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  • 1.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An axiomatic fluid-flow model for congestion control analysis2011In: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC), 2011, p. 3122-3129Conference paper (Refereed)
    Abstract [en]

    An axiomatic model for congestion control isderived. The proposed four axioms serve as a basis for theconstruction of models for the network elements. It is shownthat, under some assumptions, some models of the literature canbe recovered. A single-buffer/multiple-users topology is finallyderived and studied for illustration.

  • 2.
    Briat, Corentin
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A conservation-law-based modular fluid-flow model for network congestion modeling2012In: 2012 Proceedings - IEEE INFOCOM, IEEE Computer Society, 2012, p. 2050-2058Conference paper (Refereed)
    Abstract [en]

    A modular fluid-flow model for network congestion analysis and control is proposed. The model is derived from an information conservation law stating that the information is either in transit, lost or received. Mathematical models of network elements such as queues, users, and transmission channels, and network description variables, including sending/ acknowledgement rates and delays, are inferred from this law and obtained by applying this principle locally. The modularity of the devised model makes it sufficiently generic to describe any network topology, and appealing for building simulators. Previous models in the literature are often not capable of capturing the transient behavior of the network precisely, making the resulting analysis inaccurate in practice. Those models can be recovered from exact reduction or approximation of this new model. An important aspect of this particular modeling approach is the introduction of new tight building blocks that implement mechanisms ignored by the existing ones, notably at the queue and user levels. Comparisons with packet-level simulations corroborate the proposed model.

  • 3.
    Briat, Corentin
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Impact of Queueing Delay Estimation Error on Equilibrium and Its Stability2011In: NETWORKING 2011, PT II, 2011, p. 356-367Conference paper (Refereed)
    Abstract [en]

    Delay-based transmission control protocols need to separate round-trip time (RTT) measurements into their constituting parts: the propagation and the queueing delays. We consider two means for this; the first is to take the propagation delay as the minimum observed RTT value, and the second is to measure the queueing delay at the routers and feed it back to the sources. We choose FAST-TCP as a representative delay-based transmission control protocol for analysis and study the impact of delay knowledge errors on its performance. We have shown that while the first method destroys fairness and the uniqueness of the equilibrium, the stability of the protocol can easily be obtained through tuning the protocol terms appropriately. Even though the second technique is shown to preserve fairness and uniqueness of the equilibrium point, we have presented that unavoidable oscillations can occur around the equilibrium point.

  • 4.
    Chen, Zhaofei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Demo of a collaborative music sharing system2012In: MobiOpp'12 - Proceedings of the 3rd ACM International Workshop on Mobile Opportunistic Networks, New york: ACM , 2012, p. 77-78Conference paper (Refereed)
    Abstract [en]

    We demonstrate a wireless real-time music-sharing application that lets users play music directly from their mobiles through a jukebox. We have designed and implemented the application by using a previously developed content-centric opportunistic networking middleware. The jukebox plays the music file that is first in its playlist by streaming it in real-time from the publishing user device. All users can observe the collaboratively formed playlist on their mobiles in real-time. The application shows the usefulness of our middleware and demonstrates a new form of situated applications. The application handles churn and garbage collection after departed users.

  • 5.
    Chen, Zhaofei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    What a juke! A collaborative music sharing system2012In: 2012 IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks, WoWMoM 2012 - Digital Proceedings, IEEE , 2012, p. 6263751-Conference paper (Refereed)
    Abstract [en]

    The fast spreading of smart mobile devices has changed the way people create and share multimedia contents. A recently proposed idea is to distribute contents opportunistically when devices are within each other's communication range. In this work we have seized this idea and designed and implemented a real-time music-sharing application that allows people to share a sound system for collective listening. The system utilizes a content-centric opportunistic networking middleware. The application provides an interface for users to play audio files stored in their own mobile devices through a shared jukebox that is within direct communication range. The jukebox plays the audio file that is first in queue in its playlist by streaming it from the publishing user device. All devices synchronize with the jukebox so that the users can observe the contents of the playlist on their displays in real-time. This paper presents the idea and motivation for such a system as well as its design and evaluation.

