Parallel simulation techniques for large-scale networks

Simulation has always been an indispensable tool in the design and analysis of telecommunication networks. Due to performance limitations of the majority of simulators, usually network simulations have been done for rather small network models and for short timescales. In contrast, many difficult design problems facing today's network engineers concern the behavior of very large hierarchical multihop networks carrying millions of multiprotocol flows over long timescales. Examples include scalability and stability of routing protocols, packet losses in core routers, of long-lasting transient behavior due to observed self-similarity of traffic patterns. Simulation of such systems would greatly benefit from application of parallel computing technologies, especially now that multiprocessor workstations and servers have become commonly available. However, parallel simulation has not yet been widely embraced by the telecommunications community due to a number of difficulties. Based on our accumulated experience in parallel network simulation projects, we believe that parallel simulation technology has matured to the point that it is ready to be used in industrial practice of network simulation. This article highlights work in parallel simulations of networks and their promise     

Deregistration strategies for PCS networks

This paper studies three deregistration strategies (explicit, implicit, and timeout (TO) deregistration) for personal communication service (PCS) networks to determine the network conditions under which each strategy, gives the best performance. Two performance measures are considered: (1) the probability α that a portable cannot register (and receive service) and (2) the number of deregistration messages sent in a strategy. For the same database size, α is smaller for explicit deregistration (ED) than it is for TO or implicit deregistration (ID). On the other hand, ID does not create any deregistration message traffic. With an appropriate TO period, the deregistration message traffic for TO deregistration is much smaller than the traffic for ED. Suppose that there are N portables in a registration area (RA) on the average. To ensure that α<10^-3 our study indicates that if the database size is larger than 4N, then the implicit scheme should be selected (to eliminate deregistration traffic). If the database size is smaller than 1.5 N, then the explicit scheme should be selected. Otherwise, the TO scheme should be selected to achieve the best performance     

Group deregistration strategy for PCS networks

This letter proposes a novel deregistration strategy-group deregistration-for PCS networks. In the proposed strategy, instead of deregistering a mobile terminal (MT) right after the MT leaves its registration area (RA), the home location register (HLR) keeps the MT's identification in a list associated with the RA. When the next registration from the RA arrives, the HLR sends the MT identification list to the RA along with the registration acknowledgment message. The RA then deregisters these MTs. Compared to the conventional deregistration strategy, the proposed strategy greatly reduces both the signaling traffic and the database load     

Modeling PCS networks under general call holding time and cellresidence time distributions

In a personal communication service (PCS) network, the call completion probability and the effective call holding times for both complete and incomplete calls are central parameters in the network cost/performance evaluation. These quantities will depend on the distributions of call holding times and cell residence times. The classical assumptions made in the past that call holding times and cell residence times are exponentially distributed are not appropriate for the emerging PCS networks. This paper presents some systematic results on the probability of call completion and the effective call holding time distributions for complete and incomplete calls with general cell residence times and call holding times distributed with various distributions such as gamma, erlang, hyperexponential, hyper-erlang, and other staged distributions. These results provide a set of alternatives for PCS network modeling, which can be chosen to accommodate the measured data from PCS field trials. The application of these results in billing rate planning is also discussed     

An efficient multicast protocol for PCS networks

In a Personal Communication Services (PCS) network, mobile hosts communicate with other mobile hosts through base stations on a wired (static) network. The mobile hosts connect to different base stations through wireless links and the base stations to which mobile hosts are connected change depending on the current location of the mobile hosts. In this environment, the problem of efficiently delivering a multicast message from one mobile host to a group of other mobile hosts becomes challenging. In this paper, we present a multicast protocol that delivers multicast messages from a mobile host to a group of other mobile hosts without flooding the wired network. The multicast protocol is built on top of a user location strategy that should follow one of the three models of user location described in the paper. The basic multicast protocol proposed guarantees exactlyonce message delivery to all mobile hosts in the multicast group and also ensures that multicast messages are delivered in FIFO order from the point of view of the base station that originates the multicast message (referred to as BSFIFO). More importantly, an extension of the basic protocol is provided that, unlike earlier work, delivers multicast messages in FIFO order from the point of view of the mobile host that initiates the multicast message (referred to as MHFIFO). The modifications to be made to the multicast protocol to accommodate each of the three models of user location is also described.     

Optimal dynamic mobility management for PCS networks

We study a dynamic mobility management scheme: the movement-based location update scheme. An analytical model is applied to formulate the costs of location update and paging in the movement-based location update scheme. The problem of minimizing the total cost is formulated as an optimization problem that finds the optimal threshold in the movement-based location update scheme. We prove that the total cost function is a convex function of the threshold. Based on the structure of the optimal solution, an efficient algorithm is proposed to find the optimal threshold directly. Furthermore, the proposed algorithm is applied to study the effects of changing important parameters of mobility and calling patterns numerically     

Historical based location management strategies for PCS networks

Wireless Networks - Due to the current popularity of wireless communication, personal communication service networks have attracted a lot of attention. As mobile terminals (MTs) in such networks...     

