Circuit-switched Networks Research Articles

A cross-layer optical circuit provisioning framework for data intensive IP end hosts

Using circuit-switched optical networks for next generation e-science applications is gaining increasing interest. In such applications, circuits are provisioned for end hosts to accomplish data-intensive or QoS-stringent communication tasks. Existing provisioning methods provide point-to-point connectivity for end hosts, that is, an established circuit connects one end host to another, and during the lifetime of the circuit, only communication tasks between the connected end hosts can be served. This inhibits circuits from being used in more general cases, where each end host communicates with different remote parities simultaneously through a single network interface. We propose V-STONES - a data flow-based VLAN tagging and switching technique to increase the connectivity of end host network interfaces in circuit-switched networks. With V-STONES, not only can an IP end host communicate with different remote systems concurrently through bandwidth guaranteed connections, but also protocol entities at different stack layers can talk to their counterparts through dedicated bandwidth pipes. In this article, we review the existing circuit provisioning methods and then discuss V-STONES and the architecture of cross-layer circuit provisioning for end hosts. We also introduce a prototype implementation in an optical network testbed and present the experimental results.

Asymptotic Analysis of a Loss Model with Trunk Reservation I: Trunks Reserved for Fast Traffic

We consider a model for a single link in a circuit‐switched network. The link has C circuits, and the input consists of offered calls of two types, that we call primary and secondary traffic. Of the C links, R are reserved for primary traffic. We assume that both traffic types arrive as Poisson arrival streams. Assuming that C is large and R = O(1), the arrival rate of primary traffic is O(C), while that of secondary traffic is smaller, of the order . The holding times of the primary calls are assumed to be exponentially distributed with unit mean. Those of the secondary calls are exponentially distributed with a large mean, that is, . Thus, the primary calls have fast arrivals and fast service, compared to the secondary calls. The loads for both traffic types are comparable (O(C)), and we assume that the system is “critically loaded”; that is, the system′s capacity is approximately equal to the total load. We analyze asymptotically the steady state probability that n1 (resp., n2) circuits are occupied by primary (resp., secondary) calls. In particular, we obtain two‐term asymptotic approximations to the blocking probabilities for both traffic types.

On the viscosity solutions of hybrid HJB equations arising in optimal control of loss networks

E § Abstract. Call admission and routing controls for loss (circuit-switched) networks with semi- Markovian, multi-class call arrivals and general connection durations, were formulated as optimal stochastic control problems in (12, 13). Each of the resulting so-called (network) hybrid HJB equations corresponds to a collection of coupled first-order partial differential equations for which, when it exists, the continuously differentiable value function is a solution to the associated hybrid HJB equations. In general, the smoothness of the value functions and uniqueness of the solutions to the hybrid HJB equations may not hold. In this paper, viscosity solutions to a general class of hybrid HJB equations are developed and under mild conditions it is shown that the value function is continuous and, further, any continuous value function is the unique viscosity solution to the hybrid HJB equations.

A non-competing hybrid optical burst switch architecture for QoS differentiation

In this paper, we present a new hybrid optical burst switch architecture (HOBS) that takes advantage of the pre-transmission idle time during lightpath establishment. In dynamic circuit switching (wavelength routing) networks, capacity is immediately hard-reserved upon the arrival of a setup message at a node, but it is used at least a round-trip time delay later. This waste of resources is significant in optical multi-gigabit networks and can be used to transmit traffic of a lower class of service in a non-competing way. The proposed hybrid OBS architecture, takes advantage of this idle time to transmit one-way optical bursts of a lower class of service, while high priority data explicitly requests and establishes end-to-end lightpaths. In the proposed scheme, the two control planes (two-way and one-way OBS reservation) are merged, in the sense that each SETUP message, used for the two-way lightpath establishment, is associated with one-way burst transmission and therefore it is modified to carry routing and overhead information for the one-way traffic as well. In this paper, we present the main architectural features of the proposed hybrid scheme and further we assess its performance by conducting simulation experiments on the NSF net backbone topology. The extensive network study revealed that the proposed hybrid architecture can achieve and sustain an adequate burst transmission rate with a finite worst case delay.

