Cell‐level/call‐level ATM switch simulator

A B‐ISDN national project in Korea has been carried out to develop a National Information Superhighway since 1992. An ATM switching system has been developed as one of the most important parts in the project, and has been tested in the National Information Superhighway testbed. In this paper, we develop a cell‐level/call‐level ATM switch simulator using cell‐level and call‐level input traffic models for evaluating the ATM switching system. The cell‐level simulator models various cell‐level switching functions such as priority control and multicast, and evaluates the cell‐level performance indices of the ATM switch in terms of cell delay, throughput, and cell loss probability. On the other hand, the call‐level simulator uses call‐level traffic models and evaluates the call blocking rate as a call‐level quality of service (QoS). This revised version was published online in August 2006 with corrections to the Cover Date.     

Modified least loaded routing in virtual path based ATM networks

We consider a Virtual Path (VP) based ATM network supporting multiple traffic classes with heterogeneous traffic characteristics. Using simple FIFO scheduling policy at the ATM multiplexer, we assume that all traffic require identical end‐to‐end quality of service (QoS) requirement. The concept of effective bandwidth is used to determine the required bandwidth to guarantee the specified QoS requirement. We study the problem of using dynamic routing to VP‐based ATM networks by transforming it into an equivalent multi‐rate circuit‐switched network problem. To further simplify the analysis, we restrict the choice of path to single‐link and two‐link routes. We propose a dynamic routing algorithm based on the Least Loaded Routing (LLR) with packing. Simulation results are used to compare the performance of this algorithm with other dynamic routing schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

A signaling architecture for wireless ATM access networks

A multiservice wireless Asynchronous Transfer Mode (ATM) access system is considered from a signaling protocol viewpoint. In an attempt to generalize and extend results and experiences obtained from the specification, design, and implementation of fixed ATM‐based access networks, we extend the concept of the broadband V interface (referred to as VB) for application to wireless ATM access networks. The proposed architecture follows the signaling structure of Broadband ISDN (B‐ISDN) User–Network Interface (UNI), thus offering the possibility for integration of the wireless ATM access system into fixed B‐ISDN. It is shown that the use of the proposed access signaling architecture provides cost effective implementations without degrading the agreed Quality of Service (QoS), and simplifies call/connection and handover control. The evaluation of the proposed access signaling protocol structure yields results that fall within acceptable ATM signaling performance measures. A performance comparison of our approach with an alternative access signaling configuration is also carried out to quantify the relative gains. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chapar: A Persistent Overlay Event System for MANETs

In this paper, we present Chapar, an event system designed for mobile ad hoc networks that supports the publish/subscribe model as well as point–to–point and point–to–multipoint message delivery. Chapar supports event persistency to resist transient disconnections and network partitioning. Following a cross-layer approach, Chapar is designed as an overlay network that uses Multipoint Relays (MPRs) defined in OLSR, as distributed brokers to disseminate the events in a mobile network. Chapar handles topology changes as it uses the underlaying OLSR routing protocol for message delivery. The implementation performance is promising in the sense that no extra signaling is generated for mobility support and the generated overlay traffic is considerably less than the underlying routing protocol traffic.     

Fluid analysis of a TCP connection over ABR

This paper reports on an analytical study of the performances of the ATM‐ABR service category in transporting TCP/IP flows over an ATM network. We explore the behavior of a TCP connection over an ATM‐ABR VC, in presence of exogenous non‐controlled traffic. This fluid analysis of the system allows the study of the interaction between the window‐based end‐to‐end flow control TCP protocol and the rate‐based flow control ABR mechanism, which is restricted to the ATM part of the network. The main aim of this study is to give performance evaluation formulae to model the behavior of such a TCP over ABR connection. This revised version was published online in June 2006 with corrections to the Cover Date.     