  • 6. Fortetsanakis, G.
    et al.
    Papadopouli, Maria
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dramitinos, M.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    To subscribe, or not to subscribe: Modeling and analysis of service paradigms in cellular markets2012In: 2012 IEEE International Symposium on Dynamic Spectrum Access Networks, DYSPAN 2012, IEEE , 2012, p. 189-200Conference paper (Refereed)
    Abstract [en]

    Traditionally customers subscribe to specific providers and are served by accessing base stations (BSs) of the network of their provider. Inevitably subscribers with relatively 'high' usage pattern and data-rate requirements are subsidized by the ones with lower usage and data-rates. As the wireless technology advances, a diverse set of services will be available. This paper introduces the 'flex service' paradigm that allows a customer to dynamically access BSs of different providers based on various criteria, such as profile, network conditions, and offered prices. 'Flex users' can select the appropriate provider and BS on a per-session basis. This work considers a diverse customer population with respect to their demand, their preference on data-rate over price, their tolerance on the blocking probabilities of their sessions, and their willingness to pay for certain services. Users can dynamically decide to buy a long-term subscription or become flex users. In this paper, we develop a rich framework for modeling and analysis of such markets in different spatio-temporal scales. We analyze the evolution of markets with the flex service paradigm, focusing on whether it can improve the quality-of-service (QoS), social welfare, flexibility and further enhance the competition among providers. The main contribution of this paper is detailed modeling and indepth performance analysis of such complex markets, in different spatial and temporal scales. It considers the perspective of clients, providers, and regulators. It demonstrates the benefits of markets with the flex service paradigm and compares them with the ones that only offer subscription contracts.

  • 7.
    Helgason, Ólafur
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kouyoumdjieva, Sylvia T.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pajevic, Ljubica
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Middleware for Opportunistic Content Distribution2016In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069Article in journal (Refereed)
    Abstract [en]

    In this work we present a middleware architecture for a mobile peer-to-peer content distribution system. Our architecture allows wireless content dissemination between mobile nodes without relying on infrastructure support. In addition, it supports the dissemination of contents between the wireless ad-hoc domain and the wired Internet. In the ad-hoc domain, contents are exchanged opportunistically when nodes are within communication range. Applications access the service of our platform through a publish/subscribe interface and therefore do not have to deal with low-level opportunistic networking issues or matching and soliciting of contents. Our middleware consists of three key components. A content structure that facilitates dividing contents into logical topics and allows efficient matching of content lookups and downloading under sporadic node connectivity. A solicitation protocol that allows nodes to solicit content meta-information in order to discover contents available at a neighboring node and to download content entries disjointedly from different nodes. An API that allows applications to access the system services through a publish/subscribe interface. In this work we present the design and implementation of our middleware and describe a set of applications that use the services provided by our middleware. We also assess the performance of the system using our Android implementation as well as a simulation implementation for large-scale evaluation.

  • 8.
    Helgason, Ólafur
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kouyoumdjieva, Sylvia
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Pajevic, Ljubica
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    A mobile peer-to-peer system for opportunistic content-centric networking2010In: Proceedings of the 2nd ACM SIGCOMM Workshop on Networking, Systems, and Applications on Mobile Handhelds, MobiHeld '10, Co-located with SIGCOMM 2010, 2010, p. 21-26Conference paper (Refereed)
    Abstract [en]

    In this work we present a middleware architecture for a mobile peer-to-peer content distribution system. Our architecture allows wireless content dissemination between mobile nodes without relying on infrastructure support. Contents are exchanged opportunistically when nodes are within communication range. Applications access the service of our platform through a publish/subscribe interface and therefore do not have to deal with low-level opportunistic networking issues or matching and soliciting of contents. Our architecture consists of three key components. A content structure that facilitates dividing contents into logical topics and allows for efficient matching of content lookups and downloading under sporadic node connectivity. A solicitation protocol that allows nodes to solicit content meta-information in order to discover contents available at a neighboring node and to download content entries disjointedly from different nodes. An API that allows applications to access the system services through a publish/subscribe interface. In this work we describe the design and implementation of our architecture. We also discuss potential applications and present evaluation results from profiling of our system.

  • 9.
    Karlsson, Gunnar
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Polyzos, George C.
    A Future Wireless Internet Beyond Generations2010In: Proceedings of the 5th International Conference on Future Internet Technologies, CFI10, 2010, p. 5-9Conference paper (Refereed)
    Abstract [en]

    The use of licensed spectrum for wireless communication is driven by the need to control interference between operators. This regulation leads to inefficient utilization of spectrum and causes shortage of free spectrum that hinders the entry of new operators and introduction of new wireless technologies. In this work, we present an evolutionary model for which license-free operation is the spectrum sharing mode so that networks can be built freely by anyone and new technologies can be deployed as soon as they become available. The paradigm assumes users to have open access to all public networks without prior contracts with operators. Hence, freely roaming users will drive competition among wireless network access providers, who in turn can meet demand quickly by offering access at low price, high quality, in hitherto uncovered areas, and by means of novel superior technology. We present a straw-man design and discuss the inherent technical challenges that must be addressed.

