Pramod Pancha

A wireless broadband ad-hoc ATM local-area network

We describe the theory, design and ongoing prototyping of a wireless ATM LAN/PBX capable of supporting mobile users with multi-Mb/s access rates and multi-Gb/s aggregate capacities. Our proposed LAN Consists of network nodes called Portable Base Stations (PBS) providing microcell coverage. The PBSs are designed to be low-cost, compact and high-speed and can be relocated conveniently. We employ a concept ofad-hoc networking in the layout of the PBS-to-PBS interconnection. That is, the PBSs can be distributed in an arbitrary topology to form a backbone network and can be reconfigured with relative ease. The PBS-to-PBS backbone links are high-speed (Gb/s) for supporting high system capacity. Although they can either be wired or wireless, our emphasis is on wireless implementations. The user-to-PBS links, on the other hand, are primarily for mobile access (e.g., 2–20 Mb/s) and therefore are wireless. Wired connections from stationary users to PBSs are also possible. Typical mobile users are assumed to be laptops or notebook computers. Services supported include conventional data applications (e.g., over TCP/IP or SPX/IPX) as well as multimedia (video, voice and data) applications with QoS (Quality-of-Service) guarantees. A “wireless ATM” concept is proposed so as to provide seamless internetworking with other wired ATM local and wide-area net-works. Algorithms and control in our network are highly distributed for simple implementations and ease of mobility management. A new wireless VP/VC concept and a Homing Algorithm are described to provide ATM cell routing and connections in the network. PBS hardware and software architectures are discussed. Call management, network management and signaling are designed for simplicity, high performance and modular implementations. A fast network restoration scheme is proposed to cope with the potential link or node failures in the ad-hoc network. Error control is addressed taking the unreliable wireless links into consideration. Finally, a prototyping project called BAHAMA (Broadband Ad Hoc ATM Anywhere) for demonstrating this network concept is briefly outlined.

Forward error control for MPEG-2 video transport in a wireless ATM LAN

The possibility of providing multimedia services to mobile users has led to interest in designing broadband wireless networks that can guarantee quality of service for traffic flows. However, a fundamental problem in these networks is that severe losses may occur due to the random fading characteristics of the wireless channel. Error control algorithms which compensate for these losses are required in order to achieve reasonable loss rates. In this paper, the performance of error control based on forward error correction (FEC) for MPEG-2 video transmission in an indoor wireless ATM LAN is studied. A random bit error model and a multipath fading model are used to investigate the effect of errors on video transport. Combined source and channel coding techniques that employ single-layer and scalable MPEG-2 coding to combat channel errors are compared. Simulation results indicate that FEC-based error control in combination with 2-layer video coding techniques can lead to acceptable quality for indoor wireless ATM video.

Leaky bucket access control for VBR MPEG video

The leaky bucket (LB) access control scheme has been widely proposed as the usage parameter control (UPC) mechanism at the user-network interface (UNI) for B-ISDN. An important goal for any UPC scheme is that it be able to accommodate a wide range of services. In this paper, we investigate the performance of the LB as an access control mechanism for transmission of variable bit rate (VBR) MPEG video. In particular, we focus on the following issues: 1) the requirements for lossless video transmission, 2) the trade-offs between token pool size and token regeneration rate, 3) the effect of traffic smoothing and 4) the performance of different encoded video sequences. Finally, we present a new technique for VBR video transmission using multiple LBs and we discuss the advantages of this techniques when cell losses occur.

Guaranteeing bandwidth and minimizing delay in packet-switched (ATM) networks

Future high-speed networks that will support integrated video, voice and data applications are expected to utilize the concepts of ATM fast packet switching. The concepts of isolating misbehaving users and sharing resources to achieve optimal delay performance are extremely important to consider when designing queue service policies for practical implementations. Most previous service policies have been designed to satisfy one, but not both, of these goals. We present a novel service policy that combines the desirable features of isolation and sharing to provide guaranteed bandwidth for real-time traffic while attempting to minimize system delay. This service policy, guaranteed-bandwidth minimum-delay (GBMD), operates in two phases. The first phase of the policy ensures that the requested guaranteed bandwidth is delivered to each flow. The second phase, which only occurs when excess bandwidth is available, optimizes given performance criteria (e.g., system delay) by appropriately serving packets. The GBMD policy is easy to implement and flexible to tune based on system requirements. Simulation results show that overall system performance is superior to several other service policies.