Predictive distance-based mobility management for multidimensional PCS networks

This paper presents a mobile tracking scheme that exploits the predictability of user mobility patterns in wireless PCS networks. In this scheme, a mobile's future location is predicted by the network, based on the information gathered from the mobile's recent report of location and velocity. When a call is made, the network pages the destination mobile around the predicted location. A mobile makes the same location prediction as the network does; it inspects its own location periodically and reports the new location when the distance between the predicted and the actual locations exceeds a threshold. To more realistically represent the various degrees of velocity correlation in time, a Gauss-Markov mobility model is used. For practical systems where the mobility pattern varies over time, we propose a dynamic Gauss-Markov parameter estimator that provides the mobility parameters to the prediction algorithm. Based on the Gauss-Markov model, we describe an analytical framework to evaluate the cost of mobility management for the proposed scheme. We also present an approximation method that reduces the computational complexity of the cost evaluation for multidimensional systems. We then compare the cost of predictive mobility management against that of the regular, nonpredictive distance-based scheme, for both the case with ideal Gauss-Markov mobility pattern and the case with time-varying mobility pattern.     

A new random walk model for PCS networks

This paper proposes a new approach to simplify the two-dimensional random walk models capturing the movement of mobile users in personal communications services (PCS) networks. Analytical models are proposed for the new random walks. For a PCS network with hexagonal configuration, our approach reduces the states of the two-dimensional random walk from (3n²+3n-5) to n(n+1)/2, where n is the layers of a cluster. For a mesh configuration, our approach reduces the states from (2n2-2n+1) to (n²+2n+4)/4 if n is even and to (n ²+2n+5)/4 if n is odd. Simulation experiments are conducted to validate the analytical models. The results indicate that the errors between the analytical and simulation models are within 1%. Three applications (i.e., microcell/macrocell configuration, distance-based location update, and GPRS mobility management for data routing) are used to show how our new model can be used to investigate the performance of PCS networks     

An improved random walk model for PCS networks

We propose an improvement to a random walk model for personal communications services networks with hexagonal configuration. The number of states required is reduced from n(n + 1)/2 to (n/sup 2/ + 2n + 4)/4 if n is even, and to (n/sup 2/ + 2n + 5) /4 if n is odd, where n is the layers of a cluster.     

A data request scheduling policy for PCS networks

This paper proposes a scheduling policy called latest preempted, earliest resumed (LPER) for personal communications services (PCS) systems that support voice services as well as the circuit mode data services. The policy gives priority to the voice services over the data services. The scheduling of voice requests is performed as if no data requests exist. Thus, if no idle channel is available when a voice request arrives, a data channel (if exists) is interrupted and the channel will be used for the voice request. The interrupted data request will be resumed when an idle channel is available. In LPER, the data channel selected for interruption is the one that serves the latest outstanding data request (i.e., other outstanding requests enter the system earlier than this request). When an occupied channel is released, LPER resumes the earliest request that entered the system. An analytic model is proposed to study the performance of LPER and provides guidelines to select the input parameters for the PCS systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modeling and measurement techniques in packet communication networks

Considerable advances in the modeling and measurements of packet-switched networks have been made since this concept emerged in the late sixties. In this paper, we first review the modeling techniques that are most frequently used to study these packet transport networks; for each technique we provide a brief introduction, a discussion of its capabilities and limitations, and one or more representative applications. Next we review the basic measurement tools, their capabilities, their limitation, and their applicability to and implementation in different networks, namely land based wire networks, satellite networks, and ground packet radio networks; we also show the importance of well-designed experiments in satisfying the many measurement goals. Finally we discuss briefly some open problems for future research.     

Dynamic mobile user location update for wireless PCS networks

The basic architecture of a personal communication network consists of a wireline network and mobile terminals. Each mobile terminal communicates with the wireline network through a nearby base station. In order to route incoming calls to a destination mobile terminal, the network must keep track of the location of each mobile terminal from time to time. This is achieved bylocation update such that each mobile terminal reports its current location to the network at specific time points. When an incoming call arrives, the network will page the mobile terminal starting from the last updated location. A trade-off, therefore, exists between the frequency of location update and the number of locations paged in order to track down the mobile terminal. This paper introduces a location update policy which minimizes the cost of mobile terminal location tracking. A mobile terminal dynamically determines when to update after moving to a new cell based on its mobility pattern and the incoming call arrival probability. The performance of this scheme is close to that of the optimal policy reported earlier. However, the processing time requirement of this scheme is very low. The minimal computation required by this scheme enables its usage in mobile terminals which has limited energy supply and computational power.     