LMDS/LMCS hub interconnection alternatives and multiple access issues

LMDS/LMCS is a broadband wireless local loop, millimeter‐wave alternative to emerging integrated multiservice access networks. Significantly large amounts of bandwidth – in the order of one GHz of spectrum – are made available to residential subscribers or supported business users respectively that employ highly directional antennas and signal polarization to establish communication with a central hub. Besides the requirement for dynamic bandwidth allocation capabilities, these networks should be able to guarantee negotiated quality of service (QoS) levels to a number of constant‐length (ATM) – and possibly variable length (TCP/IP) – packet streams. In this context, we analyze the performance of contention, polling/probing and piggybacking mechanisms that will be used by the LMDS MAC protocol for the dynamic support of both real‐time and non‐real‐time traffic streams. More specifically, we focus on the end‐to‐end performance of a real‐time variable bit rate connection for which the LMDS link is only the access component of a multi‐link path through an ATM network. Results are presented on maximum end‐to‐end cell delays under a Weighted Round Robin service discipline and buffer requirements are calculated for no‐loss conditions. In parallel, we also consider the case in which variable length IP packet traffic is supported as such by the same wireless access network. Backbone interconnection alternatives of LMDS hubs, multiple access proposals and scheduling algorithms are addressed in this framework. This revised version was published online in July 2006 with corrections to the Cover Date.     

CLIMAX: CelL‐Interleaved Merged ATM conneXions

The realization of multiway group communications and scaleable IP switching over ATM networks requires merging of virtual connections to be possible. This capability, known as VC merging, cannot be provided by ATM networks which use a standard ATM protocol stack. This paper describes CLIMAX, a simple and efficient solution that allows for VC merging while keeping the typical advantages of cell‐switching. This revised version was published online in June 2006 with corrections to the Cover Date.     

Implementation of multipoint connections in an ATM switching network

This paper presents the problems in the implementation of multipoint connections at switching level using the example of an ATM switching network. By choosing the proper routeing mechanism and the appropriate architecture of the switching element, a switching network can gradually be adapted to an increasing share of multipoint traffic. The first section describes the problems with the handling of multipoint connections within a multiple stage connection oriented switching network. In particular this refers to the routeing of the cells through the switching network. Several alternatives on this issue are discussed. Both, the selected approach based on a differentiated self-routeing mechanism and the corresponding cell format are introduced. In the second part of this article several switch architectures are compared in respect of their multipoint capability. It is demonstrated that at present the most promising solution are switching elements based on the principle of central buffering. A single chip solution using this concept is employed in the presented switching network.     

An architecture of ATM‐based PCS network: Signaling traffic and capacity

In this paper, we propose an ATM‐based Personal Communication Service (PCS) network architecture with ring‐based access networks. We also propose a simple ring management scheme using ATM Add‐Drop‐Multiplexers (ADM). The ring has a Virtual Star topology, and we manage its bandwidth at two levels: Virtual Path (VP) level and Virtual Channel (VC) level. We consider four different types of configurations according to the locations of visitor location register (VLR) and mobile switching center (MSC) functions, and obtain signaling load and processing load. A 150 Mb/s‐dual ring can support about 5,500 homogeneous ON–OFF voice sources. This ring capacity corresponds to covering approximately 180 cells in the case of 30 connections per cell. Even though we are here concerned with evaluating the proposed network for voice traffic, we can extend this study to the analysis of the proposed ATM‐based PCS network accommodating various types of multimedia traffic as a further study. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mobile multicasting in wireless ATM networks

Multicasting is a desired function in both wired and wireless networks. Currently, multicasting‐based applications have pervasive presence and influence in our Internet. Wireless ATM aims to support different traffic types over a high speed wireless network. In particular, traditional approaches towards multicasting in wired networks cannot be directly applied to mobile ATM networks. This includes the mechanism proposed to handle mobility in wired networks. In this paper, we address the issues behind multicasting in wireless ATM networks and the underlying mechanisms to support handoffs of both unicast and multicast connections. Through simulation, we evaluated the performance of optimal core‐based tree (CBT), late‐joined CBT, optimal source‐based tree (SBT), and late‐joined SBT during changing multicast host membership conditions. In addition, we evaluated the impact of multicast receivers' migration on the total link cost of the resultant multicast tree. Simulation results revealed that source‐based trees incur more total link costs under both dynamic host membership and receivers' migration scenarios. However, it generates less control messages than the distributed CBT and SBT approaches. This revised version was published online in June 2006 with corrections to the Cover Date.     