  • 10.
    Kouyoumdjieva, Sylvia
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Helgason, Olafur
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Pajevic, Ljubica
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Opportunistic Content-Centric Networking: The Conference Case Demo2011In: Proceedings of the IEEE International Conference on Computer Communications, INFOCOM’11, 2011Conference paper (Refereed)
    Abstract [en]

    We present a demonstration scenario to evaluate a middleware architecture that we designed and implemented for distributing content over mobile ad hoc networks. The peer to-peer networking architecture allows content dissemination between mobile devices without relying on any infrastructure support. Content is exchanged opportunistically when nodes are in proximity. We developed a mobile application utilizing the services provided by the implemented middleware. The application facilitates opportunistic content distribution in both one-to-one and one-to-many dissemination modes.

  • 11.
    Pajevic, Ljubica
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Helgason, Olafur
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Kouyoumdjieva, Sylvia
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Demo: Opportunistic Mobile Social Networking2011In: Proc. ACM Annual International Conference on Mobile Systems, Applications and Services, MobiSys’11, 2011Conference paper (Refereed)
    Abstract [en]

    We present a demonstration scenario to validate a middleware architecture that we designed and implemented for distributing content between mobile users in an opportunistic manner. The peer-to-peer networking architecture allows content dissemination between mobile devices without relying on any infrastructure support. We developed a mobile application utilizing the services provided by the implemented middleware. The application facilitates opportunistic content distribution in both one-to-one and one-to-many dissemination modes.

  • 12.
    Yavuz, Emre A.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Poster: Collective Mobile Sensing for Wireless Network Performance Monitoring2011In: Proc. ACM Annual International Conference on Mobile Systems, Applications and Services, 2011, p. 411-Conference paper (Refereed)
    Abstract [en]

    Rapid growth of mobile wireless industry has generated numerous challenges for service operators. The provisioning of increasing demand in capacity and higher quality of service can be met with redimensioning of networks which makes a priori network planning difficult. We propose a network performance monitoring system to which all mobile devices contribute by voluntarily submitting periodical reports on the availability and quality of network access that they experience at their current geographical locations. Network performance measures such as signal strength, coverage, call block/drop statistics and operator service capabilities are reported to a server with a network status information database as experienced by mobile devices. The proposed database will indicate areas with lack of coverage, insufficient capacity, and high interference, which may serve as cues for operators to upgrade/retune their infrastructure equipment and for regulators to take action against operators that do not fulfill commitments made to their subscribers.

  • 13.
    Yavuz, Emre A.
    et al.
    Dept. of Electrical & Computer Engineering - University of British Columbia (UBC).
    Leung, Victor C. M.
    A practical method for estimating performance metrics of call admission control schemes in wireless mobile networks2005In: 2005 IEEE Wireless Communications and Networking Conference, Vols 1-4: WCNC 2005: BROADBAND WIRELESS FOR THE MASSES READY FOR TAKE-OFF, 2005, Vol. 2, p. 1254-1259Conference paper (Refereed)
    Abstract [en]

    Providing the desired call blocking probability to not only new but also existing calls has been a challenge for wireless mobile network service providers. To satisfy different requirements for new and handoff call blocking probabilities, several call admission control (CAC) schemes have been proposed in the literature. Exact analysis of these schemes using two dimensional Markov chain is computationally intensive. Therefore under specific assumptions computationally efficient methods to analyze these systems using one dimensional Markov chain models have been considered. The "traditional" approach assumes that channel holding time for new and handoff calls have equal mean values. While the "normalized" approach relaxes this assumption, it is accurate only for the new call bounding CAC scheme. In this paper, we reevaluate the analytical methods for computing call blocking probabilities for several widely known call admission control schemes under more general assumptions by providing an easy to implement method. The numerical results show that when the average values of channel holding times for new and handoff calls are different, the proposed approach gives more accurate results when compared with the traditional and normalized methods based on one dimensional Markov chain modeling, while keeping the computational complexity low.

