained tremendously in popularity over the last several years. Solutions to the problem of overloaded web servers have included buying more hardware, the use of transparent server replication and mirroring, and caching of hot pages. Another technique that can be used in conjunction with these other solutions is the use of multicast for the delivery of web pages. In this work we explore the use of UDP, best-effort multicast as a delivery option. Reliability is achieved through repetitive, cyclic transmission of a requested page. This solution is expected to be most efficient when used for highly requested pages. We view this cyclic multicast technique as a delivery option that can be integrated with the traditional reliable unicast and recently proposed reliable multicast options. We first describe the architecture of an integrated web server employing all three delivery options. We then describe the cyclic multicast technique and consider the various procedures needed for its successful operation. We characterize the gains in performance achieved by our proposal through an extensive performance analysis and simulation of our technique by itself, and when integrated with the other delivery options. We also describe our experience with an implementation of a prototype cyclic multicast server and its performance over the Multicast Backbone (MBone).