Design of an ATM switch for handoff support

In a wireless ATM system, a network must provide seamless services to mobile users. To support this, mobility function should be added to existing ATM networks. Through a handoff operation, a mobile user can receive a service from the network without disconnecting the communication. A handoff results in connection path rerouting during an active connection. To avoid cell loss during a handoff, cell buffering and rerouting are required in the network. A handoff switch is a connection breakdown point on an original connection path in the network from which a new connection sub‐path is established. It performs cell buffering and rerouting during a handoff. Cell buffering and rerouting can introduce a cell out‐of‐sequence problem. In this paper we propose a handoff switch architecture with a shared memory. The architecture performs cell buffering and rerouting efficiently by managing logical queues of virtual connections in the shared memory and sorting head‐of‐line cells for transmission, thus achieving in‐sequence cell delivery during a handoff. We also present simulation results to understand the impacts of handoffs on switch performance. This revised version was published online in July 2006 with corrections to the Cover Date.     

A measurement‐based performance evaluation method for IP networks and its implementation

In recent years, IP networks have become increasingly complex and the range of network applications has widened. As a result, the need for experimental evaluation of application performance has increased. We introduce a measurement‐based performance evaluation method that combines a function to generate various patterns of application traffic with one to measure end‐to‐end network performance at the application level. For our method, we also propose traffic models of various applications that can represent the characteristics of these applications, for example, the burstiness of traffic. This method has already been implemented as a benchmarking tool on UNIX operating systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Flow control schemes and delay/loss tradeoff in ATM networks

Performance and flow control mechanisms, which represent ATM (asynchronous transfer mode) flexibility, are discussed. To control performance, delay- and/or loss-sensitive service classes, and two mechanisms to realize these classes, are proposed. It is shown that it is possible to have better performance than with other mechanisms, such as no-class distinction or simple priority methods. It is further suggested that this performance controllability results in the provision of multiple logical services, including quasi-STM (synchronous transfer mode; compatible with circuit switching), by an ATM network. ATM flow control is based on a call-oriented resource allocation mechanism similar to circuit switching. The concepts of call/line bit rate ratio and multiplexing degree are seen to be significant for efficient use of resources. When the network handles calls with large call/line bit rate ratios, user-specified flow control parameters at the call setup phase are important for resource assignment. The definition of two types of maximum throughput of each call and its usage for resource management are proposed     

Semi‐Markovian modelling and performance analysis of variable rate traffic in ATM networks

Semi‐Markovian processes (SMP) serve as a versatile means to model various traffic types generated by sources or superposed from links in ATM networks. An efficient discrete time analysis method is proposed for SMP/G/1 queueing systems to evaluate ATM switches with non‐renewal input. Some basic results are derived for the autocorrelation function of semi‐Markovian processes and for the effect of state space reduction on autocorrelation, which show how to represent correlated traffic with given characteristic by an adequate SMP model of limited size. This revised version was published online in June 2006 with corrections to the Cover Date.     

ATM via satellite: A framework and implementation

This paper describes an ATM‐based satellite network, focusing on the networking (ATM) aspects of the design. The ATM requirements and the basic design of the network are outlined. In particular, a simple MAC layer is proposed in which ATM service classes are mapped onto MF‐TDMA uplink access methods. The uplink access and resource allocation approaches based on this model are described in detail. Also, this paper shows how different qualities‐of‐service can be provided by using a combination of different access schemes. This paper also covers scheduling for the uplink portion of the satellite network. The use of Hierarchical Round Robin is argued on the grounds of performance, flexibility and implementability. This revised version was published online in June 2006 with corrections to the Cover Date.     