  • 14.
    Yavuz, Emre A.
    et al.
    Dept. of Electrical & Computer Engineering - University of British Columbia (UBC).
    Leung, Victor C. M.
    Computationally efficient method to evaluate the performance of guard-channel-based call admission control in cellular networks2006In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 55, no 4, p. 1412-1424Article in journal (Refereed)
    Abstract [en]

    Many guard-channel-based call admission control (CAC) schemes for cellular networks have been proposed to provide the desired quality of service to not only new calls but also ongoing calls when they hand off to neighboring cells. Blocking/dropping probabilities of new/handoff calls are generally analyzed using one-dimensional Markov chain modeling under specific assumptions to avoid solving large sets of flow equations that makes exact analyses of these schemes using multidimensional Markov chain models infeasible. This is the case with the "traditional" approach, which assumes that channel holding times for new and handoff calls have equal mean values, and the "normalized" approach, which relaxes this assumption but is accurate only for the new call bounding CAC scheme. In this paper, we reevaluate the analytical methods for computing new/handoff call blocking/dropping probabilities for several widely known CAC schemes and develop an easy-to-implement method under more general assumptions. Numerical results show that when the mean channel holding times for new and handoff calls are different, the proposed "effective holding time" approach gives more accurate results compared with the traditional and the normalized methods while keeping the computational complexity low. The accuracy of these methods and their levels of computational complexity with the exact solution are also compared.

  • 15.
    Yavuz, Emre A.
    et al.
    Dept. of Electrical & Computer Engineering - University of British Columbia (UBC).
    Leung, Victor C. M.
    Efficient approximations for call admission control performance evaluations in multi-service networks2006In: GLOBECOM 2006: 2006 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, 2006, Vol. WLC40-5Conference paper (Refereed)
    Abstract [en]

    Several dynamic call admission control (CAC) schemes for cellular networks have been proposed in the literature to reserve resources adaptively to provide the desired quality of service (QoS) to not only high priority calls but also to low priority ones. Efficient adaptive reservations depend on reliable and up-to-date system status feedback provided to the CAC mechanism. However exact analysis of these schemes using multidimensional Markov chain models are intractable in real time due to the need to solve large sets of flow equations. Hence performance metrics such as call blocking probabilities of various QoS classes are generally evaluated using one dimensional Markov chain models assuming that channel occupancy times for all QoS classes have equal mean values and all arriving calls have equal capacity requirements. In this paper we re-evaluate the analytical methods to compute call blocking probabilities of various QoS classes for several widely known CAC schemes by relaxing these assumptions, and propose a novel approximation method for performance evaluation with low computational complexity. Numerical results show that proposed method provides results that match well with the exact solutions.

  • 16.
    Yavuz, Emre A.
    et al.
    Dept. of Electrical & Computer Engineering - University of British Columbia (UBC).
    Leung, Victor C. M.
    Efficient Methods for Performance Evaluations of Call Admission Control Schemes in Multi-Service Cellular Networks2008In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, no 9, p. 3468-3476Article in journal (Refereed)
    Abstract [en]

    Many dynamic call admission control (CAC) schemes have been proposed in the literature for adaptive reservations in cellular networks. Efficient application of these schemes requires reliable and up-to-date feedback of system performance to the CAC mechanism. However, exact analyses of these schemes in real time using multi-dimensional Markov chain models are challenging due to the need to solve large sets of flow equations. One dimensional Markov chain models have been widely used to derive performance metrics such as call blocking probabilities of multiple traffic classes assuming that all classes of calls have equal capacity requirements and exponentially distributed channel holding times with equal mean values. These assumptions need to be relaxed for a more general evaluation of CAC performance in multi-service cellular networks. In this paper we classify CAC schemes according to their Markov chain models into two categories: symmetric and asymmetric, and develop computationally efficient analytical methods to compute call blocking probabilities of various traffic classes for several widely known CAC schemes under relaxed assumptions. We obtain a product form solution to evaluate symmetric schemes and propose a novel performance evaluation approximation method with low computational cost for asymmetric schemes. Numerical results demonstrate the accuracy and efficiency of the proposed method.

  • 17.
    Yavuz, Emre A.
    et al.
    Dept. of Electrical & Computer Engineering - University of British Columbia (UBC).
    Leung, Victor C. M.
    Modelling channel occupancy times for voice traffic in cellular networks2007In: 2007 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-14, 2007, p. 332-337Conference paper (Refereed)
    Abstract [en]

    Call holding times in telephony networks are commonly approximated by exponential distributions to facilitate traffic engineering. However, for traffic engineering of cellular networks, channel occupancy times need to be modeled instead to facilitate analytical modeling or to feed network simulations. In this paper, we classify channel occupancy times and present an empirical study based on data obtained from a real cellular network to determine which probability distribution functions can approximate them better. The results are environment dependent, but no assumptions that can be influential are made, as opposed to previous analytical and simulation studies which results are highly dependent on the assumptions made by the authors. We show that all types of channel occupancy times can be approximated by lognormal distribution. For stationary users, channel occupancy times are commonly approximated by exponential distribution due to its tractability, assuming that cell residence times are also exponentially distributed. However, we show that lognormal distribution fits much better to both channel occupancy and call holding times regardless of whether users are stationary or mobile.

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