Minimum concave cost multicommodity network design

The minimum concave cost multicommodity network design problem (MCMNDP) arises in many application areas, such as transportation planning, energy distribution systems and especially in the design of both packet and circuit switching backbone networks. Exact concave cost optimization algorithms have been developed but they are applicable only if the network size is small. Therefore, MCMNDP is usually solved using non-exact iterative methods. In this paper, such heuristic techniques proposed within the context of circuit switching and packet switching network design are evaluated in detail. Following a comprehensive literature survey, Yaged’s linearization, Minoux’s greedy and Minoux’s accelerated greedy methods have been selected for the circuit switching network design case for further investigation. Minoux’s greedy methods are found to create routes that include cycles causing degradation in the quality of the solution; therefore, we propose a simple but effective modification scheme as a cycle elimination strategy. Similarly, but within the context of packet switching network design, Gerla and Kleinrock’s concave branch elimination, Gersht’s greedy, and Stacey’s concave link elimination methods have been selected for further investigation. All of these methods consider aggregate flows on each link, simultaneously re-routing more than one commodity in one step. In this paper, we propose an alternative disaggregate approach, where only one commodity is handled at a time. Our final proposal is the adaptation of the algorithms proposed for circuit switching network design to the packet switching case. Then an extensive comparative computational study is performed for a number of networks and cost structures to help establish the best method with respect to time and solution quality. Our computational results have shown that the performances of the MCMNDP algorithms heavily depend on the network type and the cost structure. The results have also revealed that our proposed modification to Minoux greedy to eliminate cycles leads to considerable improvements and our proposed disaggregate approach gives the best result in some networks with certain cost structures.

IEEE 802.1 AVB and Its Application in Carrier-Grade Ethernet [Standards Topics

Ethernet is increasingly being used in carrier networks to transport real-time traffic, including wireless backhaul network traffic, time-sensitive audio/video applications in access networks, and circuit emulation for legacy services. With the replacement of traditional circuit-switched networks with Ethernet-based packet networks, it must be ensured that the application timing and QoS requirements are met. The IEEE 802.1 Audio/Video Bridging Task Group is developing a comprehensive set of standards to enable high quality, low-latency streaming of time-sensitive applications. These standards specify a means of providing time synchronization (IEEE 802.IAS), a resource reservation protocol (IEEE 802.1Qat), and a set of forwarding and queuing rules that bound the variability of delay in an AVB network (IEEE 802.1Qav). These standards are described, including their potential application to carrier-grade Ethernet networks.

A Dynamic TCP-Aware Call Admission Control Scheme for Generic Next Generation Packet-Switched Wireless Networks

Traditional call admission control (CAC) schemes only consider call-level performance and are mainly designed for circuit-switched wireless network. Since future wireless communications will become packet-switched systems, the packet-level features could be explored to improve the system performance. This is especially true when the TCP-type of elastic applications are running over such packet-switched wireless networks, as the elasticity of TCP applications has more tolerance toward the throughput/delay variation than non-elastic traffic does. In order to efficiently utilize the system resource from an admission control perspective, we propose a TCP-aware CAC scheme to regulate the packet-level dynamics of TCP flows. We analyze the system performance under realistic scenarios in which (i) the call holding time for non-elastic traffic like voice is independent of system states and (ii) the call holding time for TCP type of traffic depends on the system state, i.e., on the TCP flow's transmission rate. Extensive simulations are presented under different scenarios to show that the proposed scheme can effectively improve the system performance in terms of call blocking probability, call-level throughput (call/min) and link utilization, in accordance with our theoretical results.

A BLOCK COPROCESSOR FOR USER DATA RATE IMPROVEMENTS TO GPRS CODING SCHEME 4

The general packet radio service (GPRS) has been developed to allow packet data to be transported efficiently over an existing circuit-switched radio network, such as GSM. The main application of GPRS are in transporting Internet protocol (IP) datagrams from web servers (for telemetry or for mobile Internet browsers). Four GPRS baseband coding schemes are defined to offer a trade-off in requested data rates versus propagation channel conditions. However, data rates in the order of > 100 kbits/s are only achievable if the simplest coding scheme is used (CS-4) which offers little error detection and correction (EDC) (requiring excellent SNR) and the receiver hardware is capable of full duplex which is not currently available in the consumer market. A simple EDC scheme to improve the GPRS block error rate (BLER) performance is presented, particularly for CS-4, however gains in other coding schemes are seen. For every GPRS radio block that is corrected by the EDC scheme, the block does not need to be retransmitted releasing bandwidth in the channel and improving the user's application data rate. As GPRS requires intensive processing in the baseband, a viable field programmable gate array (FPGA) solution is presented in this paper.