Video transport in wireless ATM

Wireless ATM LANs have the potential to support multi-Mb/s bandwidths to mobile users with guaranteed quality of service. However, the lossy nature of the wireless medium will pose problems for loss-sensitive applications. Techniques to minimize the effect of these losses will therefore be required. In this paper, we examine the use of combined source and channel coding for MPEG video transport in a wireless ATM environment. Although forward error correction (FEC) provides protection against channel bit errors, the bandwidth overhead can become a significant drawback in a fixed bandwidth scenario. Additional protection against losses can be realized by using two-layer video coding. In this work, we compare the performance of a 1-layer main profile and 2-layer data partitioning and SNR scalable MPEG-2 encoders in a system with random channel errors and forward error correction. The results indicate that if the channel bit error rate is known an optimum FEC level can be chosen for the 1-layer case; However, at this fixed FEC level, if a critical bit error rate is exceeded then video quality degrades dramatically. The 2-layer cases appear to lead to more graceful degradation in quality at this critical bit error rates. In particular, SNR scalability may lead to better video quality over a larger range of bit error rates than a 1-layer approach.

ATM switch routers for combined connection-oriented and connectionless transport

This paper demonstrates the need for an ATM network to support both connection-oriented and connectionless networking in order to be an effective integrated services network. It identifies two key properties for an efficient solution that offers both networking modes: the use of a common addressing scheme and a common routing protocol for both modes. To enhance PNNI (private network-to-network interface) based ATM networks to support both networking modes, we propose a datagram protocol called CL-ATM (connectionless ATM) that uses the same addressing scheme and routing protocol as connection-oriented ATM. ATM switches with CL-ATM packet forwarding modules are referred to as ATM switch routers. This paper also addresses the problem of how two different integrated services networks, each supporting both networking modes, can interwork. Specifically, it shows how a network based on IP interworks with a network of ATM switch routers.

Connectionless ATM Using an ATM Switch Router

Short message exchange capability is required for control plane operations of several applications in ATM networks, such as multimedia networking, Intelligent Network-based services, and to support mobility in wireless ATM networks. Existing methods to transport such messages between ATM nodes typically suffer from the disadvantages of excessive management complexity (for provisioned virtual circuits), and/or of incurring large latencies (for switched virtual circuits). In this paper, we propose a new method for connectionless transport in ATM networks using the routing data that is present in all ATM switches. The “connectionless-ATM (CL-ATM)∝ transport technique encapsulates messages into CL-ATM packets containing the source and destination ATM end system addresses in their header. By adding a CL-ATM packet forwarding module, ATM switches can be upgraded to “ATM switch routers∝ enabling them to support both connection-oriented and connectionless transport modes. Routing data collected by the PNNI (Private Network-Network Interface) routing protocol is used to route datagram packets from one ATM switch router to the next. Since the proposed solution defines a generic network-layer connectionless protocol that can be used to transport datagrams generated by any application, it can also be used for IP-over-ATM transport.

Comparison of video conference realization schemes

In this paper, we investigate the issue of how multiparty-to-multiparty communication should be realized. In order to quantify the different techniques, we examine the network-layer (bandwidth and buffer) allocations of four models for realizing multiparty-to-multiparty communication. An example application considered in this paper, where such communication will be needed, is video conferencing based on MPEG video streams. Analytical comparisons are carried out based on actual data obtained from empirical measurements of the source characteristics of MPEG video (determined to be a 40 state Markov modulated fluid source). Our results show that in order to minimize bandwidth and buffer (network-layer resources) allocations, we must exploit the effect of statistical multiplexing by using shared buffers for such multiparty-to-multiparty communication. Using these results we identify the best technique for multiparty-to-multiparty communications.

The Design and Performance of Wireless MAC Protocols

Medium access control (MAC) protocols attempt to efficiently and equitably allocate use of a shared communications channel to independent, competing users. Efficient sharing of a communications resource is particularly important in systems with scarce communications bandwidth, such as wireless networks. In this paper, we focus on some key design and performance issues associated with the DQRUMA (Distributed-Queueing Request Update Multiple Access) protocol. It is a simple, demand-assignment protocol that achieves near-optimal delay-throughput performance and has broad applicability. By separating packet scheduling from channel contention, it is also able to provide QoS guarantees. Although targeted primarily towards Wireless ATM systems, DQRUMA can be designed for use in other packet systems too. For example, it can support variable amounts of physical layer overhead and, at the same time, also support the transmission of variable-length packets. This modular slotted version of the DQRUMA protocol can provide a common MAC platform for many different systems with various operating conditions and requirements.

Combined Source and Channel Coding for Wireless ATM LANs

It is widely recognized that a viable method to provide “anytime, anywhere” communication needs is by means of wireless technologies. In the indoor wireless environment, the 1–2 Mb/s wireless link technology that is currently available from several vendors (for example, WaveLan) will soon be replaced by higher capacities in the near future. For example, several manufacturers plan to develop radios based on the HiperLan standard that is currently being discussed in ETSI. These radios are intended to support 20 Mb/s wireless links for computer networking. As a result of this increase in physical link capacity, it is now feasible to envision wireless networks that provide similar functionality to current wired Ethernet LANs with the added advantage that the end terminals can be mobile. This in turn makes it feasible for multimedia services, in particular the delivery of video, to be provided over these wireless networks.