Asynchronous transfer mode (ATM) is a connection-oriented technology in which all communication is based on virtual connections established prior to the transfer of data. It is expected that the bulk of traffic carried by the ATM network will be data traffic, e.g., local area network (LAN) internetwork traffic. Hence, a major issue regarding ATM is the support for connectionless (datagram) traffic. A scheme for the efficient support for connectionless traffic in ATM LANs based on trees of virtual connections is proposed. In this scheme, a sink tree is built for every switch in the LAN. Each tree provides an efficient means of routing connectionless traffic from any switch in the network to the sink switch (root) of the tree. The sink tree solution may also be used to broadcast connectionless messages in the reverse direction. The trees can easily be updated to adapt to topological changes or congestion in the network. A protocol for refreshing the tree structure using the ATM switch routing tables is described. An adaptive rate control solution, in conjunction with fast back pressure at the ATM layer, is presented. It is shown that this scheme achieves high utilization of available bandwidth for connectionless traffic, has low cell loss probability, and small overhead.

Shaping of traffic at its source is a prominent congestion control solution in ATM networks. The "leaky bucket" with a "cell spacer" is a very popular traffic shaping approach. By sizing the leaky bucket and spacer parameters, an end-station shapes its traffic to conform to a "good behavior" contract with the network. The leaky bucket delays the transmission of selected number of cells, while the spacer forces a minimum time-distance between transmitted cells. When a contracted transmission rate is close to the traffic generation rate by the end-station, this traffic stream will utilize most of the bandwidth available on its virtual connection. The high utilization of such a connection leads to large queues of frames and cells at the end-station, With high adverse consequences to the end-to-end delay and jitter. In this paper, based on the negotiated traffic parameters and source traffic characteristics, we study, through simulations, the contribution of the leaky bucket plus cell spacer subsystem to the delay and jitter in an end-station. We also study the distribution of the size of the burst of cells leaving the end-station and entering the network. Finally, we derive the theoretical upper bound for the size of bursts of cells.

We have proposed a tree based virtual embedded network architecture to address the resource reallocation problem for mobile users connected to an arbitrary topology ATM backbone network. The approach helps us significantly reduce the resource reallocation rate on different links of the ATM network for both linear and two dimensional arrangements of access points. We show that the resource reallocation rate may be further reduced by very small over-allocation of resources. We have proposed and evaluated two specific schemes for a better understanding of this trade-off.

A significant driver for the consumer use of high bandwidth in the near future will be interactive video on demand (IVOD). A range of service types can be deployed, based on a differing sophistication, which must be traded against the network costs (bandwidth) and component costs (switch complexity and memory). The potential aggregate bandwidth required is huge (O(1Pb/s)), and thus it is essential to properly engineer the network to reduce the bandwidth required. This paper describes a variety of IVOD scenarios, and introduces a cost function that captures the combined bandwidth and storage requirements of the network. This cost function is used to compare different network engineering alternatives, particularly program caching and stream sharing. The effects of nonlinear pricing and differing weights of bandwidth and storage are also reflected by the cost function. This cost function can be used by network designers to determine optimal topology, sharing, and caching strategies for desired bandwidth versus memory costs in a particular network deployment. In addition, a simulation model is used to evaluate caching of programs or windows within programs. We show that there are some results that are widely applicable. In particular, the level in the network at which caching should take place is at approximately 80% depth in the distribution tree, above the head end switch in the network hierarchy. We also observe that the bandwidth savings in sharing streams (actually buffered windows of program content) is fairly small for user behavior based on Zipfs law. The overall intent of this work is to evaluate the effects of various server, cache, and sharing strategies on the bandwidth and storage requirements of the network and their proper placement within the network.>

ATM is a connection-oriented technology in which all communication is based on virtual connections established prior to the transfer of data. Initially, it is expected that the bulk of traffic carried by the ATM network will be data traffic. Hence, a major issue regarding ATM is the support for connectionless (datagram) traffic. A scheme for the efficient support for connectionless traffic in ATM LANs based on trees of virtual connections is proposed. In this scheme a sink tree is built for every switch in the LAN. Each tree provides an efficient means of routing connectionless traffic from any switch in the network to the sink switch (root) of the tree. The sink tree solution may also be used to broadcast connectionless messages in the reverse direction. The trees can easily be updated to adapt to topological changes or congestion in the network. A protocol for refreshing the tree structure using the ATM switch routing tables is described.>

CATV networks are targeted to provide multimedia services to the home. This paper presents a simulation model aimed at evaluating the capacity of CATV networks. The model is based on the user profile, the service discipline and the CATV bandwidth. The issues addressed include the number of users supported by a single broadcast CATV-tree, the probability of accepting a request for multimedia service, and the number of users served over a period of time.>

Traffic shaping at a (traffic) source station as a prominent congestion control solution in ATM networks. The "leaky bucket" scheme in conjunction with a cell spacer is an extensively studied and used mechanism for such a traffic shaping. By dimensioning the leaky bucket and spacer parameters, a source station attempts to regulate the behavior of its own traffic in order to conform to a "good behavior" contract with the network. In this paper, we study the effect of the a single source's traffic characteristics and its leaky bucket parameters on the maximum burst size and the burst size distribution as seen by the network. The theoretical upper bound for the burst size is derived and simulation is used to study the effect of leaky bucket parameters on probability distribution of burst sizes. It is shown that while traffic shaping is done to abide to negotiated traffic characteristics, traffic shaping can lead to large queues of cells and result in large cell delay and delay jitter in the source station.>

The suitability of IEEE 802.5 token ring LANs for the transport of multimedia traffic is examined. The token ring priority mechanisms and end-station queuing policies are studied in order to understand their effect on the delay characteristics of multimedia traffic. The multimedia traffic is modeled as isochronous data streams. Simulation results are presented to illustrate the access and queuing delays under various load conditions and traffic mixes.

Three transport services are offered by FDDI: asynchronous, synchronous, and isochronous (FDDI-II). In order to support the stringent multimedia (e.g., real-time video and voice) delay and bandwidth requirements the asynchronous transfer service will not suffice. The isochronous and synchronous transport services differ considerably in their implementation, but the differences in the service provided can be made to appear transparent to many multimedia applications. It is shown that synchronous traffic can support a wide range of application requirements efficiently at moderate cost when the connection between source and destination are on the same physical ring. However, isochronous class traffic has advantages, particularly when the network traffic is well behaved (the peak data rate is close to the mean data rate) and when connections traverse multiple rings.>

A mechanism is required which prevents the initiation of the claim process and maintains a constant ring latency during the insertion and removal of stations into the ring. Such a mechanism, graceful insertion and removal, is described. The mechanism is designed to support the graceful insertion and removal of stations into the M-ports of concentrators and requires no hardware modification of the endstations.>

The advantages and disadvantages of isochronous and synchronous transport services of the fiber distributed data interface (FDDI) are summarized. A comparison of both services is made based on application requirements (e.g. real-time video and voice). These requirements include timing constraints, such as jitter and delay, bandwidth utilization, and end-station requirements. It is shown that synchronous traffic can support a wide range of application requirements efficiently at moderate cost when the connections between source and destination are on the same physical ring. However, isochronous traffic has advantages, particularly when the network traffic is well behaved (the peak data rate is close to the mean data rate) and when connections traverse multiple rings.>