Zvi Ganz

A stochastic optimization model for planning capacity expansion in a service industry under uncertain demand

A stochastic optimization model for capacity expansion for a service industry that incorporates uncertainty in future demand is developed. Based on a weighted set of possible demand scenarios, the model generates a recommended schedule of capacity expressions, and calculates the resulting sales under each scenario. The capacity schedule specifies the size, location, and timing of these expansions that will maximize the companys expected profit. The model includes a budget constraint on available resources. By using Lagrangian relaxation and exploiting the special nested knapsack structure in the sub‐problems, an algorithm was developed for its solution. Based on the initial computational results, this algorithm appears to be more efficient than linear programming for this special problem.

Security protocol for IEEE 802.11 wireless local area network

As Wireless Local Area Networks (WLANs) are rapidly deployed to expand the field of wireless products, the provision of authentication and privacy of the information transfer will be mandatory. These functions need to take into account the inherent limitations of the WLAN medium such as limited bandwidth, noisy wireless channel and limited computational power. Moreover, some of the IEEE 802.11 WLAN characteristics such as the use of a point coordinator and the polling based Point Coordination Function (PCF) have also to be considered in this design. In this paper, we introduce a security protocol for the IEEE 802.11 PCF that provides privacy and authentication, and is designed to reduce security overheads while taking into account the WLAN characteristics. We prove this protocol using the original and modified BAN logic.

Robust superpoll protocol for IEEE 802.11 wireless LANs

As wireless local area networks (WLANs) are rapidly deployed to expand the field of wireless products in military settings, the provision of robust and efficient communication in the face of noisy environments will be mandatory. Such design needs to take into consideration the WLANs limited bandwidth and high error rates. We introduce the concept of super polling which can be implemented within the IEEE 802.11 Point Coordination Function (PCF) media access control scheme. We notice a dramatic throughput increase (up to 85%) when compared with the single poll mechanism used in IEEE 802.11 PCF. The throughput increase is measured as a function of the channel noise, the superpoll overhead per data packet and the packet size.

Converged voice, video and data wired-wireless LANs testbed

We have developed and implemented novel solutions that provide quality of service (QoS) support for voice, video and data applications in wired and wireless LANs that can also follow standards such as Ethernet IEEE 802.3 or wireless IEEE 802.11. Since our solutions can transform existing legacy LANs to an environment that provides the bandwidth, time-delay and other requirements needed to provide users satisfactory quality, the LAN users can achieve significant productivity increase and cost savings. The limited bandwidth wireless segments are particularly important since wireless devices, such as cordless IP telephones, will be part of future networks. Our solutions can also manage the often limited bandwidth pipeline that connects the LAN to the backbone network or Internet service provider. In this paper we report initial successful results of our solutions on a Windows based testbed consisting of wired and wireless LAN segments. Our testbed incorporates a novel software framework, provides a research and development platform for implementing, debugging and testing various MAC policies and their QoS provision for multimedia applications in wired and wireless LANs. The developed testbed is built using Windows operating system, off-the-shelf wired and wireless network interface cards, and standard applications. The testbed is the first phase in the ongoing process of having a testbed comprised of a number of wired and wireless segments interconnected through routers, switches, bridges, and T1 lines which provide the interconnection to the Internet.

Media access control development platform for wireless LANs

We introduce a Media Access Control (MAC) development platform for wireless LANs that (1) complements traditional simulation and analytical tools, and (2) provides a pioneering platform in academia based on the de-facto standard Windows operating system in addition to the legacy Unix environment. Our implementation includes two main modules (1) a wireless LAN network interface card (NIC) that includes only transmit/receive functionality and (2) a NIC device driver in which we have implemented a flexible plug-in module which allows us easy MAC protocol implementation. The proposed approach has the advantage that the testing of the protocol is performed in realistic environments, i.e., we use real traffic coming from off-the-shelf applications and a real wireless channel. We have implemented the proposed approach using Harris PRISM PC cards with the AMD PCnet microcontroller and Windows PCs. We introduce the implementation procedure and the performance results obtained from a wireless point-to-point experimental setup.

Robust re-authentication and key exchange protocol for IEEE 802.11 wireless LANs

We introduce a robust re-authentication and key exchange protocol for IEEE 802.11 wireless LANs. Based on an authentication protocol that we have previously published, we introduce a low computational complexity re-authentication and key exchange procedure that provides enhanced robustness in face of cryptographic attacks. This procedure accounts for the wireless media limitations, e.g., limited bandwidth and noise. We introduce the re-authentication period (RP) that reflects the frequency that the re-authentication procedure should be executed. We provide the user with suitable guidelines that will help in the determination of the re-authentication period.

The capacity expansion problem in the service industry with multiple resource constraints

Abstract Consider the problem of determining the location, size and schedule of capacity expansions in a service chain under multiple resource constraints. We investigate a linear version of the problem which suits organizations that rent or lease their facilities. We also investigate another version in which there is a fixed cost paid for each resource anytime capacity is expanded. The latter version results in a mixed integer programming problem. Algorithms and heuristics to solve both versions are presented.

Experimental measurements and design guidelines for real-time software encryption in multimedia wireless LANs

To secure interactive multimedia applications in wireless LANs (WLANs), it is pertinent to implement real time cryptographic services. In this paper we evaluate the use of software based encryption algorithms that are implemented in the layer service provider as defined by WinSock 2 for Windows 95/NT. Our measurements show that software implementation of various encryptors can sustain the throughput requirements of interactive multimedia applications for WLANs such as telephone-quality audio, video conferencing, and MPEG video. We present a design methodology that includes guidelines for a secure multimedia system design in terms of the encryption method chosen as a function of required application throughput, system configuration, protocol layers overhead and wireless LAN throughput.

Inline network encryption for multimedia wireless LANs

To secure real-time communication in wireless LANs it is pertinent to implement real time cryptographic services in software or hardware. We evaluate the use of software based inline encryption algorithms for wireless LANs that are implemented in the Layer Service Provider as defined by WinSock 2 for Windows. The evaluated encryption algorithms run on each PC that is part of the wireless LAN. We present the throughput requirements from the inline encryptors for various multimedia applications such as video conferencing, collaborative work, distributed data bases and distributed processing. Our measurements show that software implementation of various encryptors provides enough throughput as required by the above applications.