On the Teletraffic Capacity of Optical CDMA

The capacity of an optical code-division multi-access (CDMA) [OCDMA] network has traditionally been defined as the number of continuously transmitting circuits supported by the network. In this paper, we use teletraffic models to determine the teletraffic capacity of a circuit-switched OCDMA network where circuits carry bursty traffic. Our analysis is independent of the OCDMA implementation or spreading code. In conventional networks, e.g., a wavelength-routed network (WRN), new circuits are blocked when all wavelengths are occupied. In OCDMA when the number of codewords exceeds number of network subscribers, new circuits need not be blocked. Instead, capacity is limited by multiple access interference: when the number of actively transmitting circuits becomes excessive, the bit-error rate (BER) of all circuits on the network degrades, causing an outage. We find that through statistical multiplexing, the capacity of OCDMA exceeds that of a WRN except when circuit activity is very high while the constraints on outages are more stringent than those on blocking. In such cases, we show how OCDMA with call admission control can be used to match or exceed the capacity of a WRN. Overall, our analysis shows that OCDMA is well suited to applications when conventional blocking is undesirable, and/or circuits carry bursty traffic.

Accounting for link load correlation in the estimation of blocking probabilities in arbitrary network topologies

In this paper, we discuss an efficient analytical framework that can accurately account for the link correlation in generic-topology circuit-switched networks. The model takes all active paths, as well as all free links, as independent objects on the network topology. Therefore, the actual sets of sequentially connected busy links (paths) and free links are seen as they appear in the network and the link correlation can be straightforwardly considered. Comparisons with results obtained from simulations show the excellent performance of the proposed analytical modeling for a variety of network topologies.

Enhanced Blocking Probability Evaluation Method for Circuit-Switched Trunk Reservation Networks

We consider the problem of estimating steady-state blocking probability for circuit-switched networks that allow alternate routing with particular emphasis on networks protected by trunk reservation. We use a recently proposed blocking probability estimate, the Overflow Priority Classification Approximation (OPCA) as an alternative to the currently used Erlang's Fixed-Point Approximation (EFPA). We demonstrate empirically that OPCA provides a better blocking estimate than EFPA for circuit-switched networks with alternate routing, that are reasonably protected by trunk reservation.

An integrated call agent of the converged VoIP network

The traditional circuit-switched telecommunication network and the packet-switched data network are converging to a single packet-switched network. One important application of the converged network is telephony communications, also referred to as VoIP (Voice over IP). Call signaling protocols, such as H.323, SIP and MGCP, have been developed to support VoIP communications. To enable devices using different VoIP protocols to communicate, gateways are needed to translate messages of one protocol to messages of another. In this paper, we present a simple, flexible framework for this interworking function. The framework is based on a half-call model where a call is controlled by two half-call finite state machines (FSMs), one representing the state of the caller and the other representing the state of the callee. The interworking function has been implemented such that the caller FSM of one VoIP protocol can interact with the callee FSM of any VoIP protocol. The development effort of the interworking function is minimized since only two half-call FSMs for each VoIP protocol are needed and they can be developed independently as long as the design conforms to the same interface specification. We have developed an integrated call agent (ICA) that contains the halfcall FSMs of H.323, SIP and MGCP. Calls between devices using these VoIP protocols can be set up, maintained and terminated by the ICAs.

Low Diameter Interconnections for Routing in High-Performance Parallel Systems

A new class of low diameter interconnections (LDI) is proposed for high-performance computer systems that are augmented with circuit switching networks. In these systems, the network is configured to match the communication patterns of applications, when these patterns exhibit temporal locality, and to embed a logical topology to route traffic that does not exhibit locality. The new LDI topology is a surprisingly simple directed graph which minimizes the network diameter for a given node degree and number of nodes. It can be easily embedded in circuit switching networks to route random traffic with high bandwidth and low latency

CATZ: Time-Zone-Aware Bandwidth Allocation in Layer 1 VPNs

The layer 1 virtual private network framework has emerged from the need to enable the dynamic coexistence of multiple circuit-switched client networks over a common physical network infrastructure. Such a VPN could be set up for an enterprise with offices across a wide geographical area (e.g., around the world or by a global ISP). Additionally, emerging IP over optical WDM technologies let IP traffic be carried directly over the optical WDM layer. Thus, different VPNs can share a common optical WDM core, and may demand different amounts of bandwidth at different time periods. This type of operation would require dynamic and reconfigurable allocation of bandwidth. This article evaluates the state of the art in layer 1 VPNs in the context of globally deployable optical networks and cost-efficient dynamic bandwidth usage. While exploiting the dynamism of IP traffic in a global network in which the nodes are located in different time zones, we study different bandwidth allocation methods for setting up a worldwide layer 1 VPN. We propose and investigate the characteristics of a cost-efficient bandwidth provisioning and reconfiguration algorithm, called capacity allocation using time zones (CATZ)