ATM cell encryption and key update synchronization

This paper presents a data compaction/randomization based approach as a mode of block encryption for ATM (Asynchronous Transfer Mode) cells. The presented approach converts a plaintext into pseudo‐random plaintext before ciphering to conceal patterns in the plaintext. The underlying idea behind this scheme is the Shannon's principles of “confusion” and “diffusion” which involve breaking dependencies and introducing as much randomness as possible into the ciphertext. In this scheme, confusion and diffusion are introduced into the system by first compressing the ATM cell payload and then spreading a continuously changing random data over the entire content of the cell. As a mode of operation for block ciphering, this scheme offers the following attractive features:(i) plaintext patterns are pseudo‐randomized and chained with ciphertext (thereby, preventing against “dictionary”, “known plaintext”, and “statistical analysis” attacks), (ii) it is self‐synchronizing, (iii) cell loss has no additional negative effect, (iv) no IV (Initialization Vector) storage is required, (v) it is encryption‐algorithm independent, (vi) there is no cell‐to‐cell dependency (no feedback from previous cells), and (vii) it is highly scalable (i.e., cells from the same stream can be ciphered and deciphered in parallel). This paper also presents a secure mechanism for in‐band synchronization of encryption/decryption key updates using a “marker‐cell” that is carried within the data channel. An important aspect of both the above mechanisms is that they do not require any changes to the ATM cell header or ATM infrastructure. This revised version was published online in June 2006 with corrections to the Cover Date.     

Studies of random demands on network costs

When network demands are uncertain, a planner might design a network based on some nominal set of point‐to‐point demands, and later be faced with a different set of offered demands. To accommodate the offered demands, modification of the network may be required. Given this scenario, it seems natural to question how these modification costs might affect the overall cost. To address such questions, we study the effects of random demands on network costs. In this study, we design a network based on nominal demands, generate random demands based on the nominal demands, and then modify the designed network to carry the random demands. We generate the offered demands randomly from four different distributions. For each demand distribution we perform 300 simulations. This paper describes our observations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Error correction and error detection techniques for wireless ATM systems

Error correction and error detection techniques are often used in wireless transmission systems. The Asynchronous Transfer Mode (ATM) employs Header Error Control (HEC). Since ATM specifications have been developed for high‐quality optical fiber transmission systems, HEC has single‐bit error correction and multiple‐bit error detection capabilities. When HEC detects multiple‐bit error, the cell is discarded. However, wireless ATM requires a more powerful Forward Error Correction (FEC) scheme to improve the Bit Error Rate (BER) performance resulting in a reduction in the transmission power and antenna size. This concatenation of wireless FEC and HEC of the ATM may effect cell loss performance. This paper proposes error correction and error detection techniques suitable for wireless ATM and analyzes the performance of the proposed schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

A new ATM adaptation layer for TCP/IP over wireless ATM networks

This paper describes the design and performance of a new ATM adaptation layer protocol (AAL‐T) for improving TCP performance over wireless ATM networks. The wireless links are characterized by higher error rates and burstier error patterns in comparison with the fiber links for which ATM was introduced in the beginning. Since the low performance of TCP over wireless ATM networks is mainly due to the fact that TCP always responds to all packet losses by congestion control, the key idea in the design is to push the error control portion of TCP to the AAL layer so that TCP is only responsible for congestion control. The AAL‐T is based on a novel and reliable ARQ mechanism to support quality‐critical TCP traffic over wireless ATM networks. The proposed AAL protocol has been validated using the OPNET tool with the simulated wireless ATM network. The simulation results show that the AAL‐T provides higher throughput for TCP over wireless ATM networks compared to the existing approach of TCP with AAL 5. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preplanned rerouting optimization and dynamic path rerouting for ATM VP restoration

The survivability for ATM based B‐ISDN has become an important challenge for telecommunication network planners and engineers. In this paper, we consider multiple grades of reliability concept and a multilayer survivable network architecture for survivable ATM networks. We address two complementary ATM VP restoration schemes in this paper. First, we propose preplanned rerouting models and algorithms based on combinatorial optimization to prepare efficient backup VP configuration. We test two formulations and algorithms for this problem. Efficient column generation technique to solve linear programming relaxation and strong valid inequalities incorporating the branch‐and‐bound scheme are suitable to solve the problem to optimality within small time limits. Second, we propose a new dynamic VP path restoration scheme to restore nonprotected VPs by the preplanned rerouting. Our protocol has shown the advantage in restoration effectiveness comparing a well‐known protocol in computational simulation. We, finally, address the relationships between the suggested models of this paper and the expected results of our ongoing project. This revised version was published online in August 2006 with corrections to the Cover Date.