Dynamic hierarchical database architecture for location managementin PCS networks

This paper introduces a dynamic hierarchical database architecture for location management in personal communications service (PCS) networks. The proposed scheme allows the dynamic adjustments of user location information distribution based on the mobility and calling patterns of the mobile terminals (MTs). A unique distribution strategy is determined for each MT, and location pointers are set up at selected remote locations which indicate the current location of the MTs. This method effectively reduces the signaling and database access overhead for location registration and call delivery. Besides, the required processing is handled by a distributed network of directory registers and centralized coordination is not necessary. The functions of the other network elements, such as the home location register (HLR) and the visitor location registers (VLRs), remain primarily unchanged. This greatly facilitates the deployment of this scheme in current PCS networks     

A layered protocol architecture for multimedia wireless‐PCS networks

Coupled with the growing interest in the Universal Mobile Telecommunication System (UMTS) as a standard for future mobile communications, the need for a set of functions to effectively support multimedia teleservices in such an environment is also increasing. Starting from the idea that multimedia means the integrated manipulation of different information and hence the independent handling of separate information is not satisfactory, an enhanced protocol architecture for the support of multimedia teleservices in Wireless Personal Communication Systems based on UMTS is proposed. It involves Physical, MAC, Data Link, and Network layers. A Synchronisation Sub-Layer is introduced on the MAC level with the main aim of assuring a rough multimedia inter-stream synchronisation over the air interface, which is a first step prior to a fine end-to-end synchronisation performed by higher layers. Proposed functions, their basic algorithms, their location in the protocol stack, as well as the signalling exchange among modules implementing them, on network and user sides, are described in detail in the paper. The resulting architecture well fits the demanding nature of multimedia services and can be easily interfaced with the wired backbone of the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

EDBLU: enhanced direction-based location update scheme for PCS networks

An enhanced direction-based location update scheme (EDBLU) is presented. Unlike the direction-based location update (DBLU) scheme, in EDBLU the location update depends on both the moving direction and the moving distance. The performance of EDBLU is analysed based on the discrete-time 2D Markov walk model. The results confirm that the EDBLU scheme reduces the signalling cost significantly for different mobility patterns.     

Two-level pointer forwarding strategy for location management in PCS networks

For a IPCS network to effectively deliver services to its mobile users, it must have an efficient way to keep track of the mobile users. The location management fulfills this task through location registration and paging. To reduce the signaling traffic, many schemes such as a local anchor (LA) scheme, per-user caching scheme and pointer forwarding scheme have been proposed in the past. In this paper, we present a new location management scheme which intends to mitigate the signaling traffic as well as reduce the tracking delay in the PCS systems. In this strategy, we choose a set of visitor location registers (VLRs) traversed by users as the mobility agents (MA), which form another level of management in order to make some registration signaling traffic localized. The idea is as follows: instead of always updating to the home location register (HLR), which would become the bottleneck otherwise, many location updates are carried out in the mobility agents. Thus, the two-level pointer forwarding scheme is designed to reduce the signaling traffic: pointers can be set up between VLRs as the traditional pointer forwarding scheme and can also be set up between MAs. The numerical results show that this strategy can significantly reduce the network signaling traffic for users with low CMR without increasing much of the call setup delay.     

PCS mobility support over fixed ATM networks

As broadband multimedia services and wireless services become popular, there is growing interest in the industry to support ATM over a wireless link, and wireless access to fixed ATM networks. We focus on the internetworking of PCS and ATM networks, in which the air interface remains one of the PCS standards and the backbone is an ATM network with mobility support. It is desirable to minimize the impact of the internetworking and mobility support on the existing/emerging PCS and ATM specifications. A network architecture, a protocol reference model, and signaling protocols for PCS mobility support over fixed ATM networks are described. They are compared against other implementation alternatives and the trade-offs are discussed. Some performance results of the proposed architecture are also presented     

A fair protocol for fast resource assignment in wireless PCS networks

Efficient sharing of communication resources is essential to PCS networks since the wireless bandwidth is limited. The Resource Auction Multiple Access (RAMA) protocol was recently proposed for fast resource assignment and handover in wireless PCS networks. The RAMA protocol assigns available communication resources (e.g., TDMA time slots or frequency channels) to subscribers one at a time using a collision resolution protocol based on subscriber ID's. However, the RAMA protocol encounters an unfairness problem; furthermore, performance results also indicate that it is inefficient at transmitting fixed-length subscriber ID's. Moreover, the emerging services such as teleconferencing have been presenting new challenges to dynamic-priority resource assignment. In this paper, we propose a modification to the RAMA protocol to improve its performance and resolve the unfairness problem. The proposed protocol also adopts dynamic priority assignment to improve the QOS for subscribers in overload environments.     

A new analytic framework for dynamic mobility management of PCS networks

This paper presents a new analytic framework for dynamic location management of PCS networks. Based on the theory of hexagonal cellular patterns, a novel two-dimensional Markov walk model with six states is proposed to characterize the dynamic behavior of the intercell movements for a mobile station. We discover a broad class of isotropic processes having an identical uniform steady-state distribution of the six directions, but distinct circulant transition probability matrices. Six special isotropic processes exhibiting IID, directional, turning, ping-pong, h-spin, and t-spin mobility patterns are identified for performance comparison. We also generalize the selective paging strategy by introducing the concept of probabilistic selective paging (PSP) to reduce the paging cost. A unified analysis using recursive computations is carried out to compute the exact probability distribution for the number of per-call location updates. We calculate the location profile with respect to an incoming call and derive an exact expression of the average paging cost for PSP. With its ability to distinguish subtle performance variations and unveil new features of various dynamic location management schemes, our analytic framework is demonstrated to provide more precise and insightful results than conventional analysis.