The capacity of VoIP over 802.11

As Voice over IP (VoIP) technology becomes a reality, service providers will be able to offer enhanced VoIP applications not presently possible with circuit-switched type networks. Combining new applications and services with the IP Multimedia Subsystem (IMS) network will increase revenue potential. The combination of wireless local area network (WLAN) technology with VoIP and IMS features could become an attractive solution for enterprise voice infrastructure. Service providers can quickly enable enterprise Voice over WLAN (VoWLAN) services, which does not require any investment in re-wiring the premise. In this paper, we introduce the VoIP architecture over WLAN, and study, through both queuing analysis and simulations, the limiting capacity of such systems when operating in the distributed coordination function (DCF) or enhanced distributed channel access function (EDCAF) mode as defined in the IEEE 802.11b/802.11e standards. Our major conclusions are that: 1) packet aggregation and using short preambles can significantly increase VoIP capacity; 2) request to send (RTS)/clear to send (CTS) message exchange does not benefit VoIP; 3) In order to support simultaneous data and voice traffic on the same carrier, it is necessary to employ EDCAF as defined in 802.11e. © 2007 Alcatel-Lucent.

Routing algorithm using the flooding mechanism in a hybrid optical-CDMA and WDM all-optical network

This study describes specific characteristics of optical technology and the requirements they place on routing and path selection. Moreover, a concept for an all-optical circuit-switched network is presented that utilizes near future WDM and optical-CDMA technologies. Mainly this study emphasizes on devising a routing algorithm for all-optical networks that use these technologies and taking into consideration the optical technology attributes. The assumption that parallel channels traversing the same path have the same metric (cost) is no longer valid. The algorithm adopts a flooding mechanism to compute metrics corresponding to every possible path between source and destination nodes based on link impairments and switch characteristics. From amongst computed costs, a selection is taken minimizing the cost by using Viterbi algorithm. This way, codes and wavelengths are assigned based on the characteristics of each link for each possible route, thus optimizing the network's performance.

A new method for approximating blocking probability in overflow loss networks

In this paper, we present a new approximation for estimating blocking probability in overflow loss networks and systems. Given a system for which an estimate of blocking probability is sought, we first construct a second system to act as a surrogate for the original system. Estimating blocking probability in the second system with Erlang's fixed point approximation (EFPA) provides a better estimate for blocking probability in the original system than if we were to use the conventional approach of directly using EFPA in the original system. We present a combination of numerical and theoretical results that indicate our new approximation offers a better estimate than EFPA for a certain pure overflow loss network. Moreover, we demonstrate the accuracy of our new approximation for circuit-switched networks using alternative routing. We argue that the success of our new approximation is due to its ability to utilize congestion information imbedded in overflow traffic, whereas the conventional approach fails to utilize such information.

Distributing digital TV over a hybrid packet- and circuit-switched network

Distributing digital TV over a hybrid packet- and circuit-switched network

Circuit-Switched Coherence

Circuit-switched networks can significantly lower the communication latency between processor cores, when compared to packet-switched networks, since once circuits are set up, communication latency approaches pure interconnect delay. However, if circuits are not frequently reused, the long set up time and poorer interconnect utilization can hurt overall performance. To combat this problem, we propose a hybrid router design which intermingles packet-switched flits with circuit-switched flits. Additionally, we co-design a prediction-based coherence protocol that leverages the existence of circuits to optimize pair-wise sharing between cores. The protocol allows pair-wise sharers to communicate directly with each other via circuits and drives up circuit reuse. Circuit-switched coherence provides overall system performance improvements of up to 17% with an average improvement of 10% and reduces network latency by up to 30%.

Architecture of a Dual-Stage Optical Label Switch Using Out-of-Band Wavelength and Code Optical Properties

A method of generating circuits in an optical network is optical multiple-protocol lambda switching (OMPlambdaS). For OMPlambdaS, the wavelength of the optical carrier is used as an out- of-band label to route data through the network without requiring periodic conversion to the electrical state. A method of adding a second dimension of optical encoding as an out-of-band label used for routing data through a label-switched network is presented. Combining wavelength and code multiplexing techniques generates an O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> circuit-switched network with a data capacity of up to 5.7 Tb/s on each point-to-point link in the network. The proposed architecture uses two stages to process and map labels for each bit transmitted through the network. The architecture and simulation results for the dual-stage optical label switch (DSOLS